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HomeMy WebLinkAbout721174008 Geotech Assessment-~--. SUBSURFACE EXPLORATION, GEOLOGIC ~L~ARD, AND GEOTECHNICAL ENGINEERING REPORT NORDSTROM PARCEL A THORNDYKE 1~oAD - PORT LUDLOW, WASHINGTON ~c~a~~~ YAY t i X000 PREPARED FOR: -- L_.___ ERII~ AND JULIE NORDSTROM . ~ MAY 16, 2000 AESI PROJECT NO. BE00041A ~~ ,~~•~ ~-s~uorrEo ~,~-~„o ti-x (~ ~~s SCIENCE, INC coRPOaA~ oFRCi: 911 Fifth Avenue, Suite~100 IGrkland, Washingbn 98033 (~s1 ev-not FAx u~ 8v eau,. SUBSURFACE EXPLORATION, GEOLOGIC $A-LA,RD, ANJ) GEOTECHIVICAL ENGINEERING REPORT NOR~STROM PARCEL A, THORNDYKE ROAD PORT LUDLOW, WASHIl~TGTON 1vlay 16, iooo Project No. BE00041A I. PROJECT AND SITE CONDITIONS This relwrt presents the results of our subsurface exploration, geologic hazard and geotechnical engineering study for the proposed Nordstrom parcel A residential project location regional topographic features are ~'°.1~• The tares and the locations of the lorah'on~.s naccom shed for this sEud ~ 1.sting site fea- and Exploration Plan F' ~ ~ Y presented on the Site figure 2. In the event that any changes occur in the nature of the project on which this. report is based, the conch~sions and recommendations contained in this report should be reviewed and verified, or modified, as necessary. 1, 1 ,~ose anti Cr~.n~w The purpose of this study was to provide subsurface data to be utilized in the c~.sign and level- . opment of the project. par stud}, included a review of available geologic literature, review of aerial photographs, and performing geologic studies to assess the type, thickness, distribution and physical properties of the subsurface soils and shallow ground water conditions. This report summarizes our current Meld work and offers design recommendations based on our present understanding of the projext. . 1.2 ALthori ~±±~±*~ Written authorization to proceed with this study was granted by Mr. Jim Ray of the Reijnen Company on April 11, 2000. par study was accomplished in general accordance with our scope of work letter dated Apri17, 2000, and previous discussions with Mr. Ray. This report has been prepared for the exclusive use of the Reijnen Company, and their agents, for specific application to this project. Within the limitations of scope, schedule and budget, our services have been per- formed 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, expressed or implied is made. It must be understood that no recommendations or e yield a guarantee of stable slopes. Our observations; findings, and opiniare a men ans to identify and reduce the inherent risks to the owner. Page 1 7 i f (~: This report was completed with an understanding of the project based on our site work and dis- cussions with Mr. Ray. In addition, we met with representatives of Jefferson County to discuss Jefferson County's requirements for development within landslide hazard areas. 2.1 Lot and Site Developments The property is situated in the 2000 block of Thorndyke Road in Jefferson County, Washington. Parcel A is the southern parcel of a larger 34acre property. The parcel is bordered by similar, wooded, residential property to the west, Thorndyke Road to the north, Parcel B of the property to the east (existing Nordstrom summer home), and the beach and waterfront of Hood Canal to the south. Abroad flood plain for an unnamed creek separates parcel A from parcel B to the east. At the time of our field work, the parcel was undeveloped with the exception of a gravel driveway and a recently installed water-supply well located north and east of the proposed resi- dence. It is our understanding that flow volumes on the order of 20 gallons per minute were encountered at depths of approximately 60 feet in the water supply well. 2.2 Topoeraphv The parcel consists of a broad, relatively flat bench at an elevation of approximately. 45 feet above the level of Hood Canal. The slopes below the bench were ~ the order of 40 vertical feet, with overall slope inclinations ranging from 2H:1V (Horizontal:Vertical) to 3H:1V. Isolated areas typically less than approximately 10 vertical feet in height were as steep as 1H:1V. Slopes above the bench wore on the order of 100 vertical feet, with slope inclinations ranging from 1.SH:1V to 2H:1V. Slopes above and below the bench generally rise to the northwest from the waterfront of Hood Canal toward Thorndyke Road. Total elevation change from the waterfont to Thorndyke Road, estimated from the U:S. Geological Survey ?-1/2 minute Lofall quadrangle topographic map, is approximately 140 feet. The proposed residence is planned for the southern portion of the bench, approximately 25 horizontal feet from the top of the lower, 2H:1 V slope. '. 