Experimental Study On Mixed-mode Fracture Between Concrete And Rock

Many concrete structures are built on rock foundation. Concrete dam on rock foundation, for example, the interface between the rock foundation and concrete dam is a weak link.The dam heel generally works with cracks, and the crack propagation can reduce the shear strength of the dam, destroy the grout curtain and the drainage system. And that will result in dam leak and damage the integrity of the dam. Especially in the earthquake case, the large tensile stress may lead to the rapid propagation of existing cracks, and this will threaten the safety of the dam. Depth study of the fracture properties of the interface between the concrete dam and rock foundation is of great significance to ensure the safety of high dam and large reservoirs.Cracks in the dam heel may propagate along the dam foundation surface or split into the rock foundation. Dam safety evaluation made common to assume that the cracks propagate along the interface. But studies have shown that the cracks inclining into rock foundation are more dangerous. Only an accurate determination of the dam heel crack propagation can make a reliable assessment of the status of the dam. When using a fracture mechanics method for solving this problem, the stress field of interface crack appears multiple singularity and oscillation. The stress intensity factors for type I and type II couple with each other. And now it’s not appropriate to use the formulas for solving crack tip and displacement field of the homogeneous materials.This paper is divided into four chapters. The first chapter elaborates on basic theory of interface mechanics, the research background of the paper, the significance of the issue and related contents of the research. The second chapter describes the content of the preparation before the test. This includes early test program design, the loading device of the test as well as a variety of sensors. It also states the production, conservation and processing of four-point shear beam specimens. Finally, specific experimental steps are stated. In third chapter, cracking profiles of all specimens observed in the test are shown first, then characteristic loads of specimens and displacement of crack mouth are sorted out. In chapter four, based on the maximum loads shown in last chapter, displacement of the interface crack flanges can be calculated by the finite element program ANSYS. Then critical stress intensity factors and critical stain energy release rates are obtained based on the theory of interface mechanics. Finally, two criteria are proposed based on these two parameters. They are the interface elliptic failure criterion and interfacial fracture energy criterion, and they can provide relevant reference for fracture analysis of concrete structures on rock foundation.