Three Dimensional Liquid Bridge Contact Model And Discrete Element Numerical Simulation Study Of Unsaturated Soil

With the construction of high rock dams and ultra-high buildings,the requirements in engineering for the capacity of resisting cracks are increasing.If the tensile strength of soil is not considered,great wastes will be caused in the process of construction.Therefore,it is of great significance to study the tensile characteristics of unsaturated soil under the triaxial state.The mechanics properties of soil in triaxial state is scarcely concerned due to the limitation of testing technology and equipment in laboratory,hence many scholars mainly study the tensile properties of soil in the case of uniaxial stretching.Based on the above basic facts,this paper intends to study the tensile characteristics of unsaturated soil based on the discrete element numerical analysis software MatDEM(Matrix Discrete Element Method) and PFC(Particle Flow Code).The research results are mainly divided into the following three points.(1)In terms of the development of geotechnical engineering,it is difficult to carry out the triaxial tensile shear test of unsaturated soil.Based on the relationship between complex uniaxial tensile strength and water content under different void ratio,the numerical simulation is conducted by MatDEM.The complex uniaxial tensile strength of unsaturated soil is considered to the intermediate variables,and the relationship between the grain-scale parameters of DEM and the macro parameter water content of unsaturated soil is calibrated,then the triaxial tensile shear model of unsaturated soil is set up by MatDEM.Based on the above relationship,the numerical simulation of DEM triaxial tensile shear sample under different water content is carried out,and the triaxial tensile shear strength,failure mode of displacement field and energy field are analyzed under different water content.Finally,the tensile damage properties of unsaturated soil is discussed from the point of view of the macroscopic failure mode and the grain-scale damage mechanism under the condition of the uniaxial state.(2)In the existing DEM model for the contact model of unsaturated soil,there is no model that can consider the capillary water between two adjacent particles separated from a relative distance.The force of capillary water between particles will disappear to zero when the particles separate in the existing model.The interparticle cementation and capillary water cementation are not taken into account.In order to simulate capillary water pressure of unsaturated material more realistically,based on PFC5.0 user defined module and using C++programming language and QT graphical user interface(GUI) application development framework,a liquid bridge contact model considered the capillary water force and cementation is established.Using the executable DLL files,this model can be run in the PFC3D and PFC2D contact successfully.(3)Based on the three-dimensional liquid bridge contact model(the newly-modified lsy liquid bridge contact model),the uniaxial tensile test of unsaturated material is simulated by PFC.The influence of the grain-scale parameters in the uniaxial tensile properties of unsaturated material is analyzed from the aspects of the tensile strength of the sample,velocity field,displacement field,contact force chain,and the contact destructor.Finally the applicability of the model in simulating the unsaturated material get further verified.