Underground maintenance facilities are primarily used as a location for service and repair of underground equipment since it is often only feasible for major equipment to leave the mine for replacement or major rebuilding (Cline, 2011). Because underground shops are located in close proximity to operations, scheduled maintenance and emergency repairs can be completed promptly, with less equipment downtime.
One of the most serious and widespread errors in underground mine design is the failure to provide sufficient space and appropriate equipment required for fleet maintenance and repair work (Bullock, 2011). In order to ensure that production capacity and safety objectives are met, a variety of supporting maintenance workshops and facilities are required. These maintenance facilities are the work areas for both repair and service personnel, and can be managed by the mining company, or outsourced to a private contractor.
Maintenance infrastructure at an underground mine must be designed to provide the following maintenance services (de la Vergne, 2003):
- Scheduled servicing
- Routine maintenance
- Component or system replacement, repair, or re-calibration
- Fluid test samples
Major equipment rebuilding activities will generally be completed on surface or offsite, where the space, equipment requirements, and associated noise will be better accommodated (Cline, 2011).
Main and Satellite Shops
Generally, the amount of service infrastructure depends on the degree of difficulty of moving mobile equipment throughout the mine workings. Most decline mines do not require an underground workshop, only standalone refueling and service bays for minor repairs (Bullock, 2011). In the case of a new underground mine utilizing only trackless equipment, only a surface shop may be required. However, a surface shop can become obsolete as an underground mine becomes deeper. A small underground shop can be developed to service and repair jumbo drills, which are often the most difficult piece of equipment to transport to surface. As the mine becomes deeper, and it becomes necessary to service LHDs underground, a main underground mechanical service shop can be developed and the small jumbo shop can be transitioned into a satellite shop. A satellite shop is used for shift services such as refueling, greasing, lubricating, and tire inflation (de la Vergne, 2003). Figure 1 below, shops the layout of a typical underground mobile equipment satellite repair facility, complete with two service bays, a lube bay, and a wash bay. If both tracked and rubber-tired equipment are used in in an underground mine, maintenance infrastructure must be made available for both and a dedicated tracked equipment repair shop is often constructed. This is due to the considerable differences in the maintenance requirements of each type of equipment (Cline, 2011).
For mines with ramp or shaft access, the Hard Rock Miner’s Handbook states that as a rule of thumb, a main underground shop is only required when the mean mining depth of the operation is below 500 m. Additionally, mines with ramp access require a satellite shop complimenting the main surface shop when the mean mining depth reaches 200 m below surface, with an additional shop required at 400 m. This being said, underground shop facilities may not be required if the active working areas are totally abandoned after a short service life. Additionally, they may not be practical or safe in excessively gaseous mines (de la Vergne, 2003).
Centralized mechanical service shops are equipped with all the necessary equipment to facilitate welding, painting, drilling, lathing, metal drilling, machine lubrication, and many more maintenance related tasks. Because minor repairs can often be performed at the site of operation, these centralized shops are primarily used for overhauls and major repair or maintenance work (Cline, 2011). A main shop facility represents a major investment for the mining company and the main considerations are often the location and layout (de la Vergne, 2003).
The main underground shop facility should be located in a dedicated service area of the permanent facility and as close as practical to the ‘center of mass’ of the proposed workings over the extent of the mine life. In addition, it should be located in an area with convenient personnel access from surface, preferably near the shaft, main ramp, or with direct access to a main travelway. For fire safety reasons, it is mandatory that the main shop is located adjacent to the exhaust air stream. Finally, the location should be decided with input from the mine’s rock mechanics department in order to select an area with stable ground. When an area of stable ground is not feasible, the shop should be designed to have multiple areas of narrow width. Depending on the location of the mine itself, regional or national restrictive statutory requirements may apply. (de la Vergne, 2003) (Cline, 2011)
Design and Layout
The design of the main underground shop facility is based on the number and type of equipment in the fleet, the type of maintenance and repair to be completed, the type of surface-to-underground access available, and the cost of excavation. According to Ontario’s Occupational Health and Safety Act, the physical size of the openings is governed by the dimensions of the largest equipment to be serviced with adequate allowances for personnel traffic and working space (Ontario Ministry of Labour, 1990). The height of the main service bay should be high enough to allow for a raised truck bed with an operating crane overhead (Cline, 2011). The size of the shop and extent of services performed is generally larger in mines with a shaft access. A general rule of thumb is that a main underground shop should have the nominal capacity to handle at least 10% of the underground fleet at any particular moment (de la Vergne, 2003).
