| The rectangular roadway is widely used as an underground transportation hub,which is not easy to be developed and replaced by the rectangular roadway.However,the roof stability and shoulder stress concentration of the roadway have always been important factors perplexing the engineering safety.In fact,rock mass is the carrier for the construction and construction of underground roadway.The mechanical properties and stability of rock mass around the roadway determine the stability of the roadway itself,and the stability of rock mass is jointly determined by its mechanical properties and fracture joints.Therefore,this thesis studies a variety of different combinations of rock properties and fractures with different dip angles of roadway roof.Firstly,a simplified model of the mechanical effect of roadway roof under load is constructed and calculated;Then,based on the mechanical analysis,the indoor test is carried out,and the similar samples of roadway roof with different cracks and different lithology are constructed by means of 3D printing and concrete pouring.The three-point load test is carried out on the samples,and the DIC digital speckle technology is used for displacement monitoring;Finally,the discrete element PFC numerical method is used to construct the same numerical model as the indoor test,and the three-point load test is carried out.Combined with the failure forms and mechanical analysis of the specimens in three ways,the results show that:(1)through the study of different crack dip angles,three different rock like combinations show the law that the peak load decreases with the increase of crack angle under three-point bending loading.When the prefabricated crack is less than 90 °,its fracture angle presents obtuse angle phenomenon,and when it is equal to 90 °,its fracture angle presents acute angle phenomenon.(2)The difference of strength between specimens with cracks and intact specimens is studied through indoor three-point loading and numerical simulation.The maximum peak loads of YRR intact specimens,30 ° and 90 ° measured indoors are 7.27 KN,1.89 KN and1.07 KN.Compared with the intact specimens,the strength of 30 ° and 90 ° specimens is reduced by 74% and 85% respectively,and the simulated values are 69% and 81% respectively.Both data show that the existence of crack a great impact on the stability of specimens.(3)By comparing the rocks of different lithologic combinations,the peak loads of R-R-Y(soft and hard),R-Y-R(soft,hard and soft)and Y-R-R(hard,soft and soft)in the complete test piece are 5.70 KN,6.62 KN and 7.27 KN.When the component content is the same,different lithologic combinations will lead to the change of the strength of the test piece.When the position of hard rock is close to the bottom of the test piece,the strength of the test piece is higher,that is,the integrity of the roadway roof surface is good and the stability is better when the strength is high;(4)By comparing different combination types with the same prefabricated crack,the strength of Y-RR,R-R-Y and R-Y-R specimens with 45 ° crack is 1.41 KN,4.92 KN and 5.12 KN respectively,which is 84.5%,13.7% and 22.7% lower than that of the complete specimen.It can be seen that when the prefabricated crack is in hard rock,the strength of the specimen decreases greatly,which greatly reduces its stability.At the same time,it can be judged that hard rock stratum also plays a key role in the stability of roadway roof.(5)According to the failure diagram of the three-point loading sample,it is obtained that the fracture length varies with the angle of the prefabricated crack.When it is less than 90 °,the separated layer is partially separated,and when it is equal to90 °,the layer is completely separated from the layer,indicating that the stability is the worst when the prefabricated crack is 90 °. |
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