Effect of variable confining pressure on cyclic behaviour of granular soil under triaxial tests

2017 ◽  
Vol 54 (6) ◽  
pp. 768-777 ◽  
Author(s):  
Qi Sun ◽  
Yuanqiang Cai ◽  
Jian Chu ◽  
Quanyang Dong ◽  
Jun Wang
Keyword(s):  
Initial Stress ◽  
Stress Ratio ◽  
Permanent Deformation ◽  
Confining Pressure ◽  
Stress Path ◽  
Average Stress ◽  
Triaxial Tests ◽  
Cyclic Behaviour ◽  
Different Strains ◽  
Variable Confining Pressure

Previous studies were performed to use combined cyclic deviatoric stress and confining pressure to simulate cyclic vertical and horizontal normal stresses under traffic loading. The effect of variable confining pressure (VCP) on the permanent deformation of soils was investigated. However, some studies concluded VCP could promote the development of permanent deformation compared to the tests with constant confining pressure (CCP), while others drew the opposite conclusions. In this study, three types of CCP and VCP tests with identical maximum stress, identical average stress, and identical initial stress were conducted. Test results showed VCP tests accumulated more permanent strains when CCP and VCP tests had identical maximum or average stress, and the permanent strains increased with the decrease in the inclinations of stress paths, while similar permanent strains were generated when CCP and VCP tests had identical initial stress. In addition, larger permanent strains were generated with the increase in stress ratio or length of stress path in both CCP and VCP tests. Considering that different strains were cumulated in CCP and VCP tests with the same stress ratio, it is recommended that both stress ratio and length of stress path be considered to assess the permanent deformation.

Permanent deformation characteristics of saturated sand under cyclic loading

2015 ◽  
Vol 52 (6) ◽  
pp. 795-807 ◽  
Author(s):  
Yuanqiang Cai ◽  
Qi Sun ◽  
Lin Guo ◽  
C. Hsein Juang ◽  
Jun Wang
Keyword(s):  
Shear Stress ◽  
Stress Ratio ◽  
Permanent Deformation ◽  
Confining Pressure ◽  
Stress Path ◽  
Deviatoric Stress ◽  
Loading Path ◽  
Triaxial Tests ◽  
Deformation Characteristics ◽  
Torsional Shear

The loading path involving principal stress rotation (PSR) during shear is an important phenomenon encountered in many field conditions. Typically for traffic loading, both the magnitude and direction of principal stresses may vary with time due to the motion of vehicles, and the stress path can be mimicked by a heart shape in the deviatoric stress space. Conventional triaxial tests are not suitable to recreate this type of stress path in that no torsional shear stress can be applied on the test samples. To overcome this limitation, a series of tests using a hollow cylinder apparatus were conducted on sand to investigate the permanent deformation characteristics under drained conditions with different levels of confining pressure (σc), cyclic vertical stress ratio (CVSR), and cyclic torsional stress ratio (η). The results clearly show an increase in the permanent deformation with η, indicating that the PSR effect on permanent deformation cannot be ignored. Both σc and CVSR were found to also affect permanent deformation, which was more pronounced when PSR was coupled into the test. A five-parameter formulation that accounted for the effect of confining pressure, deviatoric stress, torsional shear stress, and number of loading cycles was subsequently established to analyze the permanent strain. The formulation coefficients were first determined and then used to explain the effects of stress variables on the permanent deformation. Validation studies were performed to address the adequacy of the formulation to predict permanent deformation.

Unbound Aggregate Rutting Models for Stress Rotations and Effects of Moving Wheel Loads

2005 ◽  
Vol 1913 (1) ◽  
pp. 41-49 ◽  
Author(s):  
In Tai Kim ◽  
Erol Tutumluer
Keyword(s):  
Test Data ◽  
Permanent Deformation ◽  
Confining Pressure ◽  
Stress Path ◽  
In Situ Stress ◽  
Triaxial Tests ◽  
Wheel Loading ◽  
Stress States ◽  
Granular Layers ◽  
Unbound Aggregate

