Research On Settlement Control Of Chongli Railway Across The Air-Raid Shelter Section

With the continuous development of China ’ s railway industry,it is inevitable to cross the shelter in the process of high-speed railway construction,which increases the difficulty of controlling the post-construction settlement of high-speed railway.In loess areas,due to the unique collapsibility of loess,the problem of subgrade settlement control is more prominent.Based on the newly built Chong li Railway,this paper takes the collapsible loess foundation of DK16 + 083 ～ DK16 + 276 crossing the air raid shelter section as the research object,Combined with the characteristics of loess and the situation of underground air-raid shelter,Establish a finite element model of the subgrade in the research section.The treatment measures of combination of column hammer pile expansion method and cement mortar backfill in air-raid shelter are put forward,The subgrade settlement after the selected measures are monitored and the post-construction settlement is predicted to verify the foundation treatment effect of the selected measures.Through the field monitoring of subgrade settlement and finite element numerical simulation,the conclusions are as follows :(1)The foundation treatment measures of the combination of column hammer expansion pile and air-raid shelter cement mortar backfill are proposed.Numerical simulation results show that this method can eliminate the hidden dangers of air-raid shelters.And the settlement control effect is better in different air-raid shelter tunnel diameter sections and before and after live load is applied,The rationality of the selected scheme was verified.(2)Based on the above selected foundation treatment method,the finite element subgrade models under different working conditions are established to explore the influence of different pile length,pile diameter,pile spacing and cement mortar elastic modulus on the bearing and settlement characteristics of composite foundation.It can be concluded that the pile length,pile diameter and pile spacing in the parameters of column hammer pile have a certain influence on the settlement values,and the sensitivity of pile length is highest.The change of elastic modulus of cement mortar has little effect on settlement value when it is much larger than the modulus of loess in reinforced area.Study and select the parameters of column hammer expansion pile and air-raid shelter cement mortar backfill treatment measures are pile length 20 m,pile diameter 0.6m,pile spacing 1.2m,cement mortar elastic modulus 50 MPa.(3)The settlement deformation monitoring of the subgrade after the selected measures are carried out,and the settlement characteristics are analyzed.Using hyperbolic method,exponential curve method,Asaoka method and three-point method to fit the measured data respectively,It is concluded that the fitting correlation coefficient and accuracy of hyperbolic method are the highest,and the predicted post-construction settlement value is 13.70 mm,which meets the requirements of specification limits.The settlement control effect of the selected treatment measures was verified.The above research results have been successfully applied in the treatment design and construction of collapsible loess foundation across the air-raid shelter section of Chongli Railway DK16+083-DK16+276.It can be seen from the settlement field monitoring and the post-construction settlement value that the overall construction is smooth and the effect is good.The relevant conclusions and success can provide useful reference for foundation treatment design and construction of similar projects in the future,and have certain research value.