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20181220 Nelson Geotech Report.pdfMain Office 173 I I 135'h Ave NE, A-500 Woodinville, WA 98072 (42s) 486-1669 FAX (425) 48r-25 l0 December 20,2018 Mr. Garth Hitchens 3380 - 126th Avenue NE Bellevue, WA 98005 ghitchens@me.com NELSON GEOTECHNICAL AssocIATEg, INc. GEoTECHNICAL ENAINEERS & GE()LOGISTS Engineering-Geology Branch 5526 Industry Lanc, #2 East Wcnatchcc, WA 98802 (509) 665-7ó9ó F AX (509) 66s-7692 N G A' ffiHffiffifr\dffiM f- :1,' O t-l ^...r¡ -t," l¿ ú , ,i l ì[ y'¡ . ¡ ¡¡,¡'i¡:[Jl $t".FìVlÇ.| i ii{.iu¡\j'i-EFl Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development 17901 Vista Del Mar Drive Edmonds, Washington NGA File No. 1065318 Dear Mr. Hitchens: We are pleased to submit the attached report titled "Geotechnical Engineering Evaluation - Hitchens Residence Development - 17901 Vista Del Mar l)rive - Edmonds, Washington." This report summarizes our observations of the existing surface and subsurface conditions within the site, and provides general recommendations for the proposed site development. Our services were completed in general accordance with the proposal signed by you on October 15,2018. The site is currently occupied by a single-family residence within the east-central portion of the parcel. The upper eastern portion of the parcel is relatively level to gently sloping from east to west. Just to the west of the existing residence a steep west-facing bluff slope descends to the BNSF railroad tracks. Vegetation within the upper portion of the site generally consists of grass-covered yard areas and landscaping plants, while the slope below and to the west of the residence is generally heavily vegetated with young to mature trees and underbrush. An existing sewer line easement runs north-south along the top of slope area within the central portion of the site. We understand the proposed developments within the site will consist of removing the existing site structures and constructing a new single-family residence with an attached patio area along the westem portion of the house. At the time this proposal was prepared, specific construction plans were not available. We explored the site subsurface soil conditions throughout the site with three geotechnical borings using a limited access track-mounted drill rig. Our explorations indicated that the site was underlain by competent, native outwash soils at relatively shallow depths, below a surficial layer of topsoil and/or undocumented fill. It is our opinion that the proposed residence development within the site is feasible from a geotechnical standpoint, provided that our recommendations are incorporated into the design and construction of this project. We have recommended that the new structures be founded on medium dense or better native glacial soils for bearing capacity and settlement considerations. It is also our opinion that the soils that underlie the site and form the core of the site slope should be stable with respect to deep-seated earth movements, due to their inherent strength and slope geometry. However, there is a potential for shallow sloughing and erosion events to occur on the steep slope below the proposed development area. We recommend that any proposed structures be set back at least 35 feet from the top of the steep west-facing Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 Dçcember 20,2018 Summary - Page 2 bluff slope. In addition to the proposed setback, we recommend that the downhill westem structure foundations be supported on drilled piers extending down a minimum of 30 feet below the existing grade. In the attached report, we have included recommendations for site grading, foundation support, and site drainage. V/e should be retained to discuss our recommendations with your design team, and to review final plans prior to construction. We also recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated in the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from these anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. We appreciate the opportunity to provide service to you on this project. Please contact us if you have any questions regarding this report or require further information. Sincerely, 'VELSON G EOTECHNICAI ASSO CIATES, INC. Khaled M. Shawish, PE Principal TABLE OF CONTENTS INTRODUCTION............ SCOPE SITE CONDITIONS............. Surface Conditions. Subsurface Conditions........ Hydrogeologic Conditions . SENSITIVE AREA EVALUATION.......... Seismic Hazard. Erosion Hazard, Landslide HazardlSlope Stability CONCLUSIONS AND RECOMMENDATIONS... General Erosion Control and Slope Protection Measures Site Preparation and Grading..... Structure Setbacks Temporary and Permanent Slopes ....... Foundation Support ..... Retaining Walls ......... Structural FiI1............. Slab-on-Grade ........... Pavements. utilities..... Site Drainage .............. CONSTRUCTION MONITORING ..... USE OF THIS REPORT. LIST OF'IIRF"S Figure 1-VicinityMap Figure2-SitePlan Figure 3 - Cross-Section A-A' Figure 4 - Soil Classification Chart Figures 5 andT - Boring Logs 1 1 2 2 2 J 4 4 4 5 6 6 7 8 9 9 0 t2 l3 l3 t4 t4 14 t6 t6 NETSOA' G EOTECH N ICAI ASSO CI ATES, I N C. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development 17901Vista Del Mar Drive Edmonds, Washington INTRODUCTION This report presents the results of our geotechnical engineering investigation and evaluation of the planned Hitchens Residence Development project in Edmonds, Washington. The project site is located at the address of 1 7901 Vista Del Mar Drive, as shown on the Vicinity Map in Figure 1 . The purpose of this study is to explore and characterize the site's surface and subsurface conditions and to provide geotechnical recommendations for the planned site development. The site is currently occupied by a single-family residence within the east-central portion of the parcel. The upper eastem portion ofthe parcel is relatively level to gently sloping from east to west. Just to the west of the existing residence a steep west-facing bluff slope descends to the BNSF railroad tracks. Vegetation within the upper portion of the site generally consists of grass-covered yard areas and landscaping plants, while the slope below and to the west of the residence is generally heavily vegetated with young to mature trees and underbrush. An existing sewer line easement runs north-south along the top of slope area within the central portion of the site. We understand the proposed developments within the site will consist of removing the existing site structures and constructing a new single-family residence. At the time this proposal was prepared specific construction plans were not available. Final development and stormwater plans have not been developed at the time this report was written. The existing site layout is shown on the Site Plan in Figure 2. SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions, and provide general recommendations for site development. Specifically, our scope of services included the following: 1. Review available soil and geologic maps of the area. 2. Explore the subsurface soil and groundwater conditions within the vicinity of the proposed residence with up to three, as deep as 40-foot geotechnical borings. Drill rig was subcontracted by NGA. 3. Map the conditions on the slope below the proposed addition, perform hand-tool excavations, and evaluate current slope stability conditions. 