Study On Bank Slope Stability Of Large Span Bridge In Mountain Valley

Guizhou province is located in the southwest of China,it is a mountainous plateau in the southwest.There are many mountains,ravines and valleys in the region,the terrain is very Steep,and there are various Undesirable geological phenomena which make it is a serious challenge whether in the process of geological disaster prevention or construction of highway.It is a key technique to evaluate the stability of bank slope in the construction of super large Bridges in the canyon area under complicated geological conditions.The Kaizhou Lake Bridge is a part of the expressway that is from Jiangkou to Duge,and The Kaizhou Lake Bridge is across the U-shaped canyon.Both Banks slope are the first grade,and the structure of bedrock on both sides is hard at the top and soft at the bottom.The unfavorable geologic bodies are developing in the bridge location of the side of Kaiyang,which has important influence on the site selection of the main pier of the bridge,especially the accumulation body and dangerous rock mass.It is the steep terrain on the side of Wengan.and the unloading fracture zone is developing in front of bank slope.The regulation and storage of karst and reservoir water and the fluctuation of underground water level also have certain influence on the stability of bank slope.Taking Kaizhou Lake Bridge as an example,the stability of the bank slope of the long span bridge in mountain valley is studied in this paper,through geological investigation of the study area,according to the survey data of the bridge area and the geological conditions of the area,the stability analysis of Kaiyang bank and Wengan bank of Kaizhou Lake Bridge is carried out by using rigid body limit equilibrium method and finite element method,through analysis and comparison,the site selection of main pier on both sides of the river is evaluated and optimized.The main conclusions are as follows:(1)The investigation results show that the study area is a Ushaped valley,there is an anticline in the middle of the valley,and the axis strike of anticline is basically the same as that of the valley.The stratigraphic lithology is the same on both sides,and two groups of joints are developed on both sides.According to the analysis of the horizontal projection,the rock area joints of Wengan Bank are all internal inclined structural planes,the rock layer surface and joint surface of Kaiyang bank are inclined structural plane.The rock strata on both sides of the river are characterized by "hard above and soft below".Under the action of external forces,the soft rocks in the lower part are eroded and hollowed out,and " concave recess " are easy to form,this makes the upper rock vulnerable to fall;In addition,the slope on both sides of the bank is steep and slow,and there are many dangerous rocks in the front,and there are relatively thick accumulation bodies in the front of both banks.(2)According to the formation occurrence,assemblage,characteristics and structural surface characteristics of the cross-strait strata,combined with the analysis of geological survey results,the instability failure mode of the cross-strait steep slope is mainly scattered collapse.Through the investigation and analysis of the instability failure mode of the upstream and downstream accumulation body in the study area,the instability failure mode of the Kaiyang bank accumulation body is consistent with that of Wengan Bank,and the instability failure mode is traction progressive failure.(3)The bed rock of Kaiyang bank leans back as a whole,and the moderately weathered bed rock is not easy to have deep sliding,Through the analysis of Kaiyang Bank using the rigid body limit equilibrium method in four working conditions(natural bank slope,bank slope deadweight + rainstorm,bank slope deadweight + seismic load,bank slope deadweight + sudden rise of water level,bank slope deadweight + sudden drop of water level),The front edge of the accumulation body slope in the bridge area faces water and has a large thickness,and the stability calculation results do not meet the safety control standards.Therefore,it is suggested to treat the bank slope.(4)By using finite element method of main piers mizar two different location,different solutions(the full clear scheme and the less clear square strong support scheme),the different operating mode(due to gravity,bank slope weight + rain,bank slope weight + earthquake)under the bank slope stability and deformation of the numerical simulation analysis of(The elastoplastic constitutive model was adopted for the materials in the analysis and the Mohr-Coulomb criterion was complied with),The slope along the bridge and the slope across the bridge have good stability in the full clear scheme and less clear square strong support scheme at the pile maked K36+640 and K36+760 on main pier site selection of Kaiyang bank.However,due to the large excavation and deformation,it is not recommended as the site selection of the main pier of the bridge.(5)The rock of Wengan bank is anti-dip,it is the reverse slope,the stability is better,There are unloading fractures developed in the leading edge,There is a dangerous rock mass at the cutting front of the unloading fracture,the stability is poor.No large unloading fractures were found in the back edge of the main pier.The rock mass is continuous and complete,the main pier bank slope is overall stable.Finite element method is used to analyze the bank slope deformation of two pile marked K35+640 and K35+660 on Wengan bank after applying bridge load.after the bridge load is applied,the maximum displacement of both occurs at the top of the bank slope accumulation body,and the maximum displacement is 5cm.The load of the bridge has little effect on the overall deformation of the bank slope,and the unloading cracks have been avoided,Both of them are suitable for the construction of bridge main pier.