Application Research Of Restraint Piles In The Treatment Of Expansive Soil Subgrade In Nanbai Section Of Nankun Railway

Expansive soils are widely distributed in China.Because the main components of expansive soils are montmorillonite,illite,kaolinite and other hydrophilic minerals,the expansive soils are extremely sensitive to moisture changes.When the outside world provides a large amount of water due to atmospheric precipitation and other factors,the expansive soil is very easy to absorb water and exhibits the characteristics of volume expansion of the expansive soil,which will cause great damage to the project.Subgrade diseases caused by the special engineering properties of expansive soils occur frequently every year.This article takes the expansive soil subgrade diseases appearing in Tiandong County,Nanbai Section of Nankun Railway as the research object,and analyzes the engineering properties of the soil samples taken on site.The physical and mechanical characteristics of the soil sample,to determine the expansion potential of the expansive soil,and to analyze the cause of the subgrade disease of the road section.The finite element software abaqus was used to analyze the constraining effect of the constraining pile on the deformation of the expansive soil subgrade after expansion and softening,and determine the optimal parameter of the constraining pile.The K149 + 852.55 ~ K150 + 008.55 of the Nankun Line was selected as the test section for roadbed disease remediation.A series of sensors were installed during the construction process to investigate the deformation law of the constrained pile and evaluate the effect of roadbed disease remediation.The main research contents and results are as follows:(1)In order to understand the engineering characteristics of railway subgrade filling in Tiandong County,the basic physical indicators of the expansive soil of Tiandong County subgrade on the Nankun Line were determined by specific gravity test,particle size test,limit moisture content test,liquid-plastic limit test and compaction test;Conduct compression test,direct shear test and triaxial test to analyze the mechanical parameters of the expansive soil,and finally analyze the expansive characteristics of the expansive soil through the free expansion rate test and the expansive force test to determine that the expansive soil has moderate expansion potential.(2)Collect data to understand the current status and improvement measures of subgrade diseases in the expansive soil area Shen and slope collapse and landslide.And analyze the causes of roadbed diseases,in which expansive soil is the internal cause of roadbed diseases,and water and train load are external factors.(3)Use the finite element software ABAQUS to establish a model to analyze the constraining effect of constrained piles on the expansion and softening process of expansive soil subgrade.Take different pile positions,pile lengths,pile spacing and pile cross-sectional dimensions,and determine the most restrictive piles for the project.The optimal scheme is: the constrained pile is located in the middle of the subgrade slope,the pile length is 12 m,the pile spacing is 6m,and the cross-sectional size is(4)Based on the results of finite element analysis,the specific measures and construction applications of the expansion roadbed disease treatment in the test section are confirmed.The analysis results show that the constrained pile continues to limit the deformation of the soil behind the pile during the remediation period and after the remediation is completed.The deformation of the constrained pile has always been within the elastic deformation range and has a large safety reserve.The final settlement of the unconstructed section is 7 times that of the test section,indicating that the expansion soil subgrade disease repair project is effective and can provide some reference and reference value for the improvement of subgrade disease in other expansive soil areas.