| Guizhou Province is a typical inland karst mountainous province and one of the provinces with the most serious geological disasters in China.Among them,rock mass collapse disasters are particularly developed.In recent years,many large rock mass collapse disasters have occurred in Guizhou Province,which seriously threaten the safety of people’s lives and property.Compared with landslides and other disasters with slow displacement and deformation,collapse is more hidden and sudden.Conventional deformation monitoring methods are difficult to accurately monitor and warn.Based on this,this paper uses acoustic emission as the main monitoring method,supplemented by strain displacement monitoring to carry out indoor and outdoor related experiments,and studies the acoustic signal evolution of the fracturing rock mass collapse incubation process under different bedding angles.The results are as follows:(1)Three-point bending(NSCB)test of straight fractures with half-disk is carried out for layered limestone samples with different bedding dip angles,and the acoustic evolution of limestone with different bedding dip angles is studied.The results show that the crack propagation of limestone is significantly affected by bedding.When the angle between bedding limestone and fracture is 0°,90°,pure mode Ⅰ crack will be produced,and when the angle is 15°,30°,45°,60°,75°,mixed mode Ⅰ-Ⅱ crack will be produced;Different bedding directions cause the difference of fracture strength of specimens,and the tensile strength presents an "M"-shaped change trend;Using acoustic emission location technology,the crack propagation of layered rock mass is visually characterized,and three types of acoustic emission evolution are further studied: stable type increases first,then stable type increases sharply.(2)The results of scanning electron microscope and three-dimensional laser scanning test show that,due to the heterogeneity and anisotropy of minerals in limestone,the more the micro-cracks are blocked from passing through the plane during compression and shear,the greater the tensile strength of the specimen is,and the greater the roughness of the fracture surface after the specimen is Based on digital image correlation(DIC),the typical displacement field and strain field evolution of fracture propagation in layered limestone are studied.The law of crack propagation velocity and acoustic emission strain response of limestone with different bedding angles is explored.The results show that the acoustic evolution of crack propagation at different angles is controlled by bedding dip angle,but it can provide effective precursor information.(3)The Abaqus finite element software was used to simulate the three-point bending fracture process of the straight slit half-disk of the layered limestone,and the crack evolution characteristics of the layered limestone at different angles were analyzed.The extended finite element simulation fracture is consistent with the mechanical test results.The results show that the deflection of cracks at different bedding angles is caused by the deflection of stress field before crack propagation.(4)In order to understand the characteristics of acoustic signals induced by crack development in rock mass fracture process,an experiment on the disposition of brittle rock similar materials was carried out.Uniaxial compression experiment combined with acoustic emission monitoring was used to study the influence of brittleness of similar materials with different material proportions,cementing materials and particle size pairs.The micro-pore structure and cementation characteristics of materials with different proportions were analyzed by NMR and SEM scanning,and it was found that the brittleness of similar materials was closely related to the pore structure,porosity and cementation of samples.The brittleness of similar materials is determined by the total amount of products produced by cementing materials and the encapsulation of aggregates.Ideal materials similar to brittle rock deformation and failure and acoustic emission characteristics are obtained.Meanwhile,water-soft materials are prepared.(5)The similar model test of rock mass collapse with different bedding dip angle under natural gradual change in laboratory shows that the angle between fracture and bedding has significant influence on rock mass collapse.When there is an angle between fracture and bedding,the shear-slip slip changes with bedding angle.Compared with the rock mass collapse with 0 bedding dip angle,the slip time of 45 collapse increases obviously,but there is no slip stage in 90 model;Through acoustic emission localization technology,it is found that the model crack propagates in divergent mode at different angles and 0 degrees,and the crack aggregation increases gradually at 45 degrees,and the acoustic emission damage accumulates linearly near the crack end face at 90 degrees;The obvious stage characteristics of the model are the initial fracture stage Ⅰ,the stable fracture stage Ⅱ,the accelerated fracture propagation stage Ⅲ and the sliding stage Ⅳ;Shear cracks in rock mass will increase suddenly before collapse,and change from tension to tension-shear interaction.(6)The model test evolution and acoustic characteristics of tensile fracture rock mass with different bedding dip angles under natural gradual change condition are studied The fracture model of bedding rock with different angles shows obvious stage characteristics.The sudden increase of shear crack near the accelerated crack propagation stage can be used as the precursor information of rock mass collapse;Compared with the cumulative impact number of AE,the abrupt drop of AE R value and B value appears before the rock mass instability,and the abrupt drop point is obviously ahead of the abrupt increase point of the cumulative impact number.In the model test,the B value can be advanced by 63 seconds at the earliest,and the R value can be advanced by 23.7 minutes.The abrupt drop of B value near the previous time can be used as an effective monitoring and early warning of rock mass instability. |
