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Effects of preloading on soft clay improvement using deep soil mixing
Poor performing soils, particularly soft clays, are more prevalent around lakes and coastal environments, where demand for construction is generally higher. It is therefore critical that suitable ground improvement techniques be developed and refined to ensure these sites perform satisfactorily under applied structural loads. There is a clear trend in geotechnical construction to further develop technologies such as Deep Soil Mixing (DSM), using cement, lime, fly ash or bottom ash, with an aim to improve the mechanical properties of problematic soils. In this study, the influence of surcharge (10 kPa to 120 kPa) applied during curing on soil-cement columns is investigated using two different clay types, namely kaolinite and bentonite. Preload provides confinement and pre-compression during curing, which in turn increases the bearing capacity of the treated ground. The results of unconfined compressive strength tests are analysed to illustrate how the mechanical properties of the clays composed of differing cement content are influenced under varying surcharges applied instantly after mixing. The results indicate that mechanical properties of cement treated soft clays, including strength and stiffness can be enhanced through the application of surcharge immediately after construction, during the curing phase. This could potentially provide a cost effective and environmentally friendly alternative by reducing the required cement content being added to soil to achieve a given strength.
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Considerations In Applying Geotextiles To Coastal Revetments
The application of geotextile membranes in breakwater and revetment design raises the issue of the appropriate soil/geotextile and geotextile/geotextile friction angles that can be adopted for stability analysis. A considerable amount of data, much derived from the design of landfills, has been published on this subject. Other data are provided by geotextile manufacturers. Much of the data refer to a variety of woven fabrics, but data exist also for non-woven needle punched geotextiles that are used in coastal engineering structures. This paper reviews the local practice and literature and proposes appropriate values for soil/geotextile and geotextile/geotextile friction angles that may be considered for the preliminary design of coastal revetment structures.
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Pile design for liquefaction effects
Although liquefaction is a rare event in Australia, with only two documented instances, a pile design must still cater for liquefaction in a design earthquake. Liquefaction can lead to a loss of shaft resistance, additional horizontal displacements and bending moment under inertia loads, pile buckling and lateral spreading. This paper describes the four loading stages suffered by a pile before, during and after an earthquake when liquefaction may or may not occur. The method of Youd et al (2001) is used to predict the potential for liquefaction with depth. The important parameters for use in a ‘design earthquake’, namely peak ground acceleration and earthquake magnitude, depend on the seismic activity of the region and have been derived for the area of Adelaide, South Australia. If the soil profile has the potential to liquefy, the geotechnical capacity, the lateral behaviour and the buckling potential of the pile under the inertia loads must be determined for the loss of soil support. If lateral spreading can occur, a further lateral analysis is required. This method is used by the author in routine pile design and an example of the design process together with four case histories is given. The importance of continuous sampling and very careful logging of the soil profile during the geotechnical investigation is emphasised for an accurate liquefaction assessment.
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Stochastic finite element analysis of pile using FOSM
With the increase in the demand for a rational treatment for uncertainty in geotechnical engineering, the use of probabilistic method has gained importance. Recent developments in reliability theory provide a way of quantifying uncertainties and handling them consistently. Stochastic finite element approaches combine well known deterministic finite element analysis with reliability methods to produce more rational design. In the present study, direct computation of the covariance matrices and solution for the variances in the finite element analysis of single pile by first order second moment methods (FOSM) has been investigated. The problems of a pile subjected to lateral load and axial load have been considered. In this study, the pile modulus is assumed to be deterministic whereas the soil modulus is considered as a random variable. Results indicated that correlation between displacements exist even if the element properties themselves were mutually independent.
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Reactive Walls: An Overview
Conventional remediation methods such as pump-and-treat have been used for decades to clean up contaminated sites. However, these technologies have limitations both in terms of cost and cleanup efficiency. Partly in response to perceived shortcomings of conventional remediation technologies and partly for their advantages, a group of alternative remediation technologies called ‘reactive walls’ are under investigation.
