| The basin of Jinsha, Yalong, Dadu and Lancang River in Southwest China have gathered a large amount of large-scale water conservancy and hydropower projects with power output more than1million kilowatt, under construction or proposal. These projects have got high-steep slopes which experienced exogenic geologic process, forming a unique geological structure, which make the slope stability problems during excavation particularly prominent, vitally affects the safe operation of hydraulic structures. Therefore, there is an urgent need for in-depth systematic study of the high-steep slopes performance during excavation.This article focuses on the key scientific issue of the deformation effect of excavation of the high-steep slope under complicated environment and the stability evolution mechanism. The right bank slope of Dagangshan hydropower station which contains unique structure like weak structural plains is taken as the target of studies. According to the engineering geology and deformation of the reflecting signs, combined with the use of micro-seismic monitoring analysis and numerical geological model of three-dimensions, the geomechanical model which represents the structure of the slopes as well as the deep cracks are established. This model have systematic reviewed the slope stability during excavation, and revealed the development of the deformation of the slopes under excavation, as well as the failure mode. The result of the model explained the reasons of the partially deformation failure during excavation of the high-steep slopes, as well as the law of disaster-inducing. Meanwhile, the numerical model of bank-slope anti-shear tunnel is established in order to analysis, during the failure of bank-slopes, the interlock mechanism of the landslides and the anti-shear tunnels as well as the mechanism of coordinated sharing deformation. The anti-shear tunnel structure has been proved correct and suitable, and provided reference in order to ensure the safety of construction and long-term operation of slope stability. The following major achievements are made in the paper:(1) Based on numerical simulation, the interlock between slope structure and the patterns of deformation&failure has been analyzed, also, the controller effect of the slope structures to the bank overall stability has been determined. A method suitable for the analysis of the stability of bank-slopes which contains weak plates has been discovered. The results for research are into direct service to the actual projects and received good effects. The results figured out that for bank slopes with critical structure plans at the same size and height, the slope angle becomes the main affection to the destruction patterns as well as the safety factors. At the same size and homogeneity, a rock bank slope with a critical plate has a lower safety factor compared to one without critical plate.(2) Associated with the sign of deformation of which the surface of bank slopes had appeared during excavation, the Microseismicity monitoring technology is used at the first time in order to track the micro fracture of the rocks during excavation. This unveils the patterns of distribution of the Microseismic activity in the high-steep slopes in a view of direct monitoring, and approximately circled the critical structural plate which affects the stability of the bank slopes. The results of the study indicates that the reason of the several deformation cracking on the surface of the slope during excavation, is that the primary critical structural plate which affects bank slope stability--the stress-release crack XL-316and f231, have gathered mass numbers of microcracks, resulting in the deformation of partly small rocks in the bank slopes.(3) According to the development features in engineering geology of the bank slopes as well as the results of the microseismic monitoring, a critical structural plate which affects the stability of the bank slopes have been added for the sake of the precise description and model construction for the rock mass structure of the bank slopes. Method of research such as numerical calculations as well as in-situ monitoring feedback are combined and a three-dimensional geological numerical model is built in order to analysis the stability of the bank slopes during the procedure of unloading. The results of the analysis figured out that after considering the microseismic effects of the bank slopes, the safety factor becomes1.03, which is14%lower than the one without considering the microseismic effects. It is due to artificial excavation which the microcracks occur, as well as the creep change of the physical/mechanical parameters in the materials of the slopes, which made the bearing capacity of the materials of slopes to decrease.(4) The numerical model of the typical disaster-proof bank slope anti-shear runnel has been established on the basis of the behavior of structural bearing. This is in order to research the deformation of the slopes after reinforced with anti-shear tunnels as well as in order to unveil the interact mechanism and the mechanism of coordinated sharing deformation between the landslide and the anti-shear tunnel under a bank slope failure. Analysis indicates that the anti-shear tunnels reinforced the anti-shear strength and stiffness to the rocks on the critical structural plate, significantly increasing the anti-shear friction force. The bank slopes after the reinforce has got a safety factor of1.83, which has got a51.2%increase compared to the un-reinforced safety factor1.21. This proves that the disaster-proof structure of the anti-shear tunnel is an effective way of reinforcement in order to control the creep failure of the bank slopes. |
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