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Liquefaction and settlement assessment for the Mortimer Road Bridge, Perth, Western Australia
This paper presents the results of an assessment of liquefaction and settlement for a freeway interchange bridge founded on siliceous sand in an area of shallow water table at a site located south of Perth in Western Australia. The effect on liquefaction of factors such as the depth to groundwater, earthquake magnitude, ground acceleration; load applied to the soil and the depth and thickness of zones of loose sand is discussed. The study confirmed that the liquefaction potential was very low.
Predicted soil settlement was relatively large and was addressed by surcharge preloading of the site. Settlement of the preload embankment was monitored leading to an improved understanding of the non-linearity of settlement versus load response, and the development of a relationship between modulus and electric friction cone penetrometer resistance. The results from this site were compared to results from a calcareous sand in Perth, for which a relationship following a similar approach has previously been derived.
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Geotechnical characteristics of aged biosolids stabilised with cement and lime
Biosolids are the remains of the sewage treatment process, which are a mixture of both organic and inorganic compounds including household and industrial wastes. Recent attempts have been made to stabilize biosolids with special admixtures, in order to improve their geotechnical properties. The aim of this paper is to report the results of a geotechnical laboratory investigation on waste-water biosolids stabilized with different percentages of cement and lime. Biosolids were sourced from the Western Treatment Plant (WTP) in Melbourne, Australia. Compaction, California Bearing Ratio (CBR), swell, hydraulic conductivity, consolidation, creep and triaxial tests were carried out on the compacted specimens. Both static and standard proctor compaction methods were used to prepare the test specimens in this research. The results suggest that the permeability values of biosolids decrease consistently by increasing the amount of lime and cement. In addition, increasing the amount of additives decreased the compression potential of biosolids. The strength of the biosolids samples increased with the addition of lime and cement but the highest shear strength was achieved with 3% cement. This paper concludes with a discussion of possible applications of the stabilized mixture in road embankments.
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AGS Victoria Symposium
Geotechnical characterisation — managing design and construction risk
Professor Mark Jaksa, Dr Richard Kelly, Peter Kingston and Associate Professor Bill Bamford
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A risk based assessment of the punch-through potential of jack-up barges
Our Client undertook a series of near-shore ground investigations for a development in the North West Shelf region of Western Australia. The ground investigations were undertaken between 2009 and 2012 using jack-up barges in water of up to 25 m depth. During the 2010 campaign a punch-through incident occurred in which equipment and samples were lost overboard.
A punch-through is the situation whereby one or more legs of the jack-up barge penetrate into the seabed without warning, having previously been supported. This can occur either during the jacking procedure or whilst at working height.
Following the incident, the Client wished to mitigate the risk of further punch-through incidents. We were engaged to develop a method of assessing the risk of punch-through across the site based on geological, geophysical and geotechnical information. The assessment was used to support the 2011 and 2012 near-shore ground investigation campaigns.
Our work involved the back analysis of the punch-though incident, the derivation of a geological model for the site, an assessment of the risk of punch-through over the whole site and the development of an interactive tool which presented location specific assessment results and operational procedures. As new site investigation information was obtained it was imported into the assessment, to improve its accuracy. The results of the assessment were also used by the Client to influence the investigation programme.
This paper presents Arup’s work. The punch-through assessment project is confidential. It is a condition of submission that the Client and the project location cannot be disclosed.
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Boundary Element Methods for the Simulation of Underground Construction
For the simulation of underground excavation (tunnelling or cavern excavation) the Boundary Element Method offers advantages. For infinite or semi-infinite domains the radiation condition is explicitly fulfilled and the effort in discretization (surface instead of volume discretization) and solving the modelling system is reduced by an order of magnitude. One of the reasons why the method is applied rarely in practice is that essential aspects, such as modelling the sequential excavation, the efficient treatment of nonlinear material behaviour, inhomogeneous ground conditions and support construction were missing. In addition the method requires more computational efforts, run times for large 3D problems can become unacceptably long. The paper will present the research work carried out at the Institute for Structural Analysis at Graz University of Technology (with European and Austrian sponsorship). The research includes the implementation of efficient methods dealing with the above mentioned requirements for a practical application of the method to underground excavation problems.
It will be shown on a 3D example in tunnelling how the method can now efficiently deal with the sequential excavation / construction. Fast solution techniques were implemented to ensure that the results are obtained in a reasonable time for large 3D problems.
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Application of high strength woven geotextile in embankment stability control on soft soils
In a fast paced construction world, the application of high strength woven geotextile as tensioned membranes to restrict the vertical displacement of ground underneath and subsequently increase the stability of road embankments is becoming more popular. Due to the relatively low permeability of soft soils, particularly clayey materials, the drainage and consolidation process is significantly slow. Road embankments need reinforcement in order to increase the soil shearing resistance before they are able to support their own weight. The main objective of this study is to quantify the effectiveness of high strength woven geotextile in stability control on soft soils in the Kedron Brook floodplain area, Brisbane. This area consists mainly of Holocene Clays up to 26 m depth. More than 1,000,000 m2 of high strength woven geotextile has been used as reinforcement to control stability in heavily instrumented road embankments located in the Airport Interchange area of Brisbane, Australia. Lateral ground movement due to the consolidation process by fill activity was computed using 2D finite element analysis and compared to the horizontal displacement recorded by inclinometers installed along the embankments and quantified as settlement ratio. The settlement ratio ranges from 1.2 to 4.0 in reinforced embankments and 0.2 to 2.7 in unreinforced embankments. The effectiveness of high strength woven geotextile increased the settlement ratio and provided an increased safety factor in stability control of road embankments on soft soil areas to enable an improved construction rate.
