河谷岩体深层破裂的形成机制与评价方法

Since 80s, deep-seated fractures of valley slopes have been found in several large hydroelectric project explorations. The tensile fractures can be found beyond several ten meters to several hundred meters under the slope surface. They are forming a special fracture system that associated with the factors of geomorphologic condition, lithologic combination, regional tectonic stress field and the dynamic load of earthquake. To study the genetic mechanism and the developing evolution regularity of the deep-seated fractures in rock masses at a river valley, it is important to select the dam site of large hydroelectric project, to prevent the geological hazards, and to analyses the regularity of fractures during the rock masses relaxed under the high confining pressure. The aims of this study are to find the geological environment of the deep-seated fracture development, to show the mechanism of its formation, to probe into the methods of forecasting its probable location in rock masses at a valley, and to found the theoretical basis of the engineering characteristic evaluation and the stability analysis to the rock masses with deep-seated fracture..In the study program, it firstly makes a summary of the existing problems and the evaluation methods during evaluating the mechanical parameters of rock masses. The geological environment and the basic types of deep-seated fracture in slope rock masses are found out basically by geological investigations. The deep-seated fractures forming mechanism of slope rock masses have been opened out by numerical simulation and geological analysis. The methods to forecast the probable part and the deepest distance of developing deep-seated fracture in slope rock masses are discussed. A theoretical system to evaluate the engineering characters of fracture rock masses has been set up preliminarily. The theoretical basis of studying the engineering characters of deep-seated fractures in slope rock masses is established..The deep-seated fractures of slope rock masses have close relationship with the geo-stress field, especially during initial stage of the fracture formation, but it also differs on the different conditions of the rock characters, the rock mass structures as well as the topography. The differences of the valley slope rock mass structure will have different characters of deep-seated fractures. If the rock mass structure is alternate with soft and rigid, the rigid rock layers will slide along the soft interlayer as well as the contact face. The plastic shearing sliding deformation will make high-tension stress in the rigid rock layers. As a result, the deep-fractures takes place from the contact faces to inner rigid rock layers. .The research put forward a new shear-tension fracturing model of the deep river valley rock masses. When initial fractures generated in the deep valley rock masses, forming a belt of tensional fractures, the stresses in the rigid rock masses adjusted along the new boundary, so the secondary shear-tension fracture was generated. The locations of the secondary shear tension fractures were usually among the initial fractures. The results of the research indicated that the deep-fractures were almost equidistant, and the different belt of the fractures formed in different time, they developed along a series of stages. But all the deep-fractures forming mechanism were shear tension formation. According to the energy conservation principle, the research drew the conclusion that the fractures would not develop infinitely. On the case of the new tectonism, the change of the ground water, earthquake and engineering activities, the deep-fractures would aggravate, even develop to landslide. The project also studied the rock burst and surrounding rock mass stability under the high geo-stresses opening..

通过地质分析和数值模拟，查明河谷岩体深层破裂发育的地质环境和基本类型，揭示河谷岩体深层破裂形成的力学机制，探讨河谷岩体深层破裂可能发育部位的预测方法，建立深层破裂岩体的工程特性评价和稳定性分析的理论基础。正确评价河谷岩体深层破裂问题对坝址选择、边坡稳定性评价、防止地质灾害的发生及合理评价河谷岩体应力场等均具有重要意义。..