MOONAMANG ROAD EXTENSION INVESTIGATION PAVEMENT DESIGN
Transcript of 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
Design Subgrade CBR 2.1%
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
Design Subgrade CBR 2.5%
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
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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
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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.
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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
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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