4. Provide recommendations for foundation support for the proposed residence. 5. Provide recommendations for deep foundation support, as needed. 6. Provide recommendations for structure setback from the steep slope. ruEtso^, GEorEcHNtcAt AssoctATEs, tMc. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 2 7. 8. 9. 10. 11. 12. Provide recommendations for earthwork. Provide recommendations for temporary and permanent slopes. Provide recommendations for slab subgrade preparation. Provide recommendations for drainage improvements. Provide recommendations for long-term slope protection and maintenance. Document the results of our findings, conclusions, and recommendations in a written geotechnical report. SITE CONDITIONS Surface Conditions The site consists of an irregular-shaped parcel covering approximately 0.53 acres. The site is currently occupied by a single-family residence structure situated within the eastern portion of the property. Topography within the eastern portion of the site consists of relatively level to gently sloping ground. A steep west-facing bluff slope descends from the central portion of the site to the BNSF railroad tracks near the western property line at gradients in the range of 35 to 50 degrees (70 to I 19 percent) as shown in Cross Section A-A' in Figure 3. The overall height of the steep slope below the upper bench area is approximately 130 to 140 feet. The site is generally vegetated with grass-covered yard areas and landscaping plants within the developed portions of the property and forested areas within the steep bluff area. The site is bound to the north, south, and east by existing residential properties, and to the west by the BNSF railroad tracks and the Puget Sound. We did not observe any surface water during our site visit on October 31, 2018. We also did not observe any groundwater emitting from the site slopes or indications of recent slope movement. Subsurface Conditions Geology: The geologic units for this site are shown on Geoloeic map of the Edmonds East and part of the Edmonds West quadrangles. Washingfon by Minard, J.P. (USGS, 1983). The site is mapped as recessional outwash (Qvr). Recessional outwash deposits were derived from the stagnating and receding Vashon glacier (Fraser Glaciation). The deposit is generally described as stratifìed sand and gravel with minor silt and clay layers, but include unstratified to poorly stratified ablation and melt-out deposits, all of which lie on older sediments. Our explorations within the property generally encountered sand and gravel with varying amounts of silt, consistent with the description of recessional outwash soils at depth. Explorations: The subsurface conditions within the site were explored on October 31, 2018 by drilling three geotechnical borings to depths in the range of 14.0 to 25.3 feet below the existing ground surface. The approximate locations of our explorations are shown on the Site Plan in Figure 2. A geologist from NGA was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the explorations. TEtSow GEOTECHNICAI ASSOCIATES, lNC. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 3 A geologist from NGA was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the explorations. A Standard Penetration Test (SPT) was performed on each of the samples during drilling to measure soil consistency at depth. The SPT consists of driving a2-inch outer-diameter, 18 Inches long, split-spoon sampler using a 140-pound hammer with a drop of 30 inches. The number of blows required to drive the sampler the final 12 inches is referred to as the "N" value and is presented on the boring logs. The N value is used to evaluate the strength and density ofthe deposit. The soils were visually classified in general accordance with the Unifìed Soil Classification System, presented in Figure 4. The logs ofour borings are attached to this report and are presented as Figures 5 through 7. We present a brief summary of the subsurface conditions in the following paragraphs. For a detailed description of the subsurface conditions, the logs of the borings should be reviewed. At the surface of Borings 1,2, and 3 we generally encountered approximately 4.0 to 5.0 feet of very loose to loose, orange-brown to gray, fine to coarse sand with silt and varying amounts of roots, iron-oxide staining, and gravel, which we interpreted as undocumented fill soils. Underlying the undocumented fill soils we generally encountered orange-brown to gray-brown, fine to coarse sand with varying amounts of silt, gravel, and iron-oxide staining, which we interpreted as native outwash deposits. Borings 7,2,and3 terminated at respective depths of 14.0, 27.5, and 25.3 feet below the existing ground surface, respectively. Hydrogeologic Conditions Groundwater seepage was not encountered within our soil explorations. If groundwater is encountered during construction we would interpret this water to be perched water. Perched water occurs when surface water infîltrates through less dense, more penneable soils and accumulates on top of a relatively low permeability material. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched groundwater to decrease during drier times of the year and increase during wetter periods. AIETSO'V GEOTECHNICAT ASSO CIATES, I NC. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 4 SENSITIVE AREA EVALUATION Seismic Hazard The 2018 International Building Code (lBC) seismic design section provides a basis for seismic design of structures. Since medium stiff to hard soils were generally encountered underlying the site at depth, the site conditions best fit the IBC description for Site Class D. Table I below provides seismic design parameters for the site that are in conformance with the 2018 IBC, which specifies a design earthquake having a 2Vo probability of occurrence in 50 years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1 - 2018 IBC Seismic Design Parameters Site Class Spectral Acceleration at 0.2 sec. (g) ss Spectral Acceleration at 1.0 sec. (g) Sr Site Coefficients Design Spectral Response Parameters Fu Fn Sos Sor D 1.290 0.s06 1.00 1.500 0.860 0.506 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program lnterpolated Probabilistic Ground Motion website (2008 data) for the project latitude and longitude. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the competent glacial material interpreted to underlie the site has a low potential for liquefaction or amplification of ground motion. The glacial soils interpreted to form the core of the steep slopes within the site are considered stable with respect to deep-seated slope failures. All steep slopes have the potential for shallow sloughing failures during seismic events. Such events should not affect planned developments provided that the foundations are designed with the recommended setback values, and the slope and drainage systems are maintained as described in this report. Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related 1o vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey of Snohomish County Area. Washingúon, by the Natural Resources Conservation Service (NRCS), was reviewed to determine the erosion hazard for the surficial soils found within the subject site. NETSO'V G EOTECH N I CAL ASSOC'A TES, I N C. