Experiment Study On Fracture Property And Tension Softening Constitutive Relationship Of Rock-Concrete Interface

Concrete dam building on rock foundation may face the potential risk from the cracking of rock-concrete interface, which easily lead to instability of the dam and induce further other security incidents. Under the action of load, water flow and temperature change, it is more possible for crack to initiate and propagate at the weak interface between concrete dam and bedrock. Usually, the crack propagates along the foundation surface quickly, until the concrete dam bursts finally. Therefore, the crack in the dam heel can be regarded as being between rock and concrete interface. However, due to the heterogeneity and anisotropy of the rock and concrete, it is more complex for the study on interfacial crack propagation. Therefore, studying the fracture properties and crack propagation of the rock-concrete interface are of great significance to the safety of the dam. Based on the above mentioned, the relative researches are carried out in this dissertation as follows:(1) Experimental investigation on the fracture properties of artificial notch interfaceIn this study, the composite specimens made by half rock and half concrete were tested to measure the fracture properties of their interfaces. Firstly, three-point bending tests were conducted on the specimens with the size of500×100×100mm3. Meanwhile, the axial tension test and splitting test were carried out. The results show that, for the rock-concrete interface, the strength, fracture toughness and fracture energy are increased significantly with the increase of interfacial roughness. Therefore, the bending and cracking resistance of the interface can be enhanced by increasing the interfacial roughness.(2) Experimental investigation on the fracture properties of natural interfaceThe natural rock sections which obtained by three-point bending test of notched rock specimens, are combined with concrete by casting on the other side. The rock-concrete composite specimens with5different initial crack-depth ratios (a0/D), whose sizes are500×100×100mm3, were tested under three-point bending. The results show that, both cracking load and peak load decrease with the increase of a0/D. However, the flexural strength increases with the increment of a0/D. In addition, the fracture toughness and fracture energy don’t change obviously with variation of a0/D, which indicates that, the fracture toughness and fracture energy are material constants independent of a0/D.(3) Determination of rock-concrete interfacial tension softening constitutive relationship and its application in numerical simulation Based on the load-displacement curves measured in three-point bending tests, the energy dissipation can be derived through modified J-integral method. The energy balance during crack propagation can be established, i.e. the energy dissipation is equal to the energy caused by fictitious cohesive force acting on fracture process zone. Then, the tension softening constitutive relationship of rock-concrete interface can be determined. The proposed softening constitutive relationship in this dissertation was applied on the numerical simulation of interface crack propagation by introducing I mode crack propagation criterion. Upon the comparison with the experimental results, the numerical ones show good agreement on the complete P-CMOD curves. Therefore, it can be verified that the interface softening constitutive relationship derived in this dissertation is appropriate to describe the nonlinear characteristic of rock-concrete interface.