MOONAMANG ROAD EXTENSION INVESTIGATION PAVEMENT DESIGN

MOONAMANG ROAD EXTENSION

INVESTIGATION

&

PAVEMENT DESIGN

7511-G-R-002-C Moonamang Road WML Investigation and Pavement Design Report.docx

Date: 5 January 2018

WML Name: Moonamang Road Investigation & Pavement Design Report

WML Project No: 7511

Distribution Record:

Revision Reviewed

By

Date Issued Purpose of Issue Issued To

A PAF 08/08/2017 Draft for comments Client

B PAF 24/8/2017 Draft final Client

C PAF 5/1/2018 Final Client

Prepared by: Tom Bond

Signed:

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About your geotechnical investigation and report………….

A geotechnical investigation is planned and conducted solely for the intended recipient of

the report and for the purposes stated in the report. The report should not be reproduced

in whole or part without agreement of WML Consultants.

A geotechnical investigation is planned and conducted based upon the information about

the site and proposed works that is made available to WML Consultants, as stated in the

report.

A geotechnical investigation typically includes investigation and testing at a few isolated

locations. The choice of the locations is usually made by the author having

consideration for the nature of the site and proposed works. Conditions for the

remainder of the site are necessarily extrapolated from the conditions observed at the

locations investigated. Thus the report will contain a mixture of facts, interpretation and

professional judgement. Facts will usually be confined to a description of the fieldwork

carried out, the observations made and any results of laboratory testing. However, field

notes and logs contain estimates of conditions observed at the time, and may differ from

the results obtained from subsequent laboratory testing of samples. Other comments

and conclusions should be considered as interpretation and professional judgement,

unless specifically stated otherwise.

As the nature of geotechnical conditions is so variable WML Consultants accepts no

liability or responsibility for the conditions encountered beyond the limits of our

investigation. Such conditions may exist between test locations or in deeper strata than

observed than can reasonably be interpreted from the limited extent of this investigation.

For various reasons (e.g. seasonal effects), the site conditions encountered during

construction may differ from those observed or extrapolated from the initial

investigation. In this instance the recommendations in the geotechnical report may not

be appropriate and it is strongly recommended WML Consultants be requested to inspect

the different conditions, review the initial report and provide follow-up advice. Unless

specifically allowed for in the brief, the follow-up review will attract an additional fee.

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EXECUTIVE SUMMARY

FINDINGS AND RECOMMENDATIONS

Finding 1 – Pavement Design

The sealed section of Moonamang Road (Ord 2) was constructed in 2013 and visual

inspection shows it to be in good condition with no surface pavement defects.

The unsealed black soil embankment extension to the sealed works (CH 47800 to CH48800)

has maintained its field moisture content near optimum moisture content (OMC) giving a

insitu Californian Bearing Ratio (CBR) value as determined from Dynamic Cone

penetrometer (DCP) testing of 12% or greater. This confirms the Coffey report finding for

Ord 2 that black soil in raised embankments can be treated as expansive clay under well

drained conditions and validates the Ord 2 pavement design and composition.

It is recommended that the pavement thickness and composition design for Ord 2 be also

applied to the Moonamang Road Extension works (Ord 2 extension).

Finding 2 – Unsealed Black Soil Ultimate Embankment (CH47800 to CH48800)

This embankment section was previously constructed to the ultimate design and covered

with a select embankment sandstone wearing course.

The sandstone layer was removed at selected sites and the black soil embankment material

tested for density and field moisture. This density/moisture testing showed that the

characteristic dry density ratio of 86% is lower than the specified 90% with average field

moisture near Optimum Moisture Content (OMC).

Dynamic Cone Penetrometer (DCP) testing was conducted on the full depth of the ultimate

black soil embankment. The CBR values determined from the DCP testing are 8% or greater

for the full depth of the embankment with a Design Subgrade CBR values of 12% or greater

for the 200mm subgrade layer. This is significantly higher than the Design Subgrade value

of 3.5% used for the pavement design of Ord 2.

Given the high insitu CBR strength of the existing black soil embankment, it is recommended

that it be retained without further work except for surface levelling and compaction of the

sandstone wearing course.

Finding 3 – Unsealed Black Soil Taper Embankment (CH48800 to CH49500)

This embankment section constructed of black soil and covered with select embankment

wearing course is the vertical taper to natural surface and the tie-in to the existing unsealed

road alignment.

The sandstone layer was removed at selected sites and the black soil embankment material

tested for density and field moisture. This density/moisture testing showed that the

characteristic dry density ratio of 86.5% is lower than the specified 90% with average field

moisture near Optimum Moisture Content (OMC).

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DCP testing was conducted on the full depth of the black soil embankment taper section.

The CBR value determined from the DCP testing is 15% or greater for the full depth of the

embankment with a Design Subgrade CBR of 16% or greater for the 200mm subgrade layer.

WML Observations of the blacksoil embankment geotechnical data:

• The Characteristic Densities of both embankment sections are the same.

• The Design Subgrade CBR strength of both embankment sections as determined by

DCP testing is 12% or greater and significantly stronger than Design Subgrade CBR

of 3.5%.

• The insitu embankment material field moisture is near OMC and in a moisture state

similar to black soil embankment construction material that is moisture conditioned

ready for compaction.

• The embankment batters at 4 horizontal to 1 vertical (4:1) can be safely compacted.

Note that Water Corporation uses a slope limit of 3:1 for clay liner construction on

dams and ponds compacted to 98% Standard Maximum Dry Density (SMDD).

Given the observations above, WML considers either of the following two options for

widening and raising the embankment taper section after the sandstone is removed is

appropriate, as either carries a low risk of long term pavement failure.

These options are:

1. The existing black soil embankment and batter surfaces are compacted before

placing and compacting the additional material required to meet the ultimate level

and profile; or

2. The existing black soil embankment material is completely removed, then mixed and

conditioned before placing and compacting as embankment construction material.

The sandstone wearing course that is removed is only used for temporary works, such as

haul road or side track construction due to the risk of black soil contamination during the

removal process.

