TRENCHLESS REHABILITATION OF A TRENCHLESS INSTALLATION

摘要

The Saratoga Road Culvert Replacement Project was intended to replace a damaged 18-inch diameter concrete culvert that crosses underneath Saratoga Road on Whidbey Island, Washington. The replacement culvert was originally planned as a 54-inch diameter steel casing with a 48-inch HDPE liner. The proposed crossing was roughly 170 feet long, and ranged in depth from approximately 35 to 45 feet below ground surface.Auger bore pipe jacking was recommended by others to install the 54-inch steel casing. However, the contractor elected to install the casing using pipe jacking combined with hand excavation at the pipe face. After roughly 100 linear feet had been installed, soil and groundwater began to flow into the casing, resulting in the formation of a significant sinkhole above the culvert. Following formation of the sinkhole, the casing was subsequently abandoned in place and the project as designed was terminated.Staheli Trenchless Consultants (STC) was contacted to evaluate feasible alternatives to complete the culvert installation which would both address the current site conditions (including the partially installed 54-inch casing) and pose minimal risk to Saratoga Road during construction. After visiting the site and reviewing the existing geotechnical report, STC recommended open-ended pipe ramming as a feasible method for completion of the culvert installation. The new design rams a 30-inch steel casing through 100 feet of the existing 54-inch casing, and through 70 feet of native soils to daylight. This paper describes the project history in light of the multiple installation attempts and details lessons learned throughout the entire process of pipeline installation.