Study On Interface Crack Propagation Of Layered Rock Mass

In this thesis,rock similar materials are used to make layered rock specimens with prefabricated cracks.Three-point bending test,static uniaxial compression test,SHPB dynamic impact test and digital image correlation technology(DIC)are used to study the static mechanical properties,dynamic mechanical properties,failure modes,fracture strength and energy dissipation of layered rock.The main research contents and conclusions are as follows :(1)The specimens used in the three-point bending test are composed of cement mortar with two mix ratios of a and b.In this experiment,two groups of A and B layered rock specimens with lithology interface offset ratios of 0,0.2,0.4,0.6 and 0.8 were set up to carry out three-point bending test,and the crack propagation process was observed by digital image correlation technology(DIC).The results show that the crack propagation direction of group A deflects to the middle of the specimen,and the deflection angle gradually increases with the increase of offset.The cracks of group B specimens propagated along the lithology interface during the propagation process,and almost no deflection occurred.After the offset reaches a certain value,both groups A and B fractured from the middle of the specimen,and the cracks were almost parallel to the lithologic interface.The fracture toughness and fracture energy of group B specimens are greater than those of group A specimens,but the variation of fracture toughness and fracture energy of group A and group B specimens increases with the increase of offset,which shows that in the process of specimen fracture,the location of lithologic interface will affect the fracture mode,fracture toughness and fracture energy of the specimens,but the influence of offset on the fracture toughness and fracture energy of the two groups of specimens is consistent.(2)Static load test The micro-controlled electronic universal testing machine combined with digital image correlation technology(DIC)method was used to study the physical and mechanical properties,failure mode and energy dissipation law of plate-type layered rock.The research shows that the peak strain of the specimen will be significantly affected when the area of the material(a material)with lower strength reaches at least 37.5%.When the area ratio of type a material reaches more than 50%,its influence on the strength of the specimen is intensified.When the inclination angle of the lithologic interface is in the range of 0 °～15 °,the failure mode of the specimen is mainly splitting tensile failure,and the tensile shear is less.When the inclination angle is 30 °～60 °,the failure mode of the specimen is mainly tensile shear crack.When the inclination angle is 60 °～75 °,the failure mode of the specimen is mainly slip failure along the lithologic interface.When the inclination angle is 75 °～90 °,the failure mode of the specimen is mainly crushing failure along the lithologic interface.With the increase of the proportion of a-type materials in group A,the accumulation rate of strain energy inside the specimen becomes slower,which causes the strain of the specimen to become larger.(3)Dynamic load test The SHPB system combined with digital image correlation technology(DIC)test method was used to study the physical and mechanical characteristics,failure mode and energy dissipation law of tabular layered rock.The results show that the lithology interface of group A specimens is parallel to the loading direction.The existence of prefabricated cracks increases the types of cracks on the surface of the specimens and increases the degree of fragmentation of the specimens,but there are fewer penetrating cracks on the surface of the specimens.The peak strain of group B specimens decreases first and then increases with the increase of the inclination angle of the lithologic interface.When the dip angle of the lithologic interface is small,the b area is a weak area,and when the dip angle is large,the a area is a weak area;when the loading pressure is small(0.08 MPa),the optimal rock breaking effect can be achieved when the lithology interface angle is 15 °～30 °.When the loading pressure is higher(0.085,0.09 MPa),the rock interface inclination angle of0°～45° is more sufficient,and the ratio of dissipated energy is higher.Therefore,loading in this angle range can obtain better rock breaking effect.