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

Lei Sun

doi:10.28991/cej-0309130

Abstract

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.

Highlights

Engineering structures founded on soft marine clay deposits are often designed to withstand cyclic loading such as earthquakes, traffic, or ocean waves etc. during their operational life
As most of the variable confining pressure (VCP) studies were conducted on granular materials or sandy soils in free to drained conditions, the pore water pressure during cyclic loading is not considered
Reliable excess pore-water pressure in the specimen during cyclic loading is the key to assessment of effective stresses that control its deformation response

Summary

Introduction

Engineering structures founded on soft marine clay deposits are often designed to withstand cyclic loading such as earthquakes, traffic, or ocean waves etc. during their operational life. Cai et al (2013) conducted a series of undrained and partially drained one-way cyclic triaxial tests on remolded saturated clay under various VCP and CCP stress paths with identical initial stress (p0, q0) to simulate traffic loading and observed that the cyclic confining pressure has great influences on the characteristics of pore water pressure and axial strain under both undrained and partially-drained conditions [20]. The literature listed above revealed that, no consensus has been reached on the coupling effect of cyclic deviator stress and cyclic confining pressure on the cyclic behavior of soils, apart from the cyclic stress amplitude and the number of cycles, the cyclic deformation and cyclic pore water pressure in clays are significantly affected by the type of VCP tests and drained conditions. Knowing the extent of the effect and the trend is important in the evaluation of the dynamic properties of soil for the analyses of cyclic response of soil deposits

Test Equipment and Test Scheme

Test Results and Discussion

Effect of Cyclic Stress Path Inclinations ηampl on Cyclic Deformation

Discussion and Conclusion