Indian Highways Vol.41 6 June 13

8/19/2019 Indian Highways Vol.41 6 June 13

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The Indian Roads Congress

E-mail: [email protected]/[email protected]

Founded : December 1934

IRC Website: www.irc.org.inJamnagar House, Shahjahan Road,

New Delhi - 110 011

Tel : Secretary General: +91 (11) 2338 6486

Sectt. : (11) 2338 5395, 2338 7140, 2338 4543, 2338 6274

Fax : +91 (11) 2338 1649

Kama Koti Marg, Sector 6, R.K. Puram

New Delhi - 110 022

Tel : Secretary General : +91 (11) 2618 5303

Sectt. : (11) 2618 5273, 2617 1548, 2671 6778,

2618 5315, 2618 5319, Fax : +91 (11) 2618 3669

No part of this publication may be reproduced by any means without prior written permission from the Secretary General, IRC.

Edited and Published by Shri Vishnu Shankar Prasad on behalf of the Indian Roads Congress (IRC), New Delhi. The responsibility of the

contents and the opinions expressed in Indian Highways is exclusively of the author/s concerned. IRC and the Editor disclaim responsibility

and liability for any statement or opinion, originality of contents and of any copyright violations by the authors. The opinions expressed in the

papers and contents published in the Indian Highways do not necessarily represent the views of the Editor or IRC.

VOLUME 41 NUMBER 6 JUNE 2013

CONTENTS ISSN 0376-7256

INDIAN HIGHWAYSA REVIEW OF ROAD AND ROAD TRANSPORT DEVELOPMENT

Page

2-3 From the Editor’s Desk

4-5 Glimpses of First Regional Level Initiative of IRC with Research Institutions

5 Green Initiative of IRC

6 Geosynthetics Reinforced Flexible Pavement : Gateway of the Sustainable Pavement

G.S. Ingle and S.S. Bhosale

16 Optimal Slope Stability Protection Strategies for Road Construction in a Hilly Terrain : A Concept

S.S. Seehra

25 Bamboo as Subgrade Reinforcement for Low Volume Roads on Soft Soils

Raja J and G.L. Siva Kumar Babu

35 Stabilisation of a Black Cotton Soil with Pond Ash & Cement Mixed with Fiber & Sodium Silicate

Alok Ranjan, R.K. Swami and Sudhir Mathur

43 Compaction and Subgrade Charactertistics of Clayey Soil Blended with Beas Sand, Fly Ash and Waste Plastic Strips

Ravi Kumar Sharma, Deen Bandhu, Rounak Maheshwari and Sukhendra Kumar

49 Obituary

50 A Study on the Performance of Sugarcane Fibre in Stone Matrix Asphalt

P.Vilvakumar, N. Senthil, S. Lakshmi, C. Kamaraj and S. Gangopadhyay

59-60 Call for Technical Papers

61 Pan India Initiative on Road Safety Audit

61 Announcement

62-66 Circulars Issued by MORT&H

67 Tender Notice of NHs Madurai

68 Tender Notice of NHs Bareilly70 Advertisement Tarrif


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2 INDIAN HIGHWAYS, JUNE 2013

Dear Readers,

Do Geotextiles make substantial difference in the sustainability of Roads? The Historical evidence shows

that Geotextiles were used in roadways construction in the days of Pharaos to stabilize the right ways of their

edges. Babylonians used palm fronds and hemp to strengthen the soil reinforced structures called “Ziggurats”

more than 3000 years ago. The Chinese have used “reeds” to construct a type of road since pre historic times.

The concept of soil reinforcement by using natural bers in a part of Great Wall of China is one of the

shining examples in this area. The Dutch and Romans have made use of willows fascines to reinforce dikeand to protect them against sea wave actions. This shows that mankind has recognized & realized the huge

potential of Geotextiles many centuries ago but its true potential have yet not been harnessed fully.

Coming to the modern time, the early use of Geotextiles as a means of strengthening road pavements is

documented in respect of the attempts made by the South Caribbean Department of Highways in USA in

1930’s. The British army used this technique during the World War II for the invasion of Normandy. Since

then the various types of Geotextiles, synthetic, woven, fabric, etc. are used for different application in the

areas of soil stabilization, controlling soil erosion specically in the coastal areas and in other large number

of civil engineering applications.

The term Geotextiles is not much in use, as most of the time the material used is synthetic material and“Geo-synthetic” is the term commonly used which are used as geo-membrane, geogrids, geonets, etc. In fact

it is one of the fastest growing segments in the textile sector. When we talk specically to road sector, which

is now one of the sunrise sectors of the economy, the geotextiles nds applications in subsurface drainage,

erosion control, separation of layers, ltration, protection of slopes and embankments in pavement, etc.

In India also the Geotextiles have been used since time immemorial for different applications. Many few

are aware that the English word “Coir” comes from tamil/malayam word “Kayara”. It is not surprising that,

out of total world’s coir ber production of about 2.5 lakh ton per year, India, mainly Kerala state produces

20% of the total world’s production. The usage of coir in various fabrics was made popular in 1840’s by

Capt. Widely who founded a well-known carpet rm of Trelor & Sons in England for manufacturing of

Coir based oor coverings. Even though coir is eco-friendly, bio-degradable and can also provide suitable

substrate for horticultural use as a “Soil less potting media”, its usage is not made so popular in roads and

other civil engineering applications. The scope is available but it requires some innovative approach so that

the connected areas of durability, sustainability, economics and technical viabilities are addressed to a larger

extent.

Another natural Geo-ber in which India is having dominated 60% world’s production share is that of jute

and allied bers. The other natural available bers materials like Bamboo, Straw, Wood, etc. have also

From the Editor’s Desk

SMALL COMPONENT BUT BIG IMPACT


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EDITORIAL

INDIAN HIGHWAYS, JUNE 2013 3

nd applications in strengthening the soil properties. The biodegradable nature of natural Geotextiles has

its own advantages as well as limitations. The related aspects of eco-friendly weather resistant, bacterial

decomposition, strength, etc. needs careful systematic study for harnessing their benecial applications in

the road sector. Polymer based Geotextiles commonly known as Geosynthetics have its own advantages

of strengthening and resistance to weathering, fungal and bacterial decomposition but they have their ownlimitation when the issue of eco-friendly and bio-degradable qualities are considered.

Considering that Geotextiles needs due consideration to optimize enhancing design exibility, cost

effectiveness, aesthetics, functionality and long term durability of transport infrastructure, their applications

should invariably be made an integral part for big ticket projects in road and multi-modal transport

infrastructure projects involving roads, railways, airports, seaports, etc. It may be heartening to mention

that, IRC has long back realized the potential of Geotextiles, Geosynthetics and published in the year

1994 the State of Art Report on Application of Geotextiles in highway engineering. Subsequently, with

the enhancement of application of Geotextiles with a focus on locally available materials a State of Art

Report titled “Use of Geotextiles in Road Construction and Prevention of Soil Erosion and Landslide” was

published. In between, the Guidelines for Use of Geotextiles in Road Pavements and associated works were

formalized and published in IRC:SP:59:2002.

It may be of interest that the current Geotextiles market in the country is about Rs.300 crores only. Considering

the amount of trillions of investment in the road infrastructure in the country by the Central government and

State government organizations, the extent of Geotextiles usage in the road infrastructure sector demands for

relook about its usage versus its usage potentiality.

Possibly the time has come to blend the tradition and innovation in this important segment which is small

but have big impact on the sustainability and cost effectiveness factors. This combination of tradition and

innovation can be termed as “Tradonnovation” Such a combination may create avenues for wider applicationas well as acceptability as use of local available materials & machines to solve local issues & demand with

the help of modern scientic instruments and techniques/technology may create a win-win situation for all. It

may also help in providing more opportunities for employment besides increasing level of condence in the

users as well as road developers. The imperative need is for more innovative handling of Geotextiles to make

its usage more popular in road sector applications by addressing the issues of strength, durability, economics

and technical viability to make its use really preferable at all stages of projects right from conceptualization,

designing to execution and maintenance. This may require synergic efforts of all stakeholders, which it

is hoped may help in furthering the versatile usage of Geotextiles in the civil engineering applications

including the road sector.

“Any process of inquiry related to learning is nding out what is transient and what is permanent”

His Holiness Sri Satya Sai Baba

Place: New Delhi Vishnu Shankar Prasad

Dated: 24th May, 2013 Secretary General


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HIGHLIGHTS


GLIMPSES OF FIRST REGIONAL LEVEL INITIATIVE OF

IRC WITH RESEARCH INSTITUTIONS

In the endeavor to increase the reach of Indian Roads

Congress (IRC), new initiatives have been taken

to collaborate with research institutions to conduct

Workshops-Cum Seminars to bring together various

stakeholders on the same platform to deliberate

upon the various possible solutions to address the

road infrastructure related issues. In this series, a

Workshop-cum Seminar on “Possible Solutions

to the city transport system including pedestrians

segregation & Automated Parking facilities”

organized in collaboration with Highway Research

Station (HRS Chennai) on 26th April, 2013. The same

was attended by various departments of Government

of Tamil Nadu i.e. Police Department, Transport

Planning Department, State PWD, CMDA, Experts

from Educational Institutions & Research Institutions

from Chennai, Bangalore, Mumbai & Delhi besides

a number of Public and Private Sector entities and

NGO’s.

