Sean Bolton - Dissertation

School of Engineering

Department of the Built Environment

BEng (Hons) in Civil Engineering, 2014

Assessing the Soil Stabilisation Potential of Vegetation

Roots for Unstable Highway Slopes in Cohesive Soil

Seán Bolton

Date Submitted: 31/03/2014 Word Count: 11,590

Assessment Submission Form

Student Name Seán Bolton

Student Number C00128310

Course, Year & Group CW_CMCEN_B. Y5. (CW428)

Subject Dissertation

Supervisor Brian Byrne

Date Submitted 31/03/2014

Assessment Title Assessing the Soil Stabilisation Potential of Vegetation Roots for

Unstable Slopes in Cohesive Soil

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i

Abstract

Shallow seated slope failure is a growing concern as the polish begins to fade on Ireland‟s

recently upgraded highway system. Rapid expansion of the roads network during the

economic boom years of the early 21st

century have left a system of steeply sloped cuts and

embankments, with the short-term benefit of reduced construction cost due to decreased land

take now giving way to a pending maintenance nightmare as these slopes slowly give way

over time. Reliance on traditional hard engineering solutions has the potential to skyrocket

maintenance costs, haemorrhaging the national budget for road maintenance, thus crippling

the national and local roads authority‟s ability to maintain the national road network,

estimated to be in excess of 100,000km of roadway.

Slope vegetation has the potential to eradicate the threat of shallow seated highway slope

failure at a fraction of the cost of hard engineering methods, whilst also providing and

enhanced aesthetic and carbon balancing aspect to the national roads network. Once

established, an adequately vegetated slope requires minimal maintenance, with a properly

maintained slope potentially providing long-term sustainable reinforcement, with a lifespan

far in excess of any manmade mechanical component.

In this paper the largely untried theories of published literature are tested in order to

investigate their validity and to determine quantitatively the reinforcement provided by the

presence of vegetation roots in soil. This paper uncovers a possible flaw in the previously

held belief that vegetation provides significant mechanical reinforcement of soil only, with

practical test results suggesting that soil containing roots may be up to 14% drier than similar

soil where vegetation is not present.

The findings of this paper suggest that soil sheltering and residual moisture uptake effect of

plants, even during the dormant winter months, provide a significant slope stabilisation effect

due to substantial year-round soil moisture reduction. It may thus be the case that the

potential moisture reduction capacity of vegetation roots has been prematurely discarded by

published literature.

ii

Table of Contents

Abstract ....................................................................................................................................... i

Acknowledgements……………………………………………………………………………...……viii

1.0 Introduction ................................................................................................................... 1

1.1 Background ................................................................................................................................... 1

1.2 Aim & Methodology ..................................................................................................................... 1

1.3 Limitations .................................................................................................................................... 2

2.0 Literature Review ......................................................................................................... 3

2.1 Introduction ................................................................................................................................... 3

2.2 Nature & Extent of the Problem .......................................................................................... 3

2.21 Vegetation & Shallow Slope Failure .......................................................................................... 3

2.22 The Need for Slope Stabilisation in Earthwork Slopes ............................................................... 4

2.22 Shallow Slope Failure Mechanism ............................................................................................. 5

2.3 Vegetation as a Slope Stabilisation Method ........................................................................ 6

2.31 Properties of Vegetation ............................................................................................................. 6

2.32 Role of Root Reinforcement in Slope Stabilisation .................................................................... 8

2.33 Role of Roots in Moisture Content Reduction ............................................................................ 9

2.34 Weaknesses of Vegetation as a Stabilisation Method ............................................................... 10

2.40 Selection of Plant Species ................................................................................................ 11

2.5 Conclusion ......................................................................................................................... 12

3.0 Methodology ................................................................................................................ 13

3.1 Required Information ......................................................................................................... 13

iii

3.2 Background ........................................................................................................................ 13

3.3 Site Visit............................................................................................................................. 15

3.31 Site Description ......................................................................................................................... 15

3.32 Observations Made on Site ....................................................................................................... 16

3.4 Sampling Process ............................................................................................................... 18

3.41 Samples Required ..................................................................................................................... 18

3.42 Sampling Process ...................................................................................................................... 18

3.51 Visual Inspection ...................................................................................................................... 21

Shear Vane Testing ........................................................................................................................... 21

3.6 Laboratory Work ................................................................................................................ 22

3.61 Laboratory Preparation ............................................................................................................. 22

3.62 Laboratory Testing .................................................................................................................... 23

3.63 Triaxial Testing ......................................................................................................................... 23

3.64 Shear Box Testing ..................................................................................................................... 24

3.65 Organic Content Testing ........................................................................................................... 25

3.66 Atterberg Limit Testing ............................................................................................................ 25

3.67 Observations & Limitations ...................................................................................................... 25

4.0 Results .......................................................................................................................... 27

4.1 Triaxial Test ................................................................................................................................ 27

4.2 Shear Vane Test .......................................................................................................................... 29

4.3 Shear Box Testing ....................................................................................................................... 29

4.4 Atterberg Limit Testing .............................................................................................................. 34

4.5 Organic Content Testing ............................................................................................................. 36

iv

5.0 Discussion..................................................................................................................... 37

5.1 Triaxial Testing ........................................................................................................................... 37

5.2 Shear Vane Testing ..................................................................................................................... 38

5.3 Shear Box Testing ....................................................................................................................... 39

5.4 Atterberg Limit Testing .............................................................................................................. 42

5.5 Organic Content Testing ............................................................................................................. 43

6.0 Conclusion ................................................................................................................... 44

7.0 Recommendations ....................................................................................................... 46

Bibliography ............................................................................................................................ 47

Appendix A – Desk Study Maps ............................................................................................. 49

Appendix B – Plasticity Chart ................................................................................................. 51

Appendix C – Lab Test Resuls ................................................................................................ 52

v

Table of Figures Figure 2 - 1: Cost Comparison of Inert & Bioengineering Projects (Barker, 1999) .................. 4

Figure 2 - 2: Soil Buttressing & Arching (Hiller & MacNeill, 2001)........................................ 6

Figure 2 - 3: Equivalent Uniform Surcharge (Coppin & Richards, 1990) ................................. 7

Figure 2 - 4: The Influence of Vegetation on a Slope (Coppin & Richards, 1990) ................... 7

Figure 2 - 5: Effect of Root Reinforcement on Shear Strength of Soil ...................................... 8

Figure 3 - 1: Site Location Map ............................................................................................... 15

Figure 3 - 2: Satellite View of Sampling Sites ........................................................................ 15

Figure 3 - 3: Shear Soil Faces Restrained by Large Tree Roots .............................................. 16

Figure 3 - 4: Heavily Vegetated Steep Cut Slope .................................................................... 16

Figure 3 - 5: Observed Approximate 0.6m Depth to Bedrock Outcrop................................... 17

Figure 3 - 6: Close up View of Soil Found on Site .................................................................. 17

Figure 3 - 7: Preparation of Sampling Tubes ........................................................................... 18

Figure 3 - 8: Driving Sampling Pipe ........................................................................................ 19

Figure 3 - 9: Pipe Exhibiting Damage ..................................................................................... 19

Figure 3 - 10: Sampling Using U100 in Greenfield Site ......................................................... 19

Figure 3 - 11: Soil Transportation from Site ............................................................................ 20

Figure 3 - 12: Heavily Vegetated Soil Sample ........................................................................ 20

Figure 3 - 13: Carlow Town Satellite View ............................................................................. 21

Figure 3 - 14: Extraction of Soil Sampled in uPVC Pipe ........................................................ 22

Figure 3 - 15: Bulk Sample for Atterberg Limits .................................................................... 23

Figure 3 - 16: Trimmed Sample in Triaxial Apparatus ............................................................ 23

Figure 4 - 1: Axial Strain Vs. Deviator Stress ......................................................................... 27

Figure 4 - 2: Mohr's Circle Sketch ........................................................................................... 28

Figure 4 - 3: 19.075kN/m2 With Vs. Without Roots ............................................................... 30

Figure 4 - 4: 13.625kN/m2 With Roots Vs. 19.075kN/m

2 Without Roots............................... 30


Figure 4 - 6: 40.875kN/m2 With Vs. Without Roots ................................................................ 31


vi


Figure 4 - 9: 81.750kN/m2 With Vs. Without Roots ................................................................ 33

Figure 4 - 10: 95.375kN/m2 With Vs. Without Roots ............................................................. 33

Figure 4 - 11: 109.000kN/m2 With Vs. Without Roots ........................................................... 34

Figure 4 - 12: Cone Penetration Vs. Moisture Content ........................................................... 35

Figure 5 - 1: Steep Vegetated Slope ........................................................................................ 37

Figure 5 - 2: Soil Deforming Under Triaxial Loading ............................................................. 37

Figure 5 - 3: Failure Plane of Triaxial Sample ........................................................................ 38

Figure 5 - 4: Trial Hole in Saturated Soil ................................................................................ 38

Figure 5 - 5: Various Depths of Investigation (Vegetated Area) ............................................. 39

Figure 5 - 6: Visible Shear Failure Plane ................................................................................. 40

Figure 5 - 7: Sample after Shear Box Test ............................................................................... 41

Figure 5 - 8: Dry Soil Passing 0.425mm Sieve ........................................................................ 42

Figure 5 - 9: Soil after Mixing ................................................................................................. 42

Figure 5 - 10: Cone Penetrometer Test .................................................................................... 42

Figure 5 - 12: Penetration at High Moisture Content .............................................................. 43

Figure 5 - 11: Plastic Limit Test Samples ................................................................................ 43

Table of Tables

Table 4 - 1: UU Test Description ............................................................................................. 27

Table 4 - 2: Triaxial Test Calculations .................................................................................... 28

Table 4 - 3: Moisture Content Calculations ............................................................................. 29

Table 4 - 4: Shear Vane Results (Vegetated Area) .................................................................. 29

Table 4 - 5: Shear Vane Results (Greenfield Area) ................................................................. 29

Table 4 - 6: Liquid Limit Test Results ..................................................................................... 34

Table 4 - 7: Plastic Limit Test Results ..................................................................................... 35

Table 4 - 8: Organic Content Test Results ............................................................................... 36

vii

Table of Terms

Cu = Undrained Shear Strength (kPa).

φ = Friction Angle.

GSI = Geological Survey of Ireland.

OSI = Ordinance Survey Ireland.

Green Field Site = The site from which samples not containing roots were obtained.

Vegetated Site = The site from which samples containing roots were obtained.

BGL = Below Ground Level.

Indicated Shear Box Stress = Initial normal stress applied to the sample

viii

Acknowledgements

I would like to thank Mr Brian Byrne for his continued support and reminders that this is an

engineering rather than horticultural degree paper. Without his input this paper would have

ran way over time, and despite possibly contributing a decorative crop plantation to a Co.

Laois hillside, much needed as it is, would have ultimately failed to hold any engineering

content past the course name on the cover page.

A thank you should also be reserved for Mr Martin Meehan of the Institute of Technology

Civil Engineering Laboratory, whose patience, not to mention his step-by-step apparatus

guides, meant that lab testing could be completed within a seemingly impossible time

window.

I wish to thank my family and friends for remembering my existence over the past nine

months and recognising me when I re-emerged in late spring. It was a long struggle that

seemed almost impossible at times, but we made it out the other side in the end.

A special mention is owed to my colleagues in the 2014 Civil Engineering class for

reminding me that no matter how impossible a task may seem, there‟s always at least ten

other people who feel just as shafted as you. Our pain is our bond, I wish you all the best for

the future.

Assessing The Soil Stabilisation Potential of Roots 2014

1

1.0 Introduction

1.1 Background

It has been long accepted that vegetation roots increase the shear strength of soil through

mechanical reinforcement against soil mobilisation in the form of shallow seated slope

failure, based on the early work carried out by Parsons & Perry (1985), as referenced by

several later studies.

Despite this, very little research has been carried out in this field, due in no small part to the

lack of financial profit to be made by private companies within this branch of bioengineering.

This has meant that much of the knowledge on the reinforcement provided by vegetation

roots is purely anecdotal, based largely on personal accounts rather than facts or research.

Traditionally hard engineering methods, such as soil nailing and anchoring, have been used to

stabilise unstable highway slopes at a great expense the relevant roads authority.

1.2 Aim & Methodology

This paper sets out to quantifiably establish the undrained strength gain due to the presence of

roots in soil, with a new perspective on the much debated moisture reduction potential of

soils also uncovered. Undrained strength of a soil depends on a number of factors, such as

stress path, volume of material, rate of shearing and orientation of stresses.

Undrained strength may be of concern in cases where the loading rate is greater than rate at

which excess pore water pressures dissipate, as is often the case with the failure of a CLAY

slope after a period of heavy rain. This test approach allowed a rapid indication of the

strength contribution of vegetation roots to be assessed.

This is achieved through practical on-site investigation and sampling of vegetated and un-

vegetated soil at a site, supported by an independent brief desk study of the ground and

bedrock at this site.

The on-site observations are complimented with an extensive series of in-situ and laboratory

testing with the aim of providing some much needed engineering basis to the widely accepted

understanding of soil stabilisation due to vegetation roots.


2

1.3 Limitations

Laboratory testing was limited to the apparatus which was available in the soils laboratory of

The Institute of Technology Carlow during the time of testing. Soil tested during the

experiments contained soil with many small diameter roots forming a mesh-like

reinforcement.

Work carried out by Greenwood et al (2001) suggests use should be made of a large shear

box, which was not available in the soils laboratory during testing, in order to carry out

testing on soil containing larger tree roots. Soil sampling during the preparation of this paper

was limited to one site due to health & safety and permission restrictions.


3

2.0 Literature Review

2.1 Introduction

This document sets out what is currently known in published literature on the suitability of

vegetation roots as a reinforcement method in the prevention of shallow slope failure.

Traditional methods of slope reinforcement include soil nailing and other hard engineering

approaches. This document intends to demonstrate that vegetation potentially provides a

more sustainable approach, both economically and ecologically.

