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HomeMy WebLinkAbout970800001 Geotech AssessmentRETURN ADDRESS: RI/MAN ENGINEERING P. O. Box 1375 ·. Port--WA 98339 Please print or type inJbrmation 9810912901 02:06P J~Iffersofl CoUnty, Idi~ TILLPI~N EN$INEERIN6 HISC 42.00 Document Title(s) (or transactions contained therein): 3. 4. Reference Number(s) of Documents: Grantor(s) (Last name first, then first name and initials) IAa o( [] Additional names on page of document. Grantee(s) (Last name first, then first name and initials) [] Additional names on page of document. Legal description (abbreviated: i.e. lot, block, plat or section, township, range) [] Additional legal on page of document. Assessor's Property Tax Parcel/Account Number [] Additional on page of document. The Auditor/Recorder will rely on the information provided on the tbrm. The staff will not read the document to verify the accuracy or completeness of the indexing intbrmation provided herein. ~8/~12Ul 02:08P Jeffer'eon County, HR TILLI~IN EN6INEE~II~ I~15¢ 42.00 W-~76-01. Geotechnicai Report Mats View Meadow Subdivision Port Ludlow,. Washington February 1996 Mr. Harold Moe 311Mats-:V~w:Road Port Ludlow. Wasfi!ngton 98365 GEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS 400 N. 34th St. · Suite 100 P.O. Box 300303 Seattle, Washington 98103 206 · 632 · 8020 _=111 $ NON &WlLSON, INC. GEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS ::..: _.. February 29, 1996 i lll ii ill Ill Il Ill Jeffer.on County, I~;I TILLIIRN EN;INEERING I~ISC 42.~0 Mr. Harold Moe 311 Mats View Road Port Ludlow, Washington 98365 RE: GEOTECHNICAL REI~RT, MATS VIEW MEADOW SUBDIVISION, PORT LUDLOW, WASHINGTON Dear Mr. Moe: This letter report presents our field explorations, conclusions, and recommendations for the proposed residential development west of Mats Mats Bay on Oak Bay Road north of Port Ludlow (Figure 1). A Jefferson County memorandum, dated December 22, 1994, regarding a preliminary State Environmental Policy Act (SEPA) review for the project indicated that for approval of the subdivision, a geoteehnical report must be prepared which addresses existing and potential landslide and erosion conditions at the site and provides mitigative measures, as needed. Therefore, the purpose of our work is to provide the geotechnieal assessment requested in the county memorandum and geotechnical recommendations for the development of the subdivision. Our work was conducted in accordance with our proposal dated February 5, 1996, as authorized by Mr. Moe on February 16, 1996. Our geotechnical evaluation is based on site reconnaissances and subsurface explorations performed on February 23 and 24, 1996. Our understanding of the proposed subdivision layout and development is based on site plans by Madrona Planning and Development Services, dated November 15, 1995, and a topographic map by David Cummins and Associates, dated May 1994. SITE DESCRIFHON 1 The proposed subdivision is located between Oak Bay Road to the west and Mats View Road on the east (Figure 2). The proposed subdivision is situated on approximately 20 acres. The configuration of the site is indicated on Figure 2. The site is roughly 1,200 feet SEA-f, TLE '""",,~,,.~rn ~ ...... J%:T©t, ?E ' [.~:. 206'632'~0::0 FA., 20["( ?.;"(: ..... TD[;' i'30~..'-',7',"!-(."i~:: W-7276-01 Mr. Harold Moe February 29, 1996 Page 2 ~810912~t)1 82: 88P CoUnty, kl~ TILLI~qN FJ~INEERII~ I~I$¢ 42.l~ long (north-south) by 950 feet wide (east-west). Mats View Road is unpaved and cuts east- west across the property and divides the property north-south. The road subsequently tums to the south and borders the east property line. The configuration of the site is indicated on Figure 2. In general, the ground slopes from the west property line down to the east, toward Mats Mats Bay and the north-south extension of Mats View Road. Elevations across the site range from about 158 feet at the southwest property comer to about 40 feet along the northeast comer. Natural slopes across the site range between 10 and 12 percent except for a small section along the south property line where the natural slope is as much as 30 percent. The section of the property south of Mats View Road is an open field with scattered, approximately 2-foot-diameter cedar, maple, and fir trees and blackberry brambles along the south property line. Vegetation north of the road typically includes up to 2-foot-diameter alder, maple, fir, and cedar, with an undergrowth of sword ferns and elder. Growth positions of the trees on the site are not indicative of soil movement on the slopes. A storm water detention pond has recently been excavated in the northeast comer of the site in conjunction with property development immediately west of the Mats View Meadows and Oak Bay Road (Mats View Terrace). Site development plans indicate that the pond is approximately 200 feet long by 60 feet wide. While at the site, we observed that a steady flow of water (5 to 10 gallons per minute) was being routed from the Mats View Terrace development in ditches alongside Mats View Drive and into the storm water detention pond. No other signs of surface water or springs were observed at the site. We did not look for springs or surface water outside of the site boundaries. PROJECt DESCRIFFION l Two final lot layouts