Study On The Influence Of The Performance Deterioration Of Cement Mixing Pile Body On The Subgrade Settlement In The Salty Soft Soil Area

With the continuous development of China’s economic construction,the railway construction begins to march to the northwest region.In the salty soft soil area of northwest region,the handling method of strengthening its foundation with the cement mixing pile has been widely applied.As the salty soil will lead to the deterioration of the cement mixing pile,resulting in the decline of the bearing capacity for the composite foundation of the cement mixing pile,and affecting the safe operation of the train,therefore,it is particularly important to study the influence of cement mixing pile deterioration on the subgrade settlement in the salty soft soil area.In this paper,based on the background of strengthening the salty soft soil foundation by the cement mixing pile in the Qinghai section project of the newly-built Ge(ermu)-Ku(erler)railway,the laboratory test research of cement-soil is carried out in combination with the actual situation of the site.By means of the 5 kinds of mixed proportion cement soil under the condition of the standard curing,and dry and wet cycling of salt solution,the variation law of the unconfined compressive strength and stress strain in the cement-soil is analyzed.Then the finite element software is applied to study the settlement law of subgrade under the action of train load caused by the change of the mechanical properties after the deterioration of the cement mixing pile,and then the operation safety of train is analyzed.The main research is as follows:(1)Under the standard curing conditions,the unconfined compressive strength in the cement soil mixed only with the moderate sulphate resistant Portland cement and the cement soil mixed with the 70% moderate sulphate resistant Portland cement,30% fly ash and granulated blast furnace slag powder increases with the increase of age;When the mixing proportion of the fly ash and granulated blast furnace slag powder is increased by 35% and 50% respectively and the moderate sulfate resistant Portland cement is reduced,the unconfined compressive strength of cement soil increases gradually before the 90 d age,and then the strength decreases after the 90 d age;the unconfined compressive strength of the cement soil with 70% ordinary Portland cement,30% fly ash and granulated blast furnace slag powder increases gradually before the 90 d age,and then the strength decreases after the 90 d age.(2)Under the action of the dry and wet cycling of sulfate solution,the 5 kinds of mixed proportion cement soil test blocks are corroded by the salt solution,and the unconfined compressive strength of cement soil decreases with the increasing of cycle times.The compressive stress-strain curves for the 5 mixture proportion of cement soil are all single deviated peak curves,which are divided into the plastic ascending section,steep descending section and plastic descending section.(3)The numerical simulation results have shown that the settlement of subgrade with the ballast track as the center is symmetrically distributed toward both sides under the action of the train load,and decreases successively gradually along the depth and level direction.The settlement of the central part in the subgrade is the largest,and the settlement of the slope foot in the subgrade is the smallest.With the increasing of the deterioration degree of cement mixing pile,the settlement of the subgrade and cement mixing pile with the same mixed proportion increases gradually.(4)The numerical simulation results have shown that under the action of the train static load,all the subgrade settlements in the cement soil mixed with the moderate sulphate resistant Portland cement conform to the 150 mm of subgrade post-construction settlement value in Code for Design of Railway Earth Structure(TB 10001-2016),and the subgrade settlements in the cement soil mixed with ordinary Portland cement under the dry-wet cycling 20 times does not meet the specification values.(5)The numerical simulation results have shown that under the action of the train dynamic load,all the subgrade settlements in the cement soil mixed only with the moderate sulphate resistant Portland cement and the cement soil with the part of moderate sulfate-resistant Portland cement replaced by the 30% fly ash and granulated blast furnace slag powder conform to the 150 mm of subgrade post-construction settlement value in Code for Design of Railway Earth Structure(TB 10001-2016),and all the subgrade settlements in the cement soil mixed with the 70% ordinary Portland cement,30% fly ash and granulated blast furnace slag powder under the dry-wet cycling 5,15 and 20 times and the cement soil with the part of moderate sulfate-resistant Portland cement replaced by the 35%,50% fly ash and granulated blast furnace slag powder under the dry-wet cycling 20 times does not meet the specification values.