2.3 Site Drainaee No standing or flowing water was observed on the upland areas of the site but is inferred to flow during periods of extended heavy rain within the various topographic low areas on the bench. The unnamed creek to the east of the parcel serves as the main drainage basin for the entire 34 acre parcel. The creek (flow estimated at approximately 50 gallons per minute) flows within a well-defined, inciscd channel upslope of Thorndyke Road Downslope of Thorndyke Road, the ' stream channel widens into a broad, essentially flat, flood plain which opens south to Hood Canal. Ongoing subsidence and landsliding of the Thorndyke Road alignment approximately '/z mile south of the site has been documented as recently as the 1998-99 winter season. In addition, ' Page 2 ~, , evidence of recent; deep-seated, ~~;=t~~tional landslide damage was .documented below the road towazd the beach. Landslide activity was identified by offset cracking and lateral translation above the beach, and by the presence of a prominent toe bulge of landslide debris on the beach r several hundred yards southwest of the subject site. Several residences within the active portion of the slide southwest of the site had been "red tagged" or mazked by Jefferson County as uninhabitable during the 1998-99 winter season: 7efferson County officials stated that the landslide problems along this section of Thorndyke Road have been ongoing for a number of years and that a moratorium on building ~ ~ effect 'in that area. Parcel A lies within a landslide hazazd area as designated by Jefferson County; but lies outside the active portion of the landslide to the south. Five sets of stereo-pair aerial photographs from the period 1975 to 1997 were reviewed to observe regional topo~aphic features in the general area, and to check for indications of land slides in the site area. The aerial photographs suggest that the hillsides west and south of the subject site have a history of deep-seated rotational landslides. 'The .geomorphology of the hill- side suggests .that the landslides are large and contain multiple levels of benches and scarps (steep failure surfaces). The active portion of the slide affecting Thorndyke Road and private properties below the mad had experienced movement as recently as the 1998-99 winter season. The prehistoric head scarp for the slide area was well-fined along the souk ~~~ appmxi- mately 1 mile south of the site. The head scarp becomes more obscure toward the north, and is inferred to terminate within the un=named creek valley north. of Parcel A. The project site is inferred to lie within the northern extent ~of the currently, inactive, pre-historic landslide area. r" ~_ Our field study included drilling two exploration borings in the vicinity of the proposed house location, and conducting ageologic -reconnaissance to obtain information about the soils, shallow ground water, and slopes in the vicinity of the site. The various types of sediments, as well as the depths where characteristics of the sediments changed, are indicated on the exploration logs presented at the back of this report. The depths indicated on the Iogs where conditions changed may represent gradational variations between sediment types in the field If changes occurred between sample intervals in our explorations, they were interpreted. Soil was classified in general accordance with American Society for Testing and Materials (~'~ Procedure D- 2488, Standard Practice for Description and Identification of Soils (yissial Manual Procedure). Our field explorations were approximately located by measuring from site features shown on Figure 2. The conclusions and recommendations presented in this report are based on the geologic recon- naissance and two exploration borings completed for this study. Because of the nature of explor- story 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 Page 3 ~~ _ ~ ~ to the random nature of deposition and the alteration of topography by past grading-and/or filling. 3.1 Exploration Bor'nas The borings were drilled by Gregory Drilling from Bellevue, Washington, using a truck mounted drilling rig, operated under subcontract to Associated Earth Sciences, Inc. (AESI). The borings were advanced through the soil using a flinch inside diameter (ID), 8-inch outside diameter (OD), hollow-stem auger. Soil samples were collected at 2'/:- and.5-foot intervals. Disturbed but representative samples were obtained from the soil boring using the Standard Penetration Test (SPT) procedure in accordance with ASTM D-1586. The SPT and .sampling method consist of driving a standard 2-inch outside diameter, split-barrel sampler a distance of 18 inches into the soil with a 144-pound hammer, free-falling a distance of 30 inches. The num- ber of blows for each 6-inch interval is recorded. The number of blows required to drive the sampler the final 12 inches is known as the Standazd Penetration Resistance. ("i~l") or blow count. If a total of SO is~recorded within one 6-inch interval, the blow count is recorded as 50 blows for the number of inches of penetration. The resistance, or N value, provides a measure of the rela- five density of granular soils. or the relative consistency of cohesive soils; these values are shown on the boring logs in the appendix of this report. Materials encountered in the a oration bo ' were studi 1 and classified in the ~ ~ ~, ~P ~, field by. an AESI geotechnical engineer. All explorations were backfilled immediately after examination and logging. Selcctea~ samples were then transported to our laboratory for fiuther visual classification and testing, as necessary. .0 SUBS FACF .ONntTION4 Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visual ce of the site and vicinity, and review of applicable geologic literature. The geologic units in the project area have been mapped as Vashon advance glacial outwash by Yount, Minard, and Glen (1993, U.S. Geological Survey Open File Report 93-233). However, our borings indicate that recessional outwash sediments were present above the advance outwash and advance glacio-lacustrine sediments. Our analysis suggests that the predominant sands, silty sands, and silts