Finding 4 – Embankment Fill Tetra 2 Borrow pit

The Embankment Fill Borrow pit near the Tetra 2 tower (Tetra 2) contains more than

150,000 bank cubic metres (bcm) of embankment fill material to a depth of 2 metres. The

surface material to a depth of about 1.5 metres is black soil with a soaked CBR strength of

about 2%. The underlying material to 2 metres is red pindan/alluvium material with a soaked

CBR of about 8%.

It is recommended that the contract specification directs the contractor to place the black

soil in the lower embankment layers and that the red pindan/alluvium be placed in the top

of the embankment to a depth of at least 200mm.

Finding 5 – Area 11 Sandstone Quarry

Test pits excavated in the floor of the Ord 2 sandstone quarry in Area 11 confirms a volume

of 80,000 bcm of highly to slightly weathered sandstone and this in turn is underlain by

unweathered sandstone. The highly to slightly weathered sandstone is similar to that used

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for Ord 2 which was won using D9 and D10 size dozers. As the percentage of slightly

weathered sandstone will be higher it will on average be more difficult to rip and win.

Due to the confined site the Ord 2 select fill material was won and stockpiled first, then

progressively removed. This left room to stockpile the harder subbase sandstone for

mechanical crushing, reducing stockpile handling costs.

WML considers that there are two options for the stockpiling of the sandstone for select fill

and subbase with no clear advantage for either. These options are;

1. The sandstone is stockpiled as a pre- construction activity. This reduces risk if the

deposit proves to be more variable that expected and gives time to address any

material quantity or quality issues that arise; or

2. The sandstone is stockpiled by the contractor using the same processes developed

for the Ord 2 works. This may potentially reduce the handling costs of providing two

separate stockpiles of select fill and subbase material at a confined site.

An analysis of the sandstone testing for Ord 2 showed that increasing the density

requirement by 2% significantly increased laboratory soaked CBR strength. It is therefore

recommended that the sandstone density requirements be increased by 2% for the select

fill and subbase layers.

Finding 6 – Area 11 Sandstone Pit Safety Risks

The steep slope of the Area 11 sandstone quarry may present safety risk issues if not well

managed.

It is recommended that the Area 11 quarry footprint and its surrounds be surveyed to

develop a comprehensive pit management plan and safe work practices that reduce this risk.

This may require a narrow extension of the pit to the west over the brow of the hill to

enable the top of the hill to be lowered reducing the steepness of the quarry floor.

Finding 7 – Area 8 Lot 4 Extension Basecourse Gravel

WML has located and investigated a small deposit of gravel, containing about 28,000bcm

adjacent to Lot 4 (Lot 4E). This gravel has similar properties to the Lot 5 gravel used for

basecourse material for Ord 2.

It is recommended that for the Ord 2 extension works that:

• This gravel is stockpiled as a pre-construction activity to provide the Lot 5 gravel

stockpile shortfall.

• This material and the stockpiled gravel in Lot 5 are presented to the contractor as

“Principal supplied gravel”.

• The basecourse gravel test results are provided in the Information for Tenderers.

• The basecourse stabilisation and construction processes developed for Ord 2 are

included in the contract specification.

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CONTENTS

EXECUTIVE SUMMARY ....................................................................................................................................................... 4

FINDINGS AND RECOMMENDATIONS ........................................................................................................................ 4

FINDING 1 – PAVEMENT DESIGN .................................................................................................................................... 4 FINDING 2 – UNSEALED BLACK SOIL ULTIMATE EMBANKMENT (CH47800 TO CH48800) ......................................... 4 FINDING 3 – UNSEALED BLACK SOIL TAPER EMBANKMENT (CH48800 TO CH49500) ............................................... 4 FINDING 4 – EMBANKMENT FILL TETRA 2 BORROW PIT ................................................................................................. 5 FINDING 5 – AREA 11 SANDSTONE QUARRY ................................................................................................................. 5 FINDING 6 – AREA 11 SANDSTONE PIT SAFETY RISKS ................................................................................................... 6 FINDING 7 – AREA 8 LOT 4 EXTENSION BASECOURSE GRAVEL ...................................................................................... 6

1 INTRODUCTION ........................................................................................................................................................... 8

2 SITE SETTING ................................................................................................................................................................ 8

2.1 SITE LOCATION AND DESCRIPTION ................................................................................................................... 8 2.2 EXISTING PAVEMENT ........................................................................................................................................ 8 2.3 GEOLOGY .......................................................................................................................................................... 9

3 DESIGN CBR AND PAVEMENT THICKNESS ..................................................................................................... 9

3.1 MOONAMANG ROAD PAVEMENT DESIGN ........................................................................................................ 9 3.2 DESIGN CBR (2017) ...................................................................................................................................... 11 3.3 DESIGN TRAFFIC AND PAVEMENT THICKNESS ................................................................................................. 12 3.4 WML MOONAMANG ROAD EMBANKMENT INVESTIGATION CH47800 TO CH49500 ................................. 13

3.4.1 Ultimate Embankment CH47800 - CH48800 ................................................................................... 13

3.4.2 Embankment Taper/Tie-in CH47800 - CH48800 ............................................................................. 14 3.5 PAVEMENT THICKNESS DISCUSSION ................................................................................................................ 15

4 PAVEMENT DESIGN RISKS ................................................................................................................................... 16

4.1 LESSONS LEARNED FROM ORD 2 CONSTRUCTION. ........................................................................................ 16 4.2 BORROW PITS ................................................................................................................................................. 16

4.2.1 Area 8 Basecourse .................................................................................................................................. 16 4.2.2 Area 11 - Select Embankment Fill/Subbase ...................................................................................... 17 4.2.3 Tetra 2 Borrow Pit ................................................................................................................................. 22

4.3 MATERIAL STOCKPILING REQUIREMENTS. ...................................................................................................... 23 4.4 CONSTRUCTION SAFETY RISKS ....................................................................................................................... 23 4.5 CONTRACT MATERIALS SPECIFICATIONS AND DENSITY COMPLIANCE ............................................................ 23 4.6 COMPACTION METHOD SPECIFICATIONS ........................................................................................................ 25

5 RECOMMENDATIONS ............................................................................................................................................. 26

5.1 PAVEMENT DESIGN ......................................................................................................................................... 26 5.2 PAVEMENT RISKS ............................................................................................................................................ 26 5.3 AMENDMENTS TO THE SPECIFICATION ............................................................................................................ 26 5.4 OTHER AMENDMENTS TO THE SPECIFICATION. .............................................................................................. 27

6 REFERENCES ............................................................................................................................................................... 27

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1 INTRODUCTION

This WML Investigation and Pavement Design Report supersedes the WML Pavement

Design Report (Revision B) issued in August 2017 and includes the interpretation of data

from the WML investigation of the Moonamang Road realignment and borrow pits that is

documented in WML Report 7511-G-R-001, ‘Proposed Moonamang Road realignment and

Borrow pits, Geotechnical Investigation’.

