A Classification System for Support Pressure in Tunnels and Caverns

Terzaghi’s (1946) rock load classification developed from tunnels excavated by conventional drill and blast method and supported with steel arches has been evaluated in the light of measured support pressures from 23 tunnel sections with widths varying from 2 to 14 m and 4 sections from 21 to 23 m wide caverns. The study shows that the support pressure in rock tunnels does not increase significantly with the excavation width. This experience has been used to propose another simple classification system for both roof and wall support pressures in tunnels and caverns. The suggested vertical support pressures stand corroborated with field measurements in India. The paper also provides data on extensive tunnel performance studies in poor rock conditions