DEVELOPMENTS IN SEGMENTAL LINING DESIGN

摘要

There has been a steady increase in the use of segmental linings for tunnelingrnworks, due to the safety benefits offered by shielded tunneling, and the increasedrnlevel of cost certainty and quality afforded by segmental linings. Segmental linings arernincreasingly being used for tunnels through rock where previously conventional excavationrnand support followed by insitu linings would have been used.rnMany of current design approaches used or specified have their genesis inrnsoft ground tunneling, and this can lead to a conservative determination of bendingrnmoment design actions that are not necessarily suitable for a segmental linings in rock.rnOvalization tolerances are typically specified to be 1% which is a typical value for softrnground tunnels where low stress ratio values can lead to squatting of 0.4–0.5%, howeverrnwhen combined with the empirical Muir Wood ring stiffness formula can lead tornan overestimation of bending moment. This can present a problem for the design ofrnsteel fiber reinforced segments, due to their inherently lower bending moment capacity.rnThe authors have been involved in the design of a 2.8m ID wastewater tunnel,rn5.2m and 8.2m ID rail tunnels and a 11.2m ID hydro-electric tunnel lining over the lastrnyear. These designs are used to demonstrate some issues with the adoption of traditionalrnanalysis methods, and some design recommendations are made.