The stabilisation of slopes against shallow failure has been identified by CIRIA as being the

key market area for the use of vegetation in civil engineering (Greenwood et al., 2001). This

literature review outlines the viability of slope stabilisation through the vegetation of unstable

slopes. The known strengths and weaknesses of this method are presented, along with outline

procedures by which further research will be carried out. This will enable for the suitability of

roots in the prevention of shallow slope failure to be determined through practical

experiments.

2.2 Nature & Extent of the Problem

2.21 Vegetation & Shallow Slope Failure

The use of vegetation in the stabilisation of slopes against shallow slope failure has long been

an area of interest in the field of civil engineering. Shallow-seated slope failures are

generally considered as being mass soil movements with a slip surface no more than 2m

below ground level.

These slope movements are generally a combination of translational and rotational

movement, with a single movement form also possible (Greenwood et al., 2001). R.A. Jewell

(1996) comments that shallow slope failures are generally due to translational slides “on

shallow slip surfaces of the order 1.5m below the slope face” (Jewell, 1996)

When considering the slope stabilisation potential of vegetation, failures occurring at depths

greater than 2m below ground level are ignored as these are unlikely to be stabilised by forms

of vegetation installed as a stabilisation method. (Greenwood et al., 2001).


4

2.22 The Need for Slope Stabilisation in Earthwork Slopes

A study of two highways located north of Cambridge, UK found more than thirty

embankment slope failures in a ten-year period after construction in the late 1970s (Johnson,

1985). Repair consisted of excavation and granular replacement, costing £10,000 to £15,000

per failure at 1980s prices (Greenwood et al., 1985). This high rate of occurrence added to the

significant cost of repair meant that understanding the causes and possible means of failure

prevention became highly desirable (Barker, 1994).

A 1985 survey of UK highway slopes examined 570km of motorway cuttings and

embankments, with this study finding that 95% of road slippages observed occurred within

the first 1.5m below ground level (when measured vertically). This was especially found to

be the case in heavy overconsolidated clay soils. Cutting and embankment slopes excavated

and constructed in a UK Gault Clay had significantly high failure rates (9.7% and 9.1%

respectively) (Parsons & Perry, 1985).

The issue of the use of vegetation as a slope stabilisation method which provides economic

and ecologic benefits has been heightened over recent years. This is due to the requirement of

highway widening to deal with increased traffic volumes. This has meant that existing

highway slopes have had to be steepened to angles of 700

in certain cases (MacNeil et al.,

2001), exceeding the angle of repose for many soil types.

A rate of failure of the order of up to 50% has been observed within 20 years of construction

in UK embankments constructed of clay to

heights exceeding 5m with a side slope of 1:2.5.

Conservative estimates go on to suggest that as

many as three times as many slopes as had failed

in the past would fail in the future if preventive

measures were not taken. (Perry, 1989).

Vegetation is viewed by many as the ideal long-

term stabilisation method for use in these newly

steepened highway and railway cuttings and

embankments. (Greenwood et al., 2001).

Figure 2 - 1: Cost Comparison of Inert & Bioengineering Projects

(Barker, 1999) Cited by (Hiller & MacNeill, 2001)


5

2.22 Shallow Slope Failure Mechanism

Shallow slope failure is common in overconsolidated clays which are exposed in cuttings or

reused to construct embankments (Greenwood et al., 2001). Overconsolidated clays may be

defined as; “clays which have gained strength by consolidation under a heavy excess

overburden pressure or by desiccation due to evaporation or the growth of vegetation”

(Blunt, 1992).

R.A. Jewell (1996) states that there are two factors which contribute to this instability. These

are the development of pore water pressures in the upper soil layer due to water ingress and

the reduction in the shearing resistance of the soil at low effective stress as the soil swells and

softens with time (Jewell, 1996). These comments were made in relation to cohesive soils

such as London clays, but a similar process occurs in exposed overconsolidated Boulder

CLAY slopes

R.A. Jewell (1996) goes on to state that weathering of the soil in the upper 1 – 2m below the

surface of the slope results in fissuring of the soil, leading to „progressive‟ failure of the

slope. Poor embankment layering and drainage installation can also lead to slope failure

(Jewell, 1996).

From the literature reviewed it can be said that shallow slope failure occurs as a consequence

of overconsolidated soil increasing in volume following the removal of pre-consolidating

pressures. When exposed in a cut or disturbed and placed on the surface as an embankment

the overconsolidated soil effectively “breathes” out, sucking in air and moisture in the

process.

Greenwood et al. (1985) concluded from the observations of Parsons & Perry (1985) and

Farrar (1984) that overconsolidated soil has the greatest suction as the greatest stress relief

has occurred. Water from rainfall or road drainage infiltrates this soil, reducing suction,

increasing pore water pressure and lowering strength over time until failure occurs

(Greenwood et al., 2001).


6

The absorption of moisture leads to an increase in destabilising pore water pressure within the

soil, whilst also reducing shear strength through softening of the material. Increased pore

water pressure reduces the effective stress within the soil, further decreasing shear strength,

leading to eventual slope failure. As the re-wetting of the soil progresses from the surface

downwards, the failure is almost always at shallow depth (1-1.5 m depth) (Blunt, 1992).

It can thus be said that the critical, fully softened, soil strength will give a good guide to slope

stability (Blunt, 1992).

Studies in UK Gault CLAY have found that failure rates may, in some cases, be higher in

less-steep cuttings and embankments than in the steepest slopes. This has been attributed to

the fact that the steepest slopes are better able to shed surface water and so will take longer to

reach the softened condition causing failure. Shallow slopes above a maximum safe angle,

generally the angle of repose, will absorb surface water more readily as the water stays on the

slope for longer, and hence fail at a younger age (Parsons & Perry, 1985).

2.3 Vegetation as a Slope Stabilisation Method

“Understanding and quantifying the mechanical effects of vegetation on steep slopes remains

an unresolved problem. Modelling approaches span a wide range of spatial scales, from

modelling of a single root to modelling the stability of an entire vegetated slope” (Schwarz et

al., 2010).

2.31 Properties of Vegetation The presence of vegetation on highway slopes can increase stability by mechanical and

hydrological means. Mechanically vegetation reinforces the

soil by the presence of roots, along with anchorage and

buttressing by long vertical tap-roots. This improves strength

and competence of the soil, increasing overall slope stability.

(MacNeil et al., 2001).

It has been found that roots of diameter greater than 20mm

act as individual soil anchors (Coppin & Richards, 1990),

providing similar buttressing support as driven piles or

anchors.

Figure 2 - 2: Soil Buttressing & Arching (Hiller & MacNeill, 2001)


7

The presence of vegetation also leads to a decrease in pore water pressure by the removal of

soil moisture by the plant during the process of transpiration. This reduction of soil moisture

content also increases soil strength and slope stability (MacNeil et al., 2001).

Vegetation prevents soil erosion in several ways. Rainfall

interception prevents impact on the soil by raindrops,

physical root retention of soil particles prevents erosion by

overland rain runoff, whilst runoff velocity is also reduced.

Depletion of soil moisture content through transpiration also

encourages infiltration, again reducing runoff velocities.

Vegetation cover shades the surface of the soil from the sun,

preventing desiccation and severe cracking (Coppin &

Richards, 1990).

The presence of vegetation on a slope also adds a surcharge loading. While this loading is

negligible in the case of grass and small shrubs, when larger trees are present this can add

significant loading to the soil. Gray & Leiser (1982) are cited by Hiller & MacNeill (2001) as

commenting that the surcharge loading of vegetation exerts both a destabilising downslope

load and a stabilising stress component perpendicular to the slope. It is said that on balance

the perpendicular stress component tends to provide and overall increase to sliding resistance

(Hiller & MacNeill, 2001).

Figure 2 - 3: Equivalent Uniform Surcharge

(Coppin & Richards, 1990)

Figure 2 - 4: The Influence of Vegetation on a

Slope (Coppin & Richards, 1990)


8

2.32 Role of Root Reinforcement in Slope Stabilisation

“Roots embedded in the soil form a composite material consisting of fibres with a relatively

high tensile strength and adhesion within a matrix of lower tensile strength.” (Hiller &

MacNeill, 2001). It can therefore be said that the presence of roots in a soil mass increases

the overall shear strength of the composite root-soil material.

Hiller & MacNeill (2001) commenting on the findings

of Wu (1995) say that this increase is dependent on

the root geometry, strength and frictional resistance

between the soil and the roots. One generally accepted

theory regarding mechanism of soil reinforcement by

vegetation proposed by Barker (1986) is that the strain

restraint in the direction of the reinforcement

increases the effective confining stress of the soil. The

soil friction angle is unchanged (Hiller & MacNeill,

2001).

This effect is said to mobilise additional shear strength beyond that generated by the

externally applied shear strength alone. Barker (1986) goes on to state that soil containing

roots has the ability to resist deformation without losing residual strength. The magnitude of

mechanical reinforcement provided is a function of; root density, tensile strength, tensile

modulus, length to diameter ratio, surface roughness, alignment and orientation with respect

to the principal strain direction (Hiller & MacNeill, 2001).

Only roots below 15-20mm contribute significantly to increased shear strength (Coppin &

Richards, 1990). A report by Gray (1978) found that root density dictated percentage increase

in shear strength due to young alder roots, with an average 30% increase being provided

under conditions of 2m of overburden (Greenwood et al., 2001).

Waldron & Dakessian (1982) found that grasses, six months after sowing, doubled the shear

resistance of soil to depth of 300mm. This report also found that certain plants may result in

shear resistance being increased to four times its un-rooted value. It was noted, however, that

the effective root mass of herbaceous plants is reduced during the dormant winter period

(Greenwood et al., 2001). This raises questions of the year-round reliability of herbaceous

plant species.

Figure 2 - 5: Effect of Root Reinforcement on Shear

Strength of Soil (Coppin & Richards, 1990)


9

The work of several authors has produced a range of soil cohesion increase due to roots of

between 1.0 – 17.5kN/m2 (Coppin & Richards, 1990). Coppin & Richards (1990) go on to

state that there is a very large range of root strength variability between single and multiple

plant species. This can depend on size, age and condition of the plants root system. Tensile

strength values of 4 to 74kN/m2 have been recorded for various alder trees, illustrating this

gross variability quite clearly (Hiller & MacNeill, 2001).

The results obtained are also very reliant on the testing method used. On investigation of a

slope failure in Tuscany, Italy the use of two different models in an attempt to quantify the

effect of roots on slope stability provided vastly different results. The Wu method (1979),

which measures shear strength contribution of roots as relating to a tensile “pull-out value”

indicated a constant value of reinforcement of about 38–50kPa. When the alternative Fiber

Bundle Method (2005) was used, a maximal peak reinforcement value of about 14kPa was

found (Schwarz et al., 2010).

The Fiber Bundle Method relies strongly on displacement and is a method by which a bundle

of roots are tested rather than the single root approach used in the Wu method. This test

illustrated the weakness in the Wu method as it was demonstrated during testing that not all

roots are activated simultaneously in reality, with the upper roots being activated first

(Schwarz et al., 2010). This, added to the previous statement regarding the variability of plant

roots, highlights the error in the Wu method, illustrating the validity of the more modern

method of testing roots as a system rather than individually.

A separate study in Hong Kong concluded that when accurately analysed and installed,

vegetated slopes can provide stability where more costly and substantial traditional methods

would have been required previously (Yim et al., 1988).

2.33 Role of Roots in Moisture Content Reduction

The presence of vegetation on a slope influences the proportion of precipitation which

reaches the soil and affects the behaviour of water within the soil through interception of

rainwater and transpiration (Hiller & MacNeill, 2001). Whilst there are benefits associated

with vegetated slopes there is also a conflict between stability and plant survival; plants need

water to live whilst the presence of water leads to slope destabilisation (MacNeil et al., 2001).


10

Several authors have reported that the balance between having a slope dry enough to ensure

stability whilst containing enough moisture to support significant plant life can be very

difficult to achieve.

Only a relatively small increase in suction of as little as 5kPa has been recorded as being

enough to stabilise a slope (Marsland, 1997) cited by (Hiller & MacNeill, 2001). Vegetation

also has the ability to modify soil moisture further laterally and to depth significantly below

root level (Hiller & MacNeill, 2001), with there being no such thing as an intrinsically

shallow or deep rooted plant species (Sutton, 1969).

Depth of roots depends largely on soil drainage, with roots in well drained soils discovered at

greater depths in nutrient rich layers. Removal of water also reduces the soil‟s bulk density,

reducing disturbing slope forces (Hiller & MacNeill, 2001).

Despite the ability of vegetation to reduce soil moisture and pore water pressures, seasonal

activity trends may negate its significance to vegetated slope stabilisation. A trial carried out

by Hiller & MacNeill (2001) found that suction rates were significantly higher during the

summer growing period than those recorded during the dormant winter months. Once the trial

area vegetation had fully established, five years after planting, significant increases in suction

were often not recorded until June, despite budburst occurring in April. Suction was then

observed to decline in October, meaning that vegetation only provides four months of

significant moisture reduction per year.

A report by Coppin & Richards (1990) found that most highway slope failures occur in

spring when ground water levels are highest, during the period where plant activity regarding

moisture reduction is negligible. As vegetation is effectively inactive during this critical

period it may be concluded that it is mechanical root reinforcement, rather than moisture

reduction, which is the most important aspect in the prevention of shallow slope failure.

2.34 Weaknesses of Vegetation as a Stabilisation Method

Whilst providing an economic alternative to a hard engineering approach, it is this economic

nature which possibly provides the greatest weakness and reason for the lack of wide-scale

uptake of the method. As vegetation occurs naturally there is no manufacturing process

required during production, meaning little financial gain for industry.


11

It has been suggested that the wide-scale use of vegetation has been avoided to support heavy

industry in which national authorities have vested interests.

Rather than attempt to fight an established system, an alternative approach may be the

incorporation of synthetic geotextiles into vegetated slope design to improve the method‟s

corporate appeal. This may lead to improved uptake of vegetation as a more sustainable

stabilisation method (Greenwood et al., 2001).

