Study On Mechanical Properties Of Rock-like Samples With A Prefabricated Crack Under Bolt Reinforcement

The existence of natural fracture in the state of natural occurrence is relatively common.Because of the discontinuity,heterogeneity and anisotropy of the cracks in various rock engineering,which change the integrity and stability of geotechnical engineering,the cracks in fractureed rock expand and link up under the influence of the surrounding forces,forming a large area of instability and even engineering collapse,causing a huge life Loss of life,safety and property.The practice of many geotechnical engineering shows that the rockbolt reinforcement method can effectively improve the safety and stability of rock engineering.In view of the wide application of bolt support technology in all kinds of civil engineering reinforcement,it is a method that can effectively play the excellent bearing capacity of rock mass engineering and has less interference to geotechnical engineering itself.Therefore,it is necessary to study the effect of various reinforcement methods including bolt reinforcement on the crack prevention of fractureed rock mass.On the basis of learning from the experience of previous studies,this paper studies the subject by combining indoor tests of different reinforcement methods of fractureed rock mass and numerical simulation of particle flow.It mainly carried out the following work:(1)More than 40 kinds of fracture samples under different working conditions,including different fracture obliquity,different anchorage angle,different anchorage position,different anchorage length,bolt reinforcement and lateral rigid constraint,were poured by using the high-precision engraving acrylic plate mold and the ratio materials determined by the measurement of basic mechanical parameters.Design and use an experimental device which can add lateral rigid constraint to the sample,which can effectively limit the horizontal lateral displacement of the sample.Use a data acquisition instrument to detect the lateral constraint fixture to ensure the effectiveness of the lateral constraint in the experimental process.(2)MTS816 test system was used to load more than 40 kinds of fracture specimens under different working conditions,including different node inclination Angle,different anchorage Angle,different anchorage position,different anchorage length,bolt reinforcement,lateral rigidity constraint,etc.During the experiment,digital photography was used to monitor the change of horizontal displacement field on the surface of the specimen and acoustic emission monitoring system was used to measure the actual situation In the process of testing,the evolution process of internal fracture with time and strain is studied.The mechanical characteristics,the law of crack evolution and the effect of different reinforcement methods on crack development and evolution of fracture specimen with simple dip angle are studied synthetically.The results show that the peak stress and strain of simple fracture specimenincrease with the increase of fracture inclination,the value of elastic modulus fluctuates slightly,but the general regularity is the same,the final failure mode of fracture inclination from small to large gradually changes from tensile splitting shear mixed failure to tensile splitting failure and even the final pure tensile failure mode.The strength of fracture specimen is optimized by bolt reinforcement and rigid lateral restraint.The optimization effect of limiting lateral displacement of fracture specimen is better than that of the former,and the phenomenon of post peak reinforcement and residual deformation are more obvious.Compared with bolt reinforcement,lateral restraint fundamentally changes the ultimate failure state of simple fracture specimen.Different anchorage angle,anchorage length and anchorage reinforcement position can effectively limit the crack developed from the expansion of prefabricated fracture stage and effectively extend the final failure time of fracture specimen,but can not prevent the crack initiation of the dominant crack and completely change the final failure mode of the specimen.(3)A 3D numerical simulation model of PFC particle flow was established,and the parameters of the model were calibrated according to the results and rules of laboratory tests.The results are verified by the numerical simulation according to the indoor test scheme,and further experimental research is carried out.The results of numerical simulation show that the instantaneous crack growth is more concentrated and the cumulative number of fractures is more.However,it is more obvious that it is difficult to form an effective shear tensile crack for the fracture specimen with limited lateral displacement.However,the total number of fractures is higher than that of single fracture and bolt anchored fracture.(4)In numerical simulation,the lateral rigidity constraint changes the displacement direction of the micro particles in the prefabricated fracture.When the fracture inclination is small,the final failure displacement of the sample is symmetrical distribution from the prefabricated fracture,and the particle movement collision is more obvious in the middle of the sample.The parameters of lms-4,including peak strength and modulus of elasticity,which limit the displacement of three sides of the specimen,are improved to varying degrees.The final failure mode has a very obvious trend of displacement from prefabricated fracture to free face.