Abstract
In view of the influence of symmetrical surcharge, unloading and excavation of soft clay soils on shield tunnels, the surface settlement, tunnel settlement, vertical additional earth pressure and tunnel additional confining pressure are measured by an indoor model test. The changes of confining pressure, tunnel settlement, surface settlement and vertical earth pressure caused by surcharge, unloading and excavation are studied and analyzed. The results show that, in soft clay, surcharge will cause tunnel settlement, and unloading and excavation will generally cause tunnel uplift. There is hysteresis in surface settlement and tunnel settlement above the shield tunnel caused by surcharge and unloading; the change of additional confining pressure of the shield tunnel caused by surcharge is mainly concentrated in the three directions of 3, 5 and 7 of the radar chart. These points belong to weak points. Unloading and excavation can effectively reduce the additional confining pressure of the tunnel in these three directions; excavation will cause the increase of vertical cumulative additional earth pressure and tunnel confining pressure in local directions. The influence range of surcharge in soft clay is wider than that in sand, but the depth is relatively shallow.
Highlights
Due to the shortage of urban land, there are usually many construction projects near existing shield tunnels, and surcharge, unloading and excavation often occur above existing shield tunnels [1,2,3]
The research methods of the influence of surcharge, unloading and excavation on shield tunnel of adjacent subway are mainly divided into field measurement method [3,4,5,6], theoretical analysis method [7,8,9,10,11,12,13,14,15,16,17], numerical analysis method [18,19,20,21,22] and model test method [23,24,25,26,27,28,29], among which the cost of model test method is controllable and the obtained test results are relatively reliable, which is a better method to study the influence of surcharge, unloading and excavation on the shield tunnel of an adjacent subway
Minggao Zhang et al [25] carried out an indoor model test on the vertical earth pressure of a tunnel caused by surface overload and established a finite element model
Summary
Due to the shortage of urban land, there are usually many construction projects near existing shield tunnels, and surcharge, unloading and excavation often occur above existing shield tunnels [1,2,3]. It is of great significance to study the influence of surcharge, unloading and excavation on existing shield tunnels. In view of this engineering problem, local and international scholars have done a lot of research. It is necessary to use the indoor model test method for further research In this test, a large proportion of indoor model tests were carried out with soft clay, and the effects of surcharge, unloading and excavation on existing shield tunnels and surrounding soil were studied. The comparative tests under surcharge conditions were carried out with sand, which has reference significance for engineering practice In this test, a total of 23 segments of a shield tunnel were selected as the research object. The similarity constants of the indoor model test are shown in Table 1, the geometric parameters and material properties of tunnel model are shown in Table 2, and the geometric parameters and material properties of tunnel connecting bolts are shown in Table 3 [30]
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