Loading...
Gold North Peer Review 1.pdf Vicinity Map, undated. Structural Plans (5 sheets including S1 through S5), prepared by Reed & Associates, PS, dated April 23, 2010. Architectural Plan Set (6 Sheets, including Sheets A-2 through A-7) prepared by Randall J. Munson, Building Designer, dated March 31, 2010. North Edmonds Earth Subsidence and Landslide Hazard Areas Map (with property location noted and signed certification as to property location), by Michael Gold and Robert J. Hughes, dated April 21 and 26, 2010. City of Edmonds Environmental Checklist, prepared by Donna L. Breske, dated April 20, 2010. Determination regarding Critical Areas Checklist CRA20100031, letter prepared by City of Edmonds Development Services Department, dated April 2, 2010. Civil Engineer’s Statement of Risk for Earth Subsidence Landslide Hazard Area, letter prepared by Donna L. Breske, P.E., dated April 22, 2010. nd Structural Engineer Declaration, SFR to be Constructed at 7510 162 Street SW, Edmonds, WA,letter prepared by Reed & Associates, PS, dated March 31, 2010. Lead Design Professional Designation and Statement, letter prepared by Reed & Associates, PS, dated March 31, 2010. Applicant/Owner liability and landslide acknowledgement, letter signed by Michael R. Gold and Nancy M. Gold, dated March, 2010. Covenant of Notification and Indemnification / Hold Harmless, signed by Mike and Nancy Gold, dated April 21, 2010. The following sections provide our review comments. GR EOTECHNICAL EPORT Note that one geotechnical report, prepared by Nelson Geotechnical Associates, Inc. (NGA) dated nd Street SW (the February 12, 2010, addresses the proposed development of two adjacent lots: 7510 162 th subject of this review) and 16220 75 Place W (the property immediately to the south). The geotechnical report provides a reasonably comprehensive evaluation and discussion of site conditions and risks, and provides geotechnical recommendations for design. However, we note that as stated within their Seismic Hazard section of their report, detailed on page 6, that “the competent cohesive soils interpreted to form the core of the site slopes are considered stable with respect to deep-seated failure.” This interpretation is further stated within the Landslide Hazard/Slope Stability section of their report, detailed on page 7, that “there is not a significant potential for deep-seated failure under current LA ANDAUSSOCIATES 6/18/2010 P:\\074\\164\\FileRoom\\R\\DraftPeerReview_tm 6-11-10.doc 2 site conditions.” We respectfully disagree that these statements adequately portray the documented large- scale, deep-seated failure mode that is documented to exist within the ESLHA. The Landau Associates summary report (2007), that is referenced in the NGA geotechnical report, also lists a study completed by Dames and Moore in 1968 which documents large scale landslides in 1947 and 1955-56. The Landau Associates (2007) summary report notes that in 1947 a large slide occurred south of the existing wharf and measured between 800 to greater than 2,400 ft long, with impacts extending up to about 1,000 ft eastward from the shoreline. The Gold property is located within the area affected by that major landslide according to mapping in the Dames and Moore (1968) report. Newspaper accounts from that time period indicate that four homes were completely destroyed, some additional homes were abandoned, and many others were significantly damaged. Photos accompanying the newspaper article are particularly compelling as to the extent of damage to the structures. It is more than likely than not that the upper 12 ft or greater, medium stiff to stiff, soils encountered within the recent NGA borings constitute slide debris soils. We also note that NGA observed slickensides in each boring “at depths ranging from about 7 to 12 feet, and as deep as 19 feet in B-1” which further supports potential past, deep-seated slide movement activities. We recommend that the hazard posed by a potential large-scale, deep-seated failure be re- evaluated and addressed in the design recommendations. The geotechnical report recommends that future vegetation management on the slope be the subject of a specific evaluation and a plan approved by the City. We concur that vegetation management is an important component in helping to maintain surficial slope stability and limit the potential for erosion. We recommend that the applicant provide additional detail regarding future landscaping plans so that the City can confirm that there is long-term plan for vegetation management beyond the measures needed for basic planting that would follow the temporary erosion and sediment control requirements. It would be appropriate that such a plan integrate common techniques to incorporate vegetation that is well-suited for protection of slopes and that does not require extensive irrigation for survival. It would also be appropriate to remind the applicant that automatic landscape irrigation systems are precluded within the ESLHA. The geotechnical report provides lateral earth pressures for retaining walls (page 16). The recommended lateral earth pressures are noted to apply to a horizontal ground surface behind the wall and the report recommends that the earth pressures be revised for other ground or surcharge loading conditions. The ground surface behind the garage retaining wall is sloping. We recommend that the lateral earth pressure design recommendations be revisited by the geotechnical engineer and revised to address the ground configuration shown on the grading plans. LA ANDAUSSOCIATES 6/18/2010 P:\\074\\164\\FileRoom\\R\\DraftPeerReview_tm 6-11-10.doc 3 SP TRUCTURAL LANS Sheet S-1 provides the basis of the structural design and we note that the structural