Study On Construction Performance Of Shallow Large Section Tunnel By Partition Freezing And Branch Construction

In this paper,Guangzhou Metro Line 6 section tunnel as the research object,combined with indoor test,using numerical simulation method,the frost heaving and thawing settlement phenomenon of shallow buried large section tunnel caused by zonal freezing is studied.On this basis,combined with horizontal grouting and frost heaving control technology,the construction method of zonal freezing and subsection construction is proposed.The main research contents and results are as follows:(1)The thermophysical and mechanical properties of artificial frozen soil are studied by laboratory test.The basic physical parameters such as density,elastic modulus and Poisson’s ratio of frozen soil and thawed soil,and the thermal physical parameters such as freezing temperature and thermal conductivity are obtained,which lay a foundation for further numerical simulation.(2)The formation process of frozen soil curtain and thawing settlement during thawing period of shallow buried tunnel during zonal freezing construction are numerically simulated and predicted by using thermal mechanical coupling numerical simulation method.The results show that the maximum frost heave displacement of the ground is 102 mm and that of the ground is 100 mm after 45 days of active freezing.During the thawing period,after thawing for 125 days,the maximum ground settlement is～50 mm and the maximum surface settlement is-51.4 mm.Therefore,strict control measures should be taken for frost heaving and thawing settlement.(3)Numerical simulation is used to verify the feasibility of the whole construction process.The results show that the vertical displacement and horizontal displacement of frost heaving are reduced from excavation to enclosure to structure construction,regardless of the upper soil or lower soil in the first freezing area,and the second freezing area is similar to the first.Because the vertical frost heave displacement is larger than the horizontal frost heave displacement and has great harm,corresponding measures and auxiliary means should be taken to control the vertical frost heave.(4)Through on-site monitoring,the frost heaving control effect is analyzed.The monitoring results show that the improvement technology of local horizontal grouting solves the problem of slow development of local frozen wall and ensures the integrity of frozen wall in active freezing period.The ground deformation caused by frost heaving reduces the influence on the existing station structure.Figure 62 table 14 reference 88...