Compaction is as much about how a machine applies weight — pound-per-linear-inch (PLI) — as how much the machine weighs. Calculate PLI by dividing weight by the combined width of all four wheels in inches. The higher the PLI, the more material will be compacted in the same space. Photo: Terex Corp.
After six passes with a landfill compactor — regardless of size — density levels plateau. Photo: Terex Corp.

At its root, the landfill business is a simple mathematical calculation. A landfill receives a permit for a certain number of acres and is relegated to how deep it can dig and how high it can go. The result is a finite number of cubic yards of space that, depending on anticipated waste stream and compaction densities, determines the landfill's projected life expectancy.

There's just one key remaining variable — how the space is filled — and this has a profound impact on the life expectancy of and revenue generated by the site.

“Choosing a compactor that delivers high pound-per-cubic-yard (lb./cu.yd.) densities can lengthen the life of a landfill by years,” says Fred Heath, president of Road Machinery Services Inc., Statesville, N.C., that's served the Carolinas for more than 30 years. “Extending the life by 5 or 10 years can lead to millions, if not tens of millions, of dollars in additional revenue.”

The distributor's employees spend much of their time teaching techniques for achieving maximum compaction densities. “Many people incorrectly believe that compaction is all about machine weight,” explains Vice President Mark Hiatt. “Actually, it's about how the machine applies this weight.”

Five tips on technique

Optimizing densities depends on how waste is compacted. Following these tips will help improve air-space utilization.

1. Thoroughly train the operator. Knowing how many machine passes are appropriate, the proper way to spread waste, and the best way to compact the face add to (or subtract from) compaction densities.

2. Avoid excessive passes. Four to six is a rule of thumb. “Beyond six, the law of diminishing returns takes over and density plateaus,” says Mike Rodriguez, a product specialist for Terex Corp. , which makes Trashmaster compactors. Going beyond six passes wastes fuel, increases wear on the machine, and decreases production.

3. The right thickness. Avoid the “smear” method — spreading an extremely thin layer of material over a wide area — because it slows production. Also, don't compact all the way to the edge to avoid waste “cliffing.”

Maximum compaction is achieved at 1-foot layers; density begins to suffer significantly when material is spread more than 2.5 feet deep.

4. Eliminate gaps. A compactor that offers full-width compaction in a single pass eliminates the need for the operator to index the machine over to compact the center tunnel of material left uncompacted on the first past. In addition, the U-shaped blade funnels material directly to the wheels across the machine's entire width to immediately begin shredding and demolishing trash.

5. Keep slopes as low as possible. Compactive effort decreases as slope increases because the machine's full weight cannot be directly exerted on the lift. If working a steep slope is a must, run at a 45-degree angle up and down. Running sideways across the slope is ill-advised because this exerts more pressure on the lower wheels and much less weight on the upper wheels.