Effect of Rock Joint on Boreability of TBM at Northern Section of Kerman Water Conveyance Tunnel

Nowadays, Tunnel Boring Machines (TBM) are widely used around the world on account of their high rate of excavation, little impact on the surrounding rock, and their high safety standards. The rock mass boreability is considered as one of the main parameters in evaluating the TBMs' performance in jointed rock masses. Boreability is a parameter reflecting the interaction between the rock mass and cutting tools. This paper aims to render an account of the effect of Joints Geometrical Parameters on the boreability by use of a database prepared to utilize the data (TBM operation and geological parameters) collected from Kerman Water Conveyance Tunnel projects in Iran. For this purpose, the joint parameters (orientation, spacing, persistence) affecting the boreability have initially been investigated. Then, the total fracturing factors (Bruland) and Persistence classification were used to investigate the effects of all three parameters on the boreability. The results showed that the boreability is also increased by increasing the joint persistency. Besides, the effect of fracturing factor (Ks-total) on boreability increases by increasing the joint persistency. In this paper, a new parameter called Rock Joint Index(RJI) is also presented according to the analysis performed on the database. The boreability value estimated based on the RJI shows a good agreement with the actual penetration rates.