The latest research findings on stress rotations caused by moving wheel loads and their effects on permanent deformation or rut accumulation in pavement granular layers are presented. Realistic pavement stresses induced by moving wheel loads were examined in the unbound aggregate base and subbase layers, and the significant effects of rotation of principal stress axes were indicated for a proper characterization of the permanent deformation behavior. To account for the rutting performances of especially thick granular layers, a comprehensive set of repeated load triaxial tests was conducted in the laboratory. Triaxial test data were obtained and analyzed from testing aggregates under various realistic in situ stress paths caused by moving wheel loading. Permanent deformation characterization models were then developed on the basis of the experimental test data to include the static and dynamic stress states and the slope of stress path loading. The models that also considered the stress path slope variations predicted the stress path dependency of permanent deformation accumulation best. In addition, multiple stress path tests conducted to simulate the extension–compression–extension type of rotating stress states under a wheel pass gave much higher permanent strains than those of the compression-only single path tests. The findings indicated actual traffic loading simulated by the multiple path tests could cause greater permanent deformations or rutting damage, especially in the loose base or subbase, when compared with deformations measured from a dynamic plate loading or a constant confining pressure type laboratory test.

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.

Laboratory study on subgrade fluidization under undrained cyclic triaxial loading

2020 ◽  
Vol 57 (11) ◽  
pp. 1767-1779 ◽  
Author(s):  
Buddhima Indraratna ◽  
Mandeep Singh ◽  
Thanh Trung Nguyen ◽  
Serge Leroueil ◽  
Aruni Abeywickrama ◽  
...  
Keyword(s):  
Stress Ratio ◽  
Confining Pressure ◽  
Cyclic Stress ◽  
Triaxial Tests ◽  
Loading Conditions ◽  
Cyclic Triaxial ◽  
Cyclic Stress Ratio ◽  
Upward Migration ◽  
Efficient Operation ◽  
Mud Pumping

A long-term issue that has hampered the efficient operation of heavy-haul tracks is the migration of fluidized fines from the shallow soft subgrade to the overlying ballast, i.e., mud pumping. This paper presents a series of undrained cyclic triaxial tests where realistic cyclic loading conditions were simulated at low confining pressure that is typical of shallow subgrade beneath a ballast track. Subgrade soil specimens with a low-plasticity index collected from a field site with recent history of mud pumping were tested at frequencies from 1.0 to 5.0 Hz and a cyclic stress ratio (CSR) from 0.1 to 1.0. The experimental results indicate that under adverse loading conditions of critical cyclic stress ratio (CSRc) and frequency, there is upward migration of moisture and the finest particles towards the specimen top and this causes the uppermost part of the soil specimen to soften and fluidize. Conversely, a smaller value of CSR tends to maintain stability of the specimen despite the increasing number of loading cycles. It is noteworthy that for any given combination of CSR and frequency, the relative compaction has a significant influence on the cyclic behaviour of the soil and its potential for fluidization.

scholarly journals Testing and Micromechanical Modelling of Rockfill Materials Considering the Effect of Stress Path

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Wang Feng ◽  
Chi Shichun ◽  
Li Shijie ◽  
Jia Yufeng
Keyword(s):  
Stress Ratio ◽  
Volumetric Strain ◽  
Stress Path ◽  
Complex Stress ◽  
Triaxial Tests ◽  
Rockfill Material ◽  
Rockfill Materials ◽  
Deformation Properties ◽  
Confining Pressures ◽  
Improved Model

We have extended the micromechanics-based analytical (M-A) model to make it capable of simulating Nuozhadu rockfill material (NRFM) under different stress paths. Two types of drained triaxial tests on NRFM were conducted, namely, the stress paths of constant stress ratio (CSR) and the complex stress paths with transitional features. The model was improved by considering the interparticle parameter variation with the unloading-reloading cycles and the effect of the stress transition path. The evolution of local dilatancy at interparticle planes due to an externally applied load is also discussed. Compared with Duncan-Chang’s E-u and E-B models, the improved model could not only better describe the deformation properties of NRFM under the stress path loading, but also present the volumetric strain changing from dilatancy to contractancy with increasing transitional confining pressures. All simulations have demonstrated that the proposed M-A model is capable of modelling the mechanical behaviour of NRFM in the dam.