of the advance outwash, as observed on ~e site, have been affected by large-scale, pre-historic landslide activity. The fairly consistent nature of the recessional outwash soils suggests that these sediments may be undisturbed. As shown on the field logs, the exploration borings generally encountered recessional outwash sands and silty sands overlying disturbed advance outwash and disturbed glacio-lacustrine silts and clays. The soil disturbance within the advance outwash sediments is attributed to pre- historic landslide activity in the azea. The following section presents more detailed subsurface information organized from the upper (youngest) to the lower (oldest) sediment types. Page 4 i i i Rece~anal Outwash The loose to medium dense sand, silty sand, and silt encountered in the upper 29 feet of EB-1 and upper 27 feet of EB-2 were interpreted as recessional outwash. These sedi- ments were deposited at the end of the Vashon-age glaciation, during the retreat of the Puget lobe ice sheet, approximately 10,000 years ago. During the retreat, sediments of variable grain sizes were deposited randomly as the ice retreated to the north. Following deposition, the majority of these soils were eroded, leaving only remnants at the tops of slopes, and within pre-existing drainage channels. The recessional soils encountered appear to be erosional remnants of this unit within what may have been apre-existing drainage channel now occupied by the creek. These soils may have been deposited after early episodes of large-scale landslide activity. Disturbed Advance Dutwd~h The dense to very dense gravel, sand, and silty sand with interbeds of stiff silt, with variable amounts of sand and clay, encountered between 29 and 42 feet in EB-1 and from 27 feet to the entire depth explored of 39.5 in EB-2, were interpreted as advance outvvash. Advance outwash sediments were deposited by pro-glacial streams exiting in front of the advancing ice sheet. While no direct evidence of distuu~ance was observed within the samples collected, these ~ sediments are inferred to have been moved en-mass by pre- historic landslide activity. Dic .rl~od,~ajy~ .v lacio-L.a ~ trineD'en~c~/s . .Vary stiff to hard, gray and tan, moist, itmerbedded to laminated, silty, clayey silt, and silty clay, was prGStnt between 42 feet and 66 feet in EB-1. These soils were interpreted to have been deposited by settling of sediment transported with glacial meltwaters into a glacial lake. Abundant evidence of dis~h~rbance in this unit was observed as prismatic fractures, shearing, inclined laminae, fractures in-filled with fine sand, and zones of struc- ., tuneless to chaotic texture. The relatively high sampler blow counts and moderate soil moisture observed in samples from this unit suggest that the noted disturbance does not result from historic landslide activity, but likely was the result of initial landsliding shortly after deglaciation of the area. Dlder. ~1 jon-Glacial De i c Very dense, .wet, brown gravel with sand encountered in the lower 15 feet of EB-1 were interpreted as older, non-glacial gravels deposited during a previous, non-glacial period. Evidence ofnon-glacial origin was primarily the lithology of the gravels encountered that suggested a source material from the Olympic Mountains instead of the glacial lithologies derived primarily from the Canadian Cascades and coast mountain ranges. The mechanics of landslides of this 'tulle are well documented. However, the causes of magna these large scale slides are poorly understood. Popular hypotheses for the instigation of these slides include loss of side slope support as a result of deglaciation, and seismically-induced landsliding. During rapid deglaciation of the Puget lowland at the end. of the last major glacia- tion, approximately 10,000 years ago, valley sidewalls, which would later become the banks of Hood Canal and Puget Sound, were left unsupported, resulting in regional landslide activity. ,~ Page 5 The other hypothes,s suggests that seismic soaking from lazge, regional eazthquakes instigated .many landslides. In general, two types of ground water may be encountered at the site. The first would be a "perched" water table. Perched water occurs when surface water infiltrates down through relatively permeable soils and becomes trapped or "perched" atop a comparatively impermeable barrier such as clay or silty soils. The second ground rwater horizon maybe encountered in exca- vations that penetrate into the underlying regional aquifer. Perched ground water was encountered in sandy soils at depths of approximately 13 and 34 feet in EB-1 and at approximately 8 and 28 feet in EB-2. Interbeds of sand in the glacio-lacustrine soils were also wet and represent a' complex perched ground water system. The pre-Vashon gravels encountered at approximately 66 feet depth represents the upper-most regional agquifer in the area. The water well on site is inferred to have been completed in these gravels. It should be noted that fluctuations in the level of the ground water may occur due to the time of the yeaz and variations in the amount of rainfall. Seepage may also occur at random depths and locations in non-uniform fills and soils. Ground water levels observed drning our site work may be lower than normal due to the mild winter season of 1999-2000. In addition, disturbed soils within pre-historic landslide terrain can create highly complex and unpredictable ground water flow. 