CS14A - Concurrent Session 14A: Dewatering, High Risk and Low Reward.

Abstract Description: Dewatering for a dam rehabilitation is often one of the most challenging components of construction and generates a high level of risk during construction. A boil in the base of an excavation is one of the biggest issues in dam rehabilitation. Our projects require emergency action plans and emergency materials for the condition. However, our specifications are often thin with blanket statements of “maintain groundwater at least 2 ft below bottom of excavation” and leave all the means and methods and generally unknown risk to the contractor. We hope the contractor has engaged a specialty dewatering subcontractor or at least a licensed design professional to help with the bidding approach. However, this dewatering designer is provided maybe a month to design and bid a dewatering approach for a critical component of the work that took the design engineers maybe a year or more to partially assess and consider the risks.

That month timeline includes reviewing the geotechnical data report to try and gain the same level of understanding as the project engineers that have been looking at it for a year or longer. That often results in order of magnitude site parameters at best. Then this dewatering designer tries to prepare an efficient design generally based on hand calculations, all while trying to coordinate the install schedule and footprint within the contractor’s mobilization plan.

The industry has improved our approach to temporary water control guidance with providing risk information and more clearly sharing risk of flood events with the entire team. This talk describes the often high-risk conditions with dam rehabilitation dewatering, alternative project approaches from assessment to construction, successes, and failures. Sometimes the risk is low, even when working below the water table, and the project could benefit from atypical project requirements and shared risk.