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Experiences with jacked piles
Experiences with jacked piles of various sizes in a variety of soil types for many major projects in Australia are described. The jacked pile has been successful in providing a “quiet” method of pile installation with negligible vibration. However, special precautions are required by the geotechnical engineer involved in jacked piles. These are related to the conventional interpretation of the installation load as the pile failure load, the forces associated with the pile rig grip mechanism, lateral soil movements induced by the rig supports, and the use of CPT and SPT to predict the installation forces. In this paper, guidelines are given on each of these aspects.
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Thermal efficiency of energy piles in stratified soil under unbalanced operation
Shallow geothermal energy piles are novel and cost-effective heat exchangers used in ground source heat pump systems for heating and cooling buildings. Pile foundations are used to exchange heat with ground besides structural support. Ground thermal conductivity is a decisive design parameter in shallow geothermal applications. Ground homogeneity relying on depth-weighted averaging has been the common assumption in wide research around energy piles in recent years, with soil layering influence remaining mostly unexplored. This becomes particularly important under unbalanced thermal operation, due to thermal accumulation in the ground. To explore this influence, a 3D finite element numerical model is built to solve for the heat conduction-convection multi-physics of energy piles embedded in layered soil. Unbalanced thermal load regimes with different building cooling-to-heating ratios are adopted for long-term assessment, showcasing the effect of this controllable parameter, for soil profiles with different thermal conductivity distributions. Results underscore the necessity to account for the thermal properties’ spatial variability in layered soil and recommend depth-specific thermal conductivity testing under unbalanced thermal load conditions. The thermal performance of the energy pile system in the considered stratified soils is shown to differ from that of their equivalent depth-weighted homogeneous ground owing to the growing difference in the accumulated temperature over the operation life, leading to underpredict the actual thermal conductivity by up to 31.5% as the contrast between layers grows and the unbalanced cooling-to-heating ratios increase. Furthermore, the depth sequence of ground layers of different conductivities is found to be important in predicting the thermal performance of energy piles.
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Improvement of iron ore stockyard berms using cementitious stabilisation
Australia is one of the largest iron ore producing countries in the world. As a result of recent increased demand for iron ore in the international market, development of new open pit mines with associated construction of new iron ore stockyard facilities and expansion of existing facilities have been on the rise in Western Australia. Design of stacker and reclaimer machine berms with the intent of optimising stocking capacity have been the key issue for construction of these iron ore handling facilities. Improvement of embankment materials is often required to ensure adequate safety against bearing capacity and global slope failure, and limit embankment deformation under reclaimer and stacker machine loadings. This paper presents ground improvement undertaken at stockyard berms of a large iron ore handling facility located in the Pilbara Region of Western Australia. The machine berms were designed to support large vertical and horizontal loadings. Locally available materials were used to construct the machine berms. Finite element analysis using PLAXIS computer program was undertaken to assess strength and stiffness requirements of the berm materials. Cement stabilisation was adopted for improvement of berm materials based on results of rigorous laboratory testing. In situ cement stabilisation of the berm materials was carried out using a Bomag stabiliser machine. Plate load tests were undertaken to assess degree of ground improvement using cementitious stabilization, and assess modulus of the stabilsed materials. Results of laboratory testing, in situ stabilisation, assessment of stabilised materials using plate load tests and finite element analysis methods are discussed in this paper.
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3.2 Blends of recycled materials as sustainable alternatives for backfilling sewer trenches
In this project, the suitability of four blends of recycled materials comprising different proportions of recycled glass, plastic, and tyre aggregates as alternative backfilling materials for deep excavated trenches was investigated. This paper presents results of an extensive testing program carried out for selecting two most appropriate blends for backfilling of trenches located in non-trafficable areas. These blends will be used for construction and instrumentation of trial sites for deformation monitoring over 12 months. Physical properties such as particle size distribution, maximum and minimum density, compaction properties, and field capacity of the blends were determined. Further, an application-specific geotechnical testing methodology was developed. This included determination of the dry density achieved using a proposed sand-raining technique (SRT) to simulate the real-life trench backfilling procedure and determination of the compressibility of the blends using a modified oedometer test. The SRT results showed that the obtained dry density (DD) increased as moisture content (MC) and height of drop increased. Based on the relative density achieved through the SRT compaction and the compressibility properties, Blends 2 and 4 showed the most advantageous characteristics. This paper presents the developed testing procedures and discussions on the results leading to the selection of the two most suitable blends for the proposed application. The paper also makes discussions on the stress-strain conditions expected on site and potential downfalls of the proposed application. The outcomes of this research aim to promote sustainable geotechnical design and construction by improving the industry’s confidence in utilising recycled materials.
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Residual soil properties of South East Queensland
This project sought to investigate parameters of residual soil materials located in South East Queensland (SEQ), as determined from a large number of historical site investigation records. This was undertaken to quantify material parameter variability and to assess the validity of using commonly adopted correlations to estimate “typical” soil parameters for this region. A dataset of in situ and laboratory derived residual soil parameters was constructed and analysed to identify potential correlations that related either to the entire area considered, or to specific residual soils that were derived from a common parent material. The variability of SEQ soil parameters were generally found to be greater than the results of equivalent studies that analysed transported soil dominant datasets. Noteworthy differences in material properties also became evident when residual soils weathered from different parent materials were considered independently. Large variation between the correlations developed for specific soil types was found, which highlighted both the heterogeneity of the studied materials and the incompatibility of generic correlations to residual soils present in SEQ. Region and parent material specific correlations that estimate shear strength from in situ penetration tests have been proposed for the various residual soil types considered.
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2018 Young Geotechnical Professionals’ Night
Vera Li, Rebecca Szczurowski, Chamindi Jayasuriya and Douglas Warne
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AGS NSW Research Award 2018
for Research in Geotechnical Engineering or Engineering Geology PresentationsDongli Zhu, Liet Dang, Ruoshi Xu, Subhani Samarakoon Jayasekara Mudiyanse and Xinyu Ye
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Electroosmotic and hydraulic flow rates through kaolinite and bentonite clays
The objective of this paper is to discuss the effects of electrokinetics on the rate of flow of water through some low permeable clay soils. Experiments were carried out on test specimens prepared by compacting commercially available kaolinite and sodium bentonite clays. Using falling head permeability tests, hydraulic conductivity values of these clay soils were determined. Subsequently, the experiments were repeated under different electric gradients to assess the effects of electrokinetics on the rate of flow. The flow characteristics were evaluated using the rate of electroosmotic flow of water Qe (cm3/s), coefficient of electroosmotic permeability ke (cm2/V/s), coefficient of water transport efficiency ki (cm3/Amp/s). The test results suggest that the rate of flow of water through low permeable clay soils is significantly increased by some orders of magnitude due to the application of a direct current. This flow increase appears to be more pronounced for clays that have lower hydraulic conductivity values. It is noticed that electroosmotic permeability is independent of clay type while the voltage gradient has minimal effect on electroosmotic rate of flow for the tested clay soils.