Innovative Microtunnel Contracting for the King County Wastewater Treatment Division Fremont Siphon Replacement Project

摘要

This paper presents an innovative public contracting method for microtunnel construction that offers a risk sharing approach that can help reduce or alleviate the impacts of differing site conditions to both the owner and the contractor. This approach assisted the owner in managing a high risk tunneling project located in a densely populated urban area where twin 86-inch, side-by-side, microtunnels were constructed to cross the commercially vital Lake Washington Ship Canal (LWSC) in Seattle, WA. Building on the experience of previous regional trenchless construction projects, the project owner, King County Wastewater Treatment Division (KCWTD), added unambiguous risk sharing provisions to their standard contract. These provisions included the purchase of a new microtunnel machine (MTBM), a bid item for an hourly mining rate, a monetary incentive provision for the timely completion of the microtunnel drives, and a “no-incentive” clause that was tied to a submission of claims for Differing Site Conditions (DSC). The culmination of these contract provisions ultimately provided that if the contractor submitted a request for additional time or money as a result of encountering a DSC, the Contractor waives