| In the domestic and reservoir engineering projects, especially large reservoirs, water storage and periodic change of water level fluctuations often triggered generation or reactivity of new and old landslide along the reservoir bank. This kind of landslides which affected by the water level along the reservoir bank slope often was referred to be as the reservoir landslide (or bank landslide). A large number of surveys and studies have shown that the reservoir in the hills and mountains can cause generation and reactivity of the reservoir landslide because of water storage. Taking Yangtze River Three Gorges Project as an example, according to the "Key Plan of geological disasters prevention in the Three Gorges Reservoir" which was approved by the State Council in2002, there were many kinds of landslides and rock falls and the number is about2490. If it included the newly created landslide after water storage and a large number of constantly new landslides which was found in the follow-up survey, and the number, size and potential harm is extremely alarming.The damaging effects caused by reservoir landslide are always much more serious than normal landslide. There are various disaster forms, including directe damage and indirecte damage. For instance, landslide deformation and failure directly caused damage to persons, buildings and other infrastructure on the top of landslide body; landslide slided into the river and reduced the effective capacity of the reservoir, and it caused the formation of lake and river blockage; secondary swell that excitated by speed landslide speed failure would make damage to shipping, coastal residents or buildings as well as construction and operation of buildings. Therefore, study deformation law and forecasting of reservoir landslide in Three Gorges Reservoir area has major theoretical and practical significance.This paper took debris landslide which has deformation after water storage in the Three Gorges Reservoir as an example and carried out based on geological survey, material collection, field monitoring and theoretical calculation. In this papar, there are four types of data have been collected. Firstly, landslide basic enviromental data, including toppgraphy, lithlogy, geological structure and so on. Secondly, hydrological data, including historical precipitation monitoring data and reservoir level scheduling data. Thirdly, detailed survey data, including engineering geological map,topographic map,profile,rock mass physical and mechanical test results and hydrogeological test results. Finally, professional landslide monitoring data, including landslide surface displacement, deep displacement and ground water level and so on. Based on these data, professional monitoring techniques and methods on typical reservoir landslides in Three Gorges Reservoir have been analyzed and the deformation characteristics and regularity of those landslides deformed after the impoundment of the Three Gorges Reservoir has been summerized from two aspects of space and time. On this basis, the influenc factors of landslide stability have been analyzed, and the deformation mechanism of three types of landslides are studied. These three types of landslides are rainfall type landslide, reservoir landslide and rainfall-reservoir landslide. In the end, the numerical simulation method has been adopted to study landslide prediction criterion. Comprehensive early warning model has been build based on multiple data sources. The results in this paper make scientific theory basis to landslide prediction and contingency plans making in Three Gorges Reservoir area.In this paper, the typical reservoir landslide monitoring system have been summerized from the following aspects:monitoring program design, monitoring contents, monitoring instruments and data processing. The reservoir landslide deformation characteristics are study on two aspects. The first aspect is from space. Based on district or rock group, a statistical analysis have carried out to study the spatial distribution regularity of deformation of reservoir landslide and the influences of the characteristics of landform, geological structure, lithologe and hydrogeologe to the spatial distribution of landslide have aslo been analyzed. The second aspect is from time. The progress of landslide deformation have been studied and the corresponding relationship between landslide high increasing deformation rate period and rainfall or reservoir level changing period have been analyzed. The reservoir landslide deformation mechanism has been studied based on the anaysis on landslide engineering geological conditions, landslide surface displacement, and rainfall and water level schuduling information. In this part, landslide stability influence factors have been analyzed to explain the deform mechanism of landslide,especially when landslide under the conditions of rainfall and reservoir water. In order to study landslide deformation prediction criterion, typical landslides have been chosed as examples. Numerical simulation method has been used to analyze the landslide defome trend under different conditions in order to determine the most dangerous condition. Based on this analysis, comprehensive early warning criterion model have been build on multiple data sources, including displacement criterion, plastic penetration of shear plane on main sliding surface and rainfall intensity criterion, etc.Through the above series of analysis and research, the paper mainly achieved the following results and conclusions:(1) Summarized monitoring system for the typical reservoir landslide in Three Gorges Reservoir.The professional monitoring methods for landslide in Three Gorges Reservoir were land deformation monitoring, surface crack displacement monitoring, landslide deep displacement monitoring, groundwater level and pore water pressure observations, landslide thrust monitoring, monitoring of predisposing factors, underlying human activity monitoring, macro-geological inspections monitoring and so on. The monitoring cycle is once a month in the non-flood time, and twice a month in the flood time. If the deformation increased, or in heavy rain time and a long period of rain time, and landslide deformation had a continuous increasing trend, the monitoring cycle must be frentenly monitored in time. The main monitoring instruments are: Total Station, GPS monitoring, inclinometer, dynamic automatic monitor for groundwater levels and fiber landslide thrust measurement system. Treatment of monitoring data in the reservoir area included collection, pre-processing and monitoring results finishing of monitoring data. Monitoring information included all outcomes measured data and calculated results data of monitoring project about monitoring surveying projects.