DEVELOPMENTS IN SEGMENTAL LINING DESIGN

摘要

There has been a steady increase in the use of segmental linings for tunneling works, due to the safety benefits offered by shielded tunneling, and the increased level of cost certainty and quality afforded by segmental linings. Segmental linings are increasingly being used for tunnels through rock where previously conventional excavation and support followed by insitu linings would have been used. Many of current design approaches used or specified have their genesis in soft ground tunneling, and this can lead to a conservative determination of bending moment design actions that are not necessarily suitable for a segmental linings in rock. Ovalization tolerances are typically specified to be 1% which is a typical value for soft ground tunnels where low stress ratio values can lead to squatting of 0.4–0.5%, however when combined with the empirical Muir Wood ring stiffness formula can lead to an overestimation of bending moment. This can present a problem for the design of steel fiber reinforced segments, due to their inherently lower bending moment capacity. The authors have been involved in the design of a 2.8m ID wastewater tunnel, 5.2m and 8.2m ID rail tunnels and a 11.2m ID hydro-electric tunnel lining over the last year. These designs are used to demonstrate some issues with the adoption of traditional analysis methods, and some design recommendations are made.