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Recommended methodology for determination of design groundwater levels
This paper describes a new methodology for the determination of Design Groundwater Levels (DGWL) or “reasonable maximum” groundwater levels required for design of road structures, such as pavements and bath structures. Existing methodologies, are not tailored for road design purposes, nor rigorously defined and suffer from gaps that may potentially result in either unacceptable risks or over-conservatism in road construction. The proposed methodology is based on hydrogeology concepts and incorporates various types of data that are collected through all the stages of a construction project. Application of the methodology is illustrated by determination of DGWL for the Gateway WA project which is a significant freight access road project around the Kewdale and Perth Airport precinct in Western Australia.
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Designing For Seismic Events – A Case Study
This paper presents a case study of the seismic design for a multi-level car park constructed over soft Holocene alluvial deposits in Brisbane. The paper presents the design approach and the structural and geotechnical analysis undertaken to assess the earthquake induced impacts on the structure to demonstrate the adequacy of the proposed foundation design.
The paper highlights the following design aspects:
- The requirements of Clause 5.2.2 of the Australian Standards AS1170.4:2007 to provide tie beams may not be appropriate in all cases.
- The use of elastic response spectrum analysis using modal superposition methods can result in refined inertia forces on the foundation compared to those computed using pseudo-static methods.
- The earthquake-induced kinematic effect should not be overlooked with respect to total deformation of the foundation.
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Footing design for residential type structures in arid climates
The parameters required for the design of footings on expansive (or reactive) soil by AS2870-1996 for arid regions of Australia are derived theoretically from established relationships based on experiences in the more temperate climates. Two critical parameters required for a footing design by AS 2870-1996 are the surface soil suction change (∆us) and the depth of the design soil suction change (Hs), and current recommendations for arid climates have a range ∆us = 1.2pF to 1.8pF, and Hs=3.7 m to 6.0 m. Using the results of solutions of the diffusion equation, with values for the diffusion coefficient for a soil profile in an arid climate that are extrapolated from the established relationships between the Thornthwaite Moisture Index, the annual cycle of wet/dry months and Hs in the more temperate climates, it was found that for an arid climate, ∆us=1.8pF and Hs=2.5 m. This finding was supported by a case history of a building in the Jackson oil-field, south west Queensland that had been distorted by the effects of an expansive soil profile. Three worked examples, using ∆us=1.8pF and Hs=2.5 m for the design of a footing for a residential type building on an expansive soil in an arid area, are given.
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Ground conditions and building protection for the New MetroRail City Project, Perth
The New MetroRail City Project is due for completion in 2007 in Perth, Western Australia. The project included construction of two underground stations, twin bored rail tunnels of 1.4 km combined length and cut and cover tunnels and dive structures of about 1 km total length. It is the first major underground construction project within the Perth Central Business District. This paper provides an introduction to the project, describes the geology and hydrogeology of the area and summarises geotechnical design parameters for the various geological units encountered. The paper presents parameters adopted for design of temporary and permanent works for the project, the selection of which was governed by the constraints of this project. The values adopted may not be the ‘best estimate’ values of these parameters, but rather reflect a degree of conservatism appropriate to a project such as this. The parameters may not be appropriate for other projects in the Perth CBD. Ground conditions vary significantly along the alignment from soft estuarine muds in an area of reclamation to very dense cemented sands and very stiff to hard clays. Deep foundations for the project extend down into the bedrock below the CBD, a Tertiary siltstone/sandstone. Key geotechnical hazards encountered during the project are discussed. The building protection methodology on the project is described, including damage assessment, condition surveys, monitoring and protection of key structures.
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The use of recycled materials for pavements in Western Australia
There have been a number of innovations and developments in Western Australia in recent years on the use of recycled materials in road pavement construction. Materials used or being researched include demolition materials (concrete, bricks and tiles), asphalt millings, existing granular pavement material, scrap rubber, glass, plastic and vitrified clay pipe. There are sound environmental reasons for making use of recycled materials. In terms of cost, savings in landfill fees are a significant factor. In some cases, the addition of recycled material to standard road pavement materials such as bitumen and asphaltic concrete results in an improvement in properties. A key objective of this paper is to facilitate the wider adoption of the use of recycled materials in road pavement construction. This document was produced by a working group from the Western Australian Pavements Group (a subcommittee of Australian Geomechanics Society comprising Consultants, Main Roads WA, Local Government, Material Suppliers, Contractors and Researchers).
“Old boots, tin kettles and other things of that kind, formed a capital first foundation for a new road over a meadow. In laying out a new estate, he knew of nothing better, except perhaps burnt ballast.” Longrove (1879).
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A Review On Performance Of Stone Columns As A Ground Improvement Technique: Lessons Learnt From Past Experiences And Prospect For Future Development
Since the population growth is creating a strong demand for urban development, the need for construction in soft soils is dramatically increasing. Accordingly, ground improvement is an important requirement to avoid problems such as non- uniform settlements, failure due to low bearing capacity or liquefaction. Stone columns are used as one of the ground improvement techniques to stabilize the soil through increasing soil stiffness and shear resistance while decreasing the compressibility and settlement. Predicting the behaviour of a stone column needs to meet technical challenges, particularly in soft cohesive soils. Therefore, the aim of this paper is to make a broad assessment of the performance characteristics of stone columns in clayey soils as a review. In this study, the stone columns behaviour has been studied through analytical, experimental and numerical techniques, and failure modes and design of stone columns and their installation techniques are discussed. Based on previous investigations, it is gathered that in very soft soils, the dry-bottom feed vibro replacement technique is preferred to other methods and usage of geosynthetic encasement is very efficient where insufficient lateral confinement of the soil is problematic. According to past findings, the friction angle of the stone material and the diameter of the column are significant parameters for the design of the bearing capacity of the column. Furthermore, apart from ground improvement benefits, stone columns are used as vertical drains, which can decrease the pore water pressure during earthquakes and therefore mitigate the liquefaction potential. In addition, the cost-effectiveness of using low priced materials instead of aggregates without disturbing the overall performance of stone columns seems to be viable and can be explored further in future. This review can give an enhanced viewpoint to engineers and practitioners considering the use of stone columns in their projects.
