Landfill compaction do’s and don’ts

Effective landfill compaction maximizes the amount of waste that can be placed in the minimal amount of space. In short, it’s all about airspace and density.

It’s also about costs. Failure to maximize airspace shortens the lifespan of a landfill, resulting in added costs related to emissions, water control, and the resources it takes to build a new cell with a liner.

“It’s important to look at the lifespan of a landfill,” says Martin Mattsson, director of key account sales for waste and recycling at Volvo. That requires considering limited airspace and getting the right density of material.

Dale Mills, vice president of sales and managing partner for Macpactor Inc., likes to use the analogy of stuffing $100 bills into a suitcase to explain the importance of density. “You’re going to try to compact those bills so you can get more in.” Compacting trash at a landfill is like putting “as much garbage in the suitcase as possible.” And, while you wouldn’t want to shred those $100 bills, you can shred garbage for even better compaction.

In addition to increasing landfill space, achieving optimal compaction has many other benefits, such as:

·        Decreasing operational and labor costs

·         Minimizing the environmental impact (pollution)

·         Improving safety

·         Enhancing public image

·         Creating a base for access roads for equipment

·         Stabilizing slopes by eliminating uneven settlement and landslides

·         Containing leachate by eliminating low spots that collect water and preventing water from seeping through the cell

·         Reducing fire risk by reducing air pockets

Bad compaction, on the other hand, shortens the lifespan of a cell. As Mattsson points out, it also impedes the work of gas systems used to fuel fleets and power homes.

So, how do you achieve maximum compaction? Attaining peak compaction comes with some do’s and don’ts—as well as some advice from the experts.

The right equipment

In some regions, environmental regulations require compaction, but whether or not it’s required, it’s standard procedure at nearly all landfills. The proper compaction technique includes shredding the material, pushing it to mix and blending it, placing it to fill any voids, and compacting it to maximize space. This requires a small fleet of equipment.

Equipment selection begins with the size and number of compactors needed at the site. “The number of tons a day, as well as peak tonnage—the busy times of day—determine which model and size of machinery you need,” Mattsson explains. Municipal solid waste at landfills has an average density of 550 to 650 pounds per cubic yard, so it’s important to size equipment accordingly.

Some landfills use a steel-wheeled/drum compactor to shred and compact the material in the waste stream. Typically, the preferred minimum operating weight is over 45,000 lbs. It should not be used on slopes with grades steeper than 25%.

While landfill compactors are often equipped with blades that can push large volumes of waste, they are not the best piece of equipment for moving material because they lack grip on loose refuse.

Track-type tractors, or dozers, are typically used to spread thin layers of waste over the working face of a cell, and to deposit daily cover. Fitted with steel tracks, they have better grip than compactors and can also chop and shred waste.

 “A compactor is not a dozer and a dozer is not a compactor,” Mattsson emphasizes, underscoring the importance of selecting the right equipment for the job. “A dozer moves and places material; a compactor runs over it and compacts it.”

Although possible to do, compacting with a dozer is not recommended due to inefficiency. Dozers are better at pushing material dumped by collection trucks and spreading layers on the working face.

Tips, cleats, cleat patterns, and cleat guards

“A landfill compactor properly equipped is required,” Mattsson states. Volvo offers one purpose-built compactor: the LC450, but it can be equipped according to the landfill’s demands. “The material dictates cleats and cleat patterns; that’s most important.”

Some landfills are 100% C&D or MSW. Others have a mix of material, including sludge, although Mattsson cautions that residential should never be mixed with C&D.

C&D requires more cleats to break up the material without wearing out the wheels. Tips should break, separate, and puncture the material into the landfill. To get the best results, “you need the right configuration for the weight of the machine.”

Placement is also important. Where the pattern of the tip is located on the wheel makes a difference. It’s based on the type of garbage.

One of the biggest mistakes some operators commit is choosing the wrong tip for the material. “The shape and size of the tip are important,” Mills affirms. If the cleat pattern has too many cleats, the wheels plug. Smaller, cleaner tips are better for compaction. Expanding the tip pattern so tips clean themselves and are more effective at puncturing garbage into smaller pieces is efficient, but that changes the price dramatically.

Macpactor’s diamond-type tips are made of chrome and last 15,000 hours. “We’re the only company that builds a tip that lasts that long and has a natural repose,” Mills says. The laterally opposed, multi-directional, all-traction M-Trax Diamond Tooth system provides:

·     Maximum demolition

·     Elimination of side slippage when working across the face

·     Improved surface finish, saving on cover

·     Cleat with high abrasion resistance

·     7- ,8- and 10-inch height options

Tips should also have “good height” and be shaped the right way, according to Mills. He advises running tips low—4 inches or less—before replacing. Much lower and you’ll lose traction. “The compactor slips and uses more fuel. It won’t compact properly, so you’ll lose compaction and density.”

Design impacts efficiency. “Some companies build cheap chopper-type wheels,” Mills observes, explaining that they were the original wheel for the logging industry. “They chop, but they don’t compact due to the big blade that flips the material up.”

