As a subconsultant to Kleinfelder, Bennett Trenchless Engineers provided full trenchless design services for the pipe rammed installation of twin 120-inch steel pipelines. The two pipelines replaced an undersized 60-inch pipeline for the passage of Ryan Creek beneath the 35-foot high Highway 101 embankment. The new pipelines were installed with inverts offset by 5 feet to provide flexibility for seasonal variations in creek flow and to provide adequate habitat for spawning fish. Challenges on the project included constrained work areas on both sides of the crossing, nearby proximity of residents, and mitigating environmental impacts to protected fish and birds while working within the stream bed.
Bennett Trenchless evaluated the geotechnical conditions and the feasibility of multiple trenchless construction methods during preliminary design. Pipe ramming was selected as the preferred trenchless construction method due to limited work areas available on both sides of the crossing which limited the work area available for auxiliary equipment and for retrieval of a tunneling machine. BTE also evaluated settlement risk, provided technical specifications for the trenchless construction work, provided edits to the trenchless drawings, developed estimates of cost and duration for the trenchless components. In addition, BTE developed qualification criteria to ensure that experienced contractors were selected for the very difficult pipe rams which are at the upper end of the method’s capabilities.