Montgomery County Underwater Bridge Inspections

Barr & Prevost, A JMT Division, performed underwater bridge inspections on 12 Montgomery County bridges in 2009 and 10 additional bridges in 2012. To provide the required services most economically to our client, each site was initially inspected for access, optimal season for lowest water depth, and to determine the number of piers that could be susceptible to scour. This preparation allowed our team to become familiar with the site conditions so each task order would be completed efficiently and cost effectively.

Substructure units for each bridge that were susceptible to scour were inspected by Barr & Prevost’s underwater-certified teams. Each team included a registered PE Level II Bridge Inspector, a Level II Bridge Inspector, and a field survey party chief. The procedure involved preparing a grid pattern of survey elevations along the face of the foundations and quarter points between spans at approximately 20 foot intervals.

Barr & Prevost employed underwater diving methods for hands-on inspection of pier bases and footings to facilitate obtaining bottom river elevations. This is a method typically used to obtain channel sections in deep water for hydraulic analysis. The data points were collected and downloaded to prepare a digital terrain (contour) model of the river bottom around the piers that would be susceptible to scour. The contour model provides a permanent baseline for future scour inspections. Additionally, if significant scour depths were noticed, cross sections could easily be prepared to determine accurate fill quantities for repair.