Research On Uniaxial Consolidation Deformation Characteristics Of Remolded Clay Under Adaptive Stress State

It has a powerful function to study the mechanical properties of soil and the geotechnical engineering subject by using the principal stress,but almost all the forces transmitted to the foundation are only the vertical pressure in the direction of gravity.In the actual project,the lateral pressure is generated during the compression process,while the soil bears the active vertical pressure,and the lateral pressure changes with the change of vertical pressure or the delay of time,and the change of lateral pressure in turn affects the deformation characteristics of soil,the lateral pressure is generated naturally in the process of soil compression,which is called adaptive stress state in this paper.In order to make the indoor compression test reflect the adaptive stress state of soil in actual engineering,the standard uniaxial compression test instrument is improved,where the lateral pressure and bottom pore water pressure test sensors are added.The active vertical pressure is expressed as??_v,adaptive lateral pressure is expressed as??_h,and the difference between vertical pressure and adaptive lateral pressure is defined as adaptive shear stress:q_z=?_v-?_h.The test is divided into two continuous stage,which contains continuous loading at the same stress rate and load remaining constant,corresponding to the construction period and completion period respectively.Taking remolded red clay as the research object,through the combination of experiment and theory,the stress-strain relationship of one-way consolidation of clay,deformation calculation model,and calculation method of earth pressure coefficient K₀,one-dimensional nonlinear permeability consolidation characteristics and creep characteristics under adaptive stress state are studied.The main achievements are as follows:(1)The influence of different stress paths,loading rates and stress durations on the deformation characteristics of soil can be reflected in the self-adaptive stress state consolidation tests with different rates of constant stress continuous loading.By analyzing the relationship between vertical strain and each stress index,it is found that the relationship curve of vertical strain and vertical pressure,effective vertical pressure,adaptive lateral pressure and effective adaptive lateral pressure develops in sections in two stages of the test,while the relationship curve of adaptive shear stress and vertical strain develops continuously in two stages,so adaptive shear stress can describe the vertical deformation in different loading stages,that is,it is not affected by the stress path,and when the soil sample is saturated,the self-adaptive shear stress and vertical strain relationship curve is not influenced by stress path,load rate and stress duration,which will promote the understanding of soil constitutive relationship and new deformation calculation method.(2)Based on the deformation mechanism of soil,the stress-strain relationship of soil under different test conditions and the effective stress principle,it is demonstrated that the adaptive shear stress is the stress condition that causes the one-way consolidation deformation of soil under the adaptive stress state,Using adaptive shear stress to describe the vertical deformation of soil can include the nonlinear characteristics of vertical pressure,Poisson's ratio,compression modulus,K₀ coefficient.Combined with the characteristics and test results of several conventional compression models,it is found that there is a good linear relationship bitweenlg??_v and lgq_z,so,an empirical model of adaptive shear stress q_z=A_z?_vⁿ is established,the model is suitable for the self-adaptive shear stress and vertical strain relationship curve in two stages of the test.In order to verify the reliability of the adaptive shear stress empirical model,taking the remolded saturated loess and the remolded unsaturated loess as the research object and adopting the equal strain loading mode,it is found that the adaptive shear stress empirical model is suitable for different loading methods and clay types,and the reliability of the adaptive shear stress empirical model is verified preliminarily.(3)According to the self-adaptive stress state one-way consolidation test,the quantitative calculation method of the coefficient K₀ in two stages of the test is given respectively.In the stage of loading consolidation,the relationship between the coefficient K₀ and the vertical pressure is established:K₀=(?v-a)/(b?_v),in which the parameters a and b have clear meaning and can be solved by the loading rate and the initial moisture content of soil.When the vertical pressure remains unchanged,three parameter index modelK₀=A_s+B _s·exp(-t/m_s)and five parameter index modelK₀=A_w+B _w·exp(-t/m_w)+C_w·exp(-t/n_w)are established respectively to describe the relationship between the coefficient of earth pressure K₀ and time.Considering that the three parameter index model has few parameters and clear meaning,three parameter index model is recommended.(4)The calculation method of the permeability coefficient in the whole process of the test is put forward,and the permeability model under the condition of fast loading and slow loading is given,which integrates the permeability and consolidation characteristics of the soil;Based on the continuous development characteristics of compression curve in two stages of the test,the compression coefficient of the whole test process can be calculated,and the consolidation coefficient in the whole process of the test is obtained,and the variation of the consolidation coefficient under the condition of fast loading and slow loading is obtained respectively.Based on the non-linear consolidation characteristics of soil,a method of calculating the degree of consolidation in sections is proposed.Strain changing with time is calculated according to the consolidation equation is highly consistent with the test measured.(5)According to the time-dependent characteristics of adaptive shear stress and vertical strain in the consolidation process of adaptive stress state,based on the viscoelastic creep theory,a semi empirical and semi theoretical generalized five element Voigt creep model is established to describe the creep change law of clay.It is found that the relationship curve of adaptive shear stress and time is similar to the creep development law.the vertical strain and time relationship curve calculated according to the adaptive shear stress empirical model,measured in the test and described by the creep model are highly consistent,which shows that the adaptive shear stress empirical model and the creep model are unified.Through the analysis of the proportion of deformation in two stages of the test,it is found that the loading rate affects the proportion of the strain in two stages,but does not affect the final deformation,that is,the final deformation of the one-way consolidation of the soil is not affected by the factors such as stress path,load rate and stress duration.