are being considered. In either layout, we understand that the site will be divided into approximately, 19 1/2-acre building lots for single-family residences and W-7276-01 Mr. Harold Moe February 29, 1996 Page 3 two septic field parcels. One conceptual lot layout is shown on Figure 2. We understand that the other lot layout under consideration is similar in that the septic field areas and general locations for residential development are the same. Both layouts under consideration will move the west end of Mats View Road to the north as indicated in Figure 2. Both layouts also provide for construction of an access road in the same general area off of Mats View Road to the residential lots on the south. The exact location of this road, however, varies somewhat between the plans. No significant cuts or fills are planned for road construction under either layout or do current plans call for the construction of retaining walls or rockeries. EXPLORATIONS AND LABORATORY TESTING An engineering geologist from our firm conducted geologic site reconnaissances on February 23 and 24, 1996. In addition, 10 test pit explorations were performed on the site on these dates with an excavator under contract to Mr. Moe. The test pits were designated TP-1 to TP-10, and their locations are shown on Figure 2. The location of each test pit was determined from the location of existing septic disposal test pits that had been previously located on site plans and from existing site features on these site plans survey points. The test pit locations were selected in the field to obtain subsurface information across the planned developed portion of the site, in the different topographic features, and in areas where differing soil conditions might be expected to occur. Test pit depths ranged from 6 1/2 to 10 1/2 feet. Soil exposed in the test pits was logged, and relative densities or consistencies were estimated in the field by our engineering geologist. Representative samples were collected in the field and returned to our laboratory. The test pit logs are presented on Figures 3 through 12. 1 Sample classification was visually checked, and sample moisture contents were determined at our laboratory. The moisture contents are shown on each test pit log. W-7276-01 Mr. Harold Moe February 29, 1996 Page 4 County, i~ TILLI~IN I~N~IN~£RING ~I$C 42.00 SUBSURFACE CONDmONS Geologic maps of the area indicate that the site is underlain by Vashon lodgement till. The test pits confirmed the presence of the lodgement fill beneath the northwest portion of the site, but the remainder of the site appears to be underlain by younger, Vashon ablation till and older, pre-Vashon (and hence very dense or hard) sediments. Till is a non-sorted mixture of clay, silt, sand, and gravel with scattered cobbles and boulders that is deposited by a glacier. I_xxlgement till is deposited at the base of a glacier and is subsequently overridden by the advancing glacier. The Vashon Ice sheet that deposited the lodgement till is estimated to have been up to 3,000 feet thick in the area, and as a result, the lodgement fill and underlying pre-Vashon soils were over consolidated to a very dense or hard state due to the great weight of the ice. Ablation fill resulted from the deposition of sediment entrained in the ice or on the surface of the ice as the glacier began to melt. While not glacially overridden nor as dense as lodgement till, the ablation fill observed at the site is nonetheless typically dense. Descriptions of the soil profiles encountered in the test pits follows. Ail the test pits across the site encountered between 1 and 2 1/2 feet of very loose to medium dense topsoil. The topsoil is typically a silt with varying amounts of sand and gravel. In the northwest portion of the site, test pits TP-8 and TP-9 encountered weathered lodgement till beneath the topsoil and extending to a depth of 3 feet below the ground surface. The weathered till is a medium dense to dense, slightly gravelly, silty sand to sandy silt with scattered cobbles. The lodgement till became unweathered and very dense at about 3 feet below the ground surface and consists of slightly gravelly silty sand to sandy silt. The lodgement till in test pit TP-9 was penetrated, below which a very dense, slightly fine sandy to fine sandy silt was encountered. t Test pits TP-1, TP-2, TP-3, TP-4, and TP-5, located in the western portion of the site south of Mats View Road encountered ablation till beneath the topsoil. This material is typically W-7276-01 Mr. I-Iarold Moe Feb~ 29, 1996 Page 5 lefforoofl Courtty, M~ TILLRP, I%I ENGINEERING RISC 42.92 a medium dense to dense, silty, gravelly sand and sandy gravel with scattered cobbles that extends from the base of the topsoil to 3 to 5 feet below the ground surface. Beneath the ablation till, these test pits typically encountered dense to very dense slightly fine sandy silt. This sediment would seem to be glaciolacustrine or fluvial in origin, being deposited in a lake or similar environment in front of the advancing glacier. It was subsequently overridden with till deposited above it. In test pit TP-7, located along the south property line, this fine .sandy silt deposit was encountered directly below the topsoil, and the ablation till was absent. Ablation till was also absent in TP-6, located