Experimental And Numerical Study On Crack Propagation In Rock-Concrete Interface

The cracks at the interface of rock and concrete have a great influence on the security of concrete structures based on rock foundation. Due to the heterogeneity, nonlinear and anisotropy of the rock and concrete, along with the variation influence of outside load and environment temperature, crack at the interface can extend either along the interface or bend towards concrete or rock foundation. This uncertainty not only threatens the structure’s normal use safety but also makes a possible tipping fracture. Therefore studying the fracture properties and crack propagation of the rock-concrete interface is of great significance.Based on the interfacial fracture mechanics, experimental and numerical studies are carried out in this dissertation. Experimental studies include three-point bending experiment to acquire fracture parameters and four-point shearing beam to investigate the effects of loading way, ratio of initial crack length to beam height and offset of pre-crack on crack propagation trajectory. In the study of numerical simulation, the interface crack propagation under four-point shearing condition is simulated, which showed a reasonable agreement with the experimental results, detailed researches are as follows:(1) Experimental study on fracture properties of natural interfaceThe rock-concrete composite specimen which size is 100mm×100mm×500mm, is made by casting concrete on natural rock section which is obtained by three-point bending test of notched rock specimen. The composite specimens with five different ratios of initial crack length to beam height(ao/D) were tested under three-point bending, cracking load and peak load is obtained and the fracture toughness and fracture energy of interface are calculated. The results show that, both cracking load and peak load decrease with the increase of α0/D. In addition, the fracture toughness and fracture energy have no obvious change with the variation of α0/D, which indicates that fracture toughness and fracture energy are material constants independent of the size of specimens.(2) Experimental study on crack propagation of natural interfaceThis part of experiment is conducted with four-point shearing beam specimens, whose size are 100mm×100mm×500mm and is made of rock and concrete. Modes for pre-crack propagation under four-point shearing loading condition are obtained by control three variables, that is loading way, ratio of initial crack length to beam height and offset of pre-crack. The relationship between modal ratio and modes of crack propagation is studied.The result is that crack will be more likely propagate toward rock part with the increase of modal ratio.(3) Numerical simulation of interface crack propagation under four-point shearing conditionBased on interface fracture mechanics theory, the stress intensity factor at a tip of crack can be calculated and a crack propagation criterion was proposed, which can determine the crack propagation in different materials. Combined with the tension softening constitutive relationship gotten in previous study, the interface crack propagation under four-point shearing condition can be simulated, which showed a reasonable agreement with the experimental results. It indicates that the proposed method can be used to determine the interface crack propagation mode subject to mixed mode I-II stress filed. Meanwhile, the whole fracture process can be simulated and these fracture parameters including initial cracking load, ultimate load and crack propagation length can be calculated numerically if tensile strength, fracture energy and the initial fracture toughness of interface, concrete and rock are obtained.