Driving shallow road tunnel under built up areas - involves driving in tension release tubes, then excavating between them

摘要

The tunnel excavation process produces min. disturbance and vibration. It enables tunnels, esp. road tunnels to be driven in urban or built-up environments with only slight rock overlayering. One or more separate tension-release tubes (1) are first driven into the rock face. The residual rock between them is then excavated in the usual way by drilling and explosive charges. The tubes may be made by the full cutting process. Their overall cross-section can amount to as much as 50% of the whole excavation cross-section.