'i'he unnamed crock to the east of the site flows within a broad alluvial plain before exiting into Hood Canal to the south. Ground water is typically shallow within the loose, alluvial sediments with a shallow gradient toward the outlet. Ground water encountered at 34 and 28 feet depth in EB-1 and EB-2, respectively, may ~be in hydraulic communication with the inferred alluvial aquifer. However, due to the infen~ed difference of hydraulic properties between the types of soils at the site and those within the valley, is our opinion these represent two distinct hydrogeologic environments. ' The slope and bench topography observed at the site is consistent with large-scale, prehistoric landslide terrain. The inferred direction of movement of the landslide mass is to the south and east. These features are additional evidence that the site lies at the northeast edge of large, pre- ' historic, regional landslide. During our limited reconnaissance, no active cracking, or signs of recent landslide activity were observed on the subject property or adjacent property to the southwest. We noted the presence of old-growth cedar stumps that appeared to be in place, and ' mature, second-growth fir and cedaz trees with no .observable signs of distress. In addition, no evidence of active landsliding was apparent on the beach. The prominent toe bulge associated with the current, active portion of the slide was located approximately %s mile to the southwest. ' ~" Page 6 t,~i... It should be n~trti that lack of obset: ved evidence `' F. l andslides does not demonstrate that damage has not occurred. in those areas between the site and the documen#ed active portion ofthe slide. The risk of landslides impacting the proposed project is difficult to assess based on the size and nature of the landslide terrain. Significant damage has occurred to structures southwest of the property within the active portion of the slide. There was no evidence of recent landslide activity at the site, as noted by the presence of mature, second-growth trees that were inferred to be approximately 50 to 75 years old The old-growth stumps may suggest that no significant landslide activity has occurred during the life span of the trees, which was inferred to be on the order of 300 to 500 years. . ~, Page T i Y May lk, 2040 AESI Project No. BE00041A II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and ground water/surface water conditions observed at the site. The discussion will be limited to . . seismic, erosion and landslide hazards. Earthquakes occur in the Puget Lowland with great regularity. The vast majority of these events are small and are usually not felt. However, large earthquakes do occur; as~ evidenced by the 1949, 7.2-magnitude event and the 1965, 6.5-magnitude event. The 1949 earthquake appears to have been the largest in this area during recorded history. 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 proposal .project is discussed below. .1 SurfiCial ('Tr»~md R~mfintr The nearest known fault trace to the project is the Seattle fault. 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-?4 and Johnson et x1.,1999, Active Tectonics of the Seattle Fault and Central et Sound Washin , Pug gton-Implications for Earthquake Hazards Geological Society of America Bulletin, July 1999, v. 111, n. 7, p. 1042-1053) suggest that a northern trace of an east west trending thrust fault zone (Seattle fault) may project about 10 miles south of the project site, in the vicinity.. of Bremerton. The recognition of this fault is relatively new and data pertaining to it are limited, with the studies still ongoing. According to the U.S. Geological Survey 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 in -excess of several thousand years. Due to the suspected long recun~ence interval, the potential for surficial ground rupture is r considered to be low during the expected life of the structure. 6.2 Seism__ically-Induced Lin .Tides a_nd LigLefaction The area of the proposed house has a Iow risk of shallow li uefaction based on the lack of q adverse shallow ground water and soil conditions. Loose saturated soils inferred to lie within the Page 8 flood plain of the creek and along the beach, however, have a high ris?c fur liquefaction. It is our understanding that current plans do not include the placement of structures in these areas. Based on the site stratigraphy and the inferred presence of pre-historic landslide activi in the area, the site is at risk for seismically-induced landslides. The risk of seismically-induced land- slides increases as duration and magnitude of ground motion increases. It should be noted that a comprehensive stability analysis for the site under these conditions which would further quantify this risk was beyond the scope of work for this study. 