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Outline of the geology of the Perth region
Perth is located on a coastal plain consisting largely of unconsolidated sediments or dune limestone, with the eastern suburbs on weathered Precambrian crystalline rocks. The coastal plain is underlain by between 30 m and 70 m of Quaternary superficial sands, limestone and clay; and below this is some 10 km of sediments of the Perth Basin. Palaeocene sediments occupy a deep erosional channel below the city, cut into the Mesozoic sediments. The Darling Fault forms the eastern boundary of the basin with the Precambrian crystalline rocks of the Yilgarn Craton, which consist of granite, gneiss migmatite with minor schist, cut by dolerite dykes. The Precambrian rocks are deeply weathered with a lateritic profile. A variety of construction materials are readily available in the Perth Region and their sources are protected from sterilisation by planning controls.
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A study on the effects of abutment cyclic movements on the approach of integral abutment bridges
Abutments in integral bridges experience rotational cyclic movements as a result of the temperature induced changes in the longitudinal dimension of the bridge deck. Cyclic movements of abutments against and away from the retained backfill result in densification and volume contraction of the soil adjacent to the abutment wall. Consequently, the retained soil will experience settlement in the vicinity of the bridge approach in addition to an increase in the lateral earth pressure exerted on the abutment. The settlement of bridge approaches causes rideability and safety issues for bridge users while the escalated earth pressure may result in structural damage to the bridge abutment in the long term. This paper used the finite element method to investigate an integral abutment wall subjected to cyclic perturbations using the ABAQUS software. Two primary modelling cases were investigated. In Case 1, a finite element model was developed and verified against centrifuge test results of an integral bridge abutment before using it to study various factors influencing the response of the approach backfill subjected to cyclic rotational movement of the abutment. In Case 2, the finite element model was modified to incorporate the use of expanded polystyrene (EPS) geofoam in the approach backfill and it was once again verified against results from a laboratory experimental study. The modified finite element model was applied to study potential solutions using EPS geofoam to mitigate the soil settlement and to prevent the stress ratcheting at the interface between the backfill and the abutment. Results from the finite element study without and with EPS geofoam (Case 1 and Case 2 respectively) in the approach backfill subjected to cyclic rotational movement of the bridge abutment are discussed.
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Predicting instability of embankments on soft ground from monitoring data
Predicting impending failure of embankments on soft ground remains a challenge to geotechnical engineers conducting routine monitoring as a way of controlling the rate of embankment construction to avoid failures. A literature study has been carried out on available methods of predicting embankment performance. The Authors then propose a method of plotting the inverse of incremental lateral displacement rate at the embankment toe against embankment height. The idea is that the plotted data can be extrapolated to find the maximum embankment height to cause failure. That is, when the inverse rate ratio reaches zero, the embankment is collapsing at infinite rate. In practice, however, embankment distress is likely to have occurred before this ratio reaches zero. Based on several case studies, the Authors propose that an iterative prediction procedure be adopted as the embankment height increases and more data points become available. A projected limit of 0.05 days/mm or 50 days/metre (i.e. incremental lateral displacement rate of 20 mm/day following an embankment lift) be used as a guide to forecast the impending failure height, together with limiting the height of construction to between 80% to 90% of the predicted failure height at any time to control the rate of embankment construction to reduce the risk of embankment failure. This method has been tested only on limited examples, and needs to be further tested on more cases. This method should not be regarded as suitable in all circumstances. In rate sensitive soils for example, failure may occur sometime after embankment construction even though it may appear stable at its final lift. It is important that a number of different methods be used to assess the performance of embankments on soft ground. An essential element in adequately controlling the rate of construction to avoid embankment failure is making sure that there are sufficient levels of instrumentation and monitoring. During embankment construction, it is essential that daily readings be taken and reviewed carefully, and the contractor is prepared to unload the embankment by removing fill if there are tell-tales of impending failure.
