| With the advancement of the "Belt and Road" and "Western Development" strategies,the road network construction has been continuously improved,and high and steep slopes have gradually formed along the route.A large number of collapsible loess are widely distributed in the northwest region,which has strong "water sensitivity" and "dynamic vulnerability",and is prone to collapse,landslide and other disasters.In this paper,aiming at the disaster problem caused by collapsible loess,by exploring the physical and mechanical properties of collapsible loess,analyzing the failure mode and disaster-causing factors of slope,the comprehensive risk assessment of collapsible loess slope is carried out,and the protective measures are taken according to the evaluation results,which can effectively avoid the geological disasters caused by slope instability.Based on the collapsible loess slope project of Tongding Expressway in Gansu Province,the comprehensive risk of collapsible loess slope is systematically studied by means of mathematical statistics,numerical simulation,fuzzy mathematics and other multidisciplinary methods.The main research work is as follows :(1)According to the geographical location,climate,hydrology,topography and other related factors of the project,the field investigation was carried out.Based on the indoor soil test,the correlation between the physical properties of loess soil samples and the collapsibility coefficient was studied.The typical representative indexes were determined by factor analysis method.The quantitative prediction model of loess collapsibility coefficient was established by BP neural network technology,and the accuracy of the model was verified by non-parent test data.(2)The failure mechanism and important disaster-causing factors of collapsible loess slope are systematically analyzed.The stability of K6+520 collapsible loess slope under rainfall and earthquake is calculated by finite element software.Through the study of the variation law of effective stress,pore water pressure,displacement and safety factor under rainfall infiltration conditions,as well as the analysis of the change mechanism of velocity,displacement response law,effective plastic zone and safety factor under horizontal seismic action,it provides a theoretical basis for further research on comprehensive risk assessment of collapsible loess slope.(3)Based on the fuzzy hierarchical analysis method,combining the characteristics of collapsible loess and risk factors of instability,the risk assessment hierarchy of collapsible loess slope instability is divided,and further subdivided into 17 secondary indicators on the basis of four major factors,such as engineering geological characteristics,slope section characteristics,triggering factors,engineering protection and greening.The weight value of each index is determined through the hierarchical analysis method,and then the risk matrix method is used to combine the risk level of instability of wet sinking loess slopes and the severity of instability consequences to obtain a comprehensive risk assessment system for wet sinking loess.(4)Taking the K6+520 slope of Tongding Expressway as an example,the comprehensive risk assessment system of collapsible loess slope is used to compare the comprehensive risk level of slope before and after protection,and the effectiveness of protective measures is tested.At the same time,the finite element software is used to simulate and analyze the protective measures,and it is verified that setting a wide platform and adding bolts under the action of rainstorm and earthquake has a significant effect on improving the slope stability. |
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