The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Hiroshi Fukuoka - One of the best experts on this subject based on the ideXlab platform.
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undrained shear behaviour of sands subjected to large shear displacement and estimation of Excess Pore Pressure generation from drained ring shear tests
Canadian Geotechnical Journal, 2005Co-Authors: Yasuhiko Okada, Kyoji Sassa, Hiroshi FukuokaAbstract:Undrained shear behaviour of fine silica and weathered granitic sand subjected to large shear displacement is examined. Parallel experiments using ring shear and the triaxial compression tests on soil specimens through a wide range of initial void ratios were conducted to investigate undrained shear strength as the key factor in the flow-like motion of landslides. The steady-state undrained shear strengths achieved in ring shear tests were, in general, smaller than those in the triaxial compression tests, probably because of the Excess Pore-Pressure generation by grain crushing within the shear zone that occurred in ring shear. Very low steady-state shear strengths were achieved, however, in triaxial compression tests on the dense silica sand in which well-defined shear surfaces developed in the cylindrical specimens. In these triaxial compression tests, shear deformation must have been concentrated on these surfaces to generate Excess Pore Pressure similar to that found in ring shear tests. An attempt wa...
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Excess Pore Pressure and grain crushing of sands by means of undrained and naturally drained ring shear tests
Engineering Geology, 2004Co-Authors: Yasuhiko Okada, Kyoji Sassa, Hiroshi FukuokaAbstract:An investigation of Excess Pore-Pressure generation of a weathered granitic sand, taken from the source area of a typical landslide caused as a result of liquefaction, and a fine silica sand was conducted, in which grain crushing within the shear zone of ring-shear test specimens was examined as the key phenomenon of rapid long-runout motion of landslides. In order to investigate and explain the low average apparent-friction angle, mobilized in a liquidized landslide, speed-controlled ring-shear tests were conducted under undrained conditions on weathered granitic-sand specimens, formed under a wide range of initial void ratios. It was revealed that very small steady-state shear resistances were obtained irrespective of the initial void ratios, which can explain the low average apparent-friction angle. In addition, two series of ring-shear tests on weathered-granitic and fine-silica sands were conducted under naturally drained conditions by keeping the upper drain valve of the shear box open during the tests. The first series of tests was performed under differing total normal stresses, but at the same shear speed, and the second series was conducted at differing shear speeds, but under the same total normal stress. In order to investigate and analyze Excess Pore-Pressure generation and dissipation within the shear zone that is associated with grain crushing, permeability analyses were conducted by passing water through the sample box of the ring-shear test apparatus before and after shearing. In addition, grain-size distribution analyses of samples taken from the shear zone after shearing were carried out. For the weathered granitic-sand samples, a significant change in bulk permeability and large amount of grain crushing were observed. In these tests on the above soil, a considerable reduction of shear resistance, which increased proportionally to the total normal stress and shear speed, were obtained. It was observed that due to grain crushing, finer grains that lowered the permeability of the soil in the shear zone, were formed. It is likely that the decrease in permeability facilitated the generation of high Excess Pore Pressures by reducing the Pore-Pressure dissipation rate from the shear zone; thus, flow behaviour was exhibited even under naturally drained conditions.
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Excess Pore Pressure generation potential within shear zone by means of ring shear tests
Landslides, 2002Co-Authors: Yasuhiko Okada, Kyoji Sassa, Hiroshi FukuokaAbstract:Excess Pore Pressure generation potential within shear zone by employment of the ring shear tests have been investigated on the saturated samples which have quite different grain crushing susceptibility. In naturally drained tests, the sample the grains of which are crushable showed the great reduction of apparent internal friction during shearing to generate rapid flow phenomena. Based on the results of permeability and grain size analyses, it is estimated that the crushed particles formed the less-permeable shear zone and Excess Pore Pressure generation rate exceeded the dissipation rate to yield flow behaviour, and it occurred heavily in high shear speed or normal stress tests. And to express the susceptibility of the samples against flows, the new parameter “potential for rapid flow phenomena” was proposed as the ratio of internal friction angle (φm) to apparent friction angle (φa).In order to estimate the Excess Pore Pressure in undrained condition from the drained tests, the concept of “equivalent normal stress” was introduced as the ratio of volumetric strain to the compressibility. Equivalent normal stress using compressibility which was obtained by changing normal stress during shearing was almost equal to Excess Pore Pressure at the same shear displacement up to 1 m at which steady state was reached. And Excess Pore Pressure ratio in undrained tests and the logarithm of equivalent normal stress divided by normal stress with compressibility obtained during consolidation process showed the linear relationship.
