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Introduction
Trucking operations are the backbone of efficient mining and logistics industries. Whether moving ore, coal, or construction materials, a well-structured trucking model ensures smooth operations, minimises costs, and enhances productivity. This blog will explore the fundamental principles of trucking, including truck configurations, rolling resistance, haulage scheduling, and truck number calculations.
Trucking model
1. Dig and dump solids
The truck cycle begins by loading under the digger, followed by hauling, dumping at the designated dump location, and returning to the dig site. Consequently, trucking models must identify dig and dump locations. Achieving this requires creating solid representations or XYZ data (nodes) for both the dig and dump locations.
2. Haul strings
Haul strings can be created manually or through software rules/logic to facilitate bulk generation. When constructing haul strings, it is important to:
- verify that no segment of your string exceeds the site maximum grade (e.g. ensuring all segments are below 10%),
- ensure that, at the connection points in the haulage network, all nodes/points of your strings are properly linked,
- review the coordinates of your string points, registering them to the topo surface if necessary.
3. Haulage software rules
Software rules can help customise the haulage model according to your desired objectives.
These rules are dependencies and constraints related to dump activities. For instance, you can instruct the software not to initiate the RL90 dump until the RL60 dump is finished.
Haulage rules, referred to as Haulage Logic in Spry, enable you to prioritise haul routes and assign them to specific dig or dump locations.
It is advisable to configure your rules before commencing the scheduling process, although there may be instances where rule adjustments are necessary during the schedule to optimise output.
A screengrab from Micromine Spry software
4. Rolling resistance
Rolling resistance is the force opposing a truck’s movement due to its contact with the ground. Several factors impact rolling resistance, including tyre pressure, road surface conditions, truck speed, and load weight.
Rolling resistance illustration
5. Truck types and configurations
Truck types are typically chosen as part of the equipment selection process in feasibility studies or operational transformation projects. When examining various truck types, it is crucial to extract and analyse the following information to construct a robust trucking model:
- Empty weight
- Payload/truck factor
- Tyre size
- Rimpull curve
- Retarding curve
- TKPH
5.1 Rimpull Curve
Rimpull curves come into play when the truck is ascending or on flat ground, either loaded or empty, to determine the truck's speed by considering the upward slope and rolling resistance. Rimpull curves can be extracted from the truck's specification book or equipment manual. It is advisable to confirm this information with the site's mechanical engineer.
How to use a rimpull curve
- Begin by determining the total resistance the truck must confront, comprising both the grade and rolling resistance. For instance, if the ramp grade is 9% and the rolling resistance is 2%, the total resistance would be 11%.
- Sketch a line from the 11% total resistance point to the zero point (green line).
- Draw a vertical line for the gross weight (the black dotted line in this example for the loaded truck).
- From the point of intersection between the green line and the black dotted line, draw a horizontal line to intercept the highest gear (depicted by the blue line).
- Proceed to draw a vertical line downward from the highest gear and read the maximum speed at which the truck will travel on that grade (red line).
5.2 Retarding curve
A retarder is a device that assists in slowing down the vehicle, especially when descending steep slopes. The retarder reduces the reliance on the service brakes, preventing overheating and prolonging their lifespan.
Retarding curves come into play when the truck is descending, whether loaded or empty. They help determine the maximum speed the truck can sustain by taking into account the downward slope and rolling resistance. Similar to rimpull curves, you can obtain retarding curves from the truck's specification book or equipment manual. Ensure that you confirm this information with the site's mechanical engineer.
How to use a retarding curve
- Begin by calculating the effective grade by combining the rolling resistance with the overall grade (downhill grade is a negative number). For instance, if the ramp grade is 9% and the rolling resistance is 2%, the effective grade would be 7%.
- Sketch a line from the 7% total resistance point to the zero point (green line).
- Draw a vertical line for the gross weight (black dotted line in this example for the loaded truck).
- From the point of intersection between the green line and the black dotted line, draw a horizontal line to intercept the highest gear (depicted by the blue line).
- Proceed to draw a vertical line downward from the highest gear and read the maximum speed at which the truck will travel on that grade (red line).
