Application And Research Of Composite Beam And Slab Pile-slab Structure For Railway Subgrade In Karst Area

The beam-plate composite pile-slab structure,as an improved new-type pile-slab structure,has the advantages of strong integrity and short construction period.At present,this type of pile-slab structure is less used in railway subgrades,and there are few corresponding projects that use this type of pile-slab structure under the karst geological conditions.The corresponding engineering practice experience is not yet mature and the related information is lacking.Therefore,in this paper,based on the engineering background of the beam-slab composite piled slab foundation in the karst area of the Xian Feng section of the Qian Zhang Chang rapid railway,theoretical analysis,on-site monitoring,and numerical simulation are used to systematically research the mechanism of the foundation of the beam-plate composite pile-slab structure in the karst area,which provided a relatively scientific technical reference for the design and calculation of the pile-slab structure foundation.Firstly,the typical section DK49+825.8 is selected under the karst geology of the Xian Feng section of the Qian Zhang Chang rapid railway,which is used to monitor and analyze the stress of the pile,the stress of the stringer and the crossbeam,the subgrade reaction at the bottom of the bearing plate,and the settlement of the foundation.In summary,the stress characteristics of the pile,the stress characteristics of the vertical and horizontal beams,the stress characteristics of the bearing plate,and the settlement deformation characteristics of the foundation were obtained.The analysis shows that under the condition of karst geology,the use of beam-slab composite pile-slab structure foundation can effectively control the subgrade settlement and improve the overall stability of the roadbed.Secondly,combining with the in-situ investigation data,the actual physical model was extracted,and the three-dimensional numerical simulation of the beam-pile composite pile-slab structure foundation was performed.The feasibility of establishing a numerical model was verified through the comparison and analysis between the in-site monitoring data and the results of numerical simulation.Finally,a large-scale finite element analysis software was used to analyze the influence of cavern on the beam-plate composite pile-slab structure.The classification study based on the spatial relationship between the cavern and the pile-plate structure has been conducted.When the cavern is located just below the pile foundation,the influence of its shape,size,and roof thickness on the bearing and deformation characteristics of the pile foundation are studied;When the cavern is located in the side of pile of pile-slab structure,the size of the cavern,the horizontal distance between the pile and the cavern,and the pile diameter are selected to study the influence on the bearing and deformation characteristics of the pile-slab structure.When the cavern is located directly below the bearing plate,the size of the cavern,the depth of burial,and the thickness of the bearing plate are selected to study the bearing and deformation characteristics of the bearing plate.It enriches the theoretical system for the study of the mechanism of the pile-plate structure in the karst area.