The Technologies & Benefits to Improving Haul Road Condition & Payload Distribution

The production and cost benefits associated with having a correct load balance on a haul truck and improving haul road conditions are difficult to quantify on paper and therefore a lot of mines do not make it a part of their standard operating procedure/best practice. But it is a relatively easy change to make to yield lower cycle time, higher production and lower costs. The premise is to create an environment where the truck is operating as close to design parameters as possible; in this blog entry, we will only focus on the design parameters of road conditions and load balance and how to utilize technology to monitor, analyze & improve these parameters.

My experience with open pit haulage has been with Caterpillar mechanical 240ton trucks (793x) so this article will use the Caterpillar line of products in the examples of technology[i]. The same best practice strategies should apply to other OEM haul trucks and if your truck isn’t currently equipped with the technologies described from hereon, there are 3rd party technologies you can look into if. Contact me if you need some direction.

First, let’s look at the “perfect” environment for haul truck (the environment which spec sheets are based on, for the most part):

1. Truck weight when loaded should be distributed as:

• •1/3 of weight to front axle
• •2/3 of weight to rear axle

• •1/2 of weight to the right side
• •1/2 of weight to the left side

2. Truck is traveling at 0% rolling resistance. The smoother the road is, the lower the rolling resistance %. 0% is “impossible” in reality; in general, 1% is great, 2% is average. A high rolling resistance causes reduced rimpull and reduced acceleration and therefore, longer cycle times and lower productivity

3. Truck box is optimally sized based on density of material to optimize payload.

4. Payload (Gross Vehicle Weight (GVW) minus Empty Vehicle Weight (EVW equals Maximum Payload) follows the 10/10/20 rule (often misunderstood, the 10/10/20 rule means that 10% of the time, the truck can be 10% overloaded, and 0% of the time can the truck be 20% loaded).

Based on the “perfect” environment above, this means that anytime you deviate away from the conditions, the truck is performing at a level slightly less than it’s potential. Translated into production/savings, it means that the changes you make to ensure proper payload weight/distribution and well-maintained haul roads will enable the following:

• Faster Cycle Times à Increase Productivity
• Extended Drive Train, Suspension, Frame & Tire Life[ii] à Lower Operating Cost & Increased Machine Availability
• Reduced Fuel Consumption à Lower Operating Cost
• Reduce Operator Fatigue à Promotes Safety
• Increased haul road maintenanceà Maximize Support Equipment Utilization

The information above begs two questions:

1. What technology tools can we use to help us monitor and analyze the conditions?

2. How do we improve our conditions to better reflect design parameters?

To answer the questions, I will first introduce a tool, then explain how this tool can help in each of the four (4) operating conditions of the “perfect” environment.

Caterpillar has designed a system called RAC[iii] (Road Analysis Control), which is an on-board information provider source that is integrated with VIMS (Vehicle Information Management System). RAC quantifies and monitors haul road conditions and identifies events at a range of severity that are damaging to the following:

• Machine Performance
• Component and Frame Life
• Availability / Utilization
• Machine Productivity

The RAC warnings can be local to the truck only with real-time feedback to the operator; or with a wireless system in the pit, this information can be transported back to the dispatcher, engineer, or supervisor. Note: If you want to utilize the data back at the office, you will need proprietary desktop Caterpillar software.

To monitor & improve road conditions: Using RAC and activating a GPS unit with your dataset, you can then start to identify where haul road problems should be avoided/corrected and better allocate your resources – grader, operators, and training dollars. Also, you can respond quicker to making repairs to the roads. With improved pit planning, haul profiles and haul road maintenance, you can see increased truck speeds (if you are not already at maximum for the corresponding road grade).

To monitor and improve load distribution: Because RAC is constantly measuring the strut pressures for correct load distributions, you can determine when the truck is not at 33%/66% front/rear and 50%/50% right/left loading. You can then identify the shovel operators that need further training.

To monitor and improve payload optimization: Within VIMS, there is a function called TPMS (Truck Payload Monitoring Systems). When the struts are property calibrated (I would advise adding that as a maintenance item at the 500 hour PM (Preventative Maintenance)), TPMS will accurately provide the payload. This data is stored and shown locally and/or streamed back wirelessly to the office. Again, this VIMS and TPMS data requires proprietary Caterpillar software to decode, review and analyze.

You can then create charts with this data to see what the payload % curve/histogram looks like. With that, you can again spot-train shovel operators. When loaded properly, you should maximize GVW minus EVW of your equipment (see spec sheets for GVW and EVW).

*Depending if you are over-trucked or under-trucked and many other parameters such as cycle time, commodity materials grade, etc., it may or may not be worth it for the shovel to engage in a partial bucket to bring the truck up to maximize payload. This is why shovel/truck pairing is so important when purchasing equipment during the capEX phase. Do the calculations to see what it shows on paper.

To monitor and improve truck box design: To review your truck box, first make sure it is loaded correctly: to avoid spillage, there should be slight extra room on the left, right and rear of the truck box. I have conventionally used 1’/1’/1’ when contributing to training materials for shovel operators when they load a truck. This could change from site to site depending on uphill loaded road grade.

If you are loading the truck properly and your scales are calibrated, but you are still not able to maximize payload (GVW minus EVW), then consider a new truck box design (lighter material/shorter life but higher payload). Do the cost analysis to see if the shorter component life is worth the higher payload (at commodity pricing currently, the payback is generally there).

If your trucks are constantly spilling but the truck scales say that you are not overloaded, then consider installing hungry boards on the side to increase the carrying volume of the box. Or engage in a redesign of the box to increase volume whilst maintaining the same box metal/liner weight.

Lastly, as with all technologies, its success is based on the users. Unless operators and/or downstream users of this information are educated and unless there is a process to create/fix the source of the alarms, the technology will not yield cost savings and other benefits for the operation.

Would love to hear everyone’s feedback on this issue; your comments are always appreciated!