Big R’s Design-Build team faced many challenges when asked to supply a flood conveyance bridge in Gastonia, NC — including poor soil conditions, complex hydraulic requirements, heavy construction loads, and tight timelines scheduled around a shopping mall opening.
Poor soil conditions had weakened the site
The roadway was skewed to the waterway on this site, which was originally home to a stream restoration project, complete with floodplains and their complications. The consultant’s geotechnical analysis determined that poor, alluvia-based soil conditions had weakened the structural integrity of the build site.
Threat of flooding was a primary concern
Economics drove the client to a Super•Cor solution, but the product’s strength and versatility quickly took center stage. To meet the project’s storm event hydraulic requirements, a minimum 1200 sf end area was required. A single, larger Super•Cor Arch was considered but could not accommodate the set sanitary sewer line elevation across the structure and maintain the required hydraulic capacity.
Dual arches provided the right solution
By switching to dual Arches, we were able to maintain the required 7-9′ cover depth and still achieve the hydraulic requirements. The arches were assembled on pile foundations, which, at the request of the city, had a sheet pile cut-off wall in front of the outer foundations, and around the middle pile cap for extra scour protection.
Big R Sheet Piling adds extra protection
As integrated into the design drawings, Big R Steel Sheet Piling was driven into the partially-weathered rock, where the piles were embedded. It also extended over 110′ on the outlet end to protect the welded-wire wall from possible erosion during peak storm events.