Study On Settlement And Thermal Insulation Of High-speed Railway Foundation Reinforced By SRC Piles In Seasonal Frozen Area

With the rapid development of high-speed railway,there must be enough solid railway subgrade to provide bearing capacity.According to the design code of high-speed railway subgrade,the post construction settlement of Ballasted Track Subgrade shall not be higher than 50mm,and the post construction settlement of Ballastless Track Sub grade shall not be higher than 15mm,otherwise,reinforcement treatment shall be carried out.At present,CFG pile and reinforced concrete pile are widely used for reinforcement,and the construction method is still in the form of on-site pouring,such as drilling and pouring,which is not only complex in technology,but also difficult to grasp the quality of pile.The steel reinforced concrete pile combines the excellent performance of steel and concrete,and has the advantages of large rigidity and prefabrication,which can greatly improve the integrity of pile-soil,reduce construction disturbance and reduce environmental pollution.In addition,in the seasonal frozen soil area,the subgrade soil is prone to frost heaving and thawing settlement.At present,the way of laying insulation board is mostly used for prevention,but there is no quantitative standard for specific laying parameters.Using the method of theoretical analysis and numerical simulation,the coupling analysis of water,heat and force of high-speed railway subgrade is carried out by using ABAQUS.The results show that the maximum value of vertical consolidation settlement is 66mm after the completion of subgrade filling;In the first year,the frost heave displacement is 7.26mm and the thaw settlement displacement is 9.84mm;In the second year,the frost heave displacement is 9.46mm,and the thaw settlement displacement is 11.26mm,which indicates that the internal water content of subgrade increases under the condition of rainfall,resulting in greater displacement of Subgrade under the effect of freeze-thaw cycle.Steel reinforced concrete piles are used to reinforce the sections whose settlement displacement exceeds the design specifications,and the influence of pile design parameters on subgrade settlement is analyzed.The simulation results show that the settlement value of subgrade changes with the changes of pile size,pile spacing and pile material,and the influence of pile length on settlement displacement depends on the bearing capacity of lower bearing stratum.Both the pile diameter and the pile spacing will change the settlement displacement because of the change of the overall stiffness of the pile and soil,but the influence of the pile diameter on the settlement of the subgrade is less than the influence of the pile spacing on the subgrade settlement.Because of the difference of modulus of elasticity between section steel and concrete,the change of concrete material has little influence on the change of subgrade settlement.In addition,the thermal insulation board is laid on the road section where frost heaving and thawing occur,and the best laying parameters of the thermal insulation board are discussed.The simulation results show that the temperature field distribution of Pu board,EPS board and XPS board is almost the same.Combined with the overall performance,tightness and economy of the material,the XPS insulation board is finally selected.As far as the subgrade is concerned,the best thermal insulation effect is to embed a 100 mm thick XPS insulation board parallel to the subgrade surface at a depth of 100 mm and extend it to the bottom of the subgrade bed.