26_04_27_AIA_JLTP_12-14 Gympie St

6.3 SUPERVISED TRENCHING & BRIDGE
When Supervised Open Trenching (with a Project Arborist present) is being undertaken within
a treed area, all necessary precautions are to be adhered to. The Project Arborist will be on
site and advise on the progression of the trench and undertake root pruning as required.

An Exclusion Zone / No-Go Zone around the tree is to be established with no spoil, materials,
or machinery to be stored inside this zone. Care is to be taken when excavating adjacent to
the tree, and retained tree roots are to be treated similarly to live services (e.g. water main,
electrical conduit, etc)

This technique can be implemented when installing pipes or services within a trench adjacent
to trees with spreading root systems. When larger roots are expected to be uncovered in the
upper section of the trench, these, where suitable, will be retained and left to span the trench
within a ‘Bridge’ of soil and turf.

The trench alignment will be dug up to a predetermined distance from the subject tree,
depending on its size, location, and species. At this point, the rate of trenching will slow to
allow for more detailed assessment by the Project Arborist and may include a short distance
of hand digging or vacuum excavation to determine the presence of roots. Roots uncovered
will be assessed, retained, or pruned depending on size and location within the trench. Where
roots are being retained within the ‘bridge’, the digging is to continue cautiously beneath the
root to create the tunnel for the pipe. The new pipe can then be installed within the tunnel
beneath the ‘Bridge’.




        Figure 8: Bridge with pipe laid beneath       Figure 9: Bridge of roots with pipe beneath




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