Study Of The Characteristics Of Wetting Deformation Under Unloading Pathways In Granite Residual Soil

Abundant occurrence of granite residual soil is prevalent in the southeastern coastal regions of China,constituting an inevitable foundational load-bearing layer in local construction projects.Due to its distinctive process of soil formation,the granite residual soil possesses significant cementitious structural characteristics within its internal composition.However,the cementitious materials that constitute this structure tend to soften upon contact with water,leading to potential soil engineering performance discontinuities and instability in deformation characteristics.Within the context of excavation projects,the impact of rainfall infiltration on the deformation properties of granite residual soil has consistently been a focal point of interest for the academic and engineering communities.Therefore,this thesis focuses on the nature granite residual soil in Shenzhen City as the research subject.Employing the stress path triaxial testing system of GDS,the study comprehensively investigates the wetting characteristics of the granite residual soil by considering factors such as unloading paths,moisture conditions,consolidation methods,confining pressure,and initial saturation.Furthermore,the wetting deformation patterns of the soil were analyzed through the integration of a computational model,aiming to explore the applicability of the wetting model.The research findings provide technical support and references for the quantitative analysis of rainfall infiltration’s impact on the deformation characteristics of granite residual soil during the design and excavation processes of foundation pits in regions enriched with such soil types.The main research content and conclusions are as follows:（1）The double-line wetting experiment study revealed that the stress-strain curve of residual granite soil in Shenzhen under unloading path exhibits a hardening behavior.The vertical wetting deformation of the soil from unsaturated to saturated state is negatively correlated with saturation degree.The vertical tensile wetting deformation potential of the soil is greater than the vertical compressive wetting deformation potential.（2）Upon conducting a single-line wetting experiment,it was discovered that the rate of axial strain development of the soil after wetting was faster under wetting stress level S_w=0.7 compared to other wetting stress levels.Overall,the values of parameters ε_a^sh（wetting axial strain）,ε_v^sh（wetting volumetric strain）,ε_r^sh（wetting lateral strain）and ε_s^sh（wetting shear strain）for the granite residual soil were positively correlated with the confining pressure during consolidation.However,ε_s^sh was negatively correlated with the confining pressure during unloading.As saturation increased,the values of ε_a^sh,ε_v^sh,ε_r^sh and ε_s^sh decreased.（3）As the wetting stress level S_w increases,the wetting axial strain A and wetting shear strain ε_s^sh of the soil show a non-linear increase.However,under axial compression unloading,there exists a wetting stress threshold S_w^th,where ε_s^sh decreases with an increase in S_w when ε_s^sh is greater than Sw,and εssh increases with an increase in ε_s^sh when ε_s^sh is less than S_w.During the process of unloading under confining pressure,the increase in S_w leads to an enhancement of the "wet dilatation" effect of the granite residual soil,while under the axial compression unloading path.The "wet dilatation" tendency of the specimen decreases progressively with an increase in the parameter S_w,and correspondingly,the wetting-induced lateral expansion of the soil also gradually diminishes.（4）In the study of the wetting characteristics using the double-line method,it was observed that the wetting axial strain of granite residual soil,as calculated by both theoretical models,exhibits a negative correlation with the soil’s initial saturation and confining pressure.The computational results indicate that the soil has a greater potential for wetting elongation deformation compared to wetting compression deformation,with a decrease in differences observed as the consolidating confining pressure increases.The models demonstrate a good level of applicability.Specifically,the hyperbolic model yields wetting axial strain values higher than those obtained from the calculations of the linear simplification model.（5）In the study of wetting characteristics using the single-line method,the computational results of the theoretical model exhibit a strong correlation with experimental data,effectively reflecting the wetting deformation characteristics of granite residual soil.Thus,it can be applied in the computation of wetting deformations of granite residual soil under unloading paths in excavation projects of foundation pits.