Guideline for Use of Rock Classification Systems for Ground Support on TBM Tunnels Featured

Rock support is arguably one of the most important aspects of any tunneling operation.
Historically, the decision about which rock support to use was made by tunnellers on a case-by-case basis.
Over the last 50 years, however, various rock classification systems have been developed to assist in selecting rock support type and quantity based on empirical data.
When these systems are applied to rock support in mechanized tunneling it becomes a problem that the empirical data is obtained almost exclusively from the drill and blast tunneling method. 
This approach has two major shortcomings when applied to the requirements of bored tunnels:
• The rock support methodology is not optimized for efficient TBM operation, which involves installing rock support while boring.
• The rock support schemes needed for a relatively smooth cylindrical TBM tunnel require less rock support as there is no blasting damage to the rock mass.
This guideline suggests a modified rock support selection methodology adapted to bored tunnels using both the Q (Barton, Lien, & Lunde, 1974) and/or RMR (Bieniawski, 1989)
rock classification systems.