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BLD2007-00385 Geotechnical Report
• • _ . Aspectconsulting IN-DEPTH PERSPECTIVE July 11, 2007 Mr. Torn Eastgard 3967 El Cimo Lane Bainbridge Island, Washington 98110 Subject: Geotechnical Review of Revised Catchment Wall Location 270 Harrington Drive Jefferson County, Washington Project No. 060266-003-01 Reference: SUBSURFACE EXPLORATION AND GEOTECHNICAL ENGINEERING REPORT, Eastgard Property, 270 Harrington Drive, Jefferson County, Washington,dated January 17, 2007, by Aspect Consulting, LLC Dear Mr. Eastgard: We have received a request from your architect to review the current design location of the catchment wall. Due to the set backs on the opposite side of the house and the large designed thickness of the catchment wall, the exterior of the wall slightly encroaches into the setback at one corner from of the house by 2 feet. Within approximately 13 linear feet, the wall meets the setback and the remaining two-thirds of the wall then exceeds the minimum setback to a maximum of approximately 2 feet. Given that the average of the setback is greater than 15 feet, Aspect Consulting believes that this minor intrusion of the structural wall does not significantly deviate from the overall geotechnical setback recommendation for the catchment wall, and that the wall will perform its intended function. We are pleased to have this continued opportunity to work with you. If you have any questions, please do not hesitate to call me at (206) 780-7720. Sincerely, Aspect consulting, LLC ,-"`\,. PcvlE, L'4. �0 �� ��• a ;' a V • .1. 1--Z :..(iCt. *Ati 4 r r�%:.' :-7/11/07 h, 18802 ...OA, - OI57c5 `1p� .a.S CS'SIONA ')1'� < „. XPIRES 6/22/0`j 1 John L. Peterson,PE Associate Geotechnical Engineer jpeterson@aspectconsulting.com cc: Daniel Dennon, Roger Katz&Associates (via e-mail) W:1_GEOTECH1060268 Eastgard Reconlwall placement Review Ltr.doc I • 9 . ' z Aspect consutting ' IN-DEPTH PERSPECTIVE I I I I SUBSURFACE EXPLORATION AND GEOTECHNICAL ENGINEERING REPORT I Eastgard Property, 270 Harrington Drive Jefferson County, Washington IPrepared for: Tom Eastgard I Project No. 060266-002-01 • January 17, 2007 I Aspect Consulting, LLC I ,pRE Wp _ ,. ofw � ,v 1'' PE D. � . �, eF� �x vAsy �oI. •lib Alit. I� • `' 7 tij1: 2r 07 NIN1S8-.5r'0311 " oNAL t*. ,- q. ,ECISrER�„ / / ,. sioNAL EXPIRES 9/3/07 !EXPIRES 5/22,' O'�T� I James A. Peterson, PE John L. Peterson, PE Project Geotechnical Engineer Associate Geotechnical Engineer i apeterson@aspectconsulting.com jpeterson@aspectconsulting.com W:\_GEOTECH\060266 Eastgard Recon\Eastgard Geotech Report.doc I I 179 Madrone Lane North Bainbridge Island,WA 98110 Tel:(206)780-9370 Fax:(206)780-9438 www.aspectconsulting.com Offices in downtown Seattle and Bainbrid.e Island WA I • 0 ASPECT CONSULTING I I Contents I1 Project Information 1 1.1 Introduction 1 I 1.1.1 Purpose and Scope 1 1.1.2 Authorization 1 1.2 Project and Site Description 1 ' 1.2.1 Slope Conditions 2 1.3 Subsurface Exploration 2 1.3.1 Exploration Borings 2 I1.4 Subsurface Conditions 3 1.4.1 Stratigraphy 3 I 1.4.2 Hydrology 3 2 Geologic Hazards and Mitigation 5 2.1 Seismic Hazards and Recommended Mitigation 5 I2.1.1 Landslides and Liquefaction 5 2.1.2 Ground Motion 6 2.2 Erosion Hazards and Mitigation 6 I2.2.1 Mitigation 6 2.3 Landslide Hazards and Mitigation 7 I 2.3.1 Rotational Type Landslides 7 2.3.2 Surficial or Debris Landslides 7 3 Design Recommendations 8 ' 3.1 Site Preparation 8 3.1.1 Clearing and Filling 8 3.1.2 Site Disturbance 8 3.2 Structural Fill 8 3.3 Foundations 9 I3.3.1 Spread Footings 9 3.4 Floor Support 10 I 3.5 Catchment Wall Recommendation 10 3.5.1 Catchment Wall Criteria 10 3.6 Drainage Considerations 11 3.7 Project Design and Construction Monitoring 11 Limitations 12 I 1 PROJECT NO. 060266-002-01 •JANUARY 17, 2007 I • ASPECT CONSULTING 1 1 Project Information 1.1 Introduction This report presents the results of our subsurface exploration and geotechnical engineering study for the Eastgard property located at 270 Harrington Drive, on the eastern shoreline of the Toandos peninsula in Jefferson County, Washington. The location of the property is shown on the Site Location Map, Figure 1. The approximate locations of the subsurface explorations accomplished for this study are presented on the Site and Exploration Plan, Figure 2. In the event that any changes in the nature, design or location of the structure are planned,the conclusions and recommendations contained in this report should be reviewed and verified, or modified, as necessary. 1.1.1 Purpose and Scope The purpose of this study was to provide geotechnical design recommendations to be utilized in the design and development of a proposed new house at the site, with appropriate landslide remediation/mitigation measures. Our study included reviewing available geologic literature, drilling two exploration borings, and performing geologic studies to assess the type, thickness, distribution and physical properties of the subsurface sediments and shallow groundwater conditions. Geotechnical engineering studies were ' conducted to formulate retaining wall and drainage recommendations. This geotechnical report summarizes our current field work and offers geologic hazard mitigation and geotechnical engineering recommendations based on our present understanding of the project. 1.1,2 Authorization Written authorization to proceed with this study was granted by Mr. Tom Eastgard on November 17, 2006. Our study was accomplished in general accordance with our scope of work proposal dated November 15, 2006. 1.2 Project and Site Description ' This report was completed with an understanding of the project based on a site plan provided by Mr. Eastgard, and by our discussions with Mr. Eastgard. At the time of our exploration program, the site was occupied by a single-family, manufactured residence and a detached garage. Preliminary plans call for the removal of the existing structures and construction of a new house in the same general area, adjacent to the toe of the slope. 