Influence Of Cumulative Friction Between Ground And Structure On Box Tunnelling-induced Ground Settlement

With developing urban underground space,rectangular tunnels are being widely used due to its high space utilization.Usually,box tunnels are mostly constructed by jacking tunneling method.The box tunnels are driven by consecutively jacking the prefabraicated linings.The friction between box linings and surrounding soils is mobilized when the jacked lining moves.The box tunnel structures bear more soil stress because the arching effect is reduced,which results in that the friction during jacking box tunnel is more siginifnicant compared with ordinary pipe jacking tunnel.The friction effect is accumulated during construction of jacking tunnel.The friction increases with the increase of cross section of box tunnel.The cumulative friction during tunnel jacking that impacts the ground settlement has not been intensively discussed.It has certain engineering guiding significance for reasonably predicting formation deformation and optimizing construction parameters.This paper proposed an analytical model to investigate the box tunnlling-induced ground settlement with consideration of the cumulative friction.As a result,a three-dimensional(3D)solution of the ground surface settlement is derived.The influence of cumulative friction on the ground settelement is discussed.The current solution is compared to the numerical simulation and in-situ measurement in real case for validation.The main content includes:(1)Study on the characteristics of ground deformation caused by box tunnels.tunneling-induced ground settlement,and study the soil layer and the force of the pipe jacking during the construction process.By summarying the exsited cases of box tunnels,the tunneling-induced ground settlement is studied by relating the maxium setttlemt to tunnel cross-sectional dimensions L×H and overburden C,δ=(Smax×C)/(L×H).The analysis results show that the box tunnelling is mainly affected by the friction,grouting pressure,support pressure and ground loss.For the coastal area,the normalized ratio distributed between 0 and 6.(2)A 3D analyitical model for the gound settlement induced by boxt tunneling is established.Based on the disturbance model of box tunneling construction in the existing semi infinite space.The cumulative effect of friction on the settlement is obtained by accumulating the friction of individual tunneling.The ground settlement subjected to ground loss is calculated using stochastic medium method.Based on above,the solution of ground surface settlement induced by box tunneling is derived.The cumulative effect of friction on ground surface settlement is explored through parametric analysis,and compared with the existing theoretical model.The results indicate that on the ground surface the soil ahead the face is uplifted and it is subsidiented behind the tunneling mechine.The maximum uplift movement is at 1H ahead the tunnel face.The gound settlement trend of the theoretical model proposed in this paper is the same as that of the existing model,and the pipe soil friction accounts for the largest proportion in the construction.Under different top distances,the friction proportion of this model considering the cumulative effect of friction increases the most,reaching 26%.It shows that the effect of friction is significant(3)Three-dimensional numerical simualtion is carried out to study the box tunneling-induced deformation.The tunnel jacking is simulated by applying the displacement on the jakcked lining.The movement induced the friction is calculated using penalty function.The ground loss is modelled using equavelant layer method.The numerical results are compared to the current analytical solution.The agreement on the ground settlement in the middle of the tunnel verifies the siginificant cumulative effect of friction that deserves more attentions in practice.(4)The current solution is validated by investigating the case of box tunnel in Suzhou.The current solution is compared to the in-situ measurement as well as to the numerical results.The comparison shows that the ground uplift deformation is attributed to the cumulative friction while the subsidence is caused by the ground loss.The current solution is capable for a certain range.The maximum uplift movement is at 1H ahead the tunnel face.