Study On The Application Of Foamed Light-Weight Soil In The Open-Cut Tunnel Backfill

In the construction of urban underground traffic network,in order to save construction cost and improve engineering economy,most tunnel construction will adopt open excavation method.It is inevitable to involve the backfill construction in the excavation area after the construction of the open excavation method.The research shows that with the increasing depth of the tunnel and the increasing height of the backfill,the traditional backfill materials are easy to cause greater earth pressure on the tunnel and threaten the safety of the tunnel under the backfill area.In this thesis,from the perspective of changing the weight of backfill soil,the foamed lightweight soil with light weight,good fluidity and convenient construction is applied to the backfill after the construction of open-cut tunnel.Through the combination of indoor test,numerical simulation and field application,the application of foamed lightweight soil in the backfill of open-cut tunnel is studied.The main research contents and conclusions are as follows :from the perspective of changing the bulk density of backfill soil,the foamed lightweight soil with light weight,good fluidity and convenient construction is applied to the backfill of complex urban underground structure.Through the combination of indoor test,numerical simulation and field application,the backfill application of foamed lightweight soil in complex urban underground structure is studied.The main research contents and conclusions are as follows:(1)Determine the raw materials used in the preparation of foamed lightweight soil,test the performance of raw materials,and compare them with the requirements of the specifications for various performance indicators of raw materials,and conclude that the raw materials used meet the specifications.Referring to the mix design method of foamed lightweight soil in the specification,the mix design of foamed lightweight soil is calculated.(2)According to the design of 9 groups of foamed lightweight soil mix ratios under different water-cement ratios,the indoor test method was adopted to verify the fluidity,wet bulk density,compressive strength and flexural strength parameters of each group of mix ratios,and compared with the relevant specifications.The amount of cement per 1m3 of foamed lightweight soil is 375.1 kg,the amount of water is 206.3 kg,and the amount of foam group is 18.6 kg.(3)With the help of finite element analysis software ABAQUS,combined with the practical application of the joint reconstruction project of Jinzhou Avenue and Xingguang Avenue extension section in Dazhulin Area of Chongqing Liangjiang New Area,the stress and displacement of the upper and lower tunnels under different backfilling schemes are simulated and analyzed.The change of the displacement shows that the foam lightweight soil backfilling can effectively reduce the vertical displacement and maximum shear stress of the bottom tunnel,and the scheme of backfilling the area between the upper left and right tunnels with foam lightweight soil is determined.(4)The field construction application of the actual project is carried out.The strain and earth pressure of the tunnel structure after backfilling are monitored by the field monitoring method.The monitoring data are analyzed and compared with the simulation results.It is concluded that the stress and displacement changes of the upper and lower tunnels are consistent with the simulation results.However,due to many interference factors in the field monitoring data,some data will deviate from the simulation results.