Research On The Optimizeddesign Method Of Deep Buried Pile And Composite Beam-slab Structure Of High-speed Railway Subgrade In Karst Area

The deepburied pile composite beam-slab structure is the latest type of deep buried pile-slab structure.The main feature is that the T-beam bears the subgrade load.Compared with the traditional pile-slab structures,the deep buried pile composite beam-slab structure has the following advantages over the traditional pile-slab structure: the plate is used by the flange of the beam,which is a two-way plate bearing four-sided forced,and the contact area with the beam is larger,which becomes easier to meet the requirements of punching shear force;simultaneous poueing of beams and slabs can speed up the construction schedule and shorten the construction period,which achieves better technical and economic performance.At present,the research on pile-slab structure has achieved many results,but there is still no relevant norms or regulations for the design method of pile-slab structure.Besides,the deep buried pile composite beam-slab structure is first applied in the domestic high-speed railway base.There is still a lack of research on how to further optimize its design method.This paper is based on the background ofthe deep buried pile composite beam-slab structure subgrade of the Qianzhangchang high-speedrailway,and the three-dimensional finite element analysis model,preliminary design method,simplified mechanical calculation model and optimization design method for deep-buried pile composite beam-slab structure are studied.The main contents are as follows:(1)This paper summarizes the current problems of constructing high-speed railway foundation in karst area,as well as the application examples,theoretical research,experimental research and numerical simulation analysis of the pile-slab structure at home and abroad,and comprehensively summarizes the current research status of pile-slab structure at home and abroad.Based on the detailed description of the characteristics of different types of pile-slab structures,the advantages and disadvantages of different types of pile-slab structures and their applicable conditions are compared and analyzed.Based on the special geological conditions in which the gap of the test section is widely developed,the deepburied pile composite beam-slab structure is proposed.(2)Through on-site monitoring of the deep buried pile composite beam-slab structure of the Qianzhangchang high-speedrailway,the monitoring data of pile internal force,longitudi-nal beam internal force and deformation,bearing plate internal force and deformation,foundation reaction force and settlement are obtained.(3)The three-dimensional finite element analysis model of the deepburied pile composite beam-slab structure in karst areais established by Midas GTS NX,and the actual monitoring data are respectively compared with the internal force of the structure,the ground reaction force and the foundation settlement,which verifies the validity of the model established.And the model is applied to the optimization design of the deepburied pile composite beam-slab structure in karst area.(4)The preliminary design method of deep-buried pile-slab structure in karst area is explained,which includes: design principle,preliminary design flow,structural member size design method,design load,internal force calculation method and the reinforcement design and verification method.(5)A simplified mechanical calculation model of deep-buried pile composite beam-slab structure considering the action of foundation reaction is proposed.The internal force of the component is deduced.The calculated internal force in combination with the on-site monitoring data is compared with the preliminary design internal force and measured data,indicating simplification.The validity of the simplified mechanical model is verified and can be used in the optimization calculation of deep-buried pile composite beam-slab structure.(6)The orthogonal analysis method is used to optimize the design of the deep-buried pile composite beam-slab structure in the karst area.In the optimization analysis,the finite element model is used to participate in the auxiliary calculation,and the optimal size range of the main components affecting the mechanical and economic benefits of the structure is obtained.After formulating the comparison scheme and introducing the simplified mechanical calculation model to participate in the optimization calculation,the most suitable design scheme for the deep-buried pile composite beam-slab structure in the karst area is obtained.