Sometimes known as ‘drill and fire’, drilling and blasting techniques are complicated processes that involve several steps to break rock efficiently and safely. These techniques are widely used for underground tunnelling and excavation, particularly in hard rock environments.

Drill and blast tunnelling method

Before any drilling can take place, a detailed plan must be put together. Things for the engineers to assess include geological conditions, rock properties, and the intended tunnel size.

From this information, the engineers can select the right drilling equipment and accurately design the blast pattern.

Drill patterns

Using specialised drilling equipment, holes are drilled into the rock for explosives to go into at the next stage.

The drill patterns are designed to optimise the breakage of rock, while keeping the number of explosives down and controlling the shape of the tunnel.

Blowing up the rock

Once the drilling stage is over, explosives are carefully loaded into the drill holes; which types are used depends on the type of rock and overall project requirements. Modern tunnelling often uses bulk emulsions or ANFO (Ammonium Nitrate Fuel Oil) due to their safety and efficiency.

Using electronic detonators to allow precise timing, the blast process begins. The timing sequence is critical to controlling the direction of the blast and helping ensure that too much isn’t blown up. It also helps with reducing vibrations and shockwaves that can cause damage to surrounding buildings.

Safety protocols are strictly followed to ensure that all personnel are clear of the blast area, and remote monitoring is often used to track blast performance.

Post-blast work

Keeping the area properly ventilated is vital to clear fumes and keep the air fresh for workers.

Once the explosion has subsided, the muck is removed from the tunnel with loaders and trucks. As soon as possible, support structures like rock bolts, shotcrete, or steel sets are installed to stabilise the newly formed tunnel walls and prevent the area collapsing.

Alternatives to drill and blast

Obviously, the above process is very destructive which means it’s not suitable for all situations. Where disruption needs to be kept to a minimum, alternative methods like Tunnel Boring Machines (TBMs) are used.

TES (UK) Ltd can supply offer a versatile TBM that can be used in either standard operation mode (suitable for a wide range of ground conditions) or with an EPB (Earth Pressure Balance) mode where the ground conditions are more tricky.  This is often associated with microtunnelling techniques.