DESCRIPTION

The new Lookout Fire Company 15,800-square foot fire station to replace the existing station on West Bell Street. The new facility includes an apparatus bay with four doors, a training room, workshop, lobby, offices, equipment room, as well as a social hall with a kitchen and pantry.

CHALLENGE

Upon excavation of the shallow foundations during construction, it was discovered the new fire station site is underlain by up to 20 feet of undocumented waste slate mine tailings consisting of materials in size from 4-foot long to small aggregate. Preliminarily, shallow foundations were recommended for support of the building provided that the fills were excavated and replaced with engineered fill. This solution had several issues including the significant volume of excavation needed, mobilization of processing equipment to convert the waste fill into structural fill, potential importation of structural fill, cold weather issues with moisture tempering the materials, and significant impacts to the schedule.

SOLUTION

Rapid Impact Compaction (RIC) is an effective alternative to over-excavation and replacement by utilizing the existing materials on site and compacting the loose upper zones of those fills. The Geotechnical Engineer directed RIC treatment under load-bearing column and wall foundations. The RIC treatment alleviated the need to excavate significant volumes of slate material and avoiding cold weather installation of fills, while mitigating differential settlement concerns for the long-term serviceability of the structure – with one piece of equipment and one treatment. The RIC treatment was completed in 3 days with set occurring in one pass and utilizing available on-site shale materials for crater fill.