USACE Howard Hanson Dam

Scope of Work:

Howard A. Hanson Dam is a U.S. Army Corps of Engineers flood control dam located near the headwaters of the Green River in King County, Washington. Its primary purpose is flood control in the winter and fish habitat enhancement in the summer.

This project was completed within a tight work window, along the bottom of the reservoir during a routine drawdown period.  Central Geotech provided geotechnical observation and testing services to support the construction of a crane pad foundation, construction staging area, roadway, and heavy equipment turn-around area.  These improvements were built to facilitate the transport and assembly of heavy transportation units associated with the construction of a Modular Barge Crane, a 100-ton crawler crane, emergency gate, a 7-ton stop log, and barge module assembly.

                                                                                                                                      

Features:

  • Unique site location – at the base of a lowered reservoir behind the dam
  • Preconstruction coordination with contractors, sampling, laboratory testing results
  • Construction observation and testing, with daily reporting
  • Robust security and environmental constraints
  • Recommendations for re-use of existing soils onsite for overall cost savings
  • Daily reporting with clear formatting of mapping, locations, elevations of testing                                                                                                                                          

Results:

In preparation for construction, Central provided laboratory testing of quarry soil and rock for conformance to the project specifications.  We additionally reviewed the construction schedule for feasibility and provided consult from a design/construction perspective to the Prime.  While onsite, subgrade evaluations, in-place moisture/density testing of structural fill, and general geotechnical observation of earthwork was completed in conjunction with the daily construction schedule.  Reports of each layer of compacted fill and construction activities were completed daily and submitted to the Contracting Prime in the form of daily maps.  These reports showed the approximate location, depth, fill layer, and results of testing.

Throughout this mass grading project, a tight budget, inclement weather, limitations due to cultural recourses, and challenging subgrade soil conditions required swift communication and on-the-spot adjustments with the project team during shifting priorities.  Stephen Eagar, PE conducted site visits as construction was commencing to observe and provide Senior oversight for technical staff stationed onsite for the duration of the work.

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