Haulage #1: Haulage Theory & Setup

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Conceptual

Truck haulage and haulage related costs can account for up to 50% of the total operating costs incurred by an open-cut mine. As such, under-performance or poor planning can impact strongly on the mine’s productivity and the bottom line. Haulage simulation plays an important role in identifying opportunities for improvements, testing the viability of haulage plans and managing considerable financial assets. This section is designed to introduce the fundamental concepts of haulage simulation both in and out of Spry, in order to best meet the individual requirements of your projects.

Running haulage simulation and analysis requires both a multi-step setup and the use of Spry’s Logic controls. The setup includes providing an input schedule, relevant equipment/truck specifications, road specifications (speed restrictions and segment codes), and the creation of road networks.

Rolling Resistance

Central to the cost of truck hauling is the concept of rolling resistance. Generally expressed as a percentage of truck’s weight, rolling resistance is the force that resists the rolling of a wheel or other circular object along a surface caused by deformations in the object and/or the surface.

The table below (Carvill, 1989) shows example rolling resistances for pneumatic tyres on various road surfaces.

Road Surface Rolling Resistance
New Asphalt/Concrete 0.01 (1%)
Worn Asphalt/Concrete 0.02 (2%)
Rolled New Gravel 0.01 (1%)
Loose Worn Gravel 0.04 (4%)
Medium Hard Soil 0.08 (8%)
Sand 0.1 – 0.2 (10 – 20%)

Reference: Carvill, J. (1993): Mechanical Engineer’s Data Handbook

Effective Grade (or Static Force)

Rolling resistance is combined with the grade of a slope to determine the effective grade (or static force applied to the truck). In up-hill calculations, the effective grade (resistance) % = grade % + rolling resistance %, and conversely for down-hill calculations the effective grade % = grade % – rolling resistance.

Example Effective Grade:
Taking a loaded truck of 376t (GVM) as an example, on a uphill ramp of 8% grade and a rolling resistance of 2%, the effective grade will be 10% and the static force on the truck will be 376 x 0.1 = 37.6tf (or 37,600 kgf).

Truck/Fleet Performance

Once your haul environment has been determined, the next stage is to choose which truck fleet options you wish to simulate. The following details what parameters of truck performance are used in Spry.

Rimpull is the force available between the tyre and the ground to propel the machine (limited by traction) and it is measured at the wheel so includes all transmission losses. Rimpull curves are used to determine the maximum speed attainable, gear range and available rimpull when machine weight and effective grade are known.

Spry has a truck database which includes over 100 common mining truck/engine combinations. If you wish to enter your own data, it is important to note that scales and units on rimpull charts range from linear to logarithmic and can use kg force, kN or lb force.

Example: If a fully loaded (324t) Caterpillar 789D travels up a 10% effective grade, there are two ways to determine the maximum speed attainable. Manually reading a rimpull graph involves

  1. 1. Finding the effective grade (10%)
  2. 2. Drawing left to the rimpull graph (~320,000N rimpull, 2nd gear)
  3. 3. Drawing down to the speed (~14.8km/h)

If no grade lines are available calculate the rimpull by multiplying the effective grade by the vehicle weight. In this example, 324,319 kg * 10% = 32,432 kgf or 318,048N (see 4. Below) and draw right.

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Retard/brake performance curves determine the speed that can be maintained when the truck is descending a grade with retarder applied. For most trucks what this means is there are 5 or 6 (depending on gears) maximum descent speeds a truck can maintain. You can read a retarding curve in the same way as a rimpull curve.

Editing rimpull data & retard data in Spry is generally not required (or recommended), and small changes generally do not effect results by a significant amount. If your schedule throws an error due to rimpull or retard data not being sufficient, you may need to look at your haul profile to make sure it is accurate rather than changing the rimpull.

TKPH

Tonne kilometre per hour (TKPH) is the measurement of the work load of a tyre and is based on the weight and speed that the tyre can handle without overheating and causing it to deteriorate prematurely. A TKPH rating for a tyre is the theoretical maximum workload it can take (average weight on the tyre * average speed of the truck OR more specifically, tonnes * km/h).

Example: On one axle, the truck has two tyres. The total load on the axle is 100 tonnes when the truck is loaded and 50 tonnes when the truck is empty. The average load on the axle is 75 tonnes which is 37.5 tonnes per tyre. If the average speed of the truck is 20km/h, the tyre rating would need to be 37.5*20 or 750 TKPH in order for TKPH to not be a limiting factor.

Coefficient of Traction

Note: Coefficient of Traction rarely enters into the frame and this part of the documentation is for completeness.

