Study On The Law Of Pore Water Movement In The Loess Zone Under The Disturbance Of Loading And Unloading

In engineering construction,foundation pit excavation,foundation treatment,slope protection,and mineral resource mining activities all involve the deformation and seepage coupling problems of rock and soil under loading and unloading.In the early studies of unsaturated zones,the two-phase motion of water and gas in the unsaturated zone was usually simplified to single-phase water flow,and the deformation of solids was ignored,and only the movement of liquid phase was considered.With the progress and development of research,when considering the migration law of pore fluid in unsaturated zone under loading and unloading,people began to consider the unidirectional effect of solid phase deformation on pore size,or the pore water pressure and pore pressure caused by seepage.Changes in the force of the soil skeleton to clarify the two-way influence mechanism between the stress,strain and seepage of the soil.This topic is not only an important topic that scholars in the hydrogeology field are working on,but also the main topic of this article,in order to provide a scientific reference for production and construction.In this paper,loess is selected as the research object to carry out research on the fluid-solid coupling of unsaturated soils.From the two aspects of unsaturated soil deformation and liquid phase seepage,the governing equations,constitutive relations and boundary conditions are sorted out,the coupling relationship between the two is analyzed,and the soil stress field and flow under different loads and precipitation excitations are set.The simulation experiment of the field,draws the following conclusions:1.Analyzed the fluid-solid coupling mechanism of unsaturated loess,explained the influence mechanism of the state variable change of the flow field on the physical properties of the solid skeleton and the influence of the state variable change of the stress field on the liquid-solid mutual physical properties related to liquid phase migration mechanism.The relationship between residual moisture content,saturated moisture content,soil-water characteristic curve parameters and stress/deformation experience,as well as physical parameters such as Young's modulus,bulk modulus and ultimate deviator stress in the Duncan-Chang model,and the moisture content of unsaturated loess are given.Empirical relationship.2.The stress and strain of unsaturated loess is directly related to the size of the load.Among them,the change of deformation and void ratio has hysteresis,and it is related to the duration of the load.The principal stress has a linear relationship with the buried depth,and the deformation and void ratio have a nonlinear relationship with the buried depth.The load affects the seepage process by affecting the physical properties of the liquid-solid mutual state.In the simulated load range and model test conditions,the larger the load value,the faster the pressure head develops toward positive pressure,and the water content develops toward saturated water content.The speed is also faster.And there is a hysteresis in the changes of the pressure head profile and the water cut profile.3.The decrease of the load will cause the rebound deformation of the soil,which is mainly manifested as the decrease of the deformation and the increase of the void ratio.Its impact on seepage is twofold.On the one hand,the diameter of the seepage channel in the soil increases and the resistance decreases.On the other hand,the saturation of the liquid phase in the soil under the same initial water content and different pressures decreases,and the connectivity of the pore water under unsaturated conditions becomes weak.4.By analyzing the changes of solid phase principal stress,deformation,void ratio,liquid pressure head and water content under the excitation of precipitation and load,it can be known that the principal stress has nothing to do with the precipitation intensity,and the increase of precipitation intensity will weaken the physical and mechanical properties of the soil skeleton.,Which leads to an increase in the deformation of the soil skeleton and a decrease in the void ratio under the same load conditions.Under the condition of increasing precipitation intensity,the reasons for the acceleration of the change rate of pressure head and water content in soil should also include the effect of loading on the physical properties of the liquid-solid interaction.5.When the precipitation intensity duration curve is first increasing and then decreasing.At the later stage of the precipitation process,the pressure head and water content of the upper part of the soil decrease after the precipitation intensity is small or stopped.This is due to the fact that the upper boundary supply water is less than the downward discharge water.of.The change of seepage state also affects the stress field through the change of pore water pressure.As the pore water pressure decreases,the stress of the soil skeleton increases and the deformation increases.