scholarly journals Effect of Soaking Time and Salt Concentration on Mechanical Characteristics of Slip Zone Soil of Loess Landslides

Water ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3465
Author(s):  
Chen Xue ◽  
Xingang Wang ◽  
Kai Liu
Keyword(s):  
Shear Strength ◽  
Salt Concentration ◽  
Mechanical Characteristics ◽  
Slip Zone ◽  
Loess Landslide ◽  
Soaking Time ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Loess Landslides ◽  
Shear Planes

Loess landslides are closely related to the variation in mechanical properties of soils due to the leaching of irrigation water in the irrigation area which causes the loss of soluble salt in the loess stratum. To investigate the effect of leaching on the mechanical characteristics of loess, ring shear tests were conducted on the slip zone soil samples obtained from a typical loess landslide under different soaking time and salt concentration. Furthermore, the microstructural observations were made on shear planes by using SEM (scanning electron microscopy) tests. The experiment revealed that: firstly, the shear strength of loess decreases with the increase of soaking time before reaching the minimum value at the soaking time of 1 d, and then increases with the soaking time until reaching a relatively stable value. Secondly, the shear strength of loess has an increasing tendency with the salt concentration before reaching a maximum value at the salt concentration of 8%, and then shear strength decreases. In addition, a “stress-softening” was found for the loess samples with the soaking time of 1 d and salt concentration of 8%. It is found that the total number of micropores and small-pores in loess samples decreases with increasing salt concentration up to 8%, but increases rapidly between salt contents of 8% and 20%. The SEM tests showed that the increase in salt concentration (0% to 8%) facilities the formation of small aggregates within loess soils, which in turn promotes the increasing of shear strength. However, further increase in salt concentration (8% to 20%) helps the development of relatively large aggregates in loess samples, resulting in the reduction in shear strength.

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.

scholarly journals Effects of High Shearing Rates on the Shear Behavior of Saturated Loess Using Ring Shear Tests

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Jianquan Ma ◽  
Xiaojie Zhao ◽  
Shibo Li ◽  
Zhao Duan
Keyword(s):  
Shear Strength ◽  
Normal Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Test Sample ◽  
Shear Behavior ◽  
Shearing Rate ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Rate Test

The shear behavior of saturated loess was examined by performing a series of ring shear tests with different shearing rates. The effects of shearing rates on the shear behavior of saturated loess with different normal stress are presented and discussed. The results showed that peak shear strength and steady-state shear strength were greater when the shearing rate was low and vice versa. Compared with high and low shearing rates, the maximum strength reduction ratios of peak shear strength and steady-state shear strength were 34.2% and 37.2%, respectively. The axial displacement during shearing was measured and was found to increase with increasing shear displacement in all tests. A comparison of sample height reduction (when the shear rate was stopped) found that the low shearing rate test sample underwent a much greater reduction than the high shearing rate test sample; however, the variation reduction range was within 4 mm. Monitoring the pore-water pressure during the shearing process revealed that it increased with shear displacement, and a higher excess pore-water pressure was generated within the shear zone during the fast-shearing process. Comparing the particle size distribution of the samples after the test and the original sample showed that the particles were crushed during the shearing process. The percentage that was finer than 0.005 mm increased with shearing rates and normal stress, and the soil structure implosion became more pronounced with increasing normal stress.

scholarly journals Effect of the Surface Roughness on the Shear Strength of Granular Materials in Ring Shear Tests

2019 ◽  
Vol 9 (15) ◽  
pp. 2977 ◽  
Author(s):  
Sueng-Won Jeong ◽  
Sung-Sik Park
Keyword(s):  
Surface Roughness ◽  
Shear Strength ◽  
Granular Materials ◽  
Rough Surfaces ◽  
Shear Velocity ◽  
Shear Tests ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Undrained Conditions ◽  
Drained And Undrained Conditions

Surface roughness plays an important role in estimating the shear strength of granular materials. A series of ring shear tests with different surface roughnesses (i.e., smooth and rough surfaces) were performed. A large-sized ring shear device, which is applicable for fine- and coarse-grained sediments, was developed to examine the shear strength of large particle sizes (i.e., commercial gravels with a mean grain size of 6 mm). In terms of surface roughness, the drainage- and shear-velocity-dependent shear strengths of the granular materials were examined. In this study, different shear velocities of 0.1, 0.5, and 1 mm/s were applied under drained and undrained conditions. The test results clearly show that shear stress is affected by drainage, shear velocity, and surface roughness. In particular, a typical strain-hardening behavior is exhibited regardless of the drainage and shear velocity condition. The measured shear strength obtained from both drained and undrained conditions increased with increasing shear velocity. All tests showed a large fragmentation using rough surfaces compared to the smooth surfaces of the device. The grain crushing was significant during shearing, even when normal stress was not applied. For a given shear velocity, surface roughness is an important feature in determining the shear strength of granular materials.

The influence of grading on the shear strength of loose sands in stress-controlled ring shear tests

Landslides ◽  
2006 ◽  
Vol 4 (1) ◽  
pp. 43-51 ◽  
Author(s):  
Ogbonnaya Igwe ◽  
Kyoji Sassa ◽  
Fawu Wang
Keyword(s):  
Shear Strength ◽  
Shear Tests ◽  
Ring Shear ◽  
Ring Shear Tests

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

2002 ◽  
Vol 39 (4) ◽  
pp. 821-837 ◽  
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.

scholarly journals Effect of particle breakage on the shear strength of calcareous sands

2021 ◽  
Vol 42 (3) ◽  
Author(s):  
Houzhen Wei ◽  
Mei Yin ◽  
Tao Zhao ◽  
Ke Yan ◽  
Jianhua Shen ◽  
...  
Keyword(s):  
Shear Strength ◽  
Particle Breakage ◽  
Sem Images ◽  
Geometrical Properties ◽  
Vertical Loading ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Shearing Deformation ◽  
Calcareous Sands ◽  
Two Parameters

AbstractThe particle breakage of calcareous sands plays a key role in determining the particle shape and shear strength. This process has been analysed in the current study by employing the ring shear tests on calcareous sands sampled from the South China Sea. In this study, a set of parameters, e.g. roundness and aspect ratio, have been employed to quantify the geometrical properties of calcareous sands pre- and after the breakage. These two parameters have been found to correlate well with the vertical loading stress level, shear strain and shear strength. The particle breakage leads to the change of micro-structure during the shear test, as illustrated by the Scanning Electron Microscopy (SEM) images. It is found that during the shearing deformation, particle breakages can effectively reduce, while particle rearrangements can increase the shear strength of the calcareous sands.

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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