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Effects of salinity and sand content on liquid limit and hydraulic conductivity
Soil conditions of construction sites have become worse than ever due to the overpopulation in the metropolitan areas throughout the world. Likewise, the prevention of environmental risks due to individual activities is one of the most important subjects in the geo
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Application Of Compound Deep Cement Mixed Walls For Retaining Structures In Excavations
Deep cement mixed (DCM) columns are widely used as retaining structures to support deep excavations due to low cost and their ability in reducing seepage. However, the tensile strength of DCM walls is very low. Hence, large wall sections are necessary to avoid development of high tensile stresses when DCM walls are used to support deep excavations. In this paper application of compound DCM walls, which integrate DCM walls and bored piles, to support deep excavations are investigated aiming to develop resilient design methods for compound DCM walls. Three- dimensional finite element modelling is used in simulating the wall behaviour during deep excavations, considering the full geometry of the compound DCM wall. Numerical model is validated using a case study of a compound DCM wall constructed in Shanghai, China. Finally the use of arched DCM walls with different curvatures in between bored piles is investigated. Results of this study clearly demonstrates the advantages and limitations of increased curvature of compound DCM walls with respect to both ground deformations surrounding the excavation and tensile stresses developed in the compound DCM wall.
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AGS Debate 2019
Debate topic: Current Quality Assurance systems adopted by major projects with multiple levels of reviews and verifications are counterproductive and do not encourage innovation and optimisation.
Chris Harrison, David Oliveira, Frances Badelow and Rob Day
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Comparison of imaging technologies for geotechnical investigation of abandoned coal mine workings: a case study
Terrestrial laser scanners have revolutionised the mapping of rock exposures, in both above and below ground environments, and they are an ideal tool to explore old abandoned underground spaces where records of mining activity are unreliable, contradictory or simply non-existent. This paper describes the deployment of a laser scanner in holes drilled into abandoned coal mine workings, to obtain data to create a model of voids and caverns left behind. From the combination of scans taken from three boreholes, with underground line-of-sight connectivity between pairs of boreholes, a three dimensional model of the workings was produced that was sufficiently detailed to make a reliable assessment of the extent of extraction, and the viability of remediation by backfilling. The model produced contained enough detail to not only give a reliable estimate of the volume of backfill that would be needed, but also information on the incremental quantities required for a progressive backfill. The laser scanner was demonstrated to give superior outcomes to a simple horizontal laser measurement tool, however, downhole photography was found to be a beneficial complement to the data from the scanner. In the case study presented, the laser scanner was able to achieve outcomes that a direct inspection of the workings could not.
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Modelling the Performance of a Permeable Reactive Barrier utilised to Reduce the Risk of Acidic Groundwater in the Shoalhaven Floodplain
Acidic groundwater generated from acid sulfate soil (ASS) usually carries high concentrations of aluminium (Al) and iron (Fe), which create unfavourable conditions to living habitat. The ASS research team at the University of Wollongong, Australia implemented an innovative geotechnical engineering technique for the remediation of acidic groundwater through a permeable reactive barrier (PRB) using recycled concrete aggregates as the reactive material. This PRB was installed at the Shoalhaven Floodplain, southeast New South Wales (NSW), Australia in October 2006 and has proved effective in neutralisation of groundwater by increasing the pH from 3.6 to 7 and removing 99% of Al and Fe from groundwater to date. Dissolved Al and Fe were removed through continuous precipitation which would clog the pore spaces of the reactive medium by secondary mineral precipitation. This paper provides a complete evaluation of the performance of the PRB through field work and groundwater flow modelling coupled with geochemistry. The developed model (using finite difference codes: MODFLOW and RT3D) describes the chemical clogging due to mineral precipitates and the associated reductions in porosity and hydraulic conductivity of the reactive medium. The results obtained from numerical modelling, groundwater samples analysis and mineralogical analysis of barrier specimens confirm that the current PRB has performed well during the last seven years. Only a smaller amount of clogging was evident at the entrance of PRB with only a 3% reduction of hydraulic conductivity. This model would be beneficial for the environmental scientists and geotechnical engineers who have to deal with the ASS problems, especially in coastal Australia.
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Factors Influencing Shear Strength And Slope Failures In Basalt Soils Of North Eastern New South Wales
Landslides are a common feature of the basalt terrain or north eastern New South Wales. Failures typically occur through residual soil layers, at strength between the peak soil substance strength, and typical residual strength values. Shear strength on soil fissures approach residual strength. Failure therefore seems to occur through a combination of turbulent or rolling shear of the soil substance and sliding shear on fissure surfaces. Fissure properties such as surface condition continuity, spacing and orientation need to be observed when investigating sites in the area, or in similar geological terrains to allow consideration of the likely influence on overall soil mass strength.
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Ground vibrations from dynamic replacement column installation
Dynamic Replacement is a ground treatment technique that involves forcing rock into a soft soil substrate using a free falling mass to improve ground conditions. The large amounts of energy involved in Dynamic Replacement result in significant ground vibrations which can result in damage to nearby infrastructure if not managed properly. Presented are monitored ground vibration records for Dynamic Replacement columns at a site in Brisbane, Queensland, and assessment of the records to provide a basis for making initial predictions on potential vibration magnitudes. Discussion on the management protocols adopted as part of the works to mitigate the risk of damage to buried electricity infrastructure is also provided.