Excavation of a tunnel
The same work phases are repeated in a certain order when a tunnel is excavated. The duration of a work cycle described below depends on the type of bedrock, and it can last from about six hours to a couple of days.
Pre-grouting
First, the bedrock is prepared for drilling by grouting.
Drilling and charging
Next, a drilling jumbo drills enough holes in the bedrock with varying lengths. The length of a so-called break is 0.5–6 metres.
Blasting and ventilation
Small amounts of explosive material placed inside the holes are blasted in a carefully planned order. The duration of the blasts is 6–20 seconds depending on the number of holes blasted at a time. The tunnel is ventilated after the blasts.
Loading and transport
Loose excavated rock is transported from the tunnel.
Scaling
A special vehicle removes any loose rocks from the walls so that the tunnel can be accessed again safely to perform pre-grouting for the next drilling.
