INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING

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The paper was published in the proceedings of the 11th Australia New Zealand Conference on Geomechanics and was edited by Prof. Guillermo Narsilio, Prof. Arul Arulrajah and Prof. Jayantha Kodikara. The conference was held in Melbourne, Australia, 15-18 July 2012.

Management of reactive and carbonaceous materials in the earthworks design for the Hunter Expressway, Minmi to Buchanan section

S. Aryal1, R. Kingsland2, D. Och1, A. Sooklall1, G. Burton2,4, G. Russell3, O. Buzzi4

1Parsons Brinckerhoff, L27, 680 George Street, , NSW, 2000, Australia, PH (612) 9272-5100; FAX (612) 9272-5101; email: [email protected] 2Parsons Brinckerhoff, 51–55 Bolton Street, Newcastle, NSW, 2300, Australia, PH (612) 4929-8300; FAX (612) 4929-8382; email: [email protected] 3Roads and Maritime Services, , 59 Darby Street, Newcastle, NSW, 2300, Australia, PH (612) 4924-0203; FAX (612) 4929-7107; email: [email protected] 4Centre for Geotechnical and Materials Modelling, The University of Newcastle, University Drive, Callaghan, 2308, NSW, Australia, PH (612) 4921-5000; FAX (612) 4985-4200; email: [email protected]

ABSTRACT

One of the greatest project challenges and risks for the eastern (Minmi to Buchanan) section of the Hunter Expressway was the management and design for the proportionally large amounts of poor quality materials derived from the Newcastle Coal Measures formation. The near balanced earthworks design, coupled with the very strict clearing restrictions and challenging terrain, compelled designers to incorporate expansive and carbonaceous materials, which would otherwise be spoiled because of their poor engineering properties, into the road formation. This paper presents the geological setting, characterisation of the earth materials, development of the encapsulation design approach used and implementation to date. In conclusion opportunities for further design development are discussed.

Keywords: earthworks, expansive soils, encapsulation

1 INTRODUCTION

The engineering challenges associated with the use of the Permian Age sedimentary rocks in the Newcastle region are widely acknowledged among local geotechnical practitioners, and the geotechnical challenges of volume change, poor strength, moisture sensitivity and rapid degradation on exposure are well documented in the proceedings in the Hunter Valley and Newcastle region specific geotechnical conferences (AGS, 1995; AGS, 1998; AGS, 2005).

Of particular note are the tuffaceous rocks, which are the most problematic and are often associated with slope instability in the region. Where found, these rocks along with the associated coal, would, by choice, be excluded from reuse in engineered embankments. However, the eastern section of the Hunter Expressway project (Alliance section) passes through the heavily vegetated Sugarloaf Range where clearing restrictions limited spoiling opportunities and the proportionally large amount of poor materials combined with a near balanced earthworks design necessitated the inclusion of tuffaceous and carbonaceous rocks in the road embankments.

2 THE HUNTER EXPRESSWAY PROJECT

2.1 Project description

The 40-km Hunter Expressway involves the construction of a four-lane freeway link between the F3 Freeway near Seahampton and the , west of Branxton. The $1.7 billion project will provide a new east-west connection between Newcastle and the Lower Hunter. It is one of the biggest road projects to be built in the Hunter Region and is scheduled to open to traffic at the end of 2013.

As a condition of approval for the project, Roads and Maritime Services (RMS) - formerly Roads and Traffic Authority - were required to reduce its ecological impact. To meet this condition, the eastern 13 km section from F3 Freeway to Kurri Kurri was realigned through the Sugarloaf Range and three large bridges (viaducts) were included. Difficulties associated with the geology and the presence of abandoned underground coal mine workings have resulted in a unique set of geotechnical challenges for the project. This section is being built under an alliance contract.

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The Hunter Expressway Alliance (HEA) was formed in April 2010, comprising the Roads and Maritime Services (RMS), Thiess Pty Ltd, Parsons Brinckerhoff and Hyder Consulting.

2.2 Project geology

The alliance route traverses Middle to Late Permian Age rocks generally getting older from south-east to north-west; respectively from Newcastle Coal Measures (NCM) to Tomago Coal Measures and to the Maitland Group. The rocks are a sequence of deltaic, alluvial and pyroclastic sediments deposited in the Sydney Basin. The main rock types within these groups are: sandstones, siltstones, conglomerates, coal, tuffs and claystones. The tuffaceous and coal/carbonaceous sediments are predominant in the Newcastle Coal Measures formation. The tuffaceous sedimentary rocks comprise tuffaceous sandstones, tuffaceous siltstones and tuffaceous claystones. These occur as thin bands within coal seams and within thick layers (up to 3 m thick) between clastic units that can have significant lateral continuity (Figure 1).