Coefficient of traction or friction refers to the maximum frictional force that can be produced between surfaces without slipping. The table below from Noon (1994, see reference below) is a selection of values that represent reasonable averages between tyre and road.

Surface Type Coefficient of Friction (µ)
Gravel and dirt road 0.35
Wet, grassy field 0.20
Dry asphaltic concrete 0.65
Wet asphaltic concrete 0.50
Dry concrete 0.75
Wet concrete 0.60
Snow 0.20 – 0.25
Ice 0.10 – 0.15
Loose moist dirt that allows tyre to sink about 5cm 0.60 – 0.65

Bear in mind that the more water present on the road, the lower the coefficient of friction. As little as 0.4mm of water should be considered “wet” (Tulloch, Stocker 2011).

Noon, R.K. (1994): Engineering Analysis of Vehicular Accidents, CRC Press, Boca Raton.
Tulloch, D. and Stocker, D. (2011) Coal Mine Road Network Surface Friction Report (http://mines.industry.qld.gov.au/assets/mines-safety-health/Coal-Mine-Road-Network-Surface-Friction-Report-2011.pdf)

Practical

The suggested set up of Haulage is as follows:

1. To start simulating haulage, first tick on the option in the Schedule settings.

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2. Add at least one Segment Code. Rolling resistance is controlled by Segment Codes which get applied to each segment along a haul profile. The primary properties of each “Segment” are Rolling Resistance and Speed Limits.

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3. Return to the Schedule settings and switch to the Haulage Tab. Set a Default Segment Code (the most common Segment, usually what your established haul roads will be)

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4. Add Corner and Ramp speed restrictions. In addition to automatically calculated speeds generated from looking up the truck’s rimpull and retard curves, speed limits can be defined for both segments codes and also roads meeting certain criteria. These criteria include the grade of the segment (for ramps) and the angle change between two segments (for corners). Corners are applied to a change in angle between the original direction of travel and the new direction of travel illustrated in the image below.

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The Distance element is how long the segment restriction will apply for (in total, not on each of the two parts of road involved).

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The Minimum Distance element in a Ramp determines how long a segment needs to be in order to have the restriction applied. In the example below distances of less than 100m would not have the Ramp restriction applied.

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5. Add at least one Truck type. Right click “Trucks” and select Add -> Trucks from Truck Database.

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6. Apply Haulage simulation to equipment and set a Truck fleet to each Equipment/Process combination

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Parameter Descriptions

Equipment (per process)

  • Truck – Pick which truck fleet is applied for Raw Truck results
  • Truck Payload – The amount of Source Quantity each Truck moves (uses whatever the Source Quantity unit of measure is)
  • Loading Time – The amount of (static) time a Truck needs for Loading per cycle
  • Dumping Time – The amount of (static) time a Truck needs for Dumping per cycle
  • Queueing Time – Estimated Queueing time per cycle
  • Additional Time – Any additional time to be reported differently
  • Efficiency Factor – Increases cycle time to account for driver inefficiency
  • Minimum & Maximum Trucks – Controls the truck fleet size. Effects discussed in the Results section.

Truck

  • Apply TKPH Limits – Tick on to apply TKPH. TKPH is addressed in a later section.
  • 0% Engine Load Factor – Fuel use when truck is considered to be not moving. Includes Loading, Dumping, Queueing and Additional Time. (L/hr)
  • 100% Engine Load Factor – Fuel use when truck is at 100% Engine Load (L/hr)
  • Maximum Acceleration – Realistic limits 1.3-2.6 m/s2
  • Maximum Deceleration – Realistic limits 0.9-1.8 m/s2
  • Maximum Traction for Braking – Realistic limits 60-80%
  • Empty Weight, Full Weight & Payload – Calculated (not changed). See Truck Axle for calculations

Truck Axle

  • Number of Tyres – Affects various parameters. Should not require change.
  • Full Weight – Change (reduce from manufacturer specs) to control under-loaded weight. See below for example
  • Empty Weight – Change (increase from manufacturer specs) to control carry-back weight
  • Driven – Affects various parameters. Should not require change.
  • Tyre Rating – If TKPH is turned on, set the tyre TKPH for each Axle here

For example: The Caterpillar 789D has a maximum payload of 181 tonnes. After calculating a Waste Payload of 72 using bucket sizes, with a density of 2.4 tonnes/m3 the final Payload weight is 172.8 tonnes.
The Full Weight on each Axle of the truck should then be reduced to bring the total Payload to 172.8 tonnes.