Fast perception of rock mass strength and integrity in TBM tunnelling using in-situ penetration test

Abstract

Tunnel boring machine (TBM) is the preferred method in the construction of long-distance and deep-buried tunnel due to its advantages in safety and high efficiency. However, the TBM method is very sensitive to the condition of the surrounding rock. The strength and integrity characteristics of rock mass have great influence on the safe and efficient tunnelling. To provide a fast perception method for these characteristics during the TBM tunnelling process, an in-situ penetration testing system is proposed in the present study. The development and testing procedure of the system are elaborated. The system is applied to a TBM-excavated water conveyance tunnel to continuously perceive the strength and integrity characteristics of the surrounding rock. Firstly, the force-penetration (F-P) responses of the surrounding rock under penetration are qualitatively studied. Then, series of penetration indices are summarized to quantify the characteristics of the F-P responses. Finally, the quantitative relationships between the rock strength and the penetration indices are studied. The results indicate that the in-situ penetration testing system can perceive the rock mass strength and integrity characteristics qualitatively and quantitatively. On the qualitative aspect, the F-P responses can be categorized into four types (Type I to Type IV), which correspond to the level of rock mass strength and integrity. On the quantitative aspect, a single penetration index cannot represent the complete information of the F-P response. The descriptive classification of the rock mass strength (class I to III) is established through multiple penetration indices. The in-situ penetration testing system can be used as a method to quickly perceive the strength and integrity characteristics of the surrounding rock in TBM tunnelling.