Strain Softening Behaviors of Clay under Fast Ring Shear Conditions

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.

scholarly journals Consolidated and Undrained Ring Shear Tests on the Sliding Surface of the Hsien-du-shan Landslide in Taiwan

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Hung-Ming Lin ◽  
Jian-Hong Wu ◽  
Erik Sunarya
Keyword(s):  
Pore Pressure ◽  
Rock Avalanche ◽  
Excess Pore Pressure ◽  
High Water Content ◽  
Sliding Surface ◽  
Shear Tests ◽  
Typhoon Morakot ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Excess Pore

A new consolidated undrained ring shear test capable of measuring the pore pressures is presented to investigate the initiation mechanism of the Hsien-du-shan rock avalanche, triggered by Typhoon Morakot, in southern Taiwan. The postpeak state of the landslide surface between the Tangenshan sandstone and the remolded landslide gouge is discussed to address the unstable geomorphological precursors observed before the landslide occurred. Experimental results show that the internal friction angle of the high water content sliding surface in the total stress state, between 25.3 and 26.1°, clarifies the reason of the stable slope prior to Typhoon Morakot. In addition, during the ring shear tests, it is observed that the excess pore pressure is generated by the shear contractions of the sliding surface. The remolded landslide gouge, sheared under the high normal stress, rendered results associated with high shear strength, small shear contraction, low hydraulic conductivity, and continuous excess pore pressure. The excess pore pressure feedback at the sliding surface may have accelerated the landslide.

scholarly journals Shear rate effect on the residual strength characteristics of saturated loess

2019 ◽  
Author(s):  
Baoqin Lian ◽  
Jianbing Peng ◽  
Qiangbing Huang
Keyword(s):  
Shear Strength ◽  
Shear Rate ◽  
Normal Stress ◽  
Rate Effect ◽  
Shear Tests ◽  
Residual Shear Strength ◽  
Shear Rates ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
The Difference

Abstract. Residual shear strength of soils is an important soil parameter for assessing the stability of landslides. To investigate the effect of the shear rate on the residual shear strength of loessic soils, a series of ring shear tests were carried out on loess from three landslides at two shear rates (0.1 mm/min and 1 mm/min). Naturally drained ring shear tests results showed that the shear displacement to achieve the residual stage for specimens with higher shear rate was greater than that of the lower rate; both the peak and residual friction coefficient became smaller with increase of shear rate for each sample; at two shear rates, the residual friction coefficients for all specimens under the lower normal stress were greater than that under the higher normal stress. The tests results revealed that the difference in the residual friction angle фr at the two shear rates, фr (1)–фr (0.1), under each normal stress level were either positive or negative values. However, the difference фr(1)–фr (0.1) under all normal stresses was negative, which indicates that the residual shear parameters reduced with the increasing of the shear rate in loess area. Such negative shear rate effect on loess could be attributed to a greater ability of clay particles in specimen to restore broken bonds at low shear rates.

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

2003 ◽  
Vol 26 (3) ◽  
pp. 10781 ◽  
Author(s):  
L David Suits ◽  
TC Sheahan ◽  
K Sassa ◽  
G Wang ◽  
H Fukuoka
Keyword(s):  
Shear Tests ◽  
Ring Shear ◽  
Saturated Sands ◽  
Ring Shear Apparatus ◽  
Undrained Shear

Study of the Effect of Shear Rates on Residual Shear of Landslide Soil

2013 ◽  
Vol 639-640 ◽  
pp. 598-601
Author(s):  
Chuan Sheng Chen ◽  
Jing Fang Liu ◽  
Shi Zhi Wen
Keyword(s):  
Friction Coefficient ◽  
Residual Strength ◽  
Slip Surface ◽  
Shear Behaviour ◽  
Residual Shear Strength ◽  
Shear Rates ◽  
Ring Shear ◽  
Ring Shear Apparatus ◽  
The Stability ◽  
Landslide Slope

The residual strength is one of the most important strength parameters to evaluate the stability of a reactivated landslide slope, but the relation between residual strength gained by using ring shear tests and shear speed still remains unclear. In order to clarify the relationship between them, the variation in residual friction coefficient of slip surface soils with shearing rates were calculated and discussed in this paper by means of an undrained ring shear apparatus on Miaowan sample of China-Loess Plateau , predominantly consists of silty-sandy(81.3%), and Kamenose sample of Japan, predominantly consists of clay(73.2%) in texture .The residual friction coefficient was observed to be lower for higher shear rates in Kamenose sample;while the variation of its shear behaviour at different shear rates is fluctuant in Miaowan sample. This change in pore water pressures and soil texture could be thought as the rate effect mechanism of residual shear strength.

