| High-speed landslides are often described as catastrophic landslides because of their high destructiveness,wide range of coverage,difficulty in prevention,and their potential for serious loss of life and property in disaster areas.High speed,long sliding distance,large volume and catastrophe are its most prominent features.High-speed landslides are common geological disasters in the world,whose mechanistic research and motion process simulation are the focus of attention at home and abroad.Regarding the dynamic mechanism of high-speed landslides,a unified and systematic understanding has not yet been formed.Due to its fast moving speed and long sliding distance,it is difficult to explain it by conventional kinematics.Some scholars believe that during the short period of the start of high-speed landslide,the shear band at bottom is strongly rubbed,resulting in extremely high heat.Under the effect of thermal pressurization,the excess pore water pressure in the shear band is sharply increased,resulting in a sudden drop in the shear strength of the sliding surface,thereby causing the overlying sliding mass to accelerate.However,due to the large difference in thickness between the overlying landslide mass and the bottom shear band,the theory is currently limited to a simplified one-dimensional model.In addition,once the high temperature generated in the shear band exceeds the boiling point of the pore water,vaporization will inevitably occur,which involves the multiphase thermodynamic coupling problem in the shear band.The above problems have not yet been solved reasonably,which seriously restrict the development of accelerated sliding mechanism of friction-heat-pressurization of high-speed landslides.This paper first summarizes the research status and existing problems in the fields of dynamic mechanism of high-speed landslide,dynamic model of frictional thermal pressurization within shear band and mechanics model of sliding mass,and introduces the main research content of this article.Then the data of 50 typical high-speed landslides are collected and analyzed statistically,and the geological conditions,triggering conditions,dynamic process and other basic characteristics of high-speed landslides are summarized.On this basis,the dynamic models of high-speed landslide based on thermo-hydro-mechanical(THM)coupling and thermos-hydro-vapor-mechanical(THVM)coupling in shear band are established respectively and verified by examples.Based on the model established above,the effects of key parameters on the start of high-speed landslide are studied,including the thickness effect of the sliding mass and the shear band,the influence of hydraulics and thermodynamic parameters,and the influence of the sliding surface inclination angle and the initial acceleration of the sliding mass.Finally,the models are applied to two actual cases,including Yigong landslide in Tibet,which has occurred high-speed sliding,and Qingyaling landslide in Gansu province,which has not occurred catastrophic failure but has potential high-speed sliding hazards.Based on the above research contents,the main results obtained in this paper are as follows:(1)The basic characteristics of high-speed landslide are summarized.A total of 50 typical high-speed landslide cases at home and abroad are collected and their basic information is included in attached table 1.Based on the collected high-speed landslide case data,statistical analysis are respectively performed on the geological conditions(such as topography,slide mass and shear band material structure),the trigger conditions(such as earthquake,rainfall,snow and ice melting,reservoir impoundment,rock fall loading,deformation accumulation(natural instability),artificial mining and volcanic eruption),the dynamic characteristics(such as velocity and displacement,residual dynamic friction angle,volume effect and Transformation of material form),and summarizing up the general laws.(2)The high-speed landslide dynamic model based on thermo-hydromechanical(THM)coupling in shear band has been developed.Using the strip method,the sliding mass is divided into a series of small slide blocks and corresponding partial shear bands at the bottom.Based on the mechanism of frictional-thermal-pressurization and the one-dimensional THM coupling model,the motion equation of each slide block is established,as well as the heat equation and pore pressure equation in each partial shear band.The model consists of three governing equations: the motion equation of overlying sliding mass,and the heat equation and pore pressure equation within shear band at the bottom.The Vaiont landslide is selected for model verification.It is proved by the model that the facilitating sliding mechanism of frictional-thermal-pressurization is greatly affected by the irregular spatial morphology of the sliding mass.The validity of the quasi-two-dimensional THM coupling dynamic model is verified by comparative analysis of simulation results.(3)A high-speed landslide dynamic model based on thermo-hydro-vapor-mechanical(THVM)coupling in shear band is proposed for the first time.Heat is generated by friction in the shear band,resulting in an increase in temperature.Once the temperature exceeds the boiling point of pore water,vaporization will occur,which will further affect the pore pressure in the shear band and the dynamic process of the overlying sliding mass.Considering the evaporation process caused by high temperature of pore water,a dynamic model for landslide based on the coupled THVM in shear band is established.The Vaiont landslide is selected for example verification.(4)The effects of key parameters on the start of high-speed landslide are studied.Based on the coupled THM dynamic model for landslide,the sensitivity analysis of key parameters,such as the thickness of sliding mass,the thickness of shear band,thermal conductivity,thermal pressurization coefficient,permeability coefficient,angle of sliding surface and initial acceleration of sliding mass,etc.,is carried out in this part,and the effects on the velocity of sliding mass,the temperature and excess pore pressure within shear band is clarified.It provides an important theoretical basis for judging whether it develops into a high-speed landslide after the landslide is started,from the perspective of frictional-thermal – pressurization in shear band.(5)Application of the TH(V)M coupling dynamic model for high-speed landslide based on the mechanism of frictional-thermal-pressurization in shear band.In this part,the TH(V)M coupling dynamic model for high-speed landslide based on the mechanism of frictional-thermal-pressurization in shear band is applied to the Yigong landslide in Tibet and the Qingyaling landslide in Gansu.The former is a catastrophic landslide that has occurred high-speed sliding,and the latter is an ancient landslide that has not occurred catastrophic failure but has potential high-speed sliding hazards.The research results of this paper not only further promote the understanding of high-speed landslide,enrich the dynamic mechanism of high-speed landslide,develop the dynamic model of high-speed landslide,but also provide a theoretical basis for the prevention of potential high-speed landslide. |
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