2007-11-28_HYDROLOGY - C1981019 - Laserfiche WebLink

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Construction Report -Section 28 Pond engineer, the wording of the Item 2 Acceptable fill material was changed as follows to add the final sentence: 2) Acceptable Fill Materials Suitable fill materials can be obtained from pond excavations or from nearby borrow sources. Suitable materials include native clay soils, clayey sand soils, and bedrock materials which are broken down to these soil types (SC, GC, CL and CH). bedrock materials should be processed to produce asoil-like material with maximum particle size of 6 inches. The materials used as embankment fill should have at least 25 percent fines (material finer than no. 200 sieve). The field engineer may approve the use of other materials following appropriate laboratory testing. This change was made because some of the available sources of borrow would not meet the original specification and this modification would have minimal impact on the overall performance of the structure. However, given the slightly higher silt content in the available borrow materials, it was determined that a drainage filter should be installed underneath the lower one-third of the embankment footprint. Considering the hydraulic gradients available, the risk of piping failure is marginally higher without this drainage blanket. As completed, the drainage blanket intercepts any phreatic surface which could exit at the downstream toe by providing a preferential drainage path through the drain that is several orders of magnitude higher than the surrounding embankment. The as-built drawing provides the specifications for the drainage blanket. As shown on Attachment 2, the silt plus clay fraction of borrow sources P7 through P10 ranged from 49 to 68 percent, well within the specification to have at lease 25 percent fines. Any rocks larger than 6 inches in maximum dimension were rejected from the embankment fill. Tom Peterson of Environmental Solutions, Inc. inspected the Section 28 Pond construction on the following days, with these inspections previously scheduled to identify critical construction events: August 8, 2007 September 13, 2007 September 20, 2007 October 8, 2007 October 12, 2007 October 19, 2007 November 1, 2007 November 13, 2007 September 12, 2007 September 18, 2007 September 28, 2007 October 11, 2007 October 17, 2007 October 30, 2007 November 2, 2007 Alan Jorgensen, Tony Tennyson and Kurtis Blunt also provided additional inspections. Generally, this was done almost every day that work was underway. The initial embankment fill was obtained from the impoundment interior. This source of borrow provided sufficient material for the embankment to reach above the outlet pipe Page 3