For better separation and puncturing, Macpactor builds tips at a natural angle of repose. “Think of a conveyor belt with a pile of sand at the end,” Mills uses another analogy, “It falls in a natural slope or angle. We build tips at that angle.” Because it’s not a straight-up wedge cleat, chopper, or a twist cleat (which has a pocket that catches dirt, he says), the material gets off the tip easily.

One thing that doesn’t come off so easily is wire wrap—fishing line, mattresses, etc. “It’s a big issue because it slows down the machine,” Mills states. “It cuts into the wheels and destroys them.”

Cleat guards prevent material from wrapping around the inside of the wheel. “Other companies use a ‘pizza cutter’ wall to divert material away from the machine,” Mills elaborates. “They have gaps. When big pieces of cable get stuck, they can snap axles. Guards work great. Our patented design turns it into a cleat for additional traction, which adds compaction.” It’s their biggest seller.

Wheels

The material at a landfill can also guide choice of wheels. According to Mattsson, Volvo asks landfill owners if their stream changed. “When replacing wheels, they may need a different style to accommodate changes.”

The type of material can vary geographically, as can the soil. Mills notes that the clay soil (like that common in Louisiana) and sludge (water waste) pack on the wheels, creating a smooth drum that doesn’t compact material. 

Reduced wheel width increases pressure and compaction. Therefore, mobile equipment with two drums instead of four wheels is less effective. Reduced wheel size increases pressure, but not necessarily compaction. Narrow wheels can break free and spin more easily if the sheer force of the wheel is higher than the compacted waste.

The least expensive wheels cost about $50,000 and last only 5,000 hours, Mills estimates. “Cheap wheels with 8-9-inch tips last about 6,000 hours, depending on the type of material the tip is made of.”

Macpactor wheels cost $80,000, but last 12,000 hours or more. “We out-wear other manufacturers two to three times on wheel life. That saves money over the life of the machine.”

He mentions one customer who saved $100,000 by buying Macpactor wheels. “It allows you to capitalize on the expense,” Mills continues. “If wheels last 12,000 hours, you can rebuild for half the price.”

The standard for wheel replacement used to be at 5 inches. Mills says it’s now 4.5 inches or less—at a cost of $50,000-$60,000.

Blades

Dozers equipped with large-capacity blades can increase productivity, but there’s more to it than just size. “What kind of blade—straight or semi-U—makes a difference,” Mattsson states.

Macpactor offers a choice of Semi-U blades and the M-blade. The Semi-U features the ability to contain waste within a concave “U” design, helping minimize waste escaping around the sides of the blade and instead, directing it under the compaction wheels. It can position cover material more accurately when attached to a compactor or dozer.

The multi-angled M-shaped blade features strong, rigid construction that stands up to the tough environment.

Tips, hints, and advice

One of Mattsson’s tips to get good compaction regards placement of material. “You need a good angle—a good slope. Work in tandem with the dozer so you don’t have to move the material too much.”

You also don’t want to make too many passes. While each pass does increase compaction, too many passes waste fuel and labor. A good balance between compaction and economics is four passes for residential waste, with a final pass at a 45-degree angle from the pattern direction. The amount of compaction achieved by more than four passes diminishes incrementally. “It’s the pinnacle point for best compaction,” Mills believes, adding that, “if you only roll over the material once—vs. four to five times—you’ll get less density.”

The exception is industrial waste, which typically requires additional passes because it’s usually drier and the items are larger. Industrial waste benefits from shredding. While shredding initially “fluffs up” waste, increasing its volume, it allows better compaction, resulting in minimizing airspace.

Uniform compaction saves fuel because it reduces rolling resistance on the working face. It’s achieved in part by spreading thin layers of waste prior to compaction. Thin layers—optimally less than two feet thick—bind, compress, and shred easily, contributing to higher density. Conversely, thicker layers often see only the top layer being compacted, with a “spongy,” uncompacted area underneath. The weight of the equipment used for compaction affects layer thickness.

Something to avoid is lifting too much. Mills suggests a technique of using small lifts for gradual spreading. “If you lift 24 inches instead of 10 inches, it increases compaction time.”

Another caution is water. While higher moisture content of waste can improve compaction, most states prohibit direct application of water for purposes other than dust control. In addition, large quantities of water applied to the working face can result in leachate issues that must be treated.

The safety factor

Increasing landfill density is an important factor in improving safety, both at the landfill and in the surrounding areas, because of reduced fire risk, fugitive odors, and rodents.

Safety is a crucial element in the equipment, as well. “Slip-and-fall is the biggest safety issue,” Mattsson confirms. In keeping with Volvo’s focus on safety, he points out features incorporated into its compactor, such as:

·         Ground-level fuel, filter, and service access points for easier and safer maintenance

·         LED lighting

·         Orange handrails at the three points of contact on entry, as well as points to hold while cleaning the windows

Ultimately, Mattsson acknowledges, waste applications are tough for heavy equipment. They should be less so for operators.