scholarly journals Undrained behaviour of intact soft clay under cyclic paths that match vehicle loading conditions

2018 ◽  
Vol 55 (1) ◽  
pp. 90-106 ◽  
Author(s):  
Lin Guo ◽  
Yuanqiang Cai ◽  
Richard J. Jardine ◽  
Zhongxuan Yang ◽  
Jun Wang
Keyword(s):  
Principal Stress ◽  
Water Pressure ◽  
Heavy Traffic ◽  
Damping Ratio ◽  
Soft Clay ◽  
Cyclic Stress ◽  
Shear Stresses ◽  
Traffic Loading ◽  
Wheel Loading ◽  
Stress Ratios

Vehicle traffic loading appears to contribute significantly to long-term settlement beneath highways, airport runways, and metro lines in China. Wheel loading imposes cycles in both the magnitude and direction of the principal stresses acting on the soils beneath pavement or rail-track structures. Conventional cyclic triaxial (CT) testing, which is not capable of imposing such stress paths, may underestimate how heavy traffic loading affects any underlying soft clay layers. A hollow cylinder apparatus (HCA) can simulate such traffic loading stress paths more accurately, including rotation of the principal stress directions. This paper presents a systematic experimental study of cyclic HCA (CHCA) tests on K0-consolidated saturated soft clay involving cyclic variations in both vertical and torsional shear stresses, along with a parallel programme of CT tests, considering the undrained response of saturated samples of intact soft clay. It is shown that when applied above certain critical cyclic stress ratios, principal stress rotation accelerates excess pore-water pressure and permanent strain development. Corresponding changes are also seen in the resilient modulus and damping ratio trends. The discrepancies between the behaviour of CHCA and equivalent CT tests grow as the cyclic stress ratios increase.

scholarly journals Effect of Variable Confining Pressure on Cyclic Triaxial Behavior of K0-consolidated Soft Marine Clay

2018 ◽  
Vol 4 (4) ◽  
pp. 755
Author(s):  
Lei Sun
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Confining Pressure ◽  
Stress Path ◽  
Cyclic Stress ◽  
Marine Clay ◽  
Stress Ratios ◽  
Variable Confining Pressure

The effect of variable confining pressure (VCP) on the cyclic deformation and cyclic pore water pressure in K0-consolidated saturated soft marine clay were investigated with the help of the cyclic stress-controlled advanced dynamic triaxial test in undrained condition. The testing program encompassed three cyclic deviator stress ratios, CSR=0.189, 0.284 and 0.379 and three stress path inclinations ηampl=3,1 and 0.64. All tests with constant confining pressure (CCP) and variable confining pressure (VCP) have identical initial stress and average stress. The results were analyzed in terms of the accumulative normalized excess pore water pressure rqu recorded at the end of each stress cycle and permanent axial strain, as well as resilient modulus. Limited data suggest that these behavior are significantly affected by both of the VCP and CSR. For a given value of VCP, both of the pore water pressure rqu and permanent axial strains are consistently increase with the increasing values of CSR. However, for a given value of CSR, the extent of the influence of VCP and the trend is substantially depend on the CSR.

Shear modulus and damping of soft Bangkok clays

2002 ◽  
Vol 39 (5) ◽  
pp. 1201-1208 ◽  
Author(s):  
Supot Teachavorasinskun ◽  
Pipat Thongchim ◽  
Panitan Lukkunaprasit
Keyword(s):  
Shear Modulus ◽  
Seismic Analysis ◽  
Damping Ratio ◽  
Soft Clay ◽  
Cyclic Stress ◽  
Large Strains ◽  
Cyclic Triaxial ◽  
Stress History ◽  
Load Frequency ◽  
Equivalent Shear Modulus

