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20170406_Resub_ soils report.pdfRECEIVED a s s o c i a t e d 04/06/2017 e a r t h s c i e n c e s incorporated Development Services Ctr. Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report EDMONDS APARTMENTS Edmonds, Washington Prepared For: CORNERSTONE ARCHITECTURAL GROUP Project No. KE140265A FebrUary 11, 2016 F4011 February 11, 2016 Project No. KE140265A Mr. Roy Gursh c/o Cornerstone Architectural Group 6161 Northeast 1751h Street, Suite 101 Kenmore, Washington 98028 Attention: Mr. Steve Barnes a s s o c i a t e d ea rt h sc i e n ces I !I .� C. � 1) '� , 11 t t� Cl Subject: Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report Edmonds Apartments Edmonds, Washington Dear Mr. Barnes: We are pleased to present the enclosed copies of the above -referenced report. This report summarizes the results of our subsurface exploration, geologic hazard, and geotechnical engineering studies and offers recommendations for the preliminary design and development of the proposed project. Our recommendations are preliminary in that construction details have not been finalized at the time of this report. We have enjoyed working with you on this study and are confident that the recommendations presented in this report will aid in the successful completion of your project. if you should have any questions, or if we can be of additional help to you, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington Kurt D. Merriman, P.E. Senior Principal Engineer KDM/pc KE140265A2 Projects\20140265\KE\WP Kirkland Office 1 911 Fifth Avenue I Kirkland, WA 98033 P 1425.827.7701 F 1425.827.5424 Everett Office 12911 Y2 Hewitt Avenue, Suite 2 1 Everett, WA 98201 P 1425.259.0522 F 1425. 827.5424 Tacoma Office 1 1552 Commerce Street, Suite 102 1 Tacoma, WA 98402 P 1253.722.2992 F 1253.722.2993 www.aesgeo.com SUBSURFACE EXPLORATION, GEOLOGIC HAZARD, AND GEOTECHNICAL ENGINEERING REPORT EDMONDS APARTMENTS Edmonds, Washington Preparedfor: Mr. Roy Gursli c/o Cornerstone Architectural Group 6161 Northeast 175 1h Street, Suite 101 Kenmore, Washington 98028 Prepared by: Associated Earth Sciences, Inc. 9115 1h Avenue Kirkland, Washington 98033 425-827-7701 Fax: 425-827-5424 February 11, 2016 Project No. KE140265A Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Project and Site Conditions 1. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of Associated Earth Sciences, Inc.'s (AESI's) subsurface exploration, geologic hazard, and geotechnical engineering study for the Edmonds Apartments project, located 8509 244 1h Avenue Southwest, in Edmonds, Washington (Figure 1). The site boundaries, the proposed building area, and the approximate locations of the explorations accomplished for this study are presented on the "Site and Exploration Plan," Figure 2. Logs of the subsurface explorations completed for this study are included in the Appendix. 1.1 Purpose and Scope The purpose of this study was to provide preliminary geotechnical engineering recommendations to be utilized in the design of the project. This study included a review of selected available geologic literature, excavation of three exploration pits, and performing geologic studies to assess the type, thickness, distribution, and physical properties of the subsurface sediments and depth of shallow ground water. Geotechnical engineering studies were completed to establish recommendations for the type of suitable foundations and floors, allowable foundation soil bearing pressure, anticipated foundation and floor settlement, and drainage considerations. Subsurface data was also used to formulate our conclusions regarding the feasibility of infiltrating storm water generated on -site. This report summarizes our fieldwork, and offers preliminary recommendations based on our present understanding of the project. We recommend that we be allowed to review the recommendations presented in this report, and revise them, if needed, when project plans have been developed. 1.2 Authorization Written authorization to proceed with this study was granted by Mr. Reider (Roy) Gursli by means of our signed scope of work and cost proposal. Our study was accomplished in general accordance with our proposal dated May 2, 2014. This report has been prepared for the exclusive use of Mr. Reider Gursli, the Cornerstone Architectural Group, and their agents, for specific application to this project. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering and engineering geology practices in effect in this area at the time our report was prepared. No other warranty, express or implied, is made. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 1 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Project and Site Conditions 2.0 PROJECT AND SITE DESCRIPTION The project site consists of the parcel (Snohomish County Parcel No. 00463303200303) located at 8509 244 1h Avenue Southwest, with an approximate total area of approximate ly 2 /3 acre in Edmonds, Washington. We understand that the proposed project will include demolition of two existing residential four-plex structures and the construction of new multifamily residential structures, along with associated access, parking, and utilities. We understand that infiltration is currently under consideration for the handling of storm water from the resulting impervious surfaces. For the purpose of preparing this report, we have assumed that the new structures will be constructed close to existing grades without the need for deep earthwork cuts or thick structural fills. We have assumed that light to moderate foundation loads typical of wood - framed, residential construction will be required. Should actual project design differ significantly from our assumptions, AESI should be allowed to review the report, and revise the recommendations, as