Tunnel excavation

Tunnel excavation proceeds about five meters at a time

Tunnel excavation begins, after initial surveys and planning, by drilling holes for blasting. Holes are drilled at the end of the tunnel filled with an emulsion explosive or a tube containing cartridge explosives. After the explosion the tunnel is ventilated, taking 30 to 60 minutes. With one explosion, the tunnel gets about five meters longer, provided the environment poses no limitations. Under normal conditions, there is one blasting per tunnel a day.

After blasting, the stone is loaded and taken out of the tunnel. After this the tunnel is scaled by machine to remove loose stones off the roof and surrounding area to ensure safety. Should the rock and occupational safety call for it, the tunnel can be strengthened with bolts or shotcrete before proceeding to the next blasting.

Tunnel excavation by blasting ensures that work proceeds at a steady pace. When blasting is planned carefully, they do not cause dangerous situations or excessive disturbance to the environment. We have carried out numerous tunnel excavations in mining infrastructure construction sites, so we know well how blasting can be done successfully and safely. Surveys and risk assessments before blasting are important in terms of how we go about blasting, and we also follow blasting vibrations were closely.

Each tunnel excavation is a unique project

Although tunnel excavation is routine work for us, excavation does contain a number of variables for each site that must be accounted for. For example, it is not always known in advance how much reinforcement will be needed. We find this out by means of probing and the result of water testing. A tunnel can be probed up to 20 meters at a time, and rock can be compacted by injection, if necessary.

The quality of the rock is a significant factor that affects the implementation of tunnel excavation. It determines, for example, how much the tunnel must be reinforced after blasting to ensure safe working conditions.

In infrastructure construction sites in particular, we have to be wary with underground spaces, crossing tunnels and any tunnels that will eventually be connected into, such as sewers. This ensures that tunnels can be excavated alongside existing tunnels or over them without undue disruption to existing tunnels and other underground spaces.

Previous tunnel excavation projects:

• Feb 2013–Sep 2013  Sewer tunnel on Merikannontie road, customer Destia Oy, developer HSY – Traffic and sewer tunnel excavation 450 m and 8,500 m3
• 2015, 2016 Länsimetro, customer Destia Oy – Excavation of western extension to Länsimetro 1,500 m
• Jun 2016–Jun 2017 Sammalvuori metro depot of Länsimetro, customer TYL Sammalvuori – Excavation of traffic tunnels and spaces of the metro depot 140,000 m3
• Jan 2019–Oct 2020 Finnoo 2, HSY – Excavation of sewer tunnels and pumping station 4,000 m
• May 2022– Oct 2022 Kevitsa mine, customer Boliden Oy – Excavation of pumping tunnel 170 m
• May 2023–Aug 2023 Parainen mine, customer Nordkalk Oy – Excavation of ramp tunnel 340 m
• Pampalo mine – Deepening of diagonal tunnel and horizontal sections approx. 1,000 m and 28,000 m3