1. Introduction
The following chapter discusses mine infrastructure and transportation and is intended to assist those engaged in the planning, design, and construction of a new mining project. Mine infrastructure is defined as the operations and utilities supporting mining operations.
Infrastructure includes administrative offices, employee housing, roadways, railways, airports, security, etc. Mine haulage roads are included in this section even though roads are not normally described as infrastructure. Some infrastructure items that deal with mine layout, water supply, sewage disposal, and surface drainage are discussed in Chapter 4, Mine Layout, and Chapter 5, Environmental Engineering.
Transportation refers to the transport of goods, products, and personnel to and from (as well as on) the mine site. The infrastructure and transportation systems for a mine in a remote location are a real challenge
and of great importance to the success of the mining venture.
2. Rules of Thumb
Surface Haul Roads
• Mine haulage costs at open pit mines may represent 50% of the mining cost and sometimes as much as 25% of the total costs, which include processing, marketing, and overheads. Source: A. K. Burton
• In general, 10% is the maximum safe sustained grade for a haul road. For particular conditions found at larger operations it has often been determined at 8%. It is usually safe to exceed the maximum sustained grade over a short distance. Source: USBM
• The maximum safe grade for a haul road over a short distance is generally accepted to be 15%. It may be 12% at larger operations. Source: Kaufman and Ault
• The maximum safe operating speed on a downhill grade is decreased by 2 km/h for each 1-% increase in gradient. Source: Jack de la Vergne
• Each lane of travel should be wide enough to provide clearance left and right of the widest vehicle in use equal to half the width of the vehicle. For single lane traffic (one-way), the lane is twice the width of the design vehicle. For double lane (two-way), the width of road required is 3½ times the width of the vehicle. Source: AASHO
• The cross slope on straight sections of a haul road (from a central crown or right across) should be ¼ inch per foot for paved surfaces and ½ inch per foot for gravel surfaced haul roads. Source: Kaufman and Ault
• The cross slope on curved sections (super elevation) of a haul road should not exceed 6% on paved haulage roads, nor 8% on gravel surfaced roads. Source: OGRA
• A crushed rock fill safety berm on a haulage road should be at least as high as the rolling radius of the vehicle tire to be of any value. A boulder-faced berm should be of height approximately equal to the height of the tire of the haulage vehicle. Source: Kaufman and Ault
• The coefficient of adhesion (resistance to skidding) can be reduced to 10 -12% of its value on a dry road surface when the road is ice covered. On melting ice (“black ice”), it may as little as 5%. Source: Caterpillar® Surface Shops
• Surface shops should be designed with one maintenance bay for six haul trucks having a capacity of up to 150 tons. This ratio is 4:1 for larger trucks. The shops should also include one tire bay and two lube bays. Additional maintenance bays are required for service trucks (1:20) and support equipment (1:12). Source: Don Mintii
• Service shops for open pit mines should be designed with plenty of room between service bays for lay-down area. As a rule of thumb, the width of the lay-down between bays should be at least equal to the width of the box of a pit truck. Source: Cass Atkinson Surface Railroads
• For preliminary calculations and estimates, a granular ballast depth of 24 inches may be assumed. The top half of the ballast will be crushed gravel (usually ¾ - 1½ inches) and the bottom portion (sub-ballast) graded gravel (typically No.4 -1 inch). This depth assumes the bearing capacity of the sub-grade (native soil) is 20 psi and the maximum unit pressure under wood ties is 65 psi. Where the sub-grade capacity is known to be less than 20 psi, it may usually be assumed that the required bearing capacity will be obtained with the use of geo-textile filter fabric. Various Sources
