As dug path

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What is it?

A 1m wide path built entirely with naturally occurring materials taken straight out of the ground – 'as dug' – from one small-scale borrow pit by the route. The material was not crushed or graded to any specification like quarried aggregates are. Instead it was dug out of the pit and used in its natural form.

as dug path oatridge college

How does it work?

You will notice the path's surface has a mixture of different stone sizes and clay in it. The path is made up of one layer of this as dug material. The larger stones have interlocked to provide most of the path's strength. The smaller stones and fines have filled in the gaps between the larger stone to help bind the path together into a reasonably solid mass when dry and firm.

What are the benefits?

As dug materials can provide a number of benefits in terms of sustainable construction practice. If the material is suitable they can also offer cost savings because you do not need to buy and transport quarried aggregates, which can be particularly expensive. When planning to create or upgrade any paths, consider the use of as dug materials before importing quarried aggregates or recycled aggregates.

  • It can provide a natural-looking surface that blends in very well with the landscape.

  • It can reduce the use of irreplaceable quarried aggregates.

  • It can help to reduce environmental impacts associated with commercial quarrying operations and road haulage.

  • It can reduce construction costs by not using or using minimal quantities of expensive quarried aggregates.

  • It can reduce any site impact from haulage of imported aggregates to the site.

Is it suitable?

A complete as dug path can be built if suitable materials exist on site. Check their suitability 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 aggregates 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. To improve the quality and suitability of as dug material, it can be graded on site using a portable non-vibrating screener attached to the dumper or a larger mobile vibrating screener.

How much will it cost?

As dug path may cost between £15 - £25/ linear metre.

How do you install it?

An as dug path can provide a reasonably good surfacing solution, if built by the right contractor. Choose a contractor with experience of building as dug paths, with good landscaping and finishing skills, and with knowledge of the material to be used.

Here at Oatridge College, the method of construction was:

  • The route through the woodland was excavated by a machine operator using a tracked excavator to form a path tray, 1000mm wide and 150mm deep, with excavated spoils used to infill low lying sections to make a formation level. Some excavated materials were set aside along the length of the excavated tray for path edge landscaping work. Remaining unwanted spoils were set aside to be used as infill to reinstate the borrow pit.

  • A borrow pit, close to the route, was opened with the tracked excavator, with ground vegetation stripped and topsoil placed to the side. The machine operator continued digging until granular materials were found, and then mixed and dug it out to load tracked power barrows.

tracked power barrow and excavator at borrow pit oatridge college

  • Path workers transported the as dug material with the tracked power barrows along the excavated tray to tip the material into the tray to the depth required. This construction method was continued until the length of excavated tray to be built each day was infilled above the existing ground levels.

  • Path workers spread the tipped as dug materials to levels and falls to form a 2.9% (1:35) cross fall, and then the material was compacted to refusal with a vibrating whacker plate, maintaining the cross fall, to finish the compacted as dug path surface flush with existing ground levels.

whacker plate on as dug path oatridge college

  • Path workers then landscaped the path edges with the set aside spoil to ensure the finished compacted as dug path surface was contained, the line of path defined and its appearance 'softened'.

  • The borrow pit, now finished with, was infilled with excess excavated spoil, then landscaped over with top soil and stripped ground vegetation.

Detailed drawing - As dug path

If you like the look of the as dug path at Oatridge College, as a potential path surface for your project, download the detail drawing here icon As Dug Path - Detail Drawing

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

What variations are available?

Instead of construction the whole path with as dug material, particularly if its quality is poor, consider using as dug materials to build the lower part of the sub base layer, and then lay a higher quality material – like recycled or quarried Type 1 – on top to bind together the as dug layer and make it stronger. This practice, called 'regulation', also removes all irregularities (low points, high points or hollows) to provide an even surface ready for laying the path surface on.

Complete as dug paths can also be machine built entirely by a tracked excavator. The machine operator with the tracked excavator carries out a technique called 'soil reversal', also known as 'sub soiling'. The machine operator uses the tracked excavator to dig the drainage system, win as dug materials from a side ditch, and build the sub base and surface using those materials. The machine operator then does all path edge and ditch landscaping work with the machine's bucket. This machine built technique is carried out on remote, sensitive moorland or upland locations where it is impractical or damaging to import or haul materials out to or around the site. For illustrated information about how as dug paths are machine built using the soil reversal technique check out 'Machine Built'.

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