From Pipe Ram to Microtunnel—How Owner and Contractor Worked Together

The city of Covington, Washington, has seen continual growth over the past decade. To accommodate the growth, Soos Creek Water and Sewer District embarked on the design and construction of a complex regional sewer project. The overall project included the installation of 6,200 feet of 18-inch diameter gravity sewer using conventional open-cut and trenchless construction methods and the construction of a new regional sewer lift station. Delivering this project required substantial effort that involved designing and constructing eight trenchless crossings from 122 to 288 feet long under state highways, environmentally sensitive areas, streams, and hills. This paper looks at the initial design and construction of the crossings using pipe ramming technology and why that method was chosen. The paper covers the challenges encountered during the pipe ramming portion of the project and how the project owner, engineer, and contractor partnered to identify the best approach for successfully completing the sewer installation when it was determined that pipe ramming could not meet the line and grade requirements for the gravity sewer. The process used to determine why the project would be completed using microtunneling technology will be examined and how the change order language was developed, protecting both the owner and the contractor.