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Effects of electrokinetic treatments on the properties of a salt affected soil
This paper presents experimental results of a study undertaken to investigate the effects of electrokinetic treatments on selected chemical and physical properties of a salt contaminated (saline) soil. The study was conducted as a laboratory scale pilot project using locally available saline soil samples. The soil was subjected to an electric gradient by passing a direct current between inserted electrodes. After certain electrokinetic treatment periods, the properties of the soil were evaluated. The experimental data reveals that electrokinetic techniques could offer a low cost, rapid solution to treat saline soils. The removal efficiency of sodium ions was found to be greater than 90% within a relatively short time period of 14 to 30 days, using low current and voltage systems. After 14 to 30 days, the degree of salinity and sodicity decreased to a very low or negligible level. The unconfined compression strength of the soil increased by between 30% to 100% in 30 days of electrokinetic treatment indicating the improvements in the physical properties, especially in the stress-strain characteristics of the soil. The liquid limit (LL) and plastic limit (PL) increased at the cathode.
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Sydney Sandstone geomaterials – Broken, crushed and friable rock products
Sandstone in fragmented form, derived from the Hawkesbury Sandstone, the Banks Wall Sandstone and the Terrigal Formation, is – by geological default – an important and growing source of geomaterials in the Sydney area. Although of only moderate strength and durability, this sandstone breaks down to produce well-graded sand with a soft gravel fraction and low plasticity fines. Crushed sandstone is good to excellent as earthfill, adequate as rubble, but is unreliable as rockfill for dams. It performs well as slope protection stone in embankments and the more durable sandstone is sometimes suitable for marine breakwater stone. It has been used in the past for concrete aggregate, especially in ‘cyclopean masonry’ dams, and is still employed as aggregate to a very limited extent in low-strength backfill and bound sub-base. Crushed sandstone is, however, generally unacceptable for unbound pavement courses because of its high inherent clay content (up to 30% <75 um), water sensitivity and only moderate particle strength. Its dry UCS is typically 10-30 MPa, and only 30-80% of this value when wet. Two important and growing sources of sandstone geomaterials are tunnel spoil (about 2 Mtpa) and quarried friable sandstone (also about 2 Mtpa). The environmental impact of sandstone quarrying is generally positive, in that it substitutes for scarce sources of high value hard rock. Because sandstone is nearly ubiquitous around Sydney, quarries can be sited in areas of low scenic value, require no blasting and can be shaped to productive end-uses. However, sand washing generates 10-30% of clay tailings, which are deposited in slurry lagoons, some of which have collapsed in the past due to inadequate spillway capacity. Although the tailings are a potential source of kaolinite and brick clay, cost-effective methods of de-sanding and dewatering have yet to be developed.
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Geotechnical Challenges Facing The Roads And Maritime Services
Heavy rainfall in early 2012 caused several highways to be temporarily closed due to flooding or slopes that had collapsed leaving the roadway impassable. Rainfall is still one of the most challenging elements for geotechnical practitioners to provide 24/7 community access to the road network. In the future limited funding for maintenance will require more accurate slope assessments, real time monitoring, innovative durable slope treatments and the development of methodology to assist in cost effective risk management of slope assets.
In the past the RTA (now RMS) has utilised subject matter experts within the organisation and the consulting industry to assess slopes and other geotechnical structures. The use of external practitioners to support the RMS to maintain the road corridor is unlikely to change in the future as the demands to finish sections of the Pacific and Princess Highways continues.
- The top five issues facing RMS geotechnical practitioners are:
- Slope risk assessment and management, and cost effective design solutions
- Deep wall excavation and the elimination of potential damage to the road corridor
- Effective site investigations, interpretation and quality reporting
- Mine subsidence and its impact on the infrastructure
- Ongoing training of young staff before the ageing practitioners retire
This paper will detail these challenges and how RMS geotechnical staff are managing the implementation of technical directions, specifications and training to manage new projects and the effective maintenance of the road corridors in NSW.
