Load-carrying capability of shield tunnel damaged by shield shell squeezing action during construction

A shield tunnel could become squeezed and damaged by shield shell such as in the case of shield tunnel floating. This would affect the load-carrying capability of the shield tunnel. To analyze this problem, a detailed 3D finite element model was developed, which takes into consideration the squeezing action of the shield shell, earth pressure, jacking force, and grouting pressure. The results show that the bending moment and shear force of the damaged tunnel are smaller than those of the undamaged tunnel while the opposite is true for the axial force. In some cases, the bending moment at the top of the damaged shield tunnel changes from positive to negative, which may result in severe leakage. Therefore, shield shell squeezing action causes the load-carrying capacity of the shield tunnel to decrease. Consequently, shield shell squeezing action should be avoided in order to ensure the safe service of the shield tunnel.