Displacement characteristics for a “π” shaped double cross-duct excavated by cross diaphragm (CRD) method

This paper presents a lateral launching scheme of shield with oblique-curve shaped (“π” shaped) double cross-duct excavated by cross diaphragm (CRD) method. A series of in-situ tests, theoretical analysis and numerical simulations were performed to obtain the displacement characteristics of the surface and the underground. Finally, an economic comparison of the traditional scheme and the proposed scheme was conducted. The investigation results show that: (1) The change of the tunnel curvature has an obvious influence on stratum stress distribution and deformation characteristics. (2) The ground loss, surface subsidence and horizontal convergence in the curve segment are correspondingly smaller than that in the straight section and the arching effect is also more easily formed in the curve segment. (3) On the contrary, the curvature change has little influence on the crown settlement. (4) The application of this proposed scheme improves the efficiency of shield tunneling, with also economical advantages.