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REVIEWED PLN BLD2024-1470+GEO REPORT+11.7.2024_1.33.34_PM+4607705GeolecEngineers, GeologistsGroup Northwest, Inc. & Environmental Specialists October 1, 2024 Ms. Molly Jenkins 18914 — 94th Ave W Edmonds, WA 98020 mo llykaiserman(d`gmail. com RECEIVED Nov 08 2024 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT G-5362-1 BLD2024-1470 Subject: GEOTECHNICAL REPORT I Reviewed by I PROPOSED DECK ADDITION : City of Edmonds ; 18914 — 94TH AVE W It Planning Division EDMONDS,WASHINGTON--------------- Dear Ms. Jenkins: In accordance with our August 21, 2024 contract with you we have prepared the following geotechnical report for the proposed development. We previously provided a geotechnical/critical areas report' and addendum2 for an earlier addition/development at the site. It is our understanding that a portion of that earlier addition work, namely the previously proposed west deck did not occur and that development was limited to a southeast entryway expansion. SITE AND PROJECT DESCRIPTION The project site consists of a developed residential lot at the subject address as shown on the attached Plate 1 - Vicinity Map. An existing one-story home with daylight basement is located near the central portion of the lot as shown on the attached Plate 2 — Topographic Survey. The house has a main floor level deck at the north side of the house. The subject site is mostly flat at the east side of the lot. At the north and west sides of the existing development there are primarily gentle to moderate inclination west and northwest - facing slopes. There is one area of around 93 square feet which appears to meet the Edmonds Development Code definition for steep slopes and this area is delineated on the attached Plate 2 — Topographic Survey. 1 "Geotechnical Report — Critical Areas Report, Proposed Addition and Deck, 18914 — 94t1i Ave W, Edmonds, Washington", GEO Group Northwest, Mar. 4, 2021. 2 "Addendum Letter, Proposed Addition and Deck, 18914 — 94t1' Ave W, Edmonds, Washington," GEO Group Northwest, Aug. 4, 2021. 13705 Bel -Red Road, Bellevue, Washington 98005 Phone 425/649-8757 • Fax 425/649-8758 October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 2 Based upon our review of the Edmonds GIS we understand that the following potential geologically critical areas are mapped for the west portion of the lot and at the adjacent west property: Severe Erosion Hazard 15-40% and Landslide Hazard 40%. GEO Group Northwest has been provided with a development plan for the proposed deck addition prepared by Alexandra Immel Residential Design and attached herein as Plate 3 — Site Plan. The plan indicates that a new deck is proposed at the west side of the residence at the northwest building corner. We understand that this deck will be at the main floor level and will be fully supported by new foundations consisting of four column footings as shown on the attached Plate 4 — Prelim. Plan — Lowest Level. GEOLOGIC CONDITIONS The geologic map3 for the site indicates that the subject lot is underlain by Quaternary aged Vashon Till (Qvt) and Advance Outwash (Qva). The till deposit consists of a mixture of gravel, silt and sand which was overridden by glacial ice during the most recent period of glaciation. The outwash soils reportedly consist of predominately sand and gravel which was deposited by flowing meltwater as glaciers advanced into the region during the last period of glaciation. SUBSURFACE CONDITIONS GEO Group Northwest explored the subsurface soil and groundwater conditions by advancing three hand-augered borings labeled HA-1 through HA-3 on February 11, 2021 and two hand- augered borings labeled HA-4 and HA-5 on September 11, 2024. The borings were located approximately as shown on the attached Plate 2 — Topographic Survey, Plate 3 — Site Plan and Plate 4 — Prelim. Plan — Lowest Level. The borings HA-4 and HA-5 were excavated specifically related to the currently proposed deck addition. Soils encountered at the HA-4 location consist of variable loose to dense sandy SILT / silty SAND with some debris indicative of fills overlying dense apparent glacial till, sandy SILT with some gravel at a depth of 28-inches below ground surface (bgs). At the boring HA-5 dense sand and silt mixtures with some gravel and cobbles were observed, indicative of the mapped glacial till soils. 3 "Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles", USGS, Minard, 1983. GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 3 Soils encountered at the borings HA-1 and HA-2 consist of medium dense to dense sandy SILT with varying amounts of gravel/cobbles (topsoil) overlying dense silty SAND and sandy SILT with varying amounts of gravel (till) at a depth of around 8-inches below ground surface (bgs). Soils encountered at the boring HA-3 consist of medium dense sandy SILT (topsoil) overlying loose to medium dense sandy SILT and silty SAND with occasional gravel, apparent fill, at a depth of 9-inches bgs. Underlying the apparent fill at a depth of 29-inches is dense gravelly fine sandy SILT (till) at the HA-3 location. The observed underlying dense soils appear to match the description for glacially consolidated Vashon Till (Qvt). Groundwater seepage was not encountered at the boring locations. It is important to note that seepage levels may vary dependent upon the time of year and changes in surrounding development conditions. The results of our subsurface investigation are shown on the attached Appendix A — Hand - Angered Boring Logs & USCS Soil Legend. EDMONDS GEOLOGIC HAZARDS — CRITICAL AREAS EVALUATION Based upon our review of the City of Edmonds GIS the subject site is mapped as having a known or suspect erosion and landslide hazards. The Edmonds Municipal Code defines Erosion Hazards and Landslide Hazards as Critical Areas — Geologically Hazardous Areas. Erosion Hazard The Edmonds Code defines Erosion Hazard Areas per the following: 23.80.020 Designation of specific hazard areas. A. Erosion Hazard Areas. Erosion hazard areas are at least those areas identified by the U.S. Department of Agriculture's Natural Resources Conservation Service as having a "moderate to severe, " "severe, " or "very severe " rill and inter -rill erosion hazard. Erosion hazard areas are also those areas impacted by shoreland and/or stream bank erosion. Within the city of Edmonds erosion hazard areas include: 1. Those areas of the city of Edmonds containing soils that may experience severe to very severe erosion hazard. This group of soils includes, but is not limited to, the following when they occur on slopes of 15 percent or greater: GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 4 a. Alderwood soils (15 to 25 percent slopes); b. Alderwood/Everett series (25 to 70 percent slopes); c. Everett series (15 to 25 percent slopes); 2. Coastal and stream erosion areas which are subject to the impacts from lateral erosion related to moving water such as stream channel migration and shoreline retreat; 3. Any area with slopes of 15 percent or greater and impermeable soils interbedded with granular soils and springs or ground water seepage; and 4. Areas with significant visible evidence of ground water seepage, and which also include existing landslide deposits regardless of slope. We have reviewed the online USDA Web Soil Survey with regard to erosion susceptibility at the subject site. The mapped site soils are Alderwood gravelly sandy loam and Alderwood-Everett gravelly sandy loam, with the former being the majority (90%). These soils are described has having a low erosion risk with K factors for the whole soil unit ranging from 0.05 to 0.1. Per the site topographic survey the maximum slope inclination at the site for a minimum run of 25-feet (min. 10-ft vertical relief) is 46 percent from the horizontal and this slope area is at the northwest portion of the lot, having a size of around 93 square feet. Other than this limited area much of the west and northwest sloping areas have moderate inclinations. Our slope inclinations noted here include the vertical relief