Investigation And Engineering Application On Shearing-softening Constitutive Relationship Of Rock-concrete Interface

As an important hydraulic structure,concrete dam bears load of gravity,water flow and temperature under normal service condition.Cracks are prone to initiate from the interface between concrete dam and bed rock under stress concentration caused by those load effects,thus damaging the stability of concrete dam.Therefore,it is necessary to study the crack propagation of rock-concrete interface.At the same time,due to the differences of the materials on both sides of the interface and the interfacial crack stress complexity,study of interfacial crack propagation considering composite stress state is of great significance for the overall safety and stability evaluation of the dam.In order to study the crack propagation process of rock-concrete interface under complex stress conditions,the following research work was carried out:(1)Study on fracture characteristics of rock-concrete interface with different roughness18 rock-concrete composite specimens containing half concrete and half rock were used to measure interfacial fracture properties,each measuring 500mm×100mm×100mm.Six kinds of interface roughnesses were prepared by mechanically cutting grooves on the rock surface and then standard three-point bending fracture tests were performed.Interfacial mode Ⅰ fracture toughness was computed with initial cracking load and commercial software ANSYS,and interfacial mode Ⅰ fracture energy was calculated with analytical formula.The experimental results show that with the increase of roughness,the interfacial tensile strength and mode Ⅰ fracture toughness increase continuously,while the mode Ⅰ fracture energy increases first and remains unchanged.(2)Experimental study on shearing-softening constitutive relationship of rock-concrete interfaceIn this part,42 rock-concrete single shear push-out composite specimens were tested,while the size of concrete part was 150mm×150mm×150mm,and the size of rock part was 160mm×50mm×10mm.6 kind of interfacial roughnesses were obtained by grooving and rock-concrete interface was bonded naturally.Rock-concrete interfacial strain data were obtained through the single shear push-out test,and the interfacial shearing-softening constitutive relation model is derived by using differential equations.A standard method for calculating values of the model control point is proposed by establishing the linear relationship between interfacial maximum shear stress and tensile strength and between interfacial mode Ⅱ fracture energy and mode I fracture energy.(3)Numerical study on crack propagation in rock-concrete interfaceNumerical calculation of the crack propagation of four-point shear beam under different mode ratios was performed by ANSYS,combined with interfacial stress intensity factor calculation program,interfacial crack propagation criterion and three kinds of shearing-softening constitutive relationships.The accuracy of shearing-softening constitutive relationship derived in this paper and numerical calculation method were validated by comparing the load-crack opening displacement(P-CMOD)curves obtained from experiment and numerical simulation,independently.(4)Numerical simulation of crack propagation process in dam-bedrock interfaceUsing the numerical method and interfacial constitutive relationship of this paper,the numerical simulation of concrete dam-bedrock interfacial crack propagation process under composite stress is carried out to verify the applicability of this method in the analysis of dam solid model.Meanwhile,the variation patterns of interfacial crack propagation and interfacial stress intensity factors were analyzed.