During this One Day programme the following

presentation were made:-

1. Presentation entitled “How to Design Safe

Streets.” By Ms. Shreya Gadepalli, RD,

ITDP.

2. ‘Parking – the Problem, the Demand

Assessment & the Solution’ by

Dr. G. Malarvizhi, Anna University.

3. “Feasibility for Development of PRT System

– A Case Study in Thiruvananthapuram”

by Prof. P.K. Sarkar, School of Planning &

Architecture, New Delhi.

4. “Automated Parking Technology – The

Robotic Valet Parking” by Shri S. Elango,

Director, Galaxy Group, Bangalore.

5. “Integration of Pedestrian Movements” by

Shri R. Narendra Kumar, Manager, Trafc

Planning, CMRL.

6. “Pedestrians & Parking – Problems & Solution”

by M. Geetha, Senior Planner, CMDA.

7. “Automatic Parking” by Er. Uganandan, ADE,

Highways

8. “Pedestrian Segregation” by Thiru. S. Santhosh

Kumar, PRO, TN Police Warden, Coimbatore.

9. “Pedestrian Facilities by Dr. Geetha Krishnan

Ramadurai, IIT, Chennai.

10. “Pedestrian Solutions” by Thiru. Utpal

Chakravarty, V.P., M/s. S.N. Bhobe.11. “Automated Parking Facilities” by Thiru.

Sanjog Bawane, CCCL.

12. “Personal Rapid Transit (PRT)” by M/s. Ultra

Fair Wood, Gurgaon.

13. “Pedestrian Crossing Facilities in Chennai” by

Ms. Sahaya, STUP Consultants.


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HIGHLIGHTS


The presentations were followed by a panel discussion

which was interactive in nature. The important

aspects which emerged from this successful One Day

initiative are:-

The trafc scenario in the cities required

concerted efforts of all stakeholders. There is a

need to reduce trafc conicts at road junctions

and the areas where pedestrian pressure is

high.

The provision of IRC Codes especially related

to pedestrian facilities/transport facilities/

bus ways needs to be impressed upon by all

stakeholders while designing and implementing

the projects to enhance the safety of the roadusers including pedestrians.

The pressure on the city roads are increasing

at a much higher pace and due attention

is required for parking facilities as well

as segregation pedestrian by planning and

providing dedicated facilities for the same.

Vehicle parking complexes may be explored

at strategic location in the cities. They may be

stand-alone facilities or as a part of shopping

malls and/or such commercial establishments/

ofce complex.

The automated parking facilities may

provide viable and cost effective solutions

in metropolitan cities and all options may be

explored to arrive at the best solution.

PRT is one of the solutions to reduce pressure

on the roads and may play an important role in

multi model/integrated transport networking

in the city conditions.

Skywalks may also be considered as an integral

part of big commercial/shopping mall projects.

The feasibility of their stand-alone viability as

well as covering the same with solar panels

to increase their nancial viability may be

explored while considering the pedestrian

friendly/conducive facilities.

IRC Codal provisions in respect of road safety

needs to be emphasized by all stakeholders and

safety of road users should be given paramount

importance.

IRC may consider initiating pan India

initiatives on road safety involving the young

school going children.

While considering new cities or transforming

semi urban areas to urban areas, due provisionsshould be made for public transport system.

It is pleasure to inform that now Indian Roads Congress (IRC) have taken initiative to start E-Version

of its monthly magazine “Indian Highways”.

The esteem members of IRC are requested to support and cooperate in this new green initiative

of IRC. Accordingly, esteem members are requested to forward their willingness to receive“Indian Highways” on regular basis in E-Version.

The esteem members of IRC are also requested to reconrm/forward their e-mail IDs to

IRC at:- [email protected]

or

alternatively at :- [email protected].

GREEN INITIATIVE OF IRC


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ABSTRACT

Pavement is the most severely dynamically loaded structure under

varied environmental conditions. Long lasting pavement with

good riding surface has always been remained challenge to the

pavement engineers. Present day trafc loading for important

roads, such as Expressways, National highways is increasing at

an accelerated rate. Most of the times vehicles are overloaded

than the legal limits. Due to such overloading pavement life

reduces drastically, particularly if the desired quality materials

are not used. Day by day the demand for good quality pavement

materials is increasing at an accelerated rate due to which natural

good quality material getting depleted rapidly. This will be threat

to an environment in near future. Geosynthetics reinforcementhas a potential in improving the engineering characteristics of

the pavement materials as well as layers, which improves the

pavement service life. In addition to this, based on stiffness

characteristics of geosynthetics it greatly reduces the thickness

of exible pavement, an illustration presented shows typically

saving of 40% in base course thickness.

In addition to direct saving of pavement materials there are

signicant environmental benets associated with it, viz. less

transportation of aggregate by trucks, hence less air pollution (dust,

gasoline vapors), less noise, carbon emission, diesel consumption,

etc. and hence geosynthetics will open gateway to greener, more

sustainable construction. Paper also presents brief information on

geosynthetics products and their standards.

1 INTRODUCTION

In India, the main problems which the roads are facing

that majority of them fail before their service life, due

to the fact that the load accounted during the design

of road is far lower than ground reality. The structural

adequacy of the pavement system is based on the

amount of stress that is acting on the subgrade layer.

For the low value of subgrade stresses, the life of the

pavement system is longer. In a multi-layered exible

pavement system, subgrade stress can be lowered by

either increasing the thickness of the base course layer

or by increasing the rigidity (E-value) of the different

layers by using good quality of natural materials.

GEOSYNTHETICS REINFORCED FLEXIBLE PAVEMENT :

GATEWAY OF THE SUSTAINABLE PAVEMENT

G.S. I NGLE* AND S.S. BHOSALE**

In many areas of the world, quality natural materials

are unavailable or are in short supply. Also bringing

quality materials from a far distance increase the fuel

consumption. Secondly for increasing the thickness

of base course layer, additional sourcing of natural

aggregate from quarries is required which is not

economical.

Due to the above mentioned facts, engineers are

concentrating towards locally available materials

i.e. soil, while the available soil may not possess

the required strength characteristics. The strength of

this soil may be increased by using soil stabilization

technique. Alternatively, use of polymeric material

namely geosynthetics could be resorted to.

2 GEOSYNTHETICS REINFORCED

PAVEMENT

A geosynthetics material is a synthetic material

manufactured from polymers such as polyethylene,

polypropylene, or polyester. Although geosyntheticshave many forms and uses (Koerner 2005), the two

forms of geosynthetics that are specically used for

separation and reinforcement in exible pavement

systems.

Geosynthetics have been studied and used for more

than 40 years as reinforcement in the base course layer

of exible pavements. Early uses of geosynthetics in

roadways included separation, ltration, and drainage

in paved and unpaved roads and reinforcement in

unpaved roads (Steward et al. 1977; Bender andBarenberg 1978). Geotextiles were rst examined

for use as reinforcement in paved roads in the early

1980s (Brown et al. 1982; Ruddock et al. 1982), while

geogrids were rst studied in the late 1980s (Barker

* Research Scholar in Civil Engineering Department, College of Engineering Pune, E-mail: [email protected]

** Professor in Civil Engineering Department, College of Engineering Pune, E-mail: [email protected]


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TECHNICAL PAPERS


1987; Haas et al. 1988; Barksdale et al. 1989). The

focus of this paper is reinforcement applications.

Geosynthetics material is typically placed in the

interface between the aggregate base course and

the subgrade or within a base course to increase the

structural or load-carrying capacity of a pavement

system by the transfer of load to the geosynthetics

material. (Hufenus et al. 2005)

The two main benets of the reinforcement are to

(1) improve the service life and/or; (2) obtain

equivalent performance with a reduced structural

section. Fig.2.1 shows the benets of geosynthetics in

terms of reduction of granular base thickness.

Fig. 2.1 Benets of Geosynthetics in Terms of Reduction of

Granular Base Thickness (After Giroud and Noiray 1981)

This improved performance of the pavement due

to geosynthetics reinforcement has been attributedto three main mechanisms, as follows: (1) lateral

restraint, (2) increased bearing capacity, and (3) the

tensioned membrane effect (Giroud and Noiray 1981,

Giroud et al. 1984, Perkins and Ismeik 1997, Holtz et

al. 1998) which are presented in next paragraph.