Destabilising rotational moments due to wind loading may also be exerted on the slope if

trees are allowed to grow too tall (Hiller & MacNeill, 2001). This may destabilise the slope or

leave holes should the tree itself overturn during high wind. These holes could allow ingress

of water into the slope, destabilising the slope further (MacNeil et al., 2001). This can be

avoided if and adequate and practicable maintenance regime is adopted (Greenwood et al.,

2001).

Whilst having the potential to provide a significantly cheaper alternative than traditional

stabilisation methods, there is still much ambiguity regarding the reliability of long-term

establishment of vegetation on highway slopes. (MacNeil et al., 2001).

2.40 Selection of Plant Species

Vegetation species selected for stabilising slopes should provide rapid transpiration along

with winter transpiration and an extensive root system to aid in the removal of water. Root

growth should also be rapid with roots capable of growing to depths of more than 1.5m below

ground level. High leaf areas are also desirable to provide surface shading during hot periods.

In order to satisfy all of these requirements, several plant species are generally necessary

(Greenwood et al., 2001).

When designing vegetation reinforced slopes an allowance must be made for plant losses as

this was found to be a common occurrence in many studies. Topsoil is generally required to

allow for growth and the plants selected must be suitable to the local soil and climatic

conditions (Greenwood et al., 2001). Vegetated slopes are especially vulnerable to failure if

planted during periods of extreme weather (MacNeil et al., 2001).


12

When selecting a plant for highway slopes it must be ensured that the plant type is suitable to

withstand contact with de-icing salts and traffic pollution. A maintenance plan must also be

produced during design which is practicable for the road authority to undertake with this

allowing for repair after accidental or vandalism damage (Hiller & MacNeill, 2001).

Despite the relatively poor success rate of vegetated highway slopes, the successful

vegetation of a 13m high 600 slope in Norway proves that when proper care is taken at the

design and construction stage, this method provides a viable alternative to traditional hard

engineering solutions (Vaslestad, 1996) cited by (MacNeil et al., 2001).

2.5 Conclusion

When correctly designed, vegetated slopes increase the shear strength of soil whilst also

providing a natural means of moisture modification during summer months. This

significantly improves the stability of slopes against shallow seated failure to depths of up to

2m below the surface of the slope, with the critical reinforcement being provided by shear

strength gain from roots. Several studies report on the improved stability of slopes after the

establishment of vegetation, although quantification of the exact level of reinforcement

provided by this method is still largely unknown.

Further studies are required to establish the exact range of reinforcement which is gained by

soil containing vegetation roots.


13

3.0 Methodology

3.1 Required Information Based on the findings of the Literature Review, information was required to quantify the

reinforcement provided to soil by vegetation roots. This information, when related to soil on a

slope, can be correlated to the increased soil stability of that slope. Reinforcement increase

was defined as an increase in measured shear strength in a soil containing roots when

compared to a sample of soil of the same composition which did not contain roots. The

difference in shear strength between the soil with and without roots was classified as the

reinforcement provided to soil by vegetation roots.

In order to obtain this information three proposals were initially put forward, the first two

unsuccessful proposals involved large shear box testing and borehole drilling within the

college campus grounds, which were rejected due to time constraints. This type of testing

may be a useful approach for future research. These tests will not be discussed, however, with

only the successful proposal dealt with in detail within this paper. The two unsuccessful

proposals may, however, be referenced in the context of the test approach adopted.

3.2 Background Having rejected two proposals on the basis of impracticality and time constraints it was

deemed that the successful approach would allow results to be taken independently, using

equipment which could be easily sourced, whilst providing good samples which could be

tested using the equipment already in the college laboratory. This posed a unique set of

problems which meant that one single testing approach would not meet the criteria as listed

above. It was therefore decided to use an approach which combined aspects of the two

rejected proposals, taking the positive aspects of each, whilst removing the negatives, where

possible.

It was decided that in order to efficiently recover undisturbed samples of the required

standard a method of coring which would produce samples of similar dimensions as those

recovered from borehole drilling would be used. This would be done manually rather than

mechanically, with samples taken by driving a cylindrical sampling device of sufficient

diameter to allow for testing with the available equipment.


14

Manual drilling meant samples could be taken quickly and in locations remote from the

college campus, greatly increasing the investigative scope of the process.

Testing of the recovered samples was decided to be of a manner which would suit the

equipment present in the soils laboratory at The Institute of Technology Carlow. This

consisted of a triaxial testing machine, a 60mm x 60mm square shear box, Atterberg Limits

and Organic Content testing apparatus. Concerns regarding the size of the shear box meant

that in the initial proposal use was to be made of a larger box. By supporting the information

obtained from the small shear box by triaxial and shear vane testing it was possible to

confirm the relative accuracy of the data, thus allowing testing to be carried out in the small

box.

Triaxial testing was originally to be done on a number of samples to provide an outline range

into which it would be expected shear box results would fall. As time progressed, however, it

was decided to use triaxial testing as an outline defining parameter rather than as the main

source of testing

The relatively simple shear box test was thus selected to from the majority of the lab testing,

to estimate the shear strength provided by root reinforcement and allowed for a large number

of individual tests to be conducted. Shear vane testing was also carried out on site to allow for

further data to be compiled on the soil quickly and in-situ.

In order to define the material found on site so as to give relevance to the results it was

decided to carry out Atterberg Limit testing in order to identify the Plastic Limit, Liquid

Limit and Plasticity Index of the soil. Defining the plasticity of the soil meant that the results

of shear box testing could be put in context of the soil which was tested. This was deemed to

be useful in adding to the relevance of the obtained results.


15

3.3 Site Visit

3.31 Site Description

Soil samples were recovered from a site in Killeshin Co. Laois, located approximately 5km to

the west of Carlow Town. As the samples of soil containing roots and the samples without

roots could be taken within 10 metres of each other, the greatest certainty of consistency

between soil type could be assured.

This made the site ideal for the purpose of the test, as only by testing soil of the same

composition when containing roots and when roots are not present could a true reflection on

the reinforcement provided by the presence of vegetation roots be made.

Figure 3 - 1: Site Location Map (OSI Maps)

The location of the site relative to the forested area can be clearly seen on the map shown above.

The steeply sloping ground profile from where the soil samples were taken can also be seen, with

soil observed as being retained to almost 90° in some

places.

It was proposed to recover soil samples containing

roots from the forested area, with samples not

containing roots taken in a field located

immediately up gradient of this location.

Test Site Location

Graiguecullen

To Carlow Town

Site 2 – Soil

Without Roots

Site 1 – Soil

With Roots

Figure 3 - 2: Satellite View of Sampling Sites (Google Maps)


16

Due to the close proximity of both sites it was assumed that the soil at both locations would

be of the same composition, though this could not be absolutely guaranteed. By recovering

samples of the same stratum it could be ensured that results best reflected the strength gain

due to root reinforcement, rather than an increase due to soil differences.

3.32 Observations Made on Site

When on site it was observed that many of the steep angled slopes along the roadways were

heavily vegetated. Whilst the presence

of this natural vegetation could not be

said to be the cause of the stability of

these slopes, it did suggest that there

was some connection between the two.

These observations were recorded and

are illustrated in the accompanying

photographs.

A desk study carried out on the site,

using data from GSI maps suggested shallow depth of overburden over a mainly shale and

limestone bedrock. The data presented on these maps suggested that average depth to bedrock

was in the region of 0.6m, with some rock outcrops in places. This led to concerns regarding

the suitability of the site for deep soil sampling. If bedrock was found at such shallow depth it

was likely that coring would have to be terminated prematurely should an outcrop be

encountered. You would also be likely to get infinite (very shallow, translational landslide)

type failures due to slope failure at the soil-rock interface.

Figure 3 - 3: Shear Soil Faces Restrained by Large Tree Roots

Figure 3 - 4: Heavily Vegetated Steep Cut

Slope


17

An initial walkover survey confirmed these fears, with clear rock outcrops observed in the

cut slopes of the minor roadway separating both sites.

A visual inspection of the soil was also made

during the initial site visit. This visual

inspection was supported by information

obtained from GSI maps, which suggested

this region contained poorly drained soil,

which was possibly even peaty in places.

Soil on site was observed as being a fine

grained brown CLAY type material, with

roots present throughout. It was noted that

decomposition of these roots over a long

period of time may indeed have led to an

organic, peaty soil.

On inspection it was observed that this soil was reasonably soft, mouldable and could be

easily rolled into a ball. This suggested a highly plastic soil, with Atterberg Limit testing

required to confirm the observations made on site.

Concerns regarding strength and uniformity of the soil across the two sites were to be

investigated by carrying out shear vane tests, using a hand shear vane.

Figure 3 - 5: Observed Approximate 0.6m Depth to Bedrock

Outcrop

Figure 3 - 6: Close up View of Soil Found on Site


18

3.4 Sampling Process

3.41 Samples Required

Undisturbed core samples were required to carry out tests which would be representative of

the root distribution as found in nature. As it was determined at an early stage that to

accurately reconstruct the distribution of vegetation roots would be almost impossible

without carrying out an extensive study it was decided that all sampling should consist of

undisturbed coring. The initial test programme as drawn up required extensive triaxial

testing.

An initial test using the triaxial apparatus within the college laboratory encountered several

technical difficulties, however, so it was ultimately decided that most of the testing should be

carried out with the small shear box. The results of this problematic triaxial test were

recorded within the results section of this report as there was noticeable correlation between

this and the observations made during in-situ shear vane testing. Samples for shear box

testing were still required to be in the form of undisturbed core samples due to the issue

regarding replication of natural root distribution as outlined above. Undisturbed samples were

required from vegetated and green field areas to provide the required comparison.

A disturbed bulk sample was required to carry out Atterberg Limit testing of the soil.

Observations made on site and when samples were returned to the lab indicated that this soil

may be highly plastic. Atterberg Limit testing was thus prescribed to investigate the initial

assessment of the soil.

3.42 Sampling Process Initial soil sampling was undertaken using uPVC pipe of

110mm diameter, cut into approximately 470mm sections, done

as uPVC pipe was easily accessible at the time of testing. These

dimensions were chosen so as to allow for seven sections be

taken from the original pipe length, whilst also leaving enough

pipe overrun to allow ease of retrieval once the required

350mm depth of soil had been taken. This was to allow for a

200mm height of sample to be accurately trimmed and tested in

the triaxial test apparatus once returned to the laboratory. Figure 3 - 7: Preparation of Sampling Tubes


19

Each pipe section was driven into the ground by placing a

timber board across the top of the pipe and using a hammer to

apply the required insertion force. Whilst proving reasonably

effective there were several issues which eventually lead to the

proposed use of a steel U100 sampling device for later

sampling. Foremost of these issues was the fact that the

diameter of drainage pipe readily available was 10mm larger

than the allowable for the triaxial testing machine in the college

laboratory.

This meant that excessive trimming of the samples was required prior to testing, which

caused unnecessary disturbance to the sample, meaning any results were open to

inaccuracies. The second issue was due to the brittle nature of the uPVC material the pipes

were made from. This meant that several pipes were cracked

as they were driven into the ground, resulting in samples

which were unsuitable for triaxial testing being recovered.

In order to overcome these issues later sampling was

proposed to be carried out using a steel U100 sampling

device. This would have allowed for 100mm diameter

samples to be recovered, with a greater degree of sample

quality.

As the testing process advanced and issues regarding the condition of the triaxial machine

came to light this approach was reviewed. Under the revised plan the majority of results were

to be obtained using the shear box, meaning that uPVC pipes

could be used as the issue regarding pipe diameter no longer

applied. Some sampling within the un-rooted zone was carried

out using the U100, however this only made up a very small

proportion of the entire sampling programme.

Figure 3 - 8: Driving Sampling Pipe

Figure 3 - 9: Pipe Exhibiting Damage

Figure 3 - 10: Sampling Using U100 in

Greenfield Site


20

During the sampling process it was observed that due to the thicker walls of the U100 a

greater force was required for insertion. The thicker walls added to the excessive vibrations

caused by hammering of the U100 sampling tubes meant that retrieved samples using this

process were likely to be disturbed to a greater degree than those retrieved in the uPVC pipes.

Sampling with the uPVC pipes could be done using only a small lump hammer and a thick

plank of wood to protect the top of the pipes from direct impact damage. This form of

sampling meant that the samples returned for testing were as representative as possible of the

soil conditions on site. The samples retrieved from the heavily vegetated area exhibited

substantial root presence, meaning that results were expected to be provide a true reflection

of the shear strength increase provided to soil by vegetation roots as found on site.

Samples were sealed by tightly wrapping each end of the sampling tube in cling film and

aluminium foil, as recommended by BS 1377 for short-

term storage when paraffin wax is not available. This

method of sealing the soil proved very effective after

initial sampling, with the soil maintaining moisture for

over a week in storage.

Once sealed, samples were transported and stored under

damp conditions in a location in Graiguecullen, to the

north of Carlow Town, approximately 2.5km north-west

of The Institute of Technology Carlow soils laboratory.

Samples were stored in this location until required for

testing, when they were transported to the soils

laboratory, with only as many samples as would be

tested transported each time.

Figure 3 - 12: Heavily Vegetated Soil Sample

Figure 3 - 11: Soil Transportation from Site


21

3.5 In-Situ Testing

3.51 Visual Inspection

During sampling a visual inspection of the soil found on site was made in order to

qualitatively asses the anticipated soil strength parameters. The findings of this are outlined in

the site observations, and indicated that in-situ shear vane testing would be required to better

assess how the soil varied across the site.

Shear Vane Testing

Shear vane testing was carried out during the later sampling stage to give quick indications of

soil strength parameters which could be used to compliment the strength values obtained in

the laboratory. This allowed for a greater understanding of the impact of roots with regard to

soil slope stability due to correlation between testing methods.

The use of shear vane testing also allowed for a quick assessment of the similarities, and

differences, between the soil found at the two separate site locations. This testing allowed for

a general strength profile of the soil at each location to be drawn up.

