Early assessment and mitigation of cracking on concrete tunnel segments – Dubai metro case study

This paper discusses the results of observations, analyses and mitigation measures on segment cracking occurred at various installation stages of concrete tunnel lining for Dubai Metro Expo Line. The study involved identification and ranking of various mechanical and geometric variables of ring installation that contribute to segment cracking. A total of 18 potential contributors were continuously monitored and evaluated daily. The crew performance, segment handling and transport, and the accuracy of geometry and surveying in ring building process exhibited the highest ranking of correlation to segment cracking. After deploying early mitigation actions, segment cracking decreased from 14.3% to 1.2% at the best performance. Cracking in Steel Fiber Reinforced Concrete (SFRC) segments is a complex and dynamic phenomenon and hence the term “contributor” rather than “root cause” is used to refer to the influencing factors in the subsequent sections of this paper.