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 5 The erosion hazard within the property is listed as Alderwood-Everett gravelly sandy loams for 25 to70 percent slopes. The erosion hazard rating is listed as severe, however, based on our experience in the area and our observations in the field, it is our opinion that the site would have a slight to moderate erosion hazard for areas where the soils are exposed. It is our opinion that the erosion hazard for site soils should be low in areas where vegetation is not disturbed. Landslide HazardlSlope Stabilify The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. The steep slopes descend from the relatively level to gently sloping upper yard area within the eastern portion of the property to the BNSF railroad tracks on the western property line at inclinations ranging from 35 to 50 degrees (70 to 119 percent). The overall height ofthe steep slope below the residence is approximately 130 to 140 feet. We did not observe evidence of significant slope instability within the immediate vicinity of the property during our investigation, such as deep-seated landsliding. Vy'e also did not observe groundwater seepage or signs of erosion or sloughing on the slope at the time of our visit. The site slopes are inferred to generally consist of sandy material. Slopes with a gradient of up to approximately 50 degrees exist in the western side of the property. It is our opinion that there is not a significant potential for large-scale, deep-seated slope instability within the development portion of this site under the current conditions. However, steep slopes are naturally prone to surface sloughing and even sizeable landslides over time. Slope activity results from weathering conditions and seasonal surface saturation, especially after large storm events. The potential for these events could be reduced by proper erosion and drainage control. The direct impact of the slope events on the proposed development should be low if the building setback, site preparation and grading, surface water management, and long- term slope maintenance are established as recommended in this report. It is our understanding that the structure will be setback approximately 35 feet from the top of the steep slope. This setback distance should be adequate provided that all the recommendations for site development and slope protection found in this report are incorporated in the design and implemented during construction. We observed that the existing house (which will be removed) appears to be setback as close as approximately 5 to 6 feet from the slope and seems to be supported on conventional shallow footings. Additionally, we observed some of the roof downspouts were disconnected, which during rainfall will discharge water within the near vicinity to the top of bluff. As detailed in this report we have provided recommendations that are intended to reduce the impact of the proposed development on slope stability and protect the future residence from any natural recession of the slope within the lifespan of the structure. Based on our observations of the existing conditions around the house and on the bluff slope below, and thorough review of the proposed plans, it is our opinion that the proposed developments, ,VELSO'V G EOTECH N I C AL ASSOC'A TES, I N C. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 10653 I 8 December 20,2018 Page 6 which will be setback further away from the slope and result in no discharge onto the slope, should not adversely impact the steep slopes within the property or in the near vicinity and will meet the general requirements and specific hazards detailed in the Edmonds Community Development Codes 23.80.060 and 23.80.070. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the planned residence is feasible from a geotechnical standpoint. Our explorations and observations indicate that the site is underlain by dense to very dense glacial soils at depth. These glacial soils should provide adequate support for foundation, slab, and pavement loads. To protect the structure against potential failures on the slope and to limit impact to the slope, we recommend that the western foundation line along with the western 10 feet of the northern and southern foundation lines be supported on drilled piers. The piers should extend a minimum of 30 feet below existing grade to achieve the recommended capacities. The piers should consist of a minimum of 16-inch diameter cast-in place reinforced concrete piles. We recommend that the remaining foundations be designed utilizing shallow foundations. Footings and slabs-on-grade should extend through any loose surficial soil or undocumented fìll and be founded on the underlying competent native bearing soils or structural fill extending to these soils. These soils should be encountered roughly two to five feet below the existing ground surface. However, deeper areas of unsuitable soils and/or undocumented fill could be encountered in the unexplored areas of the site. Recommendations for design and installation of the deep and shallow foundations are presented in the Foundation Support subsection ofthis report. It is also our opinion that the soils that underlie the site and form the core of the site slope should be stable with respect to deep-seated earth movements, due to their inherent strength and slope geometry. However, there is a potential for shallow sloughing and erosion events, and even smaller scale slides, to occur on the steeper portions of the slopes as we have recently observed. Proper erosion and drainage control measures as recommended in this report should reduce this potential. We understand that the residence is planned to be setback 35 feet from the top ofthe steep west-facing slope. Based on our site observations and the soils encountered, it is our opinion that the setback distance along with supporting the western portion ofthe residence on drilled piers should be adequate. Vy'e also understand a proposed patio will extend 5 feet off the western portion of the residence. This should also be feasible given the recommendations in this report are followed closely. A light weight patio setback of approximately 30 feet from the top of bluff should not adversely impact the existing slope stability conditions. We should be retained to review the final plans. TEISOA' GEOTECHNICAL ASSO CIATES, INC. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 PageT All grading operations and drainage improvements planned as part of this development should be planned and completed in a matter that enhances the stability of the steep slopes, not reduces it. Excavation spoils associated with the building excavations should not be stockpiled near the slopes or be allowed to encroach on the slopes. Also, runoff generated within the site should be collected and routed into a permanent discharge system and not be allowed to flow over the slopes. Future vegetation management on the slope should be the subject of a specific evaluation and a plan approved by City of Edmonds. In general, vegetation removal below the top of slope is not recommended unless specifically evaluated and addressed by NGA. Selective pruning and/or thinning of vegetation, along with removal of unhealthy trees, may be allowed as part of a specific evaluation. The slope should be monitored on an ongoing basis, especially during the wet season, for any signs of instability, and corrective actions promptly taken should any signs of instability be observed. Lawn clipping and any other household trash or debris