| The roadside backfilling wall next to the gob-side entry retaining is affected by repeated disturbances of the roof subsidence of the gob and the advancement of the working face in the lower section,and its own stability is of great significance for ensuring the control effect of the surrounding rock of the roadway along the gob.This paper adopts the methods of theoretical analysis,numerical simulation,and laboratory mechanics experiment.The stress distribution of the backfilling wall along the gob-side entry retaining under the influence of mining is studied.The nonlinear ultrasonic dynamic theory is used to determine the ultrasonic characteristic parameters during the uniaxial loading of the roadside backfilling concrete,which characterizes the degradation process of the roadside backfilling concrete bearing capacity.A multi-parameter fusion prediction model has been established to realize the prediction of the bearing capacity of the roadside backfilling concrete.The main research results are as follows:(1)The stress distribution of the roadside backfilling wall beside the roadway is affected by the breakage of the roof of the working face,and the vertical stress of the roadside backfilling is distributed asymmetrically under the influence of repeated mining,which is the largest in the middle of the roadside backfilling wall,second on the side of the goaf,and smallest on the side of the roadway.The vertical stress on each position generally increases monotonously with the advancement of the working face,and then gradually stabilizes at a higher stress level.(2)The characteristics of deformation and failure and the law of energy dissipation during uniaxial loading of roadside backfilling concrete are analyzed.According to the extreme points of elastic strain energy rate and dissipated energy rate,the characteristic values of crack closure stress and damage stress of the roadside backfilling concrete under uniaxial loading are determined.The damage evolution process of the roadside backfilling concrete specimens is divided into four stages:the initial damage stage,the stable development stage of the damage,the accelerated development stage of the damage,and the failure stage.(3)The ultrasonic time-frequency signal during the uniaxial loading process of the roadside backfilling filling concrete is extracted,and the damage factor,attenuation coefficient,main frequency variation coefficient,and nonlinear coefficient are defined.The characteristic parameter curves show obvious phased characteristics with the loading process.The crack closure stress and the damage stress of the uniaxial loading of roadside backfilling filling concrete are comprehensively determined from the characteristic change stage,and the characterization of the degradation process of the bearing capacity of the roadside backfilling concrete under uniaxial loading is realized.(4)The regression support vector machine algorithm model is constructed by the principal component analysis method and the characteristic parameters(damage factor,attenuation coefficient,main frequency variation coefficient,and nonlinear coefficient)of multi-source ultrasonic waves has good generalization,and the error of the prediction results is between 0.14%and 12.19%,the accurate prediction of the loading state and the degradation degree of the bearing capacity of the roadside backfilling concrete is realized. |