due to existing landscaping rockeries. The site qualifies as having Alderwood series soil with slope inclination in the range specified within the Code to qualify as an Erosion Hazard Area. Based upon our site investigation the subject site does not meet the criteria for items #2, 3 or 4 pertaining to Erosion Hazard classification. At the time of our subsurface investigation in both 2021 and 2024 we observed the current slope conditions at the site. We did not observe signs of recent erosion or landsliding such as bare soil areas, scarps, slumps or set -downs. Site soils consist of primarily silty SAND and sandy SILT with varying amounts of gravel. Based upon our site investigation the site is not particularly prone to erosion risks. The erosion risks for the proposed development are low. The erosion risks at the steep slope area are moderate. However, no development or alteration is proposed at the steep slope area. GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 5 We recommend that the erosion risks related to the proposed deck development are mitigated by implementing standard erosion control Best Management Practices (BMPs) and that the recommendations contained herein are properly implemented. Erosion hazard mitigation for the temporary construction condition is recommended to include the installation and maintenance of filter fabric fences (silt fences) at the downhill side of the work area and the placement of silt socks at the nearest catchbasin which has the potential to collect site surface water, if any basins are located within 50-feet of the work area and are located downhill from the work area. For the permanent condition we recommend that erosion risks are mitigated by restoring the ground surface with hardscape or by planting and maintaining appropriate drought -tolerant native vegetation. Provided that our erosion hazard mitigation recommendations are properly implemented and maintained during and following the proposed development it is the opinion of GEO Group Northwest that the proposed development: 1. Will not increase the threat of the geological hazard to adjacent properties beyond predevelopment conditions; 2. Will not adversely impact other critical areas; 3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal or less than pre -development conditions, and 4. Are certified as safe as designed and under anticipated conditions, by a qualified engineer or geologist licensed in the State of Washington. Landslide Hazard The Edmonds Code defines Landslide Hazard Areas per the following: 23.80.020 Designation of specific hazard areas. B. Landslide Hazard Areas. Landslide hazard areas are areas potentially subject to landslides based on a combination of geologic, topographic, and hydrologic factors. They include areas susceptible because of any combination of soil, slope (gradient), slope aspect, structure, hydrology, or other factors. Within the city of Edmonds potential landslide hazard areas include: GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 6 1. Areas of ancient or historic failures in Edmonds which include all areas within the earth subsidence and landslide hazard area as identified in the 1979 report of Robert Lowe Associates and amended by the 198E report of GeoEngineers, Inc., and further discussed in the 2007 report by Landau Associates; 2. Coastal areas mapped as class u (unstable), uos (unstable old slides), and urs (unstable recent slides) in the Department of Ecology Washington coastal atlas; 3. Areas designated as quaternary slumps, earthflows, mudflows, or landslides on maps published by the United States Geological Survey or Washington State Department of Natural Resources; Simple Slope Calculation The slope calculation guidance shall be used to determine the toe and top of % slope for slopes that are potentially landslide hazard areas or potentially erosion hazard areas. Toe and top of landslide hazard areas (generally slopes of 40% or greater) delineated where incline reverses or diminishes to <40% over at least 10 feet of horizon to I distance. Toe and top of erosion hazard areas (generally slopes 15-40%) delineated where incline reverses or diminishes to <15%over �f I-f 1 n foot of V.nr� �nn4�l .i � c4�nre <40%slop hazard are slope (ero area) over min 10 it 10, Top of Slope I/ 96 Slope= VNertiwlRise) x100% H (Horizontal Run) Note: Steps, gradient changes, and incline reversals or breaks below percent slopes derini ng landslide hazard areas (40%) and erosion hazard areas (15%) shall be included as part ofthe larger slope. Figure 1 4. Any slope of 40 percent or steeper that exceeds a vertical height of 10 feet over a 25 foot horizontal run. Except for rockeries that have been engineered and approved by the engineer as having been built according to the engineered design, all other modified slopes (including slopes where there are breaks in slopes) meeting overall average steepness and height criteria should be considered potential landslide hazard areas); ULU Croup Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 7 5. Any slope with all three of the following characteristics: a. Slopes steeper than 15 percent; b. Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment; and c. Springs or ground water seepage; 6. Any area potentially unstable as a result of rapid stream incision or stream bank erosion; 7. Any area located on an alluvial fan, presently subject to, or potentially subject to, inundation by debris flow or deposition of stream -transported sediments; and 8. Any slopes that have been modified by past development activity that still meet the slope criteria. GEO Group Northwest is aware of the Meadowdale area earth subsidence hazard area and the subject site is not located within this area. Based upon the DOE coastal atlas online mapping the subject site is located in an area which is mapped as "stable". GEO Group Northwest is not aware of any mapping by the USGS or WA DNR denoting the subject site as containing slumps, earthflows, mudflows or landslides. GEO Group Northwest did not find evidence of springs or seeps at the property at the time of our subsurface investigations. We also did not observe the presence of slope movement indicators such as bare earth, soil cracks, slump blocks, hillocky ground or bare soils areas. Based upon our subsurface investigation the underlying soils at the subject site consist of dense and competent glacial till soils. In general, these soils are relatively stable due to their well - consolidated condition. Alluvial fan soils are not located at the site. Loose to medium dense soils, if located overlying the dense soils at the steep slopes located at the northern half of the west yard area present a relatively low risk of soil movement. Our site investigation indicates that the competent and stable till soils are at relatively shallow depth at the investigation locations. Additionally, we did not observe groundwater seepage or surface water drainage concerns at the subject site. GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 8 GEO Group Northwest has delineated the apparent steep slope area (slope of 40% or steeper) per the code section 23.80.020 as shown on the attached Plate 2 — Topographic Survey. The code specifies that potential landslide areas may consist of steep slopes having inclinations of 40% or steeper and a minimum height of 10-feet. Additionally, there is a diagram in the code regarding the determination of top and bottom of slope using the 10-foot minimum horizontal dimension. Proposed development at the site is not proposed for the steep slope areas or anywhere within 24-feet of the delineated on -site steep slope areas. The area of delineated steep slopes having a height of 10-feet or greater is estimated to be around 93 square feet. In summary, based upon the topographic survey the area of 40% or greater slopes at the site is minimal and inconsequential such that, in our opinion, the subject site does not qualify as a Landslide Hazard Area. SEISMIC DESIGN CRITERIA Based upon the subsurface investigation it is our opinion that the