To Sampling Site

Storage Location

Institute of Technology Carlow Campus

Figure 3 - 13: Carlow Town Satellite View (Google Maps)


22

Shear vane testing was carried out in accordance with the principles of clause 3 of BS 1377-

7:1990, with samples tested in-situ rather than in the laboratory. The findings of this

investigation are detailed later.

3.6 Laboratory Work

3.61 Laboratory Preparation

Once returned to the lab, the core samples were extracted from the sampling tubes by pushing

the soil out of the tube, pushing from top to bottom, ensuring the soil exited the tube at the

same end it entered. This was done to avoid disturbing the soil sample during the extraction

process.

Samples taken using uPVC pipes required trimming to the

required 100mm diameter prior to triaxial testing. This

greatly delayed the process and caused disturbance, due to

the fact that the outer face of the cylindrical cores had to

be trimmed using a saw. Later samples for triaxial testing

were proposed to be obtained using the U100, with these

samples prepared according to clause 8 of BS 1377-

1:1990.

It must be noted that as time progressed the triaxial testing programme was abandoned in

favour of the faster shear box test. Future testing carried out under more relaxed time

constraints should possibly carry out a series of triaxial testing, using U100 core samples.

It was decided that it would be prudent to use the limited time to better classify the soil in

terms of Atterberg Limits and organic content rather than focus solely on multiple methods of

defining shear strength. This alternative testing gave a better understanding of the type of soil

being described, adding relevance to the obtained results.

Atterberg Limit testing was carried out on a bulk sample recovered from the area where soil

samples containing roots were sourced. This sample was returned to the lab, where the

contents were spread out over a large tray and allowed to air dry for three days, mixing of the

soil was carried out on day two to ensure uniform drying of the sample.

Figure 3 - 14: Extraction of Soil Sampled in uPVC

Pipe


23

Shear box samples were prepared from the soil samples taken in the uPVC pipes. These

samples were prepared in accordance with BS 1377-1:1990

3.62 Laboratory Testing

Testing was carried out on the entire soil matrix containing roots, rather than on the

individual roots themselves, due to the findings on root activation made during the literature

review process. This method most closely represents the Fibre Bundle Method as

recommended by the work of Schwarz et al., 2010.

3.63 Triaxial Testing

Triaxial testing for this experiment took the form of a

single Unconsolidated Undrained Triaxial Test. Should

greater time and resources be available for testing, it may

be advantageous to undertake consolidated drained

testing to examine the long-term strength gain of soil due

to the presence of roots.

The short-term results obtained in this experiment may be expected to provide an immediate

value for the initial strength increase provided to soil by the presence of vegetation roots.

Triaxial testing was carried out in accordance with clause 8 of BS 1377-7:1990.

Figure 3 - 15: Bulk Sample for Atterberg Limits

Figure 3 - 16: Trimmed Sample in Triaxial Apparatus


24

When calculating for the rate of loading an assumption was required on the anticipated failure

load. This was required to determine the approximate rate of pressure increase required to

achieve 20% strain in 10 minutes. On a 200mm sample it was calculated that it would require

axial displacement of 4mm/min to achieve 20% strain within this time period. Difficulties

regarding the actual rate required to achieve 20% strained are discussed within the

methodology observations section.

3.64 Shear Box Testing

Shear box testing was carried out in the small shear box in the soils laboratory of The

Institute of Technology Carlow, with testing done according to BS 1377-7:1990. Shear box

tests were carried out on the soil retrieved within the samples taken in the 110mm uPVC

pipes, as discussed earlier. Due to the significant volume of soil sampled within the uPVC

pipes, a large supply of soil meant that substantial testing could be done within the small

shear box at an early stage in the testing process.

Shear box tests were carried out on soil from the two separate sites as discussed previously.

Samples were recovered for testing by pushing a 60mm x 60mm x 20mm cutting shoe into

the soil stored within the sampling tubes. This sample was then trimmed and placed within

the shear box to be tested, allowing for an undisturbed sample to be tested.

The insertion of the cutting shoe was frequently obstructed by the presence of relatively large

stones within the sample. These stones were removed using a small pallet knife, with great

care required to ensure no disturbance of the sample was caused as the stone was extracted

from beneath the cutting shoe.

Shear box testing was carried out over a three week period in late February to mid-March

2014. The results provided are a reflection of those found during extensive testing during this

limited time period, and may require further testing to confirm the conclusions drawn from

observed results.


25

3.65 Organic Content Testing

Observation of the soil, having a reasonably dry appearance whilst measured moisture

content was in excess of 29% lead to the conclusion that the soil under inspection was most

likely a soft peaty soil with a high organic content. In order to investigate this, further testing

was carried out in partnership with the Science Department of The Institute of Technology

Carlow. Sample preparation was carried out to clause 7 of BS 1377-1:1990, whilst testing

was carried out as outlined in clause 4 of BS 1377-3:1990.

3.66 Atterberg Limit Testing

Atterberg Limit testing was carried out on the soil to determine the plasticity of the seemingly

ductile material. Testing was carried out in accordance with BS 1377-2:1990 as appropriate.

3.67 Observations & Limitations

During the triaxial testing phase it was observed that to truly achieve 20% strain would

require familiarity with the specific soil type under examination in order to for the loading

rate and gauge calibration to be correct. During triaxial testing the loading rate and

displacement gauge were initially set to a level which meant termination of the test prior to

achieving 20% strain.

This meant that the graphed data did not show an absolute peak value, although the slope of

the line was seen to peak to an allowable extent so as to interpret a failure value. If further

testing is to be carried out, explorative tests should be undertaken to obtain an indication of

how the soil deforms under loading. Only once this is known should final recorded testing be

undertaken.

When initial testing was carried out it was found that several components of the triaxial

apparatus were not functional. This lead to delays in testing and meant that the sample under

examination was open to possible moisture content losses as the array of issues were worked

through. This also meant that certain test parameters were not accurately measured as the

correction of issues meant that previously input data was often lost as a new issue was

resolved.


26

It was observed that if exposed to mild conditions the soil samples will quickly lose moisture

unless they are adequately sealed using paraffin wax or other air tight substances. During

testing it must be ensured that the core sample is kept air tight as the process is carried out,

especially if conditions in the laboratory are significantly warm, as was the case during

preparation of this paper.

It was observed that during shear box testing great care must be taken to ensure the

prescribed procedure is accurately adhered to. When the shear box is separated excessively,

shearing occurs towards the top of the sample, possibly reducing the shear strength of the

soil. It must also be ensured that the shearing plates are correctly aligned, perpendicular to the

direction of shear. This is to ensure that the soil is sheared, rather than horizontal

displacement being caused by the plates simply sliding over the soil.


27

4.0 Results

4.1 Triaxial Test

The following data was recovered during the single Unconsolidated Undrained Triaxial Test

which was carried out on a sample of soil containing roots in the soils laboratory of The

Institute of Technology Carlow. The sample was prepared as described within the

methodology section, with all issues encountered during testing are also outlined.

Table 4 - 1: UU Test Description

The recorded test results are presented below and illustrate the undrained shear strength of the

soil tested. The results presented in the following pages are discussed later in this paper. The

data obtained during testing was used to complete the following calculations in accordance

with the standard set out in clause 8 of BS 1377-7:1990.

Figure 4 - 1: Axial Strain Vs. Deviator Stress

Test Details Test Conditions

Test No.: 1 No. Specimens: 1

Date: 18/02/2014 Specimen Height: 200 mm

Location: Insitute of Technology Carlow Specimen Diameter: 100 mm

Soil Type: Cohesive Soil Specimen Mass: 2522.1 g

Roots: Yes Confining Pressure: 50 kpa

Latex Membrane Dia: 2 mm

Soil Description: Brown silty CLAY with roots

Unconsolidated Undrained Triaxial Test

0.000

10.000

20.000

30.000

40.000

50.000

60.000

70.000

80.000

90.000

0.000 2.000 4.000 6.000 8.000 10.000 12.000 14.000 16.000 18.000

De

viat

or

Stre

ss (

kPa)

Axial Strain (%)

Axial Strain Vs. Deviator Stress


28

Calculations

Initial Area (A0): 7853.982 mm2

Initial Length (L0): 200.000 mm

ΔL: -33.783 mm

Axial Strain (ε): -0.169

Deformed Area (A): 6719.044 mm2

Final Force: 540.688 N

(σ1 - σ3)max 80.471 kPa

Membrane Factor 1.750 (Table 11)

Correction Factor: 6.650

(σ1 - σ3)f: 73.821 kPa

Cu: 36.911

ρ: 1.606 Mg/m3 Table 4 - 2: Triaxial Test Calculations

Figure 4 - 2: Mohr's Circle Sketch


29

Moisture Content

Soil + Container Wet: 1725.9 g

Soil + ContainerDry: 1422.7 g

Container: 397.4 g

Soil MassWet: 1328.5 g

Soil MassDry: 1025.3 g

m.c.: 29.57 % Table 4 - 3: Moisture Content Calculations

4.2 Shear Vane Test Shear vane testing was carried out in accordance with BS 1377, as outlined in the

methodology section of this paper. The relevance of the results in relation to the other tests

carried out is discussed later in. It should be noted that values provided within the following

tables represent average values located at depth. It was observed on site that significant

variations may occur in isolated areas, as will be discussed.

Shear Vane - Vegetated Area

Depth (mm) Cu

50-100 30.00 kPa

150-250 60.00 kPa

300-400 80.00 kPa

450-550 100.00 kPa Table 4 - 4: Shear Vane Results (Vegetated Area)

Shear Vane - Greenfield Area

Depth (mm) Cu

50-100 50.00 kPa

150-250 75.00 kPa

300-400 90.00 kPa

450-550 105.00 kPa Table 4 - 5: Shear Vane Results (Greenfield Area)

4.3 Shear Box Testing The following graphs were produced based on the results from shear box testing carried out

in the soils laboratory of The Institute of Technology Carlow, following the procedure of BS

1377 as described within the methodology. The weights referred to in the graph titles refer to

the confining weight applied to the loading arm of the shear box apparatus during testing. All

shear strengths recorded are relative to these confining pressures. The tabulated results on

which the graphs are based are included within the Appendix of this paper.


30

Figure 4 - 3: 19.075kN/m2 With Vs. Without Roots

Moisture Content With Roots: 27.67%

Moisture Content Without Roots: 39.81%

Figure 4 - 4: 13.625kN/m2 With Roots Vs. 19.075kN/m2 Without Roots



0.000

5.000

10.000

15.000

20.000

25.000

30.000

0.000 2.000 4.000 6.000 8.000

She

ar S

tre

ss (

kPa)

Horizontal Displacement (mm)

19.075kN/m2 - Soil With Roots Vs Soil Without Roots

Soil With Roots

Soil Without Roots

0.000

2.000

4.000

6.000

8.000

10.000

12.000

14.000

16.000

0.000 1.000 2.000 3.000 4.000 5.000 6.000 7.000 8.000

She

ar S

tre

ss (

kPa)


13.625kN/m2 With Roots Vs. 19.075kN/m2 Without Roots

5kg With Roots

7kg Without Roots


31







0.000

5.000

10.000

15.000

20.000

25.000

30.000

0.000 2.000 4.000 6.000 8.000

She

ar S

tre

ss (

kPa)


27.25kN/m2 - Soil With Roots Vs Soil Without Roots

Soil With Roots

Soil Without Roots

0.000

10.000

20.000

30.000

40.000

50.000

60.000

0.000 2.000 4.000 6.000 8.000

She

ar S

tre

ngt

h (

kPa)


40.875kN/m2 - Soil With Roots Vs. Soil Without Roots

Soil With Roots

Soil Without Roots


32







0.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

40.000

45.000

50.000

0.000 2.000 4.000 6.000 8.000 10.000

She

ar S

tre

ss (

kPa)



Soil With Roots

Soil Without Roots

0

10

20

30

40

50

60

0 2 4 6 8

She

ar S

tre

ss (

kPa)



Soil With Roots

Soil Without Roots


33







0

10

20

30

40

50

60

0 2 4 6 8

She

ar S

tre

ss (

kPa)



Soil With Roots

Soil Without Roots

0.000

10.000

20.000

30.000

40.000

50.000

60.000

70.000

0.000 2.000 4.000 6.000 8.000

She

ar S

tre

ss (

kPa)



Soil With Roots

Soil Without Roots


34

Figure 4 - 11: 109kN/m2 With Vs. Without Roots



4.4 Atterberg Limit Testing

As shear box testing advanced, the large moisture content values recorded for the soil became

an issue which was deemed to require further investigation. Atterberg limit testing was

therefore carried out on the soil to investigate the characteristics of this soil. Atterberg limit

testing was carried out in accordance with the procedure of clause 4-5 of BS 1377-2:1990.

Liquid Limit

Test Beaker

No. Wt.

Beaker Wt. Bkr + Soil (W)

Wt. Bkr + Soil (D)

Wt. Water Moisture Content

Penetration

(g) (g) (g) (g) (%) (mm)

1 1 27.6 44.6 37.8 6.8 66.67 16.000

2 2 16.3 45.6 33.4 12.2 71.35 21.000

3 3 26.1 43.2 35.9 7.3 74.49 24.700

4 4 26.5 46.3 37.8 8.5 75.22 25.300 Table 4 - 6: Liquid Limit Test Results

0

10

20

30

40

50

60

70

80

0 2 4 6 8

She

ar S

tre

ss (

kPa)


109kN/m2 - Soil With Roots Vs. Soil Without Roots

Soil With Roots

Soil Without Roots


35

Figure 4 - 12: Cone Penetration Vs. Moisture Content

Liquid Limit: 70.40 %

Plastic Limit

Test Beaker

No. Wt.

