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Soft Clay Stabilization By Mandrel Driven Geosynthetic Vertical Drains
Geosynthetic (prefabricated) vertical band drains are now considered as one of the most cost effective ground improvement technics in many parts of the world, where construction on soft compressible clays is inevitable. However, smear effects caused by PVD installation (eg. mandrel based), drain clogging, drain kinking and well resistance of long drains retard the excess pore pressure dissipation making these drains often less effective in the field, contrary to expectations. Consequently, the rate of settlement of the stabilised soft clay becomes significantly less than what is expected from ideal drains. This paper addresses comprehensively, the numerical modelling aspects of PVD, and the interpretation of field data taken from several case studies, which elucidate the drain performance under various boundary conditions. Theoretical and finite element modelling details are described based on various research studies, mainly through the authors’ own experience. In particular, the experimental data obtained from large-scale consolidation tests are highlighted and interpreted.
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Wharf bulkhead wall geotechnical and structural capacity assessment
The paper presents the outcomes of existing conflicting views between the structural and geotechnical engineers about the approach to assessing an existing wharf retaining structure at Flinders Port, Adelaide. It demonstrates that working together is the only way to obtain a ‘best for client’ engineering solution. The paper summarises geotechnical analysis outputs for structural capacity assessment. Analysis indicates that new crane loads will have a negligible effect on the current Factor of Safety (FOS) for the overall geotechnical stability of the berth. Additional vertical crane loads only affect the vertical load on sheet piles and have little influence on geotechnical and structural capacity against rotational or translation movement.
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Collaborations In Geotechnical Engineering: Lessons From The Ballina Bypass And The National Soft Soil Field Testing Facility
Collaboration assists both academics and industry partners to achieve innovations, scientific advancement, and maintain technical competencies. The Ballina Bypass is used here to demonstrate collaboration via an Australian Research Council (ARC) Linkage project on vacuum consolidation, and to discuss how the lessons learned from the Ballina Bypass led to establishing a national facility in Ballina to field test soft soils. The outcomes of the work at the field testing facility have been transferred back to the industry via an international numerical prediction symposium. The project background, roles, and responsibilities of researchers and industry members are discussed and explained, as are the innovative outcomes, stakeholder benefits, and cultural impacts.
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Hencky’s remarkable equation
Hencky’s Equation, used extensively in the theory of plasticity, is shown to provide the basis for the solution of many routine geotechnical problems, such as the bearing capacity of footings, the lateral resistance of piles and surcharge pressures on retaining walls. The original Hencky’s Equation applicable for weightless φ = 0 soils is extended to general c,φ soils, and is shown to accurately predict the results of hollow cylinder tests. The extended Hencky’s Equation enables the derivation of the bearing capacity of strip footings and piles in weightless c,φ soils. A case example is given showing that justification of high pile base bearing capacities in very stiff to hard clay was assisted by using derivations from Hencky’s Equation. The life of Hencky is summarised and it is shown that despite experiencing a degree of hardship, Hencky’s contribution was remarkable and provides an inspiration to present day geotechnical engineers.
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Real Time Monitoring of a Road Embankment Subject to Coastal Erosion and Slope Instability
In this paper, monitoring the stability of a road embankment at Lawrence Hargrave Drive along the Illawarra coast is discussed. The embankment supports a coastal road and had been subject to an ongoing process of coastal erosion at the embankment toe and instability due to elevated piezometric pressures after heavy or sustained rainfall. In this paper, the stability issues and potential failure mechanisms are discussed. In order to allow a long term solution to be developed, an interim real time, web based monitoring system was installed. An outline of the investigations and geotechnical conditions at the site is presented. The paper discusses the monitoring system, including the instrumentation used (in-place inclinometers, piezometers, rain gauge, wave height buoy and web cam, the development of monitoring plans, the integration of instrumentation to develop a Trigger Action Response Plan (TARP), the development of trigger levels based on antecedent monitoring data, and the successful operation of the system.
