Centrifuge modelling of liquefaction of saturated sand undercyclic loading

Coelho, Palf; Haigh, SK; Madabhushi, Spg

doi:10.1201/9781439833452.ch43

Cited by 11 publications

(5 citation statements)

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“…In shallower depths the effects of soil dilation in dense soil can be clearly seen and although the excess pore pressures do not reach the initial values of effective stress, they are close. This suggests that in dense soil the generation of excess pore pressure is similar to loose soil and this has also been reported by [Seed and Lee, 1966;Coelho et al, 2004]. Evidence of liquefaction of the sandwiched loose layer can be found in the excess pore pressures recorded at a depth of 4.25 m from surface and shown in Fig.…”

Section: Test Results and Discussionsupporting

confidence: 83%

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GHOSH¹

2005

J. Earth. Eng.

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Experimental and numerical simulations are performed to evaluate the modification of ground response resulting from either the presence of soft layers or occurrence of partial liquefaction. Results from two densely instrumented dynamic centrifuge tests are presented to show the ambiguous role played by the presence of a soft layer. It was found that the lateral extent of the soft layer has significant influence on the overall response of the layered strata and any structure founded on it. The experimental observations are supported by simplified numerical analysis. The amplification or deamplification of the input motion is found to be a function of the ratio of the width of soft layer to the wave length. Based on the numerical analysis, a general function describing the site amplification is presented which may be used as a guide in seismic design of foundations in such layered strata. Keywords: Centrifuge modelling; site response; seismic design; liquefaction. 855 J. Earth. Eng. 2005.09:855-876. Downloaded from www.worldscientific.com by UNIVERSITY OF OTAGO on 07/07/15. For personal use only. J. Earth. Eng. 2005.09:855-876. Downloaded from www.worldscientific.com by UNIVERSITY OF OTAGO on 07/07/15. For personal use only.

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Section: Test Results and Discussionsupporting

confidence: 83%

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GHOSH¹

2005

J. Earth. Eng.

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“…The results reveal that S/B value varies from 3.8% for loose sample (relative density of 30%) to 1.5% for dense sample (relative density of 88%) which indicates a 55% drop in settlement amount. Literature review shows that the laboratory results presented in this study are in a good accordance with the data provided by Coelho et al and Ueng et al for similar conditions[9,10]. It is worth mentioning that in this condition, shear stiffness and subsequent elastic modulus of sample increase and a considerable decrease in static settlement is expected as well.…”

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confidence: 91%

Numerical analysis of ground improvement effects on dynamic settlement of uniform sand using DEM

Ahmadi

Sizkow

2020

SN Appl. Sci.

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Uniform fine sands are recognized as problematic soils which are highly prone to earthquake or dynamic loads effects. Cyclic and dynamic loads on such soils can destroy its structure and cause them to experience high volume change. In loose sands, volume change originated from dynamic or cyclic loadings (caused by earthquake, machineries or other similar sources) can lead to excessive settlements on the ground surface which in turn endangers the structural integrity and performance of the superstructure. As a consequence, it is important to perform soil improvements prior to putting any foundation on them. Among many known and recently developed techniques, the soil compaction (or densification) and cement injection are the widest techniques in fine sands improvement. In this research, a numerical study is employed which incorporates the distinct elements method to investigate the volume change and settlement of uniform fine sands. The results obtained numerically have been compared with those observed in a laminar shear box physical model of samples of fine sand. A surface footing is placed over the top of the specimen in the shear box which is modeled by a small rigid plate. Comparisons indicate that the applied simulation technique is suitable for the soil under study. To simulate the model and for verification purpose, Anzali sand physical and mechanical properties have been implemented. Soil particles in the discrete elements technique were modeled by spherical particles obeying the Anzali sand grain size distribution, and for the surface footing, rigid clumps of particles were used. Experiments were performed for density indices of 30-88%, and numerical simulations by the discrete elements method were performed at porosities of 0.43-0.38. The trend of dynamic settlement over the cyclic loading shows a good agreement with measured data in the laboratory. Results revealed that the improvement techniques such as compaction and cementation have a significant effect on the reduction in the final settlement under applied dynamic loads.

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“…This means that the applied sinusoidal input acceleration propagated entirely to these two layers. Coelho et al [13], who carried out cyclic loading tests on saturated sand using centrifuge apparatus, observed similar behaviour. They stated that the reason for the aforementioned behaviour might be related to the large value of the initial vertical stress at these two layers.…”

Section: Acceleration and Horizontal Displacement Responsementioning

confidence: 75%

Dynamic response of thickened tailings in shaking table testing

Alshawmar

Fall

2021

Geo-Engineering

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In this study, an instrumented thickened tailings deposit model was designed, built and employed to evaluate the behaviour of layered thickened tailings to dynamic loading by using a shaking table equipment. The thickened tailings were deposited subsequently in three thin layers in a flexible laminar shear box mounted on top of the shaking table. Cyclic loading with a peak horizontal acceleration of 0.13 g and a frequency of 1 Hz was applied to the layered tailings deposit. Different types of sensors were placed to monitor the accelerations, displacements, volumetric water content and pore water pressures at the intermediate depth of each layer. Results indicated that the acceleration for the bottom and middle layers were similar to that of the base of the shaking table; but, this was not the case for the top layer. The measurements of vertical displacements indicated that all layers of thickened tailings experienced initially contraction and subsequently dilation during the shaking. The excess pore water pressure ratios were found to exceed unity through all layers of thickened tailings when the shaking ended. In other words, the results showed that the layered thickened tailings are susceptible to liquefaction under the considered testing conditions. It is also found that upward pore water migration to the top layer and downward pore water flow to the bottom layer occurred in the thickened tailings deposit. This water migration generated additional pore water pressure and also impacted the vertical displacement and liquefaction susceptibility of the thickened tailings material. The results of this study give a better understanding of the dynamic behaviour of thickened tailings, which is crucial for the safety of thickened tailings systems as well as sustainable mining.

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Centrifuge modelling of liquefaction of saturated sand undercyclic loading

Cited by 11 publications

References 0 publications

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Numerical analysis of ground improvement effects on dynamic settlement of uniform sand using DEM

Dynamic response of thickened tailings in shaking table testing

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