Moonamang Road is located north of Kununurra and is the primary road constructed as part

of Ord Stage 2 (Ord 2). It is intended to extend Moonamang Road to the Northern Territory

border a distance of approximately 7.5km (Ord 2 extension).

This WML Investigation and Pavement Design report includes “lessons learned” from the

Ord 2 construction works and data from the WML investigation that will mitigate risk in the

following areas of the pavement construction process:

• The borrow pit investigation data for Area 8, Area 11 and the Tetra 2 pit,

• The stockpiling requirements for Area 8 and Area 11,

• The appropriate pavement specifications requirements to meet the properties of

local materials and still ensure CBR compliance,

• The appropriate density requirements to better ensure CBR compliance,

• The compaction method specifications for the sandstone select fill layer as

previously developed by WML for Ord 2.

2 SITE SETTING

2.1 Site Location and Description

The Ord 2 extension is approximately 50km north of Kununurra generally running west to

east from the end of Ord 2 at CH47800 to the Northern Territory (NT) border at CH55300.

The alignment footprint is generally level and the vegetation mostly comprises superficial

grasses on the surface with sparse mature trees up to 3-5m in height. The land use is mainly

cattle grazing activities as part of the Carlton Hill Station.

2.2 Existing Pavement

The existing Moonamang Road (Ord 2) was previously constructed north from the Weaber

Plains Road at the Carlton Hill Road turnoff. Typically, this pavement profile comprises of:

• 200mm thick cement stabilised gravel base course with coarse aggregate (40mm),

• 200mm thick cement stabilised crushed sandstone layer.

• 220mm thick select sandstone fill layer.

• Varying thickness black clay soil embankment overlying the natural surface.

The Ord 2 pavements have not been subjected to any significant traffic volumes and as

expected are in very good condition. For roads constructed on black soil plains a big issue is

cracking in the pavement caused by movement of the black soil during the annual wetting,

drying cycle.

This pavement is almost 4 years old and has completed three wetting, drying cycles with no

significant cracking issues suggesting that the moisture in the elevated black soil

embankment has remained reasonably consistent.

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2.3 Geology

Based on the 1:250,000 Geological Series map sheet ‘Cambridge Gulf’, the near surface

geology is ‘Black Soil’ which borders on ‘Sand, soil cover, alluvium, travertine’ and is

associated with the sandstone of the ‘Sorby Hills’ formation.

This is illustrated below in Figure 1.

Figure 1: Geological Map Extract with Proposed Alignment and Borrow Pit Overlayed

3 DESIGN CBR AND PAVEMENT THICKNESS

3.1 Moonamang Road Pavement Design

The 2010 Main Roads Report Ord River Irrigation Area (ORIA Stage 2) [Peter Mableson] for

the proposed expansion of the irrigation area, calculated the expected traffic in Equivalent

Standard Axles (ESA’s) based on the heaviest crop, sugar cane over a 40 year design life.

For Moonamang Road this Design Traffic estimation was:

• 34700m to 35200m 2.4x107 ESA’s

• 35200m to 46900m 1.2x107 ESA’s.

The pavement design was reviewed by Coffey (GEOTPERT09336AB-AB Rev0) who used

9.2x106 ESA’s as advised by LandCorp and was confirmed by Main Roads as the Design

Traffic for the project.

Moonamang Road

Extension

Proposed Tetra 2 borrow pit

Black Soil

Sand, soil cover.

Alluvium, travertine

Pincombe Formation –

Siliceous siltstone and

fine-grained sandstone,

micaceous shale,

quartz sandstone

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For the Design Subgrade CBR black soil samples were taken from along the proposed

alignment and laboratory soaked CBR testing were conducted. The test results for the first

part of Ord 2 are summarised in Table 1 below.

Table 1 - 2009 MRWA Moonamang Road Ord 2 - Black Soil Testing

From the soaked CBR values the Design Subgrade CBR was calculated.

Mean CBR 2.1%

Std Dev 0.7%

‘k’ factor 0.85

Design Subgrade CBR 1.5%

Using the Design Traffic and Design Subgrade CBR from the ORIA Stage 2 Report calculates

the total pavement thickness as:

• 34700m to 35200m 935mm

• 35200m to 46900m 850mm.

The Coffey Report observed that the black soil unsoaked CBR is very strong. A design

Subgrade CBR calculated using these unsoaked values is:

Mean CBR 30%

Std Dev 10%

‘k’ factor 0.85

Design Subgrade CBR 22%

Coffey concluded that the raised embankment could be classified as a highly expansive soil

in well drained conditions. For this site a correlation was developed between CBR and

moisture content giving a CBR value of between 3.5 and 4.0.

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Coffey recommended a Design Subgrade CBR of 3.5% for clay fill with a design cover of

620mm using design traffic of 9.2x106 ESA’s.

For a pavement thickness of 620mm the pavement composition was:

• Select embankment fill 220mm soaked CBR 15% or greater.

• Subbase layer 200mm soaked CBR 30% or greater

• Basecourse layer 200mm soaked CBR 80% or greater.

3.2 Design CBR (2017)

In June 2017 WML completed the geotechnical investigation of the remaining Ord 2

extension alignment through to the NT border and the Tetra 2 Borrow Pit as shown in Figure

1.

