| The interface between concrete dam and rock foundation is considered to be one of the most important area/region governing the strength and stability of gravity dams. It is one of the potential sites of crack growth which eventually lead to the weakening of mechanical strength and formation of conduits for water to seep through and exert uplift pressure. Yet, not much attention has been paid until recent years on studying interface cracks in general, and the effect of mixed mode loading in particular. Currently, it is assumed that a crack, once initiated, propagates colinearly along the interface of dam and foundation. To the best of author's knowledge, no experiment has been reported confirming this.; In this work, a comprehensive experimental program has been undertaken for carrying out mixed-mode experiments on large scale simulated bimaterial specimens. For this purpose, a biaxial testing machine has been designed and set-up by expanding on an existing servo-hydraulic, one million pounds vertical capacity, uniaxial testing machine. Realistic, combined normal and shear stresses are subjected on large, simulated rock and concrete specimens to evaluate the joint strength and to study the conditions under which the crack would depart from the interface and dip into the rock. In addition, shear tests with confining normal loads were conducted on large bimaterial specimens to obtain the shear properties namely, the angle of internal friction, the cohesion and the mode II fracture energy, that are required in numerical analysis.; For a better understanding of the experimental observations, both linear elastic fracture mechanics (LEFM) and nonlinear fracture mechanics (NLFM) analysis are performed on the mixed mode test specimens. In the LEFM analysis, interface fracture mechanics concepts which consider the oscillatory nature of the singularity at the crack tip, is used. The NLFM analysis is done using the interface crack model developed and implemented into the finite element program MERLIN, by Cervenka. These detailed analysis have guided in analyzing the behavior and obtaining the properties of rock-concrete interface.; Another important material property of the interface that is required in the numerical analysis is the mode I fracture energy. To extract this property, wedge splitting tests were performed on small limestone-concrete specimens.; The response of an interface to seismic excitation is another area that constitutes a weak link in the safety of dams during and after an earthquake. One of the major concerns in the seismic behavior of interfaces and joints is the mechanism of opening and closing of cracks and joints which probably take place continuously, i.e, gradual opening and closing without impact, although some localized impact may occur following joint separation. This is an important issue in the seismic analysis of dams that make use of discrete cracks or joint elements. To solve this problem of crack opening and closure at interfaces, a numerical model is developed and implemented in MERLIN, by improving on an existing algorithm proposed by Ayari. This model makes use of interface elements to simulate cracks and is used in conjunction with fracture mechanics.; Analysis of an existing gravity dam (Bluestone Dam), that has been targeted for major rehabilitation by the U.S. Army Corps of Engineers is done using LEFM and NLFM to demonstrate the applicability of these concepts. These analyses are performed to highlight the effect of the crack dipping into the rock foundation. |
