Rock engineering technology has its origins in the mining industry but, over time, methods, equipment and materials have been adapted to meet the needs of the construction industry. Civilian and military underground construction, particularly in cities, grew in the 1940s and 1950s, so manufacturers adapted their product development to the needs of this market.
Rock construction has developed into a comprehensive industrial process, and a strong domestic manufacturing sector has played an important role in this development. Major companies such as Atlas Copco, Sandvik, Nitro Nobel and Volvo have developed drilling machines with drill bars and rods with sophisticated cemented carbide cutting tools, blasting equipment, machines for rock reinforcement, and transport equipment for loading and removing rock spoil.
Project phases
An underground construction project can generally be divided into five phases. From the first phase starting with first assessments of functions, environmental data, initial geological and hydrogeological assessments and physical outline of the project and finally the operational phase after commissioning and maintenance and repair.
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Feasibility study
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Preliminary design
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Detailed design
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Construction
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Operation
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Rock excavation
In Sweden, drill-and-blast is the traditional and most commonly used method of building tunnels with a cross-sectional area of up to 100 m2. In recent years, new construction methods have been developed, such as full-face drilling and wire cutting, which can be more suitable in certain situations.
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Drill-and-blast: tunnels
Drill-and-blast: rock caverns
Tunnelling in sensitive urban environments
Rock reinforcement
One of the most common reinforcement methods for rock walls and roof is to spray cement on the rock surface using compressed air. The high speed of application produces a layer of very high-quality concrete that often reinforced with fibres.
Bolt reinforcement is used as a separate method or in combination with shotcrete, e.g. bolts anchored in the bottom of the hole or completely cast into rock.
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Grouting
Tunnels and rock caverns must be sealed against inflow of groundwater. This is particularly important in urban areas if the buildings above the facility have foundations in clay. A lowering of the groundwater pressure in clay may cause subsidence, damaging foundations and degrading wooden piles and support structures.
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Grouting
Rock Transport
The most common loading machines in underground constructions are diesel-driven wheel loaders (see diagram). Such machines can be used as a ‘dig-and-carry’ machine over small transport distances.
Rock spoil is normally removed on ordinary lorries or dumper trucks, operating in the service tunnel.
Disruptions to surroundings
When a rock facility is being built, disruption and inconvenience to the surroundings is unavoidable. Examples are noise and dust from drilling, vibrations, and shock waves from blasting. Transport of rock spoil is often perceived as disruptive, not least if the rock is being transported through residential areas; this is the case in many underground projects in urban areas.
The issue of disturbance to the surroundings must be addressed in various ways during planning. The size of detonations can be adapted to the surroundings, a measurement programme for vibrations can minimise damage, and blasting can be restricted to acceptable times of the day.
By using careful blasting methods, vibrations and disturbance to the surroundings can be radically reduced. Interval blasting with weak charges in contour holes is one such method.
Completion and fittings
Tunnels and rock caverns are fitted with installations and furnishings appropriate for the intended use. These can be anything from a hydraulically designed concrete base that facilitates transport of water to buildings inside the rock cavern to artistic decoration in road tunnels to create an interesting scenery and add a positive experience and help motorists orientate themselves.
