In charming Old Town Alexandria, the former Crowne Plaza hotel is undergoing a transformation. Carr City Center, LLC, and the CIM Group are converting the 12-story building into a 13-story, 122-unit upscale residential condominium tower. Plans include redeveloping the elevated parking garage deck surrounding the hotel tower into 42 individual townhomes and a performing arts theater.

Situated along the Potomac Riverfront, the hotel tower and surrounding garage are supported on a combination of shallow spread footings and Franki piles. The proposed renovations to these structures will exert additional loads on many of the existing building columns and foundations. A review of the three design options indicates that the overload may be as high as 140% for spread footings, as high as 186% for foundation wall footings, and as high as 102% for the Franki piles.

In 1972, Schnabel performed a geotechnical investigation at the site and prepared a report for the then-proposed Ramada Inn. We found that the subsurface materials consist of alluvial deposits over river terrace deposits. The river terrace deposits in turn overlay Potomac Group soils, which are the oldest sedimentary deposits in the Washington, DC, area.

For this new redevelopment, Schnabel Engineering DC (SEDC)* performed a review and analysis of both the existing boring data and pressure-injected footing (PIF) foundations currently supporting the buildings. Since the modifications will increase the loads on the existing foundations, additional deep micropile and auger-cast pile foundations were recommended to enhance support. PLAXIS analysis was used to aid in the design. Additionally, we provided micropile installation observation and materials testing, as well as micropile load testing evaluation for compression and tension piles.

*SEDC is an affiliate of Schnabel Engineering, Inc.
Rendering: © Carr Companies and CIM Group