wilmington tunnel fill slide

Utility Tunnel Abandonment

Wilmington, Delaware

wilmington tunnel fill

The Job

This utility tunnel abandonment project is located in Wilmington, Delaware. Approximately 750CY of subbasement and utility tunnel had to be filled as part of a commercial building adaptive reuse project.

The Challenge

The structural engineer had two concerns:

  • the slab over the basements were to be replaced,
  • tunnel walls required bracing to demo the roof slab
  • 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 CJFill-Ultra Lightweight low density controlled low strength material. Low density controlled low strength material is a fancy name for cellular concrete. 25lb/cuft CJFill-UL has an average of 80psi compressive strength. Because CJFill-UL 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 using load reducing fill material saved approximately 1ksf in dead load relative to conventional fill materials. CJFill-Ultra Lightweight also provides sufficient strength to brace the walls to facilitate floor removal, and also provide adequate bearing capacity for the new floor.

It took a CJGeo cellular concrete crew two days onsite to fill the tunnel and subbasement. Onsite dry batching made up to 100 cubic yards per hour of the 25lb/cuft CJFill-Ultra Lightweight. Material placement was through 4″ cores and an exterior access areaway.

Other types of lightweight fill would have been much harder to install. Foamed glass aggregate or expanded shale aggregate would be practically impossible to compact given the low headroom. The density of expanded shale aggregate is also relatively high, so would not have offered the load savings that 25lb/cuft CJFill-Ultra Lightweight does. EPS is very lightweight, but is very labor intensive in this type of application.

Speak With An Expert

Facing a similar challenge to this utility tunnel abandonment by CJGeo? Give us a shout or shoot us a text. Click the state marker for the location of your project for contact info for the appropriate rep.