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Application Of High Strength Woven Geotextile In Embankment Stability Control On Soft Soils
In a fast paced construction world, the application of high strength woven geotextile as tensioned membranes to restrict the vertical displacement of ground underneath and subsequently increase the stability of road embankments is becoming more popular. Due to the relatively low permeability of soft soils, particularly clayey materials, the drainage and consolidation process is significantly slow. Road embankments need reinforcement in order to increase the soil shearing resistance before they are able to support their own weight. The main objective of this study is to quantify the effectiveness of high strength woven geotextile in stability control on soft soils in the Kedron Brook floodplain area, Brisbane. This area consists mainly of Holocene Clays up to 26 m depth. More than 1,000,000 m² of high strength woven geotextile has been used as reinforcement to control stability in heavily instrumented road embankments located in the Airport Interchange area of Brisbane, Australia. Lateral ground movement due to the consolidation process by fill activity was computed using 2D finite element analysis and compared to the horizontal displacement recorded by inclinometers installed along the embankments and quantified as settlement ratio. The settlement ratio ranges from 1.2 to 4.0 in reinforced embankments and 0.2 to 2.7 in unreinforced embankments. The effectiveness of high strength woven geotextile increased the settlement ratio and provided an increased safety factor in stability control of road embankments on soft soil areas to enable an improved construction rate.
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An Emperical Model To Correlate Rock Mass Classification And Hydraulic Conductivity, Geotechnical Engineering Data Acquisition And Reduction Perspective
This paper presents an empirical model for estimating rock mass hydraulic conductivity of fractured Hawkesbury Sandstone in the Sydney basin. The hydraulic conductivity of a fractured crystalline rock mass can be a critical factor in tunnelling projects and dewatering designs. The Lugeon test (commonly known as the “packer test”) is a common test used to estimate the in-situ permeability of a rock mass.
The Packer test is carried out over a specific length (typically 3-6 m) within a borehole to reduce the range of variation of the affecting parameters. To construct a detailed profile of hydraulic conductivity through the rock mass a relatively large number of Packer tests are often required which can be costly and time consuming.
The new rock mass classification system called the “HC system” was proposed by Hsu et al. (2011). The HC-system assists with the hydraulic modelling of a rock mass and is based on 4 parameters which can be readily assessed from borehole logs and borehole Televiewer data, namely Rock Quality Designation (RQD), Depth Index (DI), Gouge Content Designation (GCD) and Lithology Permeability Index (LPI). A modified new rock mass classification system called the “HC-system” or HC model has been specifically developed for Hawkesbury Sandstone in the Sydney basin.
Regression analysis was conducted to assess the correlation between the calculated HC value (using the HC model) and the corresponding hydraulic conductivity from the in-situ packer tests.
To confirm the feasibility of the proposed empirical HC model, the model was subsequently used to estimate the hydraulic conductivity of similar Hawkesbury Sandstone boreholes from a range of projects that also have corresponding Packer test data for comparison.
This empirical HC model may assist with two important hydrogeological applications. The first application is to estimate hydraulic conductivity of fractured sandstone of similar geological set up based on HC-values. By using this approach, hydraulic conductivity data in a given site can be estimated from borehole data, which increases the reliability and confidence of the packer testing. Secondly, for in-situ aquifer tests the HC-system is a valuable new rock mass classification system for estimating the degree of permeability of a borehole. The results obtained confirm the validity and flexibility of the empirical approach to handle cases of onshore and offshore data sets, in relation to data acquisition and data reduction (optimisation).
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Estimation of Seismic Load for Design of Low Consequence Category Tailings Dams
Seismic design of embankment dams often requires assessment of the earthquake induced ground and dam movements. There are multiple cases where earthquakes have resulted in sliding and lateral spreading of embankments, crest settlement, and in some instances liquefaction and embankment failure. Hence, evaluation of the effects of earthquakes on embankment dams is of paramount importance for the design. A site-specific seismic hazard study is generally the first step to estimate the potential earthquake loads and the results are often presented in the form of site response spectra, earthquake time histories, and/or plots of peak ground acceleration (PGA) for “rock outcrop”. The PGA and earthquake motions which are used in liquefaction, stability and deformation analyses of embankment dams are to be further processed to develop those within or at the top of the structure. Empirical ratios or deconvolution of the input motion are used for this purpose. There are significant uncertainties involved with the former approach whilst for the deconvolution process earthquake time histories are vital, which are not readily available, at least during the early stages of a project. In this study, a series of one-dimensional response analyses of several Australian dam sites were carried out using SHAKE software (GeoMotions, 2012) to investigate the effects of material parameters (i.e. shear wave velocity) and embankment height on amplification ratios. The results are presented and compared in this paper. A general framework is also provided to estimate the PGA for the embankment analyses for low to significant consequence category tailings dams in Australia where the earthquake design load or a site-specific seismic hazard analysis is not available.
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Design of a portable triaxial compression apparatus
A portable system for performing triaxial tests has been developed for testing in the field. Portable and robust system components have been used to provide for low maintenance and simple operation for field technicians. In this study, the apparatus is primarily designed only for triaxial tests and specifically for unconsolidated un-drained triaxial tests, as this is the only test that may be conveniently performed in the field. The main advantage the portable apparatus has over existing laboratory equipment is the ability to perform triaxial tests in the field during borehole investigations. This means the entire range of soil conditions encountered on site can be replicated and the results used in engineering design. A series of unconsolidated undrained triaxial tests on clay were successfully performed with the portable apparatus and demonstrated its capability.