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A typical Type 1 and dust path, like this stretch of path at Battleby, is made up of four layers that together form the path's structure. Each layer has a function to play, so careful choice of materials is essential to ensure a durable path is built, appropriate for the location and the expected users.

type1 and dust path battleby

The first of the four layers is known as the formation level or sub grade formation. This is the prepared ground on which the path will be built. Depending on the ground conditions, the work needed to create a suitable formation level can be anything from just stripping off vegetation to form a shallow tray (called site strip), to excavating part of a tray (called semi tray excavation) or full tray (called full tray excavation). The depth of the formation level depends on the depth and strength of the existing soil and the expected use of the path, as well as the size of the granular material to be used to build the path's sub base layer. For further information about how deep should your path base be, or in this case the formation level see 'How deep should your path base be?'.

The second of the four layers is known as the separation and reinforcement layer. This is generally a geotextile sheet that separates the path's formation level from the sub base layer and will prevent soil pumping up into the path's sub base layer over time. On weak, soft ground the path may also include a geogrid on top of the geotextile sheet to prevent the sub base layer sinking into the formation level. In many situations, if the formation level is well drained, a geotextile sheet or a geogrid may not be required because the formation level is firm enough to take the weight of the path and its users. To help you to decide whether to use a separation or reinforcement layer, you should check the strength of the ground by carrying out a simple icon Field Heel Test.

The third layer is the path's sub base (also called the base). This is the main load-bearing, structural layer, designed to spread the weight of users on the path's surface evenly to the formation level below. It is generally made up of one layer, but in some cases several layers, of granular sub base that comprises a range of stone sizes from large chunks down to very fine particles (dust or fines). The larger stones, once compacted with a heavy vibrating roller, interlock together to provide most of the sub base's strength. The smaller stones and fines fill in any gaps between the larger stones to help bind the sub base layer together into a strong solid mass. The sub base layer can also regulate any imperfections in the formation tray.

The fourth and final layer is the surface. This layer is the most important part of a path for anyone who wants to use it. It is the only part they will see and make contact with on foot, wheels or hooves. From a path designer's point of view, it is the part of the path that needs to be strong enough to take the users' weight, and to transfer that weight down into the path's sub base layer below. For the path user, the surface needs to be smooth, non-slip (free of loose stones), firm and even, and well drained, so that its useable in all weathers. The path surface should also have adequate width to allow people to pass safely and rest. Vegetation on the verges and above should be maintained to ensure no vegetation encroaches onto the path, reducing its width.

You can find more technical information for the Type 1 and dust path installed at Battleby here, which will give you more details about how the path was built, including standard detail drawings and specifications for whin dust path and granite dust path.

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