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HomeMy WebLinkAbout977100414 Geotech Assessment Addendum SEATTLE NANFORD TACOMA ~ ~ FAIRBANKS OEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS AlvcNaRA~E SA{NT tOUIS BOSTON . May lb, 1996 Mr. Frank vane 405 Willow Street Port Townsend, Washington 98368 RE: GEO ~ CAL REPt3RT, LOT 18 COMBS PLACE, PART ~yVNSF~vD, WASHINGTON Dear Mr. Vane: This letter summarizes our observations, conclusions, and recommendations for the proposed residential development on the above referenced lot near Port Townsend, washin ton, In a letter to Mr. vane dated April 9, 1996,1efferson County requested that a g . geotechnical study and recommendations be developed regarding the stability of the slopes and ra sed devela ment on this lot. Therefore, the purpase of our work was to evaluate .P 1~ p the stability of the site and provide design and construction recommendations far the lanned residence to reduce the risk of slope instability. Our work u~as conducted in P accordance with our proposal dated April 16, 1996. SITE DESCRIPTION The lot is located on the east side of Discovery Bay, approximately 3 miles southwest of Port Townsend on the north end of Combs Place Figure 1}. The lot is situated on the u r rtion of a 20- to 40-degree slope that rises from sea level at Discovery Bay an the P~ ~ west, up to an elevation of approximately 500 feet to the east. The elevation of the. property, relative to sea level, is between 300 and 380 feet, The lot sha dimensions, existing and proposed topography, and the locations of the ~~ planned house and carport at the site are shown on Figure 2, The elevations indicated on the contours on this figure are based on an arbitrary project datum and are not relative to 400 NORTH 34TH STREET • SUITE 100 P.o. Box 3oo3a3 W 7194-02 SEATTLE, WASHINGTON 98103 206.632.8020 FAX 205.6336177 TDD: 1.800.8336358 Mr. Frank Vane May 16, 1996 Page 2 SHANNON F~WILSON, lNC. sea level, Naturally occurring slopes across the site generally are between 2 horizontal to 1 vertical ~2H:1V} and 1.7H:1V. An approximately 15 feet deep depression was excavated in the central rtion of the site at the location of the planned residence, and a trench was excavated across the western portion of the property far placement of the existing storm sewer see Figure 2}. The excavated slopes are typically no steeper than about ~.7H:~ 1V. Vegetation across the site typically .,consists of Madrona pup to 2, 5 feet in diameter} and fir trees (up to 1 foot in diameter live trees, 3 feet diameter stumps} with an undergrowth that includes salal, Gregon Grape, and grass. This assemblage of plants is indicative of relatively dry, well-drained, near-surface soil conditions. In addition, the growth positions of some fir trees are indicative of ~~soil~ creep. Soil creep occurs on nearly all slopes and is the im rce tiblslow, downslope movement of sails under the effects of gravity. Pe p y The proposed residence shown on Figure 2 has .a :wedge-shaped footprint, with a maximum len th east-west} of approximately 32-feet and a -maximum width north-south} of about 26 g ~ feet. We understand that the house will be a three-story structure, including a basement that ste s u to `the east and daylights out to the west. We understand from Ms. Jean P P Anderson, our architect, that the hoar elevations have not yet been determined and will be Y selected, in part, on the anticipated foundation depths. A carport is also planned at the east end of the property at the end of Combs Place. Final grades shown on Figure 2 indicate that a level yard area at elevation 194 feet is lanned for the back {east} side of the- house. A rockery, up to 5 feet high, will be P constructed on the past and north sides of the yard to step up to the existing ground surface beyond. The ground surface along the south side of the house will be graded to about 2H:1V into the existing topography. The slope along the north side of the house will alsa be graded at about ~H:1V parallel to the slope, but will be at an elevation below the existing ground surface farther north to allow for construction of a small bridge to the house main entrance. W 7194-d2 Mr, Frank vane May 16, 1996 Page 3 ~EOLOOIC .AND SUBSURFACE CONDITIONS Geologic maps of they area -indicate: that the hillside from top to bottom) is capped by vashon Lodgement ..Till, underpin vashon Advance Outwash, in turn underlain by undifferentiated stratified pre-vashon sediment. ~ The oldest sediments at the base of the hill are the pre-vashon sediments. These may range from clay to sand and gravel and are mapped about haifvvay up the .hillside .where they -are overlain by vashon Advance Outwash. The outwash was .deposited by r~eltwaters in front of the vashon Ice sheet as it advanced from the north toward the region during the Late Pleistocene. Outwash deposits are typically sands with variable amounts of gravel and silt. The advance outwash is mapped from the midpoint of the slope. ~up ~t~o .near the .crest of the hill. As the glacial ice sheet continued o advance and cover the aria, it deposited vashon Lodgement T"iiI directly beneath the ice. Till is typically anon-sorted mixture of clay, silt, sand, and gravel with scattered cobbles. and boulders. Till deposits are mapped at the top of the hill., The ice sheet that covered this area is estimated ao have -.been up to 4,0(~ feet thick, and