| The 2008 Wenchuan earthquake caused the mountain masses in the southwestern earthquake area to loosen,forming a large number of earthquake landslide deposits.The main characteristics of post-earthquake landslides in the earthquake area are increased sensitivity to rainfall,increased scale,reduced critical rainfall,and the conversion of landslide deposits into debris flows,which have become new threats.The sustained effects of mountain disasters after a large earthquake are usually reflected in the frequent occurrence of landslides and debris flows caused by rainfall.The research on the evolutionary characteristics of post-seismic landslides and spatio-temporal laws under the post-earthquake effect is necessary for the long-term defense and early warning of landslide disasters in earthquake regions.This study focuses on a typical post-earthquake landslide of Yindongzi gully in Dujiangyan County,Sichuan Province,after the Wenchuan earthquake.The evolution of temporal variation and spatial distribution on post-seismic landslide deposits under the sustainable effect of geohazards are studied by multi-temporal satellite images.A hydro-mechanical multi-parameter real-time monitoring system is applied in the post-seismic landslide.The stability and failure mechanism of the slope were investigated in a long period by combining the real-time monitoring data of five hydrological years and hydro-mechanical coupling theory.Combined with the real-time monitoring data of the landslide site and the rainfall-induced landslide physical model test,the evolution trend of soil-hydro parameters of landslide deposits was creatively inverted.Based on the soil-hydro parameter evolution model,the stability evolution of post-earthquake landslide under the sustained effects of mountain disasters is quantified and predicted in the next 10 years.Through the TRIGRS model,the prediction of the stability of the post-earthquake landslides was extended to a three-dimensional space environment,and further quantified and revealed the spatio-temporal evolution process of the land surface under the continuous recovery effect after the earthquake.This thesis mainly achieved the following research results:1.Based on field investigations,unmanned aerial vehicle(UAV)images,and multi-temporal satellite images,the evolution characteristics,time variation,and spatial distribution pattern of landslide disasters during the 10 years period after the earthquake in Yindongzi gully are revealed.A preliminary model of daily rainfall threshold for triggering landslides is proposed based on the rainfall triggering of disaster events.2.Based on the analysis of the long-term monitoring data and the unsaturated slope stability method,the change of soil moisture content,matric suction change,suction stress change,and stability change of the landslide site in a long period are established,and the rainfall-hydro-mechanical-stabality coupling mechanism of post-earthquake landslides is revealed.It provides a theoretical basis for identifying and revealing the hazard model of post-seismic landslides and transformed into debris flows.3.The migration of fine particles in slope is proved by combining on-site sampling of the post-earthquake landslides and the rainfall-induced landslide physical model tests,and the evolution trend of soil structure and soil strength parameters is quantified in post-earthquake landslides.Combined with the real-time monitoring data of 5 hydrological years,the evolution trend of soil-hydro characteristic parameters of landslide deposits is creatively inverted,including saturated hydraulic conductivity,residual moisture content,Van Genuchten model parameters ? and n.A prediction model with time is established.4.Based on the prediction model of soil-hydro parameters,the one-dimensional rainfall infiltration characteristics of post-seismic landslide are studied.It is proved that the suction dissipated due to rainfall infiltration is the main mechanism of post-seismic landslide instability.The matrix suction and suction stress of the slope showed a decreasing trend with the time after the earthquake,while the hydraulic conductivity showed an increasing trend.The stability analysis under two extreme rainfall conditions by soil-hydro parameters at different times is carried out to quantify and predict the stability evolution of post-earthquake landslide under the sustained effects of mountain disasters.A method for predicting the stability of post-seismic landslides under the effects of mountain disasters and post-earthquake recovery is constructed.5.The spatial evolution process of slope stability on the time scale under the continuous effect of post-earthquake landslides was predicted by the TRIGRS model.Under extreme rainfall conditions,the safety factor of slope in the space gradually increases year by year,and the slope failure area decreases gradually in time.After 3 years,5 years,7 years,and 10 years,the slope instability area accounted for 6.73%,1.67%,0.91%,and 0.12% of the total area respectively.A well post-earthquake recovery effect is manifested,and it is expected that the slope will reach an overall stable state after 2027.The quantified post-earthquake recovery effect results are applied to the modification of the rainfall intensity-probability threshold.The research methods and conclusions in this thesis provide an important theoretical basis and practical reference for the study on the temporal and spatial evolution,formation mechanism,and early warning and forecast of post-earthquake landslides under the sustained effects of mountain disasters and post-earthquake recovery.It aims to offer a reference and basic theory for the long-term prevention of post-earthquake geological disasters in the Wenchuan earthquake area. |
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