overlying 100-foot thickness of soils at the project site may be characterized as Site Class C soil (Very Dense Soil and Soft Rock) and may be designed accordingly for seismic loads per the IBC. According to an online Seismic Hazard tool the seismic coefficients are as follows: SS = 1.297 Si — 0.458 For the design seismic event the site modified peak ground acceleration is 0.665g. CONCLUSIONS AND RECOMMENDATIONS Based upon our subsurface investigation the proposed development is acceptable for the subject site soil conditions. We recommend that the footings for the new deck addition are constructed to bear on top of the underlying competent medium dense to very dense glacially consolidated site soils or compacted structural fills placed on top of the competent soils. Based upon our investigation it appears that over -excavation may be necessary at some footing locations, however, there are also areas where the competent soils were encountered at typical shallow foundation depths, requiring no over -excavation. Where loose soils are encountered at the footing subgrades then over -excavation and replacement with compacted structural fill is recommended. GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 9 We recommend that all foundation subgrades and compacted structural fills are approved by GEO Group Northwest at the time of construction, prior to foundation pour(s), in order to confirm compliance with the geotechnical recommendations. We recommend that the following recommendations and design parameters be incorporated into the design for the development. Site Preparation, General Earthwork and Rockeries The proposed development areas should be stripped and cleared of surface vegetation, organic soils (topsoil) and loose soils. Silt fences should be installed around areas disturbed by construction activity to prevent sediment -laden surface runoff from being discharged off -site. Exposed soils that are subject to erosion should be compacted and covered with plastic sheeting. Stockpiled soils should be covered with plastic sheeting if work is done during wet weather in order to mitigate off -site sedimentation risks. We recommend that the areal size of the excavation for the deck footings be minimized where located in close proximity to the existing rockeries, so as to mitigate the risk of damage to the rockeries and the necessity of re -building portions of the rockeries. If portions of the existing rockery having a maximum height of 2.5-feet require re -construction due to the new foundation then we recommend that the rockery is re -built in accordance with the attached Appendix B — Association of Rockery Contractors - Standard Rock Wall Construction Guidelines. As noted in the foundation section of this report, the new deck foundations shall not place loads on the rockery itself and the base of the footing shall be founded on top of the competent glacially consolidated soils or compacted structural fills placed on top of those soils. Temporary Excavation Slopes and Permanent Slopes Under no circumstances should temporary excavation slopes be greater than the limits specified in local, state and national government safety regulations. Temporary cuts greater than four feet in height should be sloped at an inclination no steeper than 1H:1V (Horizontal:Vertical) in the overlying loose to medium dense site soils. If seepage is encountered at the building pad excavations, then temporary slopes should have inclinations of no steeper than 2H:1 V.. GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 10 We recommend that permanent graded slopes shall be sloped no steeper than 3H:1V unless faced by a rockery and that any fills placed at the areas where inclinations are steeper than 4H:1 V are compacted to meet the structural fill compaction requirements. Structural Fill All fill material used to achieve design site elevations below the building areas and below non - structurally supported slabs, parking lots, sidewalks, driveways, and patios, should meet the requirements for structural fill. During wet weather conditions, material to be used as structural fill should have the following specifications: 1. Be free draining, granular material containing no more than five (5) percent fines (silt and clay -size particles passing the No. 200 mesh sieve); 2. Be free of organic material and other deleterious substances, such as construction debris and garbage; 3. Have a maximum size of three (3) inches in diameter. All fill material should be placed at or near the optimum moisture content. The optimum moisture content is the water content in soil that enables the soil to be compacted to the highest dry density for a given compaction effort. Based upon our subsurface investigation the overlying site soils consist of silty soils which are moisture sensitive and fine-grained. These soils are not recommended to be placed as structural fill due to the difficulty of achieving the compaction criteria. It may be possible to use the native soils for structural fills if they are to be placed during dry summer months if they can be adequately dried and compacted. Alternatively, it may be beneficial and more efficient to import a free -draining granular fill material meeting the specifications noted above, especially if work is to be performed during a period of wet weather. Structural fill should be placed in thin horizontal lifts not exceeding ten inches in loose thickness. Structural fill under building areas (including foundation and slab areas) and behind earth reinforced retaining walls (segmental block retaining walls and geo-grid reinforced rockery walls), should be compacted to at least 92 percent of the maximum dry density, as determined by ASTM Test Designation D-1557-91 (Modified Proctor). GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 11 Structural fill under driveways, parking lots and sidewalks should be compacted to at least 90 percent maximum dry density, as determined by ASTM Test Designation D-1557-91 (Modified Proctor). Fill placed within 12-inches of finish grade should meet the 92% requirement. We recommend that GEO Group Northwest, Inc., be retained to evaluate the suitability of structural fill material and to monitor the compaction work during construction for quality assurance of the earthwork. Spread Footing Foundations The proposed deck foundations may consist of conventional spread footings bearing on top of the underlying medium dense to dense competent glacially consolidated site soils or on compacted structural fill which is placed and compacted on top of the competent soils. The footings should not be constructed on top of loose fills and also shall not place loads on the adjacent rockery. To mitigate the risk of building surcharge at the rockery the bottom of the footing shall be lowered as necessary, dependent upon distance from the outside edge of the footing to the rear of the rockery, such that an imaginary plane projected downward at a 1H:1V from the footing does not intercept the existing rockery. The maximum height of the rockery adjacent to the deck is 2.5-feet. Loose soils present settlement related risks to the foundations. Based upon the subsurface investigation it is anticipated that the competent soils may be present at typical shallow foundation depths at some locations, however, there may be a need for over -excavation at some footing areas, specifically the northwestern -most assumed preliminary footing location. At the northwestern -most footing location, boring HA-4 the competent soils were encountered at a depth of 28-inches below the existing ground surface. We recommend that where loose soils are encountered at the footing subgrades that these areas are over -excavated to expose the underlying competent medium dense to dense glacially consolidated soils. Compacted structural fill may then be placed and compacted in the over -excavated area in order to fill the over - excavated area to the proposed footing subgrade level. Structural fills should be placed and compacted in accordance with the Structural Fill section of