appropriate. The site is bounded by existing multifamily residential structures to the north, south, and west. A restaurant and associated parking lots border the site to the east. Site access is from the south via a private drive connected to 244 th Street SW. The site currently contains two residential four-plex structures, an asphalt drive, and gravel parking pads. The property is vegetated with low grass with sparse, mature trees located along property boundaries. Site topography is gently sloping towards the east, with overall vertical relief visually estimated at about 20 feet. A moderately steep slope is present in the western half of the site, adjacent to the existing four-plex structure and gravel drive, and accommodates a grade change visually estimated at about 4 to 8 feet. A topographic survey of the site was not available at the time our subsurface exploration program was completed. 3.0 SUBSURFACE EXPLORATION Our subsurface exploration completed for this project included excavation of three exploration pits using an excavator subcontracted through AESI on September 28, 2015. The conclusions, and recommendations presented in this report are based on the explorations completed for this study. The locations and depths of the explorations were completed within site and budget constraints. In particular, the presence of underground utilities limited the locations where we could advance subsurface explorations. The exploration pits permitted direct visual observation of subsurface conditions. Materials encountered in the exploration pits were studied and classified in the field by a geotechnical February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 2 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Project and Site Conditions engineer from our firm. Selected samples were then transported to our laboratory for further visual classification, and testing, as necessary. 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visual reconnaissance of the site, and review of selected applicable geologic literature. As shown on the exploration logs, the exploration pits generally encountered topsoil and/or fill over unsorted, dense to very dense silty sand with variable amounts of gravel which we interpreted to be Vashon lodgement till. The following section presents more detailed subsurface information organized from the youngest to the oldest sediment types. Because of the nature of exploratory work below ground, extrapolation of subsurface conditions between field explorations is necessary. It should be noted that differing subsurface conditions may sometimes be present due to the random nature of deposition and the alteration of topography by past grading and/or filling. The nature and extent of any variations between the field explorations may not become fully evident until construction begins. 4.1 Stratigraphy Fill Although no fill soils were encountered in our explorations, it is likely that some areas of fill underlie portions of the site. Areas likely to contain fill include utility trenches and the area immediately surrounding the existing buildings. Topsoil A surficial, organic sod/topsoil layer was encountered at the locations of exploration pits EP-1 and EP-2. The sod/topsoil layer was approximately 6 inches thick. Because of its relatively loose condition and high organic content, the topsoil layer is not considered suitable for foundation support or for use in a structural fill. Gravel Driveway Pad Moderately compacted, crushed gravel was encountered in exploration pit EP-3 to a depth of about 1 foot below ground surface (bgs). This sequence is likely present around the site at other gravel driveway locations, and at the gravel parking pad south of the existing eastern February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMGlpc — KE140265A2 —Projects �20140265 � KE�WP Page 3 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Project and Site Conditions building. We recommend removal of the gravel pads and underlying loose soils, if present, in order to expose medium to very dense native sediments in load bearing areas. Voshon Lodgement Till Sediments encountered in all exploration pits generally consisted of unsorted, cemented, medium dense to very dense silty sand with variable quantities of gravel. These sediments were generally medium dense and tan within a couple feet of the surface, and became denser and greyer in color with depth. We interpret these sediments to be representative of Vashon lodgement till. Vashon lodgement till consists of sediments that were deposited directly from basal, debris -laden glacial ice during the Vashon Stade of the Fraser Glaciation, approximately 12,500 to 15,000 years ago. The high relative density characteristic of the Vashon lodgement till is due to its consolidation by the massive weight of the glacial ice from which it was deposited. The reduced density and lighter color observed within approximately 3 to 4 feet of the ground surface is interpreted to be due to weathering. At all exploration locations, the lodgement till extended beyond the maximum depths explored of approximately 5.5 to 8.5 feet. The lodgement till soils are suitable for foundation, floor, and pavement loads. Permeability of lodgement till is relatively low, and storm water infiltration into the till is not recommended. Published Geologic Map Our interpretations of subsurface conditions on -site are generally consistent with a published geologic map of the area, as represented by the Geologic Map of the Edmonds East and part of the Edmonds West quadrangles, Washington, by J.P. Minard (1983). The referenced map indicates that the project area is expected to be underlain at shallow depth by Vashon lodgement till. Our interpretation of lodgement till at the project site is in general agreement with the published geologic mapping of the site and vicinity. 