The evolution of damage around an opening in non-persistent jointed Rock Mass

This study investigates experimentally the time dependent damage around an opening in nonpersistent jointed rock masses. Dimensionless analysis was used for designing the physical modeling simulation. The experimental simulation technique was verified by comparing a real case study at Tai Koo MTR station in Hong Kong. Using this verified simulation technique; the jointed specimens were modeled by using a modeling material of mixture of plaster and water. To study the failure process around the opening, loading is applied until reaching a certain level and then an opening was drilled at the center of the specimen to simulate tunnel excavation. The whole failure process was observed. After the opening being drilled, cracks initiated from the tips of joints and propagated towards to the opening. Compressive cracks occurred subsequently at the sides of the opening. The growth rate of the cracks is slow at the early stage but increases at the later stage. With the observed growth rate of crack, the damage evolution around the opening can be predicted.