Evaluation of higher capacity segmental lining systems when tunnelling in squeezing rock

Overstressing of the segmental lining is a potential hazard of shielded tunnelling in squeezing rock. Due to their stiffness, segmental linings allow only very limited convergences to occur, which results in higher rock pressures than light or deformable rock supports. This paper investigates the extent to which the application range of shielded TBMs could be broadened in squeezing conditions by using linings of higher bearing capacity. Besides the obvious option of increasing segment thickness, an investigation is made into the technical and economic feasibility of double shell solutions as well as that of high performance or ultra-high performance concretes from the standpoints of structural engineering, TBM technology, process engineering, material technology and construction cost. Additionally, design aids are presented that allow a quick evaluation of the application limits of the various lining options to be made for a given geotechnical situation.