Standards and Procedures:
Locust Log Turnpike
The Pisgah Ranger District seems anything but flat. However, spots like the Pink Beds Loop and the Eastatoe Trail are examples of trails that suffer not from the usual issue of being too steep, but on the contrary being too flat to drain properly. In many cases there is simply nowhere to effectively take water off the trail because the trail is the lowest point in the immediate terrain. In these situations, certain spots saturate with water, forming muddy, wet stretches that most users don’t want to pass through. This muddy area expands as more users travel around the outside edge, and before long the trail is a muddy, unsightly mess.
An effective and elegant solution to these muddy, flat areas is the turnpike. Relatively simple to construct from locust logs, these structures effectively create a dry and stable elevated tread suitable for hikers, bikers, and horses alike. Turnpikes also blend with the landscape better than puncheons (AKA bog bridges) and similar structures used in muddy areas. The main limitation with turnpikes is that they require a very large amount of gravel/ballast/crush for fill. If there is no vehicle or UTV access nearby to deliver ballast/gravel, building a turnpike might become a challenge. In the case that there is no accessible native rock, nor any possibility of importing gravel, consider building puncheon as a last resort.
Key Points:
- Gallery
- Locust Log Turnpike
A locust log turnpike constructed through a wet area in the Great Smoky Mountains National Park. Note the elegant miter joint corners, and the gap between turnpike sections that allows water to flow across.
Log Turnpike - Recommended Tools and Equipment
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Below is a list of the essential items for building a log turnpike.
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- Chainsaw with a sharp chain
- Extra sharpened chain recommended
- Draw knives for peeling bark
- Power drill capable of drilling into locust wood (portable battery powered or gas powered are both fine, just make sure they can handle locust wood and bring extra batteries/fuel)
- ⅜ " auger drill bit
- ⅜ " landscape spikes, in 8", 10", or 12" lengths depending on log size
- Single-jaack sledge hammer -
- Tape measure
- Buckets or canvas rock bags to transport gravel. If possible, a wheelbarrow is a huge help for moving the quantities of fill needed for a turnpike. For major turnpikes, consider machinery like UTVs if terrain and access allows.
- Assorted digging tools (picks, pulaskis, etc.)
- McLeod - useful for spreading, tamping and crowning fill
Log Turnpike: General Standards
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- It’s a good idea to take measurements for a turnpike just after a heavy rain, so you can see the full extent of the area that becomes saturated. Also, look at the minor changes of elevation in the trail to determine where the trail returns above puddle spots. You can often see where the turnpike needs to begin and end by looking carefully.
- Measure turnpike length to go slightly beyond the extent of the saturated area.
- Turnpikes will be most durable if they can be constructed of whole black locust logs. However, if material availability is a concern, logs can be split down the middle to extend material.
- Make sure the turnpike is high enough to surpass the depth of standing water at its deepest point.
- Make sure the turnpike is wide enough to accommodate the designed use on the trail, and in line with the trail's class. For instance, a high use frontcountry trail like the Eastatoe (open to hikers and bikers) or an equestrian trail will have a much wider turnpike than a backcountry, hike-only trail. See Trail Class page for more information on trail widths.
- In some cases, like on trails that see lots of bike use, keep both ends of the turnpike open so that the fill blends into the trail at a gradual slope. Boxing off the ends will retain fill, and is the better option on hiker only trails, or trails where grade results in fill washing out.
Entrench logs slightly so that there are no gaps underneath the logs.
Use miter joints to create the tightest possible joints between logs.
Ideally, use crushed rock or imported railroad ballast, or other coarse gravel option, to fill the majority of the turnpike. Top with a layer of fine gravel, rock dust, or mineral soil to provide a stable treadway.
Crown the surface of the turnpike so that water drains off the sides. Tamp the surface thoroughly to compact the tread and solidify this crowned shape.
Excavate troughs along either side where practical, possible, and necessary to accommodate water displacement by the turnpike.
Construction Procedures
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These procedures are intended to provide a helpful reference guide to building log turnpikes, ensuring that you cover the essentials. If you are new to building this structure, it is best to learn hands-on from an experienced trail builder.
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A. Building the Frame
1. Survey the site, come up with a plan
2. Determine start and end points based on elevation changes and evidence of puddling.3. Cut locust to length
4. Lay out logs and determine best positioning. Take advantage of natural log contours in layout.
5. Excavate tranches for logs just enough to eliminate gaps under logs
6. Miter Cuts to join logs into a box frame.
7. Drill and spike joints together. -
8. Fill, pack, and crown with crush.
B. Finish Work
1. Add/Tamp crush where needed.
2. Top landings with fine gravel, rock dust, or mineral soil.
3. Dig troughs on either side of the turnpike if there is not adequate space for water to displace and pool or drain. Be sure troughs do not undercut the turnpike.
4. Clean up and revegetate work area
Gallery
Locust log turnpike in progress on Bennett Gap, a project collaboration between TPC and Pisgah Area SORBA. Note the use of rock for the bulk of the fill, and the mineral soil added as a surface layer.
Completed locust log turnpike on Bennett Gap mitigates what was previously a flat, boggy depression in clay soil on a ridgeline.
Turnpiking constructed on the Eastatoe Trail using locust split rails, part of a major project to mitigate wet, muddy spots on this notoriously flat, difficult to drain trail.