| In the process of construction of deep hard rock tunnel,due to the unloading action of surrounding rock,it is easy to form the fracture of the slabbing approximately parallel to the excavation face.Slabbing failure usually accompanied by destruction of the phenomenon of rock burst,The damage degree of slabbing region has an important influence on the probability and severity of rock burst,but there are still few researches on fracture characteristics of slabbing failure.Therefore,the rock of slabbing failure in deep hard rock tunnel is taken as the research object.By means of laboratory test and numerical simulation,after determining the reasonable water cement ratio of the sample material,the mechanical properties and failure characteristics of specimens under different fracture conditions and different constraint conditions are analyzed and studied.The main research results are as follows:(1)Based on the actual stress state of the deep tunnel surrounding rock,a three lateral restraint device is designed to make the mechanical boundary condition of the test block more close to the engineering practice in the loading test.based on the ratio test,Based on the proportioning test,the tensile and compressive ratio of eight different water cement ratio samples were measured by means of alpha high strength gypsum respectively.Finally,the water cement ratio of the sample was determined to be 1:3.(2)Under the two lateral confinement conditions,the fracture of rock plate,rock avalanche or spalling of rock sheet appear in the free surface of the specimen.However,the failure shape of the specimen under three sides constraint condition is closer to the reality than the one side constraint condition.The failure of the three sides restrained specimens is mainly concentrated on the failure of the free surface and the expansion or formation of cracks in the prefabricated cracks.In the loading test,there are three modes of tensile failure,shear failure and mixed shear,among which tensile failure is the main mode.In addition to the free surface,the other three sides of the specimen may appear tensile or rock spalling.The location of the new fracture is rather random,not concentrated in the area near the free surface,and the failure of the specimen is mainly tensile failure.(3)Through the tests of specimens under different fracture characteristics and restraint modes,The results show that the bearing capacity and peak strain of the test block under the three lateral restraint mode are higher than the loading capacity and peak value of the test block under one side constraint mode.With the increase of crack length,number of cracks,thickness of fracture and density of fracture,the peak strength and secant modulus of specimens decrease gradually.Finally,the acoustic emission characteristics and the strain field change of the specimen are analyzed.(4)Based on strain softening model,numerical simulation of test specimen is carried out.Because of the deficiency of the scheme in the laboratory test,the numerical method is used to study the fracture thickness and the crack spacing.The regularity of the results is consistent with the indoor test results,and the reliability of the indoor test results is verified. |
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