Figure 1 Tuffaceous claystones interbedded Figure 2 Tuffaceous and carbonaceous materials with coal bearing sediments exposed in a obtained from cut excavation being hauled to cutting being constructed as part of F3 location of placement Interchange construction

The tuffaceous claystones have volcanic textures and grading from unaltered tuff to clay; distinctive volcanic mineralogy; an igneous related geochemical composition (Fisher & Schmincke 1984; Spears & Lyons 1995) and are thin and laterally extensive.

The tuffaceous claystones are low strength rocks that are particularly susceptible to weathering and are highly reactive. The tuffaceous siltstones and sandstones have the potential to be reactive and highly susceptible to weathering unlike those massive volcaniclastic sandstones that have not been mixed with tuff. Generally the strata are mostly horizontally to sub-horizontally bedded and include igneous dykes dated the late Jurassic to the Cretaceous Age. The dykes are dominantly northeast- southwest striking and vary in width and weathering.

The project area is located in the north-eastern portion of the Sydney Basin – a bowl-shaped regional geological structure. There are regional sets of vertically dipping jointing and faulting that are zonal and closely spaced with a dominant strike to the north north-east, and the less dominant set that are widely spaced and have a strike to the north-west. The Buchanan Thrust (Hawley& Brunton 1995) intercepts the alignment west of the Buchanan Interchange, where the rock mass exposed on the cut batter excavation is intensely folded and fractured.

A thin cover of Quaternary deposits generally overlies the bedrock, except in the incised valleys of Wallis and Surveyors Creeks (Buchanan Swamp) near the Buchanan Interchange, where a thick deposit of alluvium comprising silts, sands and clays (up to 20 m) are present under the alignment.

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3 EARTHWORKS DESIGN CHALLENGE

Due to project specific geological conditions a significant proportion of materials to be generated from cut excavation was expected to be of poor quality, which encompass coal (including rocks with high carbonaceous content); and claystones, siltstones and sandstones with tuffaceous content. The materials with tuffaceous content were expected to show highly reactive behaviour (shrinking/swelling) with respect to a variation in moisture content, whereas rocks containing coal were potentially combustible and posed a fire hazard if left uncovered. These materials were unlikely to be suitable for use as general fill in embankments (Figure 2). Developing a design solution to use the materials available on site in a balanced and effective way was a specific geotechnical challenge for the project designers that required a careful examination of all possible options for managing these materials.

The earthworks design process involved completing a detailed site investigation, a laboratory testing program that targeted the characterisation of the problematic tuffaceous and carbonaceous materials, option analysis and detailed design development and documentation, as discussed below.

3.1 Design development

Possible options considered in the concept phase of design development included:

x spoiling x blending with better quality materials x stabilisation using admixtures x structural improvement of embankments using geosynthetics x zoned embankments encapsulating poor quality soils.

The major criteria considered for the option assessment were long-term durability, constructability, environmental sensitivity and restriction on clearing limit along the project corridor, soil moisture sensitivity, and potential combustion issues in soils with high coal content and structure stability. The experience of RMS with highway embankments constructed using similar types of soils in the Hunter Region (the Sydney to Newcastle F3 Freeway, West Charlestown Bypass and the ) was also taken into consideration while the concept of ‘best value for money’ for the RMS was the focus for evaluating costs with each of the options investigated. The option assessment showed that encapsulating poor quality materials in zoned embankments would provide ‘the best for the project’ solution and was selected as the preferred option. The design strategy was to encapsulate the poor quality and expansive materials with stronger, less reactive materials. The volume change of the expansive materials was then limited by controlling placement moisture to close to the long-term equilibrium moisture and/or surcharging the materials to constrain movement.

CSIRO’s broad-scale study of moisture conditions in pavement subgrades (Aitchison & Richards, 1965) demonstrated that road subgrades reach an equilibrium moisture condition where there is no significant change in suction (and moisture content) through the seasonal cycles. Furthermore, this ‘moisture stability’ suction may be correlated to climatic conditions, as measured by the Thornthwaite Moisture Index (TMI). In temperate climates the long-term equilibrium moisture condition has been found to be close to the Standard Optimum Moisture Content (AS 3798 – 2007).

3.2 Material characterisation

A plot of plasticity index (PI), California bearing ratio (CBR) and CBR swell test results available across the project at the time of the detailed design is presented in Figure 3(a). It demonstrates a wide variability of the materials with a large proportion of the test results showing a low CBR, high PI and high shrink/swell properties, which are typical for the materials associated with tuffaceous/carbonaceous rocks from NCM formation (see Section 2.2).

