Other important operations during construction work underground
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Other important operations during construction work underground

Ventilation

Ventilation is important during the construction period, to remove explosion fumes, diesel gases, rock dust and particles from the workplace, and to provide workers and combustion engines with oxygen and air of the correct temperature.

Official regulations stipulate hygienic limit values for foreign particles in respiratory air. To reduce concentrations to these levels, the atmosphere at the workplace must be diluted with a certain amount of fresh air per unit of time. The amount of rock dust and particles can be reduced by water drenching. In construction of tunnels and rock caverns, a ventilation tube usually blows fresh air towards the face where the work is taking place. Air is delivered through axial fans of the propeller type.

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 the 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 such a method.

The ‘non-productive’ parts of the work, such as setting up a work site and health and safety measures, are as time and resource demanding as the actual reinforcement and grouting activities.

Completion and fittings

Tunnels and rock caverns are fitted with installations and furnishings according to 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.

Maintenance

Rock facilities in Sweden are most often built in rock of good quality. The rock itself forms the bearing construction material, but locally may need reinforcement or sealing to fulfil its function. Facilities must be regularly inspected and maintained, including bolts, shotcrete, concrete castings, and sealing and drainage systems.

Emergency maintenance takes place when sudden and unforeseen failure occurs in a rock facility. The scale of contingency in place must be weighed against the scale of the disruption when, for example, a tunnel is closed, and the associated societal costs.

Planned maintenance involves checking the functions of a rock facility to ensure safe and economic operation.

Time available for maintenance work in tunnels and rock caverns can sometimes be very short. For road and rail tunnels, maintenance work is usually carried out at night or at weekends when traffic intensity is lower. For other types of public facilities underground, there is usually greater flexibility when it comes to maintenance work.

Inspections

The technical status of a rock facility is ascertained through an inspection. Such inspections must be fast and efficient, with no risk of missing any weaknesses or damage in the rock and reinforcement systems. Where acute instability or collapse occurs in a tunnel, the immediate priority is to rectify the problems; in these cases, the inspector’s role is to carry out inspections of the work carried out.

Maintenance and renovation work often involves replacing poor-quality shotcrete and rusted bolts. The work may also involve clearing blocked drainage systems and removing ice formations. The ‘non-productive’ parts of the work, such as setting up a work site and health and safety measures, are as time and resource demanding as the actual reinforcement and grouting activities.

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