1 The property is situated on the waterfront along Hood Canal. The site is rectangular in plan, encompasses two tax parcels, with property dimensions of approximately 200 feet along the southwest/northeast property lines, and approximately 1,000 feet along the southeast/northwest property lines. The upland portion of the site consisted of northwest- to-northeast-facing hillside, with inclinations ranging from approximately 0.75H:1V (Horizontal:Vertical) to 5H:1 V, with a typical slope angle on the order of 1.2H:1 V above 1 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 1 ASPECT CONSULTING • • to the northwest, southeast and southwest the proposed house. The site was borderedby private residential properties, and by the low tide line of Hood Canal to the northeast. The existing structures were located in the bottom of a flat to gently sloping ravine floor i in the northwest portion of the property. Vegetation around the existing residence consisted primarily of grass lawn and landscaped shrubbery, with some cedar trees in the upslope, southwestern portion of the ravine. 1 l 1.2.1 Slope Conditions The site consists of a steeply sloping southwestern portion and a flat to gently sloping, I lower, northeastern portion containing the existing and proposed house location. Average slope inclination for the steep slope was on the order of 1.2H:1 V. Overall vertical relief of the slope above the proposed house site was on the order of 50 feet. The I slope contained fir, cedar,maple, and alder trees with a dense understory of ferns, berry bushes, and other shrubs. Average slope inclinations of the lowest portion slopes near the proposed house footprint were on the order of 1 H:1 V,with one area at the toe of the slope near the existing garage cut to a maximum height of approximately 15 feet at a slope angle of approximately 0.5H:1 V. The cut was reportedly made more than 7 years previously, and shows signs of only surficial sloughing of the face. 11 1 .3 Subsurface Exploration Our field study included drilling two exploration borings, one in the vicinity of the IP proposed house footprint and one at the top of slope above the proposed house footprint. The various types of sediments, as well as the depths where characteristics of the sediments changed, are indicated on the exploration logs presented in Appendix A of this report. The depths indicated on the logs where conditions changed may represent gradational variations between sediment types. Changes logged between sample intervals in our borings were interpreted. Soils were classified in general accordance with the American Society for Testing and Materials (ASTM)D-2488, "Standard Practice for Description and Identification of Soils (Visual and Manual Procedure)". Our explorations were approximately located in the field by measuring from existing site features shown on the plan provided by Mr. Eastgard. 1.3.1 Exploration Borings On January 2,2007, two exploration borings (EB-1 and EB-2)were completed within the project site. The borings were completed by advancing a 31/4-inch inside-diameter, hollow-stem auger with a track-mounted drill rig operated under subcontract to Aspect Consulting. The boring depths were 60.9 feet in EB-1 and 20.8 feet in EB-2. The boring logs are presented in Appendix A of this report. The approximate location of each boring is shown on the Site and Exploration Plan, Figure 2. Samples were obtained using the Standard Penetration Test(SPT). This involves driving a 2-inch outside-diameter split- barrel sampler a distance of 18 inches into the soil with a 140-pound hammer free-falling from a distance of 30 inches. The number of blows for each 6-inch interval is recorded and the number of blows required to drive the sampler the final 12 inches is used to calculate the Standard Penetration Resistance ("N") or blow count. Field variations in the test method, if they occur, are incorporated into the"N" value calculation. The resistance, 2 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 • 0 ASPECT CONSULTING Ior N-value, provides a measure of the relative density of granular soils or the relative consistency of cohesive soils; these values are shown on the attached boring logs. I1 .4 Subsurface Conditions I Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visual reconnaissance of the site and vicinity, and review of applicable geologic literature. IAs shown on the boring logs, a thin layer of topsoil and grass was encountered in both borings. The topsoil layer was underlain by medium dense to very dense,glacially consolidated sand and gravel with varying amounts of silt. These sediments were Iinterpreted as pre-Fraser age, undifferentiated sediments. These sediments were encountered to the total explored depths of 60.9 feet in EB-I and 20.8 feet in EB-2. The following section presents more detailed subsurface information organized from the Iupper(youngest) to the lower(oldest) sediment types. 1.4.1 Stratigraphy ITopsoil and Grass Topsoil and grass were encountered in both borings, to depths of 0.3 foot and 1 foot, 1 respectively, in EB-1 and EB-2. These soils consisted of loose to medium dense, organic- rich, silty sand and gravel. Pre-Fraser Undifferentiated Sediments IIntact, pre-Fraser age undifferentiated sand and gravel deposits were encountered in both borings. This stratum continued to the entire depth explored in each boring. The soil consisted of stratified layers of very dense, light brown, reddish-brown and gray, silty I sand and gravel. This stratum can be seen in the driveway road cut upslope of the proposed house and in the toe of the slope adjacent to the existing garage. These sediments appeared to be in-place and appear to have been largely unaffected by past 1 slide activity. This observed geologic stratum conforms with the published geologic mapping of the 1 area as shown on the Geologic Map of Surficial Deposits in the Seattle 30'x60' Quadrangle, Washington, by Yount and Minard, 1993. I 1.4.2 Hydrology Groundwater was encountered in both borings at the time of our field study. The depth to groundwater in the exploration