5.3 TKPH
- Heat in a tyre is generated through flexing, with the primary contributors being the weight imposed on the tyre and the speed at which it rotates (kph), reflecting the number of rotations within a given time period.
- TKPH, or Tonne Kilometer Per Hour, measures a tyre's ability to shed heat.
- Tyres have a maximum TKPH at which they can be safely operated (TKPH rating).
- The TKPH rating of a tyre represents its theoretical maximum workload, calculated as the product of the average weight on the tyre and the average speed of the truck (expressed as tonnes multiplied by km/h).
- A higher TKPH rating suggests that a tyre can withstand more heat.
- Operating under the TKPH rating is crucial for ensuring tyre longevity, safety, and optimal performance.
- The TKPH rating can be obtained from the tyre supplier or the maintenance department.
How does this affect your haulage model?
- The TKPH concept implies that heavier trucks, such as waste trucks, running on long hauls can exceed tyre TKPH ratings. This poses a safety risk.
- To address this risk, mine supervisors may add an extra truck to the circuit to lower the overall TKPH. This adjustment alters the trucking number balance.
- If your mine often deals with TKPH management challenges, it's essential to incorporate this aspect into your haulage model for accurate forecasting.
6. Haulage scheduling and efficiency
The objective is to efficiently transport materials from the excavation location to the designated dump location, optimising the route selection.
The primary outcomes of these schedules include measuring material movements (bcm or tonnes), along with the corresponding haulage time.
During the scheduling process:
- Adhere to long-term dumping strategies (LOM/Budget).
- Ensure compliance with sensitive areas, including the final landform, approved disturbance boundary, and environmental compliance.
- Implement a tiered approach for material placement: direct high-level materials to higher dumps, medium-level materials to mid-level dumps, and low-level materials to lower dumps.
- Minimise significant de-elevation.
- Designate separate dumps for different fleets to reduce interactions.
- If your operations are near a community with noise constraints, consider reserving low-level dumps for winter to assist with noise management.
- If your operations are near a community with dust constraints, during summer, optimise the number of routes to manage dust levels, considering available water carts.
- Take into account the TKPH impacts.
Three key outputs from your software schedule are truck haulage time, digger hours, and material movement.
We won’t discuss haulage time calculations in this blog, as your haulage software handles them. However, for your understanding, haulage time is generally calculated using the haul route's distance and grade, along with the truck's speed, while factoring in rolling resistance, the rimpull and retarding curves, truck weight (empty and loaded), and other trucking constraints such as speed limits and operational restrictions.
7. Truck hours and truck number calculations
* Haulage time includes loaded and empty haulage time.
** Truck factor:
Initially, it can be extracted from the truck specification book.
- Consult with the site mechanical engineering manager to confirm the approved number.
- Reconcile payload data to understand the discrepancies and potential modifications.
Conclusion
Mastering trucking principles is essential for mining, logistics, and construction operations looking to optimise efficiency, reduce costs, and improve safety. By leveraging proper truck selection, optimised haulage scheduling, and strategic road design, businesses can achieve smooth and profitable trucking operations.
Consider the following points when building or using your trucking model:
- Trucking model’s data reconciliation is crucial for ensuring the accuracy and consistency of the model’s output.
- It involves comparing and aligning data sets to identify and rectify discrepancies, errors, or inconsistencies.
- Effective data reconciliation enhances data quality, supports informed decision-making, and fosters trust in the reliability of information.
- By mitigating data discrepancies, reconciliation contributes to better analytics, more reliable reporting, and overall organisational success.
- Analysing historical data is valuable, yet it is crucial to benchmark it against other operations to gauge your performance in specific areas. This comparison is essential for developing business improvement plans and enhancing overall operations.
- It's beneficial sometimes to go back to the basic principles to identify any issues in the current operation. Relying solely on past data might reinforce either good or bad practices.
- Because your model shows more required trucks, asking for more trucks may not always be the initial solution. Exploring various improvement opportunities to optimise the average cycle time should precede proposing additional trucks.
About Atlantech
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Sources
- Caterpillar Rolling Resistance Factors
- Caterpillar Specalog for 793F Mining Truck AEHQ8089-00
- iStock images: iStock-1213897760, iStock-92962238, iStock-172268149, iStock-901205926, iStock-1361770826