• The maximum railroad gradient on which cars may be parked without brake applied is 0.25 - 0.30%. Various Sources
• The cross slope on straight sections of a railroad (from a central crown) should be 48:1 (2%) on top of the base and the sub-ballast. Source: AREA
• The shoulder of the top ballast should extend 6 inches wide of the ties, and both the shoulder and the sub-ballast should be laid back at a slope of 2:1. Source: AREA
• A rotary dump on a unit train will average 35 cars per hour. Source: Hansen and Manning
• The tractive effort (TE) (Lbs.) for a diesel locomotive is approximately equal to 300 times its horsepower rating. Source: John Partridge
• The fuel efficiency of the engine in a diesel locomotive is near 30%; however, when the power required for operation of oil pumps, water pumps, governor and scavenger blower is taken into account, the efficiency at the rail is reduced to 23%. Source: John Partridge
Transport
• It is cheaper to ship 5,000 miles by ship than 500 miles by truck. Source: Marc Dutil
• The cargo bay of a Hercules aircraft is just wide enough to accommodate a Cat 966 Loader or a JDT 413 truck (drive on - drive off). Source: Unknown
Parking Lot
• The capacity of employee parking lots can be determined by the sum of the vehicles used by the
day and afternoon shift personnel. Provisions should be made for future expansion at the
outset. Source: Donald Myntti
Harbor Design
• A container ship with 4,000 TEU capacity requires a 43-foot draft at dockside. A container ship of 5,000 TEU capacity requires a 45-foot draft. (20 foot container = 1 TEU, 40 foot container = 2 TEU) Source: Engineering News Record
3. Tricks of the Trade
• The horizontal and vertical alignment (curvature) of a haulage road should be designed so that the vehicle operator can see ahead a distance at least equal to the stopping distance of the vehicle. Source: Kaufman and Ault
• Sharp curves should be avoided on a haulage road, especially near the crest of hills (not visible at night) and near the foot of a long downgrade (long stopping distance). Source: George Totten
• In temperate climates, road alignment should be kept to high ground as much as practical to minimize deposits of wind borne snow. Source: Bill Wright
• Survey stakes on the side of the roadway are marked to indicate the finished grade for sub-base, base and surface course, each with a fixed vertical off-set (typically four feet). A convenient way to monitor road grade during construction is with a hand level held on top of a plain stick (“boning rod”) that is four feet long. Source: Grant Devine
• Mine operators should encourage haul truck drivers to not use the same path on the travel lane so that rutting and furrowing will be minimized. Source: Dave Assinck
• In extremely cold weather, transport and haulage trucks may lose significant engine power due to slow fuel injection. A quick remedy is to add gasoline to the diesel fuel. Source: Dave Assinck
• To estimate the quantity of granular or slag ballast required for a railroad from cross-sections, use a unit weight of 100 pounds per cubic foot and allow for 20% shrinkage. Source: J. K. Lynch
• Smelter slag in sizes corresponding to crushed gravel normally employed makes good ballast; however, slag with a high sulfur content tends to promote dry rot in wood ties. Source: AREA
• Geo-textile filter fabric should be used when required to increase the bearing capacity of the sub-base but not to reduce the design thickness of the ballast. Source: Unknown
• A thirty-day reduced speed period should be enforced on a newly constructed railroad where the planned train velocity exceeds 30 mph. Source: AREA
• Curves on unit train lines are best laid out at less than 6 degrees. Sharper curves will likely need track lubricant and curves exceeding than 10 degrees should not be considered. Source: Hansen and Manning
• The draw bar pull of a diesel locomotive will be approximately 25% of its weight. Source: C. M. Magee
• The following shortcuts may be taken in the calculation of train resistance.