3 MECHANISM OF REINFORCEMENT

Three fundamental reinforcement mechanisms have

been identied involving the use of geosynthetics to

reinforce pavement materials are as follows.

3.1 Lateral Restraint

The primary mechanism associated with the

reinforcement function for exible pavements as

shown in Fig. 3.1 is lateral restraint or connement

(Bender and Barenberg 1978). The name is misleading

as lateral restraint develops through interfacial friction

between the geosynthetics and the aggregate, thus

the mechanism is one of a shear-resisting interface

(Perkins 1999). When an aggregate layer is subjected

to trafc loading, the aggregate tends to move

laterally unless it is restrained by the subgrade orgeosynthetics reinforcement. Interaction between the

base aggregate and the geosynthetics allows transfer

of the shearing load from the base layer to a tensile

load in the geosynthetics. The tensile stiffness of the

geosynthetics limits the lateral strains in the base

layer. (Zornberg, J.G 2010)

Fig. 3.1 Lateral Restraints Due to Geosynthetics

(After Perkins and Ismeik 1997)

Furthermore, a geosynthetics layer connes the base

course layer thereby increasing its mean stress and

leading to an increase in shear strength. Both frictional

and interlocking characteristics at the interface

between the soil and the geosynthetics contribute to

this mechanism. For a geogrid, this implies that the

geogrid apertures and base soil particles must be

properly sized.

A geotextile with good frictional capabilities can

also provide tensile resistance to lateral aggregate

movement.

3.2 Increased Bearing Capacity

Fig.3.2 shows the increased bearing capacity

mechanism leads to soil reinforcement when the

presence of a geosynthetics imposes the development

of an alternate failure surface. This new alternate

plane provides a higher bearing capacity. The

geosynthetics reinforcement can decrease the shear


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stresses transferred to the subgrade and provide

vertical connement outside the loaded area. The

bearing failure mode of the subgrade is expected to

change from punching failure without reinforcement

to general failure with reinforcement.

Fig. 3.2 Increased Bearing Capacity Due to Geosynthetics


3.3 Tensioned Membrane Effect

The geosynthetics can also be assumed to act as a

tensioned membrane, which supports the wheel loads

as shown in Fig. 3.3. In this case, the reinforcement

provides a vertical reaction component to the applied

wheel load. This tensioned membrane effect is induced

by vertical deformations, leading to a concave shape

in the geosynthetics. The tension developed in thegeosynthetics contributes to support the wheel load

and reduces the vertical stress on the subgrade.

Fig. 3.3 Tensioned Membrane Effect Due to Geosynthetics


However, signicant rutting depths are necessary to

realize this effect. Higher deformations are required to

mobilize the tension of the membrane for decreasing

stiffness of the geosynthetics. In order for this type of

reinforcement mechanism to be signicant, there is a

consensus that the subgrade CBR should be below 3%

(Barksdale et al. 1989).

3.4 Relevance of the Various Mechanisms

The aforementioned mechanisms require different

magnitudes of deformation in the pavement system to

be mobilized. Since the early studies on geosynthetic

reinforcement of base course layers focused on

unpaved roads, signicant rutting depths (in excess

of 25 mm) may have been tolerable. The increased

bearing capacity and tensioned membrane support

mechanisms have been considered for paved roads.

However, the deformation needed to mobilize thesemechanisms generally exceeds the serviceability

requirements of exible pavements. Thus, for the case

of exible pavements, lateral restraint is considered to

contribute the most for the improved performance of

geosynthetics reinforced pavements.

4 DESIGN APPROACHES FOR

GEOSYNTHETICS REINFORCED

PAVEMENT

The benecial effect of using geosynthetics

reinforcement in road sections has been studied by

many researchers both theoretically and experimentally

from last three decades. (J.G. Collin et.al 1996)

This research may be in the form of small scale

laboratory plate load tests (Al-Quadi et al. 1994;

Haas et al. 1988) theoretical evaluations using nite

element analysis (Barksdale et al. 1989; Burd and

Houlsby 1986), and full scale wheel load tests (Fannin

and Sigurdsson 1996; Webster 1992, J.G. Collin, T.C.

Kinney 1996, Perkins S.W. 1999, Rudolf Hufenus and

Rueegger 2005). This benecial effect is expressed in

terms of extension of life or by savings in base course

thickness. Extension of life is dened in terms of a

Trafc Benet Ratio (TBR). TBR is dened as the

ratio of the number of cycles necessary to reach a given

rut depth for a test section containing reinforcement,

divided by the number of cycles necessary to reach


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TECHNICAL PAPERS


this same rut depth for an unreinforced section with

the same section thickness and subgrade properties. A

TBR > 1 also provides a safety factor on the pavement

load-carrying capacity against signicantly increased

EASLs or weaker subgrade from design values.

The Base Course Reduction (BCR) is expressed as a

percentage savings of the unreinforced base thickness.

Information on base course reduction is extracted from

those studies where unreinforced and reinforced test

sections with equal AC thickness and subgrade were

created, but where the reinforced section contained

less base course material and resulted in identical

performance.

Table 1 shows some of the Design Approaches with

mode of design method and maximum range of

improvement for Base/Sub base Reinforcement by

some developer/ Organization, which indicate that the

geosynthetics material improves the performance of

road in terms of extension of service life or reduction

in the base course thickness.

Table 1 Design Approaches and Procedures for Base/Sub Base Reinforcement

Developer Geosynthetic

Type

Applicability Distress mode and

Design Format

Empirical

Support

Maximum Range of

Improvement

Giroud and Noiray (1981)

Geotextile Empirical method 75 mm Rut depth Quasistaticanalysis

30% to 50% reductionin base course

thickness

Penner et al.

(1985)

Specic geogrid Based on C.B.R

4.3 to 5.7%

20 mm Rut depth/

Equation and chart

Lab Test 30% to 50% reduction

in base course

thickness

Burd and

Houlsby (1986)

Genetic

Geosynthetic

Isotropic

elastoplastic

surface

deformation/

FE M Computer

Programe

F.E.M Improvement after

4 mm surface

deformation

Barksdale et al.

(1989)

Genetic

Geosynthetic

Isotropic

elastoplastic

surface

deformation/FE M Computer

Programe

Field Result 4% to 18% reduction

base thickness

Barksdale et al.

(1989)

Geogrid C.B.R 2.4% Vertical

deformation charts,

computer programe

Field Test 4% to 18% reduction

in base course

thickness

Webster (1993) Specic

Geogrid

Based on C.B.R 3

to 8%

Rut depth (25 mm)/

Design charts

Field Test BCR = 5% to 45%

Tensar (1996) Specic

Geogrid

Based on C.B.R

1.9 to 8%

20 to 30 mm rut

depth/equations,

charts, computer

programe

Lab & test track

correlate to eld

test

Trafc Benet Ratio

(TBR) = 1.5 to 10

J.G. Collin, T.C.

Kinney (1996)

Geogrid C.B.R 1 to 8% Surface rutting Full Scale Lab.

test

Trafc Benet Ratio

(TBR) = 2 to 10%

Akzo-Nobel

(1998)

Specic GG-GT

Composite

Not stated Bearing capacity/

Equation & charts

Plate Load Test

(Meyer 7 Elias,

1999)

BCR = 32% to 56%

Perkins S.W.

(1999)

Geogrid - Permanent surface

deformation

Full Scale Lab.

test

At least 30% reduction

in base course

thickness


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TECHNICAL PAPERS


Giroud & Han

(2004)

Geogrid Theoretical design

method

allowable rut depth,

e.g. 75 mm.

Empirical test

calibrated with

eld test

Up to 30% reduction

in base course

thickness

Rudolf Hufenus,

Rueegger et. at(2005)

Geogrid C.B.R 1 to 4% Rut depth Full scale Field

test

Up to 30% reduction

in base coursethickness

Bassam Saad

and Hani Mitri

(2006)

Geogrid - Surface

deformation

3D F.E.M Reduction of Rutting

strain up to 16 to 34%

Imad L. Al-Qadi

et.at (2010)

Geogrid C.B.R 4% Surface rutting Full scale test Reduction in

pavement response up

to 23-31%

5 PAVEMENT LIFE

Stevenson (2008) highlighted graphically (as shown

in gure 5.1) the variation of surface rut depth

of pavement with and without geosynthetics for

number of load repetition. As shown in Fig.5.1, for

an illustration surface rut depth (r) geosynthetics

pavement is able to resist higher number of repetition

as compared to unreinforced section (without

geosynthetics), which clearly indicates the increase of

pavement life due to the use of geosynthetics material

as reinforcement. Field observations and research

results conrm this increased pavement life due to

geosynthetics utilization.

Fig. 5.1 Surface Rut Depth of Pavement With and Without

Geosynthetics (After Stevenson 2008)

Most of the researchers observed this increased

pavement life in terms of a dimensionless parameter

called as TBR. In general, geosynthetics have been

found to provide a TBR in the range of 1.5 to 70,

depending on the type of geosynthetics, its location

in the road, and the testing scenario (Carthage Mills

2002). Table no.1 shows few literatures which

highlight the range of TBR, apart from this the eld

observations in terms of TBR, obtained by various

researchers are highlighted below.