because of the rent wei ht of the .ice the underl in sediments ~i.e., vashon Lodgement Till, g g a Yg Advance Outwash, and. pre-vashon.. sediment}-were overconsolidated to a very dense ar hard state. , .. Since the retreat of the ice sheet approximately 13, 0~0 years ago, the upper few feet of these very denselhard soils have weathered and loosened to form a thin rind of colluvium and to soil, colluvium is weathered soil that has reached its present location due to the p farces of water. and ravit . The topsoil and colluvium are not as dense nor as strong as g Y the underlying deposits from which they were weathered. Consequently, the topsoil and colluvium on the hillsides have a tendency to-creep or slide down the slope. Geologic hazard maps indicate -that sliding has occurred on most of this hillside at some time. A geologic reconnaissance. of the site confirms -the presence of very dense vashon Advance Outwash beneath the site, overlain by colluvium and topsoil. The reconnaissance included logging the subsurface soils exposed in the excavations across the site and in one hand-dug W 7194-OZ ~~~~I ~l ~7i~V~~ ~~~. Mr. Frank Vane May lb, 199b Page 4 test pit. The following table presents a brief description of the typical subsurface profile observed in the excavations and test pit. .:.:: .:.:::::::::. ......:.::.:::.......... . ............:::............ .. ... .:. .... :: :.:. ~eet .~ e .~: ~. .~:. . ............................................................ ~bae~::~... :~ ..............................................................5. er.. ~. .............................................................. o to 1 Loose to medium dense, silty, gravelly SAND with scattered cobbles and.. boulders; rrioist to dry {topsoillcolluvium~ 1 to 2112 Medium dense to dense, trace to slightly silty, gravelly SAND with scattered cobbles and boulders; moist to dry (weathered Vashon Advance Gutwash} 2112 to +5 Ve dense, sandy GRAVELIgravelly SAND with scattered cobbles and rY boulders; moist to dry (unweathered Vashon Advance Gutwash} ~vo areas of likel fill were observed and; are noted on Figure 2. Fill in the east end of the y lot ma be up to 3 feet thick and is .part of a cutlfill pad at the end of bombs Place. Fill is Y also likel resent near the center of the site. beneath the west .side of the .proposed yP residence. Based on the existing contour data, this fill may be 4 to b feet thick. Groundwater was not observed in the test pit or any of the excavations across the site. S rin s see s, or vegetation indicated of near surface groundwater conditions were not P g~ P observed on the site. CONCLUSIONS AND RECD ATIONS Slope Stability Based on our observations and experience with similar sites, it is our opinion that the risk of dee -seated slope instability, ~ or sliding of the very dense soils beneath the site, is P relatively low. However, the near-surface topsoillcolluvium and weathered advance outwash are susceptible to sliding. As previously indicated in this letter, the surficial soils area arentl creeping down the slob. The sliding indicated on geologic hazard maps of PP y the area likel occurs primarily in these relatively loose surficial soils. Sliding of these Y VLF 7194-02 Mr. Frank Vane May 16, 199 Page 5 SHABVf~ON ~WILS~ON, I{VC. soils may result from over steepening of the hillside ~e.g., erosion at the base of the hill due to wave action, excavation cuts into the hillside}, overloading the surfieial soils ~e.g., placing fill or foundations on the loose soil}, and saturation of the loose soils that increase the weight and :reduces the strength of the soil (e. g. , heavy rains, broken water, or sewer lines} . It is our o inion that the proposed residency may be built on the site as indicated on P Figure 2 with minimal impact on the stability of the slope, if the recommendations contained in this letter are implemented. In addition, it is our opinion that if the foundations for the house are located within the very dense outwash beneath the site in accordance with our fallowing recommendations, the risk presented to the structure by slidin and tree in of the near-surface soils can be greatly reduced. Please note that there g Pg is some risk of future instability present on ~ all hillsides, which the owner must be prepared to acce t. Such instabilit could occur because of .future water line breakslleaks, P Y uncontrolled drainage, unwise development in adjacent areas, or other actions or events on a slope that may cause sliding. Engineering Recommendations foundations we recommend that the residence and car port be founded on spread footings bearing at least 2 feet below the top of the very dense outwash. Based on the typical subsurface conditions observed at the site, this,. will require that the base of the footings be _ located approximately 4112 feet below the existing, naturally occurring ground surface. Based on this estimated excavation depth, footing elevations along the north side of the residence may be between elevations 17?. 5 feet west} and 184.5 feet feast} . Along the east side of the residence, footing depths may range between elevations 183.5 feet north} and 189 feet south . Footin elevations along the south side may be between elevations 1?0.5 ~ } g feet west} and 189 feet (east}, W ? 