(2) Analysis and research of the landslide distribution law after water storage in the Three Gorges Reservoir.Typical landslide studies were selected to do research for the space and time distribution law of landslides after water storage in the Three Gorges reservoir.1) Taking Shuping landslide as an example:expressed by the landslide monitering displacement curve, Shuping landslide presented step-deformation characteristics and regional diversity, the deformation mainly concentrated in the east, middle and west lower part of the landslide along the main slide region. Landslide deformation has obvious regional differences in the plane and elevation. The reservoir water afffects the area under the elevation of200m significantly, and the places higher than200m are almost not affected by reservoir water. The large deformation area are below the elevation of180m, and the closer the area gets to the elevation of175m, the higher deformation rate the area would be with. In the main slide region, the change of shallow landslide slip zone was greater than the deep slide zone, surface deformation was greater than the ground deformation, and the deep differences of shallow deformation is greater than the deep deformation.2) According to the analysis of monitoring results for Baijiabao landslide deformation, the landslide deformation had obvious time distribution characteristics:beginning in2007, from April to September, the displacement and rate of the monitoring points increased significantly comparing with the annual average value; while from October to March, displacement rate of each monitoring point decreased and so that the cumulative displacement-time curve for many years showed a significant "step-like" features. From2007to2012, there are totally6steps on the cumulative displacement-time curve in every April to September, especially June to July.(3) For the different major predisposing factors of landslide, the landslide deformation mechanism for rainfall-induced landslides, reservoir-induced landslides and rainfall combined reservoir-induced landslides were studied.1) The main geological impact factors of the reservoir landslide deformation in the Three Gorges Reservoir were:lithology, geological structure, topography and slope structure, and the main predisposing factors were:rainfall, water level fluctuations and human activity. Based on the landslide impact factors analysis, the relationship and the law between landslide and the impact factors have been found out in order to anlayze landsldie mechanism.2) Rainfall is one of the most important impact fact of landslide instability. This paper has studied the relationship between the occurrence of landslide and rainstorm frequency, rainfall, rainfall amount, rainfall intensity and rainfall form. Besides, find out the area rainfall distribution characteristics and the influence law to the occurrence of landslide, which would provide basis for typical landslide deformation mechanism analysis.3) Reservoir induced landslides includes three types:water softening effect induced landslide, suspended weight losee effect landslide, dynamic water pressure induced landslide. In the water impoundment process of reservoir, the characteristic changes of rock and soil and the floating force effect have influenced the stability of landslide. In the water falling process of reservoir, the dynamic water pressure, hydrostatic pressure and excess pore water pressure would cause the discrease of landslide stability.4) Select Sanjiaotan landslide as an example to analyze rainfall induced landslidedeformation mechanism. Through the analysis of the surface displacement monitoring data for three landslide from2007to2009, it can be found that the Sanjiaotan landslide was mainly affected by rainfall and belonged to goes-creeping landslide, the deformation of middle and back part of landslide is larger than the front part of landslide.5) Select Ranfang landslide as an example to analyze reservoir water induced landslidedeformation mechanism. According to the monitoring data, the deformation of front, middle and back part of landslide had obvious correlation with the reservoir water level, especially when the water level rises higher than154.5m. In the water impoundment period of reservoir, the displacement of landslide has a decreasing trend while in the slow droping water period of reservoir, the displacement of landslide has a tendency to increase slowly first and sharply after, and the displacement change has a certain hysteresis compared with the decline change of the reservoir water.6) Select Huayuanyangjichang landslide as an example to analyze rainfall-reservoir water induced landslidedeformation mechanism. Based on the analysis of the landslide displacement monitering data, in the water impoundment period of reservoir, the displacment of GPS3. GPS5and GPS6are increasing corresponding with the increase of the water level. In the smoothly running period of reservoir, there are no effect on landslide deformation. Besides, in the water falling period of reservoir, the deformation of the front part of landslide increases while the deformation of the back part of landslide is not obvious. Meanwhile, in this period, the deformation of landslide increased also due to the increase of rainfall, so the rainfall had a certain impact on the stability of Huayuanyangjichang landslide. Therefore, Huayuanyangjichang langslide subjected to the combined effects of reservoir water level and rainfall.(4) Based on numerical simulation, the establishment of early warning models and criterion for the tipical reservoir landslide in Three Gorges Reservoir.1) Sanjiaotan landslide was selected as a representative to analyze warning criterion of rainfall-induced landslides. This landslide is a soil unsubmerged landslide.Based on numerical sumulation method, extreme conditions have been chosed to study landslide prediction. When the rainfall intensity is120mm/d, the leading edge of this landslide is likely to have a partial failure. When the rainfall intensity is120mm/d～150mm/d and rainfall lasted3days, this landslide is likely to occur destruction from partial to whole, so the rainfall intensity criterion of this landslide is120mm/d.2) Ranfang landslide was selected as a representative to study the warning criterion of reservoir-induced landslides. The landslide was soil landslide and effected by the fluctuation of Yangtze River. Through the creation of three-dimensional numerical model and landslide flow field simulation, the analysis of landslide deformation and failure characteristic under different conditions and deformation prediction was conducted. The most dangerous working condition of this landslide is when the water level dropped from159.8m down to145.8m.3) Based on the study of rainfall induced landslide and reservoir induced landsldie. Huayuanyangjichang landslide was selected as a representative landslide to study the landslide warning criterion under the combined effects of rainfall and water level. Through landslide numerical simulation under different working conditions, water level in the front of the dam dropped from162m to145m+50year storm was determined as the most dangerous condition. Taking the most dangerous working conditions as an example, the research on prediction criterion for Huayuanyangjichang landslide was conducted, and it was derived that the ultimate warning value of storm rainfall intensity for this landslide is50mm/d, and the rainfall continued for three days. |
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