Research on the Stability of the Working Face of Large-diameter Shield Tun-nelling in Upper Hard and Lower Soft Composite Strata
The construction of large-diameter shield tunnels in upper hard and lower soft composite strata signifi-cantly increases the difficulty of maintaining the stability of the tunnel excavation face.To investigate the influence of the relative hardness of the upper and lower strata on the failure mechanism of the excavation face,numerical and theoretical methods were systematically employed to study the evolution mechanism of excavation face instability un-der different unconfined compressive strength ratios(Ku/Kl).Numerical simulations revealed changes in the instability modes of the excavation face as Ku/Kl increased.A theoretical model predicting excavation face instability considering different strength ratios was established and validated against related theoretical models.The results indicate that:(1)as Ku/Kl increases,the ultimate support pressure first decreases rapidly,then gradually stabilizes;(2)the Ding model is most sensitive to variations in Ku/Kl and provides more conservative predictions,while the results of the Mollon model and the model proposed in this paper are closer to numerical simulations;(3)when the failure angle is taken as 45°+φ/2,the maximum ultimate support pressure required to maintain the stability of the excavation face is obtained;(4)as cohesion and internal friction angle increase,the critical Ku/Kl decreases linearly;the critical Ku/K,remains unchanged with increasing burial ratio and soil density.
Shield tunnelComposite strataUpper hard and lower softExcavation faceLimit equilibrium method
万方数据
维普
