Deformation and Strength Characteristics of Structured Clay under Different Stress Paths

Abstract

In geotechnical applications such as deep foundation excavation, slope cutting, and tunnel construction, the stress state of the soil subjected to loading or unloading will change and undergo different stress paths with corresponding changes in its mechanical properties. Therefore, a series of comprehensive laboratory tests were conducted on the natural strong structured clay to evaluate the effects of stress paths on the stress-strain, pore water pressure-strain, deformation characteristics, shear strength behaviors, and the microscopic mechanism of the natural strong structured clay. The results show that the mechanical properties of structured clay under different stress paths are quite different and are closely related to its structure. The peak deviatoric stresses of the soil under both the compression path and the tensile path are affected by the stress path, and the order of its strength is INP > KCP > DEP. The variations of the pore water pressure reflect the shear dilation and the shear contraction characteristics of the soil under different stress paths; the pore pressure of the specimen is particularly complicated in the case of both axial stress and lateral stress unloading; therefore, the pore water pressure in the soil under unloading conditions should be monitored in real time in engineering practice. The stress path affects the total stress strength indices of the structured clay to a significant extent and the effect on soil cohesion is greater than that on the internal friction angle, and the microstructure of the specimens has been changed after shearing tests with different stress paths. Therefore, design calculations should be conducted according to the experimental mechanical parameters under the stress path experienced by the soil under the actual engineering conditions to ensure safety and stability during construction.

Experimental Study on Mechanical Properties of Structured Clay under Different Unloading Rates and Unloading Stress Paths

“…Accordingly, four representative unloading paths were selected: UC 3.0 , UU 1.0 , UL ∞ , and CU −1.5 . The stress paths were named as L for loading, C for constant load, U for unloading, and the former letter for the vertical stress state, the latter letter for the horizontal stress state, and the footnote for the stress path slope η = ∆q/∆p [23].…”

“…Zhanjiang clay is known for its strong structural properties, with an open flocculation structure and strong cementation of free oxides at the microscopic level, as well as an abnormal combination of poor physical properties and good mechanical property indices at the macroscopic level. To date, a certain understanding of the static and dynamic properties as well as microscopic mechanisms of Zhanjiang clay has been achieved [21][22][23][24], whereas the mechanical properties of strong structured clay under the influence of different unloading stress paths and unloading rates are less researched. Therefore, in this study, a series of undrained unloading tests was conducted under isotropic consolidation conditions regarding various unloading stress paths and unloading rates to simulate different unloading methods and speeds in foundation pit excavation projects as well as to investigate the influence law of different unloading stress paths and unloading rates on the strain, pore pressure, and strength characteristics of strong structured clay, with the aim of providing a reference and theoretical basis for the selection of geotechnical engineering parameters in structured clay areas.…”

Factors affecting the oedometric modulus of till soil

“…Soil mechanical behaviour and its characteristics are nonlinear, anisotropic, and elastoplastic, and they mainly depend on soil structure and stress under different loading/unloading conditions (Huang et al 2018;Li et al 2022).…”

“…Stress change is considered to be one of the most important factors affecting soil deformation properties, which are closely related to its structure (Li et al 2022). Soil settlement or compressibility under selfweight or under applied foundation loading shows that stress path and consolidation pressure critically affect the volume strain (Wei et al 2023).…”