Construction Challenges for an 84-inch Pipeline:TRWD’s Eagle Mountain Connection Project

摘要

Tarrant Regional Water District (TRWD) supplies raw water to over thirty wholesalerncustomers (approximately 1.6 million people) in ten Texas counties. TRWD’srnexisting raw water supply system includes two major reservoirs in East Texas,rnpipelines and pump stations to deliver water from East Texas to Tarrant County, thernWest Fork reservoirs, two terminal storage lakes in Tarrant County, and the BenbrookrnConnection, which delivers East Texas water to the southwest side of Fort Worth.rnTRWD has recently completed construction of the $140 million Eagle MountainrnConnection Project that allows TRWD to pump water from their East TexasrnReservoirs to Eagle Mountain Lake. The project includes 20 miles of 96-inch and 84-rninch pipeline, the 430 MGD Rolling Hills Pump Station (expandable to 630 MGD),rnthe 230 MGD Benbrook Booster Pump Station (expandable to 350 MGD), a 120-rnmillion-gallon balancing reservoir, and a number of other required facilities.rnThe 96/84-inch Eagle Mountain Pipeline runs from Benbrook Lake to EaglernMountain Lake. The pipeline contractor was faced with several challenges duringrnconstruction of the project. The paper will describe in detail two such challenges, onernplanned and one surprise, and the innovative techniques used by the engineer andrncontractor to overcome these challenges.rnThe first challenge was the installation of 700 feet of subaqueous pipe and an outletrnstructure in Eagle Mountain Lake. The pipe was installed in an underwater trenchrnand backfilled with coarse gravel. The Contractor used an innovative cable system torninstall the pipe. The outlet structure consisted of a prefabricated steel box with an Sshapernpipe that was set on H-piles and given concrete ballast for thrust restraint.rnThe second challenge was an unforeseen site condition consisting of a largernunderground marsh consisting of highly saturated, extremely loose silty sands and