scholarly journals Impact-Induced Liquefaction Mechanism of Sandy Silt at Different Saturations

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Heng Li ◽  
Zhao Duan ◽  
Chenxi Dong ◽  
Fasuo Zhao ◽  
Qiyao Wang
Keyword(s):  
Shear Strength ◽  
Moisture Content ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Silty Sand ◽  
Sandy Silt ◽  
Loess Landslides ◽  
Mechanism Of Impact ◽  
The Impact

Landslide-induced liquefaction has received extensive attention from scholars in recent years. In the study of loess landslides in the southern Loess Plateau of Jingyang, some scholars have noted the liquefaction of the near-saturated sandy silt layer that is caused by the impact of loess landslides on the erodible terrace. The impact-induced liquefaction triggered by landslides is probably the reason for the long-runout landslides on the near-horizontal terrace. In order to reveal the mechanism of impact-induced liquefaction, this paper investigates the development of pore pressure and the impact-induced liquefaction of sandy silt under the influence of saturation through laboratory experiments, moisture content tests, and vane shear tests. It has been found that both the total pressure and pore water pressure undergo a transient increase and decrease at the moment of impact on the soil, which takes 40–60 ms to complete and only about 20 ms to arrive at the peak. Moreover, silty sand with a saturation of more than 80° was liquefied under the impact, and the liquefaction occurred in the shallow layer of the soil body. The shear strength of the liquefied part of the soil is reduced to 1.7∼2.8 kPa. Soils with lower saturation did not liquefy. The mechanism of the impact-induced liquefaction can be described as follows: under impact, the water in the soil gradually fills the pores of the soil body as the pore size decreases, and when the contact between the soil particles is completely replaced by pore water, the soil body loses its shear strength and reaches a liquefied state. Soils in the liquefied state have a very high permeability coefficient, and the water inside the soil body migrates upward as the particles settle, resulting in high-moisture content in the upper soil.

scholarly journals A mechanical insight into the triggering mechanism of frequently occurred landslides along the contact between loess and red clay

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Baoqin Lian ◽  
Xingang Wang ◽  
Kai Liu ◽  
Sheng Hu ◽  
Xiao Feng
Keyword(s):  
Shear Strength ◽  
Moisture Content ◽  
Shear Zone ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Shaanxi Province ◽  
Triggering Mechanism ◽  
Shear Surface ◽  
Red Clay

AbstractThe triggering mechanism and movement evolution of loess-red clay landslides, which occurred frequently along the contact between the loess and red clay on the Loess Plateau, are closely related to the mechanical properties of the contact surface. This work presents an experimental investigation on loess, clay and loess-red clay interlaminar (LRCI) samples obtained from a typical loess-red clay landslide in northern part of Shaanxi province of China, using a series of ring shear tests, microscopic observation and scanning electron microscopy tests, in an attempt to explore the mechanical behavior of loess, clay and LRCI samples with variation in moisture content, normal stress and shear rate. The results revealed that for all specimens, both the peak shear strength $$\tau_{p}$$ τ p and the residual shear strength $$\tau_{r}$$ τ r decreased with increasing moisture content, among which, moisture content has the greatest influence on the $$\tau_{p}$$ τ p and $$\tau_{r}$$ τ r of red clay, followed by the LRCI specimen, and the loess specimen is least affected by moisture content. Meanwhile, exponential functions describing the correlations between shear strength and moisture content of LRCI, red clay and loess specimens were proposed. Furthermore, the macroscopic morphological characteristics and the microstructure of shear surface obtained from the LRCI specimens showed that a localized water accumulation was built up within the shear surface as the water content increases to some extent, and a high degree of liquefaction developed within shear surface when the moisture content reached to the saturate degree. The microstructural observation on LRCI specimen suggested that the shear surface became smoother and the larger percentage of small-sized pores was observed with moisture content. Accordingly, the built-up excess pore water pressure during shearing is difficult to be dissipated due to a close structure of small-sized pores. Due to the low permeability, high pore-water pressure built up within the shear zone and the increase in the fine particle content, the LRCI soils with a high saturation degree shows the potential for the localized liquefaction within shear zone, which further provides a scientific explanation for the triggering mechanism of loess-red clay landslides with high-speed and long- run out.

Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)

1981 ◽  
Vol 27 (97) ◽  
pp. 503-505 ◽  
Author(s):  
Ian J. Smalley
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Stress Level ◽  
Critical Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Glacial Till ◽  
Forming Process ◽  
Stress Levels

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.

scholarly journals Impact of the moisture content in medium sands on CPTU test results

2016 ◽  
Vol 48 (3) ◽  
pp. 221-231 ◽  
Author(s):  
Łukasz Zawadzki ◽  
Marek Bajda
Keyword(s):  
Moisture Content ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Degree Of Saturation ◽  
Test Results ◽  
Time Dynamic ◽  
Tip Resistance ◽  
The Impact ◽  
Resistance Value

