In-Situ Stress Measurement In Nuclear Waste Disposal Sites Preselected Area

Radioactive nuclear waste have three features:radioactivity, radiation hazards, heat release. In addition, it is hazardous, difficult to transport, store, degrade, therefore, dealing with nuclear waste have the double feature of necessity and difficulty, the safe disposal of nuclear waste has become a barrier to nuclear technology development.The most rational way to disposal nuclear waste is geological method, geological disposal process for waste isolation ultimately depends on the natural barrier to complete. Nuclear waste repository tectonic stability, mechanical stability of the rock determine the effectiveness of the nuclear waste repository natural barrier.In-situ stress is perturbations stress that existed in Stratum and unaffected by engineering, it is the fundamental forces caused deformation and destruction of underground works. As an important aspect of rock mechanics, in-situ stress is a very important issue in the process of underground laboratories and repository siting, design, construction and operation, which is indispensable and important in various stages of research. For example, in the excavation of high-level radioactive waste repository, only mastered the in-situ stress conditions of deep rock project area, can we carry out reasonable design works, long-term stability analysis is under the premise of known in-situ stress after excavation of engineering surrounding rock for geological disposal, thereby revealing the crustal stress state and the role of law plays an important role for the study and solve high-level radioactive waste repository construction and other major engineering geological issues.This paper based on in-situ stress measurement project for nuclear waste disposal site Aqishan preselected area, Yamansu-Tianhu preselected area, Beishan preselected area and Alashan preselected area and treat these four area as the study area, based on stress measurement data in the study area, combined with the results of numerical simulation of four pre-selected area, according to the seismic data and geological fault activity data of preselected area, situ stress state and the tectonic stress field of each preselected area were analyzed and discussed, we main obtain the following understanding:1. The horizontal stress of four preselected area increase linearly with depth showed an increasing trend, the stress gradient with depth values in descending order are Yamansu-Tianhu preselected area, Beishan preselected area, Alashan preselected area, Aqishan preselected areas, within the depth of tested, the stress state of the four preselected area are inverse slip stress state, horizontal stress dominate. 2. The ratio of horizontal stress and vertical stress increase linearly with depth of four preselected area converge to a constant, the stress structure shows:Aqishan preselected area stress structure make conversion of reverse fault type-slip type-normal fault type, Yamansu-Tianhu preselected area, Beishan preselected area, Alashan preselected area make conversion of reverse fault type-slip type; In the shallow crust, horizontal stress plays a dominant role, in the deep crust, the role of vertical stress enhanced; The ratio of horizontal stress in four preselected area changes little with depth, converge to a constant, horizontal tectonic of Yamansu-Tianhu preselected area is strongest, Aqishan preselected area is weakest; The ratio of shear stress and the average of the four preselected area change little with depth, and lower than the friction limit state.3. The duration collision of Indian plate and the Eurasian plate is the main driving force of the four preselected area of present tectonic stress pattern, from Aqishan preselected area to Alashan preselected area, the dominant orientation of maximum horizontal stress has a deflection of NEE to NNE.4. Simulation results and drilling results of Each preselected area coincide with each other to a good degree, within the depth of tested, the three principal stress value is relatively close, the maximum principal stress orientation is consistent with the regional tectonic stress field orientation. Compare and analysis finite element numerical simulation results feature diagram of four preselected area, we found:In the200m,400m,600m,1000m depth, four pre-selected area in the middle and low stress levels. We values the merits of pre-selected zones according to the level of shear stress and the order is Aqishan preselected area, Alashan preselected area, Beishan preselected area, Yamansu-Tianhu preselected area. The three stress of Aqishan preselected area, Beishan preselected area, Alashan preselected area change significantly with fracture, Aqishan preselected area is the most obvious, Alashan preselected area changes significantly near Engeer-Wusu fracture zone, the main stress Yamansu-Tianhu preselected area did not change significantly with the fracture.