borings was estimated at the time of drilling and ranged I from ground surface in EB-2 to approximately 54 feet in EB-1. The groundwater in EB-2 was the result of near-surface saturation in the flat area around the existing house, and occurred from ground surface to a depth of about 1 foot. Below 1 foot samples were I moist. The presence of perched groundwater in EB-1 was inferred from drill action and wet cuttings returning to the surface from approximately 33 to 34 feet. Additional wet soil samples were noted from a depth of approximately 54 feet to the bottom of EB-1; I this depth roughly coincides with small seeps within discrete sandy seams in the lower portion of the exposed slope face near the existing garage. Note that these borings were 1 PROJECT NO.060266-002-01 • JANUARY 17, 2007 3 410 ASPECT CONSULTING • 1 and December and reflect high performed after an extremely wet Novembergroundwater g conditions. Increased groundwater volumes and seepage are a direct result of precipitation. In I addition to precipitation rates and duration, fluctuations in groundwater levels will occur due to the time of the year, site usage, and other factors such as off-site usage and water supply systems in the area. Seepage may also occur at random depths and locations in relatively clean sandy or gravelly seams within the slope. 1 I 1 t 1 1, Ii I1 1! i 11 I 4 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 • ASPECT CONSULTING 1 2 Geologic Hazards and Mitigation The following discussion of potential geologic hazards is based on the geologic, slope, and groundwater/surface water conditions as observed and discussed herein. The discussion will be limited to seismic, erosion and landslide hazards. 1 2.1 Seis mic Hazards and Recommended Mitigation The nearest known, active fault trace to the project is the Seattle fault, although other north-south trending fault structures are likely located in the Hood Canal region that have not been fully characterized. Recent studies by the U.S. Geological Survey(e.g., Johnson et al., 1994, Origin and Evolution of the Seattle Fault and Seattle Basin, Washington, Geology, v. 22, p.71-74 and Johnson et al., 1999, Active Tectonics of the Seattle Fault and Central Puget Sound Washington-Implications for Earthquake Hazards, Geological Society of America Bulletin, July 1999, v. 111, n. 7, p. 1042-1053) suggest that the trace of an east-west trending thrust fault may project approximately 10 miles southeast of the project site in the vicinity of Bremerton. The trace of this fault can be seen south of Blakely Harbor on Bainbridge Island. According to the U.S. Geological Survey(USGS) studies, the latest movement of this fault was about 1,100 years ago, resulting in about 20 feet of surficial displacement. This displacement can presently be seen in the form of ' raised, wave-cut beach terraces along Alki Point in West Seattle and Restoration Point at the south end of Bainbridge Island. The recurrence interval of movement along these fault systems is still unknown, although it is hypothesized to be on the order of several thousand years. Due to the suspected long recurrence interval,the distance from the fault, the potential for surficial ground rupture as a result of faulting is considered low during the expected life of the structure. I2.1.1 Landslides and Liquefaction Seismically Induced Landslides A site specific seismic analysis was beyond the scope of this study and was not performed. However,the available data from the USGS Earthquake Hazards site was obtained in lieu of a specific site study. This value takes into account attenuating factors associated with the distance of the site from known active fault structures in the area. Aspect Consulting applied the peak ground acceleration and conservative estimates of the index properties of the site soil to a general slope stability analysis of the slope across the site. The analysis was performed using the generalized infinite slope equation, using a code-based ground acceleration of 0.34g as provided for in Chapters 16 and 18 of the 2003 International Building Code (IBC). Factors of safety of 1.25 and 1.15 were obtained for static conditions and earthquake conditions, respectively, using the code-based earthquake. I PROJECT NO.060266-002-01 • JANUARY 17, 2007 5 ASPECT CONSULTING • • Liquefaction Due to the high SPT"N"values and/or silt content of the soils, site liquefaction potential is low. 2.1.2 Ground Motion Based on the site stratigraphy and visual reconnaissance of the site, it is our opinion that earthquake damage to the proposed structure founded on a suitable bearing stratum would likely be caused by the intensity and horizontal ground acceleration associated with the event. We understand that structural design of the building will follow the 2003 IBC standards and take into consideration stress caused by seismically-induced earth shaking. The USGS National Seismic Hazard Map International indicates that the project site should be assumed to undergo a peak horizontal ground acceleration of 0.57g. Using the 2003 IBC criteria,the site would be characterized by a Seismic Site Class C. The mapped, maximum considered earthquake spectral response accelerations for short period (Se) = 1.26g; and for 1-second period (Si)=0.46g. Site coefficients for this site are Fa= g 1.0, F,,= 1.3. The maximum considered earthquake spectral response accelerations adjusted for site class effects are Sds=0.84g, Sd1 =0.41g. II I 2.2 Erosion Hazards and Mitigation The soils encountered have a moderate erosion potential where these soils will be IP exposed during construction. The erosion risk increases on sloped areas,whether natural or excavated during construction.Areas outside of the proposed construction area have low erosion potential due to the well-developed vegetative cover. Only the areas necessary for construction should be stripped of vegetation, however,trees which represent a danger to the structure should be removed. 