The surface material consists mainly of black soil overlying red pindan/alluvium material

except at two sites CH51800 and CH52200 where the red pindan/alluvium material is

present on the surface.

Soil samples of the black soil embankment foundation were taken between CH47800 and

CH55300 and tested for classification and laboratory 4 day soaked CBR testing, see

summary of test results in the Table 2 below.

Table 2 – Black soil Embankment Foundation Samples

Using the Main Roads WA Engineering Road Note 9 “Procedure for the Design of Flexible

Pavements” (ERN9) the Design Subgrade CBR was calculated for the five black soil samples

as follows:

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The Design Subgrade CBR for the five laboratory soaked CBR values are:

Mean CBR 3.0%

Std Dev 1.0%

‘k’ factor 0.85


It is of interest that the Design Subgrade CBR calculated using the equations from ERN9

Section 3.7.5 Calculation from Classification Tests is similar:

Mean CBR 3.0%

Std Dev 0.7%

‘k’ factor 0.85


The percentage swell of the five CBR samples ranged from 3.5% to 8.0%.

Four soaked CBR tests conducted on black soil samples from the Tetra 2 borrow pit gave

similar CBR values of between 1.5% and 6% with similar percentage swell values between

2.5% and 9.5%.

ERN9, Section 1.16 Minimum Cover over Reactive Material-Table 3 requires 600mm of cover

between the reactive material and the subgrade surface for untreated material with a swell

between 2.5% and 5.0%. For untreated material with a swell of 5.0% or greater the cover

required shall be 1000mm.

As the Ord 2 extension embankment is to be constructed of black soil it is not possible to

meet these ERN9 swell requirements. Section 1.16 also states that, where the swell exceeds

7% a geotechnical assessment must be carried out which can include a review of the

maintenance history and condition of existing pavements.

This is further discussed in Section 3.5 Pavement Thickness Discussion below.

3.3 Design Traffic and Pavement Thickness

For the section between CH47800 and CH55300 the design traffic of 9.2x106 ESA’s with a

Design Subgrade laboratory soaked CBR of 2.1% gives the following pavement thicknesses.

9.2x106 ESA’s -> 770mm + 10mm = 780mm

Note ERN9 recommends that 10mm is added to all pavement thickness calculations to allow

for construction tolerances.

These results are 160mm thicker than the total pavement thickness cover of 620mm over

the black soil embankment material used for the Ord 2 works.

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3.4 WML Moonamang Road Embankment Investigation CH47800 to CH49500

The unsealed embankment section between CH47800 and CH48800 was previously

constructed to the ultimate design and covered with select embankment sandstone wearing

course. The remainder between CH48800 and CH49500 is the vertical taper to natural

surface which ties into the existing road.

To assess the strength and density of the existing black clay soil raised embankment

constructed in 2013 from the end of seal at CH47800 through to CH49500, density/moisture

testing and Dynamic Cone Penetrometer (DCP) testing were conducted. The work

undertaken is detailed in WML Report 7511-G-R-001, ‘Proposed Moonamang Road

realignment and Borrow pits, Geotechnical Investigation’.

The black soil embankment thickness is about 800mm between CH47800 and 48800 then

tapers to existing road level at CH49500.

3.4.1 Ultimate Embankment CH47800 - CH48800

For the ultimate embankment the density testing showed that the average Characteristic

Density Ratio of the black soil embankment is low at 86% and less than the required 90%.

The insitu field moisture is at about Optimum Moisture Content (OMC), varying from 3% dry

to 3.5% wet.

DCP testing showed the insitu CBR strength of the black soil embankment subgrade to

200mm depth is relatively high with design subgrade DCP CBR values between 12% and

20%. See Table 3 below for summary.

Table 3 – DCP Subgrade Design CBR Values

Except for the CBR value 12%, a maximum CBR value of 15% is assigned to these results as

ERN9 states that design subgrade CBR values greater than 15% should generally not be

used.

These CBR values compare to the Main Roads 2009 laboratory unsoaked CBR testing of

black soils which gave a design CBR value of 22% (see Section 3.1 above).

Except for the edge of shoulder at the top of the embankment batter all DCP CBR values

were 8% or greater down to a depth of 800mm.

Two DCP tests conducted at the top of the embankment batter, edge of shoulder hinge

point gave weaker CBR values of 5% to 11%, to a depth of 500mm.

Given the high insitu CBR strength of the existing black soil embankment, it is recommended

that it be retained without further work except for surface levelling and compaction of the

sandstone wearing course.

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3.4.2 Embankment Taper/Tie-in CH47800 - CH48800

For the embankment taper section the density testing showed the average Characteristic

Density Ratio of the black soil embankment is low at 86.5% and less than the required 90%.

The insitu field moisture is near Optimum Moisture Content (OMC), varying from 1% dry to

4% wet.

DCP testing showed the insitu CBR strength of the black soil embankment subgrade to

200mm depth to be high with design subgrade DCP CBR values between 16% and 21%. See

Table 4 below for summary.

Table 4 – DCP Subgrade Design CBR Values

A CBR value of 15% is assigned to these results as ERN9 states that design subgrade CBR

values greater than 15% should generally not be used.

WML Observations of the Geotechnical Data:

• The Characteristic Densities of both embankment sections are the same.

• The Design Subgrade CBR strength of both embankment sections as measured by

the DCP is above 12% and significantly stronger than Design Subgrade CBR of 3.5%.

• The insitu embankment material field moisture is near OMC and in a moisture state

similar to black soil embankment construction material conditioned ready for

compaction.

• The shallow embankment batters at 4 horizontal to 1 vertical (4:1) can be safely

compacted by compaction plant. Note that Water Corporation sets a slope limit of

3:1 for the safe compaction of clay liners for dams and ponds compacted to 98%

Standard Maximum Dry Density [SMDD).

Given the observations above, WML considers either of the following two options for

widening and raising the embankment taper section after the sandstone is removed is

appropriate, as either carries a low risk of long term pavement failure.

These options are:

1. The black soil embankment and batter surfaces are compacted before placing

and compacting the additional material required to meet the ultimate level and

profile; or

2. The existing black soil embankment material is completely removed, then mixed

and conditioned before placing and compacting as embankment construction

material.