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Quantitative risk assessment for urban redevelopment adjacent to quarry Slopes
The redevelopment of Boral’s Greystanes Quarry in Western Sydney involved a risk assessment of existing shale and dolerite quarry slopes, excavated over 40 years and up to 50 m high, to assess whether reshaping of the slopes or other support was required. Immediately above the crest of the quarry slopes are three Sydney Water Corporation (SWC) reservoirs which were considered to be critical assets in Sydney’s water supply. Immediately adjacent to the toe of the quarry slopes was to be industrial and commercial development.
The risk analysis addressed risk during the construction phase and in perpetuity (agreed to be 100 years).
The hazards addressed included overall slope failure, bench scale failures, toppling failures, boulder fall, erosion and rill development, vibrations resulting from blasting, flyrock resulting from blasting and accessing the slope for maintenance.
The methodologies adopted in the analysis included AGS2000 and the “Draft Capital Investment and Risk Assessment Framework”, Technical Services Branch, February 2006 (State Water Framework 2006). This document has been adopted by the Department of Commerce NSW and Goulburn Murray Water in their risk assessment for major dams.
As part of this work a geological, geotechnical and hydrogeological model was developed, the historical slope performance was assessed, quantitative data regarding rockfalls, toppling and wedge failures were gathered and used as input to the quantitative risk analysis.
A batter management plan with limited constraints was developed. No artificial support was required and only minor regrading of the weathered profile was required. On this basis, the QRA indicated acceptable risk to life, the SWC Assets and the proposed development within the quarry.
The work was undertaken by PSM, reviewed by GHD and verified by SMEC as the independent verifier for SWC.
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Shear Strength Of Stockpiled Coking Coal – Existing Data
Flowslides and stability issues have occurred periodically within stockpiles of coking (metallurgical) coal at coal processing plants and export terminals in Queensland’s Bowen Basin, and to a lesser degree in New South Wales, since the early 1970s. A description of the issue and summary of research at James Cook University (JCU) from 1973 to 2000 was published in ACARP Report C4057 (Eckersley, 2000).
Eckersley (2022) partly updated that work with SEEP/W transient seepage modelling of a 12 m high coal stockpile constructed at Hay Point in late 1991 for which initial moisture content, pore water pressures at the stockpile base, outflows from subsoil drains and final density and moisture profiles were measured. This provided a good starting point for modelling of moisture movements within production coal stockpiles as required for meaningful slope stability analyses.
The current paper provides an accessible summary of available data from laboratory shear strength testing of coking coal to assist in selection and critical assessment of parameters for slope stability analyses of coal stockpiles. This includes data for saturated coal likely to form the base of a stockpile and currently limited data for unsaturated coal forming the bulk of a stockpile. It then highlights some issues in the selection of parameters for stability analyses of coal stockpiles.
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Bearing capacity of shallow footings in sand over clay by the punching shear method
The bearing capacity of shallow strip, square and circular footings by the punching shear model in stronger sand overlying weaker clay is examined by using published computer solutions and experimental test results on model footings. The Meyerhof punching shear coefficient is shown to be dependent on the strength ratio f’bw/fbs and the footing type, and is used to derive the punching shear model equations for the bearing capacity for sand friction angles ranging from 30˚ to 50˚, and for f’bw/fbs ranging from 0 to 1. The equations are used to explain the effect that several variables have on the bearing capacity, including the sand thickness, the clay strength, the sand strength and the surcharge. The application of these concepts to a variety of geotechnical problems is illustrated by six worked examples. Provided f’bw/fbs>0.4 to 0.5, the simple equations derived from the punching shear model provide a very rapid and convenient means of obtaining the bearing capacity of footings in sand over clay in a sufficiently accurate manner, suitable for routine geotechnical practice.
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Managing the risks associated with acid sulfate rock in NSW road projects
Acid sulfate rock (ASR) is unweathered rock that contains metal sulfide minerals (commonly iron sulfides). When ASR is exposed to both oxygen and water, oxidation of sulfides leads to the formation of sulfuric acid, sulfates and salts. The probability of ASR being present, can to some extent, be predicted from the geological origins of the rock or later hydrothermal depositions of sulfides. An ASR risk map has been prepared to assist in the pre-design phase of road construction projects.
ASR has the potential to be problematic (depending on concentrations) with respect to environmental, structural and durability risks. It is becoming increasingly common for ASR to be encountered by roadworks in New South Wales where designs include deeper cuttings into unweathered rock that has generally not been the case historically. Examples are given of New South Wales where ASR has been encountered, together with an American example where significant environmental penalties and remedial costs occurred.
Other than low risk geological formations, site investigation for roadworks must include identification of ASR and, where present, screening, detailed testing and interpretation of the distribution of sulfide contents. The details of each aspect of this assessment need to be fully understood. Where ASR is present, the design, specification and construction must include control measures to reduce environmental risks associated with exposing ASR and potentially releasing leachate into the environment. Control measures include dilution, encapsulation and treatment with crushed limestone. Control measures must also be developed to protect structures such as bridges, culverts and retaining walls, stormwater drainage pipes and pavements. The locations of where ASR is placed within the earthworks formation must be limited with respect to environmental, structural and durability constraints. For successful management of ASR in construction projects, careful planning and staging of the earthworks is critical.