Artificial Ground Freezing was used to provide temporary earth support and groundwater control for a complex system of three frozen earth cofferdams for the Milwaukee Metropolitan Sewer District’s Harbor Siphons Project in Milwaukee, Wisconsin. Site geometry and frozen earth structural design precluded construction of one large excavation, requiring the component system of the tangential cofferdams. High groundwater velocity prevented the formation of the frozen earth walls during various stages of the project. Remedial methods including external dewatering, permeation grouting, jet grouting, timber shoring and sheet piling were attempted to complete the project. Ultimately a more aggressive ground freezing program was implemented and the project was successfully excavated. The design of the ground freezing system is presented, as well as the difficulties encountered with the high ground water velocity and its impact on freezing. The failed remedial approaches are discussed in detail, including lessons learned. A description of the aggressive ground freezing approach is included as it was the final solution to a complex problem of site geometry and unexpected groundwater conditions
