Air spade investigations

Thomson Ecology’s arboriculture team carried out an investigation into tree root distribution using an air spade – a hand-held tool that uses a high speed, high pressure flow of air to displace soil around roots without damaging them.

Our client raised concerns about the potential of damage being caused to the roots of trees protected by a Tree Preservation Order during construction works. Thomson Ecology was asked to determine whether there were any roots that might be affected by the proposed works.

Tree roots tend to grow underground in the top 600mm of soil and uncovering them without damaging them requires a special piece of kit – an air spade. It allows you to determine whether there are any roots present. If there are, further excavation can reveal which direction and to what extent they are growing.

Construction activities which encroach into the root protection areas (RPAs) of trees should be avoided, but there are times when they can’t be. By using an air spade it is possible to design the construction around them to avoid damage. This can be especially helpful where foundations for buildings and other structures need to be installed in the RPAs of retained trees. By knowing where the roots are, foundation designs can be tailored to minimise potential root damage.

Several excavations were carried out by Thomson Ecology using the air spade which effortlessly displaced the soil to a depth of up to 700mm. In one of the trial pits, roots were uncovered, but further excavation traced them back to shrubs rather than the protected trees. As a result of our investigative excavations, we presented the client with a report of the findings for further consideration in their planning application submission.

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