Top: High Point landfill superintendent Steve Pendry shows some of the difficult-to-compact cotton batting the landfill regularly takes in. Bottom: At day's end, the landfill will use tarps rather than fill dirt to top the waste, conserving space. Photos: Terex|Trashmaster
More than 760 PLI force is exerted by the 115,000-pound Trashmaster 390.
Not By Weight Alone

Eric Speck, a Terex|Trashmaster compactor engineer, said that it is not just sheer weight that gives a compactor the ability to compact waste effectively. “One of the most important factors in compactor efficiency is how the landfill compactor's weight is applied to the landfill surface,” he said.

That factor is called compactive effort per linear inch (PLI). It is calculated by dividing the compactor's weight by the total wheel width. In the case of High Point's 390 Trashmaster, weighing approximately 115,000 pounds and offering a 150-inch total contact area, the landfill compactor generates about 767 PLI in a single pass.

The 390 has a high PLI due to a unique wheel configuration. Breaking away from the modified wheel loader design, the triangular wheel design of the 390 Trashmaster gives full-width coverage in a single pass. Pendry said, “We get a full 15-foot wide pass because of the machine's three-wheel design, giving us maximum compressive effort.” The design also allows the High Point Landfill to more effectively compact the waste stream to higher densities.

One final key element to a machine's compactive effort lies in the wheel design. “The wheel's cleats must deliver the necessary crushing force to penetrate and break down the refuse,” said Speck. This means that the 390 Trashmaster's cleats must stay clean to maximize penetration. The 7¼-inch high “Big Dog” self-cleaning cleats on the compactors are mounted in a chevron pattern, which prevents material from being retained between the cleats during operation.

Of equal importance to Pendry is protecting the compactors' hydrostatic drive motors, located in each wheel, from wire wrap-around. Wire wrap is a common occurrence at most landfills, but given the amount of broken springs from the furniture manufacturers, it is of greater concern for the High Point Landfill. Speck said that the 390 Trashmaster's wheel design deals with this problem. “Each drive motor is protected by a labyrinth seal formed by mounting a 1-inch-thick ring to the inside of the wheel wells,” he said. The multiple angles created by the seals leave little room for wire to get into the drive motors, reducing the occurrence.

Thirty More Years

Ten years into its permitted location, the anomaly is that the High Point Landfill continues to thrive, even with an unusual waste stream to manage. While other city-operated landfills of its size are having problems getting operating permits and operating profitably, and are thus investigating privatization, the High Point Landfill still has another 30 years of operating life. With tight management controls, a focus on landfill space maximization, and large, reliable compactors to handle the waste stream, it should be a successful 30 years.

George Denny is a director of landfill compactors with Terex|Trashmaster, Oklahoma City.