− Grade resistance is 20 Lbs./ton for each one-percent gradient
− Curve resistance is 0.8 Lb./ton for each one-degree of curvature
− Starting resistance is 18 Lbs./ton (journal bearings on car wheels)
− Starting resistance is 6 Lbs./ton (roller bearings on car wheels)
− Starting resistance is doubled for extreme cold weather
− Starting resistance is doubled for poor track conditions
− Acceleration resistance is 100 Lbs./ton for each one-mile per hour/second
− Air resistance may be ignored since acceleration resistance is higher
Source: John Partridge
• Mine building construction contracts should clearly define battery limits for utilities, such as water and sewer lines. Common practice is to have the builder responsible to a nominal distance from the building such as 5 feet or 1,500 mm. Source: Eric Seraphim
• During mine construction, it is usually more reasonable to have the mine owner provide a main first-aid station and ambulance service for all the contractors than it is to expect each individual contractor to provide separate services. Source: Harry Foster
• Aprons installed along the perimeter of the surface shop building will improve housekeeping and facilitate the completion of running repairs that can be performed out of doors. Source: Donald Myntti
• Protective bollards should be placed at either side of truck doors at surface shops. Source: Erik Seraphim
• A good way to make a bollard is to use a 2m length of small diameter culvert. Stand the culvert vertically in a hole dug 1m deep, backfill with compacted granular material, and then fill the culvert with concrete. Source: Don Bruce
• Where a mine incorporates a pump to dispense gasoline, it should be located in near vicinity to the security gate office. Source: Donald Myntti
• To discourage pilferage, the mine’s parking lot should not be laid out with parking stalls adjacent to the mine fence, but otherwise as close as practical to the main gate. Source: John Kostuik
• In the far North, personnel parking can be accommodated inside the gate and close to the work entrance, at least during the winter months. While this poses a small problem for security, it provides a great boost to morale for employees who do not have to walk 300 yards in foul weather. Source: Gerry Marshal
• To ensure reliable start-up in cold weather, fire pumps should be powered by gasoline engines. The gasoline should contain a stabilizer agent and the tank re-filled with fresh gasoline every six months. Source: Jack de la Vergne
• There is no system available on the market that can be relied upon for certain to protect the load cells of a truck scale from a lightning strike. A simple solution is to install welding cable to ground from over each cell location and provide slack with a free loop of the cable so that the accuracy of the scale is not affected. Source: Dave Assinck
4. Haul Roads
Poorly built mine haul roads will require more maintenance and reduce haulage truck productivity. Poorly built roads may also be responsible for a significant number of vehicle accidents on the mine site. In the past, mine haul roads were often built to municipal or highway design standards. With the advent of huge haulage trucks, these design parameters are no longer adequate. For example, the larger haul trucks have a longer sight distance (because the driver is high off the ground), but this is insufficient to compensate for the longer stopping distances they need. To accommodate the larger trucks, mine haul roads need to be straighter, wider, and stronger than rural highways.
Road Surfacing
In warm climates, permanent haul roads are often paved with asphalt or concrete to save on tire and fuel costs, reduce maintenance, and avoid dust. In northern climates, the advantages of paving are reduced due to the requirement for sanding and salting in winter to avoid slippery travel. The principal guidelines for good road design are to provide an adequate base (foundation) and ensure good drainage for both the surface and the base of the roadway.
Roads on Poor Soils
Design parameters for haul roads are mainly rules of thumb; however, in certain cases, engineering is required. The most difficult problems may be those concerned with assessing the requirements for roadway construction on poor soils, such as silts (frost susceptible), clays (low bearing capacity), and marls and muskegs (high compressibility). Roadways on silts and clays usually require geo-textile membranes and/or a thicker base construction. Marls and muskegs may require geo-textile membranes, special drainage, consolidation with shot rock, or even complete removal. When these “swampy” conditions occur in remote wooded areas, there is still occasional good application for “corduroy” roads built on limbed trees laid side by side across the sub-base of the road.
Curvature
Curves on a roadway may be measured in degrees of curvature or radius. (Degree of curvature is defined as the central angle subtended by a chord of length 100 feet on the arc of a circular curve.) The maximum allowable curvature may be determined by line of site; usually the critical factor is vehicle speed.
Example
Find the minimum permissible radius of curvature, R, for a gravel surfaced haulage road.
Facts:
1. The gravel surfaced haulage road has a design speed, V, of 50-mph.
2. The road has a corresponding minimum radial coefficient of friction, f, equal to 0.20.
3. The super elevation, e, on the curve is maximized at 6%.
Solution:
1. Minimum radius of curvature, R= V2/15 (f+e) = 2,500/15(0.20 +0.06) = 641 feet.
2. The corresponding degree of curvature, D, is 9 degrees obtained from the equation
D = 5729.6/R, or interpolated from the Table 27-1.