scholarly journals Excess pore pressure generation potential within shear zone by means of ring shear tests

Landslides ◽  
2002 ◽  
Vol 39 (3) ◽  
pp. 296-306
Author(s):  
Yasuhiko OKADA ◽  
Kyoji SASSA ◽  
Hiroshi FUKUOKA
Keyword(s):  
Pore Pressure ◽  
Shear Zone ◽  
Excess Pore Pressure ◽  
Shear Tests ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Excess Pore

Undrained shear behaviour of sands subjected to large shear displacement and estimation of excess pore-pressure generation from drained ring shear tests

2005 ◽  
Vol 42 (3) ◽  
pp. 787-803 ◽  
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.

scholarly journals Rate Effects on Peak and Residual Strengths of Overconsolidated Clay in Ring Shear Tests

2021 ◽  
Author(s):  
Nguyen Thanh Duong ◽  
Motoyuki Suzuki
Keyword(s):  
Shear Strength ◽  
Residual Strength ◽  
Clayey Soil ◽  
Shear Displacement ◽  
Shear Tests ◽  
Shear Rates ◽  
Ring Shear ◽  
Wide Range ◽  
Rate Effects ◽  
Ring Shear Tests

Overconsolidated (OC) clay soil is widely distributed in landslide slopes. This soil is often fissured, jointed, contains slickensides, and is prone to sliding. Thus, the shear strength behavior of OC clayey soil is complicated and has received much attention in the literature and in practice in terms of evaluating and predicting landslide stability. However, the behavior of the shear strength of OC clayey soil at different shear rates, as seen in ring shear tests, is still only understood to a limited extent and should be examined further, especially in terms of the residual strength characteristics. In this study, a number of ring shear tests were conducted on kaolin clay at overconsolidation ratios (OCRs) ranging from 1 to 6 under different shear displacement rates in the wide range of 0.02 mm/min to 20.0 mm/min to investigate the shear behavior and rate dependency of the shear strength of OC clay. Variations in the cohesion and friction angles of OC clay under different shear rates were also examined. The results indicated that the rate effects on the peak strength of OC and normally consolidated (NC) clays are opposite at fast shear displacement rates. At the residual state, as with NC clay, the positive rate effect on the residual strength is also exhibited in OC clay, but at a lower magnitude. Regarding the shear strength parameters, the variations in the cohesion and friction angles of OC clay at different shear rates were found to be different at peak and residual states.

scholarly journals Shear rate effect on the residual strength characteristics of saturated loess in naturally drained ring shear tests

2020 ◽  
Vol 20 (10) ◽  
pp. 2843-2856
Author(s):  
Baoqin Lian ◽  
Xingang Wang ◽  
Jianbing Peng ◽  
Qiangbing Huang
Keyword(s):  
Shear Strength ◽  
Shear Rate ◽  
Normal Stress ◽  
Rate Effect ◽  
Shear Tests ◽  
Residual Shear Strength ◽  
Shear Rates ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
The Difference

Abstract. Residual shear strength of soils is an important soil parameter for assessing the stability of landslides. To investigate the effect of the shear rate on the residual shear strength of loessic soils, a series of naturally drained ring shear tests were carried out on loess from three landslides at two shear rates (0.1 and 1 mm min−1). Experimental results showed that the shear displacement to achieve the residual stage for specimens with higher shear rate was greater than that of the lower rate; both the peak and residual friction coefficient became smaller with increase in shear rate for each sample; at two shear rates, the residual friction coefficients for all specimens under the lower normal stress were greater than those under the higher normal stress. Moreover, specimens with almost the same low fraction of clay (CF) showed a similar shear rate effect on the residual friction coefficient, with normal stress increasing, whereas specimens with high CF (24 %) showed a contrasting tendency, indicating that such an effect is closely associated with CF. The test results revealed that the difference in the residual friction angle ϕr at the two shear rates, ϕr(1)−ϕr(0.1) under each normal stress level are either positive or negative values, of which the maximum magnitude is about 0.8∘. However, the difference ϕr(1)−ϕr(0.1) determined under all normal stress levels was negative, which indicates that the residual shear parameters reduced with the increasing of the shear rate in the loess area. Such a negative shear rate effect on loess could be attributed to a greater ability of clay particles in specimens to restore broken bonds at low shear rates.

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