Utility Tunnel Abandonment

Wilmington, Delaware

The Job

As part of a commercial building renovation, approximately 750CY of subbasement and utility tunnel needed to be filled.

The Challenge

The structural engineer had two concerns: the slab over the basements needed to be replaced, but couldn’t be removed until the walls were braced, and the density of the fill needed to be as low as possible to reduce the chances of inducing settlement.

The Solution

CJGeo proposed 25lb/cuft cellular concrete, with an average of 80psi compressive strength for backfilling the tunnel and subbasement. Because cellular concrete is very mobile, there were no issues with filling the tunnel from just a few access points.

With an average cured unit weight of 21lb/cuft, the material saved approximately 1ksf in dead load relative to conventional fill materials, and provided sufficient strength to brace the walls to facilitate floor removal, and also provide adequate bearing capacity for the new floor.

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