A novel centrifuge permeameter to characterize flow through low permeability strata
Wendy TimmsMichael P. WhelanR. I. AcworthD. McGeeneyS. BouzalakosRichard A. CraneJohn S. McCartneyAdam Hartland
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Abstract:
A novel centrifuge permeameter (CP) system was designed to characterize and model seepage and reactive solute transport through low permeability materials and geological strata.A new CP module for the Broadbent G18 geotechnical centrifuge (2.0 m diameter), provides new capability for hydraulic conductivity (K) and transport testing of materials including drill cores, mine tailings and engineered barriers.By designing centrifuge models that maintain chemical equilibrium, reactive transport of solutes can be assessed within a reasonable experiment time at accelerated gravity.The K of minimally disturbed drill cores or porous materials having a diameter of 65-100 mm and a length of 20-200 mm can be measured using steady state flow, with a K detection limit currently within the order of 10 -12 m/s.This paper presents K values as a function of depth below ground for drill core, and K as a function of effective porosity of reconstituted silica flour specimens.Keywords:
Permeameter
Centrifuge
Abstract The flexible wall permeability apparatus was modified for the direct measurement of the hydraulic conductivity of soils in the horizontal direction. Constant head permeability tests were carried out using the radial flow flexible wall permeameter on soil samples with central sand drain to allow the water to flow radially from the central sand drain towards a peripheral drain. Tests were also conducted using the conventional flexible wall permeameter on samples that were trimmed horizontally, so as to measure the hydraulic conductivity in the horizontal directions for comparison. The test results obtained from the proposed setup agrees well with those obtained from the samples that were trimmed horizontally, proving the validity of the results obtained from the proposed apparatus.
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Hydraulic head
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An anchored geosynthetic system (AGS) is an in situ reinforcing system that can be utilised to improve the stability of earth slopes. In this study, performance of AGS slopes under seepage conditions was investigated through a series of centrifuge model tests. These tests were conducted at an acceleration of 50g on silty sand slopes having 2V:1H and 1V:1H inclinations and reinforced with AGS in a large beam centrifuge located at the Indian Institute of Technology Bombay, India. Seepage was induced through a seepage simulator system to raise the water table within the reinforced slopes. The stability and seepage analysis was carried out for AGS slope models and the results were compared with those obtained from the centrifuge model tests. The results indicated that the location of the predicted failure surface in AGS slopes depended on the type of AGS load used for the analysis. The results of seepage analyses indicate that when the phreatic line was close to the physically observed phreatic line it nevertheless exits the face at higher elevation than physically observed in the centrifuge.
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Phreatic
Piezometer
Geosynthetics
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When a jack-up rig is installed in close proximity to an existing piled jacket platform, the massive soil movements induced by spudcan penetration may damage the adjacent piles. In 2012 the authors reported the findings of an extensive centrifuge model study on spudcan–pile interaction in soft clay. As a seabed profile may consist of soft clay over stiff soils and the spudcan–pile interaction phenomenon in such case is expected to be significantly different from that in soft clay, the earlier study is extended to investigate the interaction of a spudcan with adjacent piles in a soft clay overlying sand profile. Besides centrifuge tests on model spudcans, tests on half-spudcans placed behind the transparent window of the model container have been conducted to evaluate the soil movements and failure mechanism for various model configurations and soil conditions. The experimental results and findings are presented in this paper.
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Seabed
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The 6 m diameter, 30 g-tonne geotechnical centrifuge at Queen's University is described. Results from eight model tests, carried out on plain cemented sand samples representing mine backfills, are presented. These data show that the stable prototype backfill heights obtained from centrifuge tests exceed the failure heights predicted from unconfined compression testing by factors averaging about 1.8. This factor is explained by a combination of geometrical and behavioural effects. Still photographs of typical backfill failures in the centrifuge are included and these indicate that unacceptable ore dilution and recovery costs would be associated with the prototype failures in plain cemented tailings backfills. Key words: geotechnical centrifuge, mine backfill, model tests, cemented sand.
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Permeameter
Consolidation
Overburden pressure
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