Rock Work: Standards and Procedures
Rock is the most long-lasting building material for trail work, and generally blends with the natural landscape better than wooden structures. When built well, rock structures can last almost indefinitely. Doing good rock work is typically a meticulous process that involves a lot of fine tuning and adjustments, so patience is important.
In the Pisgah Ranger District, the ability to build with rock is limited. Many areas do not have an abundance of readily accessible rock. Other areas do have plenty of rock available, but we are constrained by NEPA rules, which limit the harvesting of rock to that which is already within the trail corridor or on the surface of the soil. Digging rock out of the ground off-trail is not allowed unless a NEPA survey has been completed.
Due to the constraints of the district, building with locust logs is a more accessible option in most cases. Even so, the advantages of rock as a building material mean that it should be taken advantage of when the circumstances allow. In those cases, adhering to some general principles will result in stonework that can be both beautiful as well as extremely sustainable.
- The bigger the rock, the more stable the structure. As a general rule of thumb, if one person can lift a rock, it isn’t large enough to be used for a step or major construction piece. Strive to use the largest rocks that are safely manageable by your crew.
- Keep in mind that in some contexts, a particular rock may be so big that it’s more trouble than it’s worth. Keep in mind balancing rocks that are large enough (at least several hundred pounds) to be stable, but still able to be maneuvered effectively and safely.
- Choose rocks that are wide enough for the intended task. For instance, a step rock should be roughly as wide as the trail width.
- Use rock bars in conjunction with smaller fulcrum rocks to move massive rocks. Rock nets are another way to move large rocks over short to moderate distances if you have enough people in your crew. Be sure to use excellent communication, coordination, and situational awareness when moving large rocks!
- For especially large rocks, or cases where many rocks will need to be moved long distances, consider griphoist rigging and highline setups. These techniques require special training so make sure you have experienced maintainers on your crew.
- A strong foundation is essential for keeping structures stable over the long term.
- The foundation of the structure isn’t only physical - it also involves thinking and planning the best layout.
- Determine the size and shape of rock you need before you just go and select at random.
- The best way to keep the foundation strong is to bury the bottom layer of your structure and fill with rock/gravel, tamping to lock everything in place.
- Rock structures depend on their own weight for stability. If the foundation is weak, all of that weight will be poorly supported and will shift over time.
- Keep your structure as level as possible, especially the foundation. A level structure will be more sound over time than one that’s off-kilter. Bring a level with you for that extra degree of quality. Remember, every minute you invest in getting it “just right” will pay dividends in quality over decades.
- Spend the extra time to come up with a good initial plan and visualize how your material will come together.
- Make careful measurements and determine how you intend to place a rock to serve the intended purpose. Ideally, you only want to place a heavy rock once!
- Check for level frequently, and dig as much as necessary to adjust your foundation and make it level and stable.
- Use “batter” (tilting rock slightly back into the hillside) to build more stable structures.
- Frequently take a step back and look at your evolving structure from a distance.
- As with any structure, use crushed rock or imported ballast/gravel as your primary fill, not soil.
- Filling with rock promotes drainage and creates a hardened, stable structure that won't shift.
- Top off crush or ballast with a layer of mineral soil if available. Avoid using organic soil, as it will hold water and lead to a mucky surface.
- Crush rock to approximately golf-ball-size on site, or import gravel/ballast if logistically possible.
- Using sledgehammers, pound/tamp crushed rock into any crevices to lock everything in tightly in place. Continue compacting and adding more crush until crevices are filled and further compaction is impossible.
- Aim to eliminate all empty space within your structure, filling with crush as much as possible. Use narrower tools, like a pick or the dull end of a rock bar, to poke crush into tight spaces if needed.
- Whenever possible, rocks in a structure should be placed directly contacting each other. This ties the structure together and each rock mutually supports, and is supported by its neighbors.
- Multiple points of contact are better than one. The more stable your structure is before being filled in with crush, the more stable it will be in the long term after crush is eventually added.
- Use rock bars to carefully nudge large rocks together in order to get them contacting. Avoid the use of hands in tight places as this can lead to injuries.
- On rock retaining walls, multiple points of contact are particularly important for getting the wall to stand on its own. Rocks should not wobble.
- Shaping rock can be very useful in a tight spot. However, shaping can be time consuming, and making mistakes can cost you material.
- Consider whether shaping is worthwhile or if adequate material can be obtained without it.
- Clean up obvious marks on rock after shaping, particularly drill scars left after splitting rocks in half. Use chisels to remove evidence of the drilling.
- Consider the risk of striking metal tools together (as with chisels and hammers), as this can cause small pieces of metal shrapnel to fly at high speed. Use appropriate PPE.
- Rock can be shaped bluntly with regular sledgehammers, or more finely with specialized carbide-tipped hammers, chisels, and drills.
- Use feathers-and-wedges, also called pins-and-wedges, in conjunction with a rock drill to split large rocks in half.
- Before attempting to chisel or split a rock, take a look at the rock for existing fissures and fault lines. Often you can predict where a rock is likely to break. Sometimes this works to your advantage and other times it works against you. Decide whether shaping the rock is worth the risk of breaking it.
Use best practices when constructing rock structures by following sustainable design guidelines.
Click the links below for more detailed guidance on various rock structure designs: