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HomeMy WebLinkAboutICE_DFR 1.1147001.033116 (2).pdf Daily Field Report Prepared by: Brian Beaman Project No: 1147-001 Date: 03/31/2016 Signature: Location: Canyon Terrace, Stormwater Pond Berm Repair, Intersection of SE 192nd Street and 124th Avenue SE, Renton, Washington Arrival: 0950 Weather: Clear, 60’s Owner: Summit Homes Departure: 1305 Reviewed by: Client: City of Renton Page: 1 of 1 Report No: 1 Distribution (email): Ann Fowler, City of Renton Attachments: Photos (ICE File) At the request of Ann Fowler, Civil Engineer II with the City of Renton, Brian Beaman of Icicle Creek Engineers (ICE) completed a site visit to the stormwater pond located within the Canyon Terrace residential project located northwest of the intersection of SE 192nd Street and 124th Avenue SE in Renton, Washington. The Canyon Terrace project is owned by Summit Homes. The purpose of our site visit was to provide a secondary geotechnical review of the repair of a berm in a stormwater pond. We understand that the stormwater pond was constructed during 2015 and had been used for construction-related stormwater runoff. On December 9, 2015, heavy rain combined with other mechanical factors (the overflow system apparently was turned off), the stormwater pond overflowed and caused a breach (erosional notch) in the northeast corner of the stormwater pond. GeoGroup Northwest (NW), the geotechnical engineer of record for this project (under contract with Summit Homes), evaluated the stormwater pond breach and recommended that a “cement-treated shear key” be installed along the longitudinal crest of the berm; an approximately 20- to 22- foot long area between the existing structural concrete wall (that forms the east side of the stormwater pond) to a gravity type wall (block wall) that parallels the north side of the stormwater pond. The GeoGroup NW plan was to excavate a trench along the crest of the existing berm, with the base of the trench embedded at least 2 feet into a “dense soil” considered to be the native glacial till that underlies this area. At the time of our site visit we with met with Brad Stucco, Inspector with the City or Renton, Steve Moore with Summit Homes and Bill Chang with GeoGroup NW. The original meeting time was for 10:00 AM but was delayed as Dr. Chang did not arrive until about 11:30 AM. The trenching was completed using a Kubota KX71-7 mini-trackhoe provided by Summit Homes. Excavated soils were placed in the bucket of a Deere 544J front-end loader which transported the excavated soils away from the stormwater pond area for disposal. Excavation began at the concrete wall and extended west. The footing for the wall was encountered at about 8 feet below the top of the berm. The overlying soils were fill consisting of medium dense silty gravel with sand and cobbles and occasional pieces of straw to a depth of about 5 feet. Below a depth of about 5 feet, the fill became dense with no straw. Native soil (glacial till) was not observed. We also observed a 3-foot wide zone filled with 5/8-inch-minus crushed rock adjacent to the concrete wall. Dr. Chang indicated that this was the eroded zone of fill that occurred during the breach (overtopping) of the berm. Dr. Chang indicated that the dense fill will provide the same protection from seepage as the native glacial till. We were not in total agreement with that opinion, but because the berm did not fail as a result of seepage (the berm was overtopped and eroded), it likely does not make a difference. In our opinion, the berm could have been repaired by simple replacement of structural, low permeability fill in the eroded zone. However, the same product resulted and the berm should perform as intended with the “shear key” that is being installed. The trench was completed to the depth of 8 feet at the concrete wall, then became gradually shallower to the west (about 5-feet deep at the west end). The base of the excavation (about 2-feet wide) was cleaned to the extent this was possible, using the trackhoe bucket. The trench was about 20-feet long. We understand that the trench was to be backfilled with controlled density fill (CDF); we left the site prior to CDF placement.