Base layer

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The base layer is the main load bearing layer of a path structure which spreads the weight and forces of different users in to formation layer below. For that reason, the base layer should be built to high standard. A base layer is generally laid by tipping successive loads of well graded granular sub base material, such as Type 1 from a dumper into the prepared formation tray, which is then spread manually with a rake or an excavator with grading bucket. Alternatively, a ‘drag box’ can be used to quickly lay the base layer to any depth, creating a high quality finish with an even surface.

For detailed information about the well graded granular sub base materials used to create a base layer including how deep a base layer can be and how they are constructed, read the following sections:

Why compact the base layer?

The base layer should be thoroughly compacted in layers to maximise its strength and binding properties. Compaction of the base layer removes the air between stone particles and therefore increases the solid mass density of the well graded granular sub base material. A vibrating roller is used to compact the material until it refuses to move or settle any further, when the base layer is said to be ‘compacted to refusal’. A properly compacted base layer should not have loose material or show roller marks in the surface.

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