3.2 Mine Loading, Haulage & Materials Handling Systems

3.2 Mine Loading, Haulage & Materials Handling Systems

Materials handling represents the single largest operational expenditure in open-pit and underground mining operations, frequently accounting for 45% to 60% of total mine operating costs. Selecting, matching, and optimizing loading and transport systems determines overall mine productivity and unit cost efficiency.

1. Primary Surface & Underground Loading Equipment

Loading equipment excavates fragmented rock from the bench face or muckpile and loads it into haulage units or crushers:

• Electric Rope Shovels: High-capacity loading units utilizing wire ropes and rack-and-pinion crowd mechanisms. Equipped with bucket capacities exceeding 30 to 60 m³ (50 to 100+ tonnes per pass), rope shovels can offer low unit loading cost and long service in high-tonnage, long-life mines, subject to utilization, power, mobility, maintenance, and life-cycle economics.
• Hydraulic Mining Excavators: Available in front-shovel and backhoe configurations with dipper capacities up to 45 m³. Front shovels break out rock above track level with high crowd force, while backhoes dig effectively below track grade. Hydraulic shovels feature higher mobility and selective digging capabilities compared to electric rope shovels.
• Front-End Wheel Loaders (FEL): Highly mobile rubber-tired loaders used for primary loading in lower-tonnage pits, stockpile rehandling, and auxiliary cleanup around primary shovels.
• Load-Haul-Dump (LHD) Units: Specialized low-profile diesel or electric underground vehicles designed to scoop ore from stopes or drawpoints, tram across underground drifts, and dump into ore passes, trucks, or underground crushers.

2. Mine Haulage Fleet Configurations

Haulage transports fragmented material from loading faces to destination points (primary crusher, waste dumps, tailings facilities, or stockpiles):

• Off-Highway Rigid Dump Trucks: Rear-dump trucks ranging from 90 to 400 tonnes payload capacity. Available in mechanical drive (engine-transmission-driveline) and diesel-electric drive (engine-generator-wheel electric motors). Rigid dump trucks dominate well-maintained, heavy surface mining operations.
• Articulated Dump Trucks (ADT): Feature an articulated frame joint and all-wheel drive for payloads of 25 to 55 tonnes. ADTs excel on steep ramps, soft underfoot conditions, and narrow haul roads where rigid trucks lose traction.
• Underground Haul Trucks: Low-profile, heavy-duty rear-dump trucks (20 to 60 tonnes payload) designed for tight clearance in underground haulage drifts and ramps.

3. Continuous & Shaft Materials Handling

• Belt Conveyors: Continuous transportation systems offering significantly lower unit operating costs than truck haulage for long-distance, high-volume material movement. In-Pit Crushing and Conveying (IPCC) systems crush run-of-mine (ROM) ore directly in the pit, substituting trucks with overland belt conveyors.
• Shaft Skip Hoisting: In deep underground mines, ore is elevated to the surface via hoisting systems. Skip hoists carry broken ore in guided steel skips driven by friction (Koepe) or drum hoists mounted in surface headframes. Skip hoisting capacity is calculated from skip payload ($L_s$), velocity ($v$), hoist acceleration/deceleration, and loading/dumping dwell times.

4. Equipment Cycle Time Mechanics

Total loading and haulage productivity depends on individual equipment cycle times.

• Loader Cycle Time ($t_l$): $t_l = t_{\text{dig}} + t_{\text{swing loaded}} + t_{\text{dump}} + t_{\text{swing empty}}$ Typical shovel cycle times range from 25 to 40 seconds per pass.
• Truck Haul Cycle Time ($t_c$): $t_c = t_{\text{spot load}} + t_{\text{loading}} + t_{\text{haul loaded}} + t_{\text{spot dump}} + t_{\text{dumping}} + t_{\text{return empty}}$ where $t_{\text{loading}} = n_{\text{passes}} \times t_l$.

Equipment availability ($A = \frac{\text{Operating Hours}}{\text{Scheduled Hours}}$) and utilization ($U = \frac{\text{Actual Operating Hours}}{\text{Available Hours}}$) scale nominal fleet capacity to net operating production.

5. Shovel-Truck Match Factor & Fleet Sizing

The Match Factor ($MF$) measures the operational balance between the loading fleet and haul truck fleet: $MF = \frac{N_t \cdot t_l}{N_l \cdot t_c}$ where $N_t$ is number of active haul trucks, $N_l$ is number of active loading units, $t_l$ is time required by one loader to load one truck ($n_{\text{passes}} \times t_{\text{pass}}$), and $t_c$ is total truck cycle time.

Operational interpretations:

• $MF < 1.0$ (Under-trucked): Shovels experience idle time waiting for trucks; truck capacity is nominally in demand while loading capacity is underused in the deterministic model.
• $MF = 1.0$ (Perfect Match): Total loading capacity equals total truck transport capacity.
• $MF > 1.0$ (Over-trucked): Trucks queue at the loader waiting to be filled; loading capacity is nominally in demand while trucks queue in the deterministic model.

6. Haul Road Resistance Fundamentals

Total vehicle resistance ($TR$) determines the engine power required for a truck to maintain speed up a haul road ramp. Total resistance is expressed as an equivalent grade percentage ($TR = RR + GR$):

• Rolling Resistance ($RR$): Resistance caused by tire internal flexing and ground penetration under vehicle weight. Expressed as: $RR = RR_{\text{base}} + 0.6\% \times (\text{tire penetration in cm})$ Typical $RR$ values:
  • Hard, smooth asphalt/concrete: 1.5% to 2.0%
  • Well-maintained compacted gravel haul road: 2.5% to 3.0%
  • Soft, uncompacted earth or rutted mud: 8.0% to 12.0%+
• Grade Resistance ($GR$): Gravitational resistance encountered when traversing inclines. $GR$ equals the physical road grade percentage directly ($GR = \text{Grade %}$). For downhill travel, grade resistance becomes Grade Assistance (subtracted from $RR$).

For example, a truck ascending an 8% haul road ramp with a 3% rolling resistance experiences a Total Equivalent Grade Resistance of $TR = 3% + 8% = 11%$.

7. Vehicle Rimpull & Gradeability Performance

Rimpull is the tractive force (in kN or lbs) available between the driving tires and the road surface to overcome total resistance: $\text{Rimpull (lbs)} = \frac{375 \times HP \times \eta}{V \text{ (mph)}}$ where $HP$ is engine horsepower, $\eta$ is mechanical driveline efficiency (~80–85%), and $V$ is vehicle speed.

The maximum usable rimpull is limited by the coefficient of traction ($\mu$) between tire and road surface before wheel slippage occurs: $\text{Rimpull}_{\text{usable}} = W_{\text{drive weight}} \times \mu$

Engine rimpull curves plot available force against vehicle speed across transmission gears. When $TR$ is expressed as a percent, engineers calculate required force as $(TR/100) \times \text{Gross Vehicle Weight}$ and compare it with the performance curves to determine maximum sustainable speed and gear range for any ramp section.