6.3 Tretln~l Mnfinn Based on the site stratigiaphy encountered and visual reconnaissance of the site, it is our opinion that earthquake damage to the proposed structure, if founded on a suitable bearing stratum, would likely be caused by the intensity and horizontal ground acceleration associated with the event. Structural design of the building should follow current Uniform Building Code (UBC) standards and take into consideration stress caused by seismically-induced earth shaking. The site would be characterized in the UBC by a Seismic Zone Factor Z of 0.30 and Soil Profile of S~' Beyond the identified deep-seated prehistoric landslide activity observed at the site, we did not observe evidence of landslide activity on the southern, 40-foot-high, 2H:1V slope below the pro- posed house location with the exception of isolated, surficial landslide activity. These slides were generally less than 10 feet high and were most prevalent where subtle topographic differ- ences resulted in slope angles approaching 1H:1V. These landslides were well vegetated and appeared to have occurred prior to the 1998-99 winter season. Landslide risks are classified as high, moderate or low, depending upon the probability of. occurnnce and potential for damage of the structures. High landslide or mass-wasting risk areas are characterized by moderate (greater than 25 percent) to steep (greater than 40 percent) slopes and the presence of known past or active landslides. Moderate landslide risk areas are charac- terized by moberate to steep slopes and the absence of ongoing or known past landslides on the site. Low risk. areas are characterized by gentle. to moderate slopes and no history of landslides. The slopes south and east of the proposed residence are considered high risk by the slope geometry and the presence of past surficial landslide activity, based primarily on the probability of recurrence during the expected life span of the structure. Based on past landslide activity, the type of landslide to affect the site will likely be ongoing and incremental surficial type sliding. This type of landslide activity affects the upper 1 to 3 feet of soil on the slope and typically does not extensively affect the overall "global" stability of the slope. To mitigate the risk of these shallow landslides damaging the proposed house, we recommend a minimum horizontal setback of 25 feet from the top of the southeast slope. This setback distance is from the top of slope at existing grades and is based on the intersection of a 2H:1 V bearing slope projected through the subsurface from the toe of the slopes, including the 18-inch deep _ Page 9 r minimum touring embedment. hit recommendations prc~~vided in 5ectlott 8.0 of this report, Erosion fl[~atds and Mitigation, should be implemented. In addition, all surface drainage must be properly collected, controlled and ti tlin bottom of slo to areas. Do ~ ed to the P g wnspouts from roofs, runoff from other impermeable surfaces including driveways, and all footing/wall drains must be properly collected and tightlined into suitable storm water drainage systems. With the removal of all storm water from impervious surfaces, the effect of the planned, on-site development, including the septic system, will result in a net decrease in water input. As such, a properly designed, located, and maintained septic system should not impact existing slope stability. We recommend a minimum 100 foot hori- zontal setback for the septic system from the tops of any steep slope. Similarly, the overall project will not decrease slope stability on adjacent properties. . We understand that tree removal on the site is expected to be minimal. The area was most likely _ logged sometime around the turn of the twentieth century, when most large trees inferred to have been present in the vicinity of the proposed house were removed. Specific adverse impacts to site slopes shortly after logging are difficult to define. Currently, the house site supports mature second-growth fir and deciduous trees and young third-growth fir trees.. It is our understanding that few of the large trees around the proposed residence are planned .for removal and that .Pruning and coifing will be generally limited to the young thirdgrowth on the bench. We recommend against cutting significant amounts. of trees located on the slopes without a predeter- mined revegetation plan. In addition, we recommend against topping trees, as i# reduces root ball size and srtrength. Limbing is less damaging to root structures and is recommended in general over removal and topping of large trees. I Based on the geological conditions observed in the vicinity of the lower slope, and inferred performance of the slope doting past heavy rainfall events, it is our opinion that risk of damage to the proposed structure from landslide events resulting from periods of extended heavy precipi- tation is less than 1 in 100 in any given year. It should be noted that a regional or quantitative slope stability analysis was beyond our scope of services for this project. It must also be under- stood that the identification of landslide hazards on the site and providing geotechnical design recommendations for the project is not a guarantee of stable slopes, but is meant to provide a means to reduce the risk of slope movement. Ongoing natural erosion and shallow surf~cial landslides will continue to act on the steeper portions of the lower slopes during periods of extended heavy rains. The loose nature of the near-surface soils encountered at the site suggests a moderate to high erosion potential where these soils will be exposed during construction. Areas outside of the proposed construction area have a low erosion potential due to the well-established vegetation. As such, only the areas necessary for construction should be stripped of vegetation. To mitigate and reduce the erosion hazard potential and off-site sediment transport, we recommend the following: Page 70 .