| Perilous rock collapse is a common geological hazard in limestone area,which is different from perilous rock collapse in red beds area,it has the characteristics of large collapse scale,complex failure mode and easy disintegration of collapse rock,which leads to large damage range and serious disaster consequences.The limestone area of rock body levels and other types of structural surface is developed,by all types of surface structure of interlaced cutting,the integrity of rock mass is poor,with typical masonry structure characteristics.Under the condition of present collapse failure mode,the disintegration effect is easily produced during the collapse process,therefore studying on the disintegration of the limestone area class type rock block masonry structure collapse,and actively exploring the related mechanism of collapse block disintegration in the processt,and finding the mechanics criterion for the collapse and disintegration of the perilous rock in the limestone area are of great significance to the risk assessment of rock collapse in critical rock areas.In this paper,taken the Zhen Zi Yan Rockfall in Jinfo mountain of Chongqing Nanchuan as an example,based on the generalization of geological model,the theory of wave dynamics and fracture mechanics is applied to analyze the collapse process of dangerous rock,the propagation rule of impact stress fluctuation in multilayer structure is revealed.(1)In this paper,taken the perilous rock in limestone area as masonry structure model,based on the nonlinear displacement discontinuity characteristics when the shock wave propagates at the surface of the structure,the nonlinear displacement discontinuities model of the structural plane is established in the time domain by the nonlinear method.At the same time,based on the nonlinear model established,the wave equation of the impact stress wave propagating in the nonlinear normal deformation structure surface is derived in the time domain by using the stress-strain relationship between the structures,and the propagation rule of impact stress fluctuation in multilayer structure is revealed.(2)Based on fracture mechanics and wave mechanics,it is found that the propagation direction of impact stress wave in dangerous rock is nearly perpendicular to the dynamic propagation direction of cracks,the reflected wave and the incident wave are superimposed on the crack surface,the stress field perpendicular to the crack surface is a dynamic change of tension and pressure,and the crack propagation has the characteristics of “wave” dynamic evolution.(3)The disintegration of the masonry structure is the result of the interaction between the stress wave and the structural plane.The tensile stress at the crack will increase the crack growth.By solving the tensile stress of the crack when the impact stress wave is vertically incident to the crack at the structure surface,the expression of the stress intensity factor at the crack tip under the action of the impact stress wave is established.(4)From the perspective of energy,perilous rock impact is accompanied by a change of energy,mainly shown that the gravitational potential energy is transformed into elastic potential energy,kinetic energy and surface energy.When the elastic strain released by the crack expansion is greater than the surface energy required to establish a new surface in the crack,the crack will expand itself.In this paper,the energy determination criterion for the fracture of structural face of masonry structure is proposed.(5)By using 3DEC numerical simulation software,the simulation of masonry structure perilous rock collapse is carried out,the simulation results coincide with the process of perilous rock collapse.By extracting the displacement and velocity of the monitoring points at different heights of the dangerous rock mass,it is found that the critical rock has several characteristics of continuous impact disintegration in the process of collapse. |
