Tree Preservation Efforts: Hydrovac Excavation

August 3 2017 RHR 206

As major construction occurs across campus, there are several efforts ongoing to preserve our mature trees, including tree protection zones and hydrovac excavation.

Sometimes, sidewalks and utilities under our large trees needs to be modified, requiring disturbance of the roots. Digging a large exploratory hole with steel tools damages the critical root zone by wounding trunks and roots as well as increasing soil compaction.

Here you can see hydrovac excavation uses pressurized water to break up the soil cover.  photo credit: R. Robert

Here you can see hydrovac excavation uses pressurized water to break up the soil cover. photo credit: R. Robert

Pressurized water or air can effectively remove soil without damaging the tree’s delicate root system. Soil has voids between an assembly of solid particles (clay, sand, silt, rock, and organic matter) that are filled with air or water. When compressed air or water is directed at close range into the soil, it fills the voids and expands, fracturing the soil apart without impacting non-porous materials like metal, plastic pipes, and roots.  Hydrovac excavation uses pressurized water to break up the soil cover. As the ground is precisely excavated, a powerful vacuum system simultaneously removes the debris.

From this angle, you can see that the area under renovation is in the dripline of this mature tree. photo credit: R. Robert

From this angle, you can see that the area under renovation is in the dripline of this mature tree. photo credit: R. Robert

The precision of this method is key to creating precise cuts on roots. As result of the minimal disturbance, the roots can be cut cleanly. These precise cuts allow the root to be cleanly severed and initiate new roots at the cut point. This technique of root pruning is often used in nursery practices to maintained healthy root balls for transporting trees and shrubs.

Here you can see the newly installed sidewalk underneath our mature tree. photo credit: R. Robert

Here you can see the newly installed sidewalk underneath our mature tree. photo credit: R. Robert

If you are renovating in your mature tree’s critical root zone, use hydrovac excavation as a minimally invasive technique to help preserve your large trees.

Categorized as Garden Practices

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  1. Hello —

    How do you think hydrovac compares with a regular air spade? When would you do the hydrovac vis-a-vis the construction schedule — before, after or during?

    Thanks,
    Francesca

  2. That’s really cool!!

  3. Thanks, Hudson. They are doing some interesting things with the amount of renovation we are going through right now.
    Becky Robert
    Scott Arboretum

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