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September 2017 Dinner Meeting
September 28, 2017 @ 5:30 pm - 9:00 pm
Swift No. 2 Dam Failure (Cowlitz County PUD Washington)
Why Geology Matters, How Even Geotechnical Giants Can Get It Wrong, and How we can Design and Build Rapidly when High Costs are at Stake.
Presented By: Ken Green, PE, CH2M, Geotechnical Engineer
Biography: Ken has worked for CH2M for his entire career of over 44 years, beginning in 1973 in Denver Colorado where he served as a young resident engineer during construction of a 65-foot-high earth dam and water supply reservoir serving the City of Aurora Colorado. Early in his career, he moved often, next spending about 6 months near Reston Virginia for field work investigations for a 75-foot dam, design of a water reclamation facility and other projects. He next moved to Corvallis Oregon where he worked on a wide variety of projects for about a year before moving to Anchorage, Alaska office. While in Alaska, Ken served again as resident engineer for a City of Homer project for a couple of years. While there he performed resident engineering for the construction of a 70-foot- high zoned earth dam, a pump station, water treatment plant, storage reservoirs, and many miles of water distribution pipelines. After completion of the construction project in Homer, Alaska, Ken returned to school to obtain a Master’s Degree at Utah State University. After completing course work and thesis, he returned to work for CH2M, with his new employment located in Bellevue, WA where he has lived and worked since about 1978.
His work with CH2M has included the design and construction of numerous environmental projects including design and construction landfill liner and cover systems; and investigation, design, and construction of many waste containment sites throughout the pacific northwest. He has participated with design development and construction of numerous complex transportation projects throughout the Puget sound region and across the western united states; and he has continued developing a strong background for a wide variety of water resource projects and has worked extensively throughout Alaska and Canada with design and construction of many cold-regions projects. Ken has participated with design teams for project development, designs and construction of numerous hydroelectric and fish related projects. Ken along with his family has had the opportunity to relocate many times while temporarily assisting with resident construction of projects he has designed in areas throughout the United States and Alaska.
Ken has been extensively involved in the investigation, design development, and construction of more than 400 water resource projects including water and sewer treatment facilities, pump stations, reservoirs, pipeline conveyance, flood control, tunnels, outfall projects, stream restoration, landslides, and resource development throughout the United States, Canada, and Alaska. Today Ken continues to be a resource to CH2M, working as a consultant to project teams, assisting with design development of cost effective solutions and assists with solutions for difficult and challenging projects.
Abstract: The foundation of the 80-foot high Swift No. 2 dike embankment failed suddenly after 40 years of service on 21 April 2001, resulting in breaching of the embankment and destruction of the Swift No. 2 powerhouse and related facilities. An extensive investigation was launched to determine the cause of failure. Investigations included large open pit excavations, borings, aerial and ground surveys, geologic mapping, laboratory tests, smoke testing of the foundation and video observation of boreholes.
Results revealed that failure began when alluvial deposits forming the bottom of the forebay piped into a large open basalt lava tube in the foundation. The loss of material by piping formed a sinkhole in the forebay and provided a direct hydraulic connection to distribute large volumes of water to cavities and flow paths leading under relatively thin basalt flows upon which the dam was founded. Foundation failure under the downstream toe of the dam occurred when the water pressure and flow from the hydraulic connection to the reservoir caused the development of significant erosion paths in granular soils under the basalt, leading to eventual disruption and total collapse of the rock foundation under the dike. The failure then rapidly progressed headward into the embankment to cause complete breaching of the dike. The sudden release of water resulted in the severe downstream destruction and loss of the Swift No. 2 powerhouse, and related facilities. Although the possible mechanism of failure was recognized by the dam’s original designers including Arthur Casagrande, the field work failed to recognize the important role that a detailed understanding of the geology played in recognizing the potential for failure of the dam.
Failure of the Swift No. 2 dam and powerhouse resulted in the immediate need to bypass all flow through the emergency spillway at the upstream Swift No. 1 dam and powerhouse to avoid use of the failed canal system. To get the Swift No. 1 powerhouse back on line as soon as possible, a temporary earthen dam in the canal upstream of the failure was field designed. Modifications of the canal to form a side channel spillway capable of diverting up to 12,000 cfs with velocities exceeding 40 fps back to the Lewis River from the canal were also field designed and tested.
Swift No. 2 canal and powerhouse was rebuilt as soon as practical once the failure mechanism was thoroughly understood.