should never be allowed to reach the slope. The soils encountered on this site are considered moisture-sensitive and will disturb easily when wet. To lessen the potential impacts of construction on the steep slope and to reduce cost overruns and delays, we recommend that construction take place during the drier summer months. If construction takes place during the rainy months, additional expenses and delays should be expected. Additional expenses could include the need for placing erosion control and temporary drainage measures to protect the slopes, the need for placing a blanket of rock spalls on exposed subgrades and construction traffìc areas prior to placing structural fill, and the need for importing all-weather material for structural fill. Under no circumstances should water be allowed to flow over or concentrate on the site slopes, both during construction, and after construction has been completed. rùy'e recommend that stormwater runoff from the roof and yard drains be collected and tightlined to an approved discharge point. The slopes should be protected from erosion. We recommend that all disturbed areas be replanted with vegetation to re-establish vegetation cover as soon as possible. Specific recommendations for erosion control are presented in the Erosion Control and Slope Protection Measures subsection of this report. With all of the recommendations provided in this report being followed, the planned site improvements will meet the ECD 23.80.060 and 23.80.070 codes. Erosion Control and Slope Protection Measures The erosion hazard for the on-site soils are interpreted to be severe for exposed soils, but the actual hazard will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from the stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site or flowing over the slope. Stockpiles should be covered with plastic sheeting during wet NETSO'V G EOTEC H N I C AL ASSOC'A TES, I N C. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, V/ashington NGA File No. 1065318 December 20,2018 Page 8 weather and stockpiled material should be kept at least 50 feet away from the top of the steep slopes. Disturbed areas should be planted ¿ìs soon as practical and the vegetation should be maintained until it is established. The erosion potential for areas not stripped of vegetation should be low. Protection of the setback and steep slope areas should be performed as required by City of Edmonds. Specifîcally, we recommend that the setback area and the top of slope not be disturbed or modified through placement of any fill or removal of the existing vegetation. No additional material of any kind should be placed on the slope or be allowed to reach the slope, such as excavation spoils, lawn clippings, and other yard waste, trash, and soil stockpiles. Vegetation should not be removed from the slopes. Replacement of vegetation should be performed in accordance with City of Edmonds code. Under no circumstances should water be allowed to concentrate on the slopes. Site Preparation and Grading After erosion control measures are implemented, site preparation should consist of removing loose soils, topsoil, and any undocumented fill from foundations, slab, and pavement areas, to expose medium dense or better native bearing soils at depth. The stripped soil should be removed from the site or stockpiled for later use as a landscaping fill. Based on our observations, we anticipate native, medium dense or better soil to be encountered at approximately four to five feet across the site, but this depth could increase in unexplored areas of the site. After site preparation, if the exposed subgrade is deemed loose, it should be compacted to a non-yielding condition and then proof-rolled with a heavy rubber-tired piece of equipment. Areas observed to pump or weave during the proof-roll test should be reworked to structural fill specifications or over-excavated and replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in the foundation areas, the loose soils should be removed and replaced with rock spalls. If significant surface water flow is encountered during construction, this flow should be diverted around areas to be developed, and the exposed subgrades should be maintained in a semi-dry condition. If wet conditions are encountered, altemative site grading techniques might be necessary. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading, and covering exposed subgrade with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather, the subgrade should not be compacted, as this could cause further subgrade disturbance. In wet conditions, it may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from disturbance by machine or foot traffic during construction. The prepared subgrade should be protected from construction traffic and surface water should be diverted around areas ofprepared subgrade. /VETSOru G EOTEC H N ICAI ASSO CI ATES, I N C. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 9 Structure Setbacks Uncertainties related to building along steep slopes are typically addressed by the use of building setbacks. The purpose ofthe setback is to establish a "buffer zone" between the structure and the top of the slope so that ample room is allowed for normal slope recession during a reasonable life span of the structure. In a general sense, the greater the setback distance, the lower the risk of slope failures impacting the structure. From a geological standpoint, the setback dimension is based on the slope's physical characteristics, such as slope height, surface angle, material composition, and hydrology. Other factors such as historical slope activity, rate of regression, and the type and desired life span of the development are important considerations as well. We understand the proposed structure foundations will be set back 35 feet from the top of the steep west- facing slopes with a cantilevered roof overhang of approximately S-feet. Additionally, we understand a 5- foot wide patio is to be constructed adjacent to the west side of the proposed residence. The proposed foundation setback of 35 feet and patio setback of 30 feet from the top of bluff should be feasible given that the western downhill foundation lines will be supported on drilled piers extending to a depth of 30 feet below the existing ground surface and the patio is constructed following the recommendations in the site preparation and grading subsection of this report. We should be retained to review final residence location and to observe foundation excavations prior to placing forms. Any proposed development within the setback area, should be the subject of a specific geotechnical evaluation. Under no circumstances should water be allowed to concentrate on the slopes, during or after construction. Temporary and Permanent Slopes Temporary cut slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe slope configurations at all times as indicated in OSHA guidelines for cut slopes. The following information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job site safety. Job site safety is the sole responsibility ofthe project contractor. For planning purposes, we recommend that temporary cuts in the upper undocumented fill soils be no steeper than2 Horizontal to I Vertical (2.0H:1V). Temporary cuts in competent, native glacial soils at depth should be no steeper than 1 .5H:1V. If significant groundwater seepage or surface water flow were encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion. The slope protection measures may include covering cut slopes with NETSO'V G EOTEC H N ICAI ASSO CI ATES, I N C. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 10 plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts deeper than four feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to appropriate OSHA/WISHA regulations. Permanent cut and fill slopes should be no steeper than 2H:1V. However, flatter inclinations may be required in areas where loose soils are encountered. Permanent slopes should be vegetated and the vegetative cover maintained until established. Foundation Support Drilled Piers: We recommend that the western foundation line along with the western 10 feet of the northern and southern foundation lines and all interior foundations found within this zone be supported on 16- to 24-inch diameter reinforced concrete piers, extending a minimum of 30 feet below existing ground surface. The remainder of the foundations should be supported on native, competent bearing material or structural fill extending to that material. Our explorations did not advance the entire recommended depth of the drill piers; however, an open-hole drilling method will likely be feasible based on our field observations and prior experience with the overall site. If caving conditions are encountered, pile casing will be required. If large obstacles are encountered or refusal is met before the minimum recommended pile depths, NGA should be contacted to evaluate the existing conditions and provide alternalive recommendations. The holes should be cleaned of any slough or water prior to pouring concrete. Vy'e recommend that the concrete be readily available on site at the time of drilling. The holes should not be left open for any extended period of time, as sloughing debris andlor groundwater seepage into the excavations may hamper pier installation. In the following table, we present design friction, end bearing, and total axial compression capacities for 16-, 18- and 24-inch drilled piers, installed as recommended above. The friction component should be used to resist uplift forces only. The provided values do not include the weight of the piles. If the piles weight will be utilized to resist uplift forces, the buoyant unit weight and adequate safety factors should be used. Pile Diameter llnches) Total Pile Depth (Feet)Design X'riction (Tons)Design End Bearing (Tons) 16 30 l5 25 18 30 17 30 24 30 23 50 Lateral resistance on the piers could be calculated based on an equivalent fluid density of200 pounds per cubic foot (pcf) applied to two pile diameters. The upper two feet should be neglected for the purpose of calculating the lateral resistance. We should be retained to review pier design and observe drilled pier installation. wEtsoru GEorEcHNtcAt AssoclATEs, INc. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page ll Shatlow Foundations: For the portions of the structure supported on shallow spread footings, these footings should be placed on native medium dense or better soils, or structural fill extending to these soils. The foundation subgrade should be prepared as described in the Site Preparation and Grading subsection. Iffootings are supported on structural fill, the fill zone should extend outside the edges ofthe footings a distance equal to one-halfofthe depth ofthe over-excavation below the bottom ofthe footings. The transmission zone from pile-supported grade beams to regular foundations should be heavily reinforced. Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Minimum foundation widths of 18 and 24 inches should be used for continuous and isolated spread footings, respectively, but footings should also be sized based on anticipated loads and allowable soil bearing pressure. Standing water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. For foundations constructed as outlined above, we recommend an allowable design bearing pressure of not more than 2,000 pounds per square foot (psf) be used for the footing design for footings founded on the medium dense or better glacial soils or structural fill extending to the native competent material. The foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if higher bearing pressures are needed. Current International Building Code (lBC) guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than one inch total and ll2 inch differential between adjacent footings or across a distance of about 30 feet, based on our experience with similar projects. Lateral loads may be resisted by friction on the base of the footing and passive resistance against the subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. An equivalent fluid density of 200 pcf should be used for passive resistance design for a level ground surface adjacent to the footing. This level surface should extend a distance equal to at least three times the footing depth. These recommended values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and passive resistance, respectively. To achieve this value ofpassive resistance, the foundations should be poured "neaÍ" against the native medium dense soils, or compacted fill should be used as backfill against the front of the footing. We recommend that the upper one foot of soil be neglected when calculating the passive resistance. Frictional resistance should be neglected for footings supported on drilled piers. AIETSON GEOTECHNICAL ASSOC'A TES, INC. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, V/ashington NGA File No. 1065318 December 20,2018 Page'12 Retaining Walls Specific grading plans for this project were not available at the time this report was prepared, but retaining walls may be incorporated into project plans. In general, the lateral pressure acting on subsurface retaining walls is dependent on the nature and density of the soil behind the wall, the amount of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be less than if movement is limited by such factors as wall stiffness or bracing (at-rest condition). rWe recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces, be designed using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 40 pcf for yielding (active condition) walls, and 60 pcf for non- yielding (at-rest condition) walls. These recommended lateral earth pressures are for a drained granular backfill and are based on the assumption of a horizontal ground surface behind the wall for a distance of at least the subsurface height of the wall, and do not account for surcharge loads. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to subsurface walls and within a distance equal to the subsurface height of the wall. This would include the effects of surcharges such as traffic loads, floor slab loads, slopes, or other surface loads. We could consult with the structural engineer regarding additional loads on retaining walls during final design, if needed. A seismic design loading of 8H in psf should also be included in the wall design where ooH" is the total height of the wall. The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and by passive resistance acting on the below-grade portion of the foundation. Recommendations for frictional and passive resistance to lateral loads are presented in the Foundations subsection of this report. All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report. Care should be taken to prevent the buildup ofexcess lateral soil pressures due to over-compaction ofthe wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting the backfill with small, hand-operated compactors within a distance behind the wall equal to at least one-half the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower compactive energy of the hand-operated equipment. The recommended level of compaction should still be maintained. Permanent drainage systems should be installed for retaining walls. Recommendations for these systems are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to evaluate the proposed wall drain backfill material and observe installation of the drainage systems. lversoru G EoTEc H N tcAt Asso ct ATE9, I N c. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, \üashington NGA File No. I 0653 l8 December 20,2018 Page 13 Structural Fill General: Fill placed beneath foundations, pavement, or other settlement-sensitive structures should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in-place density tests to document the attainment of the desired degree of relative compaction. The area to receive the fiIl should be suitably prepared as described in the Site Preparation and Grading subsection prior to beginning fill placement. Sloping areas to receive fill should be benched using a minimum 8-foot wide horizontal benches into competent soils. Materials: Structural fill should consist of a good quality, granular soil, free of organics and other deleterious material, and be well graded to a maximum size of about three inches. All-weather fill should contain no more than five-percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing the U.S. 314-inc,h sieve). Some of the more granular on-site soils may be suitable for use as structural fill depending on the moisture content of the soil during construction. We should be retained to evaluate all proposed structural fill material prior to placement. Fitl Placement: Following subgrade preparation, placement of structural fill may proceed. All filling should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557 Compaction Test procedure. The moisture content of the soils to be compacted should be within about two percent of optimum so that a readily compactable condition exists. It may be necessary to over- excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction and should be tested. Slab-on-Grade Slabs-on-grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. Vy'e recommend that all floor slabs be underlain by at least six inches of free-draining gravel with less than three percent by weight of the material passing Sieve #200 for use as a capillary break. lùy'e recommend that the capillary break be hydraulically connected to the footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting (6-mil minimum), should be placed over the capillary break material. An additional 2-inch-thick moist sand layer may be used to cover the vapor barrier. This sand layer is optional, and is intended to be used to protect the vapor barrier membrane and to aid in curing the concrete. NETSO'V GEOTECHNICAI ASSO CIATES, INC. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 14 Pavements Pavement subgrade preparation and structural filling where required, should be completed as recommended in the Site Preparation and Grading and Structural Fill subsections of this report. The pavement subgrade should be proof-rolled with a heavy, rubber-tired piece of equipment, to identify soft or yielding areas that require repair. The pavement section should be underlain by a minimum of six inches of clean granular pit run or crushed rock. We should be retained to observe the proof-rolling and recommend repairs prior to placement of the asphalt or hard surfaces. Utilities We recommend that underground utilities be bedded with a minimum 12 inches of pea gravel prior to backfilling the trench with on-site or imported material. Trenches within settlement sensitive areas should be compacte d To 95yo of the modified proctor as described in the Structural Fill subsection of this report. Trenches located in non-structural areas should be compacted to a minimum 90%o of the maximum dry density. Trench backfill compaction should be tested. Site Drainage Surface Drainage: The control of surface water and near-surface groundwater is very important for the long-term stability of the site slopes. We recommend that temporary and final site grading be designed to direct surface water away from the structures and away from the steeper site slopes. Roof drains should be installed around the site structures. The roofdrains should consist ofgutters and downspouts to collect stormwater runoff from the roof. The downspouts should connect with 4-inch diameter, rigid PVC tightline pipes to the main catch basin. The footing and roof drains should be routed in separate tightlines into catch basins/cleanouts. Stormwater from the driveway and yard drains should also be collected and directed through tightlines into the main catch basin and then through the controlled drainage system. In our opinion, due to the steep slopes and high erosion susceptibility of the onsite soils interpreted to underlie the site, stormwater infiltration is not considered feasible for this project. Likewise, dispersion of stormwater near the top of slopes may increase surface flow over the steep slope and is not considered a feasible alternative for this project. In our opinion it may be most practical to install a tightline pipe down the surface of the site slopes to directrunoff to an energy dissipatoralongthetoe of the steep slope near the western property line. NELSOA' G EOTEC H N I C AL ASSOC'A TES, I N C. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, V/ashington NGA File No. 1065318 December 20,2018 Page 15 Runoff from proposed structures should be led through tightline pipes to catch basins. Water collected in the footing drains of the structure should be separately tightlined to the catch basin. The footing drain system should have a minimum of 12 inches of vertical fall before it is connected to the roof drain system. The yard areas and any proposed driveway areas should be sloped to allow collection of runoff in yard and driveway drains, and this water should be directed into the main catch basin via tightline pipes. The number and locations of catch basins, cleanouts, and downspouts may be determined during site design, and altered during construction provided the intent of the drainage mitigation system design is not changed. The water collected from the roof drains, footing drains, driveway and yard drains should be routed via buried 4- to 6-inch minimum diameter PVC tightline pipes into catch basins. The outflows from these catch basins are then routed to the main catch basin. The main catch basin should be anchored into competent, native material. From the main catch basin, the outfall pipe should be connected and constructed to maintain positive water flow. We recommend a 4-inch minimum diameter solid HDPE pipe installed over the steep slope and down to the toe of the slope near the western property line. The HDPE pipe should be anchored to the main catch basin. The HDPE pipe should also be anchored with a flange encased in a concrete deadman. The HDPE pipe draining the main catch basin should emerge from the slope and extend down the surface of the site slopes to a suitable discharge point at the toe of the slope. The pipe should lie