Shop designs should include provisions for the following areas (Bullock, 2011):
- One or two large bridge cranes over the motor pits
- A motor pit and service area for scheduled lubrications performed as part of the preventative maintenance program
- A separate area for welding operations
- A separate area and equipment for tire mounting and repair
- An enclosed separate area for recharging batteries
- Various work areas equipped with steel worktables or benches
- Close proximity to the main warehouse
- An area for washing and steam cleaning equipment
- A floor inspection pit or alternate structure to facilitate the inspection of vehicle undercarriages
- An office for the shop foreman with a view of the main shop area and warehouse and room for records, manuals, catalogues, and drawings
- Separate motor pit, locomotive and car repair shop for mines with rail haulage
The listed requirements should be arranged in a way that maximized service efficiency with easy access to supplies, spares, and consumables (Cline, 2011). Of particular importance is the need for easy access to the motor pits, and unhindered access from several directions around the cranes (Bullock, 2011). Multiple entry and exit points should be designed so that immobilized equipment doesn’t obstruct the movement of other equipment. Individual bays should be designed with a fire-rated access door and personnel door for equipment and worker access. Concrete floors should be installed in all areas of the shop to contain and control potential spills, and wash bays should be equipped with an oil-water separator in order to isolate hydrocarbons from wash water. Other items to consider in the layout of an underground maintenance shop include services, floor drainage and sumps, vehicle traffic control, personnel safety, fire suppression systems, and first aid (Cline, 2011).
The BC and Ontario regulations specify that service areas be equipped with adequate fire protection and ventilation. This includes a fire suppression system with both automatic and manual actuation capabilities from several locations inside the shop and at least one outside. Furthermore, service areas must be designed such that a fire or explosion will have minimal effect on other working areas. Concrete floors are required to be used for service pits, and provisions must be made to contain potential hydrocarbon spills. (Ministry of Energy, Mines and Petroleum Resources - Mining and Minerals Division, 2008)
Figure 2 below, shows a general arrangement of a typical underground maintenance facility. This arrangement is just one way to include and orient different service components.
Equipment and Services
In order to provide the previously described range of maintenance services, a large amount of stationary and portable equipment, furnishings, hand tools, sundry items, and stock items are required in underground shop facilities. One essential component of a main underground service shop is an overhead crane and other associated lifting devices used to move heavy parts around the shop floor (Cline, 2011). All installed equipment should be tested and commissioned according to the manufacturer’s specifications. Additionally, all equipment and spare parts manuals should be kept in a small library in the office of the main underground shop. This library should also include general catalogues for equipment, tools, and supplies, as well as trade journals. If possible, desktop computers should be setup to display electronic manuals and parts catalogues. (de la Vergne, 2003)
A number of services are also required in underground shops including compressed air, electricity, adequate lighting, and water (Cline, 2011). For safety reasons, it is extremely important that shops are well lit and well ventilated. Furthermore, clean shops provide a solid foundation for any effective safety and maintenance program, so good housekeeping practices are essential in underground shops (de la Vergne, 2003).
Drilling and blasting is the most commonly utilized excavation method for underground infrastructure openings in hard-rock mines (Cline, 2011). However, the specific construction methods used may be very different than the daily production and development activities, meaning that it may be outsourced to an independent contractor. The development cycle for this type of excavation consists of blasthole drilling, charging, blasting, ventilation and dust removal, scaling, muck handling, and ground support. Ideally, and if the operating range of the equipment allows it, underground openings should be excavated full-face. Where the cross-sectional dimensions are within the operating range of the equipment, full-face drilling can be used for small to medium excavations in hard rock mines. However, if the excavation layout or ground support does not allow full face drilling, multiple headings may be used to advance the face while limit the unsupported roof span between each phase of excavation. Other methods of excavating large facilities include driving a top heading followed by one or more bench rounds behind the heading or driving a pilot drift and slashing the back of the excavation on retreat. The service bay with service crane should be over excavated at the back in order to accommodate the overhead crane trolley and required installation equipment. (Cline, 2011)
The following factors govern the excavation and support design (Cline, 2011):
- Prevailing ground conditions
- Rock type
- Size of excavations
- Pillar sizes between openings
- Geotechnical properties
Installation and build-out of the shop, warehouse, or storage facility commences after the excavation and ground support phases of development are completed. The walls and the back should be shotcreted in light colour to enhance visibility and regularly whitewashed to avoid being darkened with exhaust soot (Cline, 2011) (de la Vergne, 2003). Construction of permanent structures generally begins with concrete pouring for floor slabs, service crane foundations, and containment facilities. Furnishing the shop with the necessary equipment, along with the instillation of compressed air, electrics, water supply, and other services happens simultaneously. (Cline, 2011)
Two cost models are used in separate editions of the SME Mining Engineering Handbook in order to estimate the excavation costs of underground repair shops. In the 1992 edition, it is stated that the cost of an underground repair shop, either on surface for smaller operations, or underground for larger ones, can be estimated using the following equation (O'Hara & Suboleski, 1992):
Cost = $14,600 * T0.4
Where T is the daily ore production in tons. If this equation is to be used as a very preliminary cost estimate, then adjustments should be made to account for inflation and rising equipment/consumables costs since 1992.
Another cost estimate can be found in the 2011 edition, this one based on the total length needed for all excavations in an underground maintenance shop layout. For a bolted and shotcreted, standard-size excavation with a 10.7 m width, 6.1 m height, and predetermined length, the price of excavation is $19.0-20.70/m3. This cost estimate is also applicable for warehouses, fuel storage, and explosive storage excavations. (Cline, 2011)
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