Abstract Soils occurring in the soil “active zone” are in contact with the surface and are directly influenced by external factors (mainly climatic changes) that cause variation in their parameters over time. Dynamic and uncontrolled changes of soil properties e.g. due to rainfall and evapotranspiration processes may affect field test results leading to the misinterpretation of the obtained data. This paper presents investigations on the influence of moisture content changes in sandy soils on CPTU results. For this purpose, a field ground model has been constructed and five CPTU tests with a different moisture content of soil were carried out. During the investigations, the tip resistance (qc), friction on sleeve (fs), and pore water pressure (u2) were measured. Moreover, a TDR probe was applied to determine the distribution of the moisture content in the studied soil columns. Differences between CPT results obtained in saturated and unsaturated soils have been shown. Furthermore, a simple equation to correct the tip resistance value due to the impact of the degree of saturation has been proposed.

scholarly journals Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)

1981 ◽  
Vol 27 (97) ◽  
pp. 503-505 ◽  
Author(s):  
Ian J. Smalley
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Stress Level ◽  
Critical Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Glacial Till ◽  
Forming Process ◽  
Stress Levels

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.

EXPERIMENT STUDY ON DYNAMIC STRENGTH OF LOESS UNDER REPEATED LOAD

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5825-5830 ◽  
Author(s):  
ZHENGHUA XIAO ◽  
BO HAN ◽  
HONGJIAN LIAO ◽  
AKENJIANG TUOHUTI
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Dynamic Strength ◽  
Triaxial Tests ◽  
Dynamic Shear ◽  
Anisotropic Consolidation ◽  
Dynamic Shear Strength

A series of dynamic triaxial tests are performed on normal anisotropic consolidation and over anisotropic consolidation specimens of loess. Based on the test results, the variable regularity of dynamic shear stress, axial strain and pore water pressure of loess under dynamic loading are measured and analyzed. The influences of the dynamic shear strength and pore water pressure at different over consolidation ratio are analyzed. The relationship between dynamic shear strength and over consolidation ratio of loess is obtained. The evaluating standard of dynamic shear strength of loess is discussed. Meanwhile, how to determine the effective dynamic shear strength index of normal anisotropic consolidated loess is also discussed in this paper. Several obtained conclusions can be referenced for studying the dynamic shear strength of loess foundation.

scholarly journals Evaluation of direct shear strength of compacted bentonite having pore-water pressure

2020 ◽  
Vol 195 ◽  
pp. 02028
Author(s):  
Tomoyoshi Nishimura ◽  
Masaaki Fukaya
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Simulation Models ◽  
Radioactive Waste Disposal ◽  
Direct Shear ◽  
Compacted Bentonite ◽  
Barrier Formation ◽  
Behaviour Simulation

Safety of great deep repository design has been investigated for high-level radioactive waste disposal system in several countries such as Belgium, Canada, China, France, Germany, Japan, Sweden and Switzerland. The repository of the disposal is in most cases based on the concept of a multi-barrier system using the host rock barrier formation and a man-made barrier formation. The man-made barrier consists of high expansive bentonite. Thermal-hydro-mechanical behaviour simulation models were developed, including some parameters described by experimental works. The complex phenomena due to the transition into saturation and chemical reactions at the bentonite barrier system have been explained. This study focused on direct shear strength for compacted bentonite related to some factors induced by uncertainty problems such as hydration effect and pore-water pressure. Measured shear strength properties of compacted bentonite had been determined at high suction values. Also, it is clear that there is some influence of direct shear speed on direct shear strength both under unsaturated-saturated conditions. A modified direct shear apparatus was used in this study to observe changes in shear strength with increments of pore-water pressures.

Analytical solutions for calculating pore-water pressure in an infinite unsaturated slope with different root architectures

2015 ◽  
Vol 52 (12) ◽  
pp. 1981-1992 ◽  
Author(s):  
C.W.W. Ng ◽  
H.W. Liu ◽  
S. Feng
Keyword(s):  
Pore Water ◽  
Water Uptake ◽  
Analytical Solutions ◽  
Root Architecture ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Root Water Uptake ◽  
Silty Sand ◽  
Wet Season ◽  
Pressure Distributions

Vegetation can reduce pore-water pressure in soil by root water uptake. The reduction of pore-water pressure results in higher shear strength, but lower soil water permeability, affecting slope stability and rainfall infiltration, respectively. Effects of different root architectures on root water uptake and hence pore-water pressure distributions are not well understood. In this study, new analytical solutions for calculating pore-water pressure in an infinite unsaturated vegetated slope are derived for different root architectures, namely, uniform, triangular, exponential, and parabolic root architectures. Using the newly developed solutions, four series of analytical parametric analyses are carried out to improve understanding of the factors affecting root water uptake and hence influencing pore-water pressure distributions. In the dry season, different root architectures can lead to large variations in pore-water pressure distributions. It is found that the exponential root architecture induces the highest negative pore-water pressure in the soil, followed by the triangular, uniform, and parabolic root architectures. The maximum negative pore-water pressure induced by the parabolic root architecture is about 77% of that induced by the exponential root architecture in the steady state. For a given root architecture, vegetation in completely decomposed granite (CDG, classified as silty sand) induces higher negative pore-water pressure than in either fine sand or silt. The zone influenced by vegetation can be about three to six times the root depth. In the wet season, after a 10 year return period rainfall with a duration of 24 h, different root architectures show similar pore-water pressure distributions.

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