directly on the ground surface and be anchored to minimize lateral movement. The anchors should be placed at locations selected for optimum performance, preferably near the top and toe of slope. A diffuser tee should be placed at the outfall of the HDPE drainpipe at the toe of the steep slope. The diffuser tee is used to slow and spread out the flow from the HDPE drainpipe to dissipate the energy and erosion potential of the flow. The diffuser tee should drain onto a diffuser pad constructed from 8- to 12- inch rock spalls or into a level-spreader dispersion trench to further disperse the flow from the outlet, armor the toe of the slope, further minimize erosion effects, and to hold the diffuser tee in place. We should be retained during construction to provide consultation on the specific location of the diffuser tee and outfall of the HDPE pipe. Subsurface Drainage: If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out of the excavation and routed into an approved outlet. We recommend that all existing and future down spouts and footing drains be tightlined to an approved discharge location at the bottom of the slope or within the street. Stormwater systems within this site should be designed in accordance with City of Edmonds regulations. 'VEISO'V G EOTEC H N ICAI ASSO CI ATES, I N C. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 16 We recommend the use of footing drains around the structure foundations. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum four-inch-diameter, rigid, slotted or perforated, PVC pipe surrounded by free-draining material wrapped in a filter fabric. We recommend that the free-draining material consist of an 18-inch-wide zone of clean (less than three-percent fines), granular material placed along the back of walls. Washed rock is an acceptable drain material, or a drainage composite may be used instead. The free-draining material should extend up the wall to one foot below the finished surface. The top foot of soil should consist of low permeability soil placed over plastic sheeting or building paper to minimize the migration of surface water or silt into the footing drain. Footing drains should discharge into tightlines leading to an appropriate collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to wall or footing drains. Under no circumstances should runoff be allowed to flow over the steep slope. CONSTRUCTION MONITORING We should be retained to provide construction monitoring services during the earthwork phase of the project to evaluate subgrade conditions, temporary cut conditions, fill compaction, and drainage system installation. USE OF THIS REPORT NGA has prepared this report for Mr. Garth Hitchens and his agents, for use in the planning and design of the development on this site only. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors' methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. There are possible variations in subsurface conditions between the explorations and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the budget and schedule. We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. We should be contacted a minimum of one week prior to construction activities and could attend pre-construction meetings if requested. ,VELSOA' G E OT EC H N I C A L A SSOC'A TES,'NC. Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, Washington NGA File No. 1065318 December 20,2018 Page 17 All people who own or occupy homes on hillsides should realize that landslide movements are always a possibility. The landowner should periodically inspect the slope, especially after a winter storm. If distress is evident, a geotechnical engineer should be contacted for advice on remedial/preventative measures. The probability that landsliding will occur is substantially reduced by the proper maintenance of drainage systems at the site. Therefore, the homeowner should take responsibility for performing such maintenance. Consequently, we recommend that a copy of our report be provided to any future homeowners of the properfy if the home is sold. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect in this area at. the time this report was prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. o-o-o ruEtSO'V G EOTECHNICAT ASSO CIATES, INC Geotechnical Engineering Evaluation - REVISED Hitchens Residence Development Edmonds, lilashington NGA File No. 1065318 December 20,2018 Page l8 It has been a pleasure to provide service to you on this project. If you have any questions or require further information, please call. Sincerely, ,vEtso^, G EoTEcH N tcAt Asso cl ATES, I N c. ,ráú Alex B. Rinaldi, GIT Staff Geologist II Khaled M. Shawish, PE Principal ABR:KMS:dy Seven Figures Attached ,VEISO'V G EOTECH NICAL ASSOC'A TES, INC. VICINITY MAP N Not to Scale t'î I Sot Corr O\1mpic View 0r ;. @ t .¡tu$ f. orlsil" I t i,q :l€ I 3ì!!, f.n Sf/ô6 5 Þ ô{ Seaview Park Q I r,ìrf 5l:ìÌ', I i15tii I'i sV/ ôì s Faso- Hutt Park : ..t 't'I fr/rh Sr Si!ø, o ì fr;?rl, 51 Sl! PERR Seaview I arl^ê1^^¡ i,., ô^!!.\/.1 Edmonds, WA Project Site Project Number I 06531 I Vista Del Mar Drive Residence Development Vicinity Map NE LsoN GEorEcHNtcAL AssocrATEs, lNc.N G A GEorEcHNrcAL ENGTNEERS & GEoLocrsrs Wædlnvllleolrcê 17311f35thAve. NE.A-S Wôodiñville WA9æ72 (425) 4861 æ9 / Fax: 4a1 -2510 m. nel$ngeolech com EåstWênâtchêê oñlcê 55æ lnduslry tane, 12 Easl W€nâlchee. W49ffi2 (ffi) æ5 7æ6/Fax:ff5 7692 No.Date Rev¡s¡on By CK 1 11tAt1A Original DPN ABR Figure 1 z./) - \____\ lr-'-¿ {t' o @ oo ot il !o .c il) ooØ (¡) o E'x oLo-o- o$ trs È o .Ë cn o II *f (E Eo? -o cn ìo > E o(! E ı(J oor (¡)o Ec(! ac .9 (!Io(t -oo tl) Q) EoL: U)oo E !o co Eoøo -o -(!o oÈo it OcoLo ot oz t¡J (, I¡JJ o .ç too-oL fL o o E'= oäs,o.f-ıbı_oc*(5ô L- .g .ÞÈı:toZo co (ıo-oı AE(!(r) -UtC.r'-\ 8g0 o- ìî ooÈ l Project Number 1 06531 I Vista Del Mar Drive Residence Development Schematic Site Plan NILSoN GEoTEcHNICAL N G A AssocrATEs, lNc GEorEcHNrcAL ENGtNEERS & GEoLoclsrs WodlnvlllêOllcê 173r1-1351h Ave. NE. A-ru Wood¡nville, WA 9æ72 Í4%) 4æjæ I Fax. &1-2510 www.nelsongeolech.con ÊåstWênåichæ qñce 5526 lnduslry Lane, 12 Eãsl We¡€tch€ê. WA 9m2 (ffi) 6t76S / Fåx: æ+7692 No.Date Rêv¡sion By CK 11tAhA Or¡g¡nal DPN ABR Figure 2 @oo-c5o U) o(o oN o @ os o EooÈåo(I'-o>Þ>(1)(I' (EEıøôc þ-,.9CE LooËo PE ¡.eıE =41!_ı --oıøıo!d) .!¿E(trr(It--*ı Ërn lYã O UJ.E'NE5eıızØÞu âñ oc! (f) o @e! o\l C\t i ooN 0)L ú)(ûo Ë c) o_(ú Ioo ocı c) o) Eo .cı Io-cIÞco ! o (') .g(t ftt co E 0)g U)o c) E Io cooo(r,o -o .9, co (Jo U) thatogo iúoc 0)L o) oú. Po.= úl EËul r- I I oo oO(ooco .ano oc! o @ (¡) ı z l-fL U) J rÌÌ o. ollf tro +,g -9ox uJ Io 1 o (5 .9)ø(¡)o ct)c'-od] o 1ıc>oOEJ(E olJ E¡'Es, o=oo I'ê' 1 oE^b9Ogo.