Trenchless Approaches to Overcome Difficult Ground Conditions in Downtown San Francisco

摘要

The potential for existing improvements and obstructions adversely impacting construction is present in nearly allrnunderground projects. This risk is escalated for projects that are undertaken in densely populated urban settings wherernextensive changes in land use and subsequent development and land reclamation have significantly altered conditionsrnbeneath the surface. Such circumstances prompted some of the more significant challenges faced by the project teamrnduring construction of the San Francisco Public Utilities Commission’s North Shore to Channel Force Main.rnLocated within downtown San Francisco, the force main alignment traverses numerous older facilities that werernabandoned and buried in-place during reclamation and development of the San Francisco Bay. Potential obstructionsrnassociated with these facilities, coupled with challenging geotechnical conditions and numerous nearby active utilities,rnposed significant project challenges. Much of the force main alignment was planned as open-cut with trenchlessrnmethods incorporated at certain locations to minimize impacts to traffic, neighboring businesses and facilities, andrnexisting utilities. While a number of methods were considered for the trenchless installations, pilot tube probes werernused to locate obstructions; and pilot tube guided pipe ramming and auger boring, and open-face pipe jacking werernused to complete the force main construction.rnThis paper provides an overview of the trenchless methods used for the project and discusses the trenchless approachrndeveloped during design, challenges associated with obstructions, modifications to the trenchless approach madernduring construction, and lessons learned.