Experiment Study of Lateral Unloading Stress Path and Excess Pore Water Pressure on Creep Behavior of Soft Soil

Wei Huang,Lin Li,Kejun Wen,Farshad Amini,Xiaojia Deng,Dongsheng Li,Haifei Jiang

doi:10.1155/2019/9898031

Abstract

The unloading creep behavior of soft soil under lateral unloading stress path and excess pore water pressure is the core problem of time-dependent analysis of surrounding rock deformation under excavation of soft soil. The soft soil in Shenzhen, China, was selected in this study. The triaxial unloading creep tests of soft soil under different initial excess pore water pressures (0, 20, 40, and 60 kPa) were conducted with the K0 consolidation and lateral unloading stress paths. The results show that the unloading creep of soft soil was divided into three stages: attenuation creep, constant velocity creep, and accelerated creep. The duration of creep failure is approximately 5 to 30 mins. The unloading creep behavior of soft soil is significantly affected by the deviatoric stress and time. The nonlinearity of unloading creep of soft soil is gradually enhanced with the increase of the deviatoric stress and time. The initial excess pore water pressure has an obvious weakening effect on the unloading creep of soft soil. Under the same deviatoric stress, the unloading creep of soft soil is more significant with the increase of initial excess pore water pressure. Under undrained conditions, the excess pore water pressure generally decreases during the lateral unloading process and drops sharply at the moment of unloading creep damage. The pore water pressure coefficients during the unloading process were 0.73–1.16, 0.26–1.08, and 0.35–0.96, respectively, corresponding to the initial excess pore water pressures of 20, 40, and 60 kPa.

Highlights

Soft soil is a kind of regional special soil with significant rheological characteristics and widely distributed in China’s Pearl River Delta, Yangtze River Delta, and other coastal areas. e total area of the coastal zone is about 280,000 km2, which is the most economically developed region in China
With the rapid development of economic construction, the abovementioned areas have carried out large-scale development of soft soil, such as soft soil deep foundation pits, underground shopping malls, and subway [1, 2]. e stress that soil body experienced is mainly an unloading process in the excavation of soft soil [3]. e engineering practice shows that the deformation, instability, and damage of the surrounding rock of soft soil do not occur immediately during the excavation or after the excavation, but they experience a period of history, that is, the unloading creep damage of soft soil occurs [4, 5]
The high-level groundwater normally exists in soft soil areas, and the disturbance or vibration of construction will lead to large excess pore water pressure. e presence of pore water pressure will weaken the microstructure of the soft soil particles, and it can make the unloading creep damage of the soft soil extremely strong and even cause the rheological disasters

Summary

Introduction

Soft soil is a kind of regional special soil with significant rheological characteristics and widely distributed in China’s Pearl River Delta, Yangtze River Delta, and other coastal areas. e total area of the coastal zone is about 280,000 km2, which is the most economically developed region in China. Erefore, the soft soil unloading mechanics caused by lateral unloading stress path and excess pore water pressure has become an inevitable problem in the design and construction of excavation of soft soil. Erefore, this study considered the lateral unloading stress path and the excess pore water pressure caused by the construction in soft soil area in Shenzhen, China.

Results

Conclusion