Investigation And Analysis On Settlement And Study On Treatment Technology Of Cement-soil Pile Composite Foundation Of Loess Subgrade In Existing Line

There are several main railway lines in the northwest of China.In recent years,some subgrades have subsided to varying degrees.In order to study the cause of the subsidence and take reasonable remediation projects,a site inspection of some subgrade settlement and remediation sites was conducted.Subgrade settlement of the compacted cement-soil pile composite foundation for high-speed railway sections K1642+400-K1642+610,the finite element analysis software is used to analyze the load transfer law of the compacted cement-soil pile composite foundation,and the characteristics of the stress and displacement fields of the foundation under the load The study can provide reference for similar subgrade subsidence treatment projects in the loess area,and provide reference for the design and construction of new railway subgrade projects.Concluded as follow:(1)Through the investigation of the settlement of An existing cable and a high-speed railway,it is concluded that the settlement of the existing line of loess subgrade is prone to occur in high fill road sections,bridge and culvert transition sections,and near gullies.Investigate the subsidence road section,most of the culverts near the settlement have accumulated water,and the drainage facilities are not well drained.The roadbed fillers are all fine-grained soil and have poor water stability.It is considered that the main reason for the settlement of the roadbed is insufficient compaction during construction,poor water stability of the filler,increasing rainfall year by year,and rainwater infiltrating the soil of the roadbed,resulting in insufficient bearing capacity of the roadbed.It is recommended that during the construction and operation of the new line,well-graded fillers be selected to drain the subgrade,minimize or prevent ground water from immersing in the railway subgrade for a long time,and strengthen operation and maintenance during the rainy season.(2)As the railway operation cannot be affected,grouting reinforcement is mainly used for the settlement settlement of existing railway lines.Because of the suspension of operation of a high-speed railway line K1642 + 400-K1642 + 610,compacted cement soil piles are adopted for treatment.(3)Through numerical simulation,it is found that the pile spacing,pile length,and pile material have a greater impact on the settlement of the composite foundation.The pile diameter increases to more than 0.4m,and the settlement does not change significantly.The axial force along the pile body first increases and then decreases.The magnitude of the axial force is proportional to the pile diameter,pile length,and cushion thickness,and inverselyproportional to the pile spacing.The vertical stress of the subgrade surface is the largest at3.3m from the centerline of the subgrade.Reinforcement of the cushion layer and increasing the cement content of the pile material can significantly improve the pile-soil stress ratio.(4)Through analysis of the stress field and displacement field characteristics obtained by numerical simulation,it is recommended that the value range of the pile spacing is 1.0m-1.2m;the value range of the pile length is 6m-8m;the value range of the pile diameter is 0.4m-0.5m;Cement blending ratio of bulk materials ranges from 6% to 8%;cushion thickness ranges from 0.8m to 1.0m;cement blending value ranges from 6% to 8%;two layers of geotechnical should be set at the bottom The grid is separated by 30 cm.