194-02 Mr. Frank Vane May lb, 1996 Page 6 SHANNON ~WiLSON, lNG. The footing depth on the west side of the residence will likely be greater than the antici ated 4112 feet for the remainder of the structure. The west footing must extend p throe h the fill believed to be resent and are additional 2 feet below the top of the very g p dense outwash. The existing ground surface in this area is approximately at elevation 175 If 6 feet of fill is resent over 2112 feet of preexisting topsoillcolluvium and feet. p vance outwash the elevation of the to of the very dense outwash would be at weathered ad p The base of the foatin would be located 2 feet below the very dense outvvash, 166.5 feet. g or at an elevation of 164.5 feet. If onl 4112 feet of filllcolluviumltopsoillweathered y outwash is resent, the base of the footing would be located at an elevation of 168 feet, p allowing for the recommended 2 feet embedment into the very dense soils. At the rt footin , de the in the cut on the east side may be as shallow as 3 feet ~ ~ g p elevation 213 feet} while on the west side,:.. footing depths may be up to 7112 feet elevation 206.5 feet} to penetrate through., fillltopsoillcolluvium/weathered autwash and 2 feet of ve dense advance outwash. To minimize excavation along the west side of the rY car~art, isolated footings may be excavated or drilled. The maximum footing elevations for the structures previously discussed are estimates. Actual footing depths and elevations will depend on the subsurface conditions and elevations found during construction. We, therefore, recommend that an experienced en ineer or geologist observe the foundation excavations and evaluate whether the g .recommended footing embedment of 2 feet .into the very dense soils has been achieved. In addition the contractor should expect .some, variation in the planned versus actual footing j de the and the owner should anticipate some .potential additional expenditures to achieve an . p adequately embedded foundation. Footin s bearin in ve dense advance outwash on this slope may be designed for g g rY an allowable sail bearing capacity of 4,000.. pounds per square foot (psf~. This allowable ca acit ma be increased b one-third under seismic loading conditions. We recommend p y y y that continuous footin s have an 18-inch minimum width; column individual} footings g should have a 24-inch minimum width. These minimum footing widths sometimes govern W 7194-02 Mr. Frank vane May 16, 1996 e ~ footing design. If footings are located at different elevations, we recommend that the horizontal distance between them be at least 1, 5 times the elevation difference. where adj wining continuous ~ footings are at different- elevations, the upper footing should be stepped down to the lower footing. Floor Slab Support Floor slabs for the residence and carport may be constructed as slabs-on-grade bearing on medium dense or more competent native soil or on structural fill placed on medium dense or more competent sail} compacted to at least 95 percent of its modified Proctor maximum density. Slab-on-grade subgrades should be observed by a qualified geologist or engineer to evaluate whether the subgrade is medium dense or denser soil. Care should be taken to compact any localized bacl~ills, such as footing or utility excavations, to the same degree as that. specified for structural fill. Additional recommendations regarding compaction of fill are provided in the "Excavations and Site Grading section of this letter. We recommend that a capillary break be placed beneath the basement floor slab. A 4-inch-thick minimum) layer of washed pea gravel placed over the prepared subgrade, as shown in Figure 3, is recommended to provide this break. The capillary break should be h draulically connected to the perimeter footing drain on the west (downslope} side of the Y house. As illustrated in Figure ~, the use of 2-inch-diameter weep holes is one method for roviding a hydraulic connection. A vapor barrier, consisting of a plastic sheet should be P laced directl over the pea gravel. Additional drainage. recommendations are presented in P Y the "Drainage" section of this letter. Lateral Earth Pressures The lateral earth pressures acting on a wall depend an the amount the wall can yield and the sla of the backfill. Typically, walls that can yield at the top an amount equal to 0.01 times the wall height can be designed for active earth pressures. Walls that yield less V~ 7194-02 ~~~~~ k7~~W~~ ~~d1. Mr. Frank vane May 16, 199 ~e 8 than this amount should be designed far at-rest earth pressures. Active earth pressures may be estimated by using an equivalent fluid weight of 35 pounds per cubic foot (pcf far horizontal bacl~ill; at-rest pressures can be estimated using and equivalent fluid weight of 55 pcf far level ground conditions. Basement walls are generally considered rigid and are designed using at-rest earth pressures. However, the structural engineer can best make this determination based on anticipated defections. To account for sloping backfill behind the wall we recommend that x.75 pcf be added to the active pressure equivalent fluid weight for each degree of upward inclination of the backslope above the wall (this is valid up to 34-degree inclinations; pressures for inclinations greater than 3o degrees will require further calculations}, For at-rest conditions, 1.25 pcf should. be added to the equivalent fluid weight for horizontal backfill for each degree of upward inclination... Lateral forces due to active