Numerical Study of Damage Localization and Failure Evolution of Rock and Soil

Author:Zhang Xiaojiang

Supervisor:Zhou Xiaoping


Degree Year:2018





In order to study the non-continuous problems and overcome the shortcomings of traditional numerical methods,such as discrete element method dependences on the size of the unit(or particle)diameter and finite element method is of mesh distortion.Therefore,a meshless numerical method is proposed in this paper,which is named as general particle dynamics method(GDP),and is applied to study local damage and gradual failure of rock-soil mass.The main research contents and conclusions are conclued as followings:(1)The GPD method is used to study the local damage and failure process of rock samples with uniaxial and triaxial compression.When the particle meets the Hoke-Brown strength criterion,it is considered as the dead particle,which is considered as failure and without affect on surrounding particles.When the load continues to increase and the number of dead particles increases,the macroscopic damage area of the rock sample are marked by these particles.Compared with the experimental results obtained by uniaxial compressive,the conclusion is obtained as follows: the GPD algorithm can effectively study the failure process of brittle materials.Meanwhile,the triaxial compression test of rock sample is simulated,and the influence of intermediate principal stress on local damage area,rock peak strength and rock ultimate failure mode is analyzed by using the GPD method.(2)The GPD is adopted to study the stability of soil slope with self-weight loading.The left-right boundary is set as the free-slip boundary through the ghost particles,the bottom is set as the fixed boundary through the virtual particles.If the influence domain of any particle is intersection with the boundary wall particles,the boundary particle is generated as a ghost particles boundary particles at the same position which corresponding to the any particle,the variables are the same as the corresponding real particles except of speed.That is to say,the tangential velocity of ghost is same with the real particles and the normal velocity of ghost is the opposite of the real particle.The fixed boundary of the bottom is fixed with three rows of virtual particles,whose velocity is set as zero.The simulation results show that the plastic equivalent strain of the soil slope is developed by the local strain and becomes the strain localization zone through the whole slope,then a critical slip surface is formed.It is proved that GPD method is a good tool to study the deformation of soil slope through the comparison of the finite element simulation results.(3)In order to further optimize the GPD algorithm and save calculation time.The virtual bond model is proposed and introduced into the GPD method,which is called as the virtual bond general particle dynamic method(VB-GPD).It is assumed that the interaction between particles are connected by the bond,namely virtual bonds,the Drucker-Prager strength criterion is choosed to determine whether the stress on a bond meet the strength criterion.When the stress on bond meets the Drucker-Prager criterion,the bond is in state of plastic.With the increase of stress,the number of plastic bond increases,and the plastic zone is determined by the non-associative flow rule.The clay is simulated by VB-GPD method under uniaxial compression,it is concluded that soil sample plastic strain localization develops and becomes the strain localization band until versed in the soil sample,the failure of soil sample is formed and the bearing capacity is lost.The strain-stress relationship of soil sample under the uniaxial compression is analyzed,it is verified that the VB-GDP method can well study the plastic deformation.Finally,the VB-GPD is applied to the simulation of homogeneous soil slope and analyzed its stability.The formation process of the critical sliding surface and safety factor of soil slope are obtained by the numerical simulation.The same finite element model is established to compare the critical sliding surface,the safety factor and the ultimate failure mode,we can conclude that the VB-GPD can effectively simulate the plastic deformation failure.(4)In order to analyze the impact of the cracks and joints on the stability of rock slope,this paper analyzes the stability of rock slope with prefabricated flaws by using the VB-GDP model.Some numerical models are established with different cracks arraies.The simulation results analyze the process of crack initiation,development and coalesces,and variety types of crack connection modes are obtained.Because the strength reduction method cannot be applied in the particle method,as for the particle method,there is no non-convergent solution for particle method.Therefore,a method of calculation method of safety factor is proposed in this paper which is based on gravity increase method.The results show that VB-GPD is feasible to analyze the deformation and failure of brittle materials,and provides a new and deeper method for studying the flawed rock slope.