Performing Undrained Shear Tests on Saturated Sands in a New Intelligent Type of Ring Shear Apparatus

This paper is concerned with an analysis of the seismic performance of infinite slopes in undrained conditions. The material assumed on the sliding surface is a loose saturated sand susceptible to a gradual loss in undrained shear strength after failure with the progress of unidirectional shear displacement. The undrained monotonic and cyclic shear behavior of this sand was investigated through an experimental study based on ring shear tests, with initial stresses corresponding to the static conditions on the sliding surface of the analyzed slopes. These tests provide the experimental framework for a modified sliding block method to estimate the earthquake-induced undrained shear displacements for conditions of no shear stress reversals on the sliding surface. The proposed estimation procedure incorporates the shearing resistance obtained from undrained monotonic ring shear tests to approximate the undrained yield resistance at a certain displacement during an earthquake. The term catastrophic failure is used in this study to define the accelerated motion of a potential sliding soil mass due to the static driving shear stress exceeding the reduced undrained yield resistance of the soil on the shear surface. The critical displacement necessary to trigger a catastrophic failure on the shear surface under seismic conditions was derived based on the shear resistance shear displacement curve obtained under monotonic loading conditions. Using the shear resistance shear displacement data from undrained monotonic ring shear tests and several processed horizontal earthquake accelerograms, the minimum peak earthquake acceleration necessary to cause a catastrophic shear failure under various seismic waveforms was estimated for conditions of no shear stress reversals on the sliding surface.Key words: earthquakes, slopes, critical shear displacement, sand, ring shear tests, undrained shear strength.

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Post-failure mobility of saturated sands in undrained load-controlled ring shear tests

Canadian Geotechnical Journal ◽

10.1139/t02-032 ◽

2002 ◽

Vol 39 (4) ◽

pp. 821-837 ◽

Cited By ~ 58

Author(s):

Gonghui Wang ◽

Kyoji Sassa

Keyword(s):

Shear Strength ◽

Steady State ◽

Stress State ◽

Initial Stress ◽

Shear Behavior ◽

Shear Tests ◽

Grain Crushing ◽

Ring Shear ◽

Ring Shear Tests ◽

Undrained Shear

The undrained shear behavior of soils with progress of shear displacement is essential to the understanding of liquefied slope failures with long travel distance. In this paper, using a newly developed ring shear apparatus, a series of ring-shear tests were conducted on a silty sand to examine the undrained behavior of sand subjected to long shear displacement. Based on the test results, the undrained shear behavior of sands with a wide range of densities is discussed. A very low effective stress corresponding to liquefaction was observed at the steady state in all of the tests on loose, medium, as well as dense sand. The effects of stress state and shear history on the undrained shear behavior were examined by performing tests on a sample with different initial stress states and shearing the same specimen repeatedly (three times) at each initial stress state. The tests at different initial stress states proved that the initial stress state has an influence on static liquefaction resistance but has no effect on the steady-state shear strength. Repeated shear tests on the same specimen showed that with increasing shear times, both the peak shear strength and the steady-state shear strength for each specimen became greater. Detailed examination of the shear deformation revealed that the liquefaction phenomena in ring shear tests are localized in the shear zone, irrespective of the initial state of the sand. Grain crushing within the shear zone was examined. Finally, it was found that there was an optimal density at which the undrained brittleness index had a minimum value; meanwhile, the undrained brittleness index became greater with increasing initial normal and shear stresses, but decreased with shear times. These findings offer some basic understanding in assessing the postfailure mobility in landslides.Key words: excess pore pressure, localized liquefaction, shear resistance, ring-shear tests, grain crushing, silty sands.

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Strain Softening Behaviors of Clay under Fast Ring Shear Conditions

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.446-449.1880 ◽

2012 ◽

Vol 446-449 ◽

pp. 1880-1883

Author(s):

Yong Hong ◽

Jun Gang Wang

Keyword(s):

Pore Pressure ◽

Strain Softening ◽

Strength Reduction ◽

The Other ◽

Silty Clay ◽

Shear Tests ◽

Shear Rates ◽

High Shear Rates ◽

Ring Shear ◽

Ring Shear Apparatus

In this study, the strain softening behaviors of an overconsolidated silty clay was studied by a ring shear apparatus. The tested results present some different properties with the traditional shear tests. It was found that the silty clay samples with relatively high shear rates are liable to the occurrence of strain softening. With shear rate increasing, both the peak strengths and the post-peak strength reduction become greater. According to the data of deformation and pore pressure measured during the tests, there are two patterns of causing the strain softening of the silty clay. One is related with the contraction of soil specimens; the other is concerned with the generation of negative pore pressure due to the dilatancy of soil body.