ar at-rest earth pressures of fill behind the walls will be resisted by passive earth pressure developed in the soils in front of the wall and by friction against the base. In our opinion, passive earth pressures in backfill could be estimated using an allowable equivalent fluid weight of 5~ pcf. We recommend that a coefficient of friction of o.5 be used between cast-in-place concrete and sail. These values assume that the structures. extend at least 24 inches, below the lowest adjacent grade and the backfill around the structure is a compacted granular fill, and no groundwater is present The recommend active, at-rest, and passive pressures assume the walls are drained so that hydrostatic pressures cannot develop. Recommendations for wall drainage and backfilling are presented on Figure 3. Excavations and Site Grading It has been our experience that a slope cut to 2H:1V in the very dense soils at the site will not ravel and will maintain vegetation, Excavations in these soils will ravel if cut steeper than about 2H:1 v. Therefore, eve ~ recommend that permanent slopes cut steeper 7194-02 Mr. Frank Vane May 1 ~, 199b Page 9 SHANNON F~VI/ILSOdV, INC. 2H:1V into the very dense site soils be protected with rockeries. we recommend that rockeries be no taller than 8 feet. Figure 4 provides additional details and recommendations for a typical rockery construction. Fill slopes should be sloped 2H:1V ar flatter. During construction, we recommend that the stability of the excavation slopes be made the responsibility of the contractor, as they 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. All fill andlor 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 9S percent of its Modified Proctor maximum dry density (American Society far Testing and Materials ~ASTM}: D 1557-70, 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 exceed S inches for heavy compaction ui ment or 4 inches for hand-operated mechanical compactors. ~ P The nonorganic portion of the on-site sails topsoil} can be used for filllbacldill if suitably compacted as previously recommended. In general, these site soils are relatively free draining and should be workable under most conditions. In heavy, or continuous rains, they may eventually become sufficiently wet to make them difficult to work and compact. If earthwork is planned during the rainy season or in wet conditions, it may be necessary to use imported, clean, granular fill rather than the an-site soils. Additionally, exposing the site sails to construction activity when wet will substantially increase their erodability. If imported soil is needed for filllbackfill, it should consist of clean, well-graded sand and ravel. It should contain not more than 5 percent fines soil passing the No. 2~4 g W 7194-U2 Mr. Frank Dane May 16,199b ` Page to . sieve, based on wet-sieving the minus 314-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. Drainage We recommend that footing subdrains be installed along the outside perimeter of the residence and on the upslope side of continuous interior footings. Footing subdrains should consist of perforated or slotted, 4-inch-diameter, plastic pipe bedded in washed 31S-inch pea ravel. Typical installation of these drains is shown in Figure 3. Figure 3 also contains g subdrainage and foundation wall backfill recommendations. ether than the topsoil, most of the on-site soils will be suitable for use as drainage sand and gravel. Note that the perimeter subdrain invert should be located at leash 1 S inches below the lowest adjacent grade or at the bottom of the footing, whichever is deeper. We also recommend that subdrains be installed~behind rockeries, as indicated on Figure 4. A drainage geotextile should not be used around the subdrain pipe for either the footing or rockery drains. Roof or rockery drains should not be connected to how into the footing subdrains, nor should roof ar footing drains be connected to how into rockery drains, The discharge from foatin , rocke drains should be routed by means of a tightline to a suitable discharge g rY int. water should not be allowed to discharge onto the surface of a slope or into slope ~' soils near or above the residence. ~ All hard surfaces around the structures should be sloped to catch basins and the collected water disposed in a controlled manner. Perimeter grades around structures should be sloped away from the structures. From the standpoint of minimizing the risk of slope movement, the ideal discharge int for an water collected from the drains would be on the beach at the base of the Po y slo As reviousl indicated in. this letter, the presence of water in the near surface soils ~ P y will increase the risk of slope instability. The storm sewer that crosses the site potentially rovides a discharge paint. However, the storm sewer presently discharges onto the slope p So feet west and downhill of the proposed residence. Water collected in the storm sewer 7194-02 V~i~~ L7~~~tll~ ~~~. Mr. Frank vane May 16, 1996 Page 11 stem and discharged onto the slope increases the risk of slope instability, I}ischarging water from the footing, roof andlor yard drains around the house into the storm sewer would locall decrease the-.risk of slope instability close to the residence but would increase y the risk at the storm sewer discharge point. Ideally, the storm sewer should be routed to the beach and discharge from drains around .the ro be routed into the storm sewer. A second best alternative would be to p l~~Y route the water collected in drains on the property in a smaller, individual tightline to the beach, and not change the discharge point of the existing storm sewer, A third, less ideal alternative would be to route the water from the site into the existing storm sewer and not change the discharge paint of the storm sever with the understanding that there is some decrease of slope instability risk,in .the immediate vicinity of house and an equal increase in risk. at the existing storm sewer discharge point. Construction. Monitoring As previously outlined in this letter, we recommend that the residence and carport footings be located at least 2 feet below the top of the very dense outwash to reduce the risk of movement of these structures. we therefore recommend that we be retained to monitor the footing excavations and evaluate whether the ..recommend 2 feet minimum embedment has been achieved. In addition, we recommend. that we be retained to monitor other earthwork at the site, including, subgrade preparation, structural fill compaction, and drainage installation, LIlVIITATiONS The conclusions and recammendatianspresentwi in this report are based on site conditions as the resently exist and assume that .the explorations are representative of the subsurface Yp conditions throughout the site; i.e., the subsurface conditions are not significantly different than those encountered in the sides of the excavations, test pit and site reconnaissance. If, ? 194-02 L~~~~~ ~~~~~ f~~. Mr. prank Dane May lb, 199b Page 12 . 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 andlor elapsed time. This report was prepared for the use of the owner, Architect, andlor Engineer in the design of the promised 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 excavations, test pit, site reconnaissance, and discussion of subsurface conditions included in this report. Unantici ated conditions are commonly encountered and cannot be fully determined merely P b making explorations. Such unexpected conditions frequently require that additional Y ex nditures be made to achieve a properly constructed project. Some contingency fund is recommended to accommodate such potential .extra casts. The scope of our services did not include any environmental assessment far the presence or absence of hazardous or toxic material in the soil, surface water, groundwater, or air on or below ar 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, ".Important Information About Your Geotechnical Report,» to assist you and others in understanding the use and limitations of our report. W-? 194-02 SH~~V~N ~1L.SON, l~C. Mr. Frank Vane May lb, 199b Page 13 If ou have any questions regarding the observations, conclusions, or recommendations Y contained in this report, please. do not hesitate to call. We appreciate the opportunity to be of service. Sincerely, S~IANNO~I & WILSON, Il~C. .`~~Ep P R~F~S ~ ~'i0 OREGON 2 ~ LIAti4 J. PE S r N 1650 ~ ~(o~ (p ~'FOLOG~S~ Og A y~`g,~ ~ ~~ ~~ ~ ;~ Z ~~ ~/~/r~ z~~ ~ Q ~~~~ ~S~QNAL£~G Ex~ ii/io/~J~o 1 William J. Perkins, R.P.G. Geologic Engineer WJP:WPG~w~p W.P. Grant, P.E. Vice President Enclosures: Figure 1- Vicinity Map Figure Z -Site Plan Figure 3 - Subdrainage & Backfilling Figure 4 -Typical Rockery Retail Important information About Your Geotechnical Report cc: Tom Morello, Tillman Engineering Jean Anderson W71 X4-02. ~.'TRf w1 1941kd~lkd W-7194-02 1 ~ '~ ~~ 7 /~ ~ ~ ~ •f , I ~ ~~ ~ a N . . ~ I N ~ ~ ~ ~ h ~~ • 11 ~ ~/ • 1 _[s • It (1 • Q' ,~f' ff • ^ • ~ ~ 1, , I ~ ~ ff H u ~{ U N ~) q ~ l ~ ~ 4 11 %! , ~ !i 1~ ~ ,~ ~ L ~ ~ !I~ Il . -- -=,, !:; -= 1f 31 ~ ~ ~,~^ s rr ~- ~ ~ ' ~ ~ v~ 1f `-1' 1 1 ~~ ~j f `1 f ' ~•~ ~ ~ ~ ~~ L O ~,,, ~t l i, + j 11' PRaJECT ::. ~ ~1. ~.~ .: ~ ~ .,111 ±~ ~ ,~, ~~ ~ ~y~1~ i A I ~ ~ ` `1f /DO ~~ ~.'`a :1,~• 11'`1 ~~~ I„ ~~ ~~ V ~ ~ ~ ~ ~ ti 1 ~`` "~` ~ ~~,, ~, ~ '': { iii ` ~ ~ ~ 1 `- .~ ,~~• \ `''1.114 ~ ' ` ` ` ;~ ~I~ • '~ 0 ~ ~ 1 t ~\ ~~ p Vii, ~~ ~ ~. s ~, ~ ~ ~~ ~ ~~ ~ ``~ ~ ~ ~ r ~ c i I ~ DISCOVERY ~~ •~ ' ~ ~' ' ; ~ ~ ' .~~ ~ ~ rid ~ ~ ~ ,~~ l .~ BAY ...,. • ~1 X44 ` I~ Jllllll L• ' I ~ ft'• ~ ! f ~C Jf ~ '. ~., ~ n \~ ~' ~ JJ .~. Cl ~ 'y X44 ~ S~! I w ` 1~ ~~ ~ ~ ~ ~ ~ f /' ~I ~4 •~~ .~~. ~~ 6g scQVexy day ~% ~~~' ~.~ ~, ~r~o Meeting ,'~ ~ 0 114 112 1 Scale in Miles 1~OTE _____ Map adapted from 1:25,004 USGS topographic map of Port Townsend, wf~ quadrangle, dated i 981. N o ~' ~ ~~~ R1 x ~ a ~•.o y cn o '~. o i x ~ z a i o m ~ -i ni ~ Z '= ~ ~ ~+ O O _ I~l f''1 y ~ a ri p_ rJ ~ (D -~ C T Sloped to Drain Away Fram Structure -wail Pavement or 10" to 15" Drainage Sand & Impervious Soii o e ° Grave! or washed Pea Gravel Backfiil Meeting Gradation 18" o Requirements far Structural Fill Min. Damp Proofing See Nate 2} • weep Holes Va or p Excavation Slope a (See Note 1 } Barrier Contractor's o Responsibility • ° 0 .Floor Slab 6"Min. Cover of Pea Gravel 0 a ~~; bo o ti - ° 'o ~ ~'o ° ' a o ~ ° °o ° ~ o o ~ ` 1 B" Min. o • ° ° a o ~6" Min. on Sides of Pipe} , o ~ o ° Subdrain Pipe" ~ 2" to 4u Washed Pea Gravel 4"Min. Not to Scale MATERIALS Drainage Sand & Gravel with the Following Speci#icatians: °/° Passing Sieve Size by weight 1-112" 140 314" 90 to 104 114" 75 to 100 No. 8 fi5 to 92 N o. 30 20 to 65 No. 50 5 to 20 Na.100 0 to 2 Eby wet sieuing} (non-pEastic~ 4"minimum diameter perforated or slotted pipe; tight joints; sloped to drain ~fi"li 00' min. slope}; provide clean-outs. Perforated pipe holes ~3~1 fi" to 318" dia.