As dug path (type 1 and dust)

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What is it?

A 1m wide recycled Type 1 granular sub base and whin dust surface provides a durable surface on top of a 'bench' formation, which goes around the woodland's side slope. The bench formation is built entirely of as dug naturally occurring materials taken straight from the side slope. Grade reversals have also been installed to shed surface water off the path.

as dug path with type1 and dust  surface oatridge college

How does it work?

Before the recycled Type 1 and whin dust path was constructed, the original path surface was built entirely of as dug, naturally occurring materials taken straight out of the ground from small scale borrow pits along the route. Unfortunately, those materials were of low quality, containing too much clay. They were not strong enough to take the weight of path users on their own, particularly after a period of wet weather when horse riders were using the route regularly.

The recycled Type 1 and whin dust path is made up of one granular sub base layer that now provides a strong durable surface for use all year around. The recycled Type 1 granular sub base, a higher quality of material with a good distribution of stone particle sizes down to 'fines', transfers the weight of path users across the bench formation, helping to make a stronger path. The larger stones have interlocked to give the sub base strength. The smaller stones and fines, contained in the recycled Type 1, have also infilled any gaps between the larger stone to help bind the sub base together into a strong solid mass on top of the bench formation.

What are the benefits?

Instead of leaving the as dug path to deteriorate, constructing the recycled Type 1 and whin dust path has provided a strong, durable surface that can continue to withstand the weight of path users. This approach has removed all irregularities (low points, high points, or hollows) in the bench formation's surface to provide an even surface, which not only improves the surface from a user's point of view but has also helped to improve the path's drainage.

Is it suitable?

It is important, when considering the use of as dug materials for path construction, that their suitability is checked first before using them, particularly for surfacing - see 'Testing the Suitability of Surfacing Materials'. As dug materials for path construction should ideally be granular in nature, with good free-draining, binding and compaction properties. Naturally occurring granular materials with sufficient clay content, such as 'hoggin', tend to be most suitable. As dug materials may be the only source of material in some areas where it would be impractical, or very expensive, to import quarried or recycled aggregates. This situation can be particularly common in remote Highland and island locations where quarries are few and far between. However, if the particle size of the as dug material is limited, resulting in a poor quality path surface, it is worth looking at other options. Consider recycled aggregates first, and quarried sources last. The use of higher quality recycled or quarried aggregates could save money in the long term, where as dug materials may fail or repairs become a costly problem.

How much will it cost?

An as dug path resurfaced with Type 1 granular sub base and whin dust surface may cost between £20 - £30/ linear metre.

How do you install it?

Here at Oatridge College, the method of construction was:

  • With the contractor in attendance, the proposed new route through the woodland was marked out with flags. These flags marked the central line of the intended route and were used as a guide to help the machine operator building the bench formation. They also acted as aids to instruct the contractor to reduce steep gradients, where reasonably practical, and to make use of the side slope's natural curves and contours. This helped to avoid the slope's fall lines – a path that follows the main slope in long straight lines is very prone to water damage, monotonous to walk on, and often unsightly.

  • A machine operator in a tracked excavator followed the marked route through the woodland forming a bench formation using the 'cut and fill' technique. All excavated naturally occurring materials were cut straight from the side slope and taken to use as 'fill' to form a 1.5m wide bench with a 2.9% (1:35) cross fall and fill slope, or to landscape out the original steep path line. The back slopes above the bench formation surface were battered back to angle of 20% (1:5) to stabilise and prevent the slope collapsing. Grade reversals were also installed in the bench formation's surface along the route to shed water off the path.

  • Once the bench formation works were completed, the next stage was for the machine operator to form a path tray to a width of 1000mm and a depth of 100mm along the central line of the bench formation. Some excavated materials were set aside along the length of the excavated tray for path edge landscaping work. The remaining unwanted spoil was cast onto the fill slope and landscaped.

  • At the start of the excavated tray, a geotextile sheet was rolled out to line the bottom and sides of the tray, whilst laying the sub base layer, to separate the laid recycled Type 1 granular sub base from the weak bench formation's surface which contains high clay content.

  • At the recycled Type 1 heap, the path workers used a tracked excavator to load tracked power barrows. The path workers then transported their loads to the start of the geotextile lined tray, at the timber bridge, and tipped the Type 1 on to the geotextile to about half the tray's depth. Path workers spread the material by rake to levels and falls that created an uncompacted stone layer suitable for running heavy loaded tracked power barrows along. This construction method was continued along the total length of the excavated tray that finished at the far side of the woodland site.

  • Path workers continued to transport recycled Type 1 with the tracked power barrows to the end of the half stone-infilled tray to lay the final stone layer on top of the first uncompacted stone layer. Working backwards, the remaining half of the tray was infilled with recycled Type 1 above the existing ground levels. Path workers spread the laid materials to levels and falls to form a 2.9% (1:35) cross fall, and then compacted the material to refusal with a vibrating whacker plate, maintaining the cross fall, to finish the compacted sub base surface flush with existing ground levels. This construction method was continued along the total length of the half stone infilled tray, back to the start of the woodland path.

transporting recycled type1 with tracked power barrow along half built path base oatridge college

  • Any part of the compacted sub base surface deviating from the required level or cross fall was raked off, or topped up with additional recycled Type 1 to form the correct level and cross fall, and then re-compacted to refusal again. The compacted base surface was now ready for surfacing.

laying second layer recycled type1 oatridge college

  • Path workers loaded the tracked power barrows with 6mm whin dust, and tracked their barrow loads to the far end of the newly laid compacted sub base surface. Working backwards, the path workers tipped the whin dust onto the compacted sub base surface. The path workers spread the tipped whin dust over the surface to a depth of 25mm, and to levels and falls to form a 2.9% (1:35) cross fall, and then compacted the whindust to refusal with a vibrating whacker plate, maintaining the cross fall. This construction method was continued along the total length of the compacted sub base surface, back to the start of the woodland path. That completed the surfacing work.

  • Path workers then landscaped the path edges with the set-aside excavated spoils, to ensure the finished whin dust surface was contained, the line of path defined, and its appearance 'softened'. All path and landscaping works were now finished!

Detailed drawing - As dug path (type 1 and dust)

If you like the look of the as dug path with Type 1 and dust surface at Oatridge College, as a potential path surface for your project, download the detail drawing here icon As Dug Path (Type 1 and Dust) - Detail Drawing

For a generic standard detail drawing and specification details, download them here icon As Dug Path (Type 1 & Dust) - Standard Detail Drawing & Specification Details

© 2014 Paths for All - Registered Scottish Charity No: SC025535, Company Limited by Guarantee No: 168554 inc. 19 Sept 1996 at Companies House, Edinburgh