Preventing Tunnel Vision in Underground Projects
Geological and Construction Risks
Going underground has reduced travel time, minimised obstacles and protected water reservoirs for thousands of years, with the oldest construction dating back to the 22nd Century BC at Babylonia.
By their very nature, tunnels are dependent on geotechnical and hydrogeological conditions. Being constructed in soil-like material or hard rock, under the sea or inside aquifers in mountains, they are susceptible to geotechnical and construction risks which, if ignored, can result in fatalities, damages and lengthy litigation proceedings.
What are the most common tunnelling techniques?
Tunnels, irrespective of their purpose or final use, are constructed mainly with conventional (NATM, SEM, SCL, ADECO-RS and Drill & Blast) or mechanised techniques (TBM). The conventional techniques, excluding Drill & Blast, refer to similar methods. NATM (New Austrian Tunnelling Method), SEM (Sequential Excavation Method) and SCL (Sprayed Concrete Lining Method) are the exact same technique, whilst ADECO-RS (Analysis of Controlled Deformation in Rocks and Soils) utilises the core of ground ahead of the face.
Typically, conventional tunnelling is linked with long tunnels in rural environments or short tunnels in urban environments, whereas the cost of a TBM (Tunnel Boring Machine) is high, both in money and time, and is based on the convergence-confinement method.
The mechanised technique with TBM can be further split into different machine types related to the ground and hydrological conditions, i.e. EPB (Earth Pressure Balance), slurry, rock and so on.
The mechanised techniques are based on full-face support (in soil like materials, soft rocks and in the underground water table) and have the advantage of limiting disturbance to the surrounding ground and produce a smooth tunnel wall. Tunnels constructed with TBM reduce the cost of the tunnel lining, making them suitable for urban areas.