4.2 HVdrologV Ground water seepage was not encountered in any of the exploration pits excavated for our study at the time of exploration, September 28, 2015. It should be noted that the occurrence and level of ground water seepage at the site may vary in response to such factors as changes in season, precipitation, and site use. 4.3 Infiltration Feasibility Vashon lodgement till underlies the site to the maximum depth explored of about 8.5 feet bgs. Permeability of lodgement till is relatively low, and storm water infiltration into the till is not recommended. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 4 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Geologic Hazards and Mitigations 11. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and shallow ground water conditions as observed and discussed herein. 5.0 SEISMIC HAZARDS AND MITIGATIONS Earthquakes occur in the Puget Lowland with great regularity. The vast majority of these events are small and are usually not felt by people. However, large earthquakes do occur, as evidenced by the 1949, 7.2-magnitude event; the 2001, 6.8-magnitude event; and the 1965, 6.5-magnitude event. The 1949 earthquake appears to have been the largest in this region during recorded history and was centered in the Olympia area. Evaluation of earthquake return rates indicates that an earthquake of the magnitude between 5.5 and 6.0 is likely within a given 20-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides, 3) liquefaction, and 4) ground motion. The potential for each of these hazards to adversely impact the proposed project is discussed below. 5.1 Surficial Ground RuDture The nearest known fault trace to the project site is the South Whidbey Island Fault Zone (SWIFZ), located approximately 4 to 5 miles northeast of the site. A 2005 study by the U.S. Geological Survey (USGS) (Sherrod et al., 2005, Holocene Fault Scarps and Shallow Magnetic Anomalies Along the Southern Whidbey Island Fault Zone near Woodinville, Washington, Open - File Report 2005-1136, March 2005) reported that "strong" evidence of prehistoric earthquake activity has been observed along two fault strands thought to be part of the southeastward extension of the SWIFZ. The study suggests as many as nine earthquake events along the SWIFZ may have occurred within the last 16,400 years. The recognition of this fault splay is relatively new, and data pertaining to it are limited with the studies still ongoing. The recurrence interval of movement along this fault system is still unknown, although it is hypothesized to be in excess of one thousand years. Due to the suspected long recurrence interval for this fault zone, the potential for surficial ground rupture is considered to be low during the expected life of the proposed structure. 5.2 Seismicallv Induced Landslides It is our opinion that the potential risk of damage to the proposed development by seismically induced slope failures is low due to the slope across the site being very gentle and the February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 5 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Geologic Hazards and Mitigations likelihood of the existing moderate on -site slope being re -graded during construction. We did not complete a quantitative slope stability analysis as part of this study, and none is warranted at this time, in our opinion. 5.3 Liquefaction It is our opinion that the risk of damage to the proposed structure by liquefaction is low due to the high relative density of the underlying sediments, and the lack of adverse ground water conditions. No mitigation of liquefaction hazards is recommended for the project. 5.4 Ground Motion It is our opinion that earthquake damage to the proposed structures, when founded on suitable bearing strata in accordance with the recommendations contained herein, will likely be caused by the intensity and acceleration associated with the event. Structural design of the buildings should follow 2012 International Building Code (113C) standards using Site Class "D" as defined in Table 20.3-1 of American Society of Civil Engineers (ASCE) 7 — Minimum Design Loads for Buildings and Other Structures. 6.0 EROSION HAZARDS AND MITIGATIONS The lodgement till sediments contain a high percentage of silt and fine sand and are sensitive to erosion, particularly in the more steeply sloping portions of the site. In order to control erosion and reduce the amount of sediment transport off the site during construction, the following recommendations should be followed. 1. Construction activity should be scheduled or phased as much as possible to reduce the amount of earthwork activity that is performed during the winter months. 2. The winter performance of a site is dependent on a well -conceived plan for control of site erosion and storm water runoff. The project temporary erosion and sediment control (TESC) plan should include ground -cover measures, access roads, and staging areas. The contractor must implement and maintain the required measures. A site maintenance plan should be in place in the event storm water turbidity measurements are greater than the Washington State Department of Ecology (Ecology) standards. 3. TESC measures for a given area to be graded or otherwise worked should be installed soon after ground clearing. The recommended sequence of construction within a given area after clearing would be to install sediment traps and/or ponds and establish perimeter flow control prior to starting mass grading. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMGlpc — KE140265A2 —Projects �20140265 � KE�WP Page 6 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Geologic Hazards and Mitigations 4. During the wetter months of the year, or when large storm events are predicted during the summer months, each work area should be stabilized so that if showers occur, the work area can receive the rainfall without excessive erosion or sediment transport. The required measures for an area to be "buttoned -up" will depend on the time of year and the duration the area will be left un-worked. During the winter months, areas that are to be left un-worked for more than 2 days should be mulched or covered with plastic. During the summer months, stabilization will usually consist of seal -rolling the subgrade. Such measures will aid in the contractor's ability to get back into a work area after a storm event. The stabilization process also includes establishing temporary storm water conveyance channels through work areas to route runoff to the approved treatment facilities. 5. All disturbed areas should be revegetated as soon as possible. If it is outside of the growing season, the disturbed areas should be covered with mulch, as recommended in the erosion control plan. Straw mulch provides a cost-effective cover measure and can be made wind -resistant with the application of a tackifier after it is placed. 6. Surface runoff and discharge should be controlled during and following development. Uncontrolled discharge may promote erosion and sediment transport. 7. Soils that are to be reused around the site should be stored in such a manner as to reduce erosion from the stockpile. Protective measures may include, but are not limited to, covering with plastic sheeting, the use of low stockpiles in flat areas, or the use of silt fences around pile perimeters. 8. On -site erosion control inspections and turbidity monitoring (when required) should be performed in accordance with Ecology requirements. Weekly and monthly reporting to Ecology should be performed on a regularly scheduled basis. Temporary and permanent erosion control and drainage measures should be adjusted and maintained, as necessary, for the duration of project construction. It is our opinion that with the proper implementation of the TESC plans and by field -adjusting appropriate mitigation elements (best management practices [BMPs]) throughout construction, as recommended by the erosion control inspector, the potential adverse impacts from erosion hazards on the project may be mitigated. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 7 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations 111111. PRELIMINARY DESIGN RECOMMENDATIONS 7.0 INTRODUCTION Our exploration indicates that, from a geotechnical standpoint, the parcel is suitable for the proposed development provided the recommendations contained herein are properly followed. The foundation bearing stratum is relatively shallow and conventional spread - footing foundations may be utilized. Consequently, foundations bearing on either the medium dense to very dense, natural glacial sediments or on structural fill placed over these sediments are capable of providing suitable building support. Infiltration of on -site stormwater is not recommended due to the presence of low -permeability lodgement till underlying the site. 8.0 SITE PREPARATION 8.1 Clearing and Stripping Site preparation of the planned building areas should include removal of all trees, brush, debris, and any other deleterious materials. These unsuitable materials should be properly disposed of off -site. Additionally, all organic topsoil within the proposed building area, or areas to receive structural fill should be removed and the remaining roots grubbed. Areas where loose surficial soils exist due to grubbing operations should be considered as fill to the depth of disturbance and treated as subsequently recommended for structural fill placement. Any existing fill soils below footing areas should be stripped down to the underlying, medium dense to dense natural sediments. These sediments were not encountered in our explorations, but can vary locally, particularly in the vicinity of the existing residences and associated buried utilities. 8.2 Temporary and Permanent Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction based on the local conditions encountered at that time. For planning purposes, we anticipate that temporary, unsupported cut slopes within the medium dense to very dense lodgement till sediments can be planned up to a 1H:1V (Horizontal:Vertical) inclination. Permanent cut and structural fill slopes should not exceed an inclination of 2H:IV. Permanent non-structural landscape fill should not exceed a 3H:1V inclination. As is typical with earthwork operations, some sloughing and raveling may occur, and cut slopes may have to be adjusted in the field. In addition, WISHA/OSHA regulations should be followed at all times. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 8 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations 8.3 Site Disturbance The lodgement till sediments contain a high percentage of fine-grained material, which makes them moisture -sensitive and subject to disturbance when wet. The contractor must use care during site preparation and excavation operations so that the underlying soils are not softened. If disturbance occurs, the softened soils should be removed and the area brought to grade with structural fill. If crushed rock is considered for the access and staging areas, it should be underlain by stabilization fabric (such as Mirafi 50OX or approved equivalent) to reduce the potential of fine-grained materials pumping up through the rock and turning the area to mud. The fabric will also aid in supporting construction equipment, thus reducing the amount of crushed rock required. We recommend that at least 10 inches of rock be placed over the fabric; however, due to the variable nature of the near -surface soils and differences in wheel loads, this thickness may have to be adjusted