Study On Force Characteristics And Loads Sharing Effect Of Existing-Newly Built Front And Rear Composite Pile-slab Wall

In the reconstruction and expansion project of existing railway lines,the width of subgrade and backfilling of subgrade and the selection of subgrade support structure are the core content of design and construction,as well as the difficulties and hotspots of scientific research in subgrade engineering.As a new type of supporting structure,the existing-new front and rear composite pile-slab wall is relatively more complicated than the ordinary single-row pile-slab wall.The previous research on the front and rear composite structure mainly focused on the slope treatment and foundation of the new construction.In the pit support project,the research on the front and rear composite pile-slab wall used in the subgrade side wide backfill project is relatively lacking.The existing-new front and rear composite pile-slab walls are improved in the structure of h-shaped anti-slide piles and double-row gantry-type anti-slide piles.Its mechanical mechanism,structural internal force characteristics,and displacement change rules are similar to those of h-shaped anti-slide piles.And the double-row gantry anti-slide piles are not the same.This thesis is mainly divided into three parts: theoretical analysis,field test and numerical simulation.The main content and results are as follows:(1)According to the current research theory of h-shaped anti-slide piles,the structural calculation mode of the existing-new front and rear composite pile-slab wall is analyzed,the load model and the calculation model of the structural internal force are described,and the existing piles are proposed.1.Theoretical law of internal force of the core component of the composite structure formed by the connection of newly-built piles and beams.(2)According to the on-site test plan and closely follow the on-site construction progress,the on-site test research was carried out,and the soil pressure on the side of the pile body was tested by the soil pressure box during the subgrade side width backfilling process,and the distribution trends and changes of the soil pressure at different stages were obtained.Laws;use the reinforcement meter installed on the main reinforcement of the pile to test the stress of the reinforcement,and then calculate the pile bending moment value of the newly built pile-slab wall,analyze the change rule of the pile bending moment along the depth;use the inclination tube to test the occurrence of the pile Lateral displacement,to study the incremental size of the lateral displacement of the pile top with the width of the subgrade in the process of backfilling.(3)The finite element method was used to establish a numerical calculation model,and by simulating the complete construction phase of the actual project,the internal force form and the lateral direction of the existing-new front and rear composite pile-slab wall retaining structure after the new railway line was completed and operated were summarized.The displacement verifies the safety of the subgrade engineering after the design and construction,evaluates the safety reserve of the existing pile-slab wall,and analyzes the load-sharing effect of the existing-built front and rear composite pile-slab wall.Using the finite element model,the influence of the new pile section,the distance between front and rear combination rows,the relative stiffness of the new beam and the connection method on the bearing performance of the existing-new front and rear combination pile-slab wall was analyzed by changing the parameters of the new structure.(4)The theoretical analysis part discusses the classic earth pressure theory and the basic law of loading mode and internal force displacement of the existing-newly built composite pile-slab wall;the field test part studies the existing-new building through the test components installed during the on-site construction The variation law of the front and rear composite pile-slab wall during the width phase of the subgrade slope,the pile body bending moment,and the pile body horizontal displacement;the numerical simulation part uses Midas GTS NX software to calculate the existing-new front and rear composite pile-slab wall The internal force and horizontal displacement of the pile body are evaluated and analyzed,the safety reserve of the existing pile-slab wall,the load sharing effect of the existing-new composite pile-slab wall before and after the new construction,and the influence of the new structure parameter change on the mechanical characteristics of the composite retaining structure.