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Characteristics and evaluation of recycled crushed rock in railway subgrade applications
The present research represents several laboratory experiments to evaluate the characteristics of recycled crushed rock (RCR) in railway sub-grade applications. Excessive amounts of construction and demolition (C&D) materials have gone to landfill every year and therefore it is necessary to recycle and reuse to reduce the carbon footprint generated throughout the world. A great way to reuse these materials is to put into operation for new construction projects. Although several recycled materials have been used recently in construction industry, little knowledge and research has been undertaken on RCR, which is generated from construction and housing industries. The RCR has previously been used as a structural element of highway pavements and has shown positive results, where very limited and undefined parameters are available. Laboratory test includes sieve analysis, California bearing ratio (CBR), compaction, Atterberg limit and Repeated Load Triaxial (RLT) tests were carried out on specimens sourced locally in Victoria. This research also investigates the resilient moduli (MR) and permanent deformation characteristics of RCR using RLT equipment to gain a thorough and definite understanding of how the material reacts under cyclic loading due to heavy and continuous cyclic loads on the railway track. A finite element modelling was also developed using laboratory experimental results to compare the permanent deformation obtained from the laboratory and numerical modelling. The physical properties, geotechnical properties and finite element modelling shows that the results were satisfied with the Australian standards and Australian Rail Track Cooperation (ARTC) guidelines for the application in railway systems as sub-grade materials.
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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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A preliminary study of strength behaviour of lime-slag treated pyrite bearing soft Coode Island Silt
The prime locations of the central business district of Melbourne are underlain by extensive deposits of a very soft and highly compressible soil, locally known as Coode Island Silt (CIS). This soft deposit poses serious challenges for the design and construction of economic foundations. The conventional practice for almost any construction over this soft soil is to use pile foundations extended to Melbourne mudstone layer situated at about 30 m depth. Results from recent researches on employing soil mixing technique to improve the engineering properties of this soft soil by using different additives have been found to be promising. Pyrite bearing CIS was treated with lime-activated slag of various proportions. Presence of pyrite is responsible for creation of acidic environment through its oxidation and thereby hindering the progress of cementitious reactions. Through experimental study it has been found that providing higher amount of lime can be an effective way of overcoming the adverse effect of pyrite. Initial Consumption of Lime (ICL) test can be a useful tool to determine the minimum amount of lime required for the stabilization to be effective. The results of experimental investigations, consisting of unconfined compressive strength tests and XRD analyses, on soft CIS treated with lime-activated slag are presented in this paper. In addition, the importance of carrying out ICL test for the selection of additive dosage is highlighted by presenting the results of strength tests of CIS treated with lime contents both above and below ICL.
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North Strathfield Rail Underpass A One Pass Synthetic Fibre Reinforced Shotcrete Lining For A Very Shallow Cover Tunnel
The single track North Strathfield Rail Underpass (NSRU) consists of two dive structures either end of a 148m long driven tunnel. The underpass is for diesel hauled freight trains up to 1.5km in length. The tunnel excavation dimensions are 7 to 8m in height and 9m in width with has a horseshoe shaped profile. The permanent tunnel structural lining consists of synthetic fibre reinforced shotcrete. The ground cover over the crown of the tunnel varies between 2.5m and 3.5m. The ground profile is predominately Ashfield Shale with graded weathering from the surface to fresh shale. Finite Element analysis, calculated the stresses in the shotcrete lining, was also used to assist in predicting surface settlements. Apart for the initial steel canopy tubes no other steel support is installed in the driven tunnel (a first for civil transport tunnel in Australia). A repeated grid pattern of thirty-five grouted 12m long fibreglass dowels ensured tunnel face stability. The tunnel face was mapped daily. The 12m long canopy tube array installations are staggered relative to the 12m long face dowels by 4.5m. The excavation/shotcrete support cycle advanced in increments and the next cycle cannot commence until the initial 150mm thickness of shotcrete has reached an early strength of 6MPa. Early strength measurements of the shotcrete are a vital part of the construction. At the tunnel face, to support the train live loads, there are three levels of redundancy, the canopy tubes, the shear capacity of the ground slot to the surface and the structural/deflection capacity of the rails. The synthetic fibres in the shotcrete provide shrinkage crack control, residual strength if cracking occurs due to deformation and enhanced durability of the tunnel lining compared any alternative using steel such as steel lattice girders(and with no electrical stray current issues). Both the macro and micro synthetic fibres (the latter in the final 100mm fire protection layer placed over a spray-on waterproofing membrane) will reduce potential fire event related shotcrete spalling. Surface settlement minimisation relies on the construction methodology with the shotcrete over the arch always being very close to the tunnel face not allowing the ground to relax. Real time surface settlement monitoring was carried out using robotic scanning theodolites aimed at reflective prisms. In tunnel monitoring included convergence taping and optical targets. Excavation of the driven tunnel commenced in February 2014 was completed in late August.