scholarly journals Dynamic modulus characteristics of saturated clays under variable confining pressure

2017 ◽  
Vol 54 (5) ◽  
pp. 729-735 ◽  
Author(s):  
Chuan Gu ◽  
Zhiqiang Gu ◽  
Yuanqiang Cai ◽  
Jun Wang ◽  
Daosheng Ling
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Hyperbolic Model ◽  
Cyclic Triaxial Tests ◽  
Cyclic Shear ◽  
Dynamic Loadings ◽  
Actual Field ◽  
Variable Confining Pressure

Dynamic loadings, induced by earthquakes and other causes, will lead to the cyclic variation of both shear stress and normal stress components on the soil elements. A series of cyclic triaxial tests with and without variable confining pressure were carried out to investigate the coupling effects of cyclic shear stress and cyclic normal stress on the normalized shear modulus, G/Gmax, characteristics of saturated clays. Results indicated that both the phase differences and ratios between the cyclic deviatoric stress and cyclic confining pressure exerted a constant and pronounced influence on the G/Gmax, indicating that the G/Gmax properties under combined loadings will be more representative of actual field conditions than from single-loading conditions. A modified hyperbolic model considering the effects of cyclic confining pressure was further proposed.

scholarly journals Permanent Deformation Characteristics of Coarse Grained Subgrade Soils under Train-Induced Repeated Load

2017 ◽  
Vol 2017 ◽  
pp. 1-15 ◽  
Author(s):  
Xianzhang Ling ◽  
Peng Li ◽  
Feng Zhang ◽  
Yingying Zhao ◽  
Yan Li ◽  
...  
Keyword(s):  
Initial Stress ◽  
Deformation Behavior ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Permanent Deformation ◽  
Cyclic Stress ◽  
Coarse Grained ◽  
Mean Stress ◽  
Axial Deformation ◽  
Repeated Load

This paper presents the results of a laboratory experiment that aimed to characterize the permanent deformation behavior of coarse grained soils. To evaluate the effects of the cyclic stress amplitude, initial mean stress, and initial stress ratio on the permanent axial deformation, six series of repeated load triaxial tests were performed. The results indicate that permanent deformation of coarse grained soils increased with increasing cyclic stress amplitude. In particular, for relative low cyclic stress levels, accumulation rate of permanent deformation decreased progressively with number of cycles and eventually reached an equilibrium state. The initial stress ratio was also found to obviously facilitate the buildup of axial deformation since it means higher deviatoric stress as the mean pressure kept constant. As the initial stress ratio was less than the slope of static failure line, the experimental results indicated that the increase of initial mean stress enhanced the capability of resisting deformation. A simplified mechanistic empirical prediction model was proposed, which predicted the permanent deformation as product of four independent functions about cyclic stress amplitude, initial mean stress, initial stress ratio, and number of load cycles. Satisfactory predictions of the permanent deformation behavior of coarse grained soils were obtained with the proposed model.

Effects of Stress Path and Stress History on the Stiffness of Reconstituted London Clay

1986 ◽  
Vol 2 (1) ◽  
pp. 139-144 ◽  
Author(s):  
J. H. Atkinson ◽  
J. S. Evans ◽  
D. Richardson
Keyword(s):  
Stress Path ◽  
Triaxial Tests ◽  
Soil Parameters ◽  
Stress History ◽  
Strain Behaviour ◽  
Reconstituted Soil ◽  
Path Dependent ◽  
London Clay ◽  
Soil Behaviour

AbstractSoil behaviour is stress history dependent and stress path dependent and soil parameters, particularly those for stress-strain behaviour, measured in conventional triaxial tests may not represent the behaviour of soil in many civil engineering works.To obtain more realistic parameters it may be necessary to conduct laboratory tests which more closely represent in situ conditions before and during construction.The paper describes equipment developed at The City University to carry out stress path tests simply and economically. A series of CU triaxial tests and stress path tests on reconstituted soil illustrate the dependence of measured soil parameters on stress history and stress path.

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