Material reduced tunnel lining segments for moderately swelling soils

Abstract

Tunnels in unfavorable ground conditions are exposed to high internal stresses due to localized loading at the outer face. Addition of extra layers of compressible material as a countermeasure needs more material and greater excavation volumes which is in conflict to the global goals of CO2 reduction. Thus, two alternative types of segments with higher bearing capacities are proposed that allow for lining thickness reduction. They are derived from multi‐load topology optimization considering relevant load cases during construction and in service. The first design incorporates centered recesses that maximize segmental stiffness. The second shifts the recesses to the outer face increasing their potential to absorb deformation. Two prototypes of each type are fabricated from high performance steel fiber reinforced concrete. Experiments show that a concrete reduction of up to 55.2% is achieved with respect to a conventional design. The volume savings give space for layers of radially compressible material.