An Effective Stress-based Chemo-hydro-mechanical Coupled Constitutive Model Of Unsaturated Soils

As an indispensable theoretical tool in geotechnical engineering,soil mechanics theory is still in the development stage of semi-theoretical and semi-empirical.The prediction results of soil mechanics theory are still uncertain.In addition to the external force acting on the boundary of soil,the solid-liquid-gas interaction also has an important impact on the contact stress between soil particles,then the strength and deformation behavior of soil.The occurrence of geological disasters such as landslide induced by rainfall,environmental geotechnical engineering problems such as the design of landfill barrier and deep geological repository of high-level radioactive nuclear waste,as well as energy geotechnical engineering problems such as exploitation of oil and gas,all need to analysis the strength and deformation behavior of soils due to the interaction between soil skeleton and pore-fluids.Therefore,it is very important to quantitatively characterize the solid-liquid-gas interactions and its influence on the contact stress between soil particles,and to establish a constitutive model that can uniformly describe the soil behavior under the coupled acting of external load and the internal physicochemical interactions.In this paper,the basic behavior of unsaturated soils considering soil skeleton-pore fluids interaction is studied systematically.The main research work and the results of the thesis are listed as follows:(1)The stress variable of soils considering the interaction between soil skeleton and pore fluids are established and verified.Through the experimental data of contact stress between soil particles in the drying and wetting paths,relationship between mean effective stress and critical state shear strength of soils under different unsaturated state,compression and swelling deformation behavior of clayed soils under different concentrations of pore-solution,the ability of the stress variable to describe the contact stress,shear strength and deformation behavior of soils under saturated-unsaturated state and different concentrations of pore solution are verified.(2)Based on the established stress variable and the modified Cam Clay model,the constitutive model of soils considering saturated-unsaturated state and concentrations of pore-fluids is established.With the introduction of boundary surface model,the soil water characteristic curve equation considering capillary hysteresis and skeleton deformation is established.The volumetric water content in the soil water characteristic curve equation is taken as the internal variables of the constitutive model.(3)The constitutive behavior of saturated clayed soil is simulated by the proposed constitutive model.The consolidation deformation behavior of saturated clayed soil under different vertical stresses and concentrations of pore-solution,undrained triaxial tests of saturated clayed soil under different confined pressure and pore solution concentrations are calculated.The comparison between the calculated and measured results show that the strength and deformation behavior of saturated clayed soil are well described by the constitutive model.(4)The constitutive behavior of unsaturated soil is simulated by the proposed constitutive model.The mechanical and hydraulic behavior of unsaturated soil under isotropic compression tests with different matric suctions,drying-wetting cycle tests,triaxial shear tests with drained and undrained paths are calculated.The comparison between the calculated and measured results show that the water retention,strength and deformation behavior of unsaturated soil can be well described by the constitutive model.(5)The swelling deformation tests of bentonite with infiltration of distilled water and different concentrations of sodium chloride solution under fixed vertical stress are carried out.The swollen specimen are then shrunk with the measurement of soil water characteristic curve and shrinkage curve.The influence of concentrations of pore-solution on the mechanical behavior of bentonite under hydraulic paths is studied and reasonably explained by the stress variable established in this paper.(6)The pore water distribution and microstructure evolution of bentonite initially saturated with distilled water and different concentrations of sodium chloride solution during drying process are investigated by nuclear magnetic resonance test(NMR),mercury intrusion test(MIP)and scanning electron microscopy technology(SEM).And the pore water distribution of bentonite under coupled influence of temperature-pore solution concentrations-pore water content is investigated.