The sandstone wearing course that is removed should only be used for temporary works,

such as haul road or side track construction due to the risk of black soil contamination.

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3.5 Pavement thickness discussion

The Design Subgrade soaked CBR of 2.1% was derived from 5 samples taken from along the

alignment. By including the soaked CBR values for the 4 black soil samples from the Tetra 2

borrow pit north of the alignment at about CH50200 increases the Design Subgrade soaked

CBR value slightly to 2.4%.

As discussed above, this Design Subgrade CBR value using soaked CBR values is similar to

the Ord 2 Design Subgrade CBR value indicating the general strength consistency of the

black soil materials.

However both the laboratory unsoaked CBR values for black soil from the MRWA 2009

investigation and the DCP insitu embankment subgrade CBR values (elevated, well drained

conditions) obtained from the unsealed black soil embankment are 12%, or greater.

The laboratory soaked CBR values from the alignment black soil samples are summarized in

Table 5 below.

Table 5 – Alignment Black Soil CBR Summary

The mean moisture content of the CBR test specimen after 4 day soaking is 157% of OMC or

26% as calculated from the average OMC value of 16.6%.

The mean field moisture from the unsealed road alignment DCP testing is 15.6% which is

near OMC with the wettest sample 19.2% or about 120% of OMC.

This confirms the Coffey finding that elevated, capped black soil embankments can be

considered as highly expansive soil in well drained conditions giving CBR values stronger

than determined by the laboratory soaked CBR test. This is discussed in ERN9, 3.3 Subgrade

Design Moisture Content which recognizes the subgrade moisture content for a sealed

pavement, particularly with sealed shoulders, on raised formation will be constant.

The stable moisture content of the capped unsealed black soil embankment confirms that

the subgrade field moisture is constant and that the soaked CBR moisture condition with

the associated high swell values will not apply. Particularly as the Ord 2 sealed road

performance should be better than observed for the unsealed section.

Thus, the pavement design developed by Coffey of 620mm cover over black soil with a

subgrade design CBR of 3.5% is considered valid.

Despite the low density and relatively high field moisture results the DCP testing shows the

unsealed embankment subgrade to a depth of 200mm is strong with design CBR values of

12%, or greater.

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The performance of the existing sealed road and the WML embankment investigation data

confirms that the pavement thickness and composition for Ord 2 is validated and is

therefore recommended for the Ord 2 extension works.

4 PAVEMENT DESIGN RISKS

4.1 Lessons Learned from Ord 2 Construction.

WML experience of more than 40 years of pavement design on State Roads shows that

pavement failures are rarely the result of inadequate pavement thickness but are mainly

caused by drainage, materials, and specification issues.

For Ord 2 there were many “lessons learned” about local materials and the pavement

construction process that if implemented for Ord 2 extension will reduce pavement risks.

These include:

• The stockpiling requirements for Area 8, Area 11 and the Tetra 2 pit,

• The appropriate pavement specifications requirements to meet the properties of

local materials and still ensure CBR compliance,

• The appropriate density requirements to ensure CBR compliance,

• The compaction method specification for the sandstone select fill and subbase layers

as previously developed by WML for the Ord 2 works.

These lessons are discussed below together with WML recommendations for Ord 2

extension works.

4.2 Borrow Pits

WML has completed borrow pit investigations for Area 8, Area 11 and the Tetra 2 pit. The

results are documented in the WML Geotechnical Report 7511-G-R-001, ‘Proposed

Moonamang Road realignment and 8Borrow Pits, Geotechnical Investigation’.

For Ord 2, sources of road building materials, particularly Area 8 and Area 11 were identified

and investigated by Main Roads. The results of these investigations were included in the

Contract documentation as ‘Information for Tenderers’. The contractor was required to

stockpile these materials as part of the construction works.

While the Main Roads investigation reports were comprehensive, the materials once

stockpiled did not meet the contract specifications requirements. There were various

reasons for this, however the main lesson learned is that locally occurring materials are non-

standard road building materials and unless stabilised, either chemically, mechanically or

both, will not meet standard specification requirements. particularly the CBR strength

requirement.

The WML investigations of the following borrow pits were completed in July 2017 and the

results are summarised as follows.

4.2.1 Area 8 Basecourse

It was not possible to access Area 8 Lot 5 due to a dispute over land tenure. WML found and

investigated a potential source adjacent to Lot 4 and identified 28,000bcm of material which

together with the gravel stockpile in Lot 5 is more than sufficient for Ord 2 extension works.

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The quality is similar to the gravel stockpiled in Lot 5 except it is slightly coarser above the

5mm stone size. See Graph 1 below.

Graph 1 – Area 8 Lot 4E Gravel (red 2017) compared to Lot 5 (blue 2012)

It is difficult to successfully stockpile gravel at this site due to the sand overburden and the

underlying sandstone boulders.

It is recommended that this gravel deposit be stockpiled under strict management as a

preconstruction activity. This gravel and the stockpiled gravel from Lot 5 can then be

presented to the contractor as Principal Supplied Material.

4.2.2 Area 11 - Select Embankment Fill/Subbase

It is intended to source about 70,000bcm of select fill and subbase from Area 11 just south

of Moonamang Road near CH40000.

Kimberley Agricultural Investment Pty Ltd (KAI) has opened a pit in the scree deposits on

the southern ridge previously identified by Main Roads. Whilst test pits were excavated by

WML in this area, the material proved too variable and this option was not pursued.

WML investigated the floor of the Northern Ridge quarry used for Ord 2 where sandstone

was won from a rocky outcrop. The resulting sandstone rubble proved to be weak, resulting

in considerable stone breakdown during compaction and this together with the relatively

high Plasticity Index, resulted in unexpectedly low laboratory soaked CBR values that did

not consistently meet specification requirements.

For Ord 2 the following processes were used to enable this low strength material to meet

the minimum laboratory soaked CBR requirements of 15% for select fill and 30% for

subbase.

