The use of local materials for rural cycle tracks
Where ever possible it is best to use materials which are obtained on site or near to the route of the track. They have the advantage of being ‘natural’ to the site, and of a colour and texture which should blend well with the local landscape.
They are also free. However, these advantages need to be balanced against the time taken to gather or dig the material, and any weakness in the available materials. The stability and usability of these on site materials can be improved dramatically by mixing in a small amount of SMR soil stabilisation binder. Providing that the methodology of blending/mixing, laying and final compaction stages are carried out correctly.
Streams
Material from streams is often suitable as an aggregate base mix providing the stones are still angular and have not yet been rounded by the action of water. It would be best to use material from the edge of the water or from shallow pools. Any fine sediment in the streams will also be useful for mixing in as fines with the angular stone. Old buckets with holes are useful for this job as they will quickly separate out any water. Always beware of taking so much from one place that the course of the stream is altered.
Outwash deposits
Outwash deposits are a good source of path making material, and are usually conveniently graded during deposition.
Scree
Scree material is usually very angular, and is excellent granular stock for the path base mix.
Borrow pits
A traditional method of gaining material for path/track construction was to dig ‘borrow pits’. These were small pits or quarries dug at intervals along the route of a track to provide suitable material for sub-base, base and surfacing. Borrow pits may still have a use in some locations where the natural soils are weak or particularly organic and lacking granular quality. They are the traditional method of supplying material for stalkers’ paths in the uplands of Scotland. These trackside mini quarries have now themselves become valuable habitats.
The location of the pit is chosen by careful inspection of the ground near to the path, and then by sinking a crowbar into the ground to find where there are stony deposits near the surface. The material is then dug out using a crowbar, pick and shovel, and moved in buckets or by power carrier to the path. Depending on the depth of the stony deposits, the pit may be several metres square and up to 1m deep. For safety reasons, pits must not be dug deeper than 1m, and no ‘tunnelling’ should be done. In suitable material, the sides of the pit should be stable, as any liability to slump would indicate that the material was unsuitable for surfacing. When ‘worked out’, the pit is backfilled with the weak or organic material from the path, and covered with clumps of vegetation. Within a few days, the site of the pit should be hard to spot. Other borrow pits are dug as necessary for other sections of path.
This method of working is cost-effective on remote rural tracks, and for the sensitive and detailed type of path construction which these sites require. The natural variety in locally-won material means that the path has a very natural look and feel, as opposed to a path constructed of imported quarried stone or recycled type 1 aggregate.
Some cycle way areas may have their own deposits of gravel or other suitable material which can be dug and used for path construction. In some areas old quarry workings or spoil from various industrial developments may provide material.
Old railways or pre-existing paths
Where the track is to following old railway routes or an existing path or track it is almost certain that the available site materials will be sufficient in themselves with just added SMR to stabilise and bind producing a strong long lasting fit for purpose cycleway, although in some cases especially where the occasional vehicle access is required a thin rolled wearing course with a surfacing layer 50mm thick of ‘fines’, ‘dust’, ‘blindings’ or other material sized about 6mm down to dust would be beneficial.
Another material for use as a wearing course where it is available is the waste material from the quarry bottom this is the cheapest type of quarried stone. It is obviously very variable, but should contain a lot of fine sediment and will bind easily to the SMR treated surface if passed over with a vibrating roller or plate.
A total depth of 200mm for base and any surfacing should be sufficient for cycle tracks, and this would normally be laid directly onto the soil or subgrade.
Tracks need sensitive treatment in their construction and repair if they are to blend into a rural or wild landscape. They should be laid with variation and irregularity avoiding hard edges where possible, drains and other features.
The hydrogel polymers in the SMR will quickly bind the recycled path material to the soils edging the path and it should be possible to avoid path edging or revetments. Any edging that has to be used to contain the path material will show up as a hard line, noticeable even after vegetation partly covers it. These edgings, (e.g. railway sleepers), are only necessary where the path has to be raised, for example above a high water table. In all other cases, it should be possible either to simply roll the surfacing into place right up to and including the untreated edge soils to form the path.
Uphill and downhill use
There is a physical and a psychological difference between cycling uphill and cycling downhill, both of which tend to make downhill cycling the more damaging to cycle tracks.
Physically, the added braking when cycling downhill will more cause more surface damage than does the slow and careful tiring pedal uphill. Travelling downhill the bike will also slide, dislodging any loose stones or earth. Cyclists tend to move more slowly when climbing uphill, because it is tiring, and the line of sight is limited to the area immediately in front.
Downhill speed and wear is much more difficult to control. The view down is often clearer, and the line of path can more easily be seen encouraging dangerous speed. Cyclists going downhill tend to be in a hurry, either racing each other, or just speeding for the thrill of it,
With these factors in mind a harder path finish and a grippier surface will be required on all slopes, as a downhill in one direction will be uphill on the return. Another factor to consider will be the number of cyclists who need or choose to walk the slopes and extra width of track will be needed on slopes to keep all users safe. Whilst a mix ratio of 50:1 should be adequate for normal path construction, increasing the SMR ratio to 40:1 for track slopes will be necessary.
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