~ i Surface water should not be allowed to flow across the see over unprotected surfaces. • All storm water from impermeable surfaces, including driveways and roofs, should be tightlined to a suitable temporary storm water collection system and tightlined down the entire .height of .the lower slope, to an appropriate, low-gradient, rock armored, discharge point. . • ~ Silt fences should be placed and maintained around the perimeter of the proposed .construction area throughout the entire construction phase of the~project until permanent landscaping and permanent storm water collections facilities have been installed. • 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 n~essarily limited to, covering with plastic sheeting, the use of low stockpiles in flat areas, or the use of hay bales and/or additional silt fences around pile perimeters. • In order to reduce potential erosion hazards, areas stripped of natural vegetation during construction should be replanted as soon as possible, or otherwise protected. It should be noted that upslope development can have sigaificant impact on the conditions at the M .project site. If off-site dewelopment occurs upslope (northwest) of the site, storm water control, and erosion control meas<u~es for the site should be reviewed and modified as necessary. M ~J M M N M ,. Page 11 M;:~- fi, 20~- AESI Project No. BE00041A III. DESIGN RECOMMENDATIONS 9.0 INTRODUCTInN Our explorations indicate that, from a geotechnical standpoint, the proposed project is feasible, provided the risks discussed are accepted and the recommendations contained herein are properly followed. The bearing soils (natural recessional outwash sands) are relatively shallow and spread footing foundations may be utilized. We understand that the distribution of foundation loads of the niggle-story, wood frame house will be typical;. no concentrated loads are antici- pated. Consequently, the loose, recessional outwash sands encountered in the upper portions of our borings are capable of providing suitable foundation support when prepared at;,cording to the recommendations given herein. 10.0 SITE P FPARA'TfON Site 'on within the h use f . preparati proposed o ootprmt should uiclude removal of all trees, brush, debris and any other deleterious material. Additionally, the surficial, organic topsoil should be removed and any remaining roots grubbed. Within foundation areas, ALL fill must be removed to expose tha underlying natural sands. This includes the fill materials recently :placed for the driveway. 'The near-surface, natural sand bearing material contains a high percentage. of fine-grained material, which makes it moisture-sensitive and subject to distiubance when wet. The contractor must use care during site. preparation and excavation operations so that the underlying loose sands are not disturbed. If this occurs, the disturbed material should be removed to expose competent, natural soils. L J The near-surface loose sand in its current condition is not suitable for foundation support. We recommend compaction of the upper 3 feet of sand (below footing subgrade) to a firm and non- yielding condition. We recommend the use of a large vibratory hce pack attached to a track- mounted excavator. Smaller compaction equipment will not adequately compact the sand at the 36-inch depth. The pcrimeter footing excavations should be a minimum of 3 feet wide and ade- quately compacted the full width. All interior column footing excavations should be a minimum of 2 feet wider than the actual footing (in all directions) and compacted the full width. All footings should be placed in the center of the excavation. ~- Page 12 Spread footings may be used for building "support when founded on _suitably compacted and approved sand. 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 at least 18 inches into the surrounding soil for frost protection Interior footings, if applicable, require only 12 inches burial. However, all footings must penetrate to the prescribed bearing stratum and no footing should be founded in or above loose; organic, or existing fill soils. It should be noted that the area bounded by lines eaten '~ downwazd at 1H:1V. ~-g from any footing must not intersect another footing, or a filled or loose area that has not been compacted to ~" at least 95 percent maximum dry density in accordance with American Society'for Testing and Materials (ASTM) test designation D-1557. In addition, a 2H:1V line extending down from any footing must not daylight onto site slopes. Thus, in addition to the setback distances described it< Section 7.0, footings should not be placed neaz the edge of steps or cuts in the bearing soils. Anticipated total settlement of footings founded on properly prepared, compacted sand subgrade .should lie on the orber of 1 inch. However, disturbed soil not removed from footing excavations, or soil not adequately compacted prior to footing placement, could result in increased settle- merits. All footing areas should be inspected by Associated Earth Sciences, Inc., prior to placing concrete, to verify that the design bearing .capacity of the soil has been attained and that construction conforms with the recommendations contained in this report. Perimeter footing drains should be provided as discussed under Section 13.U of this report. It is our understanding that structural wood floors will be used for living space and concrete slab- on-grade floors will be used for the garage. A slab-on-grade floor may be used over natural sand provided the sand is