Select fill was produced by ripping and track rolling the weathered sandstone, largely with

D9 dozers supplied by a local contractor, to achieve a mainly cobble size material with some

Page 18 of 27


300mm size boulders. This material was successfully placed, spread and compacted giving a

finished product, post compaction that was coarse of the PSD fine limit and exceeded the

minimum CBR requirement.

For subbase the stockpiled sandstone was mechanically crushed to 100mm maximum size

using crushers supplied by local contractors. This enabled cement stabilisation of the

material in the pavement using mechanical stabilisers, resulting in a material, post

compaction that consistently met plasticity, PSD and the minimum CBR requirement.

For Ord 2 the surface weathered sandstone was won and stockpiled first as select fill

material before the underlying, moderately to slightly weathered sandstone was won for

subbase material.

To minimise dozer pushing distance, the select fill material was stockpiled and progressively

removed for road construction before winning, stockpiling and crushing the subbase

material.

As several hundred thousand of cubic metres were excavated from this quarry, sections of

the floor has been left steep leaving the moderately to slightly weathered sandstone

exposed particularly at the north end.

Five holes were excavated in the quarry floor to an average depth of about 2 metres proving

about 80,000bcm of highly to slightly weathered sandstone.

The underlying sandstone is unweathered, medium strong and blocky when excavated.

Samples from this investigation gave the same results as the 2012 sandstone, see the

Particle Size Distribution (PSD) mean comparisons in Graph 2 below.

Graph 2 – Area 11 - 2017 sandstone (blue) compared to 2012 sandstone (green)

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The Ord 2 post compaction pavement PSD results (purple line) showed average stone

breakdown during the compaction process of about 10% for the finer sieves. The worst

result, a select fill sample (orange line) while finer than the PSD fine limit still exceeded the

minimum CBR requirement of 15%.

For the Ord 2 works the aim during stockpiling was to produce as coarse a product as

possible, as particle size breakdown during the pavement compaction process was

considerable.

A comparison of the mean consistency limits and CBR values also show the materials to be

near identical as shown in Table 6 below.

Table 6 – Sandstone Comparison 2017 and 2012

Note that the 2012 and 2017 investigations showed close correlation between the

laboratory soaked CBRs and the CBR value calculated from classification tests using the

equations from ERN9 Section 3.7.5 - Calculation from Classification Tests.

For the Ord 2 works the calculated CBR method was used as a “quick” quality control test to

confirm CBR conformance, post compaction.

The Ord 2 quarry area and immediate surrounds contains about 80,000bcm of highly to

slightly weathered sandstone which Ord 2 showed to be rippable with D9 and D10 size

dozers.

The highly to slightly weathered sandstone overlies unweathered, medium strong

sandstone that is blocky when excavated. The stronger sandstone will provide a subbase

material with higher CBR strength but will likely be more difficult to win and crush.

WML considers that there are two options that can be considered for the stockpiling of the

sandstone for select fill and subbase with equal advantages and disadvantages.

Option 1 is to stockpile the sandstone as a pre-construction activity as:

• The quantity and quality of the sandstone in stockpile will be known to the

contractor reducing contractual risks for the client.

• Any quality issues with the sandstone and the need for subbase stabilisation can be

addressed before the road contract proceeds.

Option 2 is for the road contractor to stockpile the sandstone using the same processes as

developed for the Ord 2 works as:

• The properties of the sandstone are well known from the pit development work

conducted for the Ord 2 works.

• The handling costs of providing two separate stockpiles of select fill and subbase

concurrently at this confined site could potentially be reduced.

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• The quantity of highly to slightly weathered sandstone of 80,000 bcm exceeds

requirements.

• For Ord 2 the sandstone was ripped, stockpiled and mechanically crushed by

Kununurra contractors, thus expertise winning and processing this material is locally

available.

Recommended amendments to the Ord 2 construct documentation for select fill and

subbase are provided below. These will need to be further modified if it is decided the

sandstone is to be stockpiled as a pre-construction activity and provided as Principal

supplied material.

302.09 SELECT EMBANKMENT FILL – AREA 11 - SANDSTONE

Unless otherwise specified or approved by the Superintendent, select fill shall be sandstone

granular material, won from the Area 11 quarry site by ripping and track rolling with large

dozers. The material should be generally free from boulders greater than 300mm and free

from roots, sticks, vegetable matter or other deleterious materials.

The grading of the material passing the 150mm sieve shall generally comply with the

particle size distribution of Table 302.01 below.

TABLE 302.01 PARTICLE SIZE DISTRIBUTION (AREA 11 SELECT EMBANKMENT FILL)

Sieve Size (mm) % Passing

150 100

75 80 – 100

9.5 33 – 100

4.75 25 – 90

2.36 18 – 75

1.18 13 – 65

0.425 8 – 50

0.075 3 – 30

The Linear Shrinkage of the select embankment fill should generally be no lower than 1.5%

and shall not exceed 8% when measured using Test Method WA 123.1.

The Plasticity Index of the select embankment fill shall not exceed 18% when measured

using Test Method WA 122.1.

The Californian Bearing Ratio (Soaked 4 days) at 94% of MDD and 100% OMC of the select

embankment fill shall not be less than 15.0% when measured using Test Method WA 141.1.

For post compaction construction quality control the CBR value shall be determined from

the classification tests Particle Size Distribution, Plasticity Index and Linear Shrinkage using

equations from Engineering Road Note 9, Section 3.7.5 Calculation from Classification Tests.

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501.06 SUB-BASE - AREA 11 - SANDSTONE

501.06.01 GENERAL

Unless otherwise specified or approved by the Superintendent, subbase shall be sandstone

granular material, won from the Area 11 quarry site by ripping and track rolling with large

dozers.

The subbase shall then be mechanically crushed to provide a sandstone granular material

that is generally free from cobbles greater than 100mm and free from roots, sticks,

vegetable matter or other deleterious materials.

501.06.02 PARTICLE SIZE DISTRIBUTION – WA 115.1

The sub-base material passing the 75mm sieve should generally meet the grading

requirements shown in Table 501.01 when tested in accordance with Test Method WA 115.1.

