Standards and Procedure:
Appalachian Rock Armoring
Many of our trails in the PRD are multi-use trails open to bikers, hikers, and in some cases equestrian users as well. For this reason, oftentimes building staircases is not the ideal way to mitigate steep grades. Using rock to armor or “pave” the trail is an alternative that hardens the tread while being more friendly to mountain bikes on multi-use trails. We’ve even got a regionally developed technique called “Appalachian Rock Armoring”, which is fairly simple to learn and implement.
In the Pisgah Ranger District, the ability to build with rock is limited. While some areas do have plenty of rock available, we are constrained by NEPA rules, which limit the harvesting of rock to that which is already within the trail corridor. Digging up rock outside the corridor requires additional NEPA surveys and approvals, a process which can take years and so must be reserved for major projects.
The good thing about rock armoring is that the size and shape of rocks can be much more flexible than that which is required for rock steps. Relatively smaller rocks can be used in trail armoring. Furthermore, a hallmark of the Appalachian Armoring technique is the use of non-native materials like broken-up concrete as a way to supplement native material.
This document will outline the basics of the Appalachian Rock Armoring technique.
Below is a recommended list of essential tools for rock armoring. Note that integrating black locust logs into the design is a recommended component for the Appalachian Armoring technique.
- Rock bars
- Pick mattocks and other digging tools as desired
- Single-jack sledge hammers
- Buckets or canvas rock bags for transporting gravel/crush
- Chainsaw PPE
- Draw knives for peeling logs
- 8, 10, or 12” landscape spikes, ⅜” diameter
- Powerful drill capable of drilling in locust wood
- ⅜” auger drill bit
- Cargo/rock net or slings for carrying larger rocks
- Armor sections where the grade exceeds 12-15%, or where erosion problems are evident.
- Constructing a locust box is recommended as it helps to contain armoring rocks and sediments. Larger, longer stones could be used in place of logs if they happened to be available.
- Be sure to peel bark from locust logs to maximize rot-resistance.
- Use miter cuts to create tight joints in the locust box.
- Use a drill and spikes to attach miter joints together. This creates a strong, unified structure.
- Rocks can be a variety of shapes and sizes.
- Entrench the locust box in the ground so that it is about flush with the tread surface. Don’t create an obstacle by having logs sticking up too high in the trail - users will avoid the structure and create trail braiding.
- Install individual small rocks vertically so that the height of the rock is sunk into the ground, like the “tombstone”/”toothed” method of setting steps.
- Larger, flatter rocks can be set horizontally as a way to cover a lot of area within the box.
- Individual rocks should be tightly pieced together like a puzzle, contacting one another.
- Dig rocks into the ground so that they form a uniform height, “cobblestone” surface.
- The height of the “cobblestone” array of rocks should be equal to the height of the log box, which should be about equal with the tread surface.
- For longer stretches of armoring on steep slopes, install a perpendicular log every 10’ or so within the box for additional retention of rock and sediments.
- The armoring needs to be able to withstand heavy bike traffic. Consider the forces at play if a biker were to hit the brakes and screech to a halt on a paved section.
- Fill all crevices between paving stones with crushed stone or gravel and tamp/pound into place with hammers to lock everything together tightly.
- Spread mineral soil over finished armoring so that it fills in on top of crush/gravel and in between armor rocks.
- Incorporate drainage above armored sections.
These procedures are intended to provide a helpful reference guide to building a stone staircase. If you have never built one of these structures before, it is best to learn hands-on from an experienced trail builder.
A. Survey the Site
1. Assess grade and determine where to begin and end armoring.
B. Build the Box Frame
1. Layout Logs, Take Advantage of Log Contours in Layout
2. Cut Logs to Length
3. Miter Cuts
4. Drill/Spike Joints
5. Dig Joined Logs into Place
6. Check for Level
7. Pack Around with Crush to Stabilize
C. Quarry Rock
1. Use rock within the trail corridor. Dig off-trail in NEPA approved sites only
2. Dig/transport to site by hand, bucket, rock bars, nets, or slings
D. Install Armoring
1. Start from one end and work your way along the box
2. Piece rocks closely together
3. Keep the surface a uniform and level height
4. Fill small crevices with crush/gravel and tamp to lock into place
E. Finish Work
1. Top exposed crush with mineral soil
2. Incorporate drainage above
3. Revegetate work area, including visible craters from quarrying