In these circumstances excavation to create the trail is necessary, and gradients need to be controlled. If possible, gradients should be found that preclude the need for steps. After initial clearance and pruning of vegetation, the route is set out with canes and the gradient checked using a simple
levelling instrument such as an Abney. Then the path can be cut across the slope. If the width is not too great or the side slope too steep, the excavated material should present few problems for disposal. On steep side slopes it may be preferable to build up the path using rockwork so as to avoid too much cut and fill or problems of disposal of surplus fill.
 |
The slope above the path should generally be cut to the natural angle of repose and shaped to prevent erosion. However, in soft soils it may need some work to prevent it from eroding. Stone revetment can be used for this, as can vertical timber shoring or woven willow branches fastened to the surface until vegetation can become established, either by natural colonization or by seeding, planting or turfing.
discharged through culverts at intervals. This
avoids the risk of washout and erosion.
(d) The top of the cut slope should be rounded off to avoid the erosion problems shown here, and to allow quick colonization of the slope by vegetation. Fill left at too steep an angle also tends to erode, taking parts of the path with it. (e) This diagram
recommends the maximum crossfalls and slope grades on which to construct a path using cut and fill. (f In the steepest slope section the path may have to be built up using stone – retaining structures backfilled with rock and subsoil. An allowance for a safety edge is made. (g) When constructing a trail through a forest the clearance should allow a reasonable space all around the walker to avoid the risk of collision with trees or branches. (h) This diagram shows that the path surfacing should be laid to a crowned shape on a general formation, which drains to a fall. This is especially important if wheelchairs or baby buggies use the path, otherwise they tend to keep pulling down slopes into the ditch.
It may be necessary to retain the sides of the path surfacing to prevent it from slipping into the side drains. Edges can be made from preserved sawn timber rails held by wooden pegs, round logs or local stone. The rails can be curved to some degree, but logs can be used only in straight sections, and this can look awkward. Stone is preferred if it is found on site, but it needs to be flat and capable of staying in place, Larger stones can also be used to vary the width of the path surface and tie it into other aspects of the local landform. Surfacing is normally crushed stone, compacted with fine material or ‘scalpings’ on the surface. Occasionally other materials can be used. Sealed (paved) surfaces such as asphalt or tarmac may have a place in more urban settings or where other materials cannot be relied upon to stay firm and smooth for wheelchairs and buggies, but they should always be top-dressed in local stone.
|
Path surfaces may need edges to retain them: (a) An unretained edge begins to erode, washing material away. (b) Wooden rails held in place by timber pegs are functional, and have low impact, but cannot be curved very easily. (c) Stone is good, and can be laid to any shape. (d) Logs may be available on site, but the path becomes a series of straight sections, which look stiff and artificial. |
Wood chips or bark can sometimes be used to give a softer, quieter surface. This might be useful in a wildlife-viewing area, where the noise from feet crunching gravel might disturb the animals. Soft surfacing can also be a welcome relief to feet fatigued by hard surfaces.
Stone paving is traditional in some areas. Dressed stone or crazy paving should be avoided in the outdoors for its urban or suburban appearance, but well-chosen stone can be laid to produce a hard-wearing surface, although probably not a smooth one. In rocky, mountainous terrain such paths may be easier to construct to permit better access and a more obvious route across boulder and rock-strewn areas where there are risks of damaging ankles. The rock needs only to be laid or rearranged in situ. Rock sections may also be useful where the gradient is steep and the surface vulnerable to washout. Stone laid to give an irregular surface gives some grip and erosion protection when combined with a decent cross-fall and good drainage alongside.