Beaker Wt. Bkr + Soil (W)

Wt. Bkr + Soil (D)

Wt. Water Moisture Content

Plastic Limit (%) (g) (g) (g) (g) (%)

1 1 26.3 27.5 27.15 0.35 41.18

40.43 2 2 25.3 27 26.5 0.5 41.67

3 3 25.5 27.3 26.8 0.5 38.46 Table 4 - 7: Plastic Limit Test Results

Plasticity Index = Liquid Limit – Plastic Limit

Plasticity Index = 70.40 – 40.43

Plasticity Index: 30

0.000

5.000

10.000

15.000

20.000

25.000

30.000

66.00 67.00 68.00 69.00 70.00 71.00 72.00 73.00 74.00 75.00 76.00

Co

ne

Pe

ne

trat

ion

(m

m)

Moisture Content (%)

Cone Penetration Vs. Moisture Content


36

4.5 Organic Content Testing Following the findings of Atterberg Limit testing it was decided to investigate the organic

content of this potentially peaty soil. Organic content testing was carried out on a sample of

soil taken from the vegetated area, with the roots removed in order to obtain the base soil

organic content. This was done by chipping a sample from the dried soil used for the triaxial

test. Organic content testing was carried out in accordance with clause 4 of BS 1377-3:1990,

as outlined in the methodology.

Organic Content Test

Container: 83.892 g

Container + SoilPre Ignition 95.656 g

Soil Pre Ignition: 11.764 g

Container + Soil Post Ignition 94.692 g

Soil Post Ignition: 10.8 g

Organic Content: 8.0 % Table 4 - 8: Organic Content Test Results

The significance of these results are discussed in the conclusions section of this paper.


37

5.0 Discussion

5.1 Triaxial Testing The triaxial test carried out on a soil

sample containing roots suggested that

the soil under inspection was highly

mouldable, deforming readily under an

applied load. A loading rate of

4mm/min had been anticipated as being

sufficient to bring this type of soil to

20% strain in 15 minutes, however as

the results show this was not the case,

with the soil reaching approximately

17% strain at such a rate as to cause the

test to be aborted prior to reaching this target.

This highlighted the soil as being highly

mouldable and readily compressible

under loading, with the recorded

undrained shear strength of

approximately 37kPa suggesting this

soil may be susceptible to movement

should a destabilising force be

introduced to the slope where the soil

was sourced. The results of this test

pointed towards the anchoring effect of

the vegetation roots as being key to the

stability of this steep slope from which samples were taken.

Figure 5 - 2: Soil Deforming Under Triaxial Loading

Figure 5 - 1: Steep Vegetated Slope


38

Observations made after the test was complete

support this theory, with the soil having failed

along a plane where vegetation was less

prevalent. The fact that the soil essentially

failed along a plane which picked its way

between the roots present in the soil suggest a

significant role played by the roots in

stabilising the slope against soil movement.

5.2 Shear Vane Testing As a result of observations from the triaxial test it was decided to carry out a series of in-situ

shear vane tests for verification. Shear vane testing was carried out at both sites, with

significant variation in undrained shear strength of the soil observed with depth below ground

level. The soil was observed to quickly gain strength as explorations were carried out at

greater depth, with this pickup being particularly great at the site where soil samples

containing roots were sourced.

These findings support the belief found during the

literature review that as water infiltrates from the top

down, soil will be weaker in its upper zone, with this

zone therefore being most susceptible to slope failure.

Soil at the surface was observed to be highly

saturated, with a trial hole filling with water after only

a short period of rain during sampling. In general the

results of the shear vane tests coincided with what was found during the triaxial test.

Soil near the surface was found to have an undrained shear strength of approximately 30kPa,

with this soil being tested at depth close to that of the failure plane of the triaxial sample. This

strength increased substantially as the zone of greatest root concentration was entered at the

vegetated site, with strength approximately doubling between 100mm BGL and 200mm

BGL. This suggested that it may be largely due to the roots that the soil on the steeply sloping

vegetated region has remained stable.

Failure Plane

Figure 5 - 3: Failure Plane of Triaxial Sample

Figure 5 - 4: Trial Hole in Saturated Soil


39

As depth was increased further it was found that the effect of the roots meant that strength at

maximum penetration depth was almost equal at both sites. It may be the case that the

concentration of roots towards 0.5m depth becomes substantial enough to significantly

increase the strength of a soil which appeared at the surface to be inherently weaker than that

found in the un-vegetated area.

5.3 Shear Box Testing

The vast majority of results came in the form of shear box testing, with this method perhaps

providing the best indication of the influence roots have in increasing the shear strength of

soil, in the undrained state, as was the case during testing. Almost every shear box indicated

that the soil samples containing roots demonstrate a higher level of undrained shear strength

than similar soil when these roots were not present.

Figure 5 - 5: Various Depths of Investigation (Vegetated Area)


40

The degree to which this strength differed was observed to be highly variable between tests,

however it is clear that in all but one test soil was made stronger when vegetation roots were

present.

It may be said from analysis of the results that the observed increase in shear strength was

caused by both varying soil moisture contents and also whether or not shear failure of the soil

was achieved. In many of the tests it was observed that the soil moisture content was lower in

the soil containing roots than that which did not contain roots, with this difference being in

excess of 10% moisture content in some cases.

Based on the literature review it was discovered that the majority of slope failures are due to

soil losing strength as it is softened due to an increase in moisture content, meaning that a

more moist soil will have lower shear strength than a drier soil. It was also discovered that the

presence of vegetation can dramatically decrease the soil moisture content due to suction of

moisture into the vegetation by the roots. It was, however, reported that this activity is only

significant to cause a decrease in moisture content during the months from June to October, a

period where rainfall and soil moisture is generally low.

These findings in the literature review meant that the moisture reduction ability of vegetation

was to be ignored for testing, as it was deemed that this effect does not take significant effect

during the critical months where slope failure is most common in late-winter to early-spring.

Sampling for these tests was carried out at the peak of this critical period, in the middle of

February, where soil was almost saturated after an especially wet start to 2014.

If the theory in the literature review was to be believed then it would be expected that soil

moisture in most samples would have been approximately equal in both sites, with the green

field site perhaps even expected to be drier due to the presence of some drainage to this field.

This was not the case in almost every test sample, suggesting that there is perhaps some

residual moisture reduction effect of vegetation even during the

dormant winter period where it is expected moisture reduction effect

of vegetation is insignificant. It may be the case that the presence of

vegetation provides a significant year round moisture reduction,

possibly meaning that it is not necessarily correct to discount this

parameter when considering vegetation as a stabilisation method.

Figure 5 - 6: Visible Shear Failure Plane


41

During testing it was also observed that in order to truly mobilise the root reinforcement

capacity the soil sample must be tested to failure. It was observed from several tests that it is

only when the soil is brought close to failure that the true impact of root reinforcement can be

defined. In tests where the slope of the line was never truly brought to a zone reflecting

failure, test results didn‟t return any real difference between soil with and without roots.

It is only when the slope of the line could be seen to become flat at peak stress that a major

difference between samples could be defined. When tested to failure the shear reinforcement

capacity of the roots is fully mobilised, significantly increasing the shear strength well above

that of the soil which does not contain roots.

The sample tested under an initial normal stress of 40.875kN/m2 provides an excellent case in

point for how roots act to reinforce soil. Before reaching

failure the soil with roots appeared to be significantly

weaker than the soil without roots.

It is only as both samples reached failure did the shear

reinforcement capacity of the roots take effect, spiking

the shear strength value right at the point of failure to a

value 40% greater than that of the soil which did not

contain roots for the same horizontal displacement.

After the failure point was passed this soil‟s residual strength was also higher than that of the

soil which did not contain roots.

It is perhaps this example which best demonstrates how roots act to reinforce soil to increase

the shear strength, with the effect only truly felt as the soil is brought to failure. This was

generally the case during testing, although some samples appeared stronger at all phases of

displacement, whilst one sample was actually weaker with roots than without. It was also

observed that as confining pressure was increased the soil containing roots demonstrated a

significantly higher shear strength value, despite moisture content being equal to or greater

than that of the soil sample which did not contain roots.

These variances are to be expected during laboratory testing, with the generalised observation

that shear is increased during roots as the soil is brought to failure generally ringing

throughout all testing phases.

Figure 5 - 7: Sample after Shear Box Test


42

5.4 Atterberg Limit Testing During shear box testing it was observed that the

soil being tested often appeared dry, only for

significant quantities of excess water to be

squeezed into the shear box apparatus once the

test had been completed.

Recorded moisture content values also appeared

to be much higher than was expected for the soil

on inspection. As a result it was decided to carry

out tests to define the characteristics of the soil

under examination.

These initial observations were proved to be

well founded once Atterberg Limit tests were

carried out. During mixing it was noted that the

soil appeared to absorb a high volume of water

before a thick paste could be formed to be

tested, suggesting a high plastic and liquid limit.

This was confirmed by the test results, with

liquid limit recorded as 70.4%, whilst the plastic

limit for the soil was found to be 40.43%. When

plotted on the table from BS 1377 (included in

the Appendix) this gave a plasticity index of

approximately 30, suggesting a highly plastic

organic CLAY soil.

This confirmed the observations made during

sample preparation for the previous tests that

the soil under inspection was a highly

mouldable soft CLAY.

Figure 5 - 8: Dry Soil Passing 0.425mm

Sieve

Figure 5 - 9: Soil after Mixing

Figure 5 - 10: Cone Penetrometer Test


43

5.5 Organic Content Testing

Having found the soil to be a highly mouldable CLAY material it was decided to inspect for

organic content, as the soil appeared to behave like a peat type material under loading, with

water being forced out of the pores much more readily than would be expected of a CLAY

soil.

The test result for organic content returned a value of 8%, correct to the nearest 1%. Whilst

this organic content is above average when considered in terms most productive agricultural

soils which have an organic content between 3-6%, it does not suggest that the soil is a peat

type material.

Organic content readings would have been higher should a section of the soil containing roots

been tested, with this being avoided as it was the organic properties of the soil rather than the

vegetation which was required for classification. Organic content testing proved that whilst

being above average in terms of organic content, this soil is not classified as a peat.

Testing was therefore concluded to have been carried out on a soft, high plasticity, brown

peaty CLAY, which contained significant large rounded gravel content due to its close

proximity to bedrock. This soil was also observed to be considerably permeable for a CLAY

material as moisture was easily squeezed from its pores during testing.

Figure 5 - 11: Penetration at High Moisture Content Figure 5 - 12: Plastic Limit Test Samples


44

6.0 Conclusion

The role of vegetation roots in slope stabilisation is a complex issue, with many contradictory

studies coming to vastly different conclusions. Several of the sources cited in the literature

review, reporting from tests on root suction, state that the moisture reduction impact of

vegetation roots is negligible or non-existent during the dormant winter months of deciduous

trees.

Soil Moisture, it has been found, is the main cause of slope failure on highway slopes. A new

option which provides a significant moisture reduction, especially during these winter

months, would be seen by many as the ideal solution to the problem of highway slope failure.

The results of this study, carried out in February-March 2014, have found that contrary to

what was stated by published literature, the presence of vegetation roots can significantly

lower the moisture content of soil, as observed at two locations located no more than ten

metres apart. Over nine comparisons carried out on soil samples it was found that soil which

did contain roots showed an average moisture content reduction of 6.4% over samples in

which roots were not present.

These findings strongly suggests, contrary to what is commonly believed, that the presence of

vegetation may provide a significant year-round reduction in soil moisture content. It may be

the case that by installing vegetation rather than traditional hard engineering methods as a

slope stabilisation system, a low cost and effective method of reducing slope failure due to

excess moisture ingress which is reliable during the critical failure period can be achieved.

Actual estimation of the quantifiable shear reinforcement of soil due to roots is difficult to

determine. The experiments carried out during the preparation of this paper indicated a highly

variable range of reinforcement due to roots, with one test even suggesting that no

reinforcement was gained at all by their presence.

The moisture reduction effect as discussed also meant that soil samples tested were not

exactly like-for-like. The significant moisture content differences meant that the soil samples

which did not contain roots were inherently softer and therefore would be expected to provide

less shear resistance than those which did contain roots.


45

A conservative estimate of the average shear strength gain due to the presence of roots based

on the results from laboratory testing put the figure at approximately 10%. Testing during

these experiments was carried out on samples containing small roots only, however the

results from the tests clearly indicate that vegetation provides a viable low-cost solution for

year-round slope stability.

Vegetation roots have been found to provide reliable and significant shear strength increase

in soil due to mechanical reinforcement and year-round moisture content reduction in the

form of soil sheltering and moisture absorption. A well respected commentator also noted

that during winter it is possible that the vegetation roots shrink and create temporary drainage

paths within the soil in the winter months. This could also be a cause of reduced moisture

content during the dormant period due to increased drainage.


46

7.0 Recommendations

Further research is required to confirm the observation that vegetation roots may provide a

degree of moisture reduction during the dormant months which is significant so as to aid in

slope stability. As the discovery was incidental during the preparation of this paper, further

research is required which sets out to determine this moisture reduction capacity by extensive

field measurements of vegetated and un-vegetated soil samples.

To fully investigate this theory, samples should be taken from several soil types, at a

multitude of locations and after varying weather conditions. Should reliable moisture

reduction be confirmed this would be crucial in the advancement of slope vegetation as a

viable stabilisation method.

The unexpected moisture variance between soil which contained roots and that which did not

meant that shear strength tests which were carried out could not be defined as having

compared like-for-like soil samples. The fact that soil which did not contain roots was wetter

means that it would be expected that this soil would be weaker even if vegetation roots were

not present in either sample. This means that any prediction of strength gain due to root

reinforcement based on the results of this experiment do not represent a truly comparative

value.

Future testing on quantifying root reinforcement should ensure samples tested are of similar

moisture content, taking cognisance of the possibility that even if obtained during the

dormant season, soil samples containing vegetation may naturally be substantially drier than

soil samples of a similar composition which do not.

Future research should investigate the long-term reinforcement provided by vegetation roots,

as it has been reported that slope failure generally occurs after a long period of time. This

may be achieved through the use of Consolidated Drained Triaxial Testing. Future testing

using this method would require sampling using 100mm diameter U100 samplers, as

although providing good undisturbed samples for shear box testing, the use of uPVC pipes

would not be suitable for a triaxial testing programme.

