Research On Damage-Fracture Mechanism Of Unstable Rock

Unstable rock is a serious disaster in the Three Gorges Reservoir. Up to now, research on unstable rock is still weak and controlling technique is stayed at conceptional design stage. During the systemic research on unstable rock, the developing mechanism is a key problem. With the endowment of visiting professor fund item "Research on developing mechanism of unstable rock" from the Ministry of Education PR.C, the paper studied the damage-fracture mechanism of unstable rock in the Thee Gorges Reservoir generally. The conclusions are listed in the following:1). Main structural surface in unstable rock is the key area controlling the stability of unstable rock. There are three stress states at the tip of crack: pulling, pulling-shearing and compacting-shearing. To the first type fall unstable rock, the mechanism of main crack is pulling, to the second type fall unstable rock and topple unstable rock is pulling-shearing, and to the slide unstable rock is compacting-shearing. By incomplete statistical, the main mechanism is pulling and pulling-shearing mechanism.2). At the damage zone of unstable rock, the main shapes of damage include micro-hole, micro-crack, micro shearing zone, micro unconformable face, particle boundary and weaken zone. The process of the damage growth at the tip of crack in rock is the process of those flaws propagating, connecting and developing.3). The paper establishes the damage consititutive relation and damage evolvement equation of unstable rock. The author takes Taibaiyan unstable rock as an example and calculates the initial damage ratio is equal to 0.028, the present damage ratio is 0.05 and the extended damage ratio is 0.457.4). The author deduces the stress intensity factor calculating formula for every type unstable rock, and establish the method how to solve the size of damage zone and damage coefficient considering the affect of damage to stress intensity factor with damage coefficient. Using ADINA software, the author gains the stress intensity factor of damage-fracture, To Taibaiyan unstable rock, the damage-fracture critical value(plane strain fracture resilience) is 1.796 Mpam^1/2 .5). The author chooses W25 unstable rock in Nanpo to analysis the damage-fracture stress intensity factor under every condition and every loads combination. The result match well the present norm and reality.6). Using creep damage theory, the author studies the development and stability time of micro-chain mechanism and gains that the chain mechanism growth periodicity of Taibaiyan unstable rock by itself. The periodicity is 820 year long. When the connection ratio is more than 50%, the unstable rock is during the mid-old stage of chain mechanism and should be paid more attention to control engineering.h). The author studies the falling stage with fracture mechanics and catatrophe theory, and then establishes mutation model and equation.The damage-fracture mechanism and chain mechanism are new knowledge to the research on unstable rock. That simplifying the analysis model and analysis method is important for engineering utility. And they should serve the engineering basing on data from practice.