Study On Creep Characteristics Of Weak Interlayer Under Periodic Disturbance

At present,a large number of open pit mines in southwest China use blasting mining as the main mining method.During the process of blasting mining,the rock mass in the mining area is subjected to varying degrees of disturbance.Under such repeated disturbance,the creep effect of weak intercalation significantly changes,its strength parameters continue to decrease,and the slope continues to produce creep deformation along the weak intercalation.When the damage and deformation accumulation of the weak intercalation reaches a certain degree,the slope will likely undergo overall sliding deformation and failure along the weak intercalation.Therefore,the long-term repeated impact of blasting disturbance on the weak intercalation will pose a serious threat to the stability of high slopes in open pit mining.Therefore,it is necessary to study the creep characteristics of the weak intercalation under the influence of blasting disturbance.This paper takes the Permian carbonaceous shale weak intercalation widely existing in southwest China as the research object,uses the rock impact shear creep test system to simulate the long-term repeated disturbance caused by mining blasting operations with periodic perturbation(In this paper,the role of periodic perturbation mainly revolves around the number of consecutive perturbations.The number of consecutive perturbations is taken as a cycle,and the interval between each disturbance within the perturbation cycle does not exceed 5 seconds),and conducts shear creep tests of weak intercalation under different normal stress functions and different perturbation periods,revealing the shear creep characteristics of weak intercalation under periodic perturbation.Based on the creep characteristics,a new shear creep model of weak intercalation considering periodic perturbation is further constructed.The main research results are as follows:(1)Based on the analysis of shear creep test results,it is concluded that when periodic perturbation is applied consistently,the instantaneous shear strain increases with the increase of normal stress at the same shear stress level,and the instantaneous shear strain gradually decreases with the increase of shear stress level under the same normal stress;When the normal stress is applied consistently,the instantaneous shear strain gradually decreases with the increase of the shear stress level without disturbance.After periodic perturbation is applied,a sudden increase in instantaneous shear strain occurs in the weak interlayer,and the sudden increase in instantaneous shear strain gradually increases with the extension of the perturbation period.(2)During the decelerating creep stage and the steady state creep stage,the creep rate of the weak intercalated layer is characterized as first decreasing,then gradually tending to zero.After entering the accelerated creep stage,the creep rate suddenly increases,and the weak intercalated layer undergoes shear failure within a short period of time,reflecting the sharp nature of its accelerated creep failure.(3)The periodic perturbation effect is mainly applied to simulate the repeated perturbation effect generated after actual mine blasting operations,which causes the carbon and argillaceous cement structures inside the weak interlayer to be subjected to multiple impacts and damage.The original microcracks inside the weak interlayer continue to extend and expand,and new microcracks continue to sprout,resulting in further aggravation of its damage level and continuous reduction of its original integrity.With the continuous extension of the disturbance period,the internal cracks of the weak intercalation are further damaged and deteriorated,and the strength continues to decrease.Finally,shear failure occurs under the last level of shear stress,indicating that periodic disturbance has a significant impact on the mechanical properties of the weak intercalation.(4)By introducing a perturbation sudden deformation element and improving Kelvin and traditional viscoplastic bodies,a periodic perturbation shear creep model capable of describing the instantaneous elastic strain,nonlinear viscoelastic strain,and nonlinear viscoplastic strain of weak intercalations under periodic perturbation is established.Based on the experimental data of cyclic disturbed shear creep of weak intercalations,the correctness and applicability of the established creep model were verified using Levenberg-Marquardt nonlinear least square method,and the model parameters were determined,indicating that the cyclic disturbed shear creep model of weak intercalations can better depict the nonlinear characteristics of the three stages of creep.