~ to be in lower half of the pipe with lower quarter segment unperforated far water flow. NOTES 1. Drainage gravel beneath floor slab should be hydraulically connected to subdrain pipe ~alang the west ~downslope} footing. Use of 2"diameter weep holes as shown is one applicable method. 2. Imported structural fill should consist of well-graded granular soil with not more than 5°/a fines Eby weight based on minus 3l4" portion} passing Na, 204 sieve Eby wet sieving} with no plastic fines. 3. Backfill within 18" of wail 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. 4. 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°l° modified Proctor maximum density ~ASTM: D1551-?0, Method C}. Otherwise compact to 92°/° minimum. Slotted pipe to have 118" maximum width slots. Frank Vane Residence Port Townsend, Washington SUSDRAIIUAGE & BACKFILLIhIG May 199fi Vlf-1194-a2 SHANNON & ViIIISON, INC. F~~, ~ GeotechrNCal and Environmental Consultants Maximum slope behind rockery is 3N to ~ U far a horizontal distance equal to the height of the rockery. 3 ..•., ' • ' • ' • ' • • • ' • ' • • • ' • ' • ' • ' • ' • ' Stable Excavation S lope i n . 1 . 1 . 1 . ~ . 1 • 1 • 1 • , • • • • 1 , • •••'•'•'~'•`•'•'•'•'•` Dense Native Svil . • . • 1 ~ 1 • • • • • • • • • • • * • ~ . •' •' •' •''' •'' `'' •' •' Contractor's Responsibility} . • ~ • 1 • . • . • / ~ 1 • . • . .. • • 1 l 1 . 1 . 1 / 1 . - •' '• • • •'• ' • ~ • ' openings Chinked ' • ' • ' • ' • ' • ' with Quarry Spalls ............. ....... .... .............. ''''''''' •' •'' Backfill H=8' Max. 4 ' •' •' •' •' •' •' ' ' ' ' ' ' ' ' ' ' ' ' Glean, well graded sand ~ grave! or ' ' " ' ' ' ' ' ' ' ' ' ' crushed rock, 2"max. size, 40 to 60 ' • ' ~ ' • ' • ' • ' • ' ' gravel, less than 5% fines (passing #200 • • • • • • ` • ' • ' ' ' sieve}. l=ines shall be non-plastic. `' ' ' ' ' ' ' ' ' `' ' Compact in 6" lifts with min. of 4 coverages ' ' ' ' ' ' ` ' ' ' ' ' ' byhand-operated Pamper. Compact to at ' ' ' ' ` ' ' ' ' ' ' leas f 92 % of Modifr`ed Proctor maximum • ' ' ` • ' • ' • ' dry density ~ASTM D-1557 70~. Backfr'll .•.•.• • • • • • • ' • ' • ' • ' • ' ~ and rock placement should be bur t up fiery ''''' '''''' ~' •' ~' .•.•. •~•••~•••~• together. Dense 12"Min. •~'•' '''''''''''' Soil '•`•'• '' ~ ~ . ~ . ~ • • • ' . . • , 1 1 1 , 1 . • ~ '' `''''''''''' `'''''''''''''' 4" Diameter Slotted ABS Pipe ' ' ' ' ' . , . , `''`:~``:'::::: ~~~.~ . .:.,...Bedded in washed 3/8"pea gravel {6"cover around pipe), sloped to drain and connected Hl3 Min. U1lidth ~ by tightline to storm drain outfall. No fabric #or Base Rack around pipe. . ~; - All loose to dense soil at rockery foundation should be overexcavated down to very dense soil and ` ~ ~ ~ replaced :with compacted backfill as described above. ;The excavation shall be kept free of water. The prepared rockery foundation shall be evaluated by a soils engineer prior to placement of rock. -blot to ~Scale~~: MINIMUM WEIGHT ~F R4Clt ' ~ '~~ ~ ' ` Portion of wall below fi feet, 2400 Ib. -~ - ~_' ~"6-man"} rock. Portion of wall above 5 feet,l fi00 Ib. 4"4-man"~ rock. ~ SHAN-NON & WILSON, INC. ~ Geatechnical and Environmental Consultants W-7194-02 Attachment to Report Page 1 of 2 Dated: May 16 , 1996 To: Mr. Frank Vane Port Townsend, Washingtan Important Information About Your Geotechnical/Environmental Report CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC P[TRPOSES AND FOR SPECIFIC CLIENTS. Consultants prepare reports to meet the specific needs 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 otherwisey your consultant prepared your re art ex ressl for ou and expressly for the purposes you indicated... No .one other than you should apply this report for its P P Y y 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. TIIE CONSULTANT'S REPORT IS BASED aN PROJECT-SPECIFIC FACTORS. A geotechnicallenvironmental report is based on a subsurface exploration plan designed to consider a unique set of project- specific fac#ors. Depending on the project, these. may include; the general nature of the structure and property involved; its sire and confi ration; its historical use .and practice; the 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 otherwisey 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 refrigerated warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site}; (2} when the sia~e, 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 ~S} for application to an adjacent site Consultants cannot accept responsibility for problems that. may occur if they are not consulted after factors which werz considered in the development of the report have changed. sUBsURFACE CaN~rrlarrs CAN CHANGE. Subsurface conditions may be affected as a result of natural processes or humaa activity. Because a geotechnicailenvironmental report is based on conditions that existed at the time of subsurface exploration,- construction decisions should not be based an 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 geotechnicallenvironmental report. The consultant should be kept apprised of any such events, and should be consulted to determine if additional tests are necessary. M05T RECONIlVIENDATIONS ARE PROFESSIONAL JUDGMENTS. 