| The dam encloses the waves,and the high gorges emerge from the horizontal lake.The Three Gorges Dam is the largest water conservancy project in China and even the world nowadays.The operation of the dam has not only brought huge social benefits to power generation,flood control and shipping,but also greatly changed the original geological environment and induced a large number of geological disasters,especially landslides.According to statistics,there are more than 5,300 landslides along the banks of the reservoir in the Three Gorges Reservoir area(TGRA),and more than 60 landslides have been triggered since the reservoir operated.Under the comprehensive effects of the historical geological background and the present surrounding environment in the TGRA,a lot of complex reservoir landslides with multiple sliding zones are developed.Usually,such landslides have huge scale,complicated cause and structure,serious harm,high treatment difficulty and expensive cost.The data showed that the impoundment and operation of the TGRA had awakened these landslides to be reactivated and even destroyed,threatening the safety of residents and property in the reservoir area.Therefore,research on complex reservoir landslides,with a focus on analyzing its evolution mechanism and evaluating the overall stability,is an imperative issue for landslide prediction and mitigation in the whole TGRA.In this thesis,the Huangtupo Riverside Slump Ⅰ#,a typical complex reservoir landslide in the TGRA,is taken as the case study.The multi-parameter monitoring data of the landslide under the action of reservoir water level and rainfall are obtained by physical model test.The spatial-temporal evolution rules of each parameter,the deformation and failure characteristics of the landslide,and the sliding process are analyzed accordingly.The finite element numerical simulation which matches with the test is carried out,and then the test results are compared and verified.The evolution mechanism of the landslide under the action of reservoir water level and rainfall is revealed.The co-evolution mechanism of shallow landslide and deep landslide is clarified,as well as the evolution phases.The stability of the landslide under the action of reservoir water level and the combined actions of reservoir water level and rainfall is analyzed.The main research contents and results are shown as follows:(1)The physical model test of the Riverside Slump Ⅰ# under the action of reservoir water level and rainfall is carried out:(1)The reservoir water level mainly affects the moisture content of soils within its fluctuation range,while the rainfall increases the overall moisture content of the landslide.Due to the lag effect,the change of the moisture content at different measuring points has obvious difference.(2)The pore water pressure and earth pressure in the middle front of the landslide increase when the reservoir water level rises,and decrease otherwise.The fluctuation of reservoir water level mainly affects the middle front of the landslide,but has little effect on the trailing edge.All monitoring values of the pore water pressure and earth pressure increase during rainfall,which are proportional to rainfall duration and intensity,but are limited by the height of overlying soils.(3)The rise of reservoir water level have little effect on the surface displacement.The drop of reservoir water level increases the surface displacement of the middle front of the landslide,while the influence on the trailing edge is unobservable.Rainfall changes the overall surface displacement of the landslide,and this influence can be amplified by longer rainfall duration and greater rainfall intensity.(4)The rise of reservoir water level reduces the deep deformation in the middle front of the landslide.On the contrary,the drop of reservoir water level increases the deep deformation,and the increase is greater than the previous decrease caused by the rise.In the early rainfall,the deformation of the middle front of the landslide is usually greater than that of the trailing edge,but after several times of rainfall,the displacement increment of the trailing edge is gradually greater than that of the middle front.(2)The numerical simulation of the physical model test is conducted:(1)The saturation line gradually goes down as the reservoir water level drops and goes up as the reservoir water level rises.The change rate of the saturation line is proportional to the fluctuation of reservoir water level,and the lag effect can be observed.The rainfall results in a rapid increase of the saturation line,and the increment is proportional to the rainfall duration and intensity.By comparing the seepage results from the reservoir water level and rainfall,it can be seen that the reservoir water level mainly affects the middle front of the landslide where the shallow landslide is located,while rainfall affects the whole landslide,including the shallow landslide and deep landslide.(2)The parameters obtained from the numerical simulation are basically consistent with the physical model test,but the results obtained from numerical simulation are ideal,so there are some differences between the numerical simulation and the test as well.(3)The stability of the shallow landslide and deep landslide has the similar rules during the test.The stability increases with the rise of reservoir water level,and decreases with the drop of reservoir water level and rainfall.The effect of fluctuation of reservoir water level and rainfall on the stability of the shallow landslide is greater than that of the deep.(3)The evolution mechanism of the landslide under the action of reservoir water level and rainfall is revealed:(1)The deformation of shallow landslide has the characteristics of large in leading edge and small in trailing edge,showing the rules of retrogressive landslide as a whole.The shallow landslide extends backward gradually by the way of block destruction caused by successive cracks,and draws the adjacent sliding body.As a result,the anti-sliding force at the leading edge of the landslide is reduced.(2)The deformation of deep landslide can be divided into two parts: the leading edge is retrogressive failure driven by shallow landslide;the trailing edge is progressive failure driven by rainfall.Under the actions of shallow landslide and deep landslide,that is,pull at the leading and push at the trailing,the cracks will gradually close overall,and then form the sliding boundary.As a result,the instability occurs.(3)The shallow landslide shows the whole deformation evolution phases of the retrogressive failure,which is in the initial deformation during 0～230 h,constant deformation during 230～384 h,accelerated deformation during 384～498 h,and sharp deformation during 498～594 h.During the test,the middle front of the deep landslide is in the initial deformation phase of the retrogressive failure,and the trailing edge shows the first three deformation evolution phases of the progressive failure,which is in the initial deformation during 0～384 h,constant deformation during 384～498 h,accelerated deformation during 498～594 h.(4)The stability of the Riverside Slump Ⅰ# under the action of reservoir water level and the combined actions of reservoir water level and rainfall is analyzed within the framework of probability:(1)When the reservoir water level rises,the failure probabilities of the shallow landslide and deep landslide decrease.When the reservoir water level drops,the corresponding failure probabilities increase.The most dangerous probability occurs in shallow landslide when the reservoir water level drops to the lowest level.Rainfall can also increase the failure probabilities of the shallow landslide and deep landslide.Compared with deep landslide,the failure probability of the shallow landslide is more sensitive to the reservoir water level and rainfall.(2)The system failure probability of landslide decreases with the rise of reservoir water level and increases with the drop of reservoir water level and rainfall.Although Ditlevsen boundary method can obtain narrower failure probability than Cornell method,it is not universally acceptable because it is limited by the conditions of application.With this issue in mind,the sequential compounding method is introduced in this thesis.The method can obtain the system failure probability more accurately,which has important reference significance for evaluating the stability of analogous complex reservoir landslides with multiple sliding surfaces. |
PDF Full Text Request