Observations on cracking in concrete tunnel segments - An assessment of correlations

Faced with the combined challenge of aging sewer infrastructure and rapid population growth, the Abu Dhabi Sewerage Services Company (ADSSC) has embarked on a bold approach to build an enhanced sewer infrastructure with a deep gravity sewer tunnel at the centre. The primary lining of the new 41 km-long deep sewer tunnel has been completed by tunnel boring machines (TBM). The concrete segmental lining has an internal diameter varying from 4 to 5.5 m internal diameter and is located at depths of 20 to 80 m below the ground surface. This paper discusses the results of observations made on segment cracking experienced at different stages in the installation of concrete lining for the first of three TBM drives in Contract T-02 of the Abu Dhabi Strategic Tunnel Enhancement Program (STEP). It also attempts to quantify correlations and ranking among various mechanical and geometrical variables of ring installation based on their contribution to segment cracking. The method of assessment used in the case study has been successfully verified on a separate project, which encouraged the author to develop and propose a generalized procedure for investigation to serve as a roadmap in the future projects with segment cracking issues.