Originally published on MSW Management, December 31, 2000
By Neal Bolton
Chances are, if you're reading this article, you really dig landfills. But if by chance you find yourself in some tough ground, just digging might not be enough: You might have to rip.
If you are still in the planning stage, or haven't yet dug deep enough to have to rip, you can use seismic velocity information to estimate when you'll have to begin ripping. In basic terms, seismic velocity is a measure of how fast a shock wave travels through the ground. To determine this, a series of receivers is placed across the excavation area. Next, an impact is induced into the ground. The receivers then measure the speed of the shock wave. This seismic velocity is expressed in feet per second (fps). Typically, the harder the material, the faster the velocity.
But if you don't have seismic velocity charts, how will you know when ripping is necessary? Don't worry, you’ll know: The dozer won’t be able to cut, and the scrapers won’t be able to load. Those cutting edges will smoke and screech and...you’ll know.
But even more important than knowing when to rip is knowing how to rip. As a construction process, ripping is both simple and complex. On one hand, it’s as simple as pulling a ripper through the ground. On the other hand, it’s as complex as matching tip size, style, and number to machine size and speed and to soil type - and doing it in essence with your eyes closed. Here are some things to think about when it comes to ripping.
Know Your Material
Understanding the material you're ripping is the first step to success.
What kind of soil are you dealing with?
Is it fractured or homogeneous?
Is it stratified?
Are the layers tilted in a certain direction?
How does the material break up? Does it come out in big chunks, crumble, or shatter?
Select the Right Equipment
The size of dozer and the type of ripper depend to a certain extent on the type of material you intend to rip. If you're working in thin layers of fractured shale, it’s a good bet that you can use a midsize dozer with multiple ripper shanks. This is especially true if you’re ripping shallow in order to have the material break up into relatively small pieces.
If you're ripping granite, basalt, or caliche (you desert operators know what this is), however, you’ll need a big dozer and probably a single ripper shank. And even at that, the material will likely come out in big chunks.
As noted above, if you have seismic velocity information, you can use it to size the machine to the material. For example, according to the Caterpillar Performance Handbook (No. 30), to rip granite with a seismic velocity of 8,300 fps, you’d need a D11R with a single-shank ripper. If the granite had a seismic velocity of 5,800 fps or less, however, you could use a D8R with single or multiple shanks.
Keep in mind that seismic velocity is only an approximate indicator of rippability. Much more depends on site-specific conditions and the operator's skill and experience.
Use the Proper Technique
The correct ripping technique is often achieved by trial and error. It is based not just on being able to rip the material but on ripping it so that it comes out in the right form.
A big dozer using a single ripper shank can often rip quite deep. Deep ripping, however, often results in big chunks of material that make for difficult loading if you’re using scrapers. If you’re planning to load with scrapers or use the material as daily cover, it's often better to use multiple shanks and rip shallow so that the material comes out more fractured. Try several methods and see which yields the best production and the most usable material.
The dozer operator should also try varying the "angle of attack" of the ripper shank and ripping in various directions. This is especially important when ripping material that is stratified (layered). To be effective in layered material, the tip must be able to get under or between the layers and break them out.
Ripping can't be reduced to a recipe or formula. Get out there, try several different techniques, and see which one works best.
If your landfill is one of those sites with deep, loamy potato soil, congratulations. If not, learning how to rip efficiently can save you lots of grief and money.
Author's Bio: Neal Bolton is a consultant specializing in landfill operations and management.
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