Abstract:

The force characteristics of prestressed composite linings with a cushion layer for water
conveyance shield tunnel are studied. To simulate this structure, a three-dimensional finite-element model of
whole structure is developed on a platform of the FEM code ANSYS and applied to the design of the Yellow
River-crossing tunnel for the middle route project of south-to-north water diversion. For two cases of the
composite structure with or without a cushion layer, stress distributions in the inner lining and outer lining
are compared, and force transmission mechanism between the two linings are analyzed for different stiffness
of the cushion. And the effect of a change in cushion stiffness on the hoop stress in the linings is examined.
The results reveal that for the structure of prestressed composite linings, if a cushion layer is added
appropriately, its prestressed tension can be in full use and the design objective for the inner or outer lining
to work independently in load bearing can be achieved. This improves the distributions of stress in the
linings and makes the outer lining bear greater compressive stress, hence improving the overall safety of
lining structure. And a decrease in cushion stiffness results in a lower ratio of water pressure transfer from
the inner to outer lining and a better effect of prestressed tension in the inner lining. Thus, the composite
structure with a cushion layer is superior in stress distribution, waterproof performance, and overall
structural safety for a water conveyance shield tunnel of high internal pressure and great buried depth in soft
soil foundation.