Tread is the actual travel surface of the trail. This is where the rubber (or hoof) meets the trail. Tread is constructed and maintained to support the designed use for your trail.
Trail construction requires creating a solid, sustainable tread. To do so, make sure that you locate the trail on the contour. Forces such as soil type, annual precipitation, and other factors may influence how long the tread remains stable before maintenance is needed.
Soil type and texture have a major influence on soil drainage and durability. Texture refers to the size of individual soil particles. Clay and silt are the soil components with the smallest particles. Small particles tend to be muddy when wet and dusty when dry. Clay and silt don't provide good drainage. Sand is made of large particles that don't bind together at all and are very unstable.
The best soil type is a mixture of clay, silt, and sand. If your soil is lacking any one of these, you can attempt to add what's missing. Knowing the soil types that you will encounter when building trails will help you develop a solid, stable tread. A lot of information on soils can be found at the USDA Natural Resources Conservation Service (http://soils.usda.gov) office or at your county extension service office.
Get To Know Your Soil With the Ribbon Test
Roll a handful of moist soil into a tube shape with both hands. Squeeze it between your thumb and forefinger to form the longest and thinnest ribbon possible.
|Sand||Grainy||Can't form a ribbon|
|Loam||Soft with some graininess||Thick and very short|
|Silt||Floury||Makes flakes rather than a ribbon|
|Sandy Clay||Substantial graininess||Thin, fairly long—50 to 76 mm (2 to 3 inches)—holds its own weight|
|Clay||Smooth||Very thin and very long—76 mm (3 inches)|
The tread surface should match the intended use. Easier trails should have a smooth tread surface. Backcountry trails can be rougher and more challenging. Leaving some obstacles in the trail helps slow down users and reduce conflict.
Tread is also the travel surface on structures such as turnpikes and puncheon. Tread, whenever elevated, should be slightly crowned (higher in the center than on either side) to drain better.
An outsloped tread is one that is lower on the outside or downhill side of the trail than it is on the inside or bankside. Outsloping lets water sheet across the trail naturally. The tread should be outsloped at least 5 percent.
Loss of outslope is the first maintenance problem that develops on all trails. If you can do nothing else when budgets are tight, reestablish the outslope. Doing so pays big dividends.
Removing roots and stumps is hard work. Explosives and stump grinders are good alternatives for removing stumps, but chances are you'll have to do the work by hand. Often, a sharpened pick mattock or Pulaski is used to chop away at the roots. If you are relying on some type of winch system to help you pull out the stump, be sure to leave the stumps high enough to give you something to latch onto for leverage.
Rule of Thumb for Roots
- If roots are perpendicular
to the tread, fairly flush,
and not a tripping hazard,
- Remove roots that are
parallel with the tread.
They help funnel water
down the trail and create
- Route your trail above large trees. Building below trees undermines their root systems—eventually killing the trees.
Not all roots and stumps are problems. You should not have to remove many large stumps from an existing trail. Before you remove a stump, consider whether other crews might have left it to keep the trail from creeping downhill.
Rock work for trails ranges from building rock walls to blasting solid rock. These tasks involve specialty work. When rock needs to be removed, a good blaster can save a crew an astounding amount of work. When rock needs to be used, someone building a rock retaining wall may be a true artisan, creating a structure that lasts for centuries. Rock work requires good planning and finely honed skills.
Brains First, Muscle Last
Remember that the two most common injuries in rock work are pinched (or smashed) fingers and tweaked (or blown out) backs. Both sets of injuries are a result of using muscles first and brains last. High-quality rock work is almost always a methodical, even tedious, task. Safe work is ALWAYS faster than taking time out for a trip to the infirmary.
The secret to moving large rocks is to think first. Plan where the rock should go and anticipate how it might roll. Be patient—when rocks are moved in a hurry they almost always end up in the wrong place. Communicate with all crewmembers about how the task is progressing and what move should occur next.
Tools of the trade include:
- Lots of high-quality rockbars. Don't settle for the cheap digging
bars. You need something with high tensile strength.
- Pick mattock.
- Sledge hammer.
- Eye protection, gloves, and hardhat. Don't even think of
swinging a tool at a rock without wearing the required personal
- Gravel box, rock bag, rucksack, rock litter—all useful for carrying rocks of various sizes.
- Winch and cable systems. Some rocks can be dragged or
lifted into place.
- All sorts of motorized equipment, including rock drills and rock breakers.
Blasting can help remove rocks or greatly reduce their size. Careful blasting techniques can produce gravel-sized material. Motorized equipment can be used to split boulders or to grind down obstacles in the tread. Chemical expansion agents can be poured into holes drilled into large rocks, breaking them without explosives. Drills and wedges can be used to quarry stone for retaining walls or guide structures. Devices like the Boulder Buster, Magnum Buster, and BMS Micro-Blaster crack rocks without explosives and can be used by persons who are not certified blasters.
Your specific trail maintenance specifications may call for removing embedded rocks. Use good judgment here. Often, large rocks are best removed by blasting. Other solutions include ramping the trail over them, or rerouting the trail around them.
Rocks should be removed to a depth of at least 100 millimeters (4 inches) below the tread surface, or in accordance with your specific trail standards. Simply knocking off the top of a rock flush with the existing tread may leave an obstacle after soil has eroded around the rock.
Rockbars work great for moving medium and large rocks. Use the bars to pry rocks out of the ground and guide them off the trail. When crewmembers have two or three bars under various sides of a large rock, they can apply leverage to the stone and virtually float it to a new location with a rowing motion. Use a small rock or log as a fulcrum for better leverage.