Nabil Sultan - One of the best experts on this subject based on the ideXlab platform.
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Deep sea in situ Excess Pore Pressure and sediment deformation off NW Sumatra and its relation with the December 26, 2004 Great Sumatra-Andaman Earthquake
International Journal of Earth Sciences, 2009Co-Authors: Nabil Sultan, Antonio Cattaneo, Jean-claude Sibuet, Jean-luc SchneiderAbstract:The swath bathymetric data acquired during the “Sumatra Aftershocks” cruise from the Sunda trench in the Indian Ocean to the north of the Sumatra Island imaged several scars and deposits. In situ Pore Pressure measurements using the Ifremer piezometer and coring demonstrate that high Excess Pore Pressure and sediment deformation was generated by a recent event in the scar of the slope failure zone identified by J.T. Henstock and co-authors. This Excess Pore Pressure is localized in the upper sedimentary layers and is not related to an interplate subduction process. Numerical simulations of the hydrological system that take into account the hydro-mechanical properties of the upper sediment layer show that the Excess Pore Pressure and sediment deformations could be generated at the time of the December 26, 2004 Great Sumatra Earthquake.
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comment on Excess Pore Pressure resulting from methane hydrate dissociation in marine sediments a theoretical approach by wenyue xu and leonid n germanovich
Journal of Geophysical Research, 2007Co-Authors: Nabil SultanAbstract:While it is well accepted that gas hydrate dissociation at the base of the Gas Hydrate Stability Zone (GHSZ) can generate high Excess Pore Pressure and leads to sediment deformation, the consequence in terms of Pore Pressure of the dissolution of the gas hydrate at the top of the Gas Hydrate Occurrence Zone (GHOZ) remains neglected. The purpose of this comment on Xu and Germanovich [2006] article is to demonstrate that gas hydrate dissolution in the GHSZ may generate Excess Pore Pressure and to point out the risk related to hydrate dissolution at the top of the GHOZ.
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Excess Pore Pressure and Slope Failures Resulting From Gas-Hydrates Dissociation and Dissolution
Offshore Technology Conference, 2007Co-Authors: Nabil SultanAbstract:Parameters affecting gas hydrate formation include temperature, Pore Pressure, gas chemistry, and Pore-water salinity. Any change in the equilibrium of these parameters may result in dissociation (gas-hydrate turns into free gas/water mixture) and/or dissolution (gas-hydrate becomes mixture of water and dissolved gas) of the gas hydrate. While, gas-hydrate dissociation at the base of the Gas Hydrate Occurrence Zone (GHOZ) is often considered as a major cause of sediment deformation and submarine slope failures the consequence in terms of Pore Pressure and sediment deformation of the dissolution of the gas hydrate at the top of the GHOZ remains neglected. In this study, we quantify and compare the Excess Pore Pressure resulting from gas hydrate dissociation and dissolution. Based on theoretical development it is demonstrated that Excess Pore Pressure and shear discontinuities generated by hydrate dissociation is unlikely to be a hazardous factor. In natural environment, the Excess Pore Pressure generated by hydrate dissociation is bounded by the gas hydrate stability law inducing for a natural temperature increase a limited amount of Excess Pore Pressure and limited shear discontinuities at the base of the GHOZ. On the other hand, we show that under natural temperature changes hydrate dissolution at the top of the gas hydrate stability zone, which can occur at a regional scale, is a hazardous process that can lead to catastrophic landslides.
Fernando Lopez-caballero - One of the best experts on this subject based on the ideXlab platform.
