The Study On Coupled Thermo-hydro-mechanical Model For Stability Analysis Of Permafrost-related Slope On The Qinghai-Tibet Plateau

Climate warming has increased the frequency and intensity of extreme weather events and temperatures,accelerated the hydrothermal processes in the permafrost degradation and active layer,and changed the soil structure and mechanical properties,thus affecting the stability of slopes in permafrost areas.In order to study the stability of permafrost slopes,some scholars have developed infinite slope models based on mechanical equilibrium processes,the stability coefficient is described visually by analyzing the mechanical parameters of the slope.However,such models do not take into account the thermo–hydro–mechanical interaction processes in permafrost.With the development of numerical simulation technology,numerical models based on thermo–hydro–mechanical processes have been widely used.Currently,climate change is having a serious impact on slopes in permafrost zones.Therefore,issues such as considering the thermo–hydro–mechanical changes inside the permafrost slope under extreme temperature or extreme rainfall conditions need to be addressed.We integrated the Mohr-Coulomb criterion into the coupled thermo-hydro-mechanical model(THM)of unsaturated permafrost,and developed a coupled thermo-hydro-mechanical model of permafrost slopes(CTHM).Numerical simulation of a permafrost landslide in Qinghai-Tibet Plateau was carried out,compared with the measured parameters.The main results are as follows:(1)The conventional limit equilibrium calculation results match with the simulation results of the THM model,and the location,displacement magnitude and final form of the slip surface obtained from the numerical simulation are consistent with the field observation data.It is proved that the CTHM model established in this paper is reliable.(2)The THM model can effectively account for the impacts of VWC variation under different rainfall conditions.Rainfall with different intensities has a great effect on the VWC within a depth of 1.0 m,but has little influence at 1.35 m.Under the condition of high-intensity,short-term rainfall,the accumulated rainfall exceeds75 mm and the internal friction angle decreased from 39° to 26°,with the mudflow.In contrast,under the condition of low-intensity,long-duration rainfall,with accumulated precipitation exceeding 60 mm,the cohesion and internal friction angle decrease to 4.2 k Pa and 8.1°,respectively,with the active layer detachment.(3)Under the extreme high temperature condition in summer,when the active layer of permafrost slope melted to 1.45 m,the active layer was destabilized along the melting front,and the sliding surface is basically parallel to the slope.