Construction

Construction of vehicle width surfaced tracks normally requires the hire of a suitable machine and operator. The simplest tracks, for example made by clearing and grading a track on well drained ground, can cost as little as 20p per metre. Where suitable material can be obtained from a borrow pit, and working conditions are fairly straightforward for a suitable machine, costs may be about £2-3 per metre. Costs rise sharply where stone has to be purchased or where geotextile is needed, up to about £9 per metre (Forestry Commission 1999). Grants may be available towards the cost of track construction where this improves recreation access, or makes possible the management of neglected woodland.

When planning new woodlands, the site survey should include possible sources of surfacing material from within the woodland area. Any gravel deposits for example could provide useful surfacing material, at the same time as creating a wildlife pond. Soil reorganisation is a cheap method of track construction, which is very much easier to do before the woodland is planted.

Where tracks for management purposes cannot be provided, or will be too damaging to the woodland environment, other options include:

• Converting the woodland crop on site to a product which is easier to extract. This could include conversion to charcoal, drying the wood for a season or more until it is lighter and easier to extract, or converting it with a mobile bandsaw.
• Extraction by horse, or by pedestrian controlled harvesting machine may be possible even where there are no tracks.

Drainage

Many lowland woods are on poorly drained land. The shady sheltered conditions in woodlands reduces evaporation from the soil surface, and fallen branches and leaves impede surface drainage. Unlike pastures and cultivated land, which may have underdrainage systems installed, woodlands generally have no artificial drainage systems.

Paths in lowland woods or those on heavy soils are therefore likely to be on poorly drained ground, and trampling in wet weather can rapidly reduce the surface to mud. Paths which are intended to attract regular use are likely to need some sort of drainage and surfacing work.

Waterlogged ground without any discernible flow is best dealt with by raising the path level. Any water that flows across a path should be drained away by grading the profile of the path, by installing cross-drains or culverts, or crossed by bridges.

Paths in upland woods or on sloping ground are likely to suffer from surface erosion, as rainfall runs across and down paths, washing away thin soils and exposing subsoil and rock. Path grading, cross-drains and cut-offs to take the water off the path without damaging it are the basic requirements. For full details see Footpaths.

Grading

Grading involves altering the profile of a path or track to encourage water to drain off the surface. Grading either requires making a camber, which sheds water both ways, or a cross-fall, to shed water one way. Cambers are generally used on flatter ground, and cross-falls on slopes. For small projects this work can be done by hand, but most work will require an excavator and skilled operator. The camber or cross-fall can be formed by the base material, or by surfacing material which is imported to the site from borrow pits or commercial quarries. A suitable camber and cross-fall for walkers, cyclists and wheelchair users is shown in the diagram.

A tracked 3 tonne mini-excavator with a bucket and blade can be used to clean, regrade and widen an existing path. On slopes, the bucket can be used to ‘cut and fill’ as necessary, excavating on the uphill side of the path and building up on the lower side. The blade is used to create a free-draining profile. The cross-fall of the track should be no more than 5%. The diagram gives a guide to forming a 2m width track on a 25% slope. To reduce erosion down the track, the slope of the track should not exceed 7%.

A skilled operator can complete 50-100m per hour, depending on conditions. The resulting track, of about 2m width, should be suitable for all-weather walking, and for extracting timber in dry conditions only, using pedestrian controlled harvesting equipment, horses or manual labour. To further improve the track, drainage and surfacing works could be completed. For further details on machine-built tracks, see Forestry Commission Technical Note 27/98 Access Track Construction in Small Woodlands.

Cross-drains

These are used mainly on paths to take surface flow which crosses paths after rainfall, but which does not flow all year. Cross-drains are best made of large stones, to be resistant to erosion and trampling. Cross-drains of logs or planks can be constructed, but are not usually robust enough to last long. Cross-drains smaller than about 100mm across tend to block up quickly with stones and debris.

Cut-offs

These can be made of round timber, sawn timber or stone, angled to direct water off the path and prevent it flowing down the path. The timber or stone should be set into the ground as shown, with a small ditch on the upper side to catch the water. Install at frequent intervals on sloping paths which have evidence of erosion. Cut-offs need regular cleaning to remain effective.

Culverts

These should be installed at points where the track needs to cross small streams or ditches. Depending on the size of the flow, flexible perforated plastic, solid plastic or concrete pipes can be used. It is important that the pipe is installed carefully at the correct level and with supporting headwalls as necessary, so that the drain functions properly over a long period, and does not become exposed from erosion by water or the action of trampling.

Where the construction of a culvert is likely to alter the flow of a watercourse, approval must first be obtained from the Environment Agency. Where the track is used by vehicles, the culvert must be built to a suitable standard as shown below.

