Elastobrittle Discretized Virtual Internal Bond Model And Its Application In Dynamic Fracture Simulation Of Rock

Discretized virtual internal bond(DVIB)model is a newly developed lattice model.Its discrete structure consists of unit bond cells.Each unit bond cell can represent a mineral grain of rock.Thus it can represent the characteristics of the mesostructure of rock.In this thesis,the rock is firstly modeled with DVIB and then explore the law of spalling fracture induced by stress-wave and the dynamic failure process of rock induced by blast through the numerical simulation.Rock is a typical elastobrittle material.In order to represent this mechanical characteristic,an elastobrittle Stillinger-Weber potential is proposed.It holds that that the bond energy is not only related to its stretch,but also related to the bond angles subtended with other bonds.When its deformation exceeds a critical value,the bond breaks.Before bond breaks,it is assumed linear elastic.While the mechanical resistance of bond angle is determined by two factors.The first one is the bond angle variation.When the variation exceeds a certain value,then the bond angle will lose mechanical resistance.The mechanical resistance and the variation of bond angle are linear relationship before losing the mechanical resistance.Since a bond angle is subtended by two bonds,its mechanical resistance is also subjected to the status of the two bonds.As long as one of them breaks,the bond angle is failed.The elastobrittle SW potential function is used to describe the energy of a unit bond cell,then the elastobrittle property and different Poisson ratio of rock could be reproduced.The numerical simulation results show that the DVIB model based on elastobrittle SW potential could simulate the stress wave propagation effectively and the spalling fracture process induced by stress wave under impact loading.The results of numerical simulation further show that the elastic modulus of rock has a great influence on spalling fracture.The obvious spalling phenomenon will be induced in hard rock,but not induced in the soft rock.Furthermore,the influence of the heterogeneity of rock on the spalling fracture induced by stress wave is minor.Usually,the surrounding rock of tunnel contains numerous joints in the shallow layer.To explore the effect of these shallow-buried joints on the spalling fracture for surrounding rock,the elastobrittle DVIB is used to simulate the spalling fracture behavior of rock mass with shallow joints.Take the spalling fracture location of the rock without shallow joints as the reference location.The simulation results show that when the shallow parallel joints are inside the reference location,it has almost no effect on the spalling process.But when they are outside the reference position,they have great influence on the spalling process.Subjected to the stress wave,the outside parallel joints will be opened and propagate.Simultaneously,a spalling fracture initiates at the reference location.The extended parallel joint coalesce with the initiated spalling fracture.When the shallow joints are inclined with the reference location,their effects depends on the relative location to the reference position.When they are located inside the reference location,their effect is significant.Not only the inclined joints propagate,but the spalling fracture also initiates at the reference location.However,when the inclined joints are outside the reference location,they have little effect on the spalling fracture.The hyperelasticity of crack tip material governs the dynamic fracture.In order to represent the hyperelasticity of rock crack tips,the elastobrittle SW potential is modified.Before bond breaks,its behavior is described by a hyperelasticity potential while when its deformation exceeds a critical value,the bond breaks.This model is used to simulate the dynamic fracture process of rock subjected to blast.To characterize the gas pressure,the JWL equation is employed.The numerical simulation results demonstrate that this model can simulate the fracture process of rock under blast.The in-situ stress has a significant effect on fracture propagation direction.The crack always tends to propagate along the maximum in-situ stress direction.And this tendency increases with the increasing the in-situ stress difference.This thesis presents a new lattice approach for the dynamic fracture simulation of rock and some valuable references for the practical engineering,such as rock blasting,landslide and water split of rock.