A future testing programme may also include assessing the impact of winter shrinkage of

vegetation roots causing temporary drainage during the winter months, if found to be

significant this may shed light on the cause of the moisture variance observed between soils.


47

Bibliography

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Conference Report. London: Thomas Telford University of Oxford.

Blunt, S.M., 1992. The Longham Wood Cutting Literature Reiew. Literature Review.

London: CIRIA Richards, Moorehead and Laing.

British Road Engineering Standards Policy Committee, 1990. BS 1377-1-9:1990. British

Standard. London: British Standards Institute.

Coppin, N.J. & Richards, I.G., 1990. Use of Vegetation in Civil Engineering. Research

Report. London: CIRIA CIRIA.

Farrar, D.M., 1984. Long term changes in pore water pressure within an embankment built of

London Clay. Technical Report. London: Transport and Road Research Laboratory Report

Transport and Road Research Laboratory Report.

Greenwood, J.R., Holt, P.A.D. & Herrick, J.W., 1985. Shallow slips in highway embankments

constructed of over-consolidated clay. Technical Report. London: ICE ICE.

Greenwood, J. et al., 2001. Bioengineering - The Longham Wood Cutting Field Trial. Field

Trial. London: CIRIA CIRIA.

Hiller, D.M. & MacNeill, D.J., 2001. A review of the use of live willow poles for stabilising

highway slopes. Technical Report. London: Transport Research Laboratory Transport

Research Laboratory.

Jewell, R.A., 1996. Soil Reinforcement With Geotextiles. Technical Report. London: CIRIA

CIRIA.


48

Johnson, P.E., 1985. Maintenance and repair of highway embankments: studies of seven

methoh of treatment. Research Report. London: Transport and Road Research Laboratory

Transport and Road Research Laboratory.

MacNeil, D.J., Steele, D.P., McMahon, W. & Carder, D.R., 2001. Vegetation For Slope

Stability. Filed Case Study. London: TRL TRL.

Parsons, A.W. & Perry, J., 1985. Slope Stability Problems In Ageing Highway Earthworks.

Technical Report. London: Institution of Civil Engineers Institution of Civil Engineers.

Schwarz, M. et al., 2010. Quantifying the role of vegetation in slope stability: A case study in

Tuscany (Italy). Ecological Engineering - The Journal of Ecosystem Restoration, 36(3),

pp.285-91.

Sutton, R.F., 1969. Soil Properties and Root Development in Forest Trees: a Review.

Information Report. Toronto: Forestry Canada Forestry Canada.

Yim, K.P., Heung, L.K. & Greenway, D.R., 1988. Effect of Root Reinforcement on The

Stability of Three Fill Slopes in Hong Kong. In Second International Conference on

Geomechanics in Tropical Soils. Rotterdam, 1988. Balkema.

1

Appendix A – Desk Study Maps

Proposed

Site

Proposed

Site

2

Proposed

Site

Location of

Bored Well

1

Appendix B – Plasticity Chart

Appendix B – Plasticity Chart ML: SILT.

OL: Organic SILT, organic CLAY.

CL: CLAY of low plasticity, lean CLAY.

CH: CLAY of high plasticity, fat CLAY.

OH: Organic CLAY, organic SILT.

MH: SILT of high plasticity, elastic SILT.

: Soil classification (OH, as discussed).

1

Appendix C – Lab Test Resuls

Axial Displacement Cell Pressure Force Axial Strain Deviator Stress

(mm) (kPa) (N) (%) (kPa)

0.000 50.000 0.000 0.000 0.000

0.442 49.467 13.209 0.221 1.686

0.849 49.467 17.612 0.424 2.252

1.300 49.467 22.015 0.650 2.821

1.725 49.467 26.418 0.863 3.393

2.746 47.333 105.672 1.373 13.639

3.753 47.172 154.105 1.877 19.989

4.801 47.333 189.329 2.401 24.685

5.813 47.866 215.747 2.907 28.268

6.833 48.133 242.165 3.417 31.887

7.863 48.400 264.180 3.931 34.959

8.918 48.933 286.195 4.459 38.064

9.972 48.933 303.807 4.986 40.611

10.980 49.200 319.216 5.490 42.875

12.032 49.467 335.949 6.016 45.348

13.062 49.467 347.837 6.531 47.180

14.079 49.467 364.568 7.039 49.686

17.238 50.000 401.994 8.619 55.595

18.283 50.000 413.882 9.141 57.514

19.297 50.000 422.688 9.649 59.011

20.317 50.000 432.815 10.159 60.706

21.322 50.000 441.621 10.661 62.223

22.329 50.000 452.628 11.165 64.065

23.331 50.000 460.114 11.666 65.418

24.355 50.000 468.920 12.178 66.975

25.369 50.160 477.726 12.685 68.541

26.427 50.000 485.651 13.214 70.006

27.441 50.000 493.136 13.721 71.403

28.493 50.000 501.942 14.247 73.014

29.547 50.000 510.748 14.774 74.638

30.611 50.000 519.554 15.306 76.277

31.673 50.160 523.957 15.837 77.277

32.725 50.000 532.763 16.362 78.933

33.783 50.000 540.688 16.891 80.471

UU Triaxial Test - Test Readings

2

Date: 24/02/14 Width (m) Length (m)

Test: Direct Shear Test 0.06 0.06

Sample: 001 60 mm2

Description: Soil with roots Mass: 2 kg

Proving Ring No: 10230 Lever Arm Effect 10

Proving Ring Size: 3kN Effective Mass 20 kg

Calibration Factor: 0.00147 Force 0.1962 kN

Comment: Forward run on sample 001

Moisture Content: 30.56 %

Horizontal

DisplacementArea

Load Ring

GaugeHorizontal Load

Increasing

Strain

Shear

Stress

Normal

Stress

(mm) (m2) (divisions) (kN) (%) (kN/m2) (kN/m2)

0.000 0.003600 0.000 0.000 0.000 0.000 54.500

0.250 0.003585 35.000 0.051 0.417 14.351 54.728

0.500 0.003570 40.000 0.059 0.833 16.471 54.958

0.750 0.003555 47.000 0.069 1.250 19.435 55.190

1.000 0.003540 53.000 0.078 1.667 22.008 55.424

1.250 0.003525 57.000 0.084 2.083 23.770 55.660

1.500 0.003510 61.000 0.090 2.500 25.547 55.897

1.750 0.003495 64.000 0.094 2.917 26.918 56.137

2.000 0.003480 67.000 0.098 3.333 28.302 56.379

2.250 0.003465 70.000 0.103 3.750 29.697 56.623

2.500 0.003450 72.000 0.106 4.167 30.678 56.870

2.750 0.003435 72.000 0.106 4.583 30.812 57.118

3.000 0.003420 74.000 0.109 5.000 31.807 57.368

3.250 0.003405 76.000 0.112 5.417 32.811 57.621

3.500 0.003390 78.000 0.115 5.833 33.823 57.876

3.750 0.003375 79.500 0.117 6.250 34.627 58.133

4.000 0.003360 80.500 0.118 6.667 35.219 58.393

4.250 0.003345 81.500 0.120 7.083 35.816 58.655

4.500 0.003330 82.000 0.121 7.500 36.198 58.919

4.750 0.003315 83.000 0.122 7.917 36.805 59.186

5.000 0.003300 83.000 0.122 8.333 36.973 59.455

5.250 0.003285 84.000 0.123 8.750 37.589 59.726

5.500 0.003270 84.000 0.123 9.167 37.761 60.000

5.750 0.003255 84.500 0.124 9.583 38.161 60.276

6.000 0.003240 85.000 0.125 10.000 38.565 60.556

6.250 0.003225 87.000 0.128 10.417 39.656 60.837

6.500 0.003210 87.500 0.129 10.833 40.070 61.121

6.750 0.003195 88.000 0.129 11.250 40.488 61.408

7.000 0.003180 89.000 0.131 11.667 41.142 61.698

7.250 0.003165 90.000 0.132 12.083 41.801 61.991

7.500 0.003150 91.000 0.134 12.500 42.467 62.286

7.750 0.003135 91.000 0.134 12.917 42.670 62.584

8.000 0.003120 91.000 0.134 13.333 42.875 62.885

8.250 0.003105 91.000 0.134 13.750 43.082 63.188

Average Area: 0.003353

Area:

3



Sample: 002 60 mm2

Description: Soil with roots Mass: 0.7 kg




Comment: Sample sheared near top.


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.004 0.000 0.000 0.000 0.000 19.075

0.250 0.004 19.000 0.028 0.417 7.791 19.155

0.500 0.004 25.000 0.037 0.833 10.294 19.235

0.750 0.004 30.000 0.044 1.250 12.405 19.316

1.000 0.004 31.000 0.046 1.667 12.873 19.398

1.250 0.004 34.000 0.050 2.083 14.179 19.481

1.500 0.004 35.000 0.051 2.500 14.658 19.564

1.750 0.003 37.000 0.054 2.917 15.562 19.648

2.000 0.003 39.000 0.057 3.333 16.474 19.733

2.250 0.003 39.000 0.057 3.750 16.545 19.818

2.500 0.003 40.500 0.060 4.167 17.257 19.904

2.750 0.003 41.000 0.060 4.583 17.546 19.991

3.000 0.003 43.000 0.063 5.000 18.482 20.079

3.250 0.003 44.000 0.065 5.417 18.996 20.167

3.500 0.003 44.000 0.065 5.833 19.080 20.257

3.750 0.003 44.000 0.065 6.250 19.164 20.347

4.000 0.003 45.000 0.066 6.667 19.688 20.438

4.250 0.003 46.000 0.068 7.083 20.215 20.529

4.500 0.003 47.000 0.069 7.500 20.748 20.622

4.750 0.003 48.000 0.071 7.917 21.285 20.715

5.000 0.003 49.000 0.072 8.333 21.827 20.809

5.250 0.003 49.000 0.072 8.750 21.927 20.904

5.500 0.003 50.000 0.074 9.167 22.477 21.000

5.750 0.003 50.500 0.074 9.583 22.806 21.097

6.000 0.003 49.000 0.072 10.000 22.231 21.194

6.250 0.003 51.000 0.075 10.417 23.247 21.293

6.500 0.003 52.000 0.076 10.833 23.813 21.393

6.750 0.003 52.000 0.076 11.250 23.925 21.493

7.000 0.003 53.000 0.078 11.667 24.500 21.594


Area:

4



Sample: 003 60 mm2





Comment: Sample sheared almost exactly along centreline


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.004 0.000 0.000 0.000 0.000 27.250

0.250 0.004 21.000 0.031 0.417 8.611 27.364

0.500 0.004 26.000 0.038 0.833 10.706 27.479

0.750 0.004 29.000 0.043 1.250 11.992 27.595

1.000 0.004 31.000 0.046 1.667 12.873 27.712

1.250 0.004 34.000 0.050 2.083 14.179 27.830

1.500 0.004 36.000 0.053 2.500 15.077 27.949

1.750 0.003 37.000 0.054 2.917 15.562 28.069

2.000 0.003 38.000 0.056 3.333 16.052 28.190

2.250 0.003 38.000 0.056 3.750 16.121 28.312

2.500 0.003 42.000 0.062 4.167 17.896 28.435

2.750 0.003 42.500 0.062 4.583 18.188 28.559

3.000 0.003 43.500 0.064 5.000 18.697 28.684

3.250 0.003 44.500 0.065 5.417 19.211 28.811

3.500 0.003 46.000 0.068 5.833 19.947 28.938

3.750 0.003 47.000 0.069 6.250 20.471 29.067

4.000 0.003 48.000 0.071 6.667 21.000 29.196

4.250 0.003 49.000 0.072 7.083 21.534 29.327

4.500 0.003 49.500 0.073 7.500 21.851 29.459

4.750 0.003 50.500 0.074 7.917 22.394 29.593

5.000 0.003 51.500 0.076 8.333 22.941 29.727

5.250 0.003 52.000 0.076 8.750 23.269 29.863

5.500 0.003 53.000 0.078 9.167 23.826 30.000

5.750 0.003 54.000 0.079 9.583 24.387 30.138

6.000 0.003 54.500 0.080 10.000 24.727 30.278

6.250 0.003 55.000 0.081 10.417 25.070 30.419

6.500 0.003 55.500 0.082 10.833 25.416 30.561

6.750 0.003 55.500 0.082 11.250 25.535 30.704

7.000 0.003 55.500 0.082 11.667 25.656 30.849


Area:

5



Sample: 004 60 mm2

Description: Soil without roots Mass: 2 kg




Comment:


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.004 0.000 0.000 0.000 0.000 54.500

0.250 0.004 16.000 0.024 0.417 6.561 54.728

0.500 0.004 26.000 0.038 0.833 10.706 54.958

0.750 0.004 35.000 0.051 1.250 14.473 55.190

1.000 0.004 42.000 0.062 1.667 17.441 55.424

1.250 0.004 48.000 0.071 2.083 20.017 55.660

1.500 0.004 52.000 0.076 2.500 21.778 55.897

1.750 0.003 55.000 0.081 2.917 23.133 56.137

2.000 0.003 59.000 0.087 3.333 24.922 56.379

2.250 0.003 61.000 0.090 3.750 25.879 56.623

2.500 0.003 63.000 0.093 4.167 26.843 56.870

2.750 0.003 65.000 0.096 4.583 27.817 57.118

3.000 0.003 68.000 0.100 5.000 29.228 57.368

3.250 0.003 68.000 0.100 5.417 29.357 57.621

3.500 0.003 70.500 0.104 5.833 30.571 57.876

3.750 0.003 72.000 0.106 6.250 31.360 58.133

4.000 0.003 74.000 0.109 6.667 32.375 58.393

4.250 0.003 75.000 0.110 7.083 32.960 58.655

4.500 0.003 77.000 0.113 7.500 33.991 58.919

4.750 0.003 78.000 0.115 7.917 34.588 59.186

5.000 0.003 79.000 0.116 8.333 35.191 59.455

5.250 0.003 80.000 0.118 8.750 35.799 59.726

5.500 0.003 81.000 0.119 9.167 36.413 60.000

5.750 0.003 82.000 0.121 9.583 37.032 60.276

6.000 0.003 85.000 0.125 10.000 38.565 60.556

6.250 0.003 86.000 0.126 10.417 39.200 60.837

6.500 0.003 86.000 0.126 10.833 39.383 61.121

6.750 0.003 86.000 0.126 11.250 39.568 61.408

7.000 0.003 86.000 0.126 11.667 39.755 61.698

m.c % Calcs

Container: 178.500 g

Soil+ContainerWet 279.000 g

Soil+ContainerDry 249.800 g

Area:

6



Sample: 005 60 mm2





Comment: Sample sheared near top.


