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Beaver Dam Secant Pile Wall Completion Report.

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Final rept.,

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The report presents a comprehensive project history, beginning in 1966 with the initial Beaver Lake Located near Eureka Springs, in northwest Arkansas, U.S.A. impoundment against Dike 1, which produced observable surface seepage from five areas downstream of Dike 1. Seepage continued to increase due to limestone rock weathering and solutioning, combined with removal of colloidal sized soil material from the overburden and weathered rock zones, particularly along two faults that formed a graben beneath Dike 1. The pervasive seepage distress evolved until a muddy water boil was discovered during a pool of record event in December 1984, and ultimately warranted a remedial construction project. The selected method for alleviating the seepage distress consisted of a 1,475-foot-long concrete diaphragm wall located immediately upstream of Dike 1 and penetrating to depths of 80 to 185 feet. Utilizing a request for proposalstechnical evaluationprice negotiation contractual process, the construction was accomplished by two separate joint venture contractors under two contracts. The first contractor performed site preparation and constructed an upstream work platform however, the contractor faiLed to complete the project because the specialized rock mill excavation equipment could not excavate the proposed overlapping trench segments into the high compressive strength unweathered rock that typically exceeded 15,000 psi. The inability to construct the wall resulted in the first contract being terminated for convenience to the Government. The second contractor, after overcoming shaft excavation instability problems, completed the wall using a large diameter down-the-hole air percussion hammer drill for excavation. A total of 739 overlapping, 34-inch diameter shafts were drilled on 24-inch centers. MM

Subject Categories:

  • Soil Mechanics
  • Civil Engineering
  • Construction Equipment, Materials and Supplies
  • Geology, Geochemistry and Mineralogy
  • Hydrology, Limnology and Potamology

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