United States of Army Corps of Engineers performed a

eld test on unpaved road with and without a geotextile,

the test result indicate that for a rut depth of 0.28 m

the TBR is 12.5.Webster (1993) performed eld test

on exible pavement, where the researcher found that

reinforced section with a stiff geogrid carried 21 times

the number of trafc loads as compared to unreinforced

section. Barksdale et al. (1989) conducted a eld

test, for comparing the performance of different

geosynthetics products; the researcher found that for

12.5 mm rut depth TBR values are 17 and 2.5 for

the geogrid and geotextile sections respectively. J.G.Collin et.al (1996) performed a full scale eld test on

two different geogrid, where the researchers obtained

the range of TBR in between 2.2 to 4.4 for 25 mm rut

depth.

The above eld result obtained by various researchers

clearly shows the increase of pavement life due to the

use of geosynthetics material as reinforcement.


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6 SUSTAINIBILITY IN PAVEMENT

Bruntland Commission’s (1987) denes the sustainable

development as “meeting the basic needs of the present

generation without compromising the ability of future

generations to meet their needs”.

Ludomir Uzarowski (2008) have stated that over one

quarter of the world’s Greenhouse Gas emissions

(GHG) are caused by transportation and especially road

transportation. It is critical for the road construction

industry to become part of the solution by proactively

implementing technology and construction practices

that assist in achieving these challenging green house

gas emission reduction goals, and more attention

needs to be focused on pavement sustainability.

Pavement sustainability can be dened as a pavement

that minimizes environmental impacts through the

reduction of energy consumption, natural resources and

associated emissions while meeting all performance

conditions and standards. In essence, this is a pavement

that has less maintenance demands and longer time

between major rehabilitation interventions (Ludomir

Uzarowski 2008). Currently there are numerous

innovative pavement preservation technologies thatconserve aggregates, reduce GHG emissions, and

minimize energy consumption (Kazmierowski 2012);

one of the technologies is to use geosynthetics material

in a pavement as reinforcement.

Colascanada (2008) states that there is a 20% reduction

in the energy consumption and GHG emissions for the

reduced granular structure of the reinforced section.

Table 1 highlights the benets of geosynthetics in

terms of reduction in the Base Course Thickness

(BCR), in our paper indirectly we are achieving this;

hence we can say that the geosynthetics reinforced

exible pavement is a sustainable pavement.

The environmental savings associated with the reduced

granular structure are offset by the environmental

costs associated with the manufacturing, transport

and placement of the geosynthetics. Although there

is a potential environmental savings anticipated with

the reinforced pavement structure, these savings

cannot be conrmed without knowing the energy

consumption and GHG emissions associated with the

manufacturing and production of geosynthetics (Brian

Morrison 2011).

To nd out the sustainable benets of pavement, it is

essential to determine pavement lifecycle assessment

for environmental and economic effect. This can be

determined by using Sustainability index, which is

a non-monetary cost-benet analysis that includes

environmental and social impact assessment into the

benet-cost calculation. It also ties sustainability to

human development goals. Therefore, a SustainabilityIndex (SI) or a Sustainability Condition (SC) must

include marginal present and future benets and

costs, where costs must account for all damages to

the Natural and Social Environments (NSE) that

may possibly restrain future well-being. (Hasnat

Dewan 2011)

Therefore a working denition of sustainable

development can, be to nd the optimal human

development (H), with minimal damage to natural

and social environments (D) and Future Development

Potentials (FDP), in order to maximize the well-being

of the largest number of people in present and future

generations (Dewan A.H 1998).

It emphasizes end goal such as human development,

rather than consumption expenditures, focuses on

intra-generational as well as inter-generational

equity, includes both monetary and non-monetary

indicators, and also emphasizes both ecological and

social sustainability. Hence, the set of sustainability

indicators should include the Human Development

Index (H), a damage index (D), an equity index (E) and

the indices for Future Development Potentials (FDP).

The Capital-Debts Index (CDI) and the Productivity

Index (P) can be good measures of FDP. Therefore,

a possible set of sustainability indicators could be:

{H, D, E, CDI and P}. In the Human Development


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Index, two-third weight is assigned to quality of life,

i.e. income and education, and one-third to longevity,

which is a better indicator than consumption, though

the Human Development Index and consumption

should be highly, but imperfectly correlated (Hasnat

Dewan 2011)

The damage index is dened as: D = Max {ENV,

NAT, AMN, SOC}, where ENV = an index for

environmental degradation, NAT = an index for

natural resource depletion, AMN = an index for the

destruction of natural amenities, and SOC = an index

for the change or degradation of socio-cultural political

and institutional conditions. All indices are in [0, 1].

Since maximum damage to a sub-system of Naturaland Social Environments (NSE) is used to calculate

D, the coefcient of variation (V) of various damage

indices also needs to be monitored (Hasnat Dewan

2011). The computational details of these indices are

beyond the scope of this paper.

Sustainability issue is not about computing benets

and costs; it’s about ensuring sustainable levels of

ecological resources, which can be determined by

comparing Human Development Index (H) with

damage index (D). Hence sustainability indices is a

need of any nation or region for nding out the level

of economic development, the nature of damage

to Natural and Social Environments (NSE), social

perceptions etc. (Hasnat Dewan 2011)

7 GEOSYNTHETICS PRODUCT

STANDARDS

To obtain reliable material parameters and guidelines

for adequate pavement design construction, apparently

standardized testing is critical in selecting the

proper geosynthetics materials and providing basis

for specication (Guang-xin Li et.al 2008). These

standards reassure consumers that product is safe,

efcient and good for environment. Geosynthetics

products in the form of geotextile, geogrid or geocell

are easily available in market; also custom-made

geosynthetics products are available. Following

table 2 shows the list of geosynthetics standards which

are available at international level.

Table 2 List of Geosynthetics Standards Available at

International Level

Sr. No. Geosynthetics Product Standards

1 ASTM Standards

2 ISO Standards (ISO/TC221)

3 Indian Standards (BIS)

4 AASHTO Standards

5 FHWA Standards

6 NORDIC Guidelines

7 British Standards

8 International Geosynthetic Society Standards

(IGS)

9 Geosynthetic Research Institute (GRI)

10 Geosynthetic Materials Association (GMA)

11 US Provinvcial Standards

12 Industrial Fabrics Association International

(IFAI)

13 Geo-synthetica14 International Erosion Control Association

(IECA)

15 European Center For Standardization (CEN)

Numerous geosynthetics product manufacturing

industries are available at international level;

table 3 highlight the list of few geosynthetics product

manufacturing industries with their URL Site.

Table 3 List of Geosynthetics Product Manufacturing

Industries and Their URL Sites

Sr.

No.

Geosynthetics Product

Manufacturing Industries

URL Site

1 ACE Geosynthetics Inc. www.geoace.com

2 Agru America, Inc. www.agruamerica.com

3 Belton Industries www.beltonindustries.com

4 Carthage Mills www.carthagemills.com

www.gxgeogrid.com


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5 Crown Resources LCC www.crownresources.net

6 Dalco Nonwovens www.dalcononwovens.com

7 Fibreweb Geosynthetics www.breweb.com

8 GSE Lining Technology inc. www.gseworld.com9 Huesker Inc. www.huesker.com

10 L & M Supply Co.Inc. www.landmsupplyco.com

11 Maccaferri Inc. www.maccaferri-usa.com

12 Mattex Geosynthetics www/mattexgeo.com

13 Propex Geosynthetics www.geotextile.com

14 SKAPS Industries www.skaps.com

15 TechFab India www.techfabindia.com

16 TenCate Geosynthetics www.tencate.com

www.miraf.com17 Tensar International Corp. www.tensarcorp.com

8 ILLUSTRATIVE EXAMPLE

To nd out the maximum range of improvement for a

geosynthetics material in exible pavement, a data for

a ctitious exible pavement has been considered, and

the effectiveness of geosynthetics in terms of reduction

of Base course thickness has been found out by using

Giroud and Han (2004) design methodology.