this report. We recommend that all foundation subgrades are approved by GEO Group Northwest at the time of construction, prior to the foundation pour, in order to confirm that the subgrades consist of the competent soils and that they have been properly prepared. Individual spread footings may be used for supporting columns and strip footings for bearing walls. Our recommended minimum design criteria for foundations bearing on the medium dense GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 12 to dense competent glacial till site soils or on compacted structural fill placed on top of these soils are as follows: Allowable bearing pressure, including all dead and live loads Medium dense to dense glacially consolidated soils = 2,000 psf Compacted structural fill on top of the medium dense to dense competent native soils = 2,000 psf - Minimum depth to bottom of perimeter footing below adjacent final exterior grade = 18 inches Minimum width of wall footings = 16 inches - Minimum lateral dimension of column footings 24 inches - Estimated post -construction settlement = 1 /4 inch A one-third increase in the above allowable bearing pressures can be used when considering short-term transitory wind or seismic loads. Lateral loads can also be resisted by friction between the foundation and the supporting compacted fill subgrade or by passive earth pressure acting on the buried portions of the foundations. For the latter, the foundations must be poured "neat" against the existing undisturbed soil or be backfilled with a compacted fill meeting the requirements for structural fill. Our recommended parameters are as follows: - Passive Pressure (Lateral Resistance) 350 pcf equivalent fluid weight for compacted structural fill 350 pcf equivalent fluid weight for native dense soil. - Coefficient of Friction (Friction Factor) 0.35 for compacted structural fill 0.35 for native dense soil GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 13 Drainage Considerations Groundwater seepage conditions were not encountered at the borings and it is understood that column footings are proposed for the new deck. Therefore, we do not have subsurface drainage recommendations related to the proposed deck addition. If it is discovered that the building perimeter footing drains are missing or damaged than we recommend that footing drains are installed in accordance with the following. We recommend that subsurface drains (footing drains) be installed at the perimeter of continuous spread footings and tightlined to an approved discharge point or stormwater system. Footing drains should consist of a four -inch minimum diameter, perforated, rigid PVC drain pipe laid at the bottom of the footing with a gradient sufficient to generate flow. The footing drain line should be bedded on and surrounded with drain rock or other appropriate, free -draining, granular material. The drain rock should be wrapped in a layer of geotextile fabric such as Mirafi 18ON or equivalent. After the footing drains are installed, the excavation should be backfilled with compacted structural fill material. Under no circumstances should roof downspout drain lines be connected to the footing drainage system. All roof downspouts should be separately tight lined to an appropriate storm -water discharge point. We recommend that sufficient cleanouts be installed at strategic locations in each of the drainage systems to allow for periodic maintenance of and clearing of possible future blockages. ADDITIONAL SERVICES We recommend that GEO Group Northwest Inc. be retained to perform a general plan review of the final design and specifications for the proposed development to verify that the earthwork and foundation recommendations have been properly interpreted and implemented in the design and in the construction documents. We also recommend that GEO Group Northwest Inc. be retained to provide monitoring and testing services for geotechnically-related work during construction. This is to observe compliance with the design concepts, specifications or recommendations and to allow design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. We anticipate that geotechnical construction monitoring inspections may be necessary for the following construction tasks: GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 14 1. Foundation subgrade preparation and verify bearing conditions; 2. Structural fill placement and compaction; LIMITATIONS This report has been prepared for the specific application to this site for the exclusive use of Molly Jenkins and her authorized representatives. Any use of this report by other parties is solely at that parry's own risk. Our findings and recommendations stated herein are based on field observations, our experience and judgement. The recommendations are our professional opinion derived in a manner consistent with the level of care and skill ordinarily exercised by other members of the profession currently practicing under similar conditions in this area and within the budget constraint. No warranty is expressed or implied. In the event that soil conditions not anticipated in this report are encountered during site development, GEO Group Northwest, Inc., should be notified and the above recommendations should be re-evaluated. If there are any questions, please do not hesitate to contact us. Sincerely, GEO GROUP NORTHWEST, INC. 2011� o F FGI STE�`� SS�ONAL EN 10-1-24 Adam Gaston William Chang, P.E. Project Engineer Principal GEO Group Northwest, Inc. October 1, 2024 G-5362-1 Geotechnical Report — 18914 — 94th Ave W, Edmonds, WA Page 15 Attachments: Plate 1 — Vicinity Map Plate 2 — Topographic Survey Plate 3 — Site Plan Plate 4 — Prelim. Plan - Lowest Level Appendix A — Hand-Augered Boring Logs and USCS Soil Legend Appendix B — Standard Rock Wall Construction Guidelines GEO Group Northwest, Inc. Chris SolilhWeal CounV Park I-W Crosswis) E Park Cyphers Jeannette A United States Postal Service 9 in Seaview Park Off -leash ©Lynndade DugArea Hull Park Brandon Maldonado 9 Seaview 45 dernentairy School PEARINVILLE 19 is 4 AW. &Edrn.r d O11 A 98020 P;jrk T 9 As-sociales Maggie Lawrerce 9 Portofino 1, Restaurant & Bar Edmonds Sovonlh-Day Adyiuntim Church V Royal India Lyn%vo<A Pizza Flu, 7 Grace Lo1hr-ran Church QFC 19611, �l sw 9 'F'1'r`rn0Pn4v'iry School I'"inwood Ice Ctrwn Maplewood all VICINITY MAP Group Northwest, Inc. 18914 - 94TH AVE W 13705 Bel -Red Rd, Bellevue, WA 98005 Phone 425/649-8757 FAX 425/649-8758 EDMONDS, WASHINGTON Email info@geogroupnw.com SCALE: NTS DATE: 9-26-24 1 MADE: AG JOB NO.: G-5362-1 PLATE: 1 SYMBOLS MONUMENT IN CASE FOUND SURVEY MARKER AS NOTED ���O,,,JJJ CONIFER TREE DECIDUOUS TREE Q. DNA SURVEY CONTROL SHRUB/RHODODENDRON m POWERITELEPHONE JUNCTION BOX ® GAS METER m GAS VALVE CULVERT It YARD LIGHT ❑ STORM CATCH BASIN O SANITARY SEWER MANHOLE ® WATER METER A POWER POLE GC= ROCKERY 0 .p I IMrs MIE-2:41 ABBREVIA BONS M MAPLE TREE F FIR TREE C CEDAR TREE HEM HEMLOCK TREE B BIRCH TREE CH CHERRY TREE DEC DECIDUOUS TREE SSMH SANITARY SEWER MANHOLE CB STORM DRAIN CATCH BASIN IE INVERT ELEVATION BOT BOTTOM STRUCTURE P.A. PLANTED AREA II TYPES: EDGE OF ASPHALT - RIGHT OF WAY CENTERLINE - - RIGHT OF WAY BOUNDARY LINE �[ i_ FENCE LINE ---- 0---- O — UNDERGROUND GAS LINE ----E--- UNDERGROUND POKER LINE ----/E---- OVERHEAD POWER LINE ---T----T— UNDERGROUND COMMUNICA DONS LINE ---10----W— UNDERGROUND STORM LINE ----M----N— UNDERGROUND SEWER LINE --- N---- 9— UNDERGROUND WATER LINE / N8 fEN� � 8••00 4Dj / .