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 aboutoverall subsurface conditions The actual interface betwuen 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 situations, 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. . Page ~ of Z A REPORT'S CONCLUSIONS ARE PRELIlV~INARY, The conclusions contained in your consultant's report are preliminary because they must be based an the assumption that conditions revealed through selecti~ exploratory sampling are indicative 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 heeded to d~terntirie ~' = ~ ~ '~ whether or not the report's recommendations based on those conclusions are valid and whether or not the contractor-is ~ abiding i by ~ ~~ applicable recommendations. The consultant who developed your report cannot assume ° respa~~siblity~~~or lia~l~ity for- the `adegi~ciy r ' ` ~~ ~'' ~ .. `.l t..~.~. ~,~ r i..,5 ,`1'i ~.I ~.'~~-~, 4. ~ '..~[ ~. a .i,- ~ .~ tt ) ~. ~..:)~ l.:i '^-.a y, . ~f 1,---~'. of the report s raecommendatians if another party is retained to observe construction. THE CONSCJLTANT'S REPORT IS SUBJECT TO MISINTERPRETATION. ,~. i , ~:'. ~ '' :~ - . ~ } ;~ .. ~~ t`:: h ~.~ ~ ~.~': ' '~ ~ j ' ~ ~:,~ '_ Costly pmblerns can occur when other design professionals develop their plans based ~r`misintcrpietatiori., of ~' geotecluticle~rivir-' ~ ` '~, . ~ ~~ onmental ,report. To help avoid these problems, the consultant should be retained to mirk' with"'~oth~er prtyjeet~ desi,~'n`~Jp'rafession~s ~ ~ '~~, to explain. relevant geotechnical, geological, hydrageological, and. environmental findings,an~ to review` the adequac~~ of tler`plans~`'.~~ `~ ~ti t.. and specifications relative to these issues. ~ } ~ t { , ° ~ . ~ . DORING LOGS ANDIOR MONITORING WELL DATA SHOULD NOT BE SEPTET) ~'R~OM THE` REPORT; Final boring logs developed by the consultant are based upon interp~tation of field lags assembled by site personnel}, field test results, and laboratory andlar office evaluation of field samples and data.. Only final boring logs and data are customarily included in geotechnicaUenvironmental reports. These final Togs should not, under any circumstances, be redrawn for inclusion in~ architectural ~ ~ . ar other design drawings, because drafters may commit errors or omissions in the transfer process. - . ~ ~ ~ _ ,~, ,, . To reduce the likelihood of boring lag or monitoring well.misinterpretatian, contractors should be given ready 'access to the conip~lete ' ~~~ geotechnical engineeringlenvironmental report prepared or authorised for their use. If access 'is provided only to the report prepared ~ ` for you, you should advise contractors of the report's limitations, assuming that a contractor'was not gone of the specific persons,t'ar whom the report was prepared, and that developing construction cast estimates was not one of thespecific ~~urpose"s l~or which it was ` ~~ prepared. while a contractor may gain important knowledge from a report, prepared for another patty,' the contractor should discuss the repor# with your consultant and perform the additional or alternative .work believed necessary' ~to abta"in the data specifically appropriate for construction cost estimating purposes. Some clients bald the mistaken impnesson~ that simply d'iscl~imi~g'responsibility ~ :~ for the accuracy of subsurface information always insulates them from attendant liabilitjC Pmvi~ding~ "the best available in~rmatior ~~ to contractors helps prevent costly construction problems and the adversarial attitudes that aggravate' them ~o a di'spmportionate scale. READ RESPONSIBILITY CLAUSES CLOSELY. ~ - ~ ~ ~ ~ ~~ * ° ' ' ~ ~ „ ~ ~ ' .: Because geatechnicallenvironmental engineering is based extensively on judgment and opinion, it is far Tess exact-than other design''` ~~~ disciplines fihis situation has resulted. in wholly unwarranted claims being lodged against consultants To help prevent this problem, consultants have developed a number of clauses for use in their contracts, reports and other docu~~nts. Then re'sponsibilty'clauses ~~~ ~' ~'~ are not exculpatory clauses designed to transfer the consultant's liabilities to other parties;-`rather, they are definitive clauses that' identif'y` ' ~ ~~~ where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual responsibilities `' ~ ~ . ~~ and take appropriate action. Same of these definiti~ clauses are likely to appear in your report} and -you are ericonraged to read: them ~' ~ + `~ closely. Your consultant will be pleased to give full and frank answers to your questions ` ~ ~ ~ ~ - ~ ., ~' ; i -:~ ; The preceding paragraphs are based on information provided by the ~ k ~: } : ~~ ::;-,<, ASFEIAssociatian of Engineering Firms Practicit~ in the Geosciences, Silver Spring, Maryland ~ ~ ~ ; . ~ ~ ~~ . tl96 Page 2 of 2 A REPORT'S CONCLUSIONS ARE PRELIlVIINARY. The conclusions captained in your consultant's report are preliminary because they must be based on the assumption that conditions revealed through selective exploratory sampling are indicative of actual conditions throughout a sits 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 °need~d to determbe ~r whether or not the report's recommendations based on those conclusions are valid and whether or"not the contractor =is abiding by ~ ~° a licable recommendations. The consultant who developed your report cannot assume }.res~o~sibilrty'or lia~ility~for° the adeq~aey' ' ~~'~' `' PP of the report's recommendations if another party is retained to observe construction. s '' , r : ~.