along the east property line. The elevation of TP-6 is the lowest of the test pits excavated at the site and likely exposes the oldest/lowest sediment observed at the site. Interbedded, very stiff to hard silt and dense to very dense sand was encountered below the topsoil at this location, indicative of a slightly more energetic deposition than the presumably overlying glaciolacustrine/fluvial silt deposit observed in the test pits higher up on the site. Test pit TP-10, in thc northwest comer of the site, encountered medium dense to dense, slightly gravelly, slightly sandy silt immediately below the top soil and extending to a depth of 3 feet below the ground surface. Below 3 feet, the sediment becomes very dense with somewhat more silt and only a trace of gravel. While the origin of the sediment below the topsoil is unclear, it is apparent that it has been glacially overridden with some weathering occurring within 3 feet of the ground surface. 1 Perched groundwater was observed in all of the test pits. The groundwater was typically encountered at the base of the topsoil (1 to 2 1/2 feet below the ground surface). Where the ablation till is present (test pits TP-1, TP-2, TP-3, TP4, and TP-5), thc perched water extends through the till and perches on the underlying, very dense or hard, unweathered, glacially overridden soil at depths of 3 to 5 feet below the ground surface. In test pits TP-7, TP-8, TP-9, and TP-10 where the ablation till is absent, the perched groundwater does not extend significantly below the base of the topsoil. In test pits TP-5 and TP-6, slight to moderate seepage was observed in some of the coarser portions of the glacially overridden deposits to a depth of 7 feet in TP-5 and throughout the sandy sediment in TP-6. W-7276-01 Mr. Harold Moe Feb~ 29, 1996 Page 6 CONCLUSIONS AND RECOMMENDATIONS Slope Stability and Project Impact Based on the subsurface conditions observed at the site and our experience with similar soils in the Puget Sound area, it is our opinion that the existing slopes are relatively stable, and provided that the recommendations contained in this report are implemented, the impact of the proposed subdivision on the stability of the site and adjacent slopes will be small. Please note that there is some risk of future instability present on all hillsides which the owner must be prepared to accept. Such instability could occur because of future water breaks/leaks, uncontrolled drainage, unwise development in adjacent areas, or other actions or events on a slope that may cause sliding. Excavations and Site Grading It is our opinion that permanent excavations into the sediment below the topsoil across the site will be stable at slopes of 2 Horizontal to 1 Vertical (2H: IV). Permanent slopes cut steeper than 2H: 1V in these soils should be protected with rockeries, and structures located above these cuts should be located so that their foundations are behind an imaginary 1 1/2H: 1V line drawn from the base of the rockery, back toward the structure. We recommend that rockeries be no taller than 8 feet. Figure 13 provides additional detail and recommendations for rockery construction. Fill slopes should be sloped 2H: 1V or flatter. During construction, we recommend that the stability of the excavation slopes be made the responsibility of the Contractor, as he/she will be the one most familiar with conditions exposed in the excavation and will be at the site on a full-time basis. The Contractor should be responsible for following all current and applicable safety regulations regarding excavations, shoring, etc. The Contractor should also be responsible for the control of all ground or surface water wherever encountered on the project. 1 W-7276-01 Mr. Harold Moe February 29, 1996 Page 7 Jeffornon County, I~1=1 TILLI~IN EN~XNEERIN6 8XSC 42.88 All fill and/or backfill beneath pavements, slabs-on-grade, and other areas where settlements are to be minimized, should be structural fill compacted to a dense, unyielding state, and to at least 95 percent of its Modified Proctor maximum dry density (American Society for Testing and Materials (ASTM): D 1557-91, Method C or D). In areas where moderate settlements can be accepted, such as in non-structural landscape areas, the compaction requirement could be reduced to a dense, unyielding condition and to at least 92 percent of the Modified Proctor maximum dry density. We recommend that the thickness of fill/backfill layers before compaction not exce~ 8 inches for heavy compaction equipment or 4 inches for hand-operated mechanical compactors. The non-organic portion of the on-site soils can be used for fill/backfill if suitably compacted as previously recommended. However, because of the relatively high silt content and natural water content, most of the site soils are moisture sensitive, making them difficult to work with and to compact when wet. The natural moisture content of these soils is often sufficiently high to require some drying/aeration before compacting. If earthwork is planned during the rainy season or in wet conditions, it will likely be necessary to use imported, clean, granular fill rather than the on-site soils. If imported soil is needed for fill/backfill, it should consist of clean, well-graded sand and gravel. It should contain not more than 