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A Numerical Parametric Study Of The Effectiveness Of The 4-Sided Impact Roller
Rolling dynamic compaction (RDC) is a specific type of dynamic compaction, which involves towing a heavy non-circular module at a relatively constant speed. This paper investigates the effects of module mass, operating speed and varying ground conditions on the effectiveness of the 4-sided impact roller using a developed finite element method (FEM)-discrete element method (DEM) model. Numerical results were analysed from four aspects, namely the energy imparted to the ground, soil velocity vectors, module imprint lengths and soil displacements at different depths. It is found that, a heavier module mass induces greater ground improvement in terms of both energy delivered to the soil per impact and the magnitude of soil displacements. The energy imparted to the underlying soil by the module increases with greater operating speed. The rotational dynamics of the module also change with increasing operating speed, whereby the impacts are delivered by the faces of the module at typical operating speeds; however, at faster speeds the impacts are delivered towards the corners of the module and the behaviour is less reproducible. The modelling showed that soil with a higher initial Young’s modulus and a higher internal angle of friction decreases the magnitude of soil displacements, which confirms that the impact roller is less able to significantly improve soils that are stiff or have a high initial shear strength.
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Offshore ground improvement records
Numerous ground improvement technologies have been in use for many years on land based projects with various applications. These techniques have provided alternatives that are frequently more affordable and require shorter construction periods than deep foundations. Implementation of these methods in the sea and marine environments is more challenging as specialised equipment is usually either only appropriate for land based projects or have low efficiency and production capability at sea. However, requirement of seabed treatment and improving the characteristics of marine foundations has necessitated the introduction of soil improvement technologies to offshore projects. Some of the ground improvement techniques that have especially evolved to satisfy the requirements of offshore and seabed ground improvement are dynamic compaction, vibro compaction, dynamic replacement, and stone columns. The first two techniques are used for the treatment of granular seabed while the latter two technologies are most appropriate for improving silty and clayey marine foundations. In this paper initially marine and offshore ground improvement techniques with a focus on the mentioned above methods will be discussed. Two case studies of ground improvement for the treatment of soft clays in record water depths will also be introduced. In the first case offshore dynamic replacement was carried out in Southeast Asia at a location where seabed was approximately 30 m below sea level. In the second project stone columns were installed beneath the quay wall and breakwater of the first and second phases of Port of Patras (Greece). The sea depth was up to approximately 40 m and the columns were as long as 20 m.
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The CBR test – A case for change?
The origin of this paper lies in a perceived inconsistency between the laboratory CBR’s poor reproducibility and the CBR’s special place within pavement technology. The paper summarises the reproducibility and repeatability of the laboratory CBR and discusses the implications of the poor reproducibility on design and product quality decisions. It shows that the load-deformation properties assumed for the standard crushed rock (CBR=100) differ significantly from the measured properties of crushed rocks and that this inconsistency results in an undesirable bias in the reported CBR. It explores the laboratory test’s ability to replicate the in situ CBR and investigates the practicality of replacing the CBR of cohesive subgrades with the undrained shear strength. It contends that continuing reliance on the CBR hinders the development of pavement technology.
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Soil Stabilization Using Lignosulfonate
Chemical stabilisation of soil using commercial admixtures is a common technique often adopted by industry to improve the behaviour of erodible and unstable deposits such as those forming the subgrade for roads and rail infrastructure. Although traditional alkaline admixtures such as cement, gypsum, lime have been effective in strengthening and stiffening the natural formations of transport and other civil infrastructure, the consequential impact on the soil and groundwater chemistry has been an environmental concern for many years. While being cost-effective, these alkaline and sometimes corrosive admixtures have directly contributed to substantial rise in the soil and groundwater alkalinity (pH about 8-9) apart from the significant reduction in soil porosity (void space) thus adversely affecting the growth and development of certain native vegetation and sub-surface fauna. In contrast, the use of nontoxic lignosulfonates (LS) with much smaller quantities has been reported to achieve similar results without harming the environment.
Lignosulfonate is a soluble dark brown liquid, and it is a by-product of the timber and paper industry. The use of lignosulfonate as a soil stabilizer has significant advantages in relation to traditional admixtures with respect to soil and groundwater environment quality. This is because lignosulfonate is readily diluted in water and causes no pH change in the soil upon treatment. Furthermore, it is also non-corrosive to metals and non-flammable, and classified as nonhazardous. An additional benefit is associated with the reduction of brittle behaviour during shear loading that is well known for alkaline mixtures. This paper showcases a number of applications of LS in controlling erosion and swelling of expansive soil for which the use of lignosulfonate has yielded comparable and in cases superior performance to that of traditional admixtures.