Award of Merit: Special Projects Category
Valley Creek Wastewater Treatment Plant Repairs
Submitted by Walter P Moore
Jefferson County Environmental Services Department
Walter P Moore
Brasfield & Gorrie
Ready Mix USA
Built 100 ft (30.5 m) deep into dolomite bedrock, the $52 million influent pump station at Valley Creek Wastewater Treatment Plant is approximately 360 ft (110 m) long and 230 ft (70 m) wide.
Several elements of this underground structure, including the mat floor slab, failed in April 2005, partially flooding the pump station and rendering it inoperable. On the day of the failure, the groundwater pressure uplifted the mat slab, causing cracking and spalling in many interior beams, columns, and walls. In addition, the mat slab ruptured at a demising wall, leaving a 2 in. (51 mm) wide crack approximately 100 ft (30.5 m) long.
The forensic engineering team’s post-failure investigation included field observation of the structure, a comprehensive structural analysis using conventional and finite element methods, material testing, geotechnical analysis, groundwater studies, and geophysical testing for possible sinkhole conditions. The engineer selected an optimum repair option based on the owner’s requirements in consultation with the contractor for constructibility, cost, and schedule. The repairs included wall and floor thickening using 25,000 epoxy grouted steel dowels, uplift stabilization using 700 high-capacity rock anchors, installation of concrete and steel transverse bracing for previously laterally unsupported vault walls, modifications to various structural elements for reconfigured load paths by new transverse bracing, hydrophilic urethane crack injection to reduce groundwater infiltration, and epoxy injection of cracked concrete. The total cost of repairing the pump station was $33 million.
Despite the magnitude and the challenges of the repairs, the pump station was restored within 3 years of the failure and is fully operational. The success of these unique repairs is due to the exceptional team work and creative structural solutions by all involved parties.