A Study On Damage And Failure Mechanism Of High-stress Rock Triggered By Slight Cyclic Disturbance

When excavation is carried out under high stress environment,the external disturbance will change the stress field of the rock,which may lead to potential engineering damage such as large deformation and large displacement of the free surfaces of the engineering surrounding rock,and even cause instability damage,rockburst and other engineering disasters.However,the existing researches usually did not take the effects of low-frequency slight disturbances,such as mechanical rock breaking vibration,remote blasting vibration,heavy machine vibration,on the mechanical properties of rock into consideration.In fact,the mechanism of rock damage and failure induced by coupling effects of slight cyclic disturbance and high stress is very complicated,and common understanding has not yet been formed.Therefore,finding out the mechanisms of high-stress rock triggered by slight cyclic disturbance may be conducive to solving many stability problems in rock engineering.In order to clarify mechanical response and mechanism of how slight cyclic disturbance induces deformation,damage and failure of rock,a series of "slight cyclic disturbance+uniaxial/triaixal high stress" coupling loading tests are carried out on the red sandstone rock samples by using the rock electro-hydraulic servo triaxial test system.Then,a new damage constitutive equation of red sandstone is established,and the mechanism of slight cyclic disturbance leading to damage and sudden failure of rock samples is explained.Finally,a numerical method of rock damage indeced by slight cyclic disturbance is proposed.By embedded the numerical method into RFPA2D software,a new software named RFPA2D-Cycle is developed and the physical tests are numerically reproduced by employing it.The main work in this study can be summarized as follow:(1)a series of loading tests of rock damage and failure induced by slight cyclic disturbance under high stress conditions are carried out,effects of frequency,amplitude of quasi-dynamic disturbance and confining pressure on the stressstrain curves,the number of cycles and the time that lasts from beginning of dynamic disturbance applying to failure of rock samples are analyzed,and mechanical responses and failure modes of rock samples after tests are clarified;(2)three physical quantities(residual strain,average dynamic axial stiffness and maximum strain)are chosen to define damage variables that can be used to characterize the progressive damage process of rock induced by slight cyclic disturbance under high stress conditions,resulting that the variation trends of damage variables are in good agreement with the actual damage and degradation process induced by slight cyclic disturbance loads;(3)a new constitutive model of rock is established based on the assumption that the damage of representative elemental volume obeys Weibull distribution and Hoek-Brown strength criterion in rock samples and on the characteristic parameters such as stress peak,modulus of elasticity and poisson's ratio;(4)cusp catastrophe theory is introduced into mechanical model of the system of rock sample&test machine by referring previous research results,and the instantaneous conditions of rock failure are deduced,which explain the phonominon of rock failure under high stress induced by slight cyclic disturbance in a mathematical sense;(5)a new numerical method for simulating progressive damage of rock indeced by cyclic disturbance is established based on the basic theories of RFPA2D software,which takes heterogeneity of rock materials into consideration,and employs statistical damage and the phase change theory.By employing this new method,RFPA2D-Cycle code is developed,and its validity is verified.