In its simplest form, a permeable material is placed in a trench downgradient of the contaminant plume and the contaminant is transported through the soil by the natural hydraulic gradient into the reactive wall where it is modified in some way. Beneficial modification of the groundwater may be achieved by the correct selection of a biological or chemical process in the reactive wall. Possible treatment options include sorption, biodegradation, precipitation, metal-enhanced abiotic dechlorination, oxidation and photoremediation. Because of the range of treatment methods available, reactive walls can be helpful in managing a whole range of contaminants; these include heavy metals, inorganics, chlorinated solvents, hydrocarbons and other organic contaminants.
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Exploring The Impacts Of Abundantly Available Sustainable By-Product Materials In Australia On Stabilizing Expansive Soils
This paper aims to examine the effects of utilizing readily available sustainable by-product materials in Australia for the purpose of stabilizing expansive soils. Some waste by-products, commonly found in Australia that can be employed for soil stabilisation are cement kiln dust, blast furnace slag, quarry dust, bagasse ash and fibre, rice husk ash, fly ash and bottom ash.
With support of industry a number of materials have been selected for characterisation. Extensive experimental tests utilizing bagasse fibre, bagasse ash, bottom ash, fly ash, and eggshell powder have been conducted at the University of Technology Sydney (UTS) to enhance the engineering properties of expansive soils. These tests have been supplemented by microstructural tests, numerical analysis, and comprehensive discussions. These pozzolanic materials are characterized by significant levels of calcium carbonate, silica, and alumina. Numerous tests have been performed using these by- products to investigate the impact of their composition in conjunction with lime or cement, the curing time, the particle size, the optimal blending ratios, on both treated and untreated soil properties.
Based on research and laboratory investigations, sustainable by-product materials have demonstrated substantial potential for enhanced durability, cost savings and long-term environmental benefits, compared to traditional cementitious agents in treating expansive soils. These materials offer improved soil strength, reduced swelling potential, enhanced soil ductility, and controlled deformation over time. However, the implementation of these sustainable materials in practice is not yet widespread among construction companies and road authorities in Australia. This paper addresses this concern and provides practical recommendations for adoption of these sustainable by-products in weak subgrade of roads.
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2020 Young Geotechnical Professionals’ Night
Lavinia Lamipeti, Timothy Kelly, Janarthan Kumarakuruparan and Yun Bai
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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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Landslide impacts on the South Coast Railway during the 1988-90 El Nino event
Major landslides occurred along a 25 km length of the railway connecting Sydney and Wollongong, on the south coast of NSW, as a result of significant and long duration rainfall during the El Nino event of the late 1980s. The impacts commenced with the tragic event at Coledale in April 1988, involving a major embankment failure with two fatalities, and culminated in over 100 individual sites being activated along the route. These sites were mainly embankment failures, but also included rock cutting instability, which were identified and treated progressively under a risk priority and safety management system. The repairs, which cost in excess of $70M, were implemented over a number of years, and included an intensive track closure (track possession) of the South Coast Railway during January 1990. The management system was developed, in close association with SRA personnel, with an over-riding early-warning system linked directly to the railway control co-ordinator in Wollongong.
The paper presents an overview of the instability experienced on the South Coast Railway, and its remediation at the time, the links to antecedent rainfall, and the philosophy of the risk management system. A selection of case histories is given, with their associated monitoring, and a listing of back-analysed geotechnical parameters is provided for reference purposes.
The paper serves to document a presentation given to the Sydney Chapter of the Australian Geomechanics Society in June, 1991 and is intended to be factual as at that time.
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Estimation of foundation movement and design of footing systems on reactive soils for the effects of trees
The paper details the method of designing for the effects of trees as set out in a new informative Appendix H in the revised Residential Slabs and Footings Standard, AS2870, published by Standards Australia in February 2011. Background to the recommendations is given along with an introduction into research efforts that may improve designs in the future. In essence, the recommendations have been formulated in the light of more than 20 years successful use in South Australia of simple rules promulgated by the Footings Group (South Australia). Other evidence, generally from case studies of damaged houses, has been gathered in different climates, which supports the general premises of the recommendations and the extrapolation of the method to areas with wetter climates.