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Effect of coupling Excess Pore Pressure and soil deformation on nonlinear SSI in liquefiable soil deposits
Bulletin of Earthquake Engineering, 2017Co-Authors: Silvana Montoya-noguera, Fernando Lopez-caballeroAbstract:The current seismic design philosophy is based on nonlinear behavior of structures where the foundation soil is often simplified by a modification of the input acceleration depending on the expected site effects. The latter are generally limited to depend on the shear-wave velocity profile or a classification of the site. Findings presented in this work illustrate the importance of accounting for both soil nonlinearity due to seismic liquefaction and for soil-structure interaction when dealing with liquefiable soil deposits. This paper concerns the assessment of the effect of Excess Pore Pressure ( $$\Delta p_{w}$$ ) and deformation for the nonlinear response of liquefiable soils on the structure’s performance. For this purpose a coupled $$\Delta p_{w}$$ and soil deformation (CPD) analysis is used to represent the soil behavior. A mechanical-equivalent fully drained decoupled (DPD) analysis is also performed. The differences between the analyses on different engineering demand parameters are evaluated. The results allow to identify and to quantify the differences between the analyses. Thus, it is possible to establish the situations for which the fully drained analysis might tend to overestimate or underestimate the structure’s demand.
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Effect of coupling Excess Pore Pressure and deformation on nonlinear seismic soil response
Acta Geotechnica, 2016Co-Authors: Silvana Montoya-noguera, Fernando Lopez-caballeroAbstract:The Excess Pore Pressure ( $$\Delta p_w$$ Δ p w ) generation and consequent reduction in effective stress lead to the softening of a liquefiable soil deposit that can alter ground motions in terms of amplitude, frequency content and duration. However, total stress models, which are the most currently used, do not take into account coupling of Excess Pore Pressures and soil deformations. To assess this effect, two analyses were made: (1) a Biot hydraulic and mechanical computation of a saturated soil deposit with coupling Pore Pressures and soil deformations and (2) a mechanical computation of a decoupled model with same initial behaviour. Both analyses were performed with a fully nonlinear elastoplastic multi-mechanism model. As $$\Delta p_w$$ Δ p w depends on the soil properties, two soils were analysed: loose-to-medium and medium-to-dense sand. The results regarding the profile of maximum accelerations and shear strains, the surface accelerations and their corresponding response spectra are analysed. The mean values of the normalized response spectra ratio of surface accelerations between the coupled and decoupled model show a deamplification of low and high frequencies (i.e. at frequencies lower than 1.0 Hz and higher than 10 Hz) that tend to increase with the liquefaction zone size. Coupling of $$\Delta p_w$$ Δ p w and soil deformation is therefore of great importance to accurately model the ground motion response. On the contrary, while peak acceleration predictions could be conservative, the amplification on the low frequencies could be largely underestimated which could be highly prejudicial for flexible buildings.
Elise Delavaud - One of the best experts on this subject based on the ideXlab platform.
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Spectral element modeling of seismic wave propagation in visco-elastoplastic media including Excess-Pore Pressure development
Geophysical Journal International, 2017Co-Authors: Elif Oral, Céline Gelis, Luis Fabian Bonilla, Elise DelavaudAbstract:Numerical modelling of seismic wave propagation, considering soil nonlinearity, has become a major topic in seismic hazard studies when strong shaking is involved under particular soil conditions. Indeed, when strong ground motion propagates in saturated soils, Pore Pressure is another important parameter to take into account when successive phases of contractive and dilatant soil behaviour are expected. Here, we model 1-D seismic wave propagation in linear and nonlinear media using the spectral element numerical method. The study uses a three-component (3C) nonlinear rheology and includes Pore-Pressure Excess. The 1-D- 3C model is used to study the 1987 Superstition Hills earthquake (ML 6.6), which was recorded at the Wildlife Refuge Liquefaction Array, USA. The data of this event present strong soil nonlinearity involving Pore-Pressure effects. The ground motion is numerically modelled for different assumptions on soil rheology and input motion (1C versus 3C), using the recorded borehole signals as input motion. The computed acceleration-time histories show low-frequency amplification and strong high-frequency damping due to the development of Pore Pressure in one of the soil layers. Furthermore, the soil is found to be more nonlinear and more dilatant under triaxial loading compared to the classical 1C analysis, and significant differences in surface displacements are observed between the 1C and 3C approaches. This study contributes to identify and understand the dominant phenomena occurring in superficial layers, depending on local soil properties and input motions, conditions relevant for sitespecific studies.
Yasuhiko Okada - One of the best experts on this subject based on the ideXlab platform.
