A Micro-macro Model For Creep Failure Under Dynamic Disturbance In Brittle Rocks

In recent years,our demand for energy and mineral resources is still increasing,and with the decrease of shallow resources,mining depth increase imperative.The surrounding rock of deep underground engineering is always in the initial state of high ground stress,and the dynamic disturbance will induce engineering disasters such as rock bursts and deep rock bursts,which seriously threaten the construction safety of deep resources mining.The static creep characteristics of brittle rock under the dynamic disturbance of stress wave is of great practical significance to the evaluation of surrounding rock deformation in deep underground engineering.Dynamic mesoscopic crack damage seriously affects the mechanical behavior of brittle rock in static creep failure.The study on the dynamic characteristics of brittle rock in preloaded stress can provide data reference for further research on the mechanical behavior of brittle rock in creep under the influence of local mesoscopic crack damage caused by the dynamic load.In this paper,the perturbation mechanism of dynamic load on rock creep failure is analyzed,and the influence of dynamic disturbance on the creep characteristics of brittle rock is described based on the theoretical method.A micro and macro-mechanical model which can better reflect the creep failure characteristics of rock caused by dynamic damage is established.The main research work is as follows:(1)Based on the relationship model between microscopic crack growth and stress,crack rate and dynamic fracture toughness,crack rate and strain rate,and strain rate and strain relationship,a microand macro-mechanical model is proposed which can explain brittle rock under dynamic load considering the axial stress and confining pressure of prepressure.The relationship model between crack rate and strain rate is obtained by solving the time derivative of strain-dependent crack length.The strain rate and strain relation model describes the evolution curve of strain rate caused by the dynamic load of prestressed rock.The stressstrain relationship curve of brittle rock under the influence of axial stress and strain rate of preloading is studied,and the rationality of the model is verified by the experimental results.The effects of confining pressure,initial crack size,initial crack Angle and initial crack friction coefficient on the dynamic stress-strain relationship,prestressed crack length,axial strain and dynamic peak strength of prestressed rock are discussed.(2)Based on a proposed macro and micro mechanical model which can explain brittle rock under dynamic load considering axial stress and confining pressure of prepressure.By defining different strain rate-strain relations and crack growth rate strain relations,the rock state subjected to external dynamic disturbance after preloading is approximately described.By comparing the stress-strain curves of different paths,the influences of strain rate and crack growth rate on rock dynamic constitutive are discussed.(3)Based on the relationship model between microscopic crack growth and stress,static crack growth rule,dynamic disturbance damage evolution function,static and dynamic load evolution path function and viscoelastic constitutive model,a micro and macro-mechanical model of creep fracture characteristics of brittle rock under dynamic stress wave disturbance is proposed.The dynamic damage is realized by controlling the number of microcracks in the rock.The model describes the strain time evolution curve of rock under the dynamic disturbance of stress wave and explains the creep failure characteristics of rock under the dynamic disturbance.The strain-time curves of brittle rock under the influence of different stress amplitudes and periods are studied,and the rationality of the model is verified by the experimental results.The effect of dynamic damage variation form,mutation time and mutation quantity on creep failure characteristics of rock is discussed.The effects of stress wave amplitude,period,initial crack Angle,initial crack size and friction coefficient on dynamic and dynamic damage effects and creep failure characteristics of rock are discussed.(4)Based on a proposedmicro and macro-mechanical model of creep fracture characteristics of brittle rocks under dynamic stress wave perturbations,the dynamic damage evolution forms under single multi-cycle stress wave(single continuous cyclic load)and multiple multi-cycle stress wave(multiple continuous cyclic loads)perturbations are studied.The effect of the equivalent mutation times,transition surge and linear increase of dynamic damage on the creep failure characteristics of rock is discussed under a multi-cycle stress wave disturbance.The dynamic damage transition,linear increase and linear coupling increase,and the influence of the relationship between the values of each dynamic damage change on the creep failure characteristics of rock are discussed under the disturbance of multiple and multi-cycle stress waves.