by the contractor in the field. Crushed rock used for access and staging areas should be of at least 2-inch size. 9.0 STRUCTURAL FILL Placement of structural fill may be necessary to establish desired grades in some areas. All references to structural fill in this report refer to subgrade preparation, fill type, and placement and compaction of materials as discussed in this section. If a percentage of compaction is specified under another section of this report, the value given in that section should be used. 9.1 Subgrade Compaction After overexcavation/stripping has been performed to the satisfaction of the geotechnical engineer/engineering geologist, the upper 12 inches of exposed ground should be recompacted to a firm and unyielding condition. If the subgrade contains too much moisture, suitable recompaction may be difficult or impossible to attain and should probably not be attempted. In lieu of recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. Where the exposed ground remains soft and further overexcavation is impractical, placement of an engineering stabilization fabric may be necessary to prevent contamination of the free - draining layer by silt migration from below. After recompaction of the exposed ground is tested and approved, or a free -draining rock course is laid, structural fill may be placed to attain desired grades. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 9 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations 9.2 Structural Fill Compaction Structural fill is defined as non -organic soil, acceptable to the geotechnical engineer, placed in maximum 10-inch loose lifts, with each lift being compacted to at least 95 percent of the modified Proctor maximum dry density using American Society for Testing and Materials (ASTM):D 1557 as the standard. Utility trench backfill should be placed and compacted in accordance with applicable municipal codes and standards. The top of the compacted fill should extend horizontally a minimum distance of 3 feet beyond footings or pavement edges before sloping down at an angle no steeper than 2H:1V. Fill slopes should either be overbuilt and trimmed back to final grade or surface -compacted to the specified density. 9.3 Moisture -Sensitive Fill Soils in which the amount of fine-grained material (smaller than No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture -sensitive. Use of moisture -sensitive soil in structural fills should be limited to favorable dry weather conditions. The on -site sediments below the root zone are suitable for use as structural fill; however, the lodgement till sediments contain significant amounts of silt and are considered highly moisture -sensitive. If the moisture content of these sediments is elevated at the time of construction, moisture -conditioning would be recommended prior to their use as structural fill. Such moisture -conditioning could consist of spreading out and aerating the soil out during periods of warm, dry weather. Construction equipment traversing the site when the soils are very moist or wet can cause considerable disturbance. If fill is placed during wet weather or if proper compaction cannot be attained, a select import or on -site material consisting of a clean, free -draining gravel and/or sand should be used. Free -draining fill consists of non -organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction. 9.4 Structural Fill Testing The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material at least 3 business days in advance to perform a Proctor test and determine its field compaction standard. A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and perform a representative number of in - place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMGlpc — KE140265A2 —Projects �20140265 � KE�WP Page 10 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing frequency. 10.0 FOUNDATIONS 10.1 Allowable Soil Bearing Pressure Spread footings may be used for building support when founded either directly on the medium dense to very dense, natural lodgement till, or on structural fill placed over these materials. Lodgement till sediments suitable for foundation support were encountered in our explorations at depths of approximately 2 to 3.5 feet but may be locally deeper, particularly in the vicinity of the existing structures and buried utilities. For footings founded either directly upon the medium dense to very dense glacial sediments, or on structural fill as described above, we recommend that an allowable bearing pressure of 3,000 pounds per square foot (psf) be used for design purposes, including both dead and live loads. We recommend that the footing subgrade be recompacted to a firm and unyielding condition prior to footing placement. An increase in the allowable bearing pressure of one-third may be used for short- term wind or seismic loading. If structural fill is placed below footing areas, the structural fill should extend horizontally beyond the footing edges a distance equal to or greater than the thickness of the fill. 10.2 Footing Depths Perimeter footings for the proposed building should be buried a minimum of 18 inches into the surrounding soil for frost protection. No minimum burial depth is required for interior footings; however, all footings must penetrate to the prescribed stratum, and no footings should be founded in or above loose, organic, or existing fill soils. 10.3 Footinas Adiacent to Cuts The area bounded by lines extending downward at 1H:1V from any footing must not intersect another footing or intersect a filled area that has not been compacted to at least 95 percent of ASTM:D 1557. In addition, a 1.5H:lV line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus footings should not be placed near the edges of steps or cuts in the bearing soils. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 11 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations 10.4 Footing Settlement Anticipated settlement of footings founded as described above should be on the order of 1 inch or less. However, disturbed soil not removed from footing excavations prior to footing placement could result in increased settlements. 10.5 Footing Subgrade Bearing Verification All footing areas should be observed by AESI prior to placing concrete to verify that the exposed soils can support the design foundation bearing capacity and that construction conforms with the recommendations in this report. Foundation bearing verification may also be required by the governing municipality. 10.6 Foundation Drai Perimeter footing drains should be provided as discussed under the "Drainage Considerations" section of this report. 11.0 LATERAL WALL PRESSURES All backfill behind walls or around foundations should be placed following our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls, which are free to yield laterally at least 0.1 percent of their height, may be designed using an equivalent fluid equal to 35 pounds per cubic foot (pcf). Fully restrained, horizontally backfilled, rigid walls that cannot yield should be designed for an equivalent fluid of 50 pcf. Walls that retain sloping backfill at a maximum angle of 50 percent should be designed for 60 pcf for yielding conditions and 75 pcf for restrained conditions. If parking areas or driveways are adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in determining lateral design forces. 11.1 Wall Backfill The lateral pressures presented above are based on the conditions of a uniform backfill consisting of either the on -site glacial sediments or imported sand and gravel compacted to 90 percent of ASTM:D 1557. A higher degree of compaction is not recommended, as this will increase the pressure acting on the walls. A lower compaction may result in unacceptable settlement behind the walls. Thus, the compaction level is critical and must be tested by our firm during placement. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 12 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations 11.2 Wall Drainage It is imperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum 1-foot-wide blanket drain for the full wall height using imported, washed gravel against the walls. 11.3 Passive Resistance and Friction Factor Lateral loads can be resisted by friction between the foundation and the natural, medium dense to dense glacial sediments or supporting structural fill soils, or by "passive" earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with compacted structural fill to achieve the passive resistance provided below. We recommend the following design parameters: • Passive equivalent fluid = 250 pcf • Coefficient of friction = 0.30 11.4 Seismic Surcharge As required by the 2012 IBC, retaining wall design should include a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. Considering the site soils and the recommended wall backfill materials, we recommend a seismic surcharge pressure of 5H and 10H psf, where H is the wall height in feet for the "active" and "at -rest" loading conditions, respectively. The seismic surcharge should be modeled as a rectangular distribution with the resultant applied at the midpoint of the walls. 12.0 FLOOR SUPPORT Slab -on -grade floors may be constructed either directly on the medium dense to very dense natural sediments, or on structural fill placed over these materials. Areas of the slab subgrade that are disturbed (loosened) during construction should be recompacted to an unyielding condition prior to placing the pea gravel, as described below. We recommend that structural fill be placed below slab -on -grade floors where necessary to raise floor subgrades above the seasonal high water table. If moisture intrusion through slab -on -grade floors is to be limited, the floors should be constructed atop a capillary break consisting of a minimum thickness of 4 inches of washed pea gravel or washed crushed rock. The pea gravel/crushed rock should be overlain by a 10-mil (minimum thickness) plastic vapor retarder. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 13 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations 13.0 DRAINAGE CONSIDERATIONS Most of the natural glacial sediments encountered in our explorations contained significant amounts of silt and are considered to be highly moisture -sensitive. Traffic from vehicles, construction equipment, and even foot traffic across these sediments when they are very moist or wet will result in disturbance of the otherwise firm stratum. Therefore, prior to site work and construction, the contractor should be prepared to provide drainage and subgrade protection, as necessary. 13.1 Wall/Foundation Drains All retaining and perimeter footing walls should be provided with a drain at the footing elevation. The drains should consist of rigid, perforated, polyvinyl chloride (PVC) pipe surrounded by washed pea gravel. The level of the perforations in the pipe should be set approximately 2 inches below the bottom of the footing, and the drains should be constructed with sufficient gradient to allow gravity discharge away from the building. All retaining walls should be lined with a minimum, 12-inch-thick, washed gravel blanket provided to within I foot of finish grade, and which ties into the footing drain. Roof and surface runoff should not discharge into the footing drain system, but should be handled by a separate, rigid, tightline drain. Exterior grades adjacent to walls should be sloped downward away from the structure to achieve surface drainage. Final exterior grades should promote free and positive drainage away from the building at all times. Water must not be allowed to pond or to collect adjacent to the foundation or within the immediate building area. It is recommended that a gradient of at least 3 percent for a minimum distance of 10 feet from the building perimeter be provided, except in paved locations. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. Additionally, pavement subgrades should be crowned to provide drainage toward catch basins and pavement edges. 14.0 DETENTION VAULT We anticipate that the proposed project may utilize a vault for detention of storm water generated on site. The vault may be constructed of cast -in -place concrete walls, likely with prefabricated flat roof panels. For storm water vault foundation elements cast on very dense lodgement till sediments, prepared as recommended above, we recommend designing for an allowable foundation soil bearing pressure of 5,000 psf. This value may be increased by one-third to accommodate transient wind and seismic loads. The vault may be designed to resist lateral earth pressures represented by an equivalent fluid of 35 pcf if the walls are free to February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMGlpc — KE140265A2 —Projects �20140265 � KE�WP Page 14 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations yield during backfill placement, and 50 pcf if the walls are structurally restrained from deflection during backfill. An allowable base friction coefficient of 0.32 may be assumed. These lateral pressures assume that the walls will be provided with a blanket drain that extends from the ground surface and connects to a footing drain at the foundation elevation. If a footing drain is not installed, or if the footing drain is constructed higher than the base of foundation due to available discharge locations, lateral earth pressures used for design should be adjusted to reflect saturated conditions below the level of the footing drain. A saturated, restrained lateral earth pressure of 90 pcf should be assumed for design. If roads or parking areas are to be constructed above the vault, a lateral earth pressure surcharge equivalent to 2 additional feet of soil should be added. 15.0 PROJECT DESIGN AND CONSTRUCTION MONITORING We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this report is based. If significant changes in grading are made, we recommend that AESI perform a geotechnical review of the plans prior to final design completion. In this way, our earthwork and foundation recommendations may be properly interpreted and implemented in the design. We are also available to provide geotechnical engineering and monitoring services during construction. The integrity of the foundations depends on proper site preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this current scope of work. If these services are desired, please let us know, and we will prepare a proposal. February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMG/Pc — KE140265A2 —Projects �20140265 � KE�WP Page 15 Subsurface Exploration, Geologic Hazard, and Edmonds Apartments Geotechnical Engineering Report Edmonds, Washington Preliminary Design Recommendations We have enjoyed working with you on this study and are confident that these recommendations will aid in the successful completion of your project. If you should have any questions, or require further assistance, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington Danika M. Globokar, E.I.T., G.I.T. Senior Staff Geotechnical Engineer Attachments: Figure 1: Vicinity Map Figure 2: Site and Exploration Plan Appendix: Exploration Logs 23,E80 G /S'T ks-;� I . C'� '/ '7 -- '-�' -1 Kurt D. Merriman, P.E. Senior Principal Engineer February 11, 2016 ASSOCIATED EARTH SCIENCES, INC. DMGlpc — KE140265A2 —Projects �20140265 �KE� WP Page 16 --J —X�; —11 A I— , f Afkl n J, s IS v? oc Lake UnincorporAed bwo , �,04 no MIX) U.-N �LKE TERRA ALI t-7 .9 so Z. I ank Lake T SITE inger !14 h b iUJSH ft dl vi 7 V L ,o 99 g; r � . I - t z T ;-7 . ...... 4w (3 J16 % 475 Lr Ri is N 909 7 0 1000 2000 NOTE BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REFERENCE: USGS, SNOHOMISH CO REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. FEET T FIGURE 1 c i a t I d VICINITY MAP e a r t h s c i e In c e s EDMONDS APARTMENTS DATE 10/15 E i n c o r p o r a t e d EDMONDS, WASHINGTON 0 PROJ. NO. KE140265A a 2() fkm OIJTA,L TO CS IN PARKINC WT U) -am 0 20 40 NOTE: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY FEET 7: REFERENCE: BING 2010/ CORNERSTONE REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. FIGURE 2 10 a s s o c i a t e d SITE AND EXPLORATION PLAN E I Lu e a r t h s c i e n c e s EDMONDS APARTMENTS DATE 10/15 n c o r p o r a t e d EDMONDS, WASHINGTON PROJ. NO. KE140265A APPENDIX Exploration Logs C� C� C 0 Well -graded gravel and Terms Describing Relative Density and Consistency ILL M,� 6W gravel with sand, little to Density SPT")blows/foot 4) a) S D'Z3 C no fines Coarse- Very Loose 0 to 4 E2 0) M 0 LL �GR LO �—_ �-_. 0 0oo. 0 00000 Poorly -graded gravel Loose 4 to 10 Grained Soils Medium Dense 10 to 30 Test Symbols 8 "a Iq Vil 000q 00000 OP and gravel with sand, Dense 30 to 50 C. C) 6 00000 00000 little to no fines Very Dense >50 G = Grain Size C-4 Z 00000 M = Moisture Content (2 )blows/foot 6 Consistency SPT A = Atterberg Limits Z r_ LO 0 0 a �� , Silty gravel and silty Very Soft 0 to 2 C = Chemical 0 0 itil 0 GM gravel with sand Fine -Soft 2 to 4 DID = Dry Density Grained Soils 0 3 Medium Stiff 4 to 8 K = Permeability stiff 8 to 15 Clayey gravel and Very Stiff 15 to 30 t4l M ac clayey gravel with sand Hard >30 el C) U) Component Definitions Descriptive Term Size Range and Sieve Number ..... Well -graded sand and 0 15 xx SW sand with gravel, little Boulders Larger than 12" 0 12 LL to no fines Cobbles 3" to 12" E2 Poorly -graded sand Gravel 311 to No. 4 (4.75 mm) 0 (J) 0 SP and sand with gravel, Coarse Gravel 311 to 