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undrained shear behaviour of sands subjected to large shear displacement and estimation of Excess Pore Pressure generation from drained ring shear tests
Canadian Geotechnical Journal, 2005Co-Authors: Yasuhiko Okada, Kyoji Sassa, Hiroshi FukuokaAbstract:Undrained shear behaviour of fine silica and weathered granitic sand subjected to large shear displacement is examined. Parallel experiments using ring shear and the triaxial compression tests on soil specimens through a wide range of initial void ratios were conducted to investigate undrained shear strength as the key factor in the flow-like motion of landslides. The steady-state undrained shear strengths achieved in ring shear tests were, in general, smaller than those in the triaxial compression tests, probably because of the Excess Pore-Pressure generation by grain crushing within the shear zone that occurred in ring shear. Very low steady-state shear strengths were achieved, however, in triaxial compression tests on the dense silica sand in which well-defined shear surfaces developed in the cylindrical specimens. In these triaxial compression tests, shear deformation must have been concentrated on these surfaces to generate Excess Pore Pressure similar to that found in ring shear tests. An attempt wa...
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Excess Pore Pressure and grain crushing of sands by means of undrained and naturally drained ring shear tests
Engineering Geology, 2004Co-Authors: Yasuhiko Okada, Kyoji Sassa, Hiroshi FukuokaAbstract:An investigation of Excess Pore-Pressure generation of a weathered granitic sand, taken from the source area of a typical landslide caused as a result of liquefaction, and a fine silica sand was conducted, in which grain crushing within the shear zone of ring-shear test specimens was examined as the key phenomenon of rapid long-runout motion of landslides. In order to investigate and explain the low average apparent-friction angle, mobilized in a liquidized landslide, speed-controlled ring-shear tests were conducted under undrained conditions on weathered granitic-sand specimens, formed under a wide range of initial void ratios. It was revealed that very small steady-state shear resistances were obtained irrespective of the initial void ratios, which can explain the low average apparent-friction angle. In addition, two series of ring-shear tests on weathered-granitic and fine-silica sands were conducted under naturally drained conditions by keeping the upper drain valve of the shear box open during the tests. The first series of tests was performed under differing total normal stresses, but at the same shear speed, and the second series was conducted at differing shear speeds, but under the same total normal stress. In order to investigate and analyze Excess Pore-Pressure generation and dissipation within the shear zone that is associated with grain crushing, permeability analyses were conducted by passing water through the sample box of the ring-shear test apparatus before and after shearing. In addition, grain-size distribution analyses of samples taken from the shear zone after shearing were carried out. For the weathered granitic-sand samples, a significant change in bulk permeability and large amount of grain crushing were observed. In these tests on the above soil, a considerable reduction of shear resistance, which increased proportionally to the total normal stress and shear speed, were obtained. It was observed that due to grain crushing, finer grains that lowered the permeability of the soil in the shear zone, were formed. It is likely that the decrease in permeability facilitated the generation of high Excess Pore Pressures by reducing the Pore-Pressure dissipation rate from the shear zone; thus, flow behaviour was exhibited even under naturally drained conditions.
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Excess Pore Pressure generation potential within shear zone by means of ring shear tests
Landslides, 2002Co-Authors: Yasuhiko Okada, Kyoji Sassa, Hiroshi FukuokaAbstract:Excess Pore Pressure generation potential within shear zone by employment of the ring shear tests have been investigated on the saturated samples which have quite different grain crushing susceptibility. In naturally drained tests, the sample the grains of which are crushable showed the great reduction of apparent internal friction during shearing to generate rapid flow phenomena. Based on the results of permeability and grain size analyses, it is estimated that the crushed particles formed the less-permeable shear zone and Excess Pore Pressure generation rate exceeded the dissipation rate to yield flow behaviour, and it occurred heavily in high shear speed or normal stress tests. And to express the susceptibility of the samples against flows, the new parameter “potential for rapid flow phenomena” was proposed as the ratio of internal friction angle (φm) to apparent friction angle (φa).In order to estimate the Excess Pore Pressure in undrained condition from the drained tests, the concept of “equivalent normal stress” was introduced as the ratio of volumetric strain to the compressibility. Equivalent normal stress using compressibility which was obtained by changing normal stress during shearing was almost equal to Excess Pore Pressure at the same shear displacement up to 1 m at which steady state was reached. And Excess Pore Pressure ratio in undrained tests and the logarithm of equivalent normal stress divided by normal stress with compressibility obtained during consolidation process showed the linear relationship.
