Study On The Process Simulation And Hazard Prediction Method Of Landslide Damming

With the "Belt and Road" initiative and the deep implementation of the western development strategy,kinds of large-scale infrastructure,such as the western route of the southnorth water diversion project,hydropower development,west-to-east power transmission project,west-east natural gas transmission,Sichuan-Tibet railway and the expressway network in the western region,have been built,or are under construction or have been included in the national development plan.The site selection,line selection and long-term safe operation of these large-scale infrastructures directly affect the security of national transportation,energy and ecological environment,and exert far-reaching influence on regional economic cooperation and development.However,due to the impact of the Himalayas,such large-scale infrastructure construction is often difficult to detour from the mountainous areas with complex geological structure,which poses a major challenge to the early identification,prediction and early warning of geological disasters.Steep and high slopes along the river in mountainous areas may fail under the load of earthquake,rainstorm and other disasters.Then the landslide mass may move into rivers,forming landslide dams and blocking rivers.This kind of engineering geological phenomena can induce a series of regional disasters,such as barrier lake flood and dam breaching-induced debris flow.Due to the frequently occurring,wide range of influence and difficult predicting of landslide-induced river blocking,it poses a great threat to the safety of engineering and human life and property.Therefore,it is of great scientific significance and engineering value to study the evolution of landslide-induced river blocking,and to establish the prediction method for the disaster chain of landslide-induced river blocking.In view of this,the main contents of this paper are as follows:(1)Based on the similarity principle,a set of flume model test equipment including landslide simulation module,water supply module and river simulation module for the disaster chain of landslide-river blocking-dam failure was independently developed,and its reliability and stability were verified through a series of pre-tests.Using this device,based on the principle of Structure from Motion(SfM),a three-dimensional non-contact image measurement method on laboratory-scale was developed,and the effectiveness of the measurement method on laboratory-scale was verified by comparing and analyzing the measurement results of 100 groups of parallel tests on two kinds of rock and soil materials.(2)Flume model tests for the evolution of deposit landslide-induced river blocking considering different landslide volumes and river flows have been carried out.The physical model experiment truly reproduces the evolution of landslide-induced river blocking,such as landslide-generated waves,landslide dam formation,barrier lake formation,landslide dam overtopping failure,and dam breaching-generated flooding and debris flow.Based on physical model experiment,a dimensionless River Blocking Criterion(RBC)is put forward to predict the landslide dam formation.The River Blocking Criterion is defined as the ratio of landslide discharge to the river flow discharge.When the landslide discharge is 1.5 times of the river flow discharge,it can be considered that a landslide dam may form;otherwise,a landslide dam may not form.(3)A DEM-CFD fluid-solid coupling numerical method is developed,which considers the drag force,lift force and buoyancy force.The mechanism of the action of river water on the evolution of river blocking is revealed,and a river blocking coefficient(Ic)is defined to evaluate whether a landslide completely blocks a river.Furthermore,based on the dimensionless parameters of landslide velocity,landslide volume,river velocity,river depth and river width,a prediction model for river blocking coefficient is established,and its adaptability is analyzed.(4)Based on the generalization of landslide dam formation process,the mathematical expression of landslide dam geometry characteristics is put forward.Based on physical model tests,a model for predicting the geometry of landslide dam is proposed.The prediction model includes seven parameters,which are the repose angle of landslide mass,the landslide volume,the bottom width of river valley,the two riverbank angles,the slope sliding surface angle,and the riverbed inclination.The prediction model of landslide dam geometry is verified by experimental data and 42 historical cases.The Tangjiashan landslide dam induced by 2008 Wenchuan earthquake is also taken as an example to verify the prediction model.(5)A database contains 1328 cases of landslide-induced river blocking is established.Furthermore,a rapid prediction model for landslide dam stability contains three parameters,which are the dam length,dam height and the reservoir capacity of barrier lake,is presented based on the principle of logistic regression.The accuracy of the prediction model is compared and analyzed.The overall accuracy of the proposed rapid stability prediction model of landslide dam is 86.7%.In addition,the overtopping failure model of landslide dam is generalized,and on this basis,a time prediction model for landslide dam overtopping failure based on the geometry of landslide dam is established.The prediction model for landslide dam failure time has been verified by experiments and the Baige landslide-induced river blocking case.Finally,based on the above work,a quantitative prediction method of the disaster chain of deposit landslide-induced river blocking is proposed.The quantitative prediction method includes four steps,which are the prediction of river blocking,the prediction of landslide dam geometry,the rapid stability prediction of landslide dam,and the time prediction of landslide dam breaching.The research results and conclusions summarized from the current study are helpful to advance the study of the evolution mechanism and critical conditions of landslide-induced river blockage on the theoretical level.As for practical engineering,the current study is helpful to provide theoretical reference and technical support for the early identification,prediction and early warning of the disaster chain of landslide-induced river blocking.