The design data as follows

i) Trafc = 10964 ESAL Per Day

ii) C.B.R For Subgrade soil = 2%

iii) C.B.R For Base course material = 35%

iv) Wheel Load = 40 KN

v) Tire pressure = 550Kpa

vi) Assume allowable rut depth = 75 mm

vii) Geogrid of Aperture stability modulus= 0.65 mN/degree

vii) Design life = 15 Years

In Indian condition the exible pavement is to be

designed as per IRC:37.

for CBR 2% & Trafc 43.17 msa, the total pavement

thickness and conguration of pavement layers as

per IRC:37-2001, Plate No.2 page No.29 are as

follows:

Total pavement thickness = 916.46 mm say 920 mm

Base course = 250 mm

Subbase course = 460 mm

Bituminous surfacing = 210 mm

IRC:37-2001 considers three layer but Giroud and

Han design methodology is for unpaved road consider

only base course layer. Hence if the surface course is

not provided the remaining layers i.e. base and sub

base course, their thickness is bound to increase, so it

will be additional saving as shown in Fig. 2.1

Conclusion for base course thickness by using Giroud

and Han (2004) design methodology:

a) For unreinforced section base

course thickness = 450 mm

b) For reinforced section base

course thickness = 260 mm

Hence

Reduction in base course

thickness is = 190 mm

The reduction of base course thickness is up to 40 %

for a geogrid, placed at the interface of subgrade &

base course of the pavement, similarly the

effectiveness of geosynthetis can be nd out for

different reinforcement location such as within the

base course or combination of both.

9 CONCLUDING REMARK

Result for above illustrative example shows that the

impact of geosynthetics material in terms of reduction

of the base course thickness up to 40% as compared

to unreinforced section, this effect may be increased

for different geosynthetics stiffness and quality of

subgrade. Also the design methodologies proposed by

various researchers shows the benet of gosynthetics

materials in terms of extension of service life or

reduction in the base course thickness. In addition to


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the basic economical benets discussed above, there

are signicant environmental benets associated with

aggregate savings: less transportation of aggregate by

trucks, hence less air pollution, energy consumption

and less GHG emissions. Since geosyntheticsreinforcement addresses these issues it will open

gateway for the sustainable pavement.

10 ACKNOWLEDGEMENT

The Director, College of engineering Pune is hereby

acknowledged for permitting this research paper.

Indian institute of Technology Delhi and of Bombay

are acknowledged for providing library facility for the

literature survey.

REFERENCES

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and Behavior of Soil-Fabric Aggregate Systems”,

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2. Burd, H.J. and Houlsby, G.T. (1986), “A Large Strain Finite

Element Formulation for one Dimensional Membrane

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pp 3-22.

3. Bassam Saad and Hani Mitri (2006), “3D FE Analysis of

Flexible Pavement with Geosynthetic Reinforcement”,

Journal of Transportation Engineering Vol.132,

pp. 402-415.

4. Brian Morrision (2011), “ Geosynthetics as component of

sustainability in pavement Structure Design for Arterial

Roadways”, 2011 Annual Conference of the Transportation

Association of Canada.

5. Bruntland Commission (1987), “Our Common Future.

Oxford University Press, Oxford”.

6. Chan, F. Barksdale, R.D. and Brown, S.F. (1989),“Aggregate Base Reinforcement of Surfaced

Pavements”, Geotextiles and Geomembranes, Vol. 8,

No. 2, pp. 165-189. Collin.

7. Colascanda (2008), “The environmental road of the future:

Analysis of Energy Consumption and Greenhouse Gas

Emissions”, 2008 Annual Conference of the Transportation

Association of Canada, Toronto, Ontario.

8. Carthage Mills (2002), “A Handbook of Geosynthetics”,

Geosynthetics Material Association.

9. Collin J.G, Kinney T.C and Fu, X., (1996), “Full Scale

Highway Load Test of Flexible Pavement Systems With

Geogrid Reinforced Base Courses”, Geosynthetics

International,Vol. 3, No. 4, pp. 537-549.

10. Dewan A.H. (1998) “Measuring Sustainable Development:

Problems and Prospects” Ph.D. dissertation, TheUniversity of Texas, Austin.

11. Fannin, R. J. and Sigurdsson, O. (1996), ‘‘Field

Observations on Stabilization of Unpaved Roads with

Geosynthetics.’’ Journal of the Geotechnical Engineering,

Vol.122 No.7, pp. 544–553.

12. Giroud, J.P. and Noiray, Laure (1981), “Geotextile

–Reinforced Unpaved Road Design” Journal of the

Geotechnical Engineering Division, ASCE 107,

pp.1233–1254.

13. Giroud, J.P.and Jie Han (2004), “Design Method for

Geogrid -Reinforced Unpaved Roads Calibration

and Applications” Journal of Geotechnical and

Geoenvirinmental Engineering, ASCE pp.787-797.

14. Guang-xin Li, Yunmin Chen and Xiaowu Tang (2008),

“Geosynthetics in Civil and Environmental Engineering”

Geosynthetics Asia 2008, proceeding of the fourth Asian

Regional Conference on Geosynthetics in Shanghai,

China.

15. Hasnat Dewan (2011), Does the Primary Condition for

a Sustainable Human Development Meet the Feasibility

Condition of Cost-Benet Analysis? Journal of Sustainable

development Vol.4, No. 2.

16. Hausmann, M. R. (1987), “Geotextiles for Unpaved

Roads -- A Review of Design Procedures.” Geotextile and

Geomernbrane Vol. 5, pp. 201-33.

17. Hass, R., Walls, J., and Carroll, R.G., (1988), “Geogrid

Reinforcement of Granular bases in Flexible Pavements”,

Transportation Research Record. No. 1188, Washington,

DC, 19–27.

18. Koerner, R.M. (2005), “Designing With Geosynthetics”,

5th Edition, Prentice-Hall Inc., Englewood Cliffs,

NJ, 1998.

19. Kazmierowski Tom (2012) “Quantifying the Sustainable

Benets of Flexible Pavement Preservation Techniques

in Canada”, 2012 National pavement preservationconference.

20. Loyns,C.K.and Fannin, J.(2006), “A Comparision of

Two Design Methods for Unpaved Roads reinforced

with Geogrid” ,Canadian Geotechnical Journal 43

pp.1389-1396.

21. Ludomir Uzarowski (2008), “Sustainable Pavements –

Making the Case for Longer Design Lives for Flexible

Pavements” 2008 Annual Conference of the Transportation

Association of Canada, Toronto, Ontario.


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22. Penner, R., Haas, R., Walls, J. (1985), “Geogrid

Reinforcement of Granular Bases”, Presented to Roads and

Transportation Association of Canada Annual Conference,

Vancouver.

23. Perkins, S.W. and Ismeik,M.(1997),“A Synthesis and

Evaluation of Geosynthetics Reinforced Base Course

Layers in Flexible Pavements: Part I Experimental

Work”,Geosynthetics International, Vol. 4, No. 6,

pp. 549-604.

24. Perkins, S.W. (1999),“Mechanical Response of

Geosynthetic-Reinforced Flexible Pavements”,

Geosynthetics International, Vol. 6, No. 5, pp. 347-382.

25. Perkins,S.W. and Christopher, B.R. (2009),“ A

Mechanistic – Empirical Model for Base Reinforced

Flexible Pavements”, International Journal of pavement

Engineering Vol.10 No.2 pp.101-114.

26. Rueegger, Rudolf Hufenus, R., Robert Banjac and Mayor

P (2005),“Full Scale Test on Geosynthetic Reinforced

Unpaved Roads on Soft Subgrde”,Geotextile and

Geomebrane pp. 21-27.

27. Stevenson P. E. (2008),“Geosynthetics — Characteristics

and Applications”, Engineering materials for technological

needs Vol.1 page 299.

28. Tang Xiaocho and Chehab Ghassan R. (2008), “Evaluation

of Geogrids for Stabilizing Pavement Subgrade”

International Journal of pavement Engineering Vol. 9

No. 6 PP. 413-429.

29. Tom Kazmierowski (2012),“ Quantifying the Sustainable

Benets of Flexible Pavement Preservation Techniques

in Canada” 2012 National pavement preservation

conference

30. Venkatappa Rao G., Banerjee P.K.,Shahu J.T.and

RamanaG.V ( 2004),“Geosynthetic - New Horizons“

Asian books private limited, New Delhi.

31. Venkatappa Rao G. and Pothal Goutam K.

(2002),“Geosynthetics Testing- A Laboratory Manual”

Technical Publication Division.

32. Webster, S.L. (1993), “Geogrid Reinforced Base Courses

for Flexible Pavements for Light Aircraft, Test Section

Construction, Behavior Under Trafc, Laboratory Tests

and Design criteria.” Technical Report GL-93-6, USAE

Waterways Experiment Station,Vicksberg, MS, USA,

pp 86.

33. Zornberg, J.G. and Gupta, R. (2010),“Geosynthetics

in Pavements: North American Contributions”

9th International Conference on Geosynthetics, Brazil.


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ABSTRACT

Slope failures are always the major issues for the highway

safety and stability in a hilly terrain. The optimal Slope Stability

protection strategies generally mean the engineering feature of

providing selectivity a protective layer of suitable material on a

slope which is otherwise vulnerable to erosion. Slope failure are

the result of gravitational forces acting on a mass which can creep,

slide or ow as slurry. The failures of slopes take place in the form

of landslides or landslips.

