The Development Characteristics Of Landslides On Xiangxi River Segment Of The Three Gorges River Area And The Influence Reservoir Impounding Has On The Stability Of Bank-Slope

Xiangxi river segment of the three gorges reservoir is located in northwest of Hubei Province. It is 34km long in total with the estuary about 34.5 km away from the Three Gorges Dam. The geological environment of it is fragile so that landslide and collapse develop. Water storage of three gorges reservoir destroyed the originally natural balance there, not only making the old, stable landslide resurrect and the embankment along the river collapse, but also making new landslide development possible. Bank-slope stability concerns about the coastal residents'safety, waterway and highway's normal operations. Therefore, researching development characteristic, deformation and failure mechanism as well as bank-slope deformation behavior of the landslide caused by the reservoir impoundment is of realistic significance for Disaster Prevention and Mitigation and of great theoretic value for enriching the research of bank slope's deformation characteristics and failure mechanism under the action of reservoir water.This paper is based on the systematic research of the geological environmental conditions, structure, deformation and destruction features of the bank-slope, focusing on its deformation and failure mode, development law and formation mechanism Through water rock mechanism research, we combine the thinking of geology and mechanics and analyze the resurrection mechanisms of landslide under the action of reservoir water. Considering the influence of water dispatching, we apply limiting equilibrium calculation and numerical modeling finite-element to analyze of the stability of resurrected landslides. According to the analysis of landslide development conditions and its inducing factors, we establish the stability of the prediction and evaluation index system. We also adopt Comprehensive geological prediction and Fuzzy Forecast to forecast the stability of the rocky bank after Reservoir impounding. Obtaining the following achievements:(1)The researched bank-slopes are mainly rock slope and soil slope. Rock slopes are divided into middle-obliquity Anti-dip layered slope, middle-obliquity bedding layered slope and a few oblique Layered Slope, cross Layered Slope. Soil slopes are mainly coasting deposit and a few slopes made by alluvial, slopes made by deposit, colluvial deposit and man made accumulation.According to the stratigraphic lithology, the relation between rock-slope direction and bank-slope direction, development feature of landslide etc, we divided both sides of Xiangxi river segment into 7 parts and elaborated the engineering geological characteristic of all the 7 parts.(2)The left and right side of bank-slope in Study area is in different deformation failure modes, middle-obliquity bedding layered slope on the left bank is mainly in the form of "sliding– cracking", part of them appear "sliding - bending" .Middle-obliquity Anti-dip layered slope on the right bank is mainly in the form of "bending– cracking. Part of the layered shore-slopes basically suffer from the combination cutting on adverse structure and appear Small-scale of Collapse and landslide damage. Horizontal layer shore-slope deformation damage is not obvious. Landslide development density for shore-slope differs in geologic structure with the bedding slope landslide having the highest density, reverse slope landslide next and oblique slope landslide lowest and the horizontal slope landslide not developed.(3)We researched the landslide revival mechanism combining the influence of Water dispatching in the three gorges reservoir. Research results show that water rock interaction is the essential cause of landslide resurrection. Physical effects caused by Water-rock interaction such as degradation in water, erosion and chemical effects such as ion exchange, dissolution, hydration all reduce the mechanical parameters of rock mass, thus deteriorating the stability of landslide. Water rock effects generate mechanics effect such as static water pressure, moving water pressure, all of which changing the dynamic function system of landslide occurrence and creating conditions for landslide resurrection .(4)We conduct the stability study of Bazimen landslide which has Clear signs of resurrection by limiting equilibrium calculation and numerical modeling finite-element. The results of the study show that when the reservoir water lifts to 175m, the landslide is in under steady state; when it drops from 175m to 145m, the landslide is in the possibility of instability. In order to discuss whether the reservoir water will effect landslide stability is universal, we select 8 typical landslide to analyze and calculate their stability. The results showed that 62.5% of landslide is effected by Reservoir, making their stability from stable state to basic stable and to under steady state .(5)Bank-slope deformation damage are influenced and controlled by many factors. This paper based on the development conditions and predisposing factors of the landslide and respectively apply the geological prediction and fuzzy forecast to predict the stability of rocky bank after reservoirfilling. It tells us that favorably good and favorably bad each occupies 50%. Forecasting results also indicate that the reservoir water only has weak influence on Anti-dip rocky bank of the landslide on the right while has strong influence on the Landslides and the bedding slope on the left is remarkable. Therefore, it is considered that after reservoir impounding , the main bank-slope engineering geological problems of study area is the resurrection of the old landslide on the right bank and the occurrence of new landslide on the left bank.