Effect Of Particle Scale On Deformation And Effect Of Pore Sacle On Seepage And Consolidation

Soil is the most extensive engineering material in nature.In order to ensure the safety and stability of engineering,it is important to master the mechanical properties of soil.However,because of the complex material composition and variable microscopic structure,it is difficlut to master the mechanical properties accurately.As a result,although some geotechnical engineering is designed "carefully",serious engineering problems or even engineering safety accidents happen very often.The complexity of soil mechanical properties derives from the interaction mechanism between particles and the pore scale characteristics and their evolution.The interaction between particles is mainly realized by the physicochemical effect on the interface,such as interparticle friction and extrusion,adsorption of particle on water and gas,cementation of clay particles and colloidal particles on sand.That is,the interaction property is closely related to the particle scale.Therefore,the mechanical property of soil presents a scale effect of particle.Soil deformation is usually accompanied with pore compression and seepage.Pore compression leads to the soil skeleton damage,aggregated particles breakage and adjustment of grain arrangement position,as well as macropore “obliteration” and micropore “initiation”,resulting in that the consolidation deformation presents a scale effect of pore.Soil seepage characteristic is significantly affected by the physicochemical effect between particle and fluid,which is closely related to the pore scale.With decreasing scale of pore,the effect gradually becomes more significant,resulting in that the seepage presents a scale effect of pore.In this paper,based on the internal mechanism of the above effect,we establish some theory and give analysis of them.The main research work and results are as follows:(1)With different stress/strain state,the effect of particle scale on the mechanical properties of soil is different,such as,the direct shear states and triaxial states.The particle scale effect under direct shear states is theoretically analyzed based on the “shear flow around” and the interaction between matrix and reinforced particles.Morever,the difference of particle scale effects between direct shear state and triaxial state is explained reasonably.(2)Based on the multiscale cell model,a multiscale constitutive relation of soil was derived by using the relationship between different scale levels and the energy equilibrium law.In addition,the stress and the couple stress was coupled by introducing a dimensional equilibrium parameter,and then a characteristic length parameter was obtained to represent the intrinsic characteristics of the soil.(3)Based on the multiscale model,a multiscale mohr-coulomb criterion including meso characteristic parameters was derived by using equivalent inclusion theory.And then,the yield curves of soil with the different reinforced particle contents were demonstrated.In addition,a material matrix is derived by introducing the relative rotational gradient and intrinsic scale,and then a finite element program is developed to analyze the stress localization,strain localization and scale effect of particles.(4)A one-dimensional(1D)nonlinear consolidation equation was reformulated based on the property relationships related to pore evolution,and the nonmonotonic change in the consolidation coefficient with an increase in the effective stress was described.In addition,a series of calculation curves for the dissipation of excess pore pressure,consolidation compression deformation and the change of average consolidation degree were given by using the present theory,and the complex consolidation characteristics of soil under different consolidation loads were explained reasonably.(5)Based on the friction mechanism of solid-liquid interface,the boundary slip model related to hydraulic gradient was established by considering the bond strength of pore liquids.And then,the permeability theory was derived by using Poisson equation,thermodynamic equilibrium condition and Navier-Stokes equation for low permeability soil.Finally,the influence mechanism of seepage characteristic at micro-nano pores was analyzed by using the permeability theory.