Slope stability is affected by the factors such as topography,

geology, weather, pore water pressure characteristics and

seismic activity. Increased stability will result by eliminating or

controlling the factors contributing to sliding. Elimination factors

can be the measures such as relocating the route, removing the

landslide material at the toe and providing drains to intercept

seepage, bridging over the two extremities of the sliding area

etc. Controlling factors can be measures such as providing rock

fall barriers or retaining devices like buttresses, retaining walls,

gabion walls, piling etc.

Soil investigations are important for determining the type of

distribution of geology material in the slope, the geologic structure,

existing ground water conditions and the potential for future rise

in seepage pressure during rainy periods. Seismic refraction

proling is also valuable in identifying the likely failure planes

in rocky strata. Once the fact of land movement is established,

the type of likely landslide can be identied and optimal slope

protection strategies can be decided.

1 INTRODUCTION

Gravitational forces are always acting on a mass of soil

or rock beneath a slope. As long as the strength of the

mass is equal to or greater than the gravitational forces,

the forces are in balance, the mass is in equilibrium

and movement does not occur. An imbalance of forces

results in slope failure and movement in the forms

of creep, falls, slides, avalanches, or ows. Failureoccurs when driving forces exceed resisting forces.

Slope failures are a major issue for the highway

safety and stability. Such slope failures as landslides

are predominant in warm, humid climates and occur

OPTIMAL SLOPE STABILITY PROTECTION STRATEGIES FOR

ROAD CONSTRUCTION IN A HILLY TERRAIN : A CONCEPT

DR . S.S. SEEHRA*

during years of unusually heavy precipitation or during

period’s heavy concentration of rainfall or during wet

years. However, prediction of landslip failure is often

uncertain and slope stability is an important element

depending upon slope geometry, inherent soil strength

and ground or pore water pressure characteristics.

A landslide is triggered if the shearing (tangential)

stresses appearing in a soil mass exceed the magnitudes

that the soil is able to resist. An increase of active

shearing force can be due to erection of an engineering

structure on the slope, increase in the weight of soil

mass, higher gradients etc. A reduction of resisting

forces can be due to removal of lateral support, say,

when excavating a cut across the slope. In such a case,

the prediction of landslide failure is often uncertain

and slope stability becomes frequently costly.

Erosion is the natural process of removing soil

particles by external agents such as wind or water.

This involves rainfall which is responsible for the

removal of surface layer, resulting in gullies of about

10-60 cm depth. However, over time the sills andgullies deepen further and cause slope to overstepped,

thus precipitating slope instability the slope protection

generally means the engineering feature composed of

suitable material constructed as a selectively thin layer

on a slope otherwise vulnerable to erosion.

Vegetation is an important slope stabilizer. Planting the

slope with thick native vegetation serves to strengthen

the shallow soils with root systems, prevents erosion,

deters inltration and increasing seepage pressures.

Vegetation also discourages desiccation which causesssuring. Deep ssures provide channels for rain water

to enter the slide mass, increasing seepage pressure

within the mass as well as applying hydrostatic

pressure against the walls of the ssure or crack .

* Advisor (Technical), LEA Associates South Asia Pvt. Ltd, New Delhi E-mail: [email protected]


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Seeding can also be used for slope treatment. Asphalt

mulch technique can be used in which the slopes

are prepared into vast seed beds. Asphalt mulch is

then spread by a sprayer. The asphalt lm gradually

disintegrates, its place being gradually taken up by acarpet of green vegetation. The carpet of grass, that

supplants the asphaltic lm, acts as an immediate

cover for the slopes till the more deep rooted species

of shrubs and trees develop and take root.

2 CAUSES OF SLOPE FAILURE

Slope failures are the result of gravitational forces

acting on a mass which can creep slowly, fall freely

or slide along some failure surface, As stresses are

usually highest at the toe of the slope, failure often begins there and may progress upslope. Stability

generally depends on the following variables:

- Topography – in terms of slope inclination and

height

- Geology – in terms of material structure and

strength

- Weather – in terms of seepage forces and run

off quantity and velocity

- Seismic activity in terms of interial forcesonly.

The basic factors that must be considered in the

evaluation of slope instability are the type and

distribution of geologic materials in the slope, the

geologic structure, existing ground water conditions,

and the potential for future rise in seepage pressures

during rainy periods and the inclination and height

of slopes. On these conditions are imposed changes

brought about by construction activity, such as theexcavation for cuts or the placement of ll. These

activities change the natural slope stability.

A landslide is triggered if the shearing (tangential)

stresses acting in a soil mass exceed the available

resistance of that soil is able to resist. In the majority

of situations, slope failures are caused by water either

acting on the surface or through the subsurface. On

the surface, heavy ows result in erosion down slope

or along the toe of slope, increasing slope angles and

slope inclination as well as natural drainage conditions.

The removal of vegetation also tends to decrease slopestability. Over the geologic long term, slope stability

can decrease naturally due to decomposition of the

geologic materials and also by seismic activities. A

rising ground water table results in increased pore

pressures in soil masses and increased ‘cleft’ water

pressure acting along fractures in rock masses.

In rock masses slope failures will occur along

discontinuities representing weakness planes, the

major forms which are joints, faults, foliations,

bedding planes and slickensided surfaces. Even in

highly weathered rock it is the discontinuities that

generally control the strength of the mass. Fig.1

shows the control of seepage forces and driving

forces and increasing the resisting forces for slope

stabilization (6).

Fig.1 The General Methods of Slope Stabilization : Control of Seepage Forces and (B) Reducing the Driving Forces and Increasing

the Resisting Forces. (Reference 6)


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Once the fact of land movement has been established

the next step is to identify the type of landslide.

Having identied the land slide type together with the

necessary data, appropriate choice of the corrective

measures shall be made. Fig. 2 shows the benching

scheme for cut in highway erodible soils. Low benches

permit maximum inclination to reduce the effect of

run off erosion (6).

Fig.2 Benching Scheme for Cut in Highway Erodible Soils in a Tropical Climate. Low Benches Permit Maximum Inclination to

Reduce the Effect of Runoff Erosion (Reference 6)

3 SLOPE STABILITY PROTECTION

MEASURES

3.1 General

Increased stability will result by eliminating or

minimizing the effect of any contributing factor for

sliding, particularly that of the effect of the force

of gravity. Water is also a contributing factor in

practically all landslides.

For a given land slide problem there can be more than

one method of correction and the decision is reduced

to a problem of economics. For example, a retaining

wall can be designed sufciently large to withstand

any given landslide. However, a wall design that will

be successful may be outside a reasonable range of

economics for a given landslide, Correction measuresfor a landslide can be by elimination or control

methods. Fig.3 shows various types of retaining walls

to withstand landslides (6)

Fig.3 Various Types of Retaining Walls: (a) Rock:Filled Buttress: (b) Gabion Wall; (c) Crib Wall; (d) Reinforced Earth Wall;

(e) Concrete Gravity Wall; (f) Concrete-Reinforced Semi Gravity Wall; (g) Cantilever All; (h) Counterfort Wall;

(i) Anchored Curtain (Reference 6)


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3.2 Elimination Mehod

The elimination method avoids or removes the

landslide. The following measures can be taken when

the elimination method is used:(i) Route relocation. Geologic conditions often

differ from one side of a valley or mountain

slope to the other, even where the materials are

similar. For example, on one slope dipping beds

or foliations may incline downward and out of

a cut slope representing an unstable condition,

whereas on the opposite side of the valley or

mountain the dip of the beds or foliations is into

the slope providing stable conditions. Where colluvial soils exist they often are

thickest and most unstable along the lower

slope elevations and at times can be avoided

by locating an alignment at higher elevations

up slope. Residual soils can also be found with

higher strengths and less exposure to changes

in seepage conditions upslope.

(ii) Bridging, whereby the landslide area is avoided

by a bridge between the two solid extremitiesof the moving area

(iii) Cementation of loose material. The material

to be cemented should be permeable. Cement

grout is injected into the moving area in order

to achieve stability. It produces a material that

has higher shear resistance. In cohesive soils

vertical columns are obtained and their effect

is that of a system of piles. The resisting forces

are increased by transference of load from themoving mass to the underlying stable material.

(iv) Heavy inow of surface and Sub-Surface water

from the uphill slide to the landslide zone is

shown in the Fig.4 (7).

(v) Fig.5 shows the slope and management of roads

in high precipitation areas (13).

Fig.4 Proper Drainage Provisions for a Side Hill Fill.

(Reference 6)

Fig.5 Slope and Drainage Management (Reference 13)

3.3 Control Method

The control method produces a static condition of thelandslide for a nite period of time. The following

measures can be taken when the control method is

used:

(i) Rock fall barriers, retaining devices such as

buttresses, retaining wall of masonry stone

or concrete, gabion walls and piling can be

used. Rock-lled buttresses are used when

good foundation is available at toe in shallow

or deep soil. Buttress should extend below

the slip plane. The buttresses are constructedwith non degradable, equi-dimensional rock

fragments with at least 50% between 30 to

100 cm and not more than 10% passing 50mm

sieve. Gradation is important to maintain free-

draining characteristics and high friction angle.