~ s x i. ~ `~ , k ~;~,~.~ d .. ~ :'- , ~ ~ ` ~ . `i f:' ' ~ .~' ` , t. `., ' ° ~ :E ~; THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION. -` : .' - :.. ~ . ' "~~ .:~' . ~~ Costly problems can occur when other design professionals develop their plans based `od`misinf~~.~tatoii.~f ~' g~~ ;'c~'~e~vi~- ; ` ~r onmental re rt. To heI avoid these problems, the consultant should be retained to work with" ~oth~er projeot~ deli~i'° ~'rofe~sivri~s ~ `~ ~} ~~ p° P , ~ . . ~ ., ~, .,.. ~~ .,. flans , ~ > ..;~ to explain relevant geotechnical, geological, hydrogeological, and environmental findings, and do review the adequac~ri of their. p '.r .~ F and specifications relative to these issues. ..: ± ~ ~~ ~ ,' ' :. , ~ ° ; ` : £;~ ° .: ~ ~ . . BARING LOGS ANDlOR MONITORIl~IG wELL DATA SHOULD NOT BE SEPARATES FROM THE REPORT. ~ ~-.: ~ ti, Final boring logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test results, and laboratory andlor once evaluation of field samples and data. Only final boring lags and data are customarily included in geotechnicallenviranmental 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. ~ ~. , ~ ; :. -:~ t ; ~.. To reduce the likelihood of boring Iog or monitoring well.misinterpnetation, contractors should be given ready 'access to"the complete ~ ~ ` `~~' geotechnical engineeringlenvironmental report prepared or authorised for their use. If access ~is provided only- to~the report prepared ~ :` for you, you should advise contractors of the report's limitations 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~~urposes ~Or 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 alternative .work believed necessary' to obra'in the ~ data specifically appropriate for construction cost estimating purposes. Some clients hold the mistaken impressions that simply di'sclaimir~{respousibility for the accuracy of subsurface information always insulates them from attendant liabilit}t Providing the best available in~rmation' to contractors helps prevent costly construction problems and the adversarial attitudes that aggravate them~~to~ a~ disproportionate scale. READ RESPONSIBILITY CLAUSES CLOSELY. ~ , `: ~ r ~ ~_ ° . Because geotechnicallenvironmental engineering is based extensively an judgment and opinion, it is far less exact than other`design .,~ disciplines This situation has resulted in wholly unwarranted claims being lodged against consultants To help prevent this pro em, consultants have developed a number of clauses for use in their contracts, reports and other docui~enfs. These resporisibility'cla~uses ` 1' '; ,,,. .a 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 ~ rec~gnitie their individual responsibilities ~~ ~~ ~ ~ ~ `~ and take a ro riate action. Some of these definitive clauses are likely to appear in your- report; and you are encouraged ~ to read. `them ' ~ ~ ~~ ` ~~ PP P , closely. Your consultant will be pleased to give full and frank answers to your questions ~ ` ~ ~ -- ~ ~ ~ ~ ~. ~ ; : ~ ~ f ~ :~ *i 4..f The preceding paragraphs are based on information provided by the ~ ~ t ASFEIAssociation of Engineering Firms Practicing in the Geosciences, Silver- Spring, Maryland ~ ' ~ ' ~ ~ ~ ~- 1196 ~ SH~NNfJN $c V1~1L5-0N,1NC. ~ Geatechnicaf and Environmental Consultants w-'194-02 Attachment to Report Page t of 2 Dated: ~ a~ 16 , 19 9 G To: Mr, Frank Vane Part Townsend, washington Important Information About Your Geotechnical/Environmental Report CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS. :: Consultants prepare reports to meet the specific needs of specific individuals A report prepared far 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 far you and expressly for the purposes you indicated.. No one other thaw 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 geotechnicallenvironmental report is based on a subsurface exploration plan designed to consider a unique set of praject- specific factors. Depending on the project, these may include: the general nature of the structure and property involved; its sire and configuration; its historical use ,and practice; the location of the structure an 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 vastly problems, ask the consultant to evaluate haw 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: ~i} 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 refrigerated warehouse will be built instead of an unrefrigerated one, ar chemicals are discave~ed ~ on or near the situ; ~~,} when the sip, elevation,, or configuration of the proposed project is altered; ~3) when the l~atian 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 -+Cansultants 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 geotechnicallenvironmental 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 constructioa starts; far 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 continuir~ adequacy of a geotechnicaUenvironmental report. The consultant should be kept apprised of any such events, and should be consulted to determine if additional tests are necessary. iUIOST RECOMII~NDATIONS ARE PROFESSIONAL JUDGMENTS. Site exploration and testing identifies actual surface and subsurface conditions Daly 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 conditions The actual interface between materials may be far mare 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 situations-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.