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.004 0.000 0.000 0.000 0.000 27.250

0.250 0.004 12.000 0.018 0.417 4.921 27.364

0.500 0.004 19.000 0.028 0.833 7.824 27.479

0.750 0.004 24.000 0.035 1.250 9.924 27.595

1.000 0.004 29.000 0.043 1.667 12.042 27.712

1.250 0.004 32.500 0.048 2.083 13.553 27.830

1.500 0.004 34.000 0.050 2.500 14.239 27.949

1.750 0.003 36.000 0.053 2.917 15.142 28.069

2.000 0.003 38.500 0.057 3.333 16.263 28.190

2.250 0.003 40.000 0.059 3.750 16.970 28.312

2.500 0.003 41.500 0.061 4.167 17.683 28.435

2.750 0.003 42.500 0.062 4.583 18.188 28.559

3.000 0.003 43.500 0.064 5.000 18.697 28.684

3.250 0.003 45.000 0.066 5.417 19.427 28.811

3.500 0.003 47.000 0.069 5.833 20.381 28.938

3.750 0.003 48.500 0.071 6.250 21.124 29.067

4.000 0.003 49.500 0.073 6.667 21.656 29.196

4.250 0.003 50.500 0.074 7.083 22.193 29.327

4.500 0.003 51.000 0.075 7.500 22.514 29.459

4.750 0.003 51.500 0.076 7.917 22.837 29.593

5.000 0.003 52.000 0.076 8.333 23.164 29.727

5.250 0.003 52.500 0.077 8.750 23.493 29.863

5.500 0.003 53.000 0.078 9.167 23.826 30.000

5.750 0.003 54.000 0.079 9.583 24.387 30.138

6.000 0.003 55.000 0.081 10.000 24.954 30.278

6.250 0.003 56.000 0.082 10.417 25.526 30.419

6.500 0.003 54.500 0.080 10.833 24.958 30.561

6.750 0.003 56.000 0.082 11.250 25.765 30.704

7.000 0.003 55.500 0.082 11.667 25.656 30.849

m.c % Calcs




Area:

7



Sample: 006 60 mm2

Description: Soil without roots Mass: 0.7 kg




Comment:


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.004 0 0.000 0.000 0.000 19.075

0.250 0.004 11 0.016 0.417 4.510 19.155

0.500 0.004 13 0.019 0.833 5.353 19.235

0.750 0.004 16 0.024 1.250 6.616 19.316

1.000 0.004 17 0.025 1.667 7.059 19.398

1.250 0.004 19 0.028 2.083 7.923 19.481

1.500 0.004 21 0.031 2.500 8.795 19.564

1.750 0.003 22 0.032 2.917 9.253 19.648

2.000 0.003 23 0.034 3.333 9.716 19.733

2.250 0.003 24 0.035 3.750 10.182 19.818

2.500 0.003 25 0.037 4.167 10.652 19.904

2.750 0.003 26 0.038 4.583 11.127 19.991

3.000 0.003 26 0.038 5.000 11.175 20.079

3.250 0.003 27 0.040 5.417 11.656 20.167

3.500 0.003 28 0.041 5.833 12.142 20.257

3.750 0.003 28 0.041 6.250 12.196 20.347

4.000 0.003 28.5 0.042 6.667 12.469 20.438

4.250 0.003 29 0.043 7.083 12.744 20.529

4.500 0.003 29 0.043 7.500 12.802 20.622

4.750 0.003 29.5 0.043 7.917 13.081 20.715

5.000 0.003 29.5 0.043 8.333 13.141 20.809

5.250 0.003 29.5 0.043 8.750 13.201 20.904

5.500 0.003 30 0.044 9.167 13.486 21.000

5.750 0.003 30 0.044 9.583 13.548 21.097

6.000 0.003 30 0.044 10.000 13.611 21.194

6.250 0.003 30.5 0.045 10.417 13.902 21.293

6.500 0.003 31 0.046 10.833 14.196 21.393

6.750 0.003 31 0.046 11.250 14.263 21.493

7.000 0.003 31 0.046 11.667 14.330 21.594

m.c % Calcs




Area:

8



Sample: 007 60 mm2





Comment:


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.004 0.000 0.000 0.000 0.000 13.625

0.250 0.004 11.000 0.016 0.417 4.510 13.682

0.500 0.004 13.000 0.019 0.833 5.353 13.739

0.750 0.004 15.000 0.022 1.250 6.203 13.797

1.000 0.004 17.000 0.025 1.667 7.059 13.856

1.250 0.004 19.000 0.028 2.083 7.923 13.915

1.500 0.004 21.000 0.031 2.500 8.795 13.974

1.750 0.003 22.000 0.032 2.917 9.253 14.034

2.000 0.003 24.000 0.035 3.333 10.138 14.095

2.250 0.003 24.000 0.035 3.750 10.182 14.156

2.500 0.003 25.000 0.037 4.167 10.652 14.217

2.750 0.003 25.500 0.037 4.583 10.913 14.279

3.000 0.003 26.000 0.038 5.000 11.175 14.342

3.250 0.003 26.000 0.038 5.417 11.225 14.405

3.500 0.003 27.000 0.040 5.833 11.708 14.469

3.750 0.003 27.000 0.040 6.250 11.760 14.533

4.000 0.003 27.500 0.040 6.667 12.031 14.598

4.250 0.003 28.000 0.041 7.083 12.305 14.664

4.500 0.003 28.500 0.042 7.500 12.581 14.730

4.750 0.003 29.000 0.043 7.917 12.860 14.796

5.000 0.003 29.000 0.043 8.333 12.918 14.864

5.250 0.003 30.000 0.044 8.750 13.425 14.932

5.500 0.003 30.000 0.044 9.167 13.486 15.000

5.750 0.003 30.500 0.045 9.583 13.774 15.069

6.000 0.003 30.500 0.045 10.000 13.838 15.139

6.250 0.003 31.000 0.046 10.417 14.130 15.209

6.500 0.003 31.000 0.046 10.833 14.196 15.280

6.750 0.003 31.000 0.046 11.250 14.263 15.352

7.000 0.003 31.000 0.046 11.667 14.330 15.425


Area:

9



Sample: 008 60 mm2





Comment: Soil Containing Roots


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.003600 0.000 0.000 0.000 0.000 40.875

0.250 0.003585 15.000 0.022 0.417 6.151 41.046

0.500 0.003570 23.000 0.034 0.833 9.471 41.218

0.750 0.003555 28.500 0.042 1.250 11.785 41.392

1.000 0.003540 34.000 0.050 1.667 14.119 41.568

1.250 0.003525 37.000 0.054 2.083 15.430 41.745

1.500 0.003510 42.500 0.062 2.500 17.799 41.923

1.750 0.003495 45.500 0.067 2.917 19.137 42.103

2.000 0.003480 49.000 0.072 3.333 20.698 42.284

2.250 0.003465 52.500 0.077 3.750 22.273 42.468

2.500 0.003450 56.000 0.082 4.167 23.861 42.652

2.750 0.003435 58.580 0.086 4.583 25.069 42.838

3.000 0.003420 62.000 0.091 5.000 26.649 43.026

3.250 0.003405 63.000 0.093 5.417 27.198 43.216

3.500 0.003390 66.500 0.098 5.833 28.836 43.407

3.750 0.003375 68.500 0.101 6.250 29.836 43.600

4.000 0.003360 70.000 0.103 6.667 30.625 43.795

4.250 0.003345 73.000 0.107 7.083 32.081 43.991

4.500 0.003330 85.000 0.125 7.500 37.523 44.189

4.750 0.003315 101.000 0.148 7.917 44.787 44.389

5.000 0.003300 125.000 0.184 8.333 55.682 44.591

5.250 0.003285 109.000 0.160 8.750 48.776 44.795

5.500 0.003270 110.000 0.162 9.167 49.450 45.000

5.750 0.003255 95.000 0.140 9.583 42.903 45.207

6.000 0.003240 91.000 0.134 10.000 41.287 45.417

6.250 0.003225 90.500 0.133 10.417 41.251 45.628

6.500 0.003210 93.000 0.137 10.833 42.589 45.841

6.750 0.003195 94.000 0.138 11.250 43.249 46.056

7.000 0.003180 96.000 0.141 11.667 44.377 46.274


m.c % Calcs




Area:

10



Sample: 009 60 mm2





Comment: Soil Not Containing Roots


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.004 0.000 0.000 0.000 0.000 40.875

0.250 0.004 20.000 0.029 0.417 8.201 41.046

0.500 0.004 35.000 0.051 0.833 14.412 41.218

0.750 0.004 40.000 0.059 1.250 16.540 41.392

1.000 0.004 45.000 0.066 1.667 18.686 41.568

1.250 0.004 50.000 0.074 2.083 20.851 41.745

1.500 0.004 63.000 0.093 2.500 26.385 41.923

1.750 0.003 68.000 0.100 2.917 28.601 42.103

2.000 0.003 71.000 0.104 3.333 29.991 42.284

2.250 0.003 75.000 0.110 3.750 31.818 42.468

2.500 0.003 76.000 0.112 4.167 32.383 42.652

2.750 0.003 78.000 0.115 4.583 33.380 42.838

3.000 0.003 79.000 0.116 5.000 33.956 43.026

3.250 0.003 82.000 0.121 5.417 35.401 43.216

3.500 0.003 83.000 0.122 5.833 35.991 43.407

3.750 0.003 84.000 0.123 6.250 36.587 43.600

4.000 0.003 85.000 0.125 6.667 37.188 43.795

4.250 0.003 85.500 0.126 7.083 37.574 43.991

4.500 0.003 86.500 0.127 7.500 38.185 44.189

4.750 0.003 88.000 0.129 7.917 39.023 44.389

5.000 0.003 89.000 0.131 8.333 39.645 44.591

5.250 0.003 90.000 0.132 8.750 40.274 44.795

5.500 0.003 90.000 0.132 9.167 40.459 45.000

5.750 0.003 91.000 0.134 9.583 41.097 45.207

6.000 0.003 91.000 0.134 10.000 41.287 45.417

6.250 0.003 91.500 0.135 10.417 41.707 45.628

6.500 0.003 91.500 0.135 10.833 41.902 45.841

6.750 0.003 91.500 0.135 11.250 42.099 46.056

7.000 0.003 91.000 0.134 11.667 42.066 46.274


m.c % Calcs




Area:

11



Sample: 010 60 mm2





Comment:


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.00360 0.000 0.000 0.000 0.000 68.125

0.250 0.00359 26.000 0.038 0.417 10.661 68.410

0.500 0.00357 43.000 0.063 0.833 17.706 68.697

0.750 0.00356 52.500 0.077 1.250 21.709 68.987

1.000 0.00354 60.500 0.089 1.667 25.123 69.280

1.250 0.00353 67.000 0.098 2.083 27.940 69.574

1.500 0.00351 72.000 0.106 2.500 30.154 69.872

1.750 0.00350 77.000 0.113 2.917 32.386 70.172

2.000 0.00348 81.000 0.119 3.333 34.216 70.474

2.250 0.00347 83.000 0.122 3.750 35.212 70.779

2.500 0.00345 86.000 0.126 4.167 36.643 71.087

2.750 0.00344 89.000 0.131 4.583 38.087 71.397

3.000 0.00342 92.000 0.135 5.000 39.544 71.711

3.250 0.00341 95.000 0.140 5.417 41.013 72.026

3.500 0.00339 96.000 0.141 5.833 41.628 72.345

3.750 0.00338 98.000 0.144 6.250 42.684 72.667

4.000 0.00336 100.000 0.147 6.667 43.750 72.991

4.250 0.00335 101.500 0.149 7.083 44.605 73.318

4.500 0.00333 103.000 0.151 7.500 45.468 73.649

4.750 0.00332 104.500 0.154 7.917 46.339 73.982

5.000 0.00330 106.000 0.156 8.333 47.218 74.318

5.250 0.00329 107.000 0.157 8.750 47.881 74.658

5.500 0.00327 108.000 0.159 9.167 48.550 75.000

5.750 0.00326 109.000 0.160 9.583 49.226 75.346

6.000 0.00324 110.500 0.162 10.000 50.134 75.694

6.250 0.00323 111.500 0.164 10.417 50.823 76.047

6.500 0.00321 112.500 0.165 10.833 51.519 76.402

6.750 0.00320 113.000 0.166 11.250 51.991 76.761

7.000 0.00318 110.000 0.162 11.667 50.849 77.123

m.c % Calcs




Area:

12



Sample: 011 60 mm2





Comment: Water squeezed from sample


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.00360 0.000 0.000 0.000 0.000 81.750

