Study On Construction Mechanics Of Shallow-Buried Large-Span Variable Section Subway Tunnel Group

With the development of the cities,the traffic space of cities could not meet the demand of people.Subway has been more and more welcomed,as for its advantages.And tunnel groups could be more and more with the development of subway.The research contents of this paper are based on 7th line subway in ShenZhen.In this paper,the construction method of shallow-buried excavation of subway tunnel group is discussed,the ground surface settlement law is studied,based on which the simplified model has been put forward to get an acceptable solution of ground surface settlement,the simulation of 7th line subway is carried on,based on which the surrounding rock of tunnel group is studied in detail,and 4 kinds of construction processes are simulated to study their differences.And the conclusions obtained are as follows.(1)Peck empirical formula could be used to study the ground surface law in metro construction in ShenZhen.The acceptable solution in engineering could be got by using simplified model.(2)The deformed surface of ground surface is saddle-shaped,after the construction of the subway tunnel group.The largest maximum principal stress of large cross-section tunnel lining structure locates at the arch springing,while the distribution of small cross-section tunnel maximum principal stress is quite symmetrical.(3)During the construction of large cross-section tunnel,the vault settled twice.The first time is when the soil under the vault is excavated.And the second time is when the temporary support is dismantled.The vault settled much larger during the second time.Therefore,if the settlement of the vault of large cross-section tunnel is wanted to be controlled,some measures should be taken when dismantling temporary support.(4)The ground surface settlement law,the stress distribution law of surrounding rock,the settlement distribution law of the vault and the distribution law of plastic zone of subway tunnel group are basically the same under the 4 kinds of construction processes.And the construction process should be chosen according to controlling value in the engineering.