111 2.2.1 Mitigation To mitigate and reduce the erosion hazard and potential for off-site sediment transport, we recommend the following: • Surface water should not be allowed to flow across the site over unprotected surfaces. All runoff water should be tightlined away from the slopes to an appropriate storm- water collection facility. Under no circumstances should surface water be allowed to flow over the top of the slopes. • All stormwater from impermeable surfaces, including driveways and roofs, should be 111 tightlined to a suitable stormwater collection system. • Silt fences should be placed and maintained around the downslope sides of any11-1 proposed excavations that will be exposed to the weather. • Soils that are to be reused around the site should be stored in such a manner as to reduce erosion from the stockpile. Suitable protective measures for the small amount111 of excavated soil at the site would be covering the stockpiles with plastic sheeting. • Areas stripped of natural vegetation during construction should be replanted as soon as possible or otherwise protected. 6 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 �1 • 0 ASPECT CONSULTING I • Provisions of the Jefferson County Grading, Drainage, Erosion, and Sedimentation Control standards should be used on the site. I 2.3 Landslide Hazards and Mitigation I Two types of landslides are common in the Puget Sound area, rotational landslides and surficial or debris landslides. These slides may be triggered by natural events such as extended, heavy precipitation or an earthquake, or by manmade features such as broken I water pipes or improperly managed storm water flow. 2.3.1 Rotational Type Landslides I Rotational landslides consist of deep-seated failures that typically involve slip along a curved shear plane. Rotational landslides may transport large masses of semi-intact soil downslope, resulting in alternating steep headscarps along the upper portion of the failure plane with more gently-sloping benches composed of displaced soil. We observed no I obvious evidence along the site slope or along the nearby slopes that suggested the presence of recent, active or incipient static slope failure associated with deep-seated, rotational landslides. The results of seismically induced sliding have been discussed in I Section 2.1.2. S 2.3.2 Surficial or Debris Landslides Surficial or debris landslides consist of sliding of the weathered colluvial soil layer and overlying vegetation that typically mantles steep slopes in the Puget Sound region. I Surficial slides commonly result from a significant increase in the moisture content within the upper weathered soil layer on slopes. Increased moisture typically results from periods of extended, heavy precipitation, groundwater seepage or concentrated surface water discharge onto a slope. We observed evidence of surficial slide activity that could I affect the proposed project. Slides of this type will occur in the future due to the steepness of the slope and the presence of surficial weathered soil. Slides that occur III within the upper several feet of weathered soils typically do not extensively impact the i underlying, parent soils. Typically, catchment walls or foundations designed as retaining walls are most effective at mitigating surficial landslide hazards, and are discussed in the Idesign recommendation section. I I I PROJECT NO. 060266-002-01 •JANUARY 17, 2007 7 ASPECT CONSULTING • I 111 3 Design Recommendations 1 ' 3.1 Site Preparation I Those portions of the existing house or garage and foundations that are not part of the proposed project should be removed. Any buried utilities that are to be abandoned should , be removed or relocated if they are under building areas. The resulting depressions should be backfilled with structural fill, as discussed under Section 3.2, Structural Fill. 3.1.1 Clearing and Filling 111 Site preparation of planned building and driveway areas should include removal of all trees,brush, debris, and any other deleterious material. Organic topsoil 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. The upper 12 inches of the soils that will be exposed, as a result of stripping and grubbing should be recompacted to a firm and non-yielding condition. This recompacted fill will serve primarily as a working surface during construction. 3.1.2 Site Disturbance The near-surface on-site soils contain areas with a high percentage of fine-grained 1 material (silt) or organic matter,which makes them moisture-sensitive (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. Consideration should be given to protecting access and staging areas with an appropriate cover of crushed rock. 3.2 Structural Fill Structural fill will be necessary to establish desired grades, particularly in areas where unsuitable loose soils have been removed, such as in the vicinity of the proposed catchment wall/residence construction. All references to structural fill in this report refer 111 to subgrade preparation, fill type,placement, and compaction of materials as discussed in this section. Different percentages of compaction may be specified in other sections of this report for other purposes. I After overexcavation/stripping have been completed, the upper 12 inches of exposed ground should be recompacted to at least 90 percent of the Modified Proctor maximum density using ASTM D 1557 as the standard. If the subgrade is within 2 feet of the final foundation bearing grade,then it should be compacted to 95 percent of maximum or as close as practical. If the subgrade contains too much moisture, adequate recompaction may be difficult or impossible to obtain and should probably not be attempted. In lieu of I1 8 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 ASPECT CONSULTING recompaction, the area to receive fill can be blanketed with compacted washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. 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. Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 12-inch-thick, loose, horizontal lifts with each lift being compacted to 95 percent of the Modified Proctor maximum density using ASTM D-1557 as the standard. ' The contractor should note that any proposed fill soils must be evaluated by Aspect Consulting prior to their use in fills. This would require that we have a sample of the material 48 hours in advance to perform a Proctor test and determine its field compaction ' standard. 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 soils contained variable amounts of silt, and while considered moisture-sensitive, may be suitable for use as structural fill,provided they can be demonstrated to compact and perform well. If fill is placed during wet weather or if proper compaction cannot be obtained, a select import material consisting of 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. 3.3 Foundations Bearing soils were encountered at a depth of approximately 1.5 feet in the vicinity of the proposed house; consequently, shallow spread footings may be used for foundation support. 3.3.1 Spread Footings Spread footings may be used for support of the house when founded on the medium dense to very dense, silty, sandy gravel encountered at approximately 1.5 feet below existing site grade near the existing house. We recommend an allowable foundation soil bearing pressure of 2,000 pounds per square foot(psf) be utilized for design purposes including both dead and live loads. An increase in the above-mentioned bearing pressures by one-third may be used for short-term wind or seismic loading. Perimeter footings should be buried a minimum of 18 inches into the surrounding soil for frost protection; however, all footings must penetrate to the prescribed bearing stratum at approximately 1.5 feet below the existing ground surface. It should be noted that the area bounded by lines extending downward at 1 H:1 V from any footing must not intersect another footing, or a filled area that has not been compacted to at least 95 percent maximum dry density in accordance with ASTM test D-1557. In addition, a 2H:1 V line extending down from any footing must not daylight onto site slopes. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. I 1 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 9 ASPECT CONSULTING • Anticipated total settlement of footings founded on properly prepared, medium dense to p g P p Y very dense, silty, sandy gravel subgrade should be on the order oft/2-inch. However, _ disturbed soil not removed from footing excavations prior to footing placement could result in increased settlements. All footing areas should be inspected by Aspect Consulting,prior to placing concrete, to verify that the design bearing capacity of the bearing soils has been attained and that construction conforms to the recommendations III contained in this report. Perimeter footing drains should be provided as discussed under Section 3.6 of this report. 3.4 Floor Support Slab-on-grade floors may be used for the house, if placed over the undisturbed, silty, sandy gravel bearing stratum or compacted structural fill bearing on that stratum. Slab- on-grade floor areas should be excavated to a minimum of 4 inches below the bottom of slab and then backfilled and compacted with a minimum of 4 inches of coarse drainage aggregate material such as pea gravel or washed,crushed rock. This provides a pad of structural fill as well as a capillary break between the ground surface and concrete slab and provides proper drainage. Additionally, an impervious moisture barrier should be �' placed directly below the slab. 1 3.5 Catchment Wall Recommendation 1111 Based on the slope conditions at the site, construction of the southeast-facing portion (facing the adjacent slope)of the proposed house foundation as a catchment wall will provide protection against future landslide activity. This section of the report presents preliminary design considerations and criteria that should be considered in the design of the catchment wall. t 3.5.1 Catchment Wall Criteria Subgrade preparation for the portion of foundation serving as the catchment wall foundation should be performed in accordance with the recommendations presented in I the Section 3.2,Structural Fill. In order to minimize the retaining wall height and required lateral design forces, and to comply with the Jefferson County critical areas setback criteria, we recommend j incorporating a minimum 15-foot-wide, flat area between the wall and the toe of the existing slope,to act as a run-out/catchment area. The run-out area will also facilitate the removal of debris when necessary. Utilizing a 15-foot-wide run-out/catchment area,the wall should extend a minimum of 10 feet above grade level in order to accommodate the volume of material capable of being mobilized. The exposed portions of walls subject to impact loading should be designed to withstand a dynamic equivalent earth pressure of 90 pounds per cubic foot(pcf)to resist the impact area of the landslide, and a static equivalent fluid pressure of 60 pcf over the full height of the wall. These two loads would 1111 not occur simultaneously. A passive resistive footing pressure of 350 pcf can be utilized if the concrete is poured"neat" against the native soil. If re-compacted fill is used for resistance, a value of 250 pcf can be utilized. 11 10 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 1� ' • • ASPECT CONSULTING Any material which accumulates against the wall must be removed as soon as possible to provide continuing protection for any subsequent event. 3.6 Drainage Considerations g at ons All footings should be provided with a drain at the footing elevation. Drains should consist of rigid, perforated, polyvinyl chloride (PVC)pipe surrounded by washed drain gravel that is sized to avoid plugging or entering the drain pipe holes. 