compacted in the same manner as for footing subgrade. Where passage of moisture through the slab is undesirable, the floor should be cast atop a minimum of 4 inches of washed pea gravel to act as a capillary break. It should also be protected from dampness by an impervious moisture barrier or otherwise sealed. ~3.0 D AiN~C;F. ['`ONSID RATIOl`T 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 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 constricted with sufficient gradient to allow gravity discharge away from the structure. Roof and surface runoff should not dischazge into the footing drain system but should be handled by a separate, rigid, tightline drain that safely discharges to a natural drainage way and subsequently to Hood Canal. In planning, exterior grades adjacent to walls should be sloped away from the structure to achieve surface drainage. " ~- Page 13 •~ ,_,,_ _ _ -- 14 U PRO: ~I~"I' DESI N ND Cii°VSTRUCTIOIv tviONITO iN(` 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 AESI review the final project design drawings to assure that the geotechnical criteria have been properly incorporated into the design. We are also available to provide geotechnical engineering and monitoring services during the construction phase of the project. The integrity of the foundation and slopes depends on proper site preparation and construction procedures. In addi- tion, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. ' We have enjoyed worldn~g with you on this study and are confident that these recommendatio ns will aid in the successful completion of your .project. ff you should have any questions, or require further assistance, please do not hesitate to call. Sincerely, ASSOCIATED lF.~R1'g SCIE1~iCES, INC. West Sound Office ~ . Robert F. Cousins, P.G. Project Geologist w:~'~~~o~-.a~ r ~' Page 14 ~. -- John L. Peterson, P.E. Senior Geotechnical Engineer ~ 0 2000 Feet ' Source: LofaN 7-1/2 Minute ~uadrange M~ ASSOCIATED NICiNITY MAP ~~ t 4 EARTH NORDSTROM PARCEL A RESIDENCE SCIENCES, INC Jefferson County, Washington ~ m _# - .~ EEC >•~ ~1Mr ara aa~ aa~ ~ r ~ a~ . wrr ~r~+ .wr ar+r. ~ ...~ - s Aw ~arr ` !^~ q71~ P~ /!./ + S m i ~~ _ g2 so ~ 48 - A~ \•~ ¢~ ~. 4? k6 Trsa makad kk for center aI / .~k ,g0 k0 / ~ + ~ . - ~9 ~ / ~ ~ If A ,~g Ir. . ..• n Y ~ - / 32 u.~ ., 3~8 + "y +:a Top of 24 a2 .~ slurwY tial. ~ . ~- unarvan~bl. ~ i i ~~ .~ Teo et atop. ~~ - ~~ APPfOXimot~ht9~°t~ lines -~ ~~ LEGEND EB-1 ~ Approximate Explonedon BoAny LooaUon A~OCIAT'SD ~ BARTFI ~~.~ ~~ 8CIBNCES. tNC ~~,~ r~ SCALE iN FEE7 0 30 80 wva~.a..rwwrAn.r.laa~w~raaerar/aaw. wu.~wwaaaw 31T! AND DLPLORATION PLAN B"E NORCEIROM PARCEL A ,.,.,. JMMaon t~aaNY, wMkMglal 2 a E.x oration ~11C Project Number Exploration Number Sheet f 4 1 o BFJGG41 E~-1 ••~ ___ Ground SurfaceElevatir,n(ft) 48 P. eject Name ~~Q~t'=s.~~PronettY• P~;-•~~A Location Thornd;;' r2o^ tPfferson County; West end of ct!1-~e-sac Datum ~~, DrilledEquipment Gtegorv DrillirmpMoUow Stain Amer 4" iDl8" OD Date Start/Finish ~,~?QOQ-4/17/2000 Hammer Weight/Drop Otrfinm~lir 41~mmear 1d[) Ib ! ~[)-inch • Rote Diameter (in) 9-1nch - - - -_-- This~ (s ~ar~ of the report prepanr Associated Earth Sciences (AESnTor 8ie named project and shoufd~be read togettrer ady v~ith that ~ ° ~ r ~ ,, t $ report for complete irrterpratatlon. This summary appppsp ~~yy b the ~ location of this exploration and at the time of explor~io~ Subsurface ro~ ~m BbWS/FOOt a a . S , E ~~ t9 conditions ma change at this bcation with the passage of time. The data are. a gf actual conditions arrooutdsred. U m T r° DESCRIPTION to 20 so. ao Surface: Brushed rode Cdriveway) . RECESSIONAL OtJ7WASH •' Loose, damp. reddish brown SAND; trace sit, trace to few organics: sand tine 2 S-1 2 s Loose. darnP. tan SAND: sand tine to mecum- - - - - - - - - 5 S2 4 5 10 S-3 6 '9fadQ6 wet; few sit 4 5 11' (4117100) . is S-4 Loose, wet. light brown to gray frdeibedded sILTY SANS and SA`ND1~ - i SILT; sand very tine, sit coarse; larrrinaded with silty daY s ~ S~ Mednm .dense, damp. tan. fine SAND - - - - - - - - - - - o to E~ n a Sampler Ty pe (S T): ~: - t.nemroa~ rr~ucs J~ No Recovery P -Permeability Logged ~~ ® 2" Split Spoon Sampler M -Moisture Af~~ ~' RFC ~ Static Water Level Figure No. A - 2 ® Grab Sample t Water Lev°' °*''"~e of drilling (ATD) - M~ M M~ r r 35 DESCRIPTION ~ .' FCEGES5rOP1AL OUTWASH -- Medium dense, damp. tan, fine SAND = DISTURt3ED ADVANCE OUTWASH S-7 • -.• •~' tlddc 'tan sity day SAND; tew • trace sit: sand fine; stratified with 1" . Q ~ (4M710ej S-0 . I $ very dense, wet, tan GRAVEL; wih sand, trace sit; gravel fine b medrurn, - ~ s~rld rrredirMrl t0 OOa1Se _s . . D,~ a..ocw~o Ex ioration Lo _ ~~Et~ ^11C Project Numtrer Expbratrorr Number Sheet _ . • BE00041 _ EB-1 2 of 4 Projec' Name , .c?; dstrom Proq~~r: Parcel A Ground S lace Elevation (ft) _ ~ G_ Location ~ ; rorndike Road Jefferson Guuntv,;~~lest end of ct±h:e-sic Datum M~~ •- - DrilkdEquipment Orif Stem 4" /8" OD Date Start/Finish 4/17/2400-4/17/2.1(]tl Hammer Weight/Drap Automatic Hammer. 1401b / 30-inch Hole Diameter (in) •9-rnch ~~ ispart of the report rod by Associated Earth Sciences ~ a ~ _ (AESI)Tor nme named and should bie read. together ony with that c ,~ ° roP°rt for cornpl~e This summary a ies on to the ° a S E ~ ~ °f thises~loration and of the ttme of expbr~on. Subsurface „~ •~~ BIOWS/Foot o T y c7 ~ data ~aarge at this loci final c~rondltioris enooir~r ., m D .8 .1. 