Research On Tensile Damage Mechanism Of Tunnel Rock-sprayed Concrete Interface Based On Laboratory Scale

Infrastructure engineering,especially tunnel engineering,play a pivotal role in the overall development of my country’s economy and the realization of common prosperity.Deep-buried tunnels（DBT）are often buried under high in-situ stress.Ensuring the stability of tunnel surrounding rock and lining support structure in complex geological environment is the prerequisite for tunnel construction and later stable operation.In the complex geological environment,various factors cause variable loads to act on the tunnel support structure.Therefore,it is of far-reaching significance to study the effect of changing loads on the tunnel support structure for the construction of tunnel engineering,the later maintenance and the previous operation.It also has certain reference significance for the later development of intelligent construction and the sustainable development of disciplines.The interface between the surrounding rock and the lining is the weakest part of the entire supporting structure,and is a material similar to rock properties,and its tensile performance is much lower than its compressive performance.Considering the influence of the most unfavorable factors on the supporting structure,laboratory tests,non-destructive testing methods（acoustic emission technology and digital image correlation technology）and numerical simulation mutual verification methods are used to study the influence of load changes on the interface tensile performance.The research contents of this manuscript are as follows:（1）The effect of cyclic loading on the tensile properties of the rock-concrete interface was investigated by laboratory three-point bending tests.Through the tensile softening constitutive relation,the relationship between the three-point bending fracture energy and the interfacial tensile strength of composite members is studied.The composite components are first loaded with pre-peak constant amplitude cyclic loading and then monotonically loaded.The flexural strength,fracture energy and mechanical strength of the obtained components all decrease with the increase of the loading amplitude.Furthermore,it is deduced that the tensile strength of the rock-concrete interface also decreases with the increase of the cycle amplitude.（2）The effect of loading rate on interfacial tensile strength was investigated by direct tensile tests at different loading rates.The same type of rock-concrete interface was loaded with three different loading rates.It is obtained that the interfacial tensile strength increases logarithmically with the increase of the loading rate.The loading rate obtained by extensometer and acoustic emission technology also has an important influence on the ductility and elastic modulus of the interface.（3）Through the discrete element software PFC^3D,the experimental verification of each working condition is carried out.Make up for the missing working conditions of several sets of laboratory tests.At the same time,the numerical simulation results can be mutually verified with the non-destructive testing technology.Capturing the type and development of fractures at the interface greatly improves the regularity and persuasiveness of the test results.（4）The uniaxial compression calibration of concrete,black sandstone and granite materials by the flat joint contact model（FJCM）.Thus,the mutual verification between macroscopic mechanical properties and onlooker parameters is realized.The effectiveness of the iterative process of fitting macro-and meso-mechanical properties is demonstrated.In this paper,based on laboratory tests and numerical simulations,the effect of load changes on the tensile properties and damage mechanism of the rock-concrete interface was investigated.The development law of the internal cracks in the interface of the tunnel surrounding rock and its lining under different loads and the change of the surface displacement field were obtained through non-destructive testing technology.Various scientific research methods and scientific methods are verified with each other,which improves the scientificity and persuasiveness of this thesis.