Study On The Mechanical Properties Of The Interface Between Tunnel Surrounding Rock And Shotcrete Layer

Shotcrete is widely used for the support of tunnels and underground engineering,as it not only provides sealing and protection for the support surface but also forms an integral and synergistic bearing system with the support surface.Good interfacial bonding performance is the precondition for shotcrete to play its supporting role.Due to the difference of material properties on both sides of the interface and the influence of supporting interface properties,sprayed concrete support often leads to peeling failure due to insufficient interlayer adhesion.In this thesis,rock is used as surrounding rock material to study the mechanical properties of tunnel surrounding rock-shotcrete interlayer interface.By preparing rock-shotcrete specimens with different rock and interfacial properties,the interfacial shear and interfacial tension tests are carried out.The interfacial bonding properties and interfacial failure patterns are analyzed by orthogonal test and digital image processing method.Finally,the interfacial failure patterns are verified by numerical simulation and test.The main research content and conclusions are as follows.(1)Three different rock-shotcrete specimens were tested in shear and tension,and the influence of rock properties on interfacial bonding performance was analyzed.The shear and tension properties of rock-shotcrete interfacial were compared and analyzed.The results show that the rock mineral composition has a great influence on the interfacial bonding performance of rock-shotcrete.When the mineral composition is similar,the rock strength is positively related to the interfacial bonding strength,but the rock with high modulus of elasticity,high strength and compactness have poor interfacial ductility and high interfacial breakage brittleness.The shear resistance of rock-shotcrete interface is better than that of interfacial tension,and the brittleness of interfacial tension failure is greater.(2)The design influencing factors were three-factor three-level orthogonal experiments of roughness,humidity and degree of contamination of interface,and the interfacial shear and interfacial tensile tests were carried out on rock-shotcrete specimens with different interface properties,and the experimental results were analyzed by orthogonal test analysis method.The results show that the interfacial bonding properties are positively related to the roughness and interface humidity and negatively related to the degree of interface contamination.The relationship between strength and weakness of influence on interfacial bonding performance is roughness > interfacial humidity >degree of contamination.At low roughness level,the hydrophobic interface deteriorates the interfacial tensile properties seriously.(3)The failure interface morphology of rock-shotcrete with different interface properties was analyzed by digital image processing technology.The results show that during shear failure,the interface is bitten and the groove is filled with concrete.When tensile failure occurs,the interface is "pulled out" and the concrete part in the tank is pulled out.With the increase of interfacial concrete residue,the interfacial failure mode changes from D1 to D3.(4)ABAQUS finite element software was used to simulate the interfacial bonding failure behavior based on the cohesion model and compare with the experimental results.The results show that the bilinear cohesion model can be used to simulate the bond failure behavior of rock-shotcrete interface,which is in good agreement with the test results.