It may seem like fun at the time, but avoid the temptation to kick a large stone loose. When rocks careen down the mountainside they may knock down small trees, gouge bark, wipe out trail structures, or start rockslides.
Even worse, an out-of-control rock might cross a trail or road below you, hitting someone. If there is any possibility that people might be below while rocks are being moved, close the trail or road, or post lookouts in safe locations to warn travelers.
You might construct a barrier of logs anchored by trees before trying to move the rock, preventing it from gaining momentum. Once a rock is moving, do not try to stop it.
When you need to lift rocks, be sure to keep your back straight and lift with the strong muscles of your legs. Sharing the burden with another person can be a good idea.
To load a large rock into a wheelbarrow, lean the wheelbarrow back on its handles, roll the rock in gently over the handles (or rocks placed there) and tip the wheelbarrow forward onto its wheels. Keep your fingers clear any time you deal with rocks.
Use Brains Not Brawn for Heavy Lifting
When dealing with rocks, work smarter, not harder. Skidding rocks is easiest. Rolling them is sometimes necessary. Lifting rocks is the last resort.
Often small rocks are needed for fill material behind crib walls, in turnpikes and cribbed staircases, and in voids in sections of trail built in talus (rock debris). Buckets and wheelbarrows are handy here. So are canvas carrying bags. If you are part of a large crew, handing rocks person-to-person often works well. Remember, it's usually not a good idea to twist your upper body while you are holding a heavy rock.
A solid, outsloped surface is the objective of trail maintenance. Remove and scatter berm material that collects at the outside edge of the trail. Reshape the tread and restore the outslope. Maintain the tread at the designed width. Remove all the debris that has fallen on the tread—the sticks and stones and candy wrappers. Maintenance includes removing obstacles such as protruding roots and rocks on easier trails. It also means repairing any sections that have been damaged by landslides, uprooted trees, washouts, or boggy conditions. Compact all tread and sections of backslope that were reworked.
On hillside trails, slough (pronounced sluff) is soil, rock, and debris that has moved downhill to the inside of the tread, narrowing the tread. Slough needs to be removed (figure 30). Doing so is hard work. Slough that doesn't get removed is the main reason trails "creep" downhill.
Loosen compacted slough with a mattock or Pulaski, then remove the soil with a shovel or McLeod. Reshape the tread to restore its outslope. Avoid disturbing the entire backslope unless it is absolutely necessary to do so. Chop off the toe of the slough and blend the slope back into the hillside. Remember to compact the tread thoroughly.
Berms are made of soil that has built up on the outside of the tread, forming a barrier that prevents water from sheeting off. Berms form when water erodes trail tread that wasn't compacted during construction, depositing it on the edge of the trail. Water runs down the tread, gathering volume and soil as it goes. Berm formation is the single largest contributor to erosion of the tread. Removing berms is always the best practice.
Berms may form a false edge, especially when berms are associated with tread creep. False edge is unconsolidated material, often including significant amounts of organic material, that can't bear weight. This is probably the least stable trail feature on most trails and a major contributor to step-throughs and wrecks.
If berms persist, an insloped turn may be an option. Essentially this is a turn with a built-up berm. Insloped turns will improve trail flow and add an element of fun on off-highway vehicle and mountain bike trails. Special attention needs to be placed on creating proper drainage. This requires a high level of trail-building experience and a good understanding of waterflow.
Does your contour trail display:
- Exposed bedrock or roots along the uphill side of the tread?
- Tread alignment that climbs over every anchor point and drops before climbing to the next anchor point?
- Pack bumpers (downhill trees scarred by packstock panniers)?
All three are indications that the tread surface has been eroded and compacted by travel along the outside edge. Insidious tread creep is at work. Tread creep should be stopped or the trail will eventually become very difficult or dangerous to travel (figure 31).
What causes tread creep? The answer is simple. Most livestock, wheeled traffic, and some hikers have a natural tendency to travel the outside edge of sidehill trails. Sloughing makes the edge of the trail the flattest place to walk. Backslopes that are too steep may slough material onto the tread, narrowing the trail. The trail becomes too narrow. The result is that traffic travels closer to the outside edge (figure 32). Your job is to bring the trail back uphill to its original location and keep it there.
To fix tread creep, cut the backslope properly, remove slough, and reestablish the 5-percent outslope. Take advantage of large stationary objects (guide structures) to prevent animals and people from walking along the edge. Trees, the ends of logs, rocks, and stumps that are left close to the downhill edge of the trail will keep traffic walking closer to the middle.
Tread material between guide structures might creep downhill, creating a situation where the trail climbs over every tread anchor and descends again, a daisy chain. At the bottom of these dips, water and sediment collect. This is the weakest portion of the tread and the most prone to catastrophic failure. The tread can be so soft that packstock may punch completely through the tread (called a step-through) or bicycles and motorcycles may collapse the edge, leading to bad wrecks.
Where soil is in short supply, you may have to install a short retaining wall and haul in tread material. The tread should be benched back into the slope in the original alignment. Guide structures should be installed on the outside edge of the tread to keep traffic toward the center.
A note on guide structures: If you use a rock, be sure it is big enough that at least two-thirds of it may be buried so people or bears won't roll it away (figure 33). Guide structures should be placed at random distances so they don't act like a wall to trap water on the tread. You might need to make the trail a little wider to accommodate the guide structure.