Flipping on a light switch or turning on a faucet: These are acts so common that we take them for granted. We never give them a thought as long as they’re working. And so it is with the roads at your landfill.
It’s assumed that you’ll keep the roads in good shape. And so when you do, there’s seldom a pat on the back or a little something extra in your paycheck; it’s just part of the job. And there lies the rub. Sure, it’s part of the job, but a darn tough job it is, even more so because it’s often a thankless job.
Wouldn’t it be great to build roads like the Romans built? With plenty of thought to site selection and careful construction (we’re talking stones that were hand-placed), these roads were built to last. In fact, many are still in use today!
Think of it: Roads that last not just through the wet season but through the centuries. Now that’s durability. Anything that can stand up to the test of time–for that length of time–is likely to offer some good lessons for today’s road builder. Let’s look at some of the things that make for durable roads.
Design Considerations
A good road starts with a good design. But don’t get hung up on the word “design.” Depending on the application, the design could be a detailed set of engineered blueprints or something sketched on the whiteboard in the back office. A design is simply the “think” before you act or the “look” before you leap. Here are some things to think about before you take the leap of building a new road at your landfill.
1. Type of Road
Good design means matching the road to the application. Consider the type of vehicles that will use the road. Must it handle 40-ton transfer trucks … or light, periodic traffic (as would be the case if the road leads only to a groundwater monitoring well)?
Developing a checklist can help you not miss some important aspect of the road design. A basic example is shown below.
| Road Design Checklist | |||
| Item | Purpose | Criteria | Typical Choices |
| Cross-Slope | Cross-slope helps direct water off the road. | Too little cross-slope will allow ponding, erosion, and increased maintenance and can ultimately lead to road failure. Too much cross-slope can make the road unsafe. | 1-2% |
| Super-Elevation | Super-elevation, the amount of banking on a turn, helps vehicles safely maintain higher speeds on turns. | The amount of super-elevation (measured in % slope) is based on vehicle speed and curve radius. Higher speeds and sharper turns require more super-elevation. Too much can cause vehicles to tip toward the inside. Too little can cause vehicles to slide outward. | Varies, but typical values are in the 1-5% range |
| Longitudinal Slope | Longitudinal slope refers to the slope of the road either uphill or downhill. | While steeper roads can reduce travel distance, roads that are too steep can cause vehicles to move too slow (uphill) or too fast (downhill). The risks can increase during periods of rain, snow, or ice. | Up to 8% |
| Width | Road width includes the driving lanes and shoulder. | Roads should be wide enough to allow for safe two-way traffic. Also, roads should have regular turnouts or enough shoulder width to get stalled vehicles off the roadway. | Varies, but typical values range from 16 to 30 ft. |
| Underlying Base | The underlying base, be it waste or soil, provides a certain amount of strength. Any additional strength required must be met by the base/sub-base. | The underlying base is typically native soil or waste. A road built on native soil is preferred to a road built on waste. Roads built on garbage will usually have settlement problems. | Varies |
| Base/ Sub-Base |
Base/sub-base refers to the prepared layer(s) of base above the waste or native soil. Sub-base is intended to provide strength to the road. | The type and quantity of sub-base varies depending on the underlying material. On native soil, 6-12 in. of gravel may suffice; however, roads built on top of waste might require 2-3 ft. of compacted prior to placement of gravel. Geotextiles or discarded asphalt/concrete rubble may also be used to replace and/or supplement a soil or gravel sub-base. | Soil, pit-run, gravel, geotextiles, asphalt/ concrete rubble, etc. |
| Surface | To provide good traction and low maintenance at a minimum cost. | While the criteria can vary from one landfill to another, the goal is to find the most economical road surface that provides good traction and durability. It’s also important to take into consideration such things as tire wear, windshield damage, and dust. | Compacted soil, gravel, asphalt, rubble, etc. |
| Drainage | To remove water quickly and safely from the roadway while minimizing erosion or sedimentation problems. | It’s important to consider traffic volume, rainfall, and even the cost of road failure when designing roadway drainage systems. | Ditches, culverts, downdrains, etc. |
2. Service Life
Will it provide short-term access to a remote corner of the landfill … or will it be used as the main access road for the next 10 years? Knowing the answers to these questions is critical. When it comes to road construction, longevity costs money.
The service life of the road will impact not only the cost of the road but also the type of road you want to build. You might be surprised to find that the break-even point (i.e., based on cost) between paved roads and gravel roads occurs fairly soon–often in just two to three years. The key lies in the reduced maintenance cost offered by a paved road. Of course, if the road is on top of waste, a paved road won’t hold up very well because of settlement.
Because of the many factors that can go into road construction, you might wish to use a computer to model various types of road designs.
3. Location
The concept of good road layout and placement is as important today as it was in Roman times. Obviously if you’re hand-placing every stone in the road, you’d want to make sure the road is in the right place. Announcing to the crew, “The last 2 miles of road–or rather the last 27 million hand-placed stones–is, uh, in the wrong place,” could mean a quick mutiny and a short trip to the lion’s den for the project engineer. There was pretty low tolerance for failure, if you know what I mean.
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Today, having to abandon and relocate an improperly placed road might not mean curtains for the planner, but it sure can be expensive. In a landfill application, proper road placement is a key part of sound planning. Although you might not expect a service life of 2,000 years, the longer your roads last, the more economical they become.
In an ideal situation, you’d want to locate the road on original soil in a well-drained area where it will be unaffected by waste settlement or the landfill operation in general. In this case, a standard asphalt road on gravel base would likely suffice. When your choices for the road location are limited, however, you might have to use an alternative design. Here are some examples:
Wood Chips. Where a short-term road must cross a poorly drained area, or as a quick fix across a muddy section of an existing road, consider using chipped wood. A layer of chipped wood will absorb lots of moisture and provide a fairly stable driving surface. Of course, this assumes that your landfill is chipping wood/greenwaste. For many landfills, chipped wood is much cheaper than gravel, especially when uses for the chipped wood/greenwaste are limited.
Manufactured Products. For a long-term road in a marginal location (e.g., over waste), many landfills use manmade materials for roadbed stabilization. These can include various types of geotextiles (grids, fabrics, and such) and mats made of wood, steel, or other material.
One business, the LOMA Company, manufactures a high-density polyethylene mat called Dura-Base. These interlocking mats can provide a stable, all-weather driving surface. And they can be used, reused, or stored onsite.
Every landfill is unique. And while I suppose that if you’re running a landfill in Rome, you’d want to build roads as the Romans did, if you’re anywhere else you’ll need to decide for yourself what type of road is best.