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Protection of road structure from the effect of tree
root damage can be achieved by placing the barrier
at the back of kerb. This will leave the maximum land
area available for the tree to live in. A standard
barrier 1200mm deep would be normal, as this will
be deep enough to prevent roots getting under the
barrier in normal undisturbed soil.
For situations where the road is built over reactive
clays, you may like to stabilise the moisture content
of the clay. A barrier to the depth of "the zone of
influence" normally 2 to 3 metres deep should be considered.
For well-constructed roads in good condition it is
possible to reduce the depth of the root barrier by
utilising the road base as part of the barrier. Using
the road base as a horizontal seal, root barrier may
be placed vertically at the back of kerb running from
the top of kerb into the road base, where it can be
bound to the road base using bentonite to provide
a waterproof and root proof seal. The benefit of this
system is that it allows more soil area for the tree
to live in under the road.
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