Ground Settlement Caused by Shield Tunneling in Soil-Rock Composite Strata

In this study, ground surface settlement induced by shield tunneling construction is investigated, where special strata composed of upper soil layers and lower rock layers are fully considered. The field data indicates that in soil-rock composite strata, the settlement trough along the transverse surface shows approximately normal distribution. The settlement that occurs during construction accounts for more than 60% of final settlement. The traditional Peck formula was modified to fit this composite strata by regression analysis of the measured data. The suggested values of modification factors alpha and beta ranged from 0.6 to 1.2 and from 0.3 to 0.9, respectively. Moreover, the results of the numerical simulation show that the settlement pattern along the transverse surface in the soil-rock composite strata is significantly influenced by the hard-layer ratio m (hard-layer depth to excavation diameter). Surface settlement decreases, but trough width increases with as the hard-layer ratio increases. In particular, a roughly linear relationship between maximum surface settlement and hard-layer ratio is presented. A method of predicting settlement in shield tunneling construction in soil-rock composite strata is also proposed in this study. (C) 2021 American Society of Civil Engineers.