- ROCK/$R/CK PATH O / � / / BRICK PLANTE! ,-HA 5 1 A-3 18914 I r I I COC PAD O 94TH AVENUE W. GRASS I DHA 3077-12 TWO-STORY HOUSE TACI IN HUB BASEMENT FINISH FLOOR N J 5499.809 ELEV-256.0' E I 55J0..305 I ELEI 253.37' 2-N l I it CD l 1 OD P. A. 4 'CHAfNUNK FENCE GGNW DELINEATE STEEP SLOPE PER CODE 23.80.020 (HATCHED AREA) Sfope Table Number 1(inlmum Slope Maximum Slope Color 1 Qoix JB.99R 7 4BOQT 400.00A 50. E MIY 28AB LE S M8 8N 7 DNA J077-4 — \ TACK IN HUB N J05552.787 E 1265602.384 ELEV 255.55' I I 1 I I lY OWALL NOT LOG TEO / I V I I I I I I I ; t 4-BB 11 L T [� I I - OR/VEAi j- I 11 DRI VF , I II'L ifI IIWLINKKRFENCE a l u E I ;I O I 1 I I 7- - WTI IASPHALT 58 �S f �s10 ^" 6 "DEC I ASPHALT DNA J DRIVE vl II MAG N N JOS. E 126: I 31 I ELEV ^yam I I I I \ o ,, W Gr--+G-- -- ----G 4 pp I GV - won I I W I I I IBASED UPON THE TOPOGRAPHIC SURVEY BY DUANE HARTMAN AND ASSOCIATES, I-28-21. o� N NOW f'-11M I l u I (E) 36 FIR TREE 2(E)8 xl6 I PARKING SPACES i I E (E)18" FIR TREE 25'-0" } STREET SETBACK WATER METER E IFIRC DATUM POINT FOR HEIGHT ti ti CALCULATIONS 0 SEE TOP OF SS MANHOLE t'.'e.. HEMLOCK TREk d I H (E) ASPHALT DRIVEWAY cn -% 1387.15 ft,%. CATCH BASIN, TYP. �) 6" MAP E 6 CHERRY \ (E)$ MAPLE APPROX. SEWER LINE TREE TREE # TREE tt ' Sd LOCATION, VERIFY AIR :`. ,��do 0114'- 6 ; } : f'�3 sq ;o0zaaz�1I n � I I E ED 36" CEDAR �6, (E) GARAGE �I i I (N)DECK ABOVE 185 fl TREt o I 505.61 sq ft/ o U 99.01 sq _�Z _ {E)6" C.TREE / I } (E) CONC. PATIO HA-4 CURB AND WALKWAYS ILDING (E) �( ?5'-0" 577.57 ft FOOTPRINT, 13.61 socl ft SETBACK H 5 1,756.36 sq ft (E) 4„ A-3 C' /(N) ADDITION y`z / DECIDUOUSz jw REE �: tt / (E) WALKWA 441.14 I :3 �'� � — — _ (N) STOOP 32.15 ft �9 I a I 1 I I � N R00 w LA _ _ — / _ 45.09 sq ft,� NDERGROUN o — _ .3... N ELEPHON a �a 4 — — (E) P 10 , d _ LINE I N, + ROPERTY LINE (E) 36- CEDAR N N N N N N N ' —/() E 36" CEDAR TREE I } (E) 3W CHERRY 1 — — — TREE N TREE 1. (E) 36" CEDAR TREE (E) 8" DECIDUOUS TREE' (E) BUILDING ROOF OUTLINE (E) 2-8" DECIDUOUS TREE (E) 4" DEC.TREE (E) 2-4" DECIDUOUS TREE (E) RETAINING WALL (E) 36" FIR THE (E) 20" FIR TREE AREA OF STEEP SLOPE PER (E)120 FIR TREE 23.80.020, SEE GEOTECH I REPORT 400 FIR TREE (E) BRICK FAT /BRICK PATH --t / N r — � E r (E) 2" CHERRY TREE 107.01 s PROPOSED POWER JUNCTION, TYP. UTILITY POLE IBASED UPON THE SITE PLAN FOR "JENKINS DECK' BY ALEXANDRA IMMEL RESIDENTIAL DESIGN, 8-26-24. 2 — — — — — — — — — — — — 7 I � I 1 HA-2 I I I I I I I I I I I 6-5" ±T-214" 23'-3117 1 (N)DECK E)CANTILEVE I ABOVE I I I o E DS I LINE OF SIDING ABOVEATLNISET GFEL 4E VE i — 'J 14" p s33A"CLG=RT] I HA-4 II (E)DEN ^ (E)MUDROOM ' II T-0 114' CLG FIT A 00wn oat A 70.75p It II I' (EIDROPPED BEAMS ABOVE. TYP I ;—---- - - - - -- HA I - — 6'-T CLG HT II T-T CLG HT *HA---r ° (E)CRAWLSPACE 009 1 ❑ A. 13898.t 1 ILE ° 1 (E)LAUNDRY (E)BATH W2 007 A811]�h ptO16pll 1 I ° 1 ° I EXISTING WALKWAY 8 PATIO I O I I (E)UTILITY ° I I Ae3wY° ° (E)CLOSET ° SEE SHEET A2.2 FOR pm1p �3n TYPICAL FLOOR NOTES A U 39 p It ° C<>A 0 LEGEND ® CARBON MONOXIDE DETECTOR SMOKE DETECTOR. SEE TYR FLOOR NOTES R6 EXHAUST FAN ON SWITCH, SEE TYR FLOOR NOTES#12, — — — — — — — — - HA-1 EXISTING WALL (E)BEDROOYNEW WALL 0011$13 I ° A1 p11 I � NEW FLOORAREA tgD1e NNE} (E) ROOF ABOVE aon�4 rL• O(E)OS �BABB@RFi001t FLLEGEND PROJECT #: G-5362-1 PRELIM PLAN - LOWEST LEVEL DATE: 9-26-24 Grog Northwest Inc PROPOSED DECK ADDITION DRAWN: AG I = HAND-AUGERED BORING NUMBER AND F-/ Bellevue, 18914 - 94TH AVE W CHECKED: WC BASED UPON THE "BASEMENT FLOOR PLAN", SHEET A2.1 FORA- 1 APPROXIMATE LOCATION 13705 Bel -Rea Rd, BellWA 98005 EDMONDS, WASHINGTON � SCALE: 111 = 81 "JENKINS DECK" BY ALEXANDRA IMMEL RESIDENTIAL DESIGN, Phone 425/649-8757 FAX 425/649-8758 PLATE: 4 8-26-24. Email info@geogroupnw.com APPENDIX A HAND-AUGERED BORING LOGS & USCS SOIL LEGEND G-5362-1 LEGEND OF SOIL CLASSIFICATION AND PENETRATION TEST UNIFIED SOIL CLASSIFICATION SYSTEM (USCS) MAJOR DIVISION GROUP TYPICAL DESCRIPTION LABORATORY CLASSIFICATION CRITERIA SYMBOL WELL GRADED GRAVELS, GRAVEL -SAND Cu = (D60 / D10) greater than 4 CLEAN Gyy MIXTURE, LITTLE OR NO FINES Cc = (D302) / (D10 ` D60) between 1 and 3 GRAVELS DETERMINE PERCENTAGES OF GRAVELS (little or no GP POORLY GRADED GRAVELS, AND GRAVEL- GRAVEL AND SAND NOT MEETING ABOVE REQUIREMENTS (More Than Half fines) SAND MIXTURES LITTLE OR NO FINES FROM GRAIN SIZE COARSE- Coarse Grains DISTRIBUTION ATTERBERG LIMITS BELOW GRAINED SOILS Larger Than No. 4 CURVE Sieve) DIRTY GM SILTY GRAVELS, GRAVEL -SAND -SILT MIXTURES CONTENT "A" LINE. GRAVELS OF FINES or P.I. LESS THAN 4 EXCEEDS ATTERBERG LIMITS ABOVE (with some GC CLAYEY GRAVELS, GRAVEL -SAND -CLAY "A" LINE. fines) MIXTURES COARSE GRAINED SOILS ARE or P.I. MORE THAN 7 CLASSIFIED AS SANDS WELL GRADED SANDS, GRAVELLY SANDS, FOLLOWS: Cu 2(D60 / D10) greater than 6 CLEAN SW LIITLE OR NO FINES Cc = (D30 ) / (D10 ` D60) between 1 and 3 SANDS (More Than Half More Than Half Coarse Grains (little or no SP POORLY GRADED SANDS, GRAVELLY SANDS, < 5 % Fine Grained: NOT MEETING ABOVE REQUIREMENTS by W eight Larger Smaller Than No. fines ) LITTLE OR NO FINES GW, GP, SW, SP Than No. 200 4 Sieve) ATTERBERG LIMITS BELOW Sieve DIRTY SM SILTY SANDS, SAND -SILT MIXTURES > 12% Fine Grained: CONTENT OF "A" LINE SANDS GM, GC, SM, SC FINES with P.I. LESS THAN 4 5 to 12% Fine EXCEEDS DS ATTERBERG LIMITS ABOVE (with some SC CLAYEY SANDS, SAND -CLAY MIXTURES Grained: use dual "A" LINE fines) symbols with P.I. MORE THAN 7 SILTS Liquid Limit INORGANIC SILTS, ROCK FLOUR, SANDY SILTS (Below A -Line on < 50% ML OF SLIGHT PLASTICITY 60 Plasticity Chart, PLASTICITY CHART A -Line Liquid Limit INORGANIC SILTS, MICACEOUS OR FINE-GRAINED Negligible FOR SOIL PASSING 50 SOILS Organic) > 500� MH DIATOMACEOUS, FINE SANDY OR SILTY SOIL NO. 40 SIEVE o CH or OH INORGANIC CLAYS OF LOW PLASTICITY, X 40 CLAYS Liquid Limit CL GRAVELLY, SANDY, OR SILTY CLAYS, CLEAN 0 (Above A -Line on < 30 % CLAYS Z Placticity Chart, 30 Liquid Limit INORGANIC CLAYS OF HIGH PLASTICITY, FAT Negligible H Organic) > 500� CH CLAYS U CL or OL 20 � More Than Half Q / by Weight Liquid Limit ORGANIC SILTS AND ORGANIC SILTY CLAYS OF o_ MH or OH Smaller Than No. ORGANIC SILTS <50% OL LOW PLASTICITY 10 - / ML 200 Sieve & CLAYS 7 L_M �Lj (Below A -Line on 4 Placticity Chart) Liquid Limit OH ORGANIC CLAYS OF HIGH PLASTICITY 0 > 50% 0 10 20 30 40 LIQUID 0 60 70 80 90 100 110 LIMIT (%) HIGHLY ORGANIC SOILS Pt PEAT AND OTHER HIGHLY ORGANIC SOILS SOIL PARTICLE SIZE GENERAL GUIDANCE OF SOIL ENGINEERING PROPERTIES FROM STANDARD PENETRATION TEST (SPT) U.S. STANDARD SIEVE FRACTION Passing Retained SANDY SOILS SILTY & CLAYEY SOILS Sieve S1Ze Sieve S1Ze Blow Relative Friction Blow Unconfined (mm) (mm) Counts Density Angle Description Counts Strength Description SILT / CLAY #200 0.075 N % 0, degree N qu, tsf SAND 0-4 0 -15 Very Loose < 2 < 0.25 Very soft FINE #40 0.425 #200 0.075 4-10 15 - 35 26 - 30 Loose 2-4 0.25 - 0.50 Soft MEDIUM #10 2 #40 0.425 10-30 35 - 65 28 - 35 Medium Dense 4-8 0.50 -1.00 Medium Stiff COARSE #4 4.75 #10 2 30-50 > 50 65 - 85 85 -100 35 - 42 38 - 46 Dense Very Dense 8 - 15 15 - 30 1.00 - 2.00 2.00 - 4.00 Stiff Very Stiff GRAVEL FINE 19 #4 4.75 > 30 > 4.00 Hard COARSE 76 19 _ Group Northwest, Inc. COBBLES 76 mm to 203 mm BOULDERS > 203 mm Geotechnical Engineers, Geologists, & Environmental Scientists ROCK FRAGMENTS >76mm 13240 NE 20th Street, Suite 10 Bellevue, WA 98005 Phone (425) 649-8757 Fax (425) 649-8758 PLATE Al ROCK >0.76 cubic meter in volume HAND AUGERED BORING NO: HA-1 LOGGED BY AG LOG DATE: 2/11/2021 DEPTH ft. USCS SOIL DESCRIPTION SAMPLE No. Water % OTHER TESTS/ COMMENTS ML Dark brown fine sandy SILT with some cobbles and roots, moist, _ medium dense to dense (planter surfacing and to�soil) SM/ Tan silty SAND with some gravel becoming gray gravelly sandy ML SILT, moist, dense (TILL) Probe 0.5" 2 Probe 0.5" Total depth of boring = 24" bgs (below ground surface) 3 No groundwater seepage observed 4 5 6 7 LOGGED BY AG HAND AUGERED BORING NO: HA-2 LOG DATE: 2/11/2021 DEPTH ft. USCS SOIL DESCRIPTION SAMPLE No. Water % OTHER TESTS/ COMMENTS ML Dark brown fine sandy SILT, moist, medium dense to dense (topsoil) --- ---- -------------------------------------------------- SM/ Tan gravelly silty SAND becoming gray fine sandy SILT with 2 ML occasional gravel, moist, dense (TILL) Probe 1-2" Probe 1" Probe 0.5" 3 Probe 0.5" Total depth of boring = 32" bgs (below ground surface) No groundwater seepage observed 4 5 6 7 Group Northwest, Inc. Geotechnical Engineers, Geologists, & Environmental Scientists HAND AUGERED BORING LOG PROPOSED DECK ADDITION 18914 - 94TH AVE W EDMONDS, WA HAND AUGERED BORING NO: HA-3 LOGGED BY AG LOG DATE: 2/11/2021 DEPTH ft. USCS SOIL DESCRIPTION SAMPLE No. Water % OTHER TESTS/ COMMENTS ML Dark brown sandy SILT, moist, medium dense (topsoil) ------------------- SM/ y------------------------- ---- Tan and brown sand SILT and silty SAND with occasional gravel, Probe 12" ML moist, loose (apparent fill) Probe 6-10" 2 ........................................................ ------------------------------------------------------ Probel-2" 3 ML Gray gravelly fine sandy SILT, moist, dense (TILL) Probe Total depth of boring = 35" bgs (below ground surface) 4 Auger refusal due to dense/gravel at 35" bgs Dense competent soils below 29" bgs No groundwater seepage observed 5 6 7 LOGGED BY AG HAND AUGERED BORING NO: HA-4 LOG DATE: 9/11/2024 DEPTH ft. USCS SOIL DESCRIPTION SAMPLE No. Water % OTHER TESTS/ COMMENTS SM/ Dark brown fine sandy SILT / silty SAND with roots and occasional Probe 2-4" ML concrete debris, ash and charcoal, moist, variable dense to loose (FILL) Probe 1-3" Probel-4" Probe10.5" 2 -- ---- -------------------------------------------------- Probel-2" ............................................................. 3 ML Tan fine sandy SILT with some gravel, moist, dense (TILL) Probe 1-2" Total depth of boring = 3 1 " bgs (below ground surface) 4 Dense competent soils below 28" bgs No groundwater seepage observed 5 6 7 Group Northwest, Inc. Geotechnical Engineers, Geologists, & Environmental Scientists HAND AUGERED BORING LOG PROPOSED DECK ADDITION 18914 - 94TH AVE W EDMONDS, WA HAND AUGERED BORING NO: HA-5 LOGGED BY AG LOG DATE: 9/11/2024 DEPTH ft. USCS SOIL DESCRIPTION SAMPLE No. Water % OTHER TESTS/ COMMENTS SM/ Moss/bark/soil thickness 1" Probe 1-2" 1 NIL Tan sandy SILT / silty SAND with some gravel, moist, dense Probe 1-2" with occasional cobble Probe 1-2" 2 ML Tan gravelly fine sandy SILT, moist, dense (TILL) Probe 1-3" Probe 1-2" 3 Total depth of boring = 30" bgs (below ground surface) Dense competent soils below 1" bgs 4 No groundwater seepage observed 5 6 7 LOGGED BY HAND AUGERED BORING NO: LOG DATE: DEPTH ft. USCS SOIL DESCRIPTION SAMPLE No. Water % OTHER TESTS/ COMMENTS 1 2 3 4 5 6 7 Group Northwest, Inc. Geotechnical Engineers, Geologists, & Environmental Scientists HAND AUGERED BORING LOG PROPOSED DECK ADDITION 18914 - 94TH AVE W EDMONDS, WA APPENDIX B ASSOCIATION OF ROCKERY CONTRACTORS STANDARD ROCK WALL CONSTRUCTION GUIDELINES G-5362-1 �Associated Rockery Contractors Standard Rock Wall Construction Guidelines P.O. Box 1794 - Woodinville, Washington 98072 Association Representatives (425) 481-3456 or (425) 481-7222 ARC STANDARD ROCKERY CONSTRUCTION GUIDELINES 1.01 Introduction: 1.01.1 These standard rock wall construction guidelines have been developed in an Historical effort to provide a more stringent degree of control on materials and construction Background methodology in the Pacific Northwest. They have been assembled from numerous other standards presently in use in the area, from expertise provided by local geotechnical engineers, and from the wide experience of the members of the Associated Rockery Contractors (ARC). 1.01.2 The primary goals of this document are to standardize the methods of construc- Goal tion for rock walls over four feet in height, and to provide a means of verifying the quality of materials used in construction and the workmanship employed in construction. This standard has also been developed in a manner that makes it, to the best of ARC's knowledge, more stringent than the other standards presently in use by local municipalities. 2.01 Materials: 2.01.1 All rock shall be sound, angular ledge rock that is resistant to weathering. The Rock Quality longest dimension of any individual rock should not exceed three times its shortest dimension. Acceptability of rock will be determined by laboratory tests as hereinafter specified, geologic examination and historical usage records. All rock delivered to and incorporated in the project shall meet the following minimum specifications: a. Absorption ASTM C 127 AASHTO T-85 b. Accelerated Expansion (15 days) CRD-C-148 * 1, *2 c. Soundness (MsSO4 at 5 cycles) ASTM C88 CRD-C-137 d. Unconfined Compressive Strength ASTM D 2938 e. Bulk Specific Gravity (155pcf) ASTM C127 AASHTO T-85 Not more than 2.0% for igneous and metamorphic rock types and 3.0% for sedimentary rock types. Not more than 15% breakdown. Not greater than 5% loss. Intact strength of 6,000 psi, or greater. Greater than 2.48 *1. The test sample will be prepared and tested in accordance with Corps of Engineers Testing procedure CRD-C-148, "Method of Testing Stone for Expansive Breakdown on Soaking in Ethylene Glycol.". *2. Accelerated expansion tests should also include analyses of the fractures and veins found in the rock. 12/2/92 PAGE 1 ARC STANDARD ROCKERY CONSTRUCTION GUIDELINES 2.01.2 Quarry sources shall begin a testing program when either becoming a supplier or Frequency when a new area of the source pit is opened. The tests described in Section of Testing 2.01.1 shall be performed for every four thousand (4000) tons for the first twelve thousand (12,000) tons of wall rock supplied to establish that specific rock source. The tests shall then be performed once a year, every 40,000 tons, or at an apparent change in material. If problems with a specific area in a pit or with a particular material are encountered, the initial testing cycle shall be restarted. 2.01.3 Recognizing that numerous sources of rock exist, and that the nature of rock will Rock vary not only between sources but also within each source, the density of the Density rock shall be equal to, or greater than, one hundred fifty-five (155) pcf. Typi- cally, rocks used for rock wall construction shall be sized approximately as follows: Rock Size Rock Weight Average Dimension One man 50-200 pounds 12 to 18 inches Two man 200-700 pounds 18 to 28 inches Three man 700-2000 pounds 28 to 36 inches Four man 2000-4000 pounds 36 to 48 inches Five Man 4000-6000 pounds 48 to 54 inches Six Man 6000-8000 pounds 54 to 60 inches In rock walls eight feet and over in height, it should not be possible to move the large sized rocks (four to six -man size) with a pry bar. if these rocks can be moved, the rock wall should not be considered capable of restraining any significant lateral load. However, it is both practical and even desirable that smaller rocks, particularly those used for "chinking" purposes, can be moved with a pry bar to achieve the "best fit". 2.01.4 The rock source shall present current geologic and test data for the minimum Submittals guidelines described in Section 2.01.1 on request by either the rock wall contrac- tor, the owner, or the applicable agency. 3.01 Rock Wall Construction: 3.01.1 Rock wall construction is a craft and depends largely on the skill and experience General of the builder. A rock wall is a protective system which helps to retard the weathering and erosion process acting on an exposed cut or fill soil face. While by its nature (the mass, size and shape of the rocks) it will provide some undeter- mined degree of retention, it is not a designed or engineered system in the sense a reinforced concrete retaining wall would be considered designed or engineered. The degree of retention achieved is dependant on the size of rock used; that is, the "mass" or weight. and the height of the rock wail being constructed. The larger the rock. the more competent the rock wall. To accomplish an appropriate 1 2/2/92 PAGE 2 ARC STANDARD ROCKERY CONSTRUCTION GUIDELINES degree of competency, all rock walls in excess of four feet in height should be built on a "mass" basis, i.e. by the ton. To provide a competent and adequate rock wall structure, all rock walls con- structed in front of either cuts or fills eight feet and over in height should be bid and constructed in accordance with these standard guidelines and the geotechnical engineer's supplemental recommendations. Both the standard guidelines and the supplemental geotechnical recommendations should be pro- vided to prospective bidders before bidding and the start of construction. 