A suite of specific laboratory testing, including CBR (with pre-treatment) at variable moulding moistures; and confined and free swell was completed on the samples collected from the tuffaceous and/or carbonaceous materials. The focus of the test program was to determine swelling characteristics as well as the swelling and strength performance of the materials under varying placement moisture content.

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90 9 30 CBR tests (HEA) 80 8 25 Confined swell test (HEA) 70 7 Plasticity index Free swell (HEA) Swell F3 Palmers Road to Minmi testing (Longworth & 60 6 20 Mackenzie, 1987) Adopted swelling profile F3 (Longworth & Mackenzie, 1987) 50 5 (%) 15 40 4 Swell Swell Swell (%)

Plasticity index(%) 30 3 10

20 2 5 10 1

0 0 0 0 10 20 30 40 50 60 70 80 90 0.1 1 10 100 CBR (%) Confining pressure (kPa) (a) (b)

Figure 3 CBR, plasticity index and CBR swell results (a) Free and confining pressure vs. swell (b)

(a) (b)

Figure 4 Remoulding moisture vs CBR swell (a) and CBR (b)

The results of swell tests are presented in Figure 3(b), which also includes the results of similar tests undertaken for the design of encapsulated embankments for the Palmers Road to Minmi section of F3 Freeway. The results show that a confining pressure of 100 kPa is appropriate to design zoning for encapsulation within the embankment in order to adequately constrain the potential swelling of the expansive materials.

The influence of moulding moisture in the CBR and swell values is demonstrated in Figures 4 (a) and (b). As the moulded moisture content increases towards the optimum moisture content, the CBR increases and the swell decreases. This relationship provides a basis for a required specification of placement moisture content in the encapsulated materials.

3.3 Design details

A zoned embankment comprises a core consisting of compacted layers of poor quality materials that is encapsulated from outer sides by engineered fill with better soil properties. The design objectives of zoning were to: x prevent direct access of weather and fire to the reactive and combustible materials by enclosing such materials in the inner part (core) of embankment and providing a fill cover from outside x maintain consistent moisture conditions in the core to minimise potential for volume changes depending on the variation of moisture in the placed materials x provide long term stable embankment slope by placing more granular fill between the slope face and the core x apply overburden pressures to counterweight the swelling pressures due to volume changes in the core and provide stable foundation for the pavement layers using better quality materials between the pavement and the core.

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A typical zoned embankment design section is shown in Figure 5. This includes a core (Zone A), subdivided into Zone A1 and A2, which is encapsulated from all sides by the outer shell (Zone B). The dimensions of the zones were based on the following principles: x minimum 6 m wide Zone B on the embankment slope on both sides of embankment (at any given elevation), determined based on safety and constructability considerations x granular materials for Zone B with a design shear strength (I’) of 280 (min) x 2.5 m thick Zone B (which also incorporates pavement layers) above core x 2.5 m thick Zone A1 x total overburden thickness of 5 m required to control the designed swell pressure in core material of 100 kPa (assuming the unit weight the overburden material of 20 kN/m3), would be achieved from the combined thickness of Zone B and A1 x compaction specifications as per R44 (characteristic relative compaction 98% within the moisture ratio of 60% to 90%) except for Zone A where the moisture ratio required for Zone A1 is 95% to 105% with no specific moisture content requirement for Zone A2.

Top of pavement

Pavement + UZF + Zone B 5m 2.5m Zone A1

Zone A2 Zone B Natural ground

Figure 5 A typical zoned embankment design section

The tight moisture content requirement for Zone A1 was imposed in order to minimise the volume changes and to simulate an equilibrium moisture content that the core materials were expected to approach to in the long term. (Literature data indicates that the soil moisture content below 1.5 m depth in the Newcastle region is typically close to equilibrium conditions which are approximated by the standard optimum moisture content.)

3.4 Design implementation

The construction of zoned embankments is in progress on site. By the time of publication of this paper, all of the embankments designated for zoning will have been constructed. The construction records have so far indicated that the materials were generally able to be placed and compacted to the project earthworks specification R44 and design requirements for compaction and moisture ranges except in some cases, where the placed moisture content tested in Zone A1 was below the specified range. Achieving the conforming moisture in the constructed layers for these materials proved to be a challenge and required additional reworking and reconditioning during layer placement and compaction. Curing with water added to the source stockpile of expansive and carbonaceous materials before the materials are hauled and placed is being trialled in an attempt to resolve these isolated conformance issues.

3.5 Future design methodology refinement

Control of the swelling of the expansive materials in the zoned embankment design presented in this paper depends upon the placement of the material close to long-term equilibrium moisture content (Zone A1) or applying sufficient surcharge pressure to constrain the volume change (Zone A2). The 5m surcharge adopted is based on the upper bound of the experimental data (100kPa).

