HDD CONSTRUCTION RISKS AND CHALLENGES ON THE KING COUNTY BELLEVUE PUMP STATION FORCE MAIN PROJECT

摘要

The King County Bellevue Pump Station Force Main project is a horizontal directional drilling project involving construction of a 5,300 lineal feet, 24-inch diameter (ID) sanitary sewer force main just south of downtown Bellevue, Washington. The two main segments of the force main were installed by HDD using 32-inch steel casing pipe and 28-inch HDPE carrier pipe. The first HDD segment is a 3,800 feet long, 200 feet deep crossing that involved: drilling under several residences, Bellevue High School, a condominium complex, and a courthouse building; settlement and vibration monitoring of numerous structures above and adjacent to the alignment; utilizing the "drill-and-intersect" method by employing two drill rigs at both sides of the crossing; and 7 tie-in welds of the steel casing pipe during the pullback due to limited pipe laydown area. The second HDD segment is a 1,000 feet long crossing under Interstate 405 that involved: installation of a 270 feet long steel conductor sleeve due to poor soils and a high groundwater table at the high end of the crossing; utilizing the "drill-and-intersect" method by employing two drill rigs at both sides of the crossing under a 10-lane highway; and setup of drilling operations adjacent to an active railroad bridge and major arterial. This paper discusses the construction risks and challenges faced by the contractor and project team, and the results and lessons learned during construction.