Stability Analysis on Curved Shield Tunnel Excavation Face Under Seepage
The curved shield tunnel of Tianjin Metro Line 11 is located at the water-rich sand layer,and it is difficult to control the excavation face stability due to the asymmetric thrust and seepage force of jack.Based on the silo theory and limit equilibrium method,the traditional wedge model was improved,and the inclined ladder-wedge prism model was established.The analytical formula of ultimate support force of shallow-buried curved shield tunnel excavation face affected by seepage was derived.The model results were verified by using numerical simulation and engineering examples,and the influence of parameters was analyzed.The result indicates that under the seepage,the seepage force constitutes an important part of ultimate support force of shallow-buried shield tunnel excavation face.Under the engineering geological conditions,the seepage force can account for 46％of ultimate support force at the highest,and the seepage force is greatly affected by the groundwater level.The theoretical calculation results of this model are close to the numerical simulation results with the error within 5％,which proves the rationality of three-dimensional calculation model proposed in this paper.To ensure the engineering safety in actual construction,the actual support force for shield tunnel is greater than the theoretical value of ultimate support force.The solution of this formula can provide the reference value for the actual engineering construction.The ultimate support force for curved tunnel is negatively correlated with the internal friction angle of soil,cohesion and line radius.When the tunnel line radius is less than 300 m,the ultimate support force for tunnel fluctuates greatly;when the tunnel line radius is over 600 m,the ultimate support force of excavation face gradually approaches the straight tunnel.During the construction on shield tunnel with sharp curve and under bad geological condition,it is necessary to adjust shield parameters in time to maintain the tunnel excavation stability.
tunnel engineeringultimate support forcelimit equilibrium methodshield tunnelseepage
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