0 40 S-8 0 .g .1. r r r ^ .: Bard. wel, txvMm to pray SANDY SILT; few day; sand fine, aik coarse S-10 - - ~ery-d ~ tan Snwo wiN sI~T; trace sand fire, yravell~me: ~~® Hard• . 9~~ 9mY SILTY SAND; sand fine, siR coarse - - - c Sampler Type (S1): z ® No Recovery o ® 2" Split Spoon Sampler ~ ® Grp Sample C -Chemical Properties P -Permeability M -Moisture ~ Static Water Level e 10 12 13 24 23 14 25 26 10 30 1a 30 ~o Zo so ao 50+ 50+ 50+ Logged by: ,~C APP~d bY= RFC Flgure No. A - 2 ,~,~ _ loration Lo r1L: Projed Number Expbratior; Nu;nber Sheet . BE00041 EB-1 3 of 4 _..._ ._ ._. Project Name Nordstrom Pre ~~~y: Parcel ~. _ ______ _ ~~rouna surface Elevation (fl) ;8 Location Tom, orndike Road, Jefferson County: We, end of cul-de-sac Datum - - On~ledEquipment r,,fec,~ry DriHinalHollow Stem Aucer 4" ID/8" OD Date StarUFinish Hammer WeightlDrop ,~ytt~m~ atic Hammer. 1401b i 30-inch ~ Hole Diameter (In) _ 9-inch a'. tls V ~ Z ~ Q~ a T~~N DESCRIPTION s-» Very dense. moot, greenish gray SILTY SAND; sand fine, eft coarse moist. dark gray CIAYEY SILT; irteguhr fraduies with floe sand ~; chaotic taxturo with 2~ mm fractured cubes ~ ~ S-1 ~ ~ S-1 65 Blows/Foot to 20 30 40 ~z ~a niiiii~. 50+ ^ • . • rr~c-~.~v~.v.~ vcrva ~ o O . $ Very dsase, wet, brown GRAVEL with SAND; trace s~ gravel fare to . t o coarse, sand predorniianty coarse I . .$ 1. 0 ~ .g o ' ~~ S-15 . 1 g ~' S0+ a . .g t. 0 . .g e. I . 8 t. . g o I Sampler Type (ST): ® No Recovery C - Chemigl Properties ~~ ~ JBC ~ P - Permeab~ity ® 2" Split Spoon Sampler M -Moisture Approved bY: RFC I ® Grab Sample ~ Static Water Levei Figure No. A - 2 ' Wa Level at ofd V dense. wek ~Y SILTI( SAND; trace day, trace graved ss~d fine ~•^. socM-~o s tee. tn~a P;^"' ~t Name 's_~ordstrom Pri L~,ation ~ -'I~horndike Ra DriltedEquipment C3reaorv Dr~itwlH hammer WeigMlDrop A~; ~ ~~ Hai _ ~sgTor r~ie a a a$ to n rof tl~~t o i y ~ ~ ~ i~ Ex loration L N~ber E~loration Number Sheet )041 EB-1 4 of 4 '~• Ground Surface Elevation eft) : _,.48 ~o~nfy West end Qf cul-de-sac Datum M~~ -- ier 4" ID/ti" OD Date Start/Fin~h 4/17/2000-4/17/2nnn ~_/ 30-inch tote Diameter (in) 9-inch DESCRIPTION ~ . t~ v oePasrrs 0 • $ Very dense. wet, brown GRAVEL. w~h SANt7 trace s~ gravel tine to ~ • aoarae, sane preaoiriinamy coarse 0 so-s Blows/Foot ~0 20 so ao .$ 1. r ~` ' ~~ 0 o 0 z o ~x location Lo ~~ ~ Project Number Cxploration Number Sheet 1 ^1 G BE00041 EB-2 1 of 2 _ Project Name ,~~C,strom Pro rho'.. p~. C~ e{ A ~ Ground Surfxe E~ '~~n (ft) " Location -. Thornrlilce-Road. Jefrerson Coz~s~ y; Datum rur~~ ~ ~ °' " DriUerlEquipment _ G ~Ilow Stem AuaeP 4" ID/8" OD Date StefVFinish 4/1 ?/2000-4117/2000 Hammer weight/Drop Automa ' Ham er. 140 ib / 30-inch Hole Diameter (in) 9-inch This is rt of the report prepared Associated Earth Sciences . (AESn the named roject aed aiau~d be with tl d t th g t ~ o = ~ p rea oge er or y ia o report far complete iMerpreption. This summary applies on bo the o b c S a E a fa ~ ocation of this expbration and at the time of er~bratiarr. Subsurface o ~" conditi h he l 81ows/FOO~ m ~ rn ons m c ange at t orationw~h the passage of time. The m o N area of actual conditions encountered. c m DESCRIPTION ° 10 20 so ao RECESSIONAL OUTWASH • : Loose, damp. tan-brown SAND; sand fine to medium S-1 8 4 5 S-2 wet. hew silt ~ s rr s • t~T~ s 10 . Mediwrr dense. damp, tan SAND; saM tips; wkly straMied - - - - S~ s s 15 Stiff. moist. tan mottled orange tlILT; tew clay; hor~izaMalyr Farr~nabed w~h dark ted aoddized fine SANDvrilh s~ s~glrtfy cemented ~ 7 4 s ~ dense, moist tan SAND, few silt: no visible sfratificadon S-5 a 12 Sampler Type (ST): . ® No Recovery C -Chemical Properties Logged by: JBC P - Pem~eability ® 2" S lit S S l ' p poon amp er M -Moisture APPro~ bY: RFC ® Grab Sample ~. Static Water Level Fgure No. A - 3 ' R L vel t 1 ~1 n n 1 i ' °c z c !n ~,^~ ~ Ex location Lo ~ E~'t"t ~~ ttNG Project Number BE00_041 Exploration Number EB-2 Sheet 2 of 2 F': ;ect Name ..i`l~dstrom Propg,~y Par~~~~ ~ A _ Ground Surface Elevation (ft) 44 - - ~~::ation Thom ike Road, Jefferson county; " ~ Datum- MSI DrilledEquipment Gresronr DriNinpMollow Stem Auger 4" IDJB" l7D Date Start/Fmish 4/17'/2Q00-4/17/2000 Hammer Weight/Drop _ g~matic Hammer. 140 Ib / 30-inch Hole Diameter (in) g~inoh This is R of the report p pared ~byy Assodated F_artlt Sciences (AESI the named project acrd should be read together ony with that ~ ~ ~ ~ a _ ~ g a E report for compote interpretation. This summary a ~v to the ~° location of this expbration and at the time of r«'Kpbra 3rubsurface o ~ ~ Bkrivs/FoOt a S ~ n ~ ~ itions m ctwnge at ~hrs logtion with the passage of time. The E €~ f' f ti l f T m a i ic:a eon o actua oarditieons encountered. ~ m DESCRIPTION fo 20 30 40 RECESSIOPUU_ OUtYYASN f+Aedium dense, moist, tan SAND; few sdt DIS7'l~BED ADVANCE OUiYYAStt S$ ~:: :: • Very dense ~, gray SAND; few gravel; sand coarse, gravel fine; 2' ~. t8 Yrlerbeds o~ ~ '~ i w d ~ . , e ay (~71~ 22 5p+ nand grades tine to medium - ~ -graveYydr~ngirom30'~2' ----------- --- S-7 Dsnse, wet, brown SMID; sand fne to medium - - - - - - - - is -t3" ~ of GRAVEL with SAND; gravel prodorrtinardy tine, sand coarse zo . 35 ' S~ Dense, wet, brown SAND; surd fine to coarse, p~sdomhraMly medium - 4d t3ottorn of bong d 39.5 fed. 45 Sampler Type (ST): No Recovery C -Chemical Propefies Logged by: JBC rUty P ® 2" Split Spoon Sampler M _ Approved by: RFC Moisdrre ® Grab Sargple $~ Static Water Level Figure No. q - 3 ' e n ' A Level at