engineer has used the lateral earth pressure and bearing values as provided in the geotechnical report. However, the geotechnical report states that the lateral earth pressure provided in the report applies to horizontal ground behind retaining walls. These lateral earth pressure values may not be appropriate for sloping ground, such as adjacent to the garage retaining wall (see previous comments regarding the geotechnical report). If the geotechnical engineer revises the lateral earth pressures to accommodate sloping ground, then it may be necessary to modify the structural design of the retaining wall accordingly. The foundation plan on Sheet S-2 provides the foundation layout and callout for footing details (F1 through F8). Five footing details (1 through 5) are provided on Sheet S-2 and four footing details (1 through 4) are provided on Sheet S-5. The numbering system and call outs for footing details need to be clarified so that there is not confusion as to which footing detail applies to which location. CP IVIL LANS Inspection, maintenance, and regular reporting of TESC measures by the Geotechnical Engineer of Record are required \[see the City of Edmonds ESLHA Temporary Erosion and Sediment Control (TESC) Requirements\]. The pre-construction meeting needs to include the Geotechnical Engineer of Record \[see City of Edmonds Earth Subsidence and Landslide Hazard Area Temporary Erosion and Sediment Control (TESC) Requirements\]. We recommend that the notes be revised accordingly. On Sheet 2, it is not clear that the perforated drains located behind the retaining walls and that surround the house foundation are to be connected to the nearby drainage system. It is not evident where the perforated drain pipe below the lower retaining wall (west of the house) will be discharged, as no drainage pipe is shown at this location. Please clarify that retaining wall drainage pipes are to be connected to the site drainage system and clearly indicate those connection locations. EC NVIRONMENTAL HECKLIST We note some incorrect statements in the Environmental Checklist section B.1. (Earth). Revisions or clarifications should be made as appropriate to address the following issues. In subsection b, we note that the maximum slope is not 36 percent as stated. The geotechnical report (NGA February 12, 2100) indicates that 36 percent is the overall slope inclination and actual slope inclinations range from 18 to 50 percent, with a small area on the east side of the property of about 100 percent. LA ANDAUSSOCIATES 6/18/2010 P:\\074\\164\\FileRoom\\R\\DraftPeerReview_tm 6-11-10.doc 4 In subsection d, the checklist states that there are no surface indications or history of unstable soils in the immediate vicinity. This is incorrect. The property is located within a well-documented landslide zone and the property and surrounding area is within the designated North Edmonds ESLHA. In subsection e, the stated quantities of cut and fill do not seem to be consistent with the quantities stated elsewhere in the permit submittal package. RSD EQUIRED TATEMENTS AND ECLARATIONS We reviewed the submittal package and confirmed that the statements and declarations from the design professional as required by the City for development within the ESLHA which include the following documents: nd Literature and Plan Review Letter, 7510 162 Street SW, Edmonds, Washington, NGA File No. 819600. Letter prepared by Nelson Geotechnical Associates, Inc., (includes a Geotechnical Hazard Identification/Declaration and Mitigation Statement of Risk), dated April 21, 2010. nd Structural Engineer Declaration, SFR to be Constructed at 7510 162 Street SW, Edmonds, WA,letter prepared by Reed & Associates, PS, dated March 31, 2010. Applicant/Owner liability and landslide acknowledgement, letter signed by Michael R. Gold and Nancy M. Gold, dated March, 2010. In general, the statements and declarations have been appropriately addressed with the exception of the Minimum Risk Statement contained in the NGA April 21, 2010 document. We recommend that the hazard posed by a potential large-scale, deep-seated failure be re-evaluated. As detailed in ECDC 23.80 “for sites where the hazards are not mitigated or where the risks from deep-seated or large-scale earth movement cannot be practically reduced by individual lot owners, the statement shall identify what hazards could not be addressed by individual lot development. The statement shall specify any risks from earth movement that are not fully mitigated by design measures and render an opinion as to whether the site will be stable within the meaning of the ordinance following installation of all proposed improvements. LA ANDAUSSOCIATES 6/18/2010 P:\\074\\164\\FileRoom\\R\\DraftPeerReview_tm 6-11-10.doc 5 * * * * * * This technical memorandum has been prepared for use by the City of Edmonds in evaluating the adequacy of permit submittal documents related to the proposed Gold (North) single family residence at nd 7510 162 Street SW. The focus of this review was the geotechnical aspects of the application. The purpose of the review was to assess the adequacy of the application documents for compliance with City requirements contained in ECDC 23.80 and ECDC 19.10 and conformance with conventionally accepted geotechnical engineering practices. This geotechnical peer review by Landau Associates does not lessen the requirements for the applicant’s geotechnical consultant and other design professionals to prepare an appropriate design for the site conditions. We appreciate this opportunity to be of service to the City. Please contact us if you have any questions or if we may be of further service. DRS/CBT/rgm LA ANDAUSSOCIATES 6/18/2010 P:\\074\\164\\FileRoom\\R\\DraftPeerReview_tm 6-11-10.doc 6