Motor Grader Techniques
Source: Blue Ridge Services
Author Neal Bolton looks at some specific grader tasks in more detail.
As noted in last week's article (Bolton on Landfill Management: Use that grader!), there are two aspects to scraper (or truck) productivity: payload and cycle time. Of course, payload is based on the size of the hauling unit. But cycle time depends on the condition of the haul road. Obviously, the condition of the haul road depends on how much (and how well) the motor grader is used.
One of the most important things that a grader can do is to keep the scraper (or off-road truck) haul roads in good shape. And often, the first thing we think of in terms of haul road maintenance is keeping the road smooth.
Keep it smooth
Have you ever driven a pickup across a recently plowed field? If you have, you know that there are two methods: the slow, bumpy method …or the slightly faster, suicidal method. Both are slow. Both are hard on driver and machine. In terms of productivity, this kind of driving is excruciatingly, slothfully slow.
Now, keeping that same concept in mind, apply it to a 40-ton, articulated machine. Multiply the bumping, jolting and cost by 25. That's what a bumpy, rutted haul road does to scrapers and haul trucks. As a basic rule of thumb, if you can't roll along in a pickup at 20-30 miles an hour, the road is too rough.
The effort required to maintain smooth haul roads will depend on many things, including: the type of soil, the subgrade (soil or garbage), the size of the hauling machines, number of loads per day, etc.
As a point of reference in regard to the importance of well-maintained haul roads, keep in mind that Caterpillar has determined, through numerous tests, that for every inch of tire penetration, the scraper "feels" a slope of 1.5%. Thus, if you notice that the scraper tires are pumping (sinking into) the surface of the haul road 10 inches, the scraper "feels" an uphill slope of approximately 15% (10 inches x 1.5% per inch). In essence, the scraper is continually climbing out of its own rut.
Pumping is a common problem on haul roads located on top of waste.
Bank the turns
The turns should be super-elevated (banked) on all haul roads. This allows the vehicles to run faster and safer. Banked turns also help to reduce machine and tire wear. Finally, banked turns reduce material spillage.
Determining how much a given turn should be banked is based on a complex interaction of gravity, friction, force vectors, velocity, and centrifugal forces. Sounds pretty intimidating, huh? Well forget it. Toss that slide rule out the window and watch the road, literally.
Experienced grader operators know that soil spillage is the best indicator of super-elevation. Excessive soil spillage on the outside edge of a turn means the turn is too flat. Spillage on the inside means the turn is too steep. Here again, common sense is better than theory and formula.
Does it pay?
If you want to know whether or not using a motor grader is cost-effective at your landfill, first calculate the total (scraper) time saved by improving the haul roads. Of course, the accuracy of this analysis is based on the estimate of how much the scraper's cycle can be reduced by using a motor grader. To figure this out, time some scraper cycles with the road rough. Then, smooth up the road and re-check the cycle times. Also, Caterpillar has a vehicle simulation software program called (VSM) that can assist in predicting scraper cycle times.
Here's an example. Based on the amount of soil to be moved (say, 7, 800 yd3), and assuming an average payload of 13 yd3, the scraper must make 600 loads. If, over the entire project, you estimate that 8 hours of motor grader work can save 1 minute per cycle, this equates to a scraper savings of 600 minutes (600 loads x 1 minute saved per load), or 10 hours. Thus, at $135/hr (estimated), saving 1 minute on the cycle time results in a savings of $1, 350 (in scraper cost).
Thus, in this example, the question is can you provide eight hours of motor grader effort for $1, 350? Chances are, yes.
Evaluating the haul roads
If you want to get a feel for the condition of the haul roads at your landfill, here's a list of things to look for.
- Are the roads graded to allow fast, smooth travel?
- Are uphill slopes limited to 12-15%?
- Are all turns super-elevated?
- Are the haul roads one-way whenever possible?
- Are the haul roads located on the shortest (an quickest) alignment?
- Where haul roads must cross other roads, are the intersections at 90 degrees"
- Is there good sight distance to allow adequate "stopping" time?
- Are there signs on the haul roads to restrict unauthorized traffic?
- Are the haul roads firm and solid (i.e., no pumping)?
- Are the average cycle times short and consistent?
If you can't answer yes to all of these questions, your haul road needs work. If you're gutsy enough, post this list as your landfill's "Haul Road Standards." Then, invite the scraper (or truck) operators to let you know when the roads aren't meeting the standard. Or better yet, just give them the freedom to jump on the grader as needed.