The shear modulus and damping ratio of undisturbed Bangkok clay samples were measured using a cyclic triaxial apparatus. Although abundant literature on this topic exists, selection of the most suitable empirical correlation for a seismic analysis cannot be done unless site specific data are obtained. The apparatus used in this research can measure the stress–strain relationships from strain levels of about 0.01%. The equivalent shear modulus measured at these strains was about 80% of the value obtained from the shear wave velocity measurements. The degradation curves of the equivalent shear modulus fell into the ranges reported in the literature, for clay having similar plasticity. The damping ratios varied from about 4–5% at small strains (0.01%) to about 25–30% at large strains (10%). The effects of load frequency and cyclic stress history on the shear modulus and damping ratio were also investigated. An increase in load frequency from 0.1 to 1.0 Hz had no influence on the shear modulus characteristic, but it did result in a slight decrease in the damping ratio. The effects of the small amplitude cyclic stress history on the subsequently measured shear modulus and damping ratio were almost negligible when the changes in void ratio were taken into account.Key words: soft clay, shear modulus, damping ratio, cyclic triaxial test, cyclic stress history.

scholarly journals Cyclic Degradation Characteristics of Undisturbed Soft Clay considering Anisotropy

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Miaomiao Sun ◽  
Jiangang Yu ◽  
Shaoheng He ◽  
Zhi Ding
Keyword(s):  
Plastic Strain ◽  
Stress Ratio ◽  
Soft Clay ◽  
Stress Path ◽  
Cyclic Stress ◽  
Loading Frequency ◽  
Degradation Index ◽  
Cyclic Stress Ratio ◽  
Stress Ratios ◽  
Logarithmic Relationship

The stress-strain characteristics of soil depend primarily on the previous stress history and stress path, thus related to both the stress magnitude and direction. To have a better understanding of the response of soft clay under heart-shaped stress paths, 18 cyclic hollow cylinders tests were performed on undisturbed Hangzhou soft clay under different cyclic stress ratios, deviatoric consolidation ratios (K0), and loading frequencies. The result shows that as the vertical dynamic stress amplitude, K0 value, and loading frequency increase, the degradation index gradually decreases. Moreover, the degradation index of the soil under the cyclic torsion shear (CTS) test is always higher than that under the cyclic triaxial (CT) test. The increase in the amplitude of the cyclic stress ratio (CSR), K0 value, and the decrease in the loading frequency will promote the initial accumulative plastic strain and accelerate the failure rate of the soil sample; it shows that the effects of cyclic stress ratio amplitude, deviatoric consolidation ratios K0, and loading frequency on the accumulative plastic deformation of soil cannot be ignored. On the basis of the test results, a logarithmic relationship between the degradation index and the loading frequency is determined. A new empirical formula of accumulative plastic strain degradation of soft clay has been established, and its accuracy has been further verified by test data. The research results can provide theories for predicting and calculating the long-term settlement and deformation of clay foundation.

scholarly journals Behavior of Nonplastic Silty Soils under Cyclic Loading

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Nazile Ural ◽  
Zeki Gunduz
Keyword(s):  
Pore Pressure ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clay Content ◽  
Cyclic Stress ◽  
Excess Pore Pressure ◽  
Stress Ratios ◽  
Silty Soils ◽  
Excess Pore

The engineering behavior of nonplastic silts is more difficult to characterize than is the behavior of clay or sand. Especially, behavior of silty soils is important in view of the seismicity of several regions of alluvial deposits in the world, such as the United States, China, and Turkey. In several hazards substantial ground deformation, reduced bearing capacity, and liquefaction of silty soils have been attributed to excess pore pressure generation during dynamic loading. In this paper, an experimental study of the pore water pressure generation of silty soils was conducted by cyclic triaxial tests on samples of reconstituted soils by the slurry deposition method. In all tests silty samples which have different clay percentages were studied under different cyclic stress ratios. The results have showed that in soils having clay content equal to and less than 10%, the excess pore pressure ratio buildup was quicker with an increase in different cyclic stress ratios. When fine and clay content increases, excess pore water pressure decreases constant cyclic stress ratio in nonplastic silty soils. In addition, the applicability of the used criteria for the assessment of liquefaction susceptibility of fine grained soils is examined using laboratory test results.

scholarly journals Influence of Intermediate Principal Stress on Undrained Behavior of Intact Clay under Pure Principal Stress Rotation