3/411 Fine Gravel 3/4" to No. 4 (4.75 mm) C0 little to no fines Sand No. 4 (4.75 mm) to No. 200 (0.075 mm) 0 0 Z Coarse Sand No. 4 (4.75 mm) to No. 10 (2.00 mm) 9 2 ra CD Silty sand and Medium Sand No. 10 (2.00 mm) to No. 40 (0.425 mm) 12 sm silty sand with Fine Sand No. 40 (0.425 mm) to No. 200 (0.075 mm) 0 u_ gravel Silt and Clay Smaller than No. 200 (0.075 mm) LO cm 00 Clayey sand and (3 Estimated Percentage Moisture Content sc clayey sand with gravel Component Percentage by Weight Dry - Absence of moisture, U) . . . . . _... , dusty, dry to the touch . I Trace <5 Slightly Moist - Perceptible sandy silt, gravelly silt, moisture W > MLISilt' silt with sand or gravel Some 5 to <12 Moist - Damp but no visible 0 Modifier 12 to <30 water Clay of low to medium C3 0 — (silty, sandy, gravelly) Very Moist - Water visible but C� 0 . plasticity; silty, sandy, or not free draining 0 Z _j CL gravelly clay, lean clay Very modifier 30 to <50 Wet - Visible free water, usually 0 (D E (silty, sandy, gravelly) from below water table 1 U) -1 Organic clay or silt of low Symbols EL T OL plasticity Blows/6" or 0 Sampler portion of 6" Cement grout 'y" surface seal silt, claye y silt, silt 2 Sampler Type IR M,IE[astic with micaceous or S�01-tOD 'I _So 15 Description poon (A4) :1 Bentonite seal C, ID diatomaceous fine sand or S ampler 3.0" OD Split -Spoon Sampler Filter pack wilth -0 silt (SPT) 3.25" OD Split -Spoon Ring Sampler (4) Ig blank casing Clay of high plasticity, U) 00 LO CH sandy or gravelly clay, fat Bulk sample pi 3.011 OD Thin -Wall Tube Sampler section Screened casing E 49:3 clay with sand or gravel (including Shelby tube) Z or Hydrotip with filter pack Cb Grab Sample End cap C: Organic clay or silt of Portion not recovered OH medium to high (1) Percentage by dry weight (4) Depth of ground water plasticity (2) (SPT) Standard Penetration Test (ASTM D-1586) Y ATD = At time of drilling 3 a Static water level (date) In General Accordance with Peat, muck and other 0) 0 PT highly organic soils Standard Practice for Description Combined USCS symbols used for U) 0 IN and Identification of Soils (ASTM D-2488) fines between 5% and 12% 0 Classifications of soils in this report are based on visual field and/or laboratory observations, which include density/consistency, moisture condition, grain size, and plasticity estimates and should not be construed to imply field or laboratory testing unless presented herein. Visual -manual and/or laboratory classification methods of ASTM D-2487 and D-2488 were used as an identification guide for the Unified Soil Classification System. a s s o c i a t e d FIGURE Al earth sciences EXPLORATION LOG KEY i n c o r p o r a ', e d 0 M LOG OF EXPLORATION PIT NO. EP-1 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be read together with that report for complete interpretation. This summ%glies only to the location of this trench at the time of Subsurface excavation. conditions may change at this location wit t e passage of time. The data presented are a simplfication of actual conditions encountered. DESCRIPTION Topsoil Loose, moist, reddish brown, silty SAND; with scattered rootlets and organics; unsorted (SM). 1 Weathered Vashon Lodgement Till 2 Loose to medium dense, moist, brown, silty fine to medium SAND, some fine to coarse gravel; unsorted (SM). 3 Vashon Lodgement Till 4 Dense, moist, brownish gray, very gravelly, silty SAND; unsorted; diamict texture (SM). 5 Very dense, moist, brownish gray, silty SAND, some gravel; cemented; unsorted; diamict texture (SM). 6 7 8 As above. 9 Bottom of exploration pit at depth 8.5 feet No seepage. No caving. 10 11 12 13 14 15 16 17 18 19 Edmonds Apartments 0 Edmonds, WA 0 n a s s o c i a t e d Project No. KE140265A Logged by: DMG earth sciences Approved by: CJK i n c o r p o r a t e d 9/28/15 0 LOG OF EXPLORATION PIT NO. EP-2 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be read together with that report for complete interpretation. This summ%glies only to the location of this trench at the time of excavation. Subsurface conditions may change at this location wit t e passage of time. The data presented are a simplfication of actual conditions encountered. DESCRIPTION Topsoil Loose, slightly moist, brown, silty SAND; abundant rootlets; unsorted (SM). 1 2 --\Washed 1 -inch gravel (old drain field/utility?) in half of pit. Vashon Lodgement Till 3 Medium dense to dense, slightly moist, tan, gravelly, silty SAND; unsorted; diamict texture (SM). 4 Becoming more dense. 5 Very dense, moist, brownish gray, gravelly, silty SAND; cemented; unsorted; diamict texture (SM). 6 7 Bottom of exploration pit at depth 6 feet No seepage. No caving. Refusal at 6 feet. 8 9 10 11 12 13 14 15 16 17 18 19 Edmonds Apartments 0 Edmonds, WA 0 n a s s o c i a t e d Project No. KE140265A Logged by: IDIVIG earth sciences Approved by: CJK i n c o r p o r a t e d 9/28/15 0 LOG OF EXPLORATION PIT NO. EP-3 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be read together with that report for complete interpretation. This summ%glies only to the location of this trench at the time of Subsurface excavation. conditions may change at this location wit t e passage of time. The data presented are a simplfication of actual conditions encountered. DESCRIPTION Gravel Driveway Pad Vashon Lodgement Till Medium dense to dense, slightly moist, tan, very gravelly, silty SAND; unsorted; diamict texture (SM). 2 3 Becoming more dense. 4 Very dense, moist, brownish gray, silty to very silty, fine SAND, some gravel to gravelly; cemented; unsorted; diamict texture (SM). 5 6 Bottom of exploration pit at depth 5.5 feet No seepage. No caving. 7 8 9 10 11 12 13 14 15 16 17 18 19 Edmonds Apartments 0 Edmonds, WA 0 n a s s o c i a t e d Project No. KE140265A Logged by: IDIMIG earth sciences Approved by: CJK i n c o r p o r a t e d 9/28/15 0