The grading of material shall vary from coarse to fine in a uniform and consistent manner.

TABLE 501.01 PARTICLE SIZE DISTRIBUTION (AREA 11A SUB-BASE)

AS Sieve Size (mm) % Passing by mass

Minimum and Maximum Limits

75.0 95 - 100

37.5 70 - 100

19.0 50 - 100

9.5 36 - 85

4.75 25 - 72

2.36 18 - 60

1.18 13 - 50

0.425 8 - 39

0.075 3 - 23

501.06.03 OTHER ACCEPTANCE LIMITS

Post compaction after stabilisation with 2% cement and cured for at least 7 days the material

shall also comply with the limits shown in Table 501.02.

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TABLE 501.02 OTHER ACCEPTANCE LIMITS (AREA 11A SUB-BASE)

Test Limits Test Method

Plasticity Index 10.0% Maximum WA 122.1

California Bearing Ratio (Soaked 4 days) at 96% of MDD and 100% of OMC

30% Minimum WA 141.1

4.2.3 Tetra 2 Borrow Pit

It is intended to source 150,000bcm of borrow from land that runs at right angles, north of

the new road alignment at CH50200 as shown in Figure 1. This area is a 1220m long by 115m

wide corridor and is to be excavated to 2m in depth to an approximate RL 19.8m.

The WML investigation showed that about 75% of the borrow material is fine black soil

material in the upper 1.5m thick horizon and that about 25% is a coarser red pindan/alluvium

material (CBR about 8%) in the lower 0.5m thick lower horizon.

Graph 3 – Tetra 2 Borrow Pit Fill Material

The mean laboratory soaked CBR of the black soil is 3% compared to a mean soaked CBR of

8% for the red pindan material.

To further reduce pavement risks it is recommended that the contract documents direct the

contractor to place the weaker black soil only in the lower layer of the raised embankment

Page 23 of 27


and place only the stronger red pindan/alluvium material in the top of the embankment to a

depth of at least 200mm.

The red pindan material is not to be placed within the black soil embankment layer as this

low plasticity material may allow moisture to fluctuate and lead to cracking in the pavement.

4.3 Material Stockpiling Requirements.

The extent of the stabilisation of non-standard road building pavement materials depends

on the quality and uniformity of the materials once stockpiled.

Where stockpiling is well managed, the quality of the materials will be known together with

the extent of the stabilisation treatments that are required to meet the CBR strength

requirements.

WML recommends that stockpiling of the basecourse material from Area 8 be stockpiled as

a preconstruction activity. This will reduce risk by:

Ensuring the required quantity of materials is available and also:

• Identify the quality of the materials and tailor the stabilisation requirements

accordingly which are then documented in the contract specifications.

• Reduce material surprises before the contract is let, giving more lead time to solve

issues if they arise.

The WML investigation shows the properties of the sandstone from Area 11 is similar to the

sandstone used for Ord 2. WML considers the advantages and disadvantages of stockpiling

and crushing the sandstone, as a pre-construction activity or as part of the contract works

are similar and provide both as options for the Ord 2 extension works.

The WML investigation shows that it is not be necessary to pre-stockpile the black soil

borrow from Tetra 2 as the material is relatively consistent with well-defined pit boundaries.

4.4 Construction Safety Risks

While the stockpiling and construction processes for material sources will generally be

regarded as standard road construction practices and industry standard safety risk

assessments will apply, the steepness of the Area 11 quarry face will require special

consideration.

It is recommended that the Area 11 pit and its surrounds be surveyed and this information is

provided to enable a comprehensive pit management plan and appropriate safe work

procedures that reduces this safety risk.

This may require a narrow pit extension to the west over the brow of the hill to enable the

top of the hill to be lowered reducing the steepness of the pit floor to be worked.

4.5 Contract Materials Specifications and Density Compliance

For Ord 2 it was necessary for the Client and the Contractor to conduct extensive testing,

stabilisation and blending trials to manufacture materials that met the Contract CBR

requirements.

paul.webb

Highlight

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This work showed that a 2% increase in compacted density gave a significant increase in CBR

strength for the sandstone material from Area 11. See copy of Graph 3.3(2) taken from the

Area 11 Report for the Ord 2 works and reproduced below as Graph 4.

Graph 4 – Area 11 Sandstone - Design CBR Vs Density Trend

This graph shows that by increasing the sandstone density requirement from 92% to 94%

for the select fill material gives more certainty that the CBR 15% minimum requirement is

exceeded.

It also showed that by increasing the subbase density requirement from 94% to 96% that

the subbase CBR 30% minimum requirement is almost met before stabilisation (with cement

to reduce plasticity) is conducted.

During the Area 8 Lot 5 gravel stockpiling process CBR testing was conducted at both 96%

and 100% of Modified Maximum Dry Density (MMDD) and graphed, see Graph 5 below.

Graph 5 - Gravel CBR Vs MMDD Trend

40

60

80

100

120

140

160

180

200

220

95.0 96.0 97.0 98.0 99.0 100.0 101.0

CB

R %

% MMDD

Gravel CBR Vs % MMDD

Page 25 of 27


This graph shows that while the Area 8, Lot 5 gravels gives CBR values of 50% to 100% at

96% MMDD, when compacted to 100% MMDD the CBR values increased to above 100%.

By increasing the basecourse density requirement from 96% to 98% gives more certainty

that the basecourse CBR minimum requirement of 80% is met once stabilised with

aggregate and cement.

For Ord 2 the contractor generally achieved Characteristic Dry Density Ratios above 100%

for the stabilised basecourse pavement layer so increasing the density requirement is not

expected to give issues during contract delivery.

WML has provided the following Compaction Values to BG&E for inclusion in the Contract

Specifications.

Recommended Minimum Characteristic Dry Density Ratio (Rc) percentages are:

• Select Subgrade Fill 94%

• Subbase layer 96%

• Basecourse layer 98%.

4.6 Compaction Method Specifications

The lesson learned from Ord 2 is that while stockpiled sandstone materials from Area 11 are

very coarse with oversize to 300mm, the stone size breakdown during the pavement

compaction process is significant and this together with relatively high plasticity resulted in

unexpected low CBR values.