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Jian Zhou ◽  
Jiajia Yan ◽  
Changjie Xu ◽  
Xiaonan Gong
Keyword(s):  
Pore Pressure ◽  
Principal Stress ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Clay ◽  
Shear Stiffness ◽  
Intermediate Principal Stress ◽  
Principal Stress Rotation ◽  
Stress Rotation

This study presents the accumulations of the excess pore water pressure and the deformation as well as the noncoaxial behavior of intact soft clay subjected to pure principal stress rotation. Series of tests were carried out by using a dynamic hollow cylinder apparatus to highlight the influence of intermediate principal stress parameterb. It was found that the rate of PWP evolution was greatly influenced byb, but the influence was not monotonous. Specimens under the conditionb= 0.75 had the highest accumulation of pore water pressure while under the conditionb= 0 had the strongest resistance to the pore pressure generation. PWP accumulated mainly in the first cycle. The failure of specimens under principal stress rotation was controlled by the strain other than the pore pressure. The shear stiffness decreased more quickly with higherbvalue. The direction of the principal strain increment was strongly dependent on the principal stress increment orientation and less influenced by thebvalue and the number of cycles.

Experimental Study on the Dynamic Characteristics of Saturated Soft Clay Under Bi-Directional Cyclic Loading

2010 ◽  
Author(s):  
Gong-xun Liu ◽  
Mao-tian Luan ◽  
Xiao-wei Tang ◽  
Qing Yang
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Clay ◽  
Cyclic Strain ◽  
Stress Path ◽  
Cyclic Stress ◽  
Cycle Number ◽  
Cyclic Shear ◽  
Saturated Soft Clay

A series of stress-controlled bi-directional cyclic shear tests under isotropic consolidation conditions were conducted for simulating the cyclic stress induced by wave loading. The area bounded by the elliptical stress path was kept unchanged, while the ratio (R) of the axial cyclic shear stress and the torsional cyclic shear stress was changed in order to research the effect of varied two cyclic stress components on the pore water pressure, strength and deformation behaviors of saturated soft clay. The test results show that with a decrease in R, the residual pore water pressure decreases at first and then increases, and it reaches the lowest at R=1 at the same cycle number, while the amplitude of fluctuated pore water pressure decreases all along. The relationship curves between normalized ratio of pore water pressure and ratio of cycle number have significant differences with different R. The cycle number at failure increases at first and then decreases with decreasing R. It reaches the maximum at R=1, indicating that the dynamic strength is the highest when the stress path is close to a circle. The dynamic stress-strain relationship curves with different R indicate that both the axial and the torsional strains caused by the bi-directional cyclic loadings are mainly the cyclic strains, at the same time, the residual strains appear. With decreasing R, the amplitude of axial cyclic strain decreases and the ratio of axial residual strain and cyclic strain increases firstly and then decreases, while the amplitude of torsional cyclic strain increases. The cyclic shear strain is basically symmetric at R=1, while the residual shear strains appear under other conditions.

Explicit Model for Cumulative Pore Pressure of Saturated Soft Clay

2012 ◽  
Vol 256-259 ◽  
pp. 267-270 ◽  
Author(s):  
Zhao Ming Yao ◽  
Jun Hao Chen
Keyword(s):  
Shear Stress ◽  
Pore Pressure ◽  
Principal Stress ◽  
Axial Stress ◽  
Soft Clay ◽  
Explicit Model ◽  
Traffic Loading ◽  
Cyclic Shear ◽  
Stress Rotation ◽  
Axial Cyclic Loading

The principal stress axial would cyclic rotate when the moving pressure passed. In order to analyze long-term settlement of the ground subjected to traffic loading, the simplified method based on explicit model for predicting the accumulative deformations is usually preferred. The traditional model could not reflect the phenomenon of principal stress rotation. After the axial stress controlled equation and circumferential shear stress controlled equation were derived, A series of consolidated undrained cyclic shear tests were performed under the condition that the general shear stress value was constant and the principal stress angle was rotating. The explicit pore pressure model reference was verified to calculate the accumulative pore pressure caused by the principal stress axial cyclic loading.

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