5 percent fines (soil passing the No. 200 sieve, based on wet sieving the minus-3/4-inch fraction). The fines should be non-plastic. It should have a maximum particle size of 3 inches, should be free of organic matter, and have a moisture content at or slightly below its optimum for compaction. Pavement Recommendations In order to provide frost protection for pavements, we recommend that a total of at least 12 inches of pavement, base course, and/or granular subbase be provided between the native site subgrade and the top of the pavement. Four inches of crushed rock should be placed immediately beneath the asphalt. The remainder of the base course and granular subbase should consist of clean pit-run sand and gravel, well-graded crushed rock, or a blend of W-7276-01 Mr. Harold Moe February 29, 1996 Page 8 I IIIlll IIII lllllll ir Illll Im IIIll II IIIiil JII rill P&~: 1~ of 35 ~81~912~01 ~2:08P Jif ration Cowry, I~1 TILLHt:IN ENGI'NEERZNG PIZ$C 42.88 commercial rock products, and contain not more than 3 percent material finer than 0.02 mm. Normally, soil containing no more than 5 percent fines will meet this criteria. Base and subbase should be thoroughly compacted to achieve a dense and unyielding surface, to at least 98 percent of its Modified Proctor maximum density. Pavement subgrades should consist of medium dense to very dense or very stiff to hard native soil or compacted structural fill. All loose, soft, or disturbed soil and all soil containing organics should be removed from beneath ~ to be paved. In general, this will require a 1 to 2 1/2 feet of stripping depth. We recommend that prepared pavement subgrades be proof-rolled with a loaded dump track or scraper prior to placement of base and subbase materials. Soft or spongy materials identified during the proof-rolling should be removed and replaced with cleaner and/or drier materials. We recommend that ditches be constructed on the uphill sides of all roads that cut across the slope. The bottom of the ditch should be 3 feet below the top of the pavement. Water collected in the ditches should be conveyed to the storm water detention facility. Wet Weather Earthwork Wet weather generally begins about mid-October and continues through about May, although rainy periods may occur at any time of the year. Therefore, it would be most advisable to schedule earthwork during the normal dry weather months of June through mid-October. Earthwork performed during the wet weather months will generally prove more costly. 1 The soils at the site generally contain sufficient silt and plastic fines to produce a cohesive, unstable mixture when wet. Such soils are highly susceptible to changes in water content, and they become muddy, unstable, and difficult or impossible to proof-roll and compact if their moisture content significantly exceeds the optimum. The condition of exposed till and underlying silt will soften rapidly when exposed to moisture and construction activity. W-7276-01 Mr. Harold Moe Feb~ 29, 1996 Page 9 Jeffernon County, I~1=1 TILLI"II:IN ENGINE~IN~ HISC 42.08 It should also be noted that particularly during the wet weather months, groundwater levels would be highest within the relatively loose top soil and ablation till, which overlie the glacial glacially overridden soils. Such groundwater could seep into site excavations and would need to be intercepted by drainage ditches, trench drains, or otherwise removed. It is our experience that the presence of standing water upon an exposed till or the other, underlying silt deposit observed at the site, along with construction activity, will result in disturbance and softening of the exposed subgrade. This could lead to deeper excavations than possibly anticipated. The following recommendations are applicable if earthwork is to be accomplished in wet weather or in wet conditions: b. C. d. e. Earthwork should be accomplished in small sections to minimize exposure to wet weather. If there is to be traffic over the exposed subgrade, the subgrade should be protected with a compacted layer (generally 8 inches or more) of clean sand and gravel or crashed rock. The size or type of equipment may have to be limited to prevent soil disturbance. Fill material should consist of clean, granular soil, of which not more than 5 percent by dry weight passes the No. 200 mesh sieve, based on wet sieving the fraction passing the 3/4-inch sieve. The fines should be non-plastic. Such soil would need to be imported to the site. The ground surface in the construction area should be' sloped and sealed with a smooth<lmm roller to promote the rapid runoff of precipitation, to prevent surface water from flowing into excavations, and to prevent ponding of water. No soil should be left uncompacted and exposed to moisture. A smooth<imm vibratory roller, or equivalent, should be used to seal the ground surface. Soils that become too wet for compaction should be removed and replaced with clean granular soil. Excavation and placement of structural fill material should be observed on a full- time basis by a geotechnical engineer, or his/her representative, experienced in wet- weather earthwork, to determine that all unsuitable materials are removed and suitable compaction and site drainage is achieved. W-7276-01 Mr. Harold Moe February 29, 1996 Page 10 llllllllllllllll