Long-term settlement behavior of ground around shield tunnel due to leakage of water in soft deposit of Shanghai

The lining of shield tunnel is usually composed of segments,in which the joints,cracks,and the grouting holes(hereafter called lining deficit)exist.During the long-term running,soils and groundwater may leak from these kinds of lining deficit.The leaking of soil and groundwater causes the long-term ground loss around tunnel and thus results in the settlement of ground surface.This paper aims to analyze the impact of the leakage of groundwater through segments on the long-term settlement of ground surface.The adopted analytical method is based on the theory of groundwater seepage by using numerical simulation.The analyzed results show that settlement of ground surface increases gradually with the increase of the leaked volume of tunnel segments.When the leaked volume was unevenly distributed,differential settlement occurred locally.Comparative analysis by changing the leaked volume was conducted.The results reveal that there is a linear relationship between settlement and leaked volume when the leaked volume was controlled within the allowable limit.

Lateral displacement of soft ground under vacuum pressure and surcharge load

Surcharge load(e.g.embankment fill)will induce settlement and outward lateral displacement,while vacuum pressure will induce settlement and inward lateral displacement of a ground.Ideally,combination of surcharge load and vacuum pressure can reduce or minimize the lateral displacement.Laboratory large scale model(length:1.50 m,width:~0.62 m,height:0.85 m)tests and finite element analyses(FEA)were conducted to investigate the main influencing factors on lateral displacement of a soft clayey ground under the combination of vacuum pressure and surcharge load.For the conditions investigated,the results indicate that the outward lateral displacement increases with the increase of the ratio of surcharge load to vacuum pressure(RL)and the loading rate of the surcharge load(LR).Also,it is shown that for a given RL and LR condition,lateral displacement reduces with the increase of the initial undrained shear strength(Su)of the ground.To predict the lateral displacement of a ground under the combination of surcharge load and vacuum pressure,the loading conditions in terms of RL and LR,and Su value of the ground have to be considered.