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Enomoto T.,Japan National Institute for Land and Infrastructure Management | Koseki J.,University of Tokyo | Tatsuoka F.,Tokyo University of Science | Sato T.,Integrated Geotechnology Institute Ltd
Soils and Foundations | Year: 2015

The creep failure behaviour of three reconstituted sands exhibiting various viscous property types was evaluated by large-, medium- and small-scale drained triaxial, and medium-scale drained unconfined compression tests. The creep characteristics were evaluated by performing sustained loading during otherwise monotonic loading at a constant loading rate. Creep failure and Isotach viscous stress-strain behaviour were observed with well-graded Miho sand compacted heavily under the optimum water content condition. Creep failure of saturated and air-dried Toyoura sand exhibiting TESRA viscosity was observed at the nearly peak stress state. Degradation of the shear modulus of Toyoura sand during creep failure process was measured by the dynamic method. Creep failure did not occur with air-dried Albany silica sand exhibiting P&N viscosity. It was experimentally shown that the stability against creep failure was higher in order of P&N, TESRA and Isotach viscosities. The creep behaviour of various viscous property types was well simulated by the non-linear three-component model taking into account the effects of particle characteristics on the viscous property parameters. © 2015 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.

Kiyota T.,University of Tokyo | Sato T.,Integrated Geotechnology Institute Ltd
Soils and Foundations | Year: 2010

In order to investigate liquefaction-induced ground displacement, we conducted a series of undrained cyclic torsional shear tests on saturated Toyoura sand using a modified torsional apparatus capable of applying and measuring double amplitude shear strain up to about 100%. The limiting value of double amplitude shear strain, at which strain localization appears during undrained cyclic loading tests, was evaluated from the test results with reference to the change in the deviator stress during liquefaction. The limiting strain values, which increase with a decrease in the relative density of the specimen, were found to be consistent with the maximum amounts of liquefaction-induced ground displacement observed in the previous shaking table model tests and most of the relevant case studies. This feature is reasonable considering the reduction in the mobilized cyclic shear stress in liquefied soil due to the degradation of the shear resistance. As long as the liquefied soil layer remains in uniform deformation, these limiting strain values may be used in estimating the maximum amount of liquefaction-induced ground displacement.

Chiaro G.,University of Wollongong | Chiaro G.,University of Tokyo | Koseki J.,University of Tokyo | Sato T.,Integrated Geotechnology Institute Ltd
Soils and Foundations | Year: 2012

This study focused on the role which static shear plays on the large deformation behavior of loose saturated sand during undrained cyclic loading. A series of undrained cyclic torsional shear tests was performed on saturated Toyoura sand specimens up to single amplitude shear strain exceeding 50%. Three types of cyclic loading patterns, i.e., stress reversal, intermediate and non-reversal, were employed by varying the initial static shear level and the cyclic shear stress amplitude. The observed types of failure could be distinguished into liquefaction (cyclic and rapid flow) and residual deformation by comparing both monotonic and cyclic undrained behavior. It was found that the presence of initial static shear does not always lead to an increase in the resistance to liquefaction or strain accumulation; they could either increase or decrease with an increasing initial static shear level depending on the type of loading pattern and failure behavior. In addition, according to the failure behavior which the specimens exhibited, three modes of development of large residual deformation were observed. © 2012 The Japanese Geotechnical Society.

Kiyota T.,University of Tokyo | Koseki J.,University of Tokyo | Sato T.,Integrated Geotechnology Institute Ltd
Soil Dynamics and Earthquake Engineering | Year: 2013

With the spread of performance-based design concepts in geotechnical earthquake engineering, conducting a practical and accurate analysis for estimating the liquefaction-induced ground deformation has become important. However, there is a difficulty in setting relevant parameters of liquefied soil that would be employed in the analysis because experimental investigations on large deformation behaviour of liquefied soil are still limited. Therefore, in order to investigate the liquefaction-induced ground deformation characteristics, a series of undrained cyclic torsional shear tests was performed by using a modified torsional shear apparatus that is capable of achieving double amplitude shear strain up to about 100%. The tested materials were saturated Toyoura sand, two kinds of in-situ frozen samples having different geological ages and their reconstituted samples. The in-situ samples were retrieved from Pleistocene deposits. In all the undrained cyclic torsional shear tests, cyclic mobility was observed and the double amplitude shear strain approached 100%, irrespective of the different initial conditions of the specimens. A limiting value of double amplitude shear strain to cause strain localization, which would be linked to the maximum possible liquefaction-induced ground deformation, was evaluated based on the change in the deviator stress during the undrained cyclic torsional loading. The limiting value was found to increase with decrease in initial values of small strain shear moduli which were evaluated by dynamic measurement. In addition, we measured tangent shear moduli at the limiting state as well as after strain localization, and evaluated a reduction ratio of shear moduli due to liquefaction, which would be employed in the ALID framework. These characteristics measured by such large strain liquefaction tests would be useful in estimating the maximum liquefaction-induced ground deformation. © 2013 Elsevier Ltd.

Enomoto T.,Public works research institute | Qureshi O.H.,READ Foundation | Sato T.,Integrated Geotechnology Institute Ltd | Koseki J.,University of Tokyo
Soils and Foundations | Year: 2013

A series of medium-scale and large-scale triaxial and unconfined compression tests was conducted in order to evaluate the strength and deformation characteristics and small strain properties of undisturbed well-graded gravelly soils retrieved from three tunnel excavation sites in Toyama prefecture, Japan. Undisturbed gravelly soils were taken by means of a new sampling method using thick water-soluble polymer solutions. The strength and deformation characteristics were evaluated mainly by performing sustained loading and large amplitude unloading and reloading cycles during otherwise monotonic loading at a constant strain rate in drained triaxial compression tests. During isotropic consolidation and shearing, at several stress states, eleven very small vertical cycles were applied to evaluate the quasi-elastic deformation property at small strain levels around 0.001% by static measurement. Dynamic measurements using a pair of accelerometers attached to the side surface of the specimen and wave sources attached to the top cap were also conducted at the same stress levels as static measurements in a single test. Several effects including grading characteristics and pressure level on the difference between the moduli measured statically and dynamically were discussed. The relationship between the small strain and strength properties of undisturbed gravelly soils was evaluated. The small strain properties of air-dried dense Toyoura sand in large-scale triaxial compression tests were also investigated in this study to compare the results of undisturbed gravelly soils. © 2013 The Japanese Geotechnical Society.

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