Damage Assessment And Post-Effect Prediction Of The Slopes Affected By Strong Earthquake In The Upper Reaches Of Minjiang River

Strong earthquakes are one of the main reason of slopes deformation and failure.Strong earthquakes not only induced a large number of collapses and landslides,but also caused many mountain deformation and cracks.Which are the main hidden dangers sources of rainfall-induced collapses and landslides after the strong earthquakes.It is the difficult point and crux for prevention and control of geo-hazards to Identifying and predicting the hidden dangers sources.There are many earthquakes which are high frequent and magnitude in the Upper Reaches of Minjiang River.The Ms7.5 earthquake occurred in Diexi and The Ms8.0earthquake occurred in Wenchuan were the two strongest earthquakes in the area.There are 3,507 collapses and lanslides caused directly the Wenchuan earthquake,and 2,318 new collapses and lanslides within 9 years after the earthquake.Which shows that the post-effects of the earthquake are obvious and will continue.Based on the author’s investigation and scientific research achievements in the Upper Reaches of Minjiang River before and after Wenchuan earthquake,we analyzed the deformation and failure characteristics of slop by strong earthquakes,evaluated the pre-earthquake vulnerability of geological environment,and the damage degree of slope caused by strong earthquakes.We established a post-effect prediction model about the slopes damaged by the strong earthquakes to predict the risk degree of geohazards with different rainfall intensity in different period.It will improve the level of Identifying geo-hazards,and guide to prevent and control the geo-hazards after the strong earthquakes.The main progresses and results is achieved as following:(1)A grid method for calculating and mapping the density of geo-hazards was proposed,the suitable control point distance and search radius were determined.The 8level grading standard of regional geo-hazard intensity was established with the area density and volume density of geo-hazard as the main indexes and the point density as the reference index.(2)The paper takes the cumulative geo-hazards intensity before the Wenchuan earthquake as the main index,combining with rainfall,terrain slope,engineering rock group,slope structure,fault structure and peak acceleration of ground motion,to comprehensively evaluate the geological environment vulnerability before the Wenchuan earthquake with the geological environment vulnerability index.From Manaoding to Gongpenghaizi section near Diexi Town in Maoxian County,the geological environment vulnerability is the highest.(3)On the basis of analyzing the characteristics of slop deformation and failure caused by the Diexi earthquake and Wenchuan earthquake,the deformation and failure modes of the slopes caused by the strong earthquakes are divided into four types,a total of nine modes.The intensity of collapses and landslides caused by the Wenchuan earthquake significantly increases.However,the cumulative intensity of the collapse and landslides caused by extreme events in the past were greater than caused by the Wenchuan earthquake.(4)It is established that the evaluation index system of slope damage degree caused by strong earthquakes basis on the correlation analysis between the geo-hazard of collapses and landslides caused by earthquake.The slope damage degree caused by strong earthquakes is evaluated by using information model according to the sensitivity analysis based on the grey correlation degree,and contribution rate analysis of main factor.It concluded that the causative fault had an obvious control effect on the slope deformation,and the seriousest damage area and seriouse damage area were mainly concentrated on the vicinity of the causative fault.The damage degree of slope caused by earthquakes is also obviously controlled by the height from river and slope gradient.(5)It set up a post-effect prediction model for damaged slopes by strong earthquake,based on the vulnerability degree of geological environment before the earthquakes,the damage degree of slope caused by earthquakes,and different periods,rainfall probability,rainfall intensity after the earthquakes.At last,the paper predicted the dangerous zoning of slopes affected by strong earthquakes under different periods and rainfall intensity once 50 years,and under different rainfall conditions,10 to 20 years after the Wenchuan earthquake.The grading results of prediction were positively correlated with the distribution of rainfall-induced collapses and landslides after the Wenchuan earthquake,and were consistent with the results of In SAR surface deformation analysis,which verified the validity of the prediction model.