3.01.2 The geotechnical engineer retained to provide necessary supplemental rock wall Geotechnieal construction guidelines shall be a practicing geotechnical/civil engineer licensed Engineer as a professional civil engineer in the State of Washington who has had at least four years of professional employment as a geotechnical engineer in responsible charge, including experience with fill construction and stability and rock wall construction. The geotechnical engineer should be hired either by the rock wall contractor or the owner. 3.01.3 The ultimate responsibility for standard rock wall construction should remain Responsibility with the rock wall builder. However, rock walls protecting moderate to thick fills, with steep sloping surfaces above or below them, with multiple steps, with foundation or other loads affecting them, protecting sandy or gravelly soils subject to ravelling, with seepage or wet conditions, or that are eight feet or more in height, all represent special design conditions and require consultation and/or advice from qualified experts. 3.01.4 All workmanship is guaranteed by the rock wall contractor and all materials are Workmanship guaranteed by the supplying quarry for a period of six years from the date of completion of erection, providing no modification or changes to the conditions existing at the time of completion, are made. 3.01.5 Such changes include, but are not necessarily limited to, temporary excavation of Changes to ditches or trenches for any utility within a distance of less than five feet from the Finished back of the top of the rock wall; excavation made either within a distance equal Product to at least two thirds of the free-standing wall height in front of the toe of a rock wall, or that will penetrate an imaginary line extended at a 1H:IV (Horizontal: Vertical) slope from the front edge of the rock wall toe (see Figure A); removal of any material from the subgrade in front of the wall, excavation of material from any location behind the rock wall within a distance at least equal to the rock wall's height, the addition of any surcharge or other loads within a similar distance of the top of the rock wall, or surface or subsurface water forced, di- rected, or otherwise caused to flow behind the rock wall in any quantity. 3.01.6 Slopes above rock walls should be kept as flat as possible, but should not exceed Slopes 2HA V unless the rock wall is designed specifically to provide some restraint to the load imposed by the slope. Any slope existing above a completed rock wall should be covered with vegetation by the owner to help reduce the potential for surface water flow induced erosion. It should consist of a deep rooted, rapid growth vegetative mat, will typically be placed by hydroseeding and covered with a mulch. It is often useful to overlay the seed and mulch with either pegged 12/2/92 peel= 1; ARC STANDARD ROCKERY CONSTRUCTION GUIDELINES in -place jute matting, or some other form of approved geotextile, to help main- tain the seed in -place until the root mat has an opportunity to germinate and take hold. 3.01.7 All rock walls constructed against cuts or fills eight feet and over in height shall Monitoring be periodically monitored during construction by the geotechnical engineer to verify that the nature and quality of the materials being used are appropriate, that the construction procedures are appropriate, and that the rock wall is being constructed in a generally professional manner and in accordance with this ARC guideline and any supplemental recommendations. On completion of the rock wall, the geotechnical engineer should submit to the client, the rock wall contractor, and to the appropriate municipality, copies of his rock wall examination reports along with a final report summarizing rock wall construction. 3.01.8 Where rock walls are constructed in front of a fill, it is imperative that the owner Fill ensure the fill be placed and compacted in a manner that will provide a compe- Compaetion tent fill mass. To achieve this goal, all fills should consist of relatively clean, organic and debris free granular materials with a maximum size of four inches. Ideally, but particularly if placement and compaction is to take place during the wet season, they should contain no more than seven percent fines (silt and clay sized particles) passing the number 200 mesh sieve. All fills should be placed in thin lifts not exceeding ten (10) inches in loose thickness. Each lift should be compacted to at least 95 percent of the maximum dry density, as determined by ASTM Test Method D-1557-78 (Modified Proc- tor), before any additional fill is placed and compacted. In -place density tests should be performed at random locations within each lift of the fill to verify that this degree of compaction is being achieved. 3.01.9 There are two methods of constructing a fill. The first, which typically applies to Fill rock walls of less than eight feet in height, is to overbuild and then cut back the Construction fill. The second, which applies to all rock walls eight feet and over in height, is Reinforcement to construct the fill using a geogrid or geotextile reinforcement. Overbuilding the fill allows for satisfactory compaction of the fill mass out beyond the location of the fill face to be protected. Overbuilding also allows the earthwork contractor to use larger and more effective compaction equipment in his compactive efforts, thereby typically achieving a more competent fill mass. Cutting back into the well compacted fill also typically results in construction of a competent near vertical fill face against which to build the rock wall. For the higher rock walls the use of a geogrid or geotextile fabric to help rein- force the fill results in construction of a more stable fill face against which to construct the rock wall. This form of construction leads to a longer lasting and more stable rock wall and helps reduce the risk of significant long term mainte- nance. 1212/92 PAGE 4 ARC STANDARD ROCKERY CONSTRUCTION GUIDELINES This latter form of construction requires a design by the geotechnical engineer for each specific case. The vertical spacing of the reinforcement, the specific type of reinforcement and the distance to which it must extend back into the fill, the amount of lapping and the construction sequence must be determined on a case by case basis. 3.01.10 The first step in rock wall construction, after general excavation, is to construct a Rock Wall keyway in which to build the rock wall. The keyway shall comprise a shallow Keyway trench of at least twelve (12) inches in depth, extending for the full length of the rock wall. The keyway subgrade should be slightly inclined back towards the face being protected. It is typically dug as wide as the rock wall (including the width of the rock filter layer). If the condition of the cut face is of concern, the keyway should be constructed in sections of manageable length, that is, of a length that can be constructed in one shift or one day's work. The competency of the keyway subgrade to support the rock wall shall be veri- fied by probing with a small diameter steel rod. The rod shaII have a diameter of between three -eighths and one-half inch, and shall be pushed into the subgrade in a smooth unaided manner under the body weight of the prober only. Penetration of up to six inches, with some difficulty, shall indicate a "competent" keyway subgrade unless other factors in the geotechnical engineer's opinion shall indi- cate otherwise. Penetration in excess of six inches, with ease, shall indicate a "soft" subgrade and one that could require treatment. Shallow soft areas of the subgrade can be "firmed up" by tamping a layer of coarse quarry spalls into the subgrade. 