Statistical and Numerical Study of Chipping and Cracking in Segmental Lining

Some of the most frequent damages of concrete segments in shield tunnels are chipping and cracking, which are followed by degradation of lining system. In this paper, these types of damages are studied in four subway and two water conveyance tunnels. More than 2100 concrete rings are examined for chipping inspection and another 3000 for determination of the cracking. Statistical analysis of the research data showed that corners of the key and counter-key segments carry the highest number of chipping, while most of the cracking occur in the middle zones and shape of the segments and number of trust jacks affect the cracking pattern. Two kinds of numerical models are used to examine the underlying damages, which are based on geometrical characteristics of tunnel lining and boring machine besides operational mistakes. Findings of the numerical simulation revealed that installation of segmental lining with the least amount of erection tolerances results in low amount of chipping, this is while using key-segments with 12–17 degrees of insertion angle reduces total magnitude of damage due to tensile and compressive stresses. Furthermore, the deviation angle of TBM’s jack and segment’s axis should never be more than 5 degrees; otherwise even high-quality concrete segments wouldn’t remain undamaged. Employment of boring machines with articulated system is proposed in this case.