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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 ◽

10.1139/t05-017 ◽

2005 ◽

Vol 42 (3) ◽

pp. 787-803 ◽

Cited By ~ 19

Author(s):

Yasuhiko Okada ◽

Kyoji Sassa ◽

Hiroshi Fukuoka

Keyword(s):

Pore Pressure ◽

Triaxial Compression ◽

Excess Pore Pressure ◽

Compression Tests ◽

Shear Tests ◽

Ring Shear ◽

Ring Shear Tests ◽

Triaxial Compression Tests ◽

Undrained Shear ◽

Excess Pore

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 was made to estimate excess pore pressure generated in undrained ring shear tests using the results of drained ring shear tests. The equivalent normal stress calculated as the ratio of volumetric strain in the drained test to the coefficient of volume change was introduced as a parameter for the estimation of excess pore-pressure generation for the large shear displacement that is usually found in landslides. Equivalent normal stress from drained tests was almost the same as the generated excess pore pressure in undrained tests with up to 1 m of shear displacement, at which the steady state was reached.Key words: undrained shear strength, excess pore pressure, equivalent normal stress, ring shear test, triaxial compression test, liquefaction.

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Shear Strength Behavior of Sand Reinforced by Kraft Paper Using the Ring Shear Apparatus

Advances in Civil Engineering ◽

10.1155/2021/8819015 ◽

2021 ◽

Vol 2021 ◽

pp. 1-14

Author(s):

Wan-li Xie ◽

Qianyi Guo ◽

Nelson N.S. Chou ◽

Rongsen Zhu ◽

Maosheng Zhang

Keyword(s):

Shear Plane ◽

Friction Angle ◽

Test Results ◽

Reinforcement Effect ◽

Shear Tests ◽

Kraft Paper ◽

Ring Shear ◽

Strength Behavior ◽

Reinforcement Material ◽

Ring Shear Apparatus

To explore the reinforcement effects of different reinforcement methods, kraft paper was used as reinforcement material, and shear tests were carried out in sand to study the reinforcement effects of kraft paper perpendicular and parallel to the shear plane. The test results show that the two reinforcement methods can effectively improve the strength of sand and the orthogonal reinforcement form is more superior. The existence of reinforced materials greatly improves the cohesion of sand, but does not significantly improve the internal friction angle. The width of reinforcement material has little effect on the reinforcement effect and shows different variation laws under different reinforcement forms.

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Constant-volume friction angle of granular materials

Canadian Geotechnical Journal ◽

10.1139/t88-006 ◽

1988 ◽

Vol 25 (1) ◽

pp. 50-55 ◽

Cited By ~ 57

Author(s):

D. Negussey ◽

W. K. D. Wijewickreme ◽

Y. P. Vaid

Keyword(s):

Phase Transformation ◽

Steady State ◽

Granular Materials ◽

Friction Angle ◽

Confining Pressure ◽

Constant Volume ◽

Ring Shear ◽

Ring Shear Apparatus ◽

Initial Packing ◽

Undrained Shear

The postulate that the constant-volume friction angle [Formula: see text] of a granular material is unique and a function of mineral composition is verified experimentally. Granular materials comprised of particles ranging from minerals to metals are tested in a ring shear apparatus. Test samples are subjected to large shear displacements until a constant lower bound friction angle [Formula: see text] is mobilized. Possible effects of confining pressure, initial packing density, gradation, and particle shape on the value of [Formula: see text] are investigated. Friction angles mobilized in drained shear at the instant of maximum contraction and in undrained shear at phase transformation and steady state are compared with [Formula: see text] values. The experimental results confirm a broader fundamental significance of [Formula: see text] as a material parameter in that it is a consistent minimum drained friction angle equal to friction angles mobilized at phase transformation and steady state in undrained shear. Key words: granular materials, sand, friction angles, constant volume, steady state, phase transformation state, ring shear test.

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