llll llllllllllllllllillll Jefferlon County, biff TILLII=IN ENGINEERING fllSC 42.88 f, Covering of work areas, soil stockpiles, or slopes with plastic, sloping, ditching, installing sumps, dewatering, and other measures should be employed, as neces~, to permit proper completion of the work. Bales of straw and/or geotextile silt fences should be aptly located to control soil movement and erosion. Drainage and Foundation Backfill For buildings that will eventually be constructed on the site, we recommend that footing drains be installed along the outside perimeter of the structures and on the up slope side of continuous interior footings. Footing subdrains should consist of slotted, 4-inch-diameter, plastic pipe bedded in washed 3/8-inch pea gravel. Typical installation details for these drains is shown in Figure 14. Figure 14 also contains subdrainage and foundation wall backfill recommendations. On-site soils will not be suitable for use as drainage sand and gravel. Note that the perimeter subdrain invert should be located at least 18 inches below the lowest adjacent grade. A drainage geotextile should not be used around the subdrain pipe. Roof drains should not be connected to the footing subdrains. The discharge from footing drains and roof drains should be routed by means of a tighfline to a suitable discharge point (i.e., road ditches, storm sewers, etc., that connect to the erdsting storm water detention pond at the northeast comer of the site). All hard surfaces around the structures should be sloped to catch basins and the collected water disposed of as previously outlined. All outside grades should be graded to slope away from the structures. Foundations 1 In our opinion, spread footings bearing in the medium dense to dense, ablation till and other dense or very stiff, glacially overridden bearing soils could be designed for 3,000 pounds per square foot (psi) maximum allowable bearing pressure. Stripping depths to reach these soils is about 1 to 2 1/2 feet, based on the subsurface conditions observed in the test pits. Footings bearing within structural fill placed over the bearing soils could be designed for allowable bearing pressures up to 3,000 psf. Continuous footings should have a minimum width of 18 inches, and column footings should have a minimum width of 24 inches. W-7276-01 Mr. Harold Moe February 29, 1996 Page 11 lU/lllmlul[m/ll][]"'"""' P~Oo: 13 of 36 ~1~12~1 O2:0OP Jefflrlon Courity, blA TILLPIRN ENOZNEERTNG PIZ$C 42.Ge Minimum footing widths may govern footing design. Footings should bear at least 24 inches below the lowest adjacent grade. The bearing pressures given above may be increased by one-third for seismic loading conditions. If footings are supported by structural fill, this fill should extend beyond the outer edges of footings a minimum distance equal to the fill thickness below the footing; If adjacent individual footings are located at different elevations, it is recommended that the horizontal distance between them be at least 1.5 times the elevation difference between their bases. Where adjoining continuous footings are at different elevations, the upper footing should be stepped down to the lower footing. Foundation subgrades should be evaluated during construction to verify the presence of competent bearing soil, and to determine that all soft or loosened, disturbed soils and all existing topsoil have been removed. This evaluation should be made by a geotechnical engineer or his/her representative. Assuming compliance with the recommendations in this report, we expect settlement of con- venfional spread footings to be no more than about 1/2-inch, with differential settlements (between adjacent footings or over a 20-foot span of continuous footing) of approximately l/4-inch, or less. Settlements would occur almost simultaneously with load application. Floor Slab Support Floors for furore structures could be constructed as slabs-on-grade bearing on dense to very dense or very stiff to hard native soil or on structural fill placed on these soils and compacted to 95 percent of its modified Proctor maximum density. Care should be taken to compact any localized backfills, such as footing or utility excavations, to the same degree as that specified for structural fill. We recommend that a capillary break be placed beneath the slab. A 4-inch-thick (minimum) layer of washed pea gravel placed atop floor subgrades, as shown in Figure 14, is one method to provide this break. The capillary break should be hydraulically connected to perimeter footing drains down slope. As illustrated in Figure 14, the use of 2-inch- W-7276-01 Mr. Harold Moe February 29, 1996 Page 13 and fill slopes with grasses will also provide long-term erosion control. grass seed mixture for this area includes: An appropriate Red fescue 40% Colonial bentgrass 10 % Perennial ryegrass 25 % Orchard grass 1:5 % White dutch clover 10% Other seed mixtures may also be appropriate. For slopes of 2H: 1V or greater, hydro- seeding is recommended. An appropriate hydroseed mixture on a per acre basis may include: 100 pounds of gross seed 2,000 pounds of wood fiber mulch 250 pounds of 12-24-24 fertilizer 40 gallons of liquid soil bonding agent If the application is done in summer add: 80 pounds moisture retention agent 500 pounds extra of wood fiber