Retaining walls of masonry stone or concrete

are effective for shallow soil where good


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foundations are available. A wall requires a

foundation in bedrock or good soil below the

slip surface. Standard practice is to include

weep holes in designing the wall. The design

formula for the safety factor may be used toestimate resistance required to lateral thrust.

(ii) Covering of the freshly cut slopes to protect

from weathering and erosion can enhance

the stability of the rock mass for a very long

duration.

(iii) For slope protection ‘soft’ or ‘green’

approach such as turng is much less

expensive, aesthetically pleasing as well as

environmentally- friendly. Even for the ‘green’

or bio-engineering solution, one has to be judicious in selecting which measure one wants

to employ to suit one’s needs based on climatic,

soil types and budgetary constraints. In addition

like all living things, plants need time to grow,

mature and establish before they can truly

function with maintenance programme in terms

of fertilising, watering, weeding etc. is essential

depending on the type of plants one is dealing

with good design during the planning stage,

careful selection of quality planting materials

that meet specications, correct planting and

maintenance techniques. It can condently be

said that good outcomes will be achieved with

the full potential of plants being realized.

(iv) Fig.6 shows the rock fall barrier to control the

falling rock boulders (12)

(v) Gabion walls are also used as retaining walls.

They are wire baskets, about 50 cm each side

and lled with broken stone of about 10-15 cm

across. The baskets are then stacked in rows.

They are free draining and retention is obtainedfrom the stone weight and it’s interlocking.

Typical heights are about 5 to 6 meters. Fig.7

shows the Gabion Baskets for constructing the

Gabion walls.

Fig.6 Rock Fall Barrier to Control the Falling Rock Boulders

(Reference 12)

Fig.7 Gabion Baskets Ancient Concept in a Modern Form

(Reference 11)

Rock buttresses and retaining walls can be used

to correct small slides especially rotational

ones, but are not generally speaking effective

on large slides. Retaining devices are seldom

applicable for correction of falls and ows.

Retaining devices placed in the path of a ow

slide receive the entire force of the moving

mass because of the fact that there is little

inherent resistance of the soil involved in the

ow. Piling can be used in shallow soil to holdthe slide mass temporarily.

For retaining rock slopes, rock bolts, wire mesh

and shotcreting can be used. Rock bolts can

retain exfoliating slabs and other loose blocks.

Wire mesh needs periodic removal of blocks.

Shotcreting stabilizes local areas of highly

fracture rocks. Additional retaining measures


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are cutting back of the rock slope, sealing

fractures and installing drains

(vi) Control of surface water (inltration) by

providing appropriate drainage and thus creating

a direct rebalance of the ratio between resistance

and shearing force. Generally drainage should

be designed to intercept water before it enters

the slide. Water affects the stability of natural

slopes by increasing pressures in the soil or

rock interstices, thereby reducing strength

and increasing the overburden weight, which

result in increased driving force. Prevention or

stabilization of slides is often simply a matter

of controlling inltration into the mass and of

relieving water pressures within the mass.(9)

.Fig. 8 shows the installation of geogrid on rock

slope by bolting/nailing

(e) Removal by cuts of thick mantle or

pervious soil if such pervious soil happens

to be a natural restraining blanket over a

soft core.

(f) Increase in seepage pressure caused

by cut or ll that changes direction and

character of ground water ow.

(g) Exposure by cut of stiff ssured clay that

is liable to soften and swell when exposed

to surface water.

(h) Removal of mantle of wet soil by side hill

cut. Such a cut may remove toe support

causing soil above cut to slide along its

contact with stable bed rock.

(i) Vulnerable soil erosion due to water

action

(j) Fig.9 shows the distance view of

landslide area and Fig.10 shows the

close view of landslide area.

Fig.8 Installation of Geogrid Rock Slope by Bolting/Nailing

(Reference 9)

(vii) Landsliding induced by proposed cuts or lls

and these are controlled as under in severe

climatic conditions (11):

(a) Restriction of ground water by side hill

soils.

(b) Overloading of relatively weak underlying

soil layer by ll.

(c) Overloading of sloping bedding planes

by heavy side hill ll.

(d) Oversteepening of cuts in unstable rock

or ll.

Fig.9 Distance View of Landslide Area (Reference 9)

Fig.10 Close View of Landslide Area. (Reference 9)


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4 GEOTECHNICAL INVESTIGATIONS FOR

SLOPE STABILIT

The geotechnical investigations for slope stability

are carried out where gravitational forces are always

acting on a soil mass or rocks beneath a slope. Aslong as the strength of the mass is equal to or greater

than the gravitational forces, the forces are in balance,

the mass is in equilibrium and movement does not

occur. However, an imbalance of forces results in

slope instability which occurs in the forms of creep,

falls, slides, avalanches or ows. Slope failure occurs

when driving forces exceed the resisting forces.

In rocks and soil masses, slope failures will occur

along discontinuities representing weak planes, the

major forms which are joints, faults, bedding planes

and soil erosion. Even in highly weathered rock, the

discontinuities generally control the strength of the

mass. Table -1 shows the slope values for different

materials (6)

Table 1 Slope Values for different Materials.

(Reference 6)

Type of Slope Material Design Slope

Rock

Hard masses of igneous or metamorphic

rocks and hard sedimentary rocks with

bedding dipping vertically or dipping

into the face of the slope

1:4 (76°)

Moderately weathered rock 1:3 (70°)

Highly weathered fractured rocks

covered by clayey silty sandy soil

mixed with angular gravels and cobbles

(based on height of slope)

1:2 to 1:1 (63°) - (45°)

Soil

Residual soils (strong) (based on height

of slope)

1:2 to 1:1 (63°) - (45°)

Colluvial soils (based on height of

slope)

5:1 to 5:2 (10°) - (20°)

Terrace Soil (Silt-sand-gravel mixtures

with angular cobbles and boulders)

(based on height of slope)

1:1 to 3:2 (45°) - (34°)

Most other soils (based on height of

slope)

2:1 to 3:2 (26°) - (34°)

Clay Shales, Black cotton soils 6:1(9.5°)

Relatively higher water content and lesser resistance to

penetration may often prove more reliable indication

of the location of the surface of rupture in borings

and samples. In many cases the surface of rupture is

determined nally by correlating zones of high water

content and low penetration resistance in several

borings.

The laboratory tests are routine identication tests

such as eld moisture content, Atterberg Limits,

mechanical analysis etc. and/or shear tests such

as the direct shear, the triaxial or the unconned

compression test, cohesion and angle of internal

friction. Laboratory strength testing should duplicate

the eld conditions of pore water pressures, drainage,

load duration and strain rate that are likely to exist as a

consequence of construction operations, and samples

should usually be tested in a saturated condition. Itmust be considered that conditions during and at the

end of construction are short term conditions and

will therefore be different from long-term stability

condition

Seismic refraction proling has been found to be

particularly valuable in determining stratigraphy where

soil thickness in hill sides can range from 1 meter to

30 meters or more. The seismic refraction surveys are

made both longitudinal and transverse to the slope.

Their primary purpose is to determine the depth tosound rock and the probable ground water table. They

are also useful in differentiating colluviums from

residuum. Resistivity proling is also considered as

a means of determining the depth to water table and

rock (12). Fig.11 and Fig.12 show rock fall occurring

on slopes in the landslides zones.

Fig.11 Control of Rock Fall Using Wire-Mesh (Reference 10)


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When residual soils are formed on steep slopes they

are subjected to movement ranging from shallow

creep to failure and total displacement. Fig. 13 showsthe vulnerable soil erosion due to water action. Fig.14

shows the vegetative surface cover for slope protection

such as turng

5 CONCLUSIONS

The adverse effects of landslides due to a slope failure

can be prevented to a considerable extent by taking

due care at the time of hill road project conception,

alignment design, construction and during subsequent

maintenance-soil erosion and landslides occur due

to both natural and man-made causes. Some of

the natural causes are geology of the area, rainfall

including cloudbursts and consequent ash oods,

toe erosion, seepage and earthquakes. The geological

and geotechnical investigations are carried out to

investigate the causes of landslides. Based on the

results of these investigations and salability analysis

of the slopes, remedial measures have to be adopted

for the slope stabilization. Some of the conclusionsare as follows:

(i) There are many natural as well as manmade

factors which are mainly responsible for the

stability. Rocks present in the area which are

soft highly jointed, folded and faulted. These

rocks are highly weathered and easily erodible.

Steep slopes present in the area are again

responsible for the instability of slopes.

(ii) The hilly road network without proper design

and lack of sufcient drainage system are the

main causes for the instability for hill slopes.