Pipes should be a minimum of 225mm (9”) diameter, set on a firm bed of aggregate (10 or 14mm nominal size), and set so that the pipe is 25mm (1”) below the bed level of the stream or ditch.

Smaller culverts suitable for pedestrian tracks should be built in a similar way, with headwalls and surfacing to protect the pipe, even if this means raising the level of the path over the culvert. Pipes which are simply set in the stream bed and covered with surfacing, without the protection of a headwall will soon become blocked as material becomes eroded from around the pipe end.

Table 13a: Materials for culverts

Side drains or ditches

This form of drainage can be used to take surface flow which runs alongside paths, or to provide storage for ground water where the water table is high. The spoil from the drains will normally need to be spread away from the ditch. Stony subsoil may be suitable for raising the level of the path.

Where stony subsoils are covered with a thin layer of topsoil or peat, it’s possible to strip away the topsoil or peat across the width of the path and side ditch, excavate the subsoil from below the line of the ditch and use it to form the path. Topsoil is then used to fill the base of the ditch. The success of this ‘soil reorganisation’ technique depends on having suitable stony subsoil without too much clay content, which forms a durable walking surface. This can be done by hand on a small scale, but any work which involves moving large volumes of surfacing, soil or other bulk material is best done by a tracked excavator operated by a suitably qualified and experienced person. See Footpaths – Side Drains for further details.

Surfacing

The rule of thumb for stone aggregate and other stone surfacing material is two tonnes per cubic metre. The table gives estimated figures in tonnes per cubic metre for a range of materials. Suppliers of commercial stone should be able to give an accurate figure. These figures can be used to assess the amount required for a particular path, the transport requirements or the amount which will have to be excavated from a borrow pit. Materials from borrow pits will be variable. For example, studies by the Forestry Commission of borrow pits in shale on four different sites yielded 1.5, 2, 3 and 3 tonnes per cubic metre respectively (Forestry Commission Technical Note 27/98).

Table 13b: Surfacing materials

The diagram below gives a simplified view of a cubic metre of surfacing and how it could be used to make a narrow footpath, or a wider track.

As a rough guideline, narrow footpaths 1m wide need only have about 100mm depth of surfacing to give adequate load bearing ability. Wider tracks, normally for vehicle use, need to have a greater depth of surfacing to take the heavier loads. Allowance must also be made for wastage. Some tracks will not require uniform depth of surfacing along their length, depending on the ground conditions and the desired finish.

Borrow pits

A borrow pit refers to a pit or small quarry which is dug to provide stone for surfacing or other construction work nearby. Many old tracks which climb slopes or hillsides have borrow pits at intervals alongside. Borrow pits provide the nearest, and normally the cheapest source of stone, and being local, should with time blend fairly naturally with the surroundings. Shale, chalk and other types of fairly soft, easily quarried stone may be suitable.

An experienced operator is required to identify and safely excavate suitable stone, using a tracked excavator or similar. The work is destructive, and can be extremely unsightly in the wrong location. However, when working is finished, most borrow pits gradually revegetate so that they become partly disguised, and often form valuable sheltered wildlife habitats.

The excavated material can then be transported by dump truck or tractor and tipping trailer. The same or another excavator then spreads, grades and consolidates the material. This work should only be done in dry conditions.

Bought stone

The choice is normally made from the nearest suitable stone, to reduce transport costs. Visit local suppliers to check on what is available and to gain their advice on the most suitable material for the location and job in question. Various different types are available:

• Crushed limestone, dolerite or other type of rock, to the specification ‘Type 1 sub-base’ is the highest grade material, as used for road building. This comprises material from 75mm diameter down to dust, with the dust making up about 25% of the total. This can be laid in a single layer, or topped with a layer of finer surfacing material, of 6mm down to dust, to give a smoother finish. ‘Type 2 sub-base’ consists of natural sands, gravel, crushed aggregate and subsoil. Type 2 is cheaper and has a lower load-bearing capability than Type 1, and should only be laid in dry weather.
• Quarry bottoms. This is the waste material from the quarry bottom, and is very variable, but should contain plenty of dust so will bind well. Inspect before purchase.
• Stone as dug. This usually contains clay or subsoil, and is very variable.
• Hoggin and self-setting gravels. These are gravels with a high clay content which bind when rolled to form a durable surface.

Recycled materials

Recycled materials can look very unattractive in a natural setting such as a woodland, and are not generally recommended. However, where they are available cheaply or for free, the benefits to access may outweigh the disadvantages. Recycled material can be fairly safely used as a base course in locations where it is unlikely to get exposed, typically on flat or gently sloping ground. Preferably top with a surfacing material of crushed stone or woodchips. Where sunlight levels are sufficient for grass growth, top with a free draining soil and either seed or allow to grass over naturally. Avoid using recycled materials as surfacing on sloping tracks, where there is a high chance of erosion exposing the material.