mulch (2,500 pound total) Summer applications must be irrigated. Seeding should be accomplished by September 15 to provide any erosional control for the following rainy, season In our opinion, erosion at the site during construction can be minimized by implementing the recommendations in the Wet Weather Ea~work section, and can be controlled through the judicious use of fabric silt curtains and/or straw bales. Temporary erosion control should be the responsibility of the Contractor since he is also responsible for the excavation, the ditching, the sumps, etc. W-7276-01 '1 Mr. Harold Moe February 29, 1996 Page 14 Page: 18 o1' 36 Jeffe~eon County, I. IR T~LLIq~ EI~ZNEERZI~ fIZ$C 42.ee Construction Monitoring and Plans Review We recommend that we be retained to review portions of plans and specifications pertaining to earthwork and foundations to determine whether they are consistent with our recommendations. We also recommend that we be retained to monitor earthwork, including structural fill placement and compaction and subgrade preparation. Additional Consideration Test pit excavations were loosely bacldilled with the excavated material. If such a test pit is located in a proposed building or pavement area, the loose material should be removed and replaced with appropriately compacted structural fill. Alternatively, the excavation could be structurally bridged. LIMITATIONS The conclusions and recommendations presented in this report are based on site conditions as they presently exist and assume that the explorations are representative of the subsurface conditions throughout the site; i.e., the subsurface conditions are not significantly different than those encountered in the test pits and site reconnaissances. If, during construction, subsurface conditions different from those encountered in the explorations are observed or appear to be present, we should be advised at once so that we can review those conditions and reconsider our recommendations where necessary. If there is a substantial lapse of time between submission of our report and the start of work at the site, we recommend that this report be reviewed to determine the applicability of the conclusions and recommendations, considering the changed conditions and/or elapsed time. W-7276-01 Mr. Harold Moe February 29, 1996 Page 15 Page; 17 of 36 e818912~81 e2:eep Jeffereo~ County, I~ T]:LLHI~I ENGINEERING HI$C 42.~ This report was prepared for the usc of the Owner and/or Engineer in the design of the development and structures. With respect to construction, it should be made available for information on factual data only and not as a warranty of subsurface conditions, such as those interpreted from the test pit logs, site reconnaissances, and discussion of subsurface conditions included in this report. Unanticipated conditions are commonly encountered and cannot be fully determined merely by taking soil samples or making explorations. Such unexpected conditions frequently require that additional expenditures be made to achieve a properly constructed project. Some contingency fund is recommended to accommodate such potential extra costs. Please note that the scope of our services did not include any investigation for the presence or absence of wetlands or environmental assessment for the presence or absence of hazardous or toxic material in the soil, surface water, groundwater, or air on or below or around this site. We are able to provide these services and would be happy to discuss these with you as the need arises. Shannon & Wilson has prepared the attached Appendix, "Important Information About Your Geotechnical Report," to assist you and others in understanding the use and limitations of our report. W-7276-01 Mr. Harold Moe Feb~ 29, 1996 Page 16 tlilimIB/Nigi'8 446544 P&l~: 1'8 of 35 Jefferaofl County, ~ TILLRi:IN SN~INLrL~ZI~ RISC 42.88 If you have any questions regarding the observations, conclusions, or recommendations contained in this report, please call us. We appreciate the opportunity to be of service. Sincerely, SHANNON & WR3ON, INC. W'flliam J. Perkins, R.P.G. Geologic Engineer Gregory R. Fischer, P.E. Senior Principal Engineer WYP:GRF:WPG:BCD/wjp Enclosures: Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 1 - Vicinity Map 2 - Site and Exploration Plan 3 - Log of Test Pit TP-1 4 - Log of Test Pit TP-2 5 - Log of Test Pit TP-3 6 - Log of Test Pit TP4 7 - Log of Test Pit TP-5 8 - Log of Test Pit TP-6 9 - Log of Test Pit TP-7 10- Log of Test Pit TP-8 11 - Log of Test Pit TP-9 12 - Log of Test Pit TP- 10 13 - Typical Roekery Detail Figure 14 - Subdrainage & Backfilling Appendix - Important Information About Your Geotechnical Report cc: Kent Anderson, Sound Planning W7276-01.LTR/W7276-1kd/Ikd W-7276-01 P&ge: 19 of 35 00/09/2091 92: 08p Jefferson County, I~1 TILLtIFIN ENG;NEERXN$ II{$C 42.00 :1 -'; ,28 PROJECT · · ' LOCATION ,, ! ~ / ".,'"..." ~,! !."v~' ~ I: ",\'.. I ~ i ~, ~ '. '.~ '- / ",. ,.' ... · ! · :o ,...~ ~.' . ,. ; "'\ , o /~\ · ,..~., ,.~-' . · Poi n._.t/ Ma ts Ma t s Bay 0 1/4 1/2 1 Scale in Miles NOTE Base map taken from USGS 1:24,000 topographic map of Port Ludlow, WA quadrangle, dated 1953, photorevised 1973. Mats View Meadow Subdivision Port Ludlow, Washington VICINITY MAP February 1996 W-7276-01 I SHANNON & WlL~ON, INC. I FIG. 1 I ~1~12~01 e2:eeP Jofforeon County, i~i T]LI. FIRN EN~]NEER]N6 PIZGC 42.eo 446544 ~: : : : :~ ..... Jeffere~ C~ty, HR TILL~ ~Z~Z~ ~ZGC 42.00 ' ~ ' ':_..:..:__2...2...2..L.