Blower Slab Stabilization

Virginia Beach, VA


During a routine inspection, extensive voids were discovered under the slab supporting a ventilation blower at a wastewater treatment plant. Staff was concerned that the lack of support under the slab would cause it to settle.  As visible in the pictures, this would easily cause extensive damage to this critical equipment.


The blower slab stabilization repair had to address the voids under the entire area of the slab, including the areas where the slab surface was unaccessible.

Backfill consolidation caused the voids. The roughly 15′ of backfill material under the slab had settled over time. Because the backfill material had been in place for a long time (nearly 20 years), ground improvement wasn’t necessary. The backfill had consolidated as much as it was going to.


CJGeo proposed polyurethane grouting for filling the voids below the blower slab, using CJGrout 20SDB. The minimum bearing capacity of the proposed materials was 3700PSF, ensuring adequate bearing capacity and long-term stability.

CJGrout 20SDB is specifically formulated for high mobility grouting and filling large voids. 20SDB’s tack free time is much longer than its rise time. It can travel very far from each injection point, and doesn’t cause lift. This is helpful in situations like this one, where equipment covers most of the slab, and access is limited. High mobility grouting is excellent for void filling because the material gently fills all voids, without lifting slabs. This is contrast to low mobility grouting, a process designed to displace soils and provide lift.

A CJGeo polyurethane grouting crew filled the voids below the blower base and adjacent sidewalk in less than two hours. The equipment stayed in service during the entire blower slab stabilization repair. 

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