Abstract: Long-distance water conveyance projects often need to be buried in deep to avoid surface and shallow underground structures when crossing urban agglomerations. Shield tunnels have become an advantageous option. When the surrounding rock of tunnel is of good bearing capacity, composite lining comprising reinforced concrete inner lining and shield can be adopted together with the surrounding rock to share the high water pressure inside the tunnel. In this case, cracks are often found on the inner lining, hence changing its force characteristics. The joint forces acting on inner lining, shield segments, and surrounding rock have been the emphasis and challenge for engineering design. Yet, mature calculation method or specification is still in lack. In view of the deformation characteristics of reinforced concrete subjected to internal pressure and cracking, a simplified method of calculating the equivalent stiffness of reinforced concrete lining after cracking is proposed to calculate the joint actions of composite lining and surrounding rock under internal water pressure. Calculation result indicate that such composite structure is of good bearing capacity when the elastic modulus of rock reaches 2 GPa; when the elastic modulus amounts to 5 GPa, the composite structure could bear an internal pressure over 1 MPa. Surrounding rock can be well utilized.

Key words: shield tunnel, high pressure water conveyance, reinforced concrete lining, composite lining, joint force