~..:.: ...... 2_.:_:._:_: ...... }...:.&_ :.._:_:_:_:_:_L.:_:...L..:..L.i...i_:_:._.L.: .......... 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' ® ._o ~o .--® .... : .................................. ~ · ~ Im '...L.L..'_.i.....'_.L.'. :.....x..LL2-L.L.L.L.L..L..L.:...L.:...L.L.L.L.L.L.L..L..2...:...L.L.L..L.L.L.L..L.L..L..L..:...L..L.L..L.L:....L.L.L..L..L..L..:~L. ~ ~~ ....... /~...,...-..-:-:....: .... ~ ......... ~ ......... ~ ......... ~ ......... · 1.4 'q~dec] o SeldLu~$ ~ue~uoo ,9'~ l~ e§~dees 1L1§!15 punoJ9 ~' .c: "'~ o ~ 'o ~i~- ___,'"' .o~: '" ~ ~'-~ °° '" ~ (/) ,-, ~ ~ ~ .7. ,-- ,,, z~j ~ .~ .... o_o o~,~ ~ FIG. 12 Pavement or 10" to 15" Impervious Soil Backfill Meeting Gradation Requirements for Structural Fill (See Note 2) Excavation Slope Contractor's Responsibility 6" Min. Cover of Pea Gravel (6" Min. on Sides of Pipe) Sloped to Drain Away From Structure 18" Min. Subdrain Pipe 2" to 4" MATERIALS Drainage Sand & Gravel with the Following Specifications: % Passing Sieve Size by Weight 1-1/2" 100 3/4" 9O to 100 1/4" 75 to 100 No. 8 65 to 92 No. 30 20 to 65 No. 50 5 to 20 No. 100 0 to 2 (by wet sieving) (non-plastic) SUBDRAIN PIPE 4" minimum diameter perforated or slotted pipe; tight joints; sloped to drain (6"/100' min. slope); provide clean-outs. Perforated pipe holes (3/16" to 1/4" dia.) to be in lower half of the pipe with lower quarter segment unperforated for water flow. Slotted pipe to have 1/8" maximum width slots. Not to Scale Wall Drainage Sand & Gravel or Washed Pea Gravel Damp Proofing Weep Holes (See Note 1) Floor Slab Washed Pea Gravel Vapor Barrier 18" Min. 4" Min. . . NOTES Drainage gravel beneath floor slab should be hydraulically connected to subdrain pipe. Use of 2" diameter weep holes as shown is one applicable method. Imported structural fill should consist of well-graded granular soil with not more than 5% fines (by weight based on minus 3/4" portion) passing No. 200 sieve (by wet sieving) with no plastic fines. Backfill within 18" of wall should be compacted with hand-operated equipment. Heavy equipment should not be used for backfill, as such equipment operated near the wall could increase lateral earth pressures and possibly damage the wall. All backfill should be placed in layers not exceeding 4" loose thickness and densely compacted. Beneath paved or sidewalk areas, compact to at least 95% modified Proctor maximum density (ASTM: D1557-70, Method C). Otherwise compact to 92% minimum. Mats View Meadow Subdivision Port Ludlow, Washington SUBDRAINAGE & BACKFILLING February 1996 W-7276-01 SHANNON & WILSON, INC. I FIG. 14 I 446544 IMPORTANT INFO~~ON ABOUT YOUR GF_~TECIINICAL REIN~RT W-7276-01 SHANNON & WILSON, INC. Geotechnical and Environmental Consultants ~v - t .'", ~ o-u ,L Attachment to Report Dated: February 29, 1996 Page 1 of 2 To: Mr. Harold Moe Port Ludlow, Washington Important Information About Your Geotechnical/Environmental Report CONSULTING SERVICES ARE PERFORMED FOR SPECIlqC PURPOSES AND FOR SPECIFIC CLIENTS. Consultants prepare reports to meet the specific nee.& of specific individuals A report prepared for a civil engineer may not be adequate for a construction contractor or even another civil engineer. Unless indicated otherwise, your consultant prepared your report expressly for you and expressly for the purposes you indicated. No one other than you should apply this report for its intended purpose without first conferring with the consultant. No party should apply this report for any purpose other than that originally contemplated without first conferring with the consultant. THE CONSULTANT'S REPORT IS BASED ON PROJECT-SPECIFIC FACTORS. A geoteclmical/cnvironmcntal report is based on a subsurface exploration plan design'ed to consider a unique set of project- specific factors. Depending on the project, these may include: the general nature of the structure and property involved; its size and configuration; its historical usc and practice; thc location of the structure .on the site and its orientation; other improvements such as access roads, parking lots, and underground utilities; and the additional risk created by scope-of-service limitations imposed by the client. To help avoid costly problems, ask the consultant to evaluate how any factors that change subsequent to the date of the report may affect the recommendations. Unless your consultant indicates otherwise, your report should not be used: (1) when the nature of the proposed project is changed (for example, if an office building will be erected instead of a parking garage, or if a reWngerated warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site); (2) when the size, elevation, or configuration of the proposed project is altered; (3) when the location or orienta- tion of the proposed project is modified; (4) when there is a change of ownership; or (5) for application to an adjacent site, Consultants cannot accept responsibility for problems that may occur if they are not consulted after factors which were considered in the development of the report have changed. SUBSURFACE CONDITIONS CAN CHANGE. Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a report whose adequacy may have been affected by time. Ask the consultant to advise if additional tests are desirable before construction starts; for example, groundwater conditions commonly vary seasonally. Construction operations at or adjacent to the site and natural events such as floods, earthquakes, or groundwater fluctuations may also affect subsurface conditions and, thus, the continuing adequacy of a geotechnical/environmental report. The consultant should be kept apprised of any such events, and should be consulted to determine if additional tests are necessary. MOST RECOI~fMENDATIONS ARE PROFESSIONAL JUDGMENIS. Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are taken. The data were extrapolated by your consultant, who then applied judgment to render an opinion about overall subsurface condition~ The actual interface between materials may be far more gradual or abrupt than your report indicates Actual conditions in areas not sampled may differ from those predicted in your report. While nothing can be done to prevent such simation~ you and your consultant can work together to help reduce their impacts. Retaining your consultant to observe subsurface construction opera- tions can be particularly beneficial in this respect. I IIlll IIII illll Ill Illin Illl Illllll III Illll fill Illl Jmffmr.on County, WR TILLIqRN ENGINEERING IqlSC 42.00 Pi~ 2 of 2 [ A REPORT'S CONCLUSIONS ARE PREI.IMINARY. The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions revealed through selective exploratory sampling are indicatixe of actual conditions throughout a site. Actual subsurface conditions can be discerned only during earthwork; therefore, you should retain your consultant to observe actual conditions and to provide conclusions, Only the consultant who prepared the report is fully familiar with the background information needed to determine whether or not the report's recommendations based on those conclusions are valid and whether or not the contractor is abiding by applicable recommendations. The consultant who developed your report cannot assume responsibility or liability for the adequacy of the report's recommendations if another party is retained to observe construction. THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION. Costly problems can occur when other design professionals develop their plans based on misinterpretation of a geotechnical/envir- onmental report. To help avoid these problems, the consultant should be retained to work with other project design professionals to explain relevant geotechnical, geological, hydrogeological, and environmental findings, and to review the adequacy of their plans and specifications relatixe to these issues. BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE REPORT. Final boring logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test results, and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are customarily included in geotechnical/environmental reports. These final logs should not, under any circumstances, be redrawn for inclusion in architectural or other design drawings, because drafters may commit errors or omissions in the transfer process. To reduce the likelihood of boring log or monitoring well misinterpretation, contractors should be given ready access to the complete geotectmical engineering/environmental report prepared or authorized for their use. If access is provided only to the report prepared for you, you should advise contractors of the report's limitationa assuming that a contractor was not one of the specific persons for whom the report was prepared, and that developing construction cost estimates was not one of the specific purposes for which it was prepared. While a contractor may gain important knowledge from a report prepared for another party, the contractor should discuss the report with your consultant and perform the additional or alternatixe work believed necessary to obtain the data specifically appropriate for construction cost estimating purposes. Some clients hold the mistaken impression that simply disclaiming responsibility for the accuracy of subsurface information always insulates them from attendant liability Providing the best available information to contractors helps prevent costly construction problems and the adversarial attitudes that aggravate them to a disproportionate scale. READ RESPONSIBIlATY CLAUSES CLOSELY. Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design diseipline.~ This situation has resulted in wholly unwarranted claims being lodged against consultant& To help prevent this problem, consultants have developed a number of clauses for use in their contracts, reports and other documents. These responsibility clauses are not exculpatory clauses designed to transfer the consultant's liabilities to other parties; rather, they are definitive clauses that identify where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual responsibilities and take appropriate action. Some of these definitixe clauses are likely to appear in your report, and you are encouraged to read them closely. Your consultant will be pleased to give full and frank answers to your questions. The preceding paragraphs are based on information provided by the ASFE/Association of Engineering Firms Practicing in the Geosciences, Silver Spring, Maryland