Before the advent of tunnel boring machines, drilling and blasting was the only economical way of excavating long tunnels through hard rock, where digging is not possible. Even today, the method is still used in the construction of tunnels, such as in the construction of the Lötschberg Base Tunnel. The decision whether to construct a tunnel using a TBM or using a drill and blast method includes a number of factors such as:
- Tunnel length
- Managing the risks of variations in ground quality
- Required speed of construction
- The required shape of the tunnel
Tunnel length is a key issue that needs to be addressed because large TBMs for a rock tunnel have a high capital cost, but because they are usually quicker than a drill and blast tunnel the price per metre of tunnel is lower. This means that shorter tunnels tend to be less economical to construct with a TBM and are therefore usually constructed by drill and blast. Managing ground conditions can also have a significant effect on the choice with different methods suited to different hazards in the ground.
Read more about Drilling And Blasting: History, Procedure, Rock Support
Famous quotes containing the word drilling:
“Don’t spend your time in drilling soldiers, who may turn out hirelings after all, but give to undrilled peasantry a country to fight for.”
—Henry David Thoreau (1817–1862)