Strain Accumulation in Soft Marine Clay due to One-Way Cyclic Load with Variable Confining Pressure

Lei Sun

doi:10.1155/2021/6624270

Abstract

The effect of variable confining pressure on the strain accumulation in soft marine clay was investigated to gain a better understanding of the deformation characteristic in the subgrade of pavements due to traffic loading. A series of variable confining pressure (VCP) experiments and corresponding constant confining pressure (CCP) experiments were conducted on Wenzhou soft clay using an advanced cyclic triaxial apparatus. A wide range of deviatoric stress amplitudes (qampl), combined with different isotropic stress amplitudes (pampl), and partially drained conditions are simulated in the experiments. The test results indicate that the variable confining pressure significantly influences the permanent axial strain and might exacerbate the potential of subgrade invalidation in soft marine clay area. The normalized permanent axial strain ( ε a , 1000 p / ε a , 1000 p , C C P ) after 1000 cycles is logarithmic with the normalized stress path length (L/LCCP), and one-unit increment in the amplitude of cyclic confining pressure will induce an increment of 0.0213% in the permanent axial strain regardless of the CSR values. Based on the data from the CCP tests, a cyclic deviatoric stress ratio threshold is determined to be about 0.7, which may suggest that the upper bound of criterion will limit the cyclic traffic loadings on soft marine clayey deposit. Finally, the effect of variable confining pressure on the permanent axial strain is quantified and incorporated in a logarithmic model for the subsoil deformation prediction under traffic loading.

Highlights

Advances in Civil Engineering of soft clay under cyclic traffic loading is not totally understood yet, while a satisfactory progress has been made in the simulation of the in situ stress paths and drainage conditions in the subsoil induced by cyclic traffic loading with the upgrade of experimental equipment
Cai et al [10] studied the variable confining pressure (VCP) effects on the permanent deformation of remolded saturated soft clay with an identical initial stress in both undrained and partially drained conditions and suggested that the VCP tests are more appropriate for the simulation of the in situ loading conditions of traffic loading than constant confining pressure (CCP) tests. e results showed that neglecting the effect of VCP in partially drained condition will lead to a relatively smaller permanent strain result, which is not safe in engineering application
Cyclic changes in the magnitude of horizontal stresses are, likely to significantly influence the observed plastic behavior of soils. These studies were focused on evaluating the influence of VCP on the permanent axial strain at a given number of cycles (e.g., N 10000), and only three stress paths have been considered, which resulted in incomplete understanding of the whole evolution of strain accumulation in subsoil under the coupling effect of vertical and lateral cyclic stresses induced by traffic loading

Summary

Test Results of Analysis

E development of permanent axial strain, εap, with the number of load applications in CCP and VCP tests, is shown, similar to the variation of permanent axial strain of granular materials due to one-way cyclic loading in free to drained conditions [15]. The εap grew rapidly with cyclic numbers and reached stability after 1,000 cycles. is phenomenon may be attributed to the partially drained

Stage I

CSR threshold

Conclusions