Propagation Characteristics Of Interface Cracks In Layered Media Under Brazilian Splitting

Layered rock mass which is widely distributed in nature is a kind of complex medium in the field of geotechnical engineering,such as water conservancy and hydropower,road traffic and mining.The deformation and strength of layered rock mass have obvious anisotropic characteristics due to the influence of bedding structural plane,which is an important factor to induce the catastrophic instability of engineering structure.The instability of rock mass is mostly the result of the evolution of internal cracks of different scales,so the propagation characteristics of interface cracks are of great significance to understand the instability mechanism of layered media.In this paper,rock mortar is used to make layered medium to study the propagation mode of interface crack under Brazilian splitting condition;based on fracture mechanics,the distribution law of fracture parameters of interface crack is analyzed;and a numerical calculation model based on insert bond element method is constructed to systematically analyze the propagation and evolution characteristics of interface crack.The main research work is as follows:(1)The experimental study on the mechanism of interface crack growth was carried out by making the rock mortar layered disk specimen with cracks.In this paper,three kinds of deep slotting treatments are carried out on the sandstone surface of the rock mortar layered disk specimen,and three kinds of mortar with different strength and seven kinds of interface loading angles are designed.Based on the load displacement curve,acoustic emission(AE)law and digital image correlation(DIC)data,the failure mode and mechanical properties of the layered disk with interface cracks are analyzed.(2)The distribution of fracture parameters of interface crack is analyzed.The dimensionless stress intensity factor,energy release rate,fracture toughness and modal angle are obtained under different loading angles.The results show that the fracture toughness increases with the increase of interface angle.The dimensionless stress intensity factor,energy release rate and modal angle are related to the elastic modulus ratio,interface crack length and loading angle of rock and mortar.(3)A numerical model of rock mortar interface crack disk is established by using the finite element numerical simulation software ABAQUS.The numerical results are basically consistent with the experimental results.The whole process of interface crack growth is studied by changing the performance parameters,loading angle,material strength ratio and confining pressure.The results show that the interface strength and loading angle have influence on the failure mode and load of the interface crack,while the material strength ratio and confining pressure have great influence on the load.