The URL can be used to link to this page

Home My WebLink AboutRS_Structural_Observation_Report_20170412_v2 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com STRUCTURAL OBSERVATION REPORT Project: Seco Development Bulkhead Purpose: Structural Evaluation Location: 1083 Lake Washington Blvd N Renton, WA Date: April 1st 2016 CG Project: 16027.10 Report: 1 Client: Seco Development General Contractor: Unknown Field Rep: Dennis Titus, PE, SE, Stephen Tabert PURPOSE AND SCOPE A field representative of CG Engineering was on site on February 2, 2016 to evaluate the condition of an existing bulkhead located on the south side of Lake Washington. While on site we met with the Greg Krape from Seco Development. EXISTING BULKHEAD The existing bulkhead is constructed form a combination of timber and concrete. Refer to SS-1. The bulkhead is approximately 585ft long and spans two properties. It was originally constructed in the mid 1920’s when the site was originally developed for a previous power plant. The bulkhead retains a sidewalk. The north portion of the sidewalk was improved during a recent site development. A concrete sidewalk and pavers were constructed and a guard rail was added along this length of the bulkhead. The sidewalk to the south, which leads to the Boeing property, is relatively unimproved and consists of a gravel base with an asphalt sidewalk. A small pier is located at the center of the bulkhead which extends approximately 20ft into Lake Washington. The bulkhead continues behind the pier. The timber portion of the bulkhead consists of 8x12 timber sheet piles. A row of timber piles spaced approximately at 8ft on center and are located directly outboard of the sheet piles. The piles vary in size but are close to 12” diameter. A 10x10 timber waler runs along the outside of the piles and tiebacks were observed spaced at approximately 15’ on center. Along most of the bulkhead the waler was no longer present and the tiebacks were no longer attached. The top of the timber sheet piles and the round timber piles are located approximately 30” below the adjacent grade. A single row of ecology blocks are located upland of the sheet pile wall. The ecology blocks are 3x3x3ft with a 10” concrete cap on top. The area below the ecology blocks was probed and it appears that only one ecology block is present which bears on the soil directly behind the sheet pile wall. The ecology blocks appear to be part of the original construction or installed shortly after the timber portion of the bulkhead was constructed. The timber bulkhead appears to support the base of the existing concrete ecology blocks which supports the subgrade for the sidewalk. OBSERVATIONS At the time of the observation the lake water level was low in anticipation of upcoming rainfall, which left the tops of the piles visible. The piles, sheet piles and walers were observed during the site visit. Each was visually inspected for structural deficiencies. They were probed above and below the water level. They were also sounded for core rot. Seco Development Bulkhead April 10, 2017 Project number: 16027.10 Page 2 of 9 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com Piles In general, the portions of the piles that were constantly submerged were in good condition. Very minor structural defects or rot was observed below the water level. Areas of rot were observed in the portion of the piles that were occasionally or consistently above the water level. Sheet Piles The sheet piles are the main retaining element of the bulkhead. They extend above the water level for a large part of the year. The tops of the sheets piles all showed signs of deterioration above the water level. Below the water level they were probed and were found to be in good condition. Walers The walers span between the piles and are used to attach the bulkhead system to the anchors. In many locations the walers were missing. The walers that were present were observed. The waler conditions varied but areas of rot were observed in several of them. Others showed signed of wear but were otherwise structurally sound. Many of the walers were missing. Tiebacks The tiebacks were observed throughout the bulkhead. They appeared to be 7/8” or 1” diameter steel rods which extended upland under the sidewalk. The spacing was somewhat irregular but appeared to be close to 15ft on center. Typically tiebacks of this era would be connected to a concrete deadman located behind the wall but this could not be verified during the site visit. The tieback rods were mostly submerged. Where the tiebacks were visible they appeared be corroded. In their current condition it does not appear that the tiebacks are functioning as there were intended. Ecology Blocks The ecology blocks are located behind the sheet piles. The area below the ecology blocks was probed and it appears that they consist of only one course of blocks and do not extend below grade. In some areas they were slightly undermined. In the area that had been improved during the recent development, the sidewalk and pavers were installed up to the ecology blocks. The ecology blocks were observed along the length of the bulkhead and appeared to be in good condition. RECOMMENDATIONS Areas of damage were observed in the bulkhead. The portion of the bulkhead that is permanently below the water level appears to be in good condition with little signs of structural defects. Where the timber portion of the bulkhead is periodically or permanently exposed to air, rot and structural defects were observed. This is common of freshwater timber construction. Typically rot will affect the wood at the air water interface. Behind the sheet piles the ecology blocks also appear to be in good condition. The surrounding site is currently being redeveloped. To maintain the integrity of the bulkhead for the new development we recommend upgrading the bulkhead. The existing timber piles, waler and spacer could be removed and a new steel sheet pile wall could be installed adjacent to the existing timber sheet pile wall. Refer to SS-2. The existing timber sheet pile wall supports the soil directly under the existing ecology block. To maintain the stability of the existing ecology blocks and the bank during construction, the existing timber pile wall should be left in place. This will help protect the Seco Development Bulkhead April 10, 2017 Project number: 16027.10 Page 3 of 9 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com shoreline and minimize disturbance to the lake. The area between the new sheet pile wall and the existing sidewalk will need to be filled to prevent settlement and movement of the sidewalk. The existing sidewalk pavers and guard rail then be extended to the steel sheet pile wall. CONCLUSIONS The proposed upgrade to the bulkhead would result in removing all of the existing piles outboard of the bulkhead. The proposed upgrade would also minimize the disturbance to the lake during construction. With regular maintenance it is not unreasonable to assume that the bulkhead could have an operational life of 50 years or more. DISCLAIMER This observation is the professional opinion of CG Engineering PLLC based on the information available during this assessment or evaluation. This report does not warrant or guarantee that all conditions were discovered at the time of the observation. This report was prepared subject to the standard of care applicable to professional services at the time the services were provided. 04/10/2017 Seco Development Bulkhead April 10, 2017 Project number: 16027.10 Page 4 of 9 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com Photo 1 – Aerial Image of Project Site Photo 2 – Bulkhead at Improved Sidewalk BULKHEAD W/ UNIMPROVED SIDEWALK PIER W/ BULKHEAD BEHIND BULKHEAD W/ IMPROVED SIDEWALK Seco Development Bulkhead April 10, 2017 Project number: 16027.10 Page 5 of 9 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com Photo 3 – Bulkhead at Unimproved Bulkhead Photo 4 – Typical Construction WALER 12” DIA PILE TIMBER SPACER SHEET PILE Seco Development Bulkhead April 10, 2017 Project number: 16027.10 Page 6 of 9 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com Photo 5 – Probing Piles above Water Level Photo 6 – Rot in Pile above Water Line Seco Development Bulkhead April 10, 2017 Project number: 16027.10 Page 7 of 9 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com Photo 7 – Probing Piles below Water Level Photo 8 – Deterioration in Pile above Water Line Seco Development Bulkhead April 10, 2017 Project number: 16027.10 Page 8 of 9 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com Photo 9 – Sound Pile at Waterline Photo 10 – Missing Waler Seco Development Bulkhead April 10, 2017 Project number: 16027.10 Page 9 of 9 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph. 425.778.8500 | f. 425.778.5536 www.cgengineering.com Photo 11 – Typical Top of Sheet Pile Photo 12 – Typical Anchor (Waler Missing)