(iii) Field investigations often indicate heavy inow

if surface and sub-surface water from the uphill

side to the landslide zone, further improvement

of the existing drains with the new drains and

culverts is a viable solution to divert the ow of

water from the landslide area.

(iv) Gabion walls are viable solution to provide

the toe support and surface erosion which iscontrolled by laying of geogrids on the slopes.

(v) The back cut slopes should be as per prescribed

slope angle as per soil strata so as to avoid

occurrence of landslides from the freshly cut

hill slopes

(vi) It is also emphasized that the landslide

awareness programme should be arranged for

Fig.12 Rock Fall on Mumbai –Pune Expressway (Reference 9)

Fig.13 Erosion and Slope Failures (Reference. 10)

Fig. 14 Vegetative Surface Cover (Reference 10)


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the local people. Therefore, people should be

aware about the do’s and don’ts They should

not use the slopes as dump yard for the garbage.

It should be ensured that the adjoining slopes of

landslides should not be used for any activitysuch as agriculture.

(vii) Covering of the freshly cut slopes to protect

from weathering and erosion can enhance

the stability of the rock mass for a very long

duration.

(viii) For slope protection ‘soft’ or ‘green’

approach such as turng is much less

expensive, aesthetically pleasing as well as

environmentally- friendly. Even for the ‘green’or bio-engineering solution, one has to be

judicious in selecting which measure one wants

to employ to suit one’s needs based on climatic,

soil types and budgetary constraints. In addition

like all living things, plants need time to grow,

mature and establish before they can truly

function with maintenance programme in terms

of fertilising, watering, weeding etc. is essential

depending on the type of plants one is dealing

with good design during the planning stage,careful selection of quality planting materials

that meet specications, correct planting and

maintenance techniques. It can condently be

said that good outcomes will be achieved with

the full potential of plants being realized.

(ix) Manmade geotextiles and natural goetextiles

made of jute (JGT) help reduce the velocity of

overland ow and entrapping the dissociated soil

particles while fostering growth of vegetation

concurrently that is very much effective for

slope protection.

REFERENCES

1. IRC: SP:48 – 1998,” Hill Road Manual,” The Indian

Roads Congress New Delhi, 1998.

2. Bishop A.W. The Use of the Slip Circle in the Stability of

Earth Slopes-Geotechnique Vol. 5 (pp.7-17), 1955

3. HRB SR.No.12, State- of -the -Art “Application of

Geotextiles in Highway Engineering,”The Indian Roads

Congress, New Delhi, 1994.

4. Gray, D H and Leiser, AT . Biotechnical slope protection

and erosion control. Van nostrand Rheinhold New

York.,1982

5. Seehra S.S “UNDP Fellowship Programme to USA on

Geotechnical Engineering relating to Highways with

special emphasis on Pavement Engineering, Pavement

Materials, their characteristics and Pavement Design”

Federal Highway Administration (FHWA), Washington,

D.C, USA, 1985

6. Ethiopian Roads Authority (ERA), “Material and

Geotechnical Investigation Working Manual for Highway

Design Services”, Federal Democratic Republic of

Ethiopia, (Africa), July 2008.

7. Seehra, Dr. S. S. et. al, “A Technical Paper on Planning and

Design of Roads in High Precipitation Areas” publishedin the proceedings of International Seminar on “Roads in

High Precipitation Areas”, organized by IRC at Guwahati

(Assam), 19-20 Feb, 2010.

8. Seehra, Dr. S. S. et. al, “ A Technical Paper on “Ground

Improvement for strategic Highway Construction in

problematic Black Cotton Soil Areas and Remedial

Measures : A Case Study” Published in the Journal of

‘INDIAN HIGHWAYS’ Vol. 38, No.11, Special Number,

November 2010, New Delhi, India.

9. Sudhir Mathur (CRRI), “A Technical presentation made in

the training course on Landslide and Corrective Measures”

Indian Academy of Highway Engineers (IAHE), Noida,

2011.

10. Sudhir Mathur (CRRI), “ A Technical presentation made

in the training course on PRS Slope and Earth solutions”,

Indian Academy of Highway Engineers (IAHE), Noida,

2011

11. Seehra, Dr. S.S., “ A Technical presentation made in the

training course on Slope Stability, Erosion control and

Landslide correction “, Indian Academy of Highway

Engineers (IAHE), Noida, 2011

12. Indian Roads Congress, “Draft Guidelines for Rock fall

protection Systems”, H-4 Committee of Indian Roads

Congress (IRC), 2012, New Delhi.

13. OPUS- Asset Management Services, PIARC InternationalSeminar, Road Asset Management (RAM), March, 2008,

Chandigarh, India.

14. Bagui, S.K Slope protection using vegetation and bio-

engineering”, Proceedings of the Seminar on Road in high

precipitation areas, February, 2010, Guwahati Assam,

India.

15. HRB SOAR No. 15-1995, “State- of -the -Art: Landslide

Correction Techniques” The Indian Roads Congress

1995.


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ABSTRACT

Problems with subgrade having low CBR values are stability and

large deformations or settlements. In many cases the thickness of

soft soils with low CBR values extends to greater depth and is not

economical to construct roads on this type of subgrade. However

as demand for infrastructure increases, the construction on this

type of subgrade with low CBR values is unavoidable. In rural

areas most of the unpaved sections lies in soft soil and in marshy

environment and the removal of the soft soil and backlling it

makes the unpaved section uneconomical. In view of the above

considerations bamboo, owing to its availability and low cost it can

be used as subgrade reinforcement. In this article the potential use

of natural material bamboo as subgrade reinforcement is analysedfor different poor subgrade CBR values. The present objective

of the study is to determine the potential use of using bamboo

as subgrade reinforcement for different subgrade strengths. It is

shown that bamboo grids serve as effective reinforcement in soft

soils and also result in savings of aggregate material. The savings

in aggregate are presented in terms of reduction of carbon foot

print with a typical example.

1 INTRODUCTION

In most places soft soils are highly plastic ne

grained soils with natural water content higher thanthe liquid limit. Soft soils are characterized by high

compressibility and low shear strength (generally less

than 25 kPa). Soft to medium dense silty and clayey

soils are found in many parts of India. In India, the

major proportion of soft clays are marine and river

delta deposits and cover more than 30% of the total

land area. Typically these types of soils will have

CBR values less than 5.0 due to which construction

of pavements on these types of soils is difcult. The

innovative concept of reinforced soil dates back from

1960s where it can be economically applied to large

structures. According to Jewell (1996), reinforced

earth can be dened as a construction material

composed primarily of soil whose performance has

BAMBOO AS SUBGRADE REINFORCEMENT FOR LOW

VOLUME ROADS ON SOFT SOILS

R AJA J* AND G.L. SIVA K UMAR BABU**

been improved by the introduction of small quantities

of other materials in the form of solid plates or bers or

brous membranes to resist tensile forces and interact

with soil through frictional resistance. In the recent

decades the materials employed as reinforcement in

soils are presently expensive and would require a

cheaper and abundant material with similar strength

and durability. In India alone at about two million

hectares of land is in current use for bamboo production

for various uses. According to Mayank (2008) India

has the largest recorded bamboo resources globallyat around 13.47 million tons harvested annually. So,

there is need for effective utilization of bamboo as

reinforcement in soft soils. The use of bamboo had

also been demonstrated by Loke (2000) in which they

presented that it could give saving of up to 45-65%

compared with using high strength geotextile alone

and conventional lling method. It may be mentioned

that the studies of bamboo as reinforcement material

in soil are limited which make them limited use in

practical purposes. Another major reason for limitedusage of bamboo as soil reinforcement is due to the

more design methodologies available for geosynthetic

material. Some of the case studies with bamboo as soil

reinforcement are detailed in the present section. Marto

and Othman (2011) discussed the potential use of

bamboo as reinforcement of soft clay in embankment

construction and concluded that the performance

in terms of settlement and lateral movement of the

bamboo geotextile composite was better compared

with high strength geotextile embankment and also

with unreinforced embankment. Bergado et al.(1987)

compared the results of the laboratory pull-out tests

using bamboo and polymer geogrid and concluded that

the bamboo has higher pull-out resistance compared

* Project Associate, IISc, Bangalore; E-mail: [email protected]

** Professor, Department of Civil Engineering, IISc, Bangalore


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with polymer geogrid. Anusha and Emmanual (2011)

studied two case histories and concluded that the

geotextile bamboo composite construction can be

successfully used for stabilization and reclamation

of deep soft soils. Construction of unpaved roadsection with poor subgrade CBR values is very often

in many rural areas Subgrade strength and stiffness

are prominent characteristic for pavement design,

construction and performance evaluation, as the

subgrade is the substructure for the pavement. Some

of the studies on bamboo as concrete reinforcement

possessed high tensile and compressive strength

Documents

Indian Highways Vol.41 6 June 13