Study On Bearing Capacity And Deformation Characteristics Of Pile-plank Structure

In recent years,with the increase of national income,the number of vehicles and the number of traffic trips have been increasing,leading to the significant decline in the level of service of highways.Therefore,it is necessary to carry out the reconstruction and expansion project to the existing highways.The traditional roadbed filling schemes have many disadvantages,such as the difficulty in land requisition,the large amount of soil filling and the long construction period.The proposed pile-plank structure can effectively solve the above problems.Besides,it is friendlier to the environment.However,the application of pile-plank structure in expressway reconstruction and extension projects has only appeared in recent years,which results in few related researches are conducted.Taking the highway reconstruction and extension project as the engineering background of pileplank structure design,a finite element model,which includes a pile-plank structure,cast-in-site sections,transverse slabs,old roadbed and soil,is built.Surface to surface contact in ANSYS is adopted to simulate the contact of pile and soil,the overlap of new concrete structure and soil,the overlap of new concrete structure and old roadbed.By means of finite element simulation and parametric analysis,the bearing capacity and deformation characteristics of pile-plank structure are systematically studied.The main research work and conclusions are as follows:(1)According to the current design experience in China,the design method of pile-plank structure and the main flow of each member in the design process are systematically expounded.In the process of highway reconstruction and extension,the control factors that should be considered in the construction of each component of the pile-plank structure by precast assembly are put forward.(2)The contact,stress and internal force of plank,deflection and torsion of pile-plank structure are studied under 27 working conditions of dead load and live load which contains single vehicle load,two-vehicle load and four-vehicle load.The results show that the cast-in-place section and the old roadbed are completely separated in the transverse direction,and the transverse slab and the old roadbed are partly separated in the transverse direction when the dead load and the live load act together on the newly built structure.The two-vehicle load can make each structure layer have larger tensile stress and shear stress at the lap joint.(3)The statics response of the structure is studied by applying the most unfavorable load and changing the thickness of plank,longitudinal rib position,pile spacing and lap width.The results show that the increase of plank thickness can effectively reduce the contact stress,normal stress of bearing plank,stress of the seam of transverse slabs,pile reaction,mid-span deflection and torsion angle of bearing plank,but also increase the mid-span positive bending moment of plank and the negative bending moment of pile top.It is suggested that the thickness of bearing plank should be controlled within 30 cm-40 cm.As the longitudinal rib center distance increases,the contact stress and the transversal stress of bearing plank will be significantly reduced,but the negative bending moment and pile reaction will be increased.It is recommended that the distance between the plank cantilever end and the central of longitudinal rib should be controlled between 1.55 m and 1.75 m.The increase of pile spacing will increase the longitudinal stress and mid-span deflection of bearing plank,the negative bending moment of pile top,the pile reaction,and the tensile stress of each structure layer at the seam of transverse slabs.It is suggested that the pile spacing should be controlled at 5 m-7 m.The increase of lap width will increase the contact stress and the transversal stress of bearing plank,and also reduce the tensile stress and shear stress of the asphalt pavement layer at the the seam of transverse slabs.It is suggested to control the lap width between 0.75 m and 2.75 m.