Table 27-1 Degree and Radius of Curvature
Dust Suppression
On gravel haul roads, treatment for dust suppression is a significant concern. For this purpose, it is usual to apply calcium chloride (CaCl2), either in liquid or granular form. A liquid application is usually longer lasting, but often not practical. In either case, it is best to scarify the road surface with a grader beforehand and fine-grade it afterwards. Between 1 and 2 Lbs. of CaCl2 per square yard of road surface are required. Usually, an initial application is made at 1 Lb. of CaCl2 per square yard, after which applications of ½ Lb. per square yard are made as needed.
5. Railways
Aside from standard railway sidings connected to main trunk railway lines, some mines employ independent unit trains to haul ore or concentrate. A unit train can be defined as a train of between 100 and 150 cars that is restricted to service between a single point of origin and a single destination.
The rail line typically involves at least a mile of track laid out in a loop formation. The loop requires a spur for shunting and access to repair shops. Many unit train locomotives are electric, employing overhead trolleys. Rotary dumps are typically employed. Unit train operations lend themselves to computer simulation and automation.
Size
Unit train railways are usually constructed with standard gage of 4’-8½ ” (1,435 mm). As with main line railroads, the gage is widened on curves over 8 degrees (to a maximum of ¾ - 1 inch). Rail size varies between 90 and 140 Lbs./yard depending on the size of locomotive employed and line speed. For example, a 50-ton locomotive with six driving wheels at a line speed of 40 mph may require rail weighing 100 Lbs./yard.
Ties
For purposes of preliminary design, ties may be assumed 7 by 10 inches, 9 feet long. Spacing for wood ties is typically 19½ inches (24 per standard rail length of 39 feet). Spacing for concrete ties may be 30 inches. Super-elevation on curves can be calculated by subtracting 3 inches from the value obtained from the equilibrium formula, e = 0.0007DV2 (e = inches, D= degree of curvature, V = line speed in mph). If the super-elevation determined exceeds 6 inches, the line speed must be reduced on the curve to meet this limitation.
Drainage
The single most important characteristic of railway design is adequate drainage for the structural foundation (ballast). To achieve this in cut sections, ditching must be provided at an elevation lower than the base of the ballast. The quality, compaction, and depth of ballast are also of primary concern.
General Design
The general design principals are similar to those for the haulage roads previously described; however, as referenced in the rules of thumb, requirements for alignment, grade, and curvature are stricter for railroads than for haulage roads. Rail haulage is much less flexible than truck haulage, which is one reason that trucking is usually favored over rail haulage, even though the unit cost of cargo transport may be higher.
Example
Find the thickness of ballast, h, required for a rail line for wood ties and concrete ties.
Facts:
1. The bearing capacity of the sub-grade, Pc, = 20 psi
2. The maximum tie pressure, Pa, is 65 psi for wood ties.
3. The maximum tie pressure, Pa, is 85 psi for concrete ties.
Solution:
1. The total thickness of ballast required beneath the ties, h =(16.8 Pa / Pc)0.8
2. For wood ties, h = (16.8 x 65/20)0.8 = 24.5 inches.
3. For concrete ties, h = (16.8 x 85/20)0.8 = 30.4 inches.
(Note that additional ballast is placed between the ties to within 2 inches of rail base.)
6. Land Drainage and Culverts
(For the design of ditches and culverts, please refer to Chapter 5 – Environmental Engineering.) In cold climates, culverts may be plugged with ice in the spring. In temperate climates, plugging can be normally avoided if culverts are properly sloped and of diameter 18 inches (450mm) or greater. In permafrost regions, culverts will invariably be plugged in spring regardless of the slope or diameter.
The traditional method of thawing culverts is with steam. A faster and less costly method is by electrical thawing – the electrical installation can consist of a No. 0 insulated copper wire running through the culvert with each end secured to stakes at opposite ends. In the spring, a portable welding machine (with leads attached to each end of the wire) will thaw a hole through the ice in one to four hours (depending on the length of culvert and the capacity of the welding machine). The water flowing through the hole in the ice will then widen it without further thawing required.
7. Aircraft Payload Capacities
Table 27-2 shows aircraft payload capacities.
Table 27-2 Aircraft Payload Capacities
1 Maximum capacities (ACL). For individual flights, these values may be reduced to account for fuel carried, weather conditions, airport altitude, as well as actual runway lengths.