3.01.11 Upon completion of keyway excavation, a shaIIow ditch or trench, approximately Keyway twelve (12) inches wide and deep, should be dug along the rear edge of the key Drainage way. A minimum four -inch diameter perforated or slotted rigid ADS drain pipe, or equivalent, approved by an engineer, should be placed in this shallow trench and should be bedded on and surrounded by a free -draining crushed rock. Burial of the drain pipe in this shallow trench provides protection to the pipe and helps prevent it from being inadvertently crushed by pieces of the rock wall rock. This drain pipe should be installed with sufficient gradient to initiate flow, and the outfall should be connected to a positive and permanent discharge. Positive and permanent drainage should be considered to mean an existing or to be installed storm drain system, a swale, ditch or other form of surface water flow collection system, a detention or retention pond, or other stable native site feature or previously installed collection system. 3.01.12 The individual rock wall thickness should be equal to the thickness of the recom- Rock Wall mended size of rock plus the thickness of the drain rock layer. This thickness, Thickness which will be determined on a case by case basis, will be dependant on the specific rock sizes recommended for each individual rock wall. For example, if four -man rock is used the rock wall thickness will be approximately five feet. 12/2/92 PAGE 5 ARC STANDARD ROCKERY CONSTRUCTION GUIDELINES 101.13 The contractor should have sufficient space available so that he can select from Rock among a number of stockpiled rocks for each space in the rock wall to be filled. Selection Rocks which have shapes which do not match the spaces offered by the previous course of rock should be placed elsewhere to obtain a better fit. Rock should be of a generally cubical, tabular or rectangular shape and selected in accordance with Section 2.01.3. Any rocks of basically rounded or tetrahedral form should be rejected or used for filling large void spaces. 3.01.14 The first course of rock should be placed on firm unyielding soil. There should Rock be full contact between the rock and soil, which may require shaping of the Placement ground surface or slamming or dropping the rocks into place so that the soil foundation conforms to the rock face bearing on it. The bottom of the first course of rock should be a minimum of twelve (12) inches below the lowest adjacent site grade. As the rock wall is constructed, the rocks should be placed so that there are no continuous joint planes in either the vertical or lateral direction. Wherever possible, each rock should bear on at least two rocks below it. Rocks should be placed so that there is some bearing between flat rock faces rather than on joints. Joints between courses (the top surface of rock), should slope back towards the cut face and away from the face of the rock wall. Smaller rocks (one to two -man size) are often used to create an aesthetically pleasing "top edge" to a rock wall. This is an acceptable practice provided none of the events described in Section 3.01.5 occur, and that people are prevented from climbing or walking on the finished wall. This is the owner's responsibility. 3.01.15 The face of the rock wall should be inclined at a gradient of about 1 H:6V back Face towards the face being protected. The inclination should not be constructed Inclination flatter than 1 H:4V. 3.01.16 Because of the nature of the product used to construct a rock wall, it is virtually Voids impossible to avoid creating void spaces between individual rocks. However, it should be recognized that voids do not necessarily constitute a problem in rock wall construction. As the size of rock used to build a rock wall increases, i.e, to six -man size, the void spaces between individual rocks should be expected to be larger. Where voids of greater than six inches in dimension exist in the face of a rock wall they should be visually examined to determine if contact between the rocks exists within the thickness of the rock wall. If contact does exist, no further action is required. However, if there is no rock contact within the rock wall thickness the void should be "chinked" with a smaller piece of rock. 3.01.17 In order to provide some degree of drainage control behind the rock wall, and as Drain Rock a means of helping to prevent loss of soil through the face of the rock wall, a Layer rock drainage filter shall be installed between the rear face of the rock wall and the soil face being protected. This drain rock layer should be at least twelve (12) inches thick; and for rock walls eight feet in height or higher, it should be at 12/2/92 PAGE 6 ARC STANDARD ROCKERY CONSTRUCTION GUIDELINES least eighteen (18) inches thick. It should be composed of 4 to 2-inch sized crushed rock quarry spalls, crushed concrete, or other material approved by the geotechnical engineer. If a random wall rock extends back to the exposed soil face, it is not necessary that the filter rock layer extend between it and the sail face. Depending on soil type and potential water seepage, a geotextile fabric may or may not be required. This can be determined on a case by case basis by the geotechnical engineer during design and prior to bidding. 3.01.18 It is the owner's responsibility to intercept surface drainage from above the rock Surface wall and direct it away from the rock wail to a positive and permanent discharge Drainage well below and beyond the toe of the rock wall. Use of other drainage control measures should be determined on a case -by -case basis by the geotechnical engineer prior to bidding on the project. 1212/92 P er;F 7 Fig. A. ROCKERY SECTION Fig. B. ROCKERY ELEVATION SCHEMATIC ONLY — NOT TO SCALE NOT A CONSTRUCTION DRAWING NOTES: Rockery construction is a craft and depends largely on the skill and experience of the builder. A rockery is a protective system Which helps retard the weathering and erosion process on an exposed soil face. While by its nature (mass, size and shape of the rocks) it will provide some degree of retention, it is not a designed or engineered sys- tem in the sense a reinforced concrete retaining wall would be considered designed or engineered. The degree of retention achieved is dependent on the size of the rock used; that is, the mass or weight, and the height of the wall being construc- ted. The larger the rock, the more competent the wall. Rockeries should be considered maintenance items that will require periodic inspection and repair. They should be located so that they can be reached by a contractor if repairs become necessary. Maximum inclination of slopes behind rock walls Is 2:1 (liorizontal:Vercical) Minimum embedment D - 12 inches undisturbed native soil or compacted fill placed in accordance with report recommendations. Maximum rock wall height H - feet. Rockeries greater than 8 feet in height to be installed under periodic observation of the geotechnical engineer. Rocks placed In the lower two-thirds of the wall should be 5 to 6 man rock, 5000 lbs. or larger. Rocks placed above this level should gradually decrease in size WLth Increasing wall height using 3 to 5 man rock, 760 to 5000 lbs. The long dimension of the rocks should extend into the earth to provide maximum stability. Rocks should be placed to avoid continuous joint planes in vertical or lateral directions. Each rock shou.c: bear on two or more rocks below it, with good flat -to -flat contact. All rockeries over 4 feet in height should be constructed on basis of wall mass, not square footage of face. Approximate Approximate Weight - lbs. Volume (0) 1 Flan 58,210 0.9 - 4.0 2 Man 265,580 4.1.- 8.25 3 Man 760 - 1830 12.3 - 27.1 4 Man 3000 - 7000 49.0 - 76.0 5 Man 5000 76 6 Man 7000 100 Reference: vocal quay we! he s udv usin average weights of no �ess t�ian s x to �f each man size conducted in January, 1988. LEGEND: • Drainage materials to consist of ••�',�,' clean angular well -graded quarry spalls, with 3-inch ma7.imum size, or other material approved by the geotechnical engineer Surface seal; may consist of imper- vious soil or asphalt 11l 111 - Undisturbed firm Native Soil =111 — I Drain pipe; 4-Lnch minimum diameter, perforates or slotted rigid plastic ADS pipe laid with a positive gradient to discharge under control well away from the wall. TYPICAL ROCi:CRY DETAILS ARC Assoclahon of Rockery Contractors Prof. No. I Date Plate