Prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum

This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of numerical analyses is performed to examine the effects of cover depth ratio(C/D),tunnel volume loss rate(h t)and volumetric block proportion(VBP)on the characteristics of subsurface settle-ment trough and soil volume loss.Considering the ground loss variation with depth,three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown.Then,analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory.The influences of C/D,h t and VBP on the key parameters(i.e.B and N)in the analytical expressions are discussed to determine the fitting formulae of B and N.Finally,the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation.Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters.Besides,the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.

Empirical evidence for estimation of subsurface settlement caused by tunneling in sand

Tunneling is vital for augmenting urban infrastructure systems in big cities.However,the ground movement or settlement induced by tunneling can cause significant damage to the surrounding buildings,bridges,roadways,pipelines,and so on.Several theoretical and empirical methods have been proposed to estimate the settlement trough at the ground surface caused by tunneling.Subsurface settlement caused by tunneling in clay has been investigated extensively to evaluate the safety of pipelines and foundations above tunnels based on the assumption of a constant volume of the settlement trough along the depth.However,subsurface settlement induced by tunneling in sand has not been understood well due to the change of volume of settlement trough along the depth.Even though an empirical method was developed by the author based on lab-scale model test results,it has not been validated using observational data from case histories.In this study,three case histories from the literature were used to verify the effectiveness of the aforementioned empirical method for estimating the subsurface settlement caused by tunneling in sand.The comparison of the calculated results and measurements from the case histories demonstrates that the empirical method is effective to predict the subsurface settlement caused by tunneling in sand.