= ã,ã Eg,ñ o v,o =-cËoz oc!oo@s (teal) uortenêl= fuerlrqrv oo(o Project Number 1 06531 I Vista Del Mar Drive Residence Development Cross-Section A-A' NE LsoN Georecxt¡lc¡t- AssocrATEs, lNc.N G A GEofEcHNICAL ENGINEERS & GEOLOGISTS WædlnvllloOficê 17311¡3Íh Ave. NÊ, A-m Woodinville, WAS72 (425) 4æ169 / Fax: 41'2510 ww.n¿bongeoleêh.6ñ EâilWênålcìæ dñcê Sã Indßlry Lónê, t2 Easl Wenalchee. WA W2 (ffi) 6t7ffi / Fax: ffi-7@ No.Date Revis¡on By CK 1 11tat18 Original DPN ABR Figure 3 UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GROUP SYMBOL GROUP NAME COARSE - GRAINED SOILS MORE THAN 50 % RETAINED ON NO.200 S|EVE GRAVEL MORE THAN 50 % OF COARSE FRACTION RETAINED ON NO.4 SIEVE CLEAN GRAVEL GW WELL-GRADED, FINE TO COARSE GRAVEL GP POORLY-GRADED GRAVEL GRAVEL WITH FINES GM SILTY GRAVEL GC CLAYEY GRAVEL SAND MORE THAN 50 % OF COARSE FRACTION PASSES NO.4 SIEVE CLEAN SAND SW WELL-GRADED SAND, FINE TO COARSE SAND SP POORLY GRADED SAND SAND WITH FINES SM SILTY SAND SC CLAYEY SAND FINE - GRAINED SOILS MORE THAN 50 % PASSES NO.2OO SIEVE SILT AND CLAY LIQUID LIMIT LESS THAN 50 % INORGANIC ML SILT CL CLAY ORGANIC OL ORGANIC SILT, ORGANIC CLAY SILT AND CLAY LIQUID LIMIT 50 % OR MORE INORGANIC MH SILT OF HIGH PLASTICITY, ELASTIC SILT CH CLAY OF HIGH PLASTICITY, FAT CLAY ORGANIC OH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES 1) Field classif¡cation is based on visual examination of so¡l in general accordance with ASTM D 2488-93. SOIL MOISTURE MODIFIERS: Dry - Absence of moisture, dusty, dry to the touch 2) Soil classificat¡on using laboratory tests is based on ASTM D 2488-93.Moist - Damp, but no visible water 3) Descr¡ptions of soil density or consistency are based on interpretation of blowcount data, visual appearance of soils, and/or test data. Wet - Visible free water or saturated, usually soil is obtained from below water table Pro.¡ect Number 1 06531 I Vista Del Mar Drive Residence Development Soil Classification Chart NELSoN GEoTECHNICAL N G A AssoctATEs, lNc GEoTEcHNICAL ENGINEERS & GEOLOGISTS Wdlnvllþ Oficê 17311-135th Ave. NE. A-ffi Woodinville, WA W72 (425) 48ê1æ9 / Fåx:41'2510 East Wenalchæ Oflce 5526 lnduslry Lãne, f2 Eã61Wenalchee. WA W2 ww.nel$nseolech.øm (æ)66f76S/Faxrffi-7692 No.Date Revision By CK ,|1'lala Orìg¡nal DPN ABR Figure 4 BORING LOG B-1 Approx¡mate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Resistance (Blows/foot - O) 10 2,O q0 { 5p 50, o) EU'(¡)F ào (E o -c)oJ Piezometer lnstallation - Ground Water Data (Depth in Feet) Description .9.go(g o o)oJ oıfootrıä }E 8,9 â_oEbp E6- SEão Moisture Content (Percent - I) 10 20 30 40 50 50,tttll Topsoil Gray, fine to coarse sand with silt (very loose, moist) GllÐ -becomes med¡um dense, with iron-ox¡de staining, wood debr¡s, and organics Orange-brown, fine to coarse sand with s¡lt, gravel, and iron-oxide staining (medium dense, moist) -becomes gray-brown, dense, w¡th no iron-oxide sta¡ning -no recovery SP-SM 2 21 l6 40 47 ! T T ! ¡ 5 10 5 -10 -15 20 -25 Boring met refusal on a cobble below ex¡sting grade at 14.0 feet on 10/31/18. Groundwater seepage was not encountered during drilling. 15 20 25 LEGEND f] sol¡c PVc Pipe ffil concrete M Moisture Content A Atterberg Lim¡ts G Grain-size Analysis DS Direct Shear PP Pocket Penetrometer Readings, tons/ft P Sample Pushed T Tr¡axial tests, analys¡s and judgement. They are not necessarily on this log. t Depth Driven and Amount Recovered with z-¡nch O.D. Split-Spoon Sampler Depth Dr¡ven and Amount Recovered with 3-¡nch Shelby Tube Sampler [=l slotte¿ PVC Pipe - Monument/ CaÞ to Piezomeler * Liquid Limit + Plastic Limit Bentonite $N Native soil H S¡t¡ca Sand V Water Level NOTE: Subsurface cond¡tions depicted represent our obseryations at the t¡me and location of this exploratory hole, modified by enginê€ring representative of other tim€s and loæt¡ons. We cannot accept respons¡bil¡ty for the use or interpretat¡on by others of infomat¡on present€d Project Number 1 06531 8 Vista Del Mar Drive Residence Development Boring Log NELSoN GEoTEcHNICAL N G A AssoctATEs, lNc. GEorEcHNtcAL ENGTNEERS & GEoLoclsrs WædlnvllleOmcê 17311-l35lh Ave. NE. A-ru Wôodinville. W498072 (4?5) 486¡69 / Fax: 481-2510 w.nelengedech.æm Eâst Wênarchæ ofrce 55æ lndusty Lane. #2 ÊastWenålchee. WASæ2 (ru) 67ffi / Fâx: 65-7æ2 No.Date Revision By CK 11t8t18 Original DPN ABR Figure 5 Page 1 of I co É6; BORING LOG B-2 Approximate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Res¡stance (Blowsffoot - O) 10 ?0 q0 10 5p 50, q, 'a Ø(¡)F Þo (5 o .cI(û J Piezometer lnstallation - Ground Water Data (Depth in Feet) Description ,(J .c, CLg o o)oJ o-o = -c¡otroô }E 8s â-o:.o:tritr-ö: es Moisture Content (Percent - t)10 20 30 40tttt 50 50, Topsoil Light brown, fine to medium sand with silt and trace roots (loose, moist) (FILL) light brown, fìne to coarse sand with silt, gravel, and trace organics (medium dense, moist) -becomes orange-brown, medium dense, with iron-oxide staining -becomes dense -becomes very dense SP-SM ô 16 33 19 49 83 I I I I 5 10 15 I20 I 5 -10 -15 20 25 Boring met refusal on a cobble below existing grade at 21.5 feet on 10131118. Groundwater seepage was not encountered during drilling. 25 LEGEND I sotic PVC Pipe [,,.'-i-T concrete M Moisture Content A Atterberg Limits G Grain-size Analysis DS Direct Shear PP Pocket Penetrometer Readings, tons/ft P Sample Pushed T Tr¡axial Slotted PVC Pipe MonumenV Cap to Piezometer Liquid Limit Plastic L¡m¡t Bentonite W Native Soil fl silica sand Y Water Level Depth Dr¡ven and Amount Recovered with 2-inch O.D. Splitspoon Sampler Depth Driven and Amount Recovered with 3-inch Shelby Tube Sampler I * + representative of olher times and locations. We ænnot accept responsib¡lity for the use or interpretat¡on by others of informat¡on presented on this log. Project Number I 06531 I Vista Del Mar Drive Residence Development Boring Log NELSoN GeorEcxNrc^Au N G A AssoctATEs, lNc. GEoTEcHNICAL ENGINEERS & GEOLOGISTS WdlnvlllêOtÍce 17311l35lhAvê NE A-ffi Woodinville. WA9æ72 1425) Æç1æ9 I Fax: ß1-2510 ww.nelsongeolech.@m Eâst wênårchêê ofrcê 5526 lndusty Lane. *2 East Wenálchee. WA 9m2 (ffi ) 65'76S / Fax: æ5-7692 No.Date Revis¡on By CK 11tgt18 Original DPN ABR Figure 6 Page 1 of 1 c BORING LOG B-3 Approximate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Resistance (Blowsfoot - O)10 10 q0 10 5p 50* q) .F Ø(¡)F ào (ú o.o(ú J Piezometer lnstallation - Ground Waler Data (Depth in Feet) Description ,E o.g o o)oJ o-ıf-OôÊoı ìc ı3 ô -o = o+ Ê6-ã o€ö: eo Moisture Content (Percent - l)l0 20 30 40 50 50,rrttt Topsoil Orange-brown, fine to coarse sand with silt, gravel, and iron-oxide staining (loose, moist) (FILL) Orange-brown, fine to coarse sand with gravel, silt, and iron-oxide staining (medium dense, moist) Orange-brown, fine to coarse sand with gravel and iron-oxide staining (medium dense, moist) -becomes orange-brown to gray-brown, dense Orange-brown, fine to coarse sand w¡th silt, gravel, and iron-oxide sta¡ning (very dense, moist) ,# .¡:. .. . .:. ¡: " --..:- t'. SP.SM SP SP-SM I 15 20 43 48 50-6 50-6 ¡ T I !10 t 15 r20 r25 5 -10 -15 20 -25 Boring met refusal on a cobble below existing grade at 25.3 feet on 10/31/18. Groundwater seepage was not encountered during drilling. LEGEND E Oeotn Driven and Amount Recovered I wit'n 2-inch O.D. Split-Spoon Sampler I mr: ""u"s.ïlff ;:tff cove red n E I * + Solid PVC Pipe Slotted PVC Pipe MonumenU Cap to P¡ezometer Liquid Limit Plastic Limit ffil Concrete Bentonite W Native Soil fl silica Sand Y Water Level M Moisture Content A Atterberg Limits G Grain-size Analysis DS Direct Shear PP Pocket Penetrometer Readings, tons/ft P Sample Pushed T Triaxial representat¡ve of other t¡mes and locat¡ons. We cannot accept responsib¡l¡ty for the use or ¡nterpretat¡on by others of informat¡on presented on this log. Project Number 1065318 Vista Del Mar Drive Residence Development Boring Log NELSoN GEoTECHNICAL N G A AssoctATEs, lNc GEorEcHNrcAL ENGtNEERS & GEoLoclsrs Wdlnvlllê øñcê. 17311l35lhAvê NE A-m woodìnvìlle. WAS072 (425) 48ç1669 / Fax:41'2510 East Wenalchæ oñlcê 55ælñduBlry Lane, #2 Eesl Wêner¿heè. wAg$m ww.ndsongeolech.@m (ru) @765/ Far 6'7æ2 No.Date Revision By CK 11t8t1g Or¡ginal DPN ABR Figure 7 Page 1 of 1 Co