Study On Genetic Mechanism And Stability Of An Ancient Landslide Group On Riverine Expressway

The riverine expressway runs from Yibin along the Jinsha River to Leibo,Jinyang,Ningnan,Huidong,Huili,and ends at Panzhihua.The total length is about 478 kilometers.It is an important Part of the highway from Chengdu to Lijiang in the National Highway Network Planning.The geological structure along the highway is complex,and the geological hazard of landslide is prominent.The ancient landslide group studied in this Paper is located in Shili Township,Ningnan County.The highway Passes through the landslide area in the form of bridge.The stability of the landslide will directly affect the construction and operation safety of the highway.Therefore,to study the genesis mechanism of the ancient landslide group,evaluate the stability of the landslide,and then put forward the landslide control plan,which has great guiding significance to ensure the highway construction and safe operation.In this Paper,by means of engineering geological mapping and drilling,on the basis of finding out the engineering geological conditions and the basic characteristics of the landslide area,the geological mechanical analysis method is used to analyze the formation conditions and genetic mechanism of the landslide.The stability of the landslide is evaluated by combining the qualitative analysis and the quantitative analysis.Taking HP05 as a typical research object,the stability of landslide before and after the construction of bridge pile foundation and the displacement characteristics of pile foundation are analyzed by means of numerical simulation.The corresponding landslide treatment scheme is proposed,and the effectiveness of landslide treatment scheme is demonstrated by FLAC 3D software.The main research results are as follows:(1)The ancient landslide group is developed in the consequent or oblique consequent slope with sandstone,mudstone and shale interbedding of unequal thickness.The landslide group includes 11 landslides.Among them,HP01,HP02,HP03,HP04 and HP05 belong to large-to-especially large landslides.HP06,HP07,HP08,HP09 and HP10 are medium-sized landslides.The route Passes through HP05,HP06,HP07 and HP08.(2)Based on the understanding of landslide development characteristics,the formation conditions of landslide are analyzed,and then the genetic mechanism of landslide is studied.The research shows that the formation of landslide is mainly caused by the combined influence of the valley cutting which leads to the dew of the weak interlayer and the softening of rainfall and mud action of the weak interlayer,the mechanical properties of the weak interlayer decrease,the internal cracks of slope body continuously ex Pand along the front edge of the weak interlayer,the anti-sliding ability of slope decreases.And that eventually leads to landslide sliding.(3)On the basis of qualitative analysis,the stability of HP01,HP02,HP03,HP05,HP06,HP07 and HP08 under the natural,rainstorm and earthquake conditions are quantitatively analyzed by using transfer coefficient method.Under the earthquake conditions,HP07 is in a stable state,while HP01,HP02,HP03,HP05,HP06 and HP08 are in a basically stable state.The rear Part of HP03,the front and near Part of HP05 are basically stable under the conditions of rainstorm and earthquake.Among them,the stability factor of HP05 under heavy rain conditions is less than the safety factor,and the stability does not meet the engineering requirements.(4)Taking HP05 as the research object,the numerical simulation method is used to study the stability of the landslide before and after the pile foundation is applied and the displacement of the pile foundation under different working conditions.The results show that HP05 is basically stable under heavy rain and earthquake conditions,and it is stable under natural conditions;The displacement of pile foundation exceeds the allowable value of bridge displacement under rainstorm and earthquake conditions,which seriously threatens the safety of the bridge.(5)On the basis of stability study of HP05 and displacement study of bridge pile foundation,a treatment scheme of "cut-off drainage + anti-slide pile" is put forward,and its effectiveness is demonstrated by FLCA 3D software.