Theoretical Analysis And Experimental Verification Of Crack Initiation Characteristics Of Plane Cracks With Seepage Pressure

The stability of surrounding rock in underground tunnel excavation is affected by joint fissures in surrounding rock,and usually underground engineering cannot avoid the existence of fissure water.In order to avoid the occurrence of engineering accidents caused by the crack initiation and expansion,it is necessary to study the crack initiation mechanism of the fracture with seepage pressure and the influence of seepage pressure and fracture geometry on the crack initiation characteristics.Only by knowing what kind of state the crack reaches the limit state,it is possible to better select the appropriate construction technology and engineering materials,arrange the engineering process,and then achieve better cost performance on the basis of ensuring the safety of the project.Previous studies on cracks are mostly three-dimensional built-in cracks.The laboratory tests of three-dimensional built-in cracks are difficult to observe the internal development.The numerical simulation studies mostly use discrete element software such as PFC and FLAC 3D.which has poor pre-processing functions and operation speed.Low,limited number of particles and other shortcomings.The research object of this thesis is a representative two-dimensional penetrating crack.The cement mortar specimens prefabricated with cracks are used for laboratory tests,and the crack initiation and expansion process can be visually seen.The test process and tunnel excavation were simulated by GDEM numerical simulation software coupled with finite element and discrete element.GDEM software uses GPU parallel technology,which is fast in calculation,and its numerical calculation method is suitable for simulation of geotechnical and tunnel engineering.The main work of this paper is as follows:(1)Contrasting the fracture criterion,the advantages and disadvantages and application scope of several fracture criteria commonly used in rock mechanics According to the research object,the mechanical model of rock mass fracture is established,and the type ? and ? stress intensity factors of the crack tip are derived according to the state of the fracture force.Based on the characteristics of the research object and the fracture criterion,the Zhou Qunli criterion is used to calculate the crack initiation strength of the prefabricated crack,and the maximum circumferential stress theory is selected to calculate the cracking angle expression of the prefabricated crack.The crack initiation strength after the crack is closed by pressure is deduced.(2)A uniaxial compression test of prefabricated plane cracks with seepage pressure was carried out.The test material is made of rock-like cement mortar material,and a test piece prefabricated with two-dimensional through cracks is poured,and a water injection hole is reserved in the test piece.Influencing factors such as fracture water pressure,prefabricated fracture angle,and crack thickness were controlled,and the crack initiation process was recorded.The stress-strain curve of the test piece was obtained,and the test results were compared with the theoretical analytical solution.The results show that the cracking direction of the prefabricated cracks tends to the original direction of the prefabricated cracks with the increase of the prefabricated crack inclination angle,water pressure and crack thickness.With the increase of water pressure,the crack initiation strength of the crack becomes smaller,that is.the fissure water promotes the cracking of prefabricated crack.(3)Using software Ansys to calculate the stress intensity factor of the crack tip and verify the analytical solution of the stress intensity factor.The software Gmsh was used to model.and the software GDEM was used to si:mulate the crack initiation of the two-dimensional crack with seepage pressure,and the influence of the shape of the prefabricated crack tip crack was discussed based on the simulation results.The software GDEM was used to simulate the stability of surrounding rock in tunnel excavation.The influence of tunnel size,excavation mode,surrounding environment and surrounding rock joint on the stability of surrounding rock was discussed.The existence of joints in surrounding rock caused the deformation and stress of the surrounding rock around the tunnel being excavated increased.