Cutter-disc consumption during earth pressure balance tunnelling in mixed strata

The wear of excavation tools is considered to be one of the critical factors affecting the scheduling of shield tunnel construction. There is presently no effective countermeasure to prevent severe wear of excavation tools during tunnelling operations in complex geological formations. In addition, such wear is likely to lead to other problems, such as face instability and an unfavourable rate of tunnel advancement. The study reported in this paper analysed the various factors that affected the wear and performance of excavation tools during earth pressure balance machine tunnelling at the Ma-Lian section of line 9 of the Guangzhou metro, China. It was found that tunnelling in mixed ground conditions (upper soft and lower hard strata) led to severe wear of the cutter discs, resulting in additional costs and schedule delays. The foam expansion ratio, concentration of foaming agent and the foam injection ratio were measured to be 20, 2.5% and 40% respectively. Pre-grouting and effective soil conditioning were also found to prevent excessive wear of the cutter discs and surface collapse incidents caused by face instability.