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

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.

Analysis of Surrounding Rock Creep Effect on the Long‐Term Stability of Tunnel Secondary Lining

“…Triaxial unloading creep tests of soft soil under different initial excess pore water pressures (0, 20, 40, 60 kPa) were carried out. e results show that the unloading creep of soft soil can be divided into three stages: attenuation creep, constant speed creep, and accelerated creep [13]. Liu et al [14] adopt the method of combining theoretical analysis and numerical simulation, adopt the nonlinear creep model, and use FLAC3D software for secondary development to study the creep characteristics of rock salt.…”

Constitutive Model of Lateral Unloading Creep of Soft Soil under Excess Pore Water Pressure

“…e sample is taken from a large foundation pit site in Shenzhen of China. e intact sample has a density of 1.82 g/ cm 3 , a saturated water content of 39.6%, a specific gravity of 2.73, a void ratio of 1.094, and a plasticity index of 16.3. e remolded soil samples were prepared with a height of 80.0 mm and a diameter of 39.1 mm according to Geotechnical Test Regulation (SL237-1999). Based on the triaxial tests of isotropic consolidation, the measured cohesion and internal friction angle of the remolded soil sample were 19.95 kPa and 28 °, respectively.…”

“…Soft soil, being a special kind of regional soil with high water content, low bearing capacity, and salient creep characteristics, is widely distributed in Northern Europe, North America, and coastal areas of Pearl River Delta and Yangtze River Delta of China [1][2][3]. Currently, with the rapid development of urban construction, many soft soil underground spaces such as foundation pits and subways in the above areas are in the development phases [4].…”

Mechanical Properties of Soft Soil considering the Influence of Unloading Stress Paths

“…As a region-specific soil with high water content, high compressibility, and low strength, soft soil is widely distributed in the coastal areas of Northern Europe, North America, and China [1,2]. Currently, with rapid urban development, large-scale underground spaces, such as underground train stations and shopping malls, have been constructed in these aforementioned areas.…”