For the subbase material it was necessary to cement stabilise the sandstone to reduce the

Plasticity Index from about 15% to less than 10% as required by the specification. To enable

the mechanical stabiliser to mix the coarse sandstone and the cement in the road pavement

it was also necessary to crush and screen the oversize to reduce maximum size to about

100mm.

For the select fill material no mixing with the stabiliser was required so the maximum

oversize allowed was increased to 300mm as larger stone in the select fill layer increases

CBR strength. The contractor had no issues dealing with oversize material, it was either

reduced during the compaction process or bladed to the road edge and either removed or

spread across the batter slope.

WML has recommended that the maximum size for the select fill layer (subgrade) be

increased to 300mm and for the subbase 100mm as shown in Section 4.2.2 above.

For Ord 2 the subbase layer compaction compliance was conducted using MDD tests

conducted on material passing the 37.5mm sieve in large “B’ moulds.

As the select fill was so coarse the Principals Method Specification for Compaction is used.

The select fill density shall be deemed to be satisfactory when compacted with not less than

fifteen (15) complete coverage of a 16t (or greater) vibratory pad-foot roller at OMC.

Non-standard density testing showed this compaction process generally gave characteristic

densities in excess of 98%.

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5 RECOMMENDATIONS

5.1 Pavement Design

The Pavement Design and Composition for Ord 2 is validated by the WML investigation and

is recommended for Ord 2 extension.

The total Pavement Thickness is 620mm over a compacted black soil raised embankment

with a pavement composition of:

• Select embankment fill 220mm soaked CBR 15% or greater.

• Subbase layer 200mm soaked CBR 30% or greater

• Basecourse layer 200mm soaked CBR 80% or greater.

5.2 Pavement Risks

This Report has identified and discussed a number of “lessons learned” from the previous

Moonamang Road construction works and lists the main recommendations below for the

extension construction works, with the object of reducing pavement risks.

1. That the proposed road building material deposits be sourced from Area 8, Area 11

and Tetra 2 as identified by the WML investigation.

2. That the stabilisation processes developed for the Ord 2 basecourse and subbase

layers are used for the Ord 2 extension works.

3. That the pavement material deposits in Area 8 Lot 4E be stockpiled and tested as

pre-construction works to confirm quantity and quality. Once completed the data is

checked and analyzed to determine if any amendments to the stabilisation

requirements used for the Ord 2 works are required.

4. That the sandstone from Area 11 for select fill and subbase is won and processed as

for the Ord 2 works, This can be done as a preconstruction activity or include the

processes in the contract documents.

5. That the Characteristic Dry Density Ratio (Rc) is increased by 2% for the select fill,

subbase and basecourse layers to give more certainty that CBR conformance is

achieved.

6. That the number of roller passes for the Principals Method Specification for

Compaction of the select fill is raised to 15 using a 16t or heavier padfoot roller.

5.3 Amendments to the Specification

The following amendments to the Ord 2 works specification are recommended as a result of

“lessons learned”. These amendments have been forwarded to BG&E by WML and include:

1. No material requirements for the basecourse layer shall be specified as the gravel

and aggregate will be supplied by the Principal from nominated stockpiles with the

test results included in the ‘Information for Tenderers’.

2. The select fill and subbase specifications are to be tailored to the properties of the

local materials if the material is to be won by the contractor.

3. That the maximum oversize requirement for select fill and subbase are increased for

the sandstone material sourced from Area 11 to compensate for stone breakdown

during compaction.

4. The density requirements for the select fill, subbase and basecourse layers are

increased to give more certainty that the CBR requirements are met.

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5. The Principals Method Specification for compaction of the coarse select fill subgrade

layer has been amended as a result of compaction trials conducted for Ord 2.

5.4 Other Amendments to the Specification.

The following amendments may also be required in the Specification.

1. The basecourse gravel and aggregate for mechanical stabilisation will be supplied in

stockpile for the Contractor and therefore no material requirements need to be

specified. However, a construction process for the placement, mixing of the gravel,

aggregate and cement will be required.

2. The processes to place and compact the select fill and subbase material from Area 11

using processes developed for Ord 2 need to be placed into the Specification.

3. If it is decided to stockpile and crush the sandstone as a pre-construction activity the

test results are to be included in the ‘Information for Tenderers’.

4. The Area 11 quarry face and surrounds need to be surveyed and this data placed into

the Specification to enable the contractor to develop a comprehensive pit

management plan and safe work procedure that reduces safety risks on the steep

quarry face.

5. That the specification is amended to allow the contractor to calculate CBR from

classification tests and the equations from ERN9 Section 3.7.5 - Calculation from

Classification Tests, as a “quick” test for post compaction quality control during the

construction process.

6. The embankment borrow from the Tetra 2 Pit consists of two materials the weaker

black soil and the stronger red pindan. To reduce pavement risks the contract

specification is to direct the contractor to place the weaker black soil in the lower

layers of the embankment and the stronger red pindan in the upper (surface)

embankment layer.

7. As both the select fill subgrade layer and the subbase layer consists of the same

sandstone material the level tolerances in the Clause 302.66 SURFACE LEVELS can be

provided only as a guide by changing the wording from “shall” to “should”.

6 REFERENCES

1. Main Roads Report ORIA Stage 2, 2010.

2. Coffey Report GEOTPERT09336AB-AB Rev0

3. Main Roads Western Australia, Procedure for the Design of Road Pavements,

Engineering Road Note 9, 2013.

4. AS 1726:1993 – Geotechnical Site Investigations.

5. WML Report 4699 Area 8 Lot 5 Basecourse Stockpiling Report May to September

2012.

6. WML Report 4699 Basecourse mixing trial July 9th 2012 V2.

7. WML Report 4699-G-R-001-0-Area 11-Report 2-1.

8. WML Report 4699-G-R-001-0-Area 11-Report 2-1 Addendum Final.

9. WML Report 7511-G-R-001-C Geotechnical Report

Documents

MOONAMANG ROAD EXTENSION INVESTIGATION PAVEMENT DESIGN