0.250 0.00359 27.000 0.040 0.417 11.071 82.092

0.500 0.00357 43.000 0.063 0.833 17.706 82.437

0.750 0.00356 55.000 0.081 1.250 22.743 82.785

1.000 0.00354 64.000 0.094 1.667 26.576 83.136

1.250 0.00353 72.000 0.106 2.083 30.026 83.489

1.500 0.00351 77.000 0.113 2.500 32.248 83.846

1.750 0.00350 82.000 0.121 2.917 34.489 84.206

2.000 0.00348 87.000 0.128 3.333 36.750 84.569

2.250 0.00347 92.000 0.135 3.750 39.030 84.935

2.500 0.00345 95.000 0.140 4.167 40.478 85.304

2.750 0.00344 97.000 0.143 4.583 41.511 85.677

3.000 0.00342 100.000 0.147 5.000 42.982 86.053

3.250 0.00341 101.000 0.148 5.417 43.604 86.432

3.500 0.00339 103.000 0.151 5.833 44.664 86.814

3.750 0.00338 104.000 0.153 6.250 45.298 87.200

4.000 0.00336 106.000 0.156 6.667 46.375 87.589

4.250 0.00335 108.000 0.159 7.083 47.462 87.982

4.500 0.00333 109.000 0.160 7.500 48.117 88.378

4.750 0.00332 110.500 0.162 7.917 49.000 88.778

5.000 0.00330 112.000 0.165 8.333 49.891 89.182

5.250 0.00329 113.000 0.166 8.750 50.566 89.589

5.500 0.00327 113.500 0.167 9.167 51.023 90.000

5.750 0.00326 114.000 0.168 9.583 51.484 90.415

6.000 0.00324 115.000 0.169 10.000 52.176 90.833

6.250 0.00323 115.500 0.170 10.417 52.647 91.256

6.500 0.00321 116.000 0.171 10.833 53.121 91.682

6.750 0.00320 116.000 0.171 11.250 53.371 92.113

7.000 0.00318 117.000 0.172 11.667 54.085 92.547

m.c % Calcs




Area:

13



Sample: 012 60 mm2





Comment: Water Squeezed from sample


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.00360 0 0.000 0.000 0.000 95.375

0.250 0.00359 35 0.051 0.417 14.351 95.774

0.500 0.00357 50 0.074 0.833 20.588 96.176

0.750 0.00356 60 0.088 1.250 24.810 96.582

1.000 0.00354 69 0.101 1.667 28.653 96.992

1.250 0.00353 75 0.110 2.083 31.277 97.404

1.500 0.00351 81 0.119 2.500 33.923 97.821

1.750 0.00350 85 0.125 2.917 35.751 98.240

2.000 0.00348 89 0.131 3.333 37.595 98.664

2.250 0.00347 92 0.135 3.750 39.030 99.091

2.500 0.00345 94 0.138 4.167 40.052 99.522

2.750 0.00344 95.5 0.140 4.583 40.869 99.956

3.000 0.00342 96.5 0.142 5.000 41.478 100.395

3.250 0.00341 98 0.144 5.417 42.308 100.837

3.500 0.00339 99.5 0.146 5.833 43.146 101.283

3.750 0.00338 100 0.147 6.250 43.556 101.733

4.000 0.00336 101 0.148 6.667 44.188 102.188

4.250 0.00335 101 0.148 7.083 44.386 102.646

4.500 0.00333 101.5 0.149 7.500 44.806 103.108

4.750 0.00332 102.5 0.151 7.917 45.452 103.575

5.000 0.00330 103 0.151 8.333 45.882 104.045

5.250 0.00329 103 0.151 8.750 46.091 104.521

5.500 0.00327 104 0.153 9.167 46.752 105.000

5.750 0.00326 104.5 0.154 9.583 47.194 105.484

6.000 0.00324 104.5 0.154 10.000 47.412 105.972

6.250 0.00323 105 0.154 10.417 47.860 106.465

6.500 0.00321 105 0.154 10.833 48.084 106.963

6.750 0.00320 105.5 0.155 11.250 48.540 107.465

7.000 0.00318 105.5 0.155 11.667 48.769 107.972

m.c % Calcs




Area:

14



Sample: 013 60 mm2





Comment:


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.00360 0.000 0.000 0.000 0.000 109.000

0.250 0.00359 25.000 0.037 0.417 10.251 109.456

0.500 0.00357 40.000 0.059 0.833 16.471 109.916

0.750 0.00356 51.000 0.075 1.250 21.089 110.380

1.000 0.00354 60.000 0.088 1.667 24.915 110.847

1.250 0.00353 69.000 0.101 2.083 28.774 111.319

1.500 0.00351 76.000 0.112 2.500 31.829 111.795

1.750 0.00350 81.000 0.119 2.917 34.069 112.275

2.000 0.00348 85.000 0.125 3.333 35.905 112.759

2.250 0.00347 89.000 0.131 3.750 37.758 113.247

2.500 0.00345 93.500 0.137 4.167 39.839 113.739

2.750 0.00344 98.000 0.144 4.583 41.939 114.236

3.000 0.00342 100.000 0.147 5.000 42.982 114.737

3.250 0.00341 104.000 0.153 5.417 44.899 115.242

3.500 0.00339 106.000 0.156 5.833 45.965 115.752

3.750 0.00338 107.000 0.157 6.250 46.604 116.267

4.000 0.00336 110.000 0.162 6.667 48.125 116.786

4.250 0.00335 112.000 0.165 7.083 49.220 117.309

4.500 0.00333 114.000 0.168 7.500 50.324 117.838

4.750 0.00332 116.000 0.171 7.917 51.439 118.371

5.000 0.00330 117.000 0.172 8.333 52.118 118.909

5.250 0.00329 118.000 0.173 8.750 52.804 119.452

5.500 0.00327 121.000 0.178 9.167 54.394 120.000

5.750 0.00326 122.000 0.179 9.583 55.097 120.553

6.000 0.00324 123.000 0.181 10.000 55.806 121.111

6.250 0.00323 124.000 0.182 10.417 56.521 121.674

6.500 0.00321 125.500 0.184 10.833 57.472 122.243

6.750 0.00320 125.500 0.184 11.250 57.742 122.817

7.000 0.00318 127.000 0.187 11.667 58.708 123.396

m.c % Calcs




Area:

15



Sample: 014 60 mm2





Comment:


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.00360 0.000 0.000 0.000 0.000 68.125

0.250 0.00359 30.000 0.044 0.417 12.301 68.410

0.500 0.00357 45.000 0.066 0.833 18.529 68.697

0.750 0.00356 56.000 0.082 1.250 23.156 68.987

1.000 0.00354 64.000 0.094 1.667 26.576 69.280

1.250 0.00353 71.000 0.104 2.083 29.609 69.574

1.500 0.00351 77.000 0.113 2.500 32.248 69.872

1.750 0.00350 81.000 0.119 2.917 34.069 70.172

2.000 0.00348 83.000 0.122 3.333 35.060 70.474

2.250 0.00347 87.000 0.128 3.750 36.909 70.779

2.500 0.00345 92.000 0.135 4.167 39.200 71.087

2.750 0.00344 95.500 0.140 4.583 40.869 71.397

3.000 0.00342 98.500 0.145 5.000 42.338 71.711

3.250 0.00341 101.000 0.148 5.417 43.604 72.026

3.500 0.00339 103.000 0.151 5.833 44.664 72.345

3.750 0.00338 106.000 0.156 6.250 46.169 72.667

4.000 0.00336 108.000 0.159 6.667 47.250 72.991

4.250 0.00335 110.000 0.162 7.083 48.341 73.318

4.500 0.00333 111.000 0.163 7.500 49.000 73.649

4.750 0.00332 112.000 0.165 7.917 49.665 73.982

5.000 0.00330 114.000 0.168 8.333 50.782 74.318

5.250 0.00329 114.000 0.168 8.750 51.014 74.658

5.500 0.00327 115.000 0.169 9.167 51.697 75.000

5.750 0.00326 116.000 0.171 9.583 52.387 75.346

6.000 0.00324 117.000 0.172 10.000 53.083 75.694

6.250 0.00323 118.000 0.173 10.417 53.786 76.047

6.500 0.00321 119.000 0.175 10.833 54.495 76.402

6.750 0.00320 120.000 0.176 11.250 55.211 76.761

7.000 0.00318 121.000 0.178 11.667 55.934 77.123

m.c % Calcs




Area:

16



Sample: 015 60 mm2







Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.00360 0.000 0.000 0.000 0.000 81.750

0.250 0.00359 22.000 0.032 0.417 9.021 82.092

0.500 0.00357 36.000 0.053 0.833 14.824 82.437

0.750 0.00356 47.000 0.069 1.250 19.435 82.785

1.000 0.00354 55.000 0.081 1.667 22.839 83.136

1.250 0.00353 60.000 0.088 2.083 25.021 83.489

1.500 0.00351 66.000 0.097 2.500 27.641 83.846

1.750 0.00350 73.000 0.107 2.917 30.704 84.206

2.000 0.00348 77.000 0.113 3.333 32.526 84.569

2.250 0.00347 81.500 0.120 3.750 34.576 84.935

2.500 0.00345 85.000 0.125 4.167 36.217 85.304

2.750 0.00344 88.000 0.129 4.583 37.659 85.677

3.000 0.00342 91.500 0.135 5.000 39.329 86.053

3.250 0.00341 95.000 0.140 5.417 41.013 86.432

3.500 0.00339 98.000 0.144 5.833 42.496 86.814

3.750 0.00338 100.000 0.147 6.250 43.556 87.200

4.000 0.00336 102.000 0.150 6.667 44.625 87.589

4.250 0.00335 103.500 0.152 7.083 45.484 87.982

4.500 0.00333 105.000 0.154 7.500 46.351 88.378

4.750 0.00332 106.500 0.157 7.917 47.226 88.778

5.000 0.00330 107.500 0.158 8.333 47.886 89.182

5.250 0.00329 109.000 0.160 8.750 48.776 89.589

5.500 0.00327 110.000 0.162 9.167 49.450 90.000

5.750 0.00326 110.000 0.162 9.583 49.677 90.415

6.000 0.00324 110.500 0.162 10.000 50.134 90.833

6.250 0.00323 111.000 0.163 10.417 50.595 91.256

6.500 0.00321 111.500 0.164 10.833 51.061 91.682

6.750 0.00320 112.000 0.165 11.250 51.531 92.113

7.000 0.00318 112.500 0.165 11.667 52.005 92.547

m.c % Calcs




Area:

17



Sample: 016 60 mm2





Comment: Major water squeezing & Significant settling under loading


Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.00360 0 0.000 0.000 0.000 95.375

0.250 0.00359 26 0.038 0.417 10.661 95.774

0.500 0.00357 42 0.062 0.833 17.294 96.176

0.750 0.00356 53 0.078 1.250 21.916 96.582

1.000 0.00354 62 0.091 1.667 25.746 96.992

1.250 0.00353 70 0.103 2.083 29.191 97.404

1.500 0.00351 76 0.112 2.500 31.829 97.821

1.750 0.00350 82 0.121 2.917 34.489 98.240

2.000 0.00348 85 0.125 3.333 35.905 98.664

2.250 0.00347 90 0.132 3.750 38.182 99.091

2.500 0.00345 92 0.135 4.167 39.200 99.522

2.750 0.00344 95 0.140 4.583 40.655 99.956

3.000 0.00342 98 0.144 5.000 42.123 100.395

3.250 0.00341 101 0.148 5.417 43.604 100.837

3.500 0.00339 103 0.151 5.833 44.664 101.283

3.750 0.00338 104 0.153 6.250 45.298 101.733

4.000 0.00336 106.5 0.157 6.667 46.594 102.188

4.250 0.00335 109 0.160 7.083 47.901 102.646

4.500 0.00333 110.5 0.162 7.500 48.779 103.108

4.750 0.00332 111.5 0.164 7.917 49.443 103.575

5.000 0.00330 116 0.171 8.333 51.673 104.045

5.250 0.00329 117 0.172 8.750 52.356 104.521

5.500 0.00327 118.5 0.174 9.167 53.271 105.000

5.750 0.00326 120 0.176 9.583 54.194 105.484

6.000 0.00324 120 0.176 10.000 54.444 105.972

6.250 0.00323 122 0.179 10.417 55.609 106.465

6.500 0.00321 123 0.181 10.833 56.327 106.963

6.750 0.00320 124 0.182 11.250 57.052 107.465

7.000 0.00318 125 0.184 11.667 57.783 107.972

m.c % Calcs




Area:

18



Sample: 017 60 mm2







Horizontal

DisplacementArea

Load Ring


Increasing

Strain

Shear

Stress

Normal

Stress


0.000 0.00360 0.000 0.000 0.000 0.000 109.000

0.250 0.00359 30.000 0.044 0.417 12.301 109.456

0.500 0.00357 54.000 0.079 0.833 22.235 109.916

0.750 0.00356 70.000 0.103 1.250 28.945 110.380

1.000 0.00354 80.000 0.118 1.667 33.220 110.847

1.250 0.00353 91.000 0.134 2.083 37.949 111.319

1.500 0.00351 99.000 0.146 2.500 41.462 111.795

1.750 0.00350 105.000 0.154 2.917 44.163 112.275

2.000 0.00348 112.000 0.165 3.333 47.310 112.759

2.250 0.00347 120.000 0.176 3.750 50.909 113.247

2.500 0.00345 123.000 0.181 4.167 52.409 113.739

2.750 0.00344 128.000 0.188 4.583 54.777 114.236

3.000 0.00342 132.000 0.194 5.000 56.737 114.737

3.250 0.00341 135.000 0.198 5.417 58.282 115.242

3.500 0.00339 137.000 0.201 5.833 59.407 115.752

3.750 0.00338 140.000 0.206 6.250 60.978 116.267

4.000 0.00336 142.000 0.209 6.667 62.125 116.786

4.250 0.00335 144.000 0.212 7.083 63.283 117.309

4.500 0.00333 145.000 0.213 7.500 64.009 117.838

4.750 0.00332 146.000 0.215 7.917 64.742 118.371

5.000 0.00330 148.000 0.218 8.333 65.927 118.909

5.250 0.00329 149.000 0.219 8.750 66.676 119.452

5.500 0.00327 150.000 0.221 9.167 67.431 120.000

5.750 0.00326 150.000 0.221 9.583 67.742 120.553

6.000 0.00324 151.000 0.222 10.000 68.509 121.111

6.250 0.00323 151.000 0.222 10.417 68.828 121.674

6.500 0.00321 151.500 0.223 10.833 69.379 122.243

6.750 0.00320 152.000 0.223 11.250 69.934 122.817

7.000 0.00318 152.000 0.223 11.667 70.264 123.396

m.c % Calcs




Area:

Documents

Sean Bolton - Dissertation