Method for calculating loosening earth pressure during construction of shield tunnels

Due to the limitations on vault displacement, such as lining segment support and synchronous grouting, the soil arching effect only plays partial function during construction of shield tunnels, and the shear stress of soil is less than its shear strength. Terzaghi's loosening earth pressure theory cannot be used for this case. To solve this problem, a method for calculating lateral pressure coefficient is deduced based on the Handy's theory. The results show that the lateral pressure coefficient is associated with the rotation angle of the principal stress, and its value varies between coefficients of active and passive earth pressures. Subsequently, the development of soil arching effect is related to the vault displacement of the tunnels. Accordingly, a computational formula for loosening earth pressure is proposed considering the ground loss and the stiffness of the segment based on the Terzaghi's theory. Finally, a simplified method for predicting construction disturbance scope of tunnels is put forward by studying soil arching height.