Managing design changes and risk during construction

The Barge Canal Crossing is being constructed as part of Sacramento Regional County Sanitation District's Lower Northwest Interceptor (LNWI) Program and consists of twin 24-inch and twin 60-inch diameter force main pipelines installed by horizontal directional drilling and microtunneling. Microtunneling operations necessitated construction of a deep shaft through a thick sequence of sand, silty sand, silt, and clay with high groundwater. The Contractor elected to use internally braced sheet piling for support of the shaft. Sheet pile penetration into clay and pumped wells were used to maintain bottom stability. Significant problems with shaft performance were encountered, which could have been reduced, if not all together eliminated, by implementation of risk management strategies developed during design. This paper reviews performance of the Barge Canal shaft and discusses the importance of risk management in design and construction.