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 structure. Roof and surface runoff should NOT discharge into 1 the footing drain system but should be handled by a separate, rigid, tightline drain that safely discharges to a natural drainway. In planning, exterior grades adjacent to walls should be sloped away from the structure to achieve surface drainage. Below-grade walls should be designed as retaining walls and should be provided with a minimum 1-foot-thick, free-draining layer of drainage aggregate along the entire height of the wall to within 12 inches of final grade, in addition to the footing drain system. All landscape walls over 3 feet high should incorporate a 1-foot-thick free-draining layer of drainage aggregate along the entire height of the wall. Shallow diversion ditches should be placed on the upslope side of the walls to collect and divert surface water and sediment so that it does not enter the wall drains. 3.7 Project Design and Construction Monitoring ' At the time of this report, site grading, structural plans, and construction methods had not been finalized. We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this report is based. We recommend that Aspect Consulting 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 foundation and retaining wall 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 contact us and we will prepare a cost proposal. I 1 1 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 11 ASPECT CONSULTING • • , i Limitations I Work for this project was performed and this report prepared in accordance with I generally accepted professional practices for the nature and conditions of work completed in the same or similar localities, at the time the work was performed. It is intended for the exclusive use of Tom Eastgard for specific application to the referenced property. This report does not represent a legal opinion.No other warranty, expressed or implied, is made. t 1 I Ii Ii Ii 1 I t' i 12 PROJECT NO. 060266-002-01 • JANUARY 17,2007 • ir ,1 ,, J I t I�f a I `n /, h\ 0 �J �� i , rttrzc......--5-) ,,,,,, I ::':., S '''\ T if , (1:--,-) I , \ t k_• tom- z �n`"/ I t 1 J , / /i \ Ty J ) ,J t / I ;;;:::!:::„r-r,/ /1) . I 1 ,), .,„,., „.,-- // • • , , /�� Hood /Canal ., . .\. , , 'I,,k.,',„,- I /.-.../.:.....'7 ,\ 1 \`+ ` „'..._'..._'..'6...„''_ ',-‘4,,' d! v.4s`_ k 7.,1. 1 l--=�J m``l :. ' ) i/ .„ \• ,.,,,;', CC • if s.j ai ` '\ i` ' /' "�-� - � „ , s„J`,r ,�_ '-',' -'(° ( ( , ..„:..._•,..-,) . • s , iv\ i , v )) ) Fr--- -'-' i. I (\\ \-7\ 17'..--i-,..' � (�-\ tr\ - -- i -_ /LS (o,• .tea ' 11 I/ \ \ ‘..lt )%li I/7* (CS 1 r F J,j: i \ _?'---7"2 I \ ; I 1' '41. 27/ e .4) ) , , :,:- r„.;-ii 1 ; cC,---1).11 t -,, )4 ?) ?-c ,;•, ze- : , - ( , , \ „ , !II \ f \ 2-,41/ i ,)) r, ,)'1 ':: ` l 1 �\I Site Location 1 ` \ l •! . Lid ,\ , w // <\ /� •'>'::.- \ ply•,,,4;•:-: __Til,n s 2 1''' \5 2 1 �Q - a° Sao/A) } �z 1 �t�i ��: 'y-' , ••.. ::••(-N) 2s rn �n';�I1 (� S%/f .i j� � ( �O ;I; j) / o:Hazel Pt ;:yz 1 ;` .f� ° ✓ �N� too ( '''.1 ,-;-, \\\ I q„Iii Q...>,,./ , ,,---_-„-----1,H \ , I A,, , . ., .. , /-- ,,\,J ,\ ,.,,.,.. ..k\,, , rj--,_- ..-.7.-. . .. '''. '‘ o ��;;.- ; ,ice' I , Oak Head i i cc I 0 �/ 2000 4000 m w Feet / m I Site Location Map GrE Jan2007 PROJECT NO o /Aspectconsutting oa,•E°°` 060266 - IN-DEPTH PERSPECTIVE JAP U 8 179 Matlrone Lane North all Fiat Avenue 8480 Eastgard Residence eV PMB FIGURE NO o i BainbritlQe Island,WA 98110 9ea2 WA971Oa aense�s. 1 (sos)7ea9a7o (706)3i&7N3 270 Harrington Drive, Jefferson County, Washington rr 6MP'ZO-99ZO9O\60-LOOZlaauepisab pie6jse3 99ZO9OWoaloaO\:O 2 (D 2 To w c � N c.) & c CD , � r H od Canal Z O a a a o • Y L U Y O • — 100%+ slope a Bluff - _ C, fo o / \ d g I \ I 0 U 0 S I �+ a \ I !Q 7 i < — \ p a g I I \ C—. CC a) . I \ \ \ \ \ \ \ \ \ \\ I \ x co im \ I \ I✓V 0) a \ n \ W = �1 \ \ (a w o —� I� \ \ \ \ \ \ \ \ \ r 0 I • y��od 1 \ DI *. ct I \ LLI H I I I \ N F. III \ oI m E o a) W o _ a , (n No 1 \ I Q c 0- I C \ c ► o_ to 0 Q \ a) c,� o N. a: - a--\ 7 cN/ 1 • 0 — F \\ I \ I w o LL \ „t I am \ a I \ \ \ V aw \ O I co ` \ \ cu f-g L Q v3 \ \ \ Ur\ \ 1 \ Q- and \ \ 1a I 1 \ I \ I 1\ E O \1 \ \ a o I \ a a) / \ a) Q O I \ 3 I \ mN I \ _ \ w \ \ \I 1 \'n I 1\ I co \ I 3 \ I• 1 1 p \ \ \ 0)\ �c°� C 1 mac.. 1 1 0 1 I Es \ o 1 1 a) I o \ C o as c� U • O ra E X _ � O Q -- Q a Cr)-- a) CD dil W r 1.111111 1111. N r APPENDIX A Boring Logs 1 `.1,., v . o o c Well-gradeeavel and Terms Describing Relive Density and Consistency o. GW gravel with sand,little to (z) `` ;,�O�Ot no fines Density SPT blows/foot v.• E J CJ C Very Loose 0 to 4 I a) o°o Coarse Loose 4 to 10 > to a) to°°°°° Poorly graded gravel Grained Soils vt°o°o°° Medium Dense 10 to 30 Test Symbols O O v O0Q0O GP and gravel with sand, Dense 30 to 50 o Y d 0°°°° G=Grain Size I ° ° little to no fines Very Dense >50 a -z 00°00 M=Moisture Content z `o 0. 0 Silty gravel and silty Consistency SPT(Z)blows/foot A=Atterberg Limits c t 0� 0. •••.( GM gravel with sand Fine- Very Soft 0 to 2 C=Chemical d .0• 0 Soft 2 to 4 DD = Dry Density I n, �o Grained Soils c ° aI . )c Medium Stiff 4 to 8 K= Permeability �° o�,►' i Stiff 8 to 15 _� �.j Clayey gravel and y Very Stiff 15 to 30 All ;Jr GC clayey gravel with sand Hard >30 IO C Component Definitions CO Well graded sand and Descriptive Term Size Range and Sieve Number a, t : sw sand with gravel,little Boulders Larger than 12" I ,� ° .•.•• to no fines Cobbles 3"to 12" Gravel 3"to No.4(4.75 mm) Poorly-graded sand 0 0 �( y-g Coarse Gravel 3"to 3/4" N w to SP and sand with gravel, Fine Gravel 3/4"to No.4(4.75 mm) a ° v little to no fines ==:•;_.'• Sand No.4(4.75 mm)to No.200(0.075 mm) m o z •:•�:5 Coarse Sand No.4(4.75 mm)to No.10(2.00 mm) o, o a Silty sand and Medium Sand No.10(2.00 mm)to No.40(0.425 mm) E to S SM silty sand with Fine Sand No.40(0.425 mm)to No.200(0.075 mm) I o a & r.