عنوان مقاله [English]
According to statistics, internal erosion and piping have been known as the main causes of the destruction of earth and rock-fill dam. In earth dams, hydraulic fracturing and internal erosion are two interdependent phenomena. Hydraulic fracturing causes expansion of the cracks. The flow of water in cracks causes the leaching of soil, materials and internal erosion occurs.The Bidwaz dam is an earth and rock-fill dam. About seven and a half years after the start of the first impounding, a subsidence appeared on the upstream face of the dam body. This dam is located in a narrow valley; therefore, hydraulic fracturing and internal erosion are proposed as one of the main causes of subsidence.Using the concepts of fracture mechanics is one of the prediction methods in hydraulic fracturing. Fracture mechanics is the field of mechanics concerned with the study of the crack propagation in materials. Fracture toughness modes I and II are two important parameters of materials in fracture mechanics, which can be determined by the method provided in ASTM E399.In this study, through 3-point and 4-point bending tests, the tensile strength, mode I and mode II fracture toughness of core's soil at different moisture contents are evaluated. Due to the low tensile strength of the soil, the direction of load is perpendicular to that of weight to reduce the influence of the weight. The ability to perform experiments is provided by making some changes in direct shear apparatus.Moisture content is the most important factor affecting the tensile strength and fracture toughness of soil. Experiments have been conducted with different moisture contents to evaluate the effect of this parameter. The results show that based on the moisture content, soils can be divided into three categories: 1. Brittle, 2. Semi-brittle, and 3. Elastic-Plastic. Increasing the moisture content reduces tensile strength and increases flexibility.In general, fracture toughness of mode 1 is obtained to be more than that of mode 2. Therefore, the probability of crack expansion with tensile mechanism is less than shear mechanism. At the end, based on the results of laboratory tests, mode I and II interaction diagram has been plotted as a fracture criterion at different moisture contents.