Cyclic Load-unload Experiment Study On Granite

In the process of engineering geological investigation of a hydropower station, there is a rather special kind of deep deformation and fracture geological phenomena, which restricts seriously the engineering design, construction and operation. So that is need to be studied and solved. On the basis of wholly understanding tothe evolution ofthe Jinsha River, design a loading and unloading rock mechanics test, then,study the formation mechanism the deep deformation and fracture geological phenomena from the three aspects:the geological environment background、rock mechanics experiments、theoretical analysis of damage. Attain the following main results.1.Summarized the general development characteristics by systemic studying the deep deformation and fracture geological phenomena.(1)These can be three categories: light,middling,stronglackrock.(2)The development degree increases with elevation increasing and the horizontal depth is 75m～180m.(3)These formed along the steep inclination of techonic structure that are parallel with the slope.2.M.J.Heap and S.Vinciguerra(2008) adequately fitted each set of unloading and subsequent loading curves for stress-cycle experiments,it used the same way to reveal the following rule:(1)Rock damage include stress-induced microcracking and cyclic fatigue microcracking.(2) Granite under cyclic loading suffer damage more easily under high confining pressure than other pressure condition.(3)The rockin saturation state under cyclic loading suffer damage more easily than in saturation statein dry state.3.Through analyzing of the elastic properties and energy evolution law of granite in condition of natural drying and saturated, the results show that(1) granit under coupling effect of high ground stress and groundwater suffer reduction of strength in the process of valley development.(2) ability of stored energy decline more easily in the condtion of saturated and high confining pressures will make it violent, it show that the dissipated energy will induce deformation failure of granit.4.Establish the statistic damage theoretical modelbased on Weibull: The model data argee well with the experimental data and can reflects well the damage evolution process of rock under three dimensional stress condition.The rock in dry state is suitable more to Griffith energy criterion than in saturation state.5. Thebasic formation conditionof the deep deformation and fracture include the material basis and loading conditions. Material basisare lithology and rock mass structure,while, oading conditions are high in-situ stress and special unloading ways.The rapid down-cutting of the river caused rock high elastic strain energy release of the geological conditionsand further unload rebound of slope rock.