�•'• gravel o ;�� Silt and Clay Smaller than No.200(0.075 mm) to I •'•' Clayey sand and (3) 2 Nl-,f sc clayey sand with gravel Estimated Percentage Moisture Content /- Percentage Dry-Absence of moisture, by Weight Modifier dusty,dry to the touch Silt, sandy silt, gravelly silt, <5 Trace Slightly Moist-Perceptible �, o ML silt with sand or gravel moisture Ia', 5 to 15 Slightly(sandy,silty, Moist=Damp but no visible co t clayey,gravelly) water 05 • 10 jj/ Clay of low to medium 15 to 30 Sandy,silty,clayey, Very Moist Water but C\' 0 a not free visible Iz c CL plasticity; silty, sandy,or gravelly) draining y ° .E gravelly clay, lean clay 30 to 49 Very(sandy,silty, Wet-Visible free water,usually y = _j clayey,gravelly) from below water table COCO ___ Organic clay or silt of low oL plasticity Symbols 4 1 Cement grout o == Blows/6"or surface seal Sampler portion of 6" Type Bentonite / : chips Elastic silt,clayey silt,silt 2.0"OD O Sampler Type o a� MH with micaceous or diatb- Split-Spoon 2 Description Bentonite I co `o maceous fine sand or silt Sampler 147 seal y to (SPT) " Continuous Push > Filter pack with •a m o ' 3.25"OD Split-Spoon Ring Sampler blank casing r o Clay of high plasticity, 1f section o D (n Bulk sample vA a) c r / CH sandy or gravelly clay,fat 3.0"OD Thin-Wall Tube Sampler C Screened casing CO to A clay with sand or gravel 0 (including Shelby tube) = or Hydrotip with o _ Grab Sampleiti filter pack 3 1 c Q i�i% /% Organic clay or silt of Q Portion not recovered ■ End cap Y b- /,;i�i% medium to high I %i��ii�/i OH plasticity g (1) Percentage by dry weight (s) Combined USCS symbols used for ;iri�fi% (2) (SPT)Standard Penetration Test fines between 5%and 15%as c rf.i�l ° o __ :: Peat, muck and other (ASTM D-1586) estimated in General Accordance m '- , (3) In General Accordance with with Standard Practice for 0 s — pT highly organic soils o o, Standard Practice for Description Description and Identification of x a and Identification of Soils(ASTM D-2488) Soils(ASTM D-2488) u (4) Depth of groundwater 2 ATD=At time of drilling o X Static water level(date) IClassifications of soils in this report are based on visual field and/or laboratory observations,which include density/consistency,moisture condition,grain size,andco plasticity estimates and should not be construed to imply field or laboratory testing unless presented herein.Visual-manual and/or laboratory classificationcn methods of ASTM D-2487 and D-2488 were used as an identification guide for the Unified Soil Classification System. P I MRONAMIr PROJECT NO. c ti o Aspectconsulting Exploration Log Key "" 0 IN-DEPTH PERSPECTIVE C) MOW Mr FIGURE NO. U 179iBainbridge Madame Ln.NAM 811 First ,WA 8100 A-1 < Btln6780-370M,WA 9E170 S..20,WA 7101 o.r. (ZOB)7848370 (208)328-7443 • s . • 1 AS ect Boring Log P consulting Project Number Boring Number Sheet I IN-DEPTH PERSPECTIVE 060266 EB-1 1 of 3 Project Name Eastgard Residence Ground Surface Elev Location 45 ft West of Bluff/Jefferson County,Washington Driller/Method Davies Drilling/8"O.D.Hollow-stem auger Depth to Water Sampling Method 2"O.D.split-spoon sampler/Hammer Weight:140 lb/Hammer Drop:30" Start/Finish Date 1/2/2007 Depth/ Elevtion Borehole Completion Sample Tests Blows/ N-value Description Material Depth 1 P (feet) 7 Type/ID 6„ 0 10 20 30 40 sc Type (ft) 9 '`' ", TOPSOIL AND GRASS c EB-1 7 PRE-FRASER UNDIFFERENTIATED DEPOSITS G 10 �\ — \ Medium dense,light brown,moist,slightly gravelly, I \ silty,fine to coarse SAND(SM) — \ \ o IT'D Very dense,light brown,moist,silty,sandy GRAVEL \ >c c (GM);horizontal bedding around gravels;gravels I o 00C predominantly basaltic — \\ L 5— Backfilled with 30 \ O O)C — 5 bentonite chips ` 50*\ I p / EB-2 50-5" o 0 O r1O°C 'O - O 0)C - O CD _ O 3° — q o IF 10— EB-3 50-6" So*A2 Brown;sand fine to coarse;gravel fine to coarse —10 0 oC Oho _ I >© 6 0 >C O _ 0 ooc O i D0C >C a — g ,c )1-_pC 11 15— 37 —15 Sp+ U C ...... 4 EB-4 50-5„ ->c I o'oo< — 0 D C — 1 I > cCD I .2t lac r IDense,brown,moist,silty,fine to coarse SAND, I g trace gravel(SM) — I 20— F.Eiii.EilitiEE 6 —20 a % EB5 26 1 I w I z w i c7 I Driller reports silt,sand,scattered gravel 20-25' O — I L•. 1I I - Very dense,light brown/reddish-brown,moist, o I slightly silty,slightly gravelly,fine to coarse SAND W — I (SW-SM) — o I 111 J Lee co z Sampler Type: PID-Photoionization Detector(Headspace Measurement) Logged by: JAP yNo Recovery 1 Static Water Level ' Spoon 2"OD Split Sampler Approved by: JAP I o p p Water Level(ATD) o Figure No. 2 I • • Aspectconsutting Boring Log I Project Number Sheet IN-DEPTH nsul PERSPECTIVE Boring Number 060266 EB 1 2 of 3 Project Name Eastgard Residence Ground Surface Elev Location 45 ft West of Bluff/Jefferson County,Washington IDriller/Method Davies Drilling/8"O.D.Hollow-stem auger Depth to Water Sampling Method 2"O.D.split-spoon sampler/Hammer Weight:140 lb/Hammer Drop:30" Start/Finish Date 1/2/2007 Depth/ N-value Borehole Completion Sample Tests Blows/ Material (feet) Type/ID 6.. T e Description Depth 180 10 20 30 40 5� Type (ft) EB-6 50 5" so. I - _ Very dense light gray to reddish-brown,slightly I _ gravelly,silty,fine to coarse SAND(SM);thin, — horizontal laminations • 30— 2--- --- I — / EB 7 40 50+ —30 50-5' — I T Driller reports possible wet layer 33'-34' — I Very dense,brown/reddish-brown,slightly silty, 35— ' slightly gravelly,fine to coarse SAND(SW-SM);no 40 • structure or bedding —35 EB-8 50-6" So+ !Ix-Or—Very dense,reddish-brown to gray,silty,very sandy 3 D GRAVEL(GM) — 1 40— gijggfii EB-9 50-5" 50+ . �ca —40 . s,ta 1 : ;p° - 00 — iiiiiiiin ;. , qp S �,) �O — , �� la 45— iiiiiiiiiiiii EB-10 50_5„ 50+ �;io. —45 U _ ;m CD — Z 0 w I. CD 0 — „ 3o I En Ix Q •i 1_,, Very dense,light gray,very moist,slightly silty, Iw slightly gravelly,fine to coarse SAND(SW-SM) o z Sampler Type: PID-Photoionization Detector;Headspace Measurement) Logged by: JAP I °m No Recovery 1 = Static Water Level ® 2"OD Split Spoon Sampler q Approved by: JAP L., Water Level(ATD) Figure No. 2 • • • I Boring Log ` HSpec4}tconsUtting Project Number Boring Number Sheet IN-DEPTH PERSPECTIVE060266 EB-1 3 of 3111 Project Name Eastgard Residence Ground Surface Elev Location 45 ft West of Bluff/Jefferson County,Washington Driller/Method Davies Drilling/8"O.D.Hollow-stem auger Depth to Water Sampling Method 2"O.D.split-spoon sampler/Hammer Weight:140 lb/Hammer Drop:30" Start/Finish Date 1/2/2007 Depth! Sample Tests Blows/ N-valueDepth Elevation Borehole Completion P Material Description (n) ' (feet) Type/ID 6„ 0 10 20 30 40 5C oy� EB-11 50-5" "+l: Driller reports cobbles 52'-53' , Very dense,gray,very moist to wet,slightly gravelly, fine to coarse SAND,trace silt(SP);sand is predominantly medium —55 55= % 31 50+A. I EB-12 50-4.5' j — — T i 60— 23 50+* —60 EB 13 50-5"— Bottom of boring at 60.9 ft. Backfilled with bentonite— chips. I —65 65— I I.; ,--i r_ c —70 m i c 70— ' Lli U Z W = N W CC Q i I— t 0 W O z Sampler Type: PID-Photoionization Detector(Headspace Measurement) Logged by: JAP m L No Recovery 7 Static Water Level = Approved by: JAPi i F ' 2"OD Split Spoon Sampler Water Level(ATD) o iu Figure No. 2 It # • .