Emergency Stabilization of 84-Inch Chapman Raw Water Pipeline Crossing the South Sulphur River, Greenville, Texas

The North Texas Municipal Water District (NTMWD) and the city of Irving (Irving) jointly operate and maintain an 84-inch raw water pipeline that transfers water from Lake Chapman to Lake Lavon and Lake Lewisville for NTMWD and Irving, respectively. In June of 2015, Irving performed an aerial survey of the pre-stressed concrete cylinder pipe to observe portions of the line difficult to access by land. The aerial survey revealed a portion of the pipeline exposed at its crossing of the South Sulphur River, near Greenville, Texas. Further investigation established that the river bottom and embankments had eroded substantially, undermining the pipeline as much as eight feet in some locations. NTMWD and Irving declared the stabilization and repair of the crossing to be an emergency, expediting design, and construction services. Competitive sealed proposals were obtained from three trusted contractors. The selection process included interviews with two finalists, with Garney Construction selected to perform the project. The project key objective was to first stabilize the at-risk 84-inch water main servicing NTMWD and Irving with concrete cradling up to the spring line of the pipe. The concrete was placed by a tremie installation after the flow of the river was controlled with cubic yard sand bags. Once the pipe was determined to be successfully stabilized, the second phase of the project was to armor the steadily eroding riverbanks that had already lost more than 30 feet of shoreline since the original investigation that qualified the project to be an emergency. The banks were armored, crest to toe, with filter fabric and 36-inch rock rip rap up and downstream of the pipeline crossing. Sequentially, the permanent easement through the river was bordered with sheet piling in which a flex base backfill encased the supported pipe. Lastly, a one-foot thick, reinforced, concrete slab capped the flex base fill protecting the endangered pipe across the span of the river. Engineering design, environmental permitting, and innovative construction methods brought this project to a successful completion in March of 2017.