HDD in an Urban Environment: The Bellevue Pump Station Force Main Project

Abstract

Horizontal Directional Drilling (HDD) is a commonly accepted construction method for installation of pipelines throughout the U.S. and abroad. Most HDD installations are performed in rural areas where there are no significant structures under the alignment and where pipe laydown area and construction staging area are plentiful. However, HDD applications in urban settings have also been gaining increased consideration despite its inherent challenges with a built-out environment and sufficient drill side and pipe side construction areas. The Bellevue Pump Station Force Main is one such HDD project that will construct 5,300 feet of 24-inch diameter (ID) sanitary sewer force main just south of downtown Bellevue, Washington. The two main segments of the force main will be installed by HDD using a 32-inch steel casing pipe and 28-inch HDPE carrier pipe. The first HDD segment is a 3800 feet long, 200 feet deep crossing that will be installed under several residences, Bellevue High School, a condominium complex, and a courthouse building with only 650 feet of pipe laydown area. The second HDD segment is a 1000 feet long crossing under State Route 405 with a 70 foot elevation difference that will require a lane closure of a major arterial in Bellevue, WA. Construction is scheduled to begin in May 2007. This paper discusses the pipeline alignment alternatives evaluated, the selection of the final HDD alignment, the final pipeline design for the HDD crossings, permitting and easement issues, and lessons learned during design.