-, Boring�Aspectconsulting Project Number BoringNumber� Log Sheet IN-DEPTH PERSPECTIVE 060266 EB-2 1 of 1 Project Name Eastgard Residence Ground Surface Elev Location 50 ft West of B-1/Jefferson County,Washington I Driller/Method Davies Drilling/8"O.D.Hollow-stem auger Depth to Water Sampling Method 2"O.D.split-spoon sampler/Hammer Weight:140 lb/Hammer Drop:30" Start/Finish Date 1/2/2007 Depth/ I Elevation Borehole Completion Sample Tests Blows/ N-value Material — (feet) Type/ID g Description Depth 0 to 20 30 40 5: Type (ft) °p° 8 TOPSOIL AND GRASS c EB-1 6 A - I L. PRE-FRASER UNDIFFERENTIATED DEPOSITS I — c D Medium dense,reddish-brown,moist,silty,sandy — �` GRAVEL(GM) cp °< Driller reports denser drilling at 2',coarse gravel at D 3' — — \ \ • CD — 5— \Backfilletl with 50 0+ — 5 1 — bentonite chips EB-2 50-5" cz, Gravel fragments in sampler;brown,silty,gravelly 8° sand in cuttings a _ Driller reports cobbles 6'-10' �° LP — Iiiiiiqii . Very dense,light brown/gray,moist,silty,gravelly SAND(SM);homogeneous,no bedding 10 EB-3 2150+ • '10 50-5" I — ' 15— EB 4 50-3"21 50+A Brown -15 o °0 Very dense,tan/light brown,moist,silty,sandy I — 7O GRAVEL GM ` 20— O°< 1 — % EB-5 29 50+ D, —20 503.5' '°5 z Bottom of boring at 20.8 ft. Backfilled with bentonite— w in _ chips. w 0 0 O Iw O O J 0 EE z Sampler Type: PID-Photoionization Detector(Headspace Measurement) Logged by: JAP m O No Recovery t x Static Water Level 2"OD Split Spoon Sampler Approvedby: JAP w o Water Level(ATD) w c.Dr Figure No. 3 • • I i I I I I I I I 1 Bainbridge Island Location 179 Madrone Lane North Bainbridge Island, WA 98110 Tel: (206)780-9370 Fax: (206)780-9438 1 Downtown Seattle Location Colman Building 811 First Avenue, Suite 480 Seattle, WA 98104 Tel: (206)328-7443 Fax: (206)838-5853 i 08/08/2007 08:51 FAX 206 780 5587 Edward Jonson Associates Z 001/002 • • Aspect 1N-DEPTH PERSPECTIVE �(� —// r.--4_, rA 'C'CL .\\I 4( �n / eL) o� ' b'S 'II,�,,, SUBSURFACE EXPLORATION AND GEOTECHNICAL ENGINEERING REPORT Eastgard Property, 270 Harrington Drive Jefferson County, Washington Prepared for: Tom Eastgard Project No. 060266-002-01 • January 17, 2007 Aspect Consulting, LLC" -ciREWp w PET 4 4 7 1 t ‘138 AC'C.* .. .- . . cl / 4, • 41.1 sG1sT 3v fi�� if''' Q 18802 ' //7/p7 -!3/ONAL ti7G Q j , 6.7 , l, ' SIONALE AC36 4- !EXPIRES 9f3/07 1 IEXPIRE� I22/ (� T James A. Peterson, PE John L. Peterson, PE Project Geotechnical Engineer Associate Geotechnical Engineer apeterson@aspectconsulting.com jpeterson@aspectconsulting.com W I_GEOTECHID6o266 Eastgard Recon\Eastgard Geotech Report.doc Y W�Y A � �. t-. it� 41J �• ;.<•?M.L. A. p,'--F , 4 �K gyp, �- :, ,' •,', [r. !u u. a7 `" .." { `pr�iS�G.�:y 445 is {{i t S y; _I.: �'jrj��'^�,•?u`1�1 k t���d�l 11. t{�x"vP f 1 .+-`l�� � �. � P 1�� ti,�X� �tl'Y1F�� �F 1�rM. 'Y"''A � �.�E� � kJ'4.` B',: i.%-'. A4;�'=''^�°y'"�'.;n;. �;.;,Y i::_11-Prr Ill °.a:, b ,.y..f i � ': �,� s`y s�'.< ti :a..:.';., �' i. 4,..,� .a� � :7, ��`t „ T,Z e'}'..,. xi�.\; cf..n.. t'�`:ia:-, .x� gip; �N a�� '•'`�rfi.: !$,4 ,,�a� 1l a r.•.i`.'f a,�+3�.{qY�`.K+: K°CwK�.'vx`.ftr,.t:r r.� 08/08/2007 08:51 FAX 206 780 5587 Edward Jonson Associates 002/002 • • ASPECT CONSULTING rdcomjgction, the area to receive fill can be blanketed with compacted washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. 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. Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer,placed in maximum 12-inch-thick, loose, horizontal lifts with each lift being compacted to 95 percent of the Modified Proctor maximum density using ASTM D-1557 as the standard. The contractor should note that any proposed fill soils must be evaluated by Aspect Consulting prior to their use in fills. This would require that we have a sample of the material 48 hours in advance to perform a Proctor test and determine its field compaction standard. 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 soils contained variable amounts of silt, and while considered moisture-sensitive, may be suitable for use as structural fill,provided they can be demonstrated to compact and perform well. If fill is placed during wet weather or if proper compaction cannot be obtained, a select import material consisting of 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. 3.3 Foundations Bearing soils were encountered at a depth of approximately 1.5 feet in the vicinity of the proposed house; consequently, shallow spread footings may be used for foundation support. 3.3.1 Spread Footings Spread footings may be used for support of the house when founded on the medium dense to very dense, silty, sandy gravel encountered at approximately 1.5 feet below existing site grade near the existing house. We recommend an alloVOle foundation soil bearing pressure of 2,000 pounds per square foot(pst)be utilized foedesign purposes including both dead and live loads. An increase in the above-mentioned bearing pressures by one-third may be used for short-term wind or seismic loading. Perimeter footings should be buried a minimum of 18 inches into the surrounding soil for frost protection; however, all footings must penetrate to the prescribed bearing stratUti-inat approximately 1.5_feet below the existing ground surface. <k= It should be noted that the area bounded by lines extending downward at 1 H:1 V from any footing must not intersect another footing, or a filled area that has not been compacted to at least 95 percent maximum dry density in accordance with ASTM test D-1557. In addition, a 2H:1V Iine extending down from any footing must not daylight onto site slopes. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. PROJECT NO.060266-002-01 • JANUARY 17, 2007 9