Repair and Retrofit of a Failed Deep Underground Sewage Pump Station

Built 100' deep into dolomite bedrock, the influent pump station at Valley Creek Wastewater Treatment Plant in Alabama is approximately 360' long and 230' wide. Several elements of this underground structure failed in April 2005 only a few weeks after its commissioning, partially flooding the pump station and rendering it inoperable. After the causes of the failure were determined, the engineer presented several repair options. The accepted repairs included wall and floor thickening using 25,000 epoxy grouted steel dowels, uplift stabilization of the entire underground structure using 700 high-capacity rock anchors, installation of concrete and steel transverse bracing for previously laterally unsupported basement walls, modifications to various structural elements for reconfigured load paths by new transverse bracing, hydrophilic urethane crack injection in the mat slab to reduce groundwater infiltration, and epoxy injection of numerous cracked structural concrete elements. Despite the magnitude and the challenges of the repairs, the pump station was restored within three years of the failure and is fully operational.