What would the observed embankment movement be at the pavement level if the Zone A1 materials were not placed at the long-term equilibrium moisture condition or if less than 5m of surcharge were applied, or the compaction specification were changed? Would these observed movements be within the project technical criteria limits?

The current design methodology targets optimal placement conditions to provide a high level of confidence in satisfactory performance but can’t predict the behaviour where deviations from these

ANZ 2012 Conference Proceedings 1308 Page 5 of 6 conditions, such as those listed in the preceding paragraph, occur. In a companion paper Buzzi (2012) presents a non-dimensional model for predicting soil swelling behaviour which has the potential, when calibrated, to be developed into a design tool. This predictive design tool could be used to analyse the impact of changes in the variables that can effect volume change; density, soil suction and stress state.

The RMS, HEA team and Centre for Geotechnical and Materials Modelling in the Faculty of Engineering (CGMM) at the University of Newcastle identified an opportunity with the Hunter Expressway project to calibrate this model with a full-scale instrumented embankment trial. At the time of preparation of this paper the instrumentation array was partially installed. Further details of this trial are reported in Buzzi (2012).

4 CONCLUSION

The earthworks design and management of the large amounts of poor quality materials derived from the Newcastle Coal Measures was acknowledged by RMS and the Alliance at the project outset as one of the key project risks for the eastern (Minmi to Buchanan) section of the Hunter Expressway.

However, by harnessing past experience, carefully characterising the materials, designing for the materials limitations and engaging the construction team in the design development, the risk has been managed and controlled.

Furthermore, the research collaboration between the Hunter Expressway Alliance, Roads and Maritime Services and the University of Newcastle has provided a legacy opportunity for the project; namely to contribute to the development of a model that could be used as a design tool to optimise future embankment encapsulation design.

5 ACKNOWLEDGEMENTS

The authors wish to thank Roads and Maritime Services for permission to publish and present this paper. We also want to acknowledge the support and encouragement provided by the leadership of the Hunter Expressway Alliance, the RMS project team and the Newcastle University Centre for Geotechnical and Materials Modelling. This has been a truly collaborative effort.

REFERENCES

AGS (1995). Australian Geomechanics Society Conference on Engineering Geology of the Newcastle – Gosford Region. Editors: Sloan, SW, Allman, MA, The University of Newcastle, Newcastle, NSW, Australia, February, 1995 AGS (1998). Australian Geomechanics Society Conference on Engineering Geology in the Hunter Valley. Editors: Fityus, S, Hitchcock, P, Allman, MA, Delaney, M, The University of Newcastle, Newcastle, NSW, Australia, February, 1998 AGS (2005). Australian Geomechanics Society Mini-Symposium on Geotechnical Challenges for Development in the Hunter Region Presented in Australian Geomechanics Volume 40 No.1 March 2005 and Volume 40 No.2 June 2005 Aitchison, G. D. & Richards, B. G. (1965). A Broad-scale Study of Moisture Conditions in Pavement Subgrades throughout Australia in Aitchison, G.D. (ed) Moisture Equilibria and Moisture Changes in Soils, A Symposium in Print, Buttsworth, Australia AS 3798 – 2007, Australian Standard Guidelines on earthworks for commercial and residential developments, Standards Australia, 2007 Buzzi O., Giacomini A., and Fityus S. (2011). Towards a dimensionless description of soil swelling behaviour, Géotechnique, 61(3), 271 –277. Buzzi O. (2010). On the use of dimensional analysis to predict soil swelling. Engineering Geology, 116, 149-156. Buzzi O (2012). Monitoring of an encapsulated embankment for the validation of a dimensionless model for soil swelling, Proceedings of the 11th Australia New Zealand Conference on Geomenchanics, Melbourne Australia, in print. Fisher, R.V. and Schmincke, H.U. (1984). Pyroclastic Rocks. Springer-Verlag, Berlin, 472 pp. Hawley, S.P. and Brunton, J.S. (1995). Notes to accompany the 1:100,000 Newcastle Coalfield regional Map. The Newcastle Coalfield. Coal and Petroleum Geology Branch, Department of Mineral Resources, Sydney, 93 pp. Herbert, C. (1997). Relative sea level control of deposition in the Late Permian Newcastle Coal Measures of the Sydney Basin, Australia. Sedimentary Geology, 107(3–4): 167–187. Longworth & Mackenzie (1987). F3 Sydney/Newcastle Freeway. Chg 127.4 to 134.0 km. Report on Geotechnical Investigation for Roads and Traffic Authority, Vol 2, Figure I2.7 Spears D.A.& Lyons P. C. 1995. An update on British Tonsteins. European Coal Geology 82, 137–146.

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