Recycled materials include:

• crushed concrete from demolished buildings.
• hardcore, including bricks, concrete and rubble from demolished buildings
• tarmac ‘planings’, which is the worn tarmac scraped off roads prior to re-surfacings.
• Industrial waste products such as fuel ash are not recommended, because of potential pollution problems.

Recycled surfacing materials may be available from suppliers of aggregates, or from demolition companies. Small amounts may be obtainable locally from various sources. As far as possible, check at source that the material does not contain steel reinforcing rods, other waste metal, glass, asbestos or other noxious substances.

Geotextiles

The term ‘geotextiles’ includes a large range of materials used in road building, landscaping and other construction work. For construction of tracks and paths, a geotextile can be used as a bottom layer in fine soils, silts and clays, to retain sub-base and surfacing material and prevent it becoming mixed with the ground beneath. Makes include Terram, Tensar, Lotrak and Wyretex, available in various grades and widths. Further details are given in Footpaths – Geotextiles, or are available from suppliers.

In woodlands, geotextiles can be used in the construction of tracks and paths across fairly level, badly drained mineral soil or areas of damp peat. Geotextiles are not generally recommended for sloping ground, as it is likely that the geotextile will become exposed as the surfacing erodes away. The finished path surface should be at least 75mm (3”) above the existing ground level, to raise it above damp ground. Excavate a level ‘formation’ for the path, removing any rocks or roots which might puncture the geotextile. Pile up the excavated material neatly so it can be re-used to make the shoulder of the path, and bury the edges of the geotextile.

Brash and woodchips

Woody material from within the wood can be used as surfacing material. At its simplest, brash is often deliberately left on the ground to provide support for machinery being used for extracting timber. For more permanent paths, bundles of brush or roundwood poles can be used to provide a sub-base for woodland paths and tracks through damp ground. Lay the material across the path, and then secure it as shown, with poles and stobs. Top with a layer of woodchips, at least 100mm thick. Periodic maintenance will be needed to top up the woodchips, and to check that the edging poles are securely held and that the wires are not exposed.

Woodchips can be produced from within the wood by chipping thinnings, brash, scrub and other unwanted woody material. A range of woodchippers are available from suppliers of forestry machinery. Woodchippers should only be used by trained and competent persons. Voluntary groups, or owners or managers of small woodlands need to assess whether their requirements for woodchipping justify the purchase or hire of a machine, together with the relevant training.

Some heathland nature reserves and other areas have an excess of woodchips, due to a continuing need to remove saplings and other woody growth to maintain open habitats. Parks departments and other authorities involved with tree management may also produce woodchips in quantity.

The weight of woodchips per cubic metre is very variable, depending on chip size, moisture content, loading procedure and settling. One tonne of newly chipped woodchips at 70% moisture can occupy up to 6 cubic metres. With drying and settling, one tonne at 20% moisture may occupy as little as 2 cubic metres. Preferably stack for a few months before use.

Table 13c: Length of path per cubic metre of woodchips

For bridleways, a deeper layer up to 250mm thick may be necessary, depending on the amount of use.

Woodchips and bark are available commercially for path and bridleway surfaces, riding arenas, play areas and for mulching. They are sold loose in bulk by weight, or by the bale. The cost will normally rule out their use for woodland paths or rural rights of way, except in special circumstances.

Grass

Where light levels are sufficient, and trampling pressure is fairly low, grass makes an attractive path surface, which should be durable on free draining soil. Grass on wet ground rapidly gets cut up by trampling. Grass will only thrive in woodland where the canopy is high and fairly sparse, for example in recently thinned or storm-damaged woods. Where there is sufficient light for bramble to thrive, there should be sufficient light for grass. On bare ground, the surface can be prepared by harrowing, and then seeded with a mixture of native shade-tolerant trample-resistant grasses. A mixture including perennial rye-grass, creeping red fescue and creeping bent may be appropriate, but each site should be individually assessed and advice sought from seed suppliers. Grasses and woodland edge flowering plants can be sown along the edges of the new ride. Where there is already some grass growth, regular cutting and light trampling will encourage a grassy sward to develop.

Once grass is established, regular mowing will encourage the development of a close turf. The path edges can be left to grow longer as desired. The mown width should be at least 1.8m (6’), to spread the trampling pressure and allow mowing by mini-tractor or other vehicle. Grazing by rabbits or deer, together with the trampling of walkers, may be sufficient to maintain a short grass sward. However, this needs regular checking, because once the grass becomes too tall for comfortable walking, trampling will be limited to the centre of the path, which will then be reduced to bare earth and mud.

In some locations, paths or tracks of crushed stone or gravel will eventually vegetate over naturally with a mixture of grasses and herbs, which helps bind the surface together.