Research On The Dynamic Behavior Of Soil Based On Mesocopic Simulation By Distinct Distinct Element Method

If one kind of soil condition needs to be kept or soil need to be changed from one kind of condition to the required condition, and the mechanical forces need to be used effectively, the dynamic behavior of soil subjected by external forces need to be understood except for the external forces themselves. The dynamic process and the influencing factors of soil behavior are relevant to many aspects directly, such as the working efficiency of terrain machines and farming tools, the cultivating quality of agriculture and so on. Because the dynamic behaviors of soil under different conditions are very complex, some phenomena, processes and problems can not be explained accurately by using traditional experimental means and study methods. The exact analyses of the varying process and the final appearance of soil behaviors have become the impending problems of soil dynamics in the mechanical field. As one numerical simulating method of analyzing discrete matters, Distinct Element Method (DEM) is very suitable for studying the varying law of the dynamic behavior of soil when the soils produce huge deformations or break up under the external forces. This dissertation is supported by National Natural Science Foundation of China "The simulation of dynamic process on the adhesion interface system between soil and solid"(Grant No. 50175045). Aiming at the complex discrete structure of soil by itself and the complex dynamic behavior of soil, the dynamic process of the mesocopic structure in the interior of soil was simulated by using DEM software PFC2D to open out the varying law of the macroscopic appearances from the exterior of soil based on model experiment under different surface shapes and cutting angles of the bulldozing plates. In this study, soil particle was the studying unit and DEM was the basic theory. Water in the soil exists in the interstices of soil particles in a pendular state. In this state, water is present in soil in the form of discrete liquid bridges. According to the liquid bridge model, the discrete liquid bridges in the interstices of soil particles produce 'static'capillary forces and 'dynamic'viscous forces between soil particles. By sufficiently considering the cohesive effects of these forces between soil particles, the parallel bonds were used in the mechanical model of particles by DEM firstly, to represent the turning restrict of the liquid bridges between soil particles. The non-linear mechanical model of soil particle was established based on the above significant factor. The mechanics model includes contact, slippage and cohesion between soil particles as well as the high collision energy dissipation caused by viscous damp between the soil particles. Therefore, the mechanical model provides the foundation for simulating the dynamic behavior of soil accurately. The performing equation is: [ ]F = ?? F c ?? + ?? F pb ?? +?? Fd?? Where, [F] is the synthetical action between soil particles; [Fc] is the contact resultant forces between soil particles; [Fpb] is the collateral constraint resultant force; [Fd] is the viscous damp resultant force. The two kinds of soil in different water content were selected as the experimental soils, and the bulldozing plates with smooth and bionic wavelike surfaces were designed as the soil-touching part in this paper. The new experimental method were introduced, and one piezoelectric three-axis force sensor of Type 9327A with high precision and one numeral camera with sequential photographing functions were used. Based the special requirement of dynamic experiment of soil, the testing system for analyzing the dynamic behavior of soil was established using the above equipments. From the qualitative and the quantitative points, the dynamic varying processes of dry soil and cohesive soil ahead the bulldozing plate were analyzed under different cutting angles and different surface shapes through experiment in soil bin. As for dry soil, when the cutting angle of the plate is increased, the cutting action of the plate decreases and the driving action increases, therefore, the piled amount, the piled angle, the undulating scope and the undulated frequency of dry soil ahead of theplate increase. The dynamic varying process is apparently influenced by the surface shape of the plate. When the dynamic behavior of dry soil ahead of the bionic plate are compared with that ahead of the smooth plate, the piled amount and the undulated frequency increase, the undulated scope decreases. The phenomena are resulted from the following reasons: the tiny vibration for the dry soil vertical to the surface of the plate and the forces of friction for the dry soil parallel to the plate by the wavelike surface of the bionic plate, the influence on the direction of dry soil on the surface by the curvature of the wavelike surface, the decrease of the relative displacements among dry soil clumps by the convex part of the wavelike surface. As for cohesive soil, when the cutting angle of the plate is increased, the driving action of the plate increases, therefore, the squeezed degree increases, the beginning cracks near the knife blade form earlier and the spreading velocities of the cracks increase. For the surface shape, the piled amount and the squeezed degree increase ahead of the bionic plate, the beginning cracks near the knife blade arise later, the cracks is tiny and irregular, and the spreading velocities of the cracks decrease. These phenomena are resulted from the following reasons: the break of cohesion between cohesive soil clumps and the resistance to the moving cohesive soil clumps by the convex and the concave parts of the wavelike surface of the bionic plate. The accurate analyses on the varying process of the macroscopic configuration of dry soil and cohesive soil in the experiment provide the reliable foundation for opening out the varying law of the dynamic behavior of soil through simulating the mesoscopic structure in the interior of soil by DEM. The creating process of the simulated soil by DEM was studied. In this creating process, the produce of the beginning soil particle aggregate, the accomplishment of the contacting balance state and the gravitational steady state of soil particle aggregate, the elimination of the "floating"particles and the creation of the final specimen with parallel bonds and viscous damps are the main steps. The simulated soil by DEM, which were created by this creating process, can reflect the mechanical characteristic of real soil. The simulated smooth plate and the bionic one are designed by using standard wall and general wall logic. According to the study emphases of the dynamic behavior of dry soil and that of the cohesive soil by DEM, the mesocopic simulating systems of soil dynamic behavior by DEM were established respectively.By comparing the experimental analyses and the simulated ones by DEM of dry soil and cohesive soil under different working conditions, the results indicated that the dynamic simulated results by DEM can accurately reproduce the typical variation of the exterior configuration of soil and the whole varying trend of the dynamic forces acting on the plate in the experiment. Concretely, the external configuration of dry soil and the dynamic forces acting on the plate by dry soil in the experiment can be more accurately simulated by DEM. Although the dynamic forces acting on the plate by cohesive soil have some errors by DEM compared to those in the experiment, the whole varying trend are similar. The varying law of the macroscopic configuration of dry soil and cohesive soil were opened out by the varying process of the mesocopic simulated soil firstly, including the dynamic configuration, the velocity field, the displacement field, the contact force field, the parallel-bond field and the parallel-bond force field. As for dry soil, when the cutting angle of the plate is increased, the scope of "disturbed vacuum"in the velocity field decrease gradually, the whole velocity of soil particles increase, and the varying scope of the relative displacements increases. For the surface shape of the plate, the forces of friction between soil particles and the wavelike surface of the plate increase, the relative velocities of soil particle aggregate and the undulated scope of soil layers ahead the bionic plate decrease. These phenomena are resulted from the action on the soil particles by the wavelike surface. At the same time, the convex parts and the soil particles stopped in the concave parts form an irregular mutual surface; the irregularity of the surface makes the forces of friction between soil particles and the surface increase, which reduces the returning slide of soil particles along the surface. The variation of the mesocopic structure in the interior of dry soil by DEM has opened out the varying law of the macroscopic configuration of dry soil ahead the plate, such as deposit, doming, climbing of dry soil. As for cohesive soil, the agglomerated and the broken processes of cohesive soil clumps were simulated firstly. At the same time, when the cutting angle is increased, the cohesive soil clumps become smaller; the contact forces among soil particles in the cohesive soil clumps become bigger and the varying scope of these contact forces becomes larger; the broken and disappearing scope of the parallel bonds and the...