Physical And Mechanical Parameters Identification And Application Of Surrounding Rock Based On Displacement Back Analysis

As the developing of human society, the exploitation and utilization of underground space such as the city subway, underground commercial street, civil air defense engineering, railway and highway tunnel, underground hydropower, underground nuclear waste repository, has obtained an unprecedented development. Compared with ground engineering, the underground engineering were built in complex and uncertain rock mass, facing enormous challenges in actual construction. So that the analysis on the deformation behavior of surrounding rock under sensitive environment and complex geological conditions of construction based on field monitoring is needed. Once the formation and structure characteristics was grasped, the mechanical deformation behavior should be controlled through the feedback construction parameters, to ensure the safety and reliability of underground engineering construction.In this thesis, the underground hydropower excavation unloading process was simulated by ANSYS and FLAC3 D based on the abundant in-situ measuring data of ground stress. Moreover, the feedback results of initial geo-stress and physical and mechanical parameters of surrounding rock were optimized by means of the artificial neural network(ANN) method. And also, the stability of surrounding rock of Wunonglong underground hydropower project located on the upper reach of Lancang River was evaluated according to the feedback results. The main achievements from this study are as followings:1. The deformation analysis during underground cavern group excavation unloading process based on in-situ measuring data of surrounding rock were as below: the axial displacement of surrounding rock was in a small range of-0.67~1.52 mm before the first excavation layer of underground cavern group, the maximum displacement of main powerhouse, main transformer cave and tail-water surge chamber were: 1.52 mm, 1.09 mm and 1.17 mm. As the excavation of center pilot tunnel, unloading springback and unloading relaxation appeared to rock mass, leading to deformation and increased step shaped curve of surrounding rock.2. The model of underground hydropower were built and analyzed by ANSYS and FLAC3 D based on its variation regularity in the process of excavation. The regression coefficient calculated by least square method was applied to the back analysis. By which the distribution characteristics and variation regularity of ?1, ?2 and ?3 in three large cavities were obtained.3. By using artificial neural network method to train the scope of parameters according to the testing results and field monitoring data based on the orthogonal design theory, the value of elastic modulus, cohesion and internal friction angle for different rock layers were determined.4. The results of stability of surrounding rock after the second excavation layer for Wunonglong underground hydropower project located on the upper reach of Lancang River based on displacement feedback analysis were as follows: partial stress release appears to the upper arch of the main powerhouse and stream side walls, ?1 and ?3 tensile stress range in upper arch decreased while the displacement of the upper arch of the main powerhouse and stream side walls increased, partial stress release appeared to stream side walls of main transformer cave and tail-water surge chamber.