Loading...
HomeMy WebLinkAbout602285001 Geotech Assessment~' z_ ;-- :` ~~ - :: _. -_ ~;~ ._.. ~>.->- ,,~{ ; . ~J~n` ~~~ry ~ :- ~~: - • , RICHLAND ~~~~ SHANNON ~VI/It..SON, INC. SEATTLE FAIRBANKS GEOTECHNICAL AND ENVIRONMENTAE CONSULTANTS ANCHORAGE SAINT LOUIS 80STON June 18, 1997 Mr. Don Knudsen P.O. Box K Shelton, Washington 98584 RE: GEOLOGIC SITE ASSESSMENT OF PROPOSID BUILDING SITES, KNUDSEN LONGPLAT, LOTS 2, 3, 4, 6, 7, 9, AND 10, BRINNON, WASHINGTON Deaz Mr. Knudsen: This letter provides our geologic assessment regarding the stability of the fanned buildin P g sites on the proposed lots 2, 3, 4, 6, 7, 9, and 10. We understand that this assessment is required by Jefferson County to complete the long plat of the property as indicated in the final Mitigated Determination of Non-Significance (MDNS) dated June 8, 1994. The conclusions and recommendations contained in this letter aze based oa a visit to the site on Apri125; -1997, bar -Mr. V.J. Perkins of Shannon & Wilson, Inc., and a review of geologic I Po~P ~P and to hic s of the azea. The work has been conducted in general accordance with our proposal dated December 8, 1995, which was subsequently authorized by Mr. Knudsen on March 21, 1997. SITE AND PROJECT DESCRIPTION The property.and proposed long plat aze located approximately two miles east-northeast of Brinnon, Washington, on the north side of the Dosewallips River Valley and east of Rocky Brook as indicated on Figure 1. The property is approximately 1,700 feet wide (east west) by 2,700 feet long .(north:south) and extends from the relatively level valley floor on the south, up the side of Mount Turner to the north. Elevations across the site range from approximately 120 feet on the valley floor, to more than 800 feet at the north side of property on the side of the mountain. Natural slopes on the portion of the property on the 400 NORTH 34TH STREET • SUITE 100 P.O. BOX 300303 W-7163-02 SEATTLE, 4~iASHINGTON 08103 206.032.8020 FAX 206.633.6777 TDD: 1.800.833.0388 ~. Mr. Don Knudsen ~' June 18, 1997 Page 2 S!-iANNON ~WiLSON, INC. mountain typically range from 10 to 35 degrees with an overall slope of about 15 to 25 degrees. Most of the west side of the property is bounded by a near vertical rock cliff that extends down to the west to Rocky Brook. We understand that the property was logged approximately 20 years ago and has since re-vegetated with alder, maple, cedar and fir trees. The proposed long-plat will- divide the property into 10 lots that will range in size from 5 to 10 acres. The dimensions and layout of the proposed lots are shown on Figure: 2. We understand that lots 1, 5 and 8 had been purchased with changes in title prior to development of Jefferson County's current long-plat procedures and requirements. Consequently, these properties are considered to already be legally subdivided (i.e., grand fathered in) and are not included in the present geologic evaluation. The proposed building locations for lots 2, 3, 4, 6, 7, 9, and 10 aze indicated ~~n Figure 2. Also, indicated on Figure 2 is the proposed septic drain field for lot 10. We understand that sewage disposal for the other lots will be off-site on flatter property to the east. The proposed house locations and septic drain field for lot 10 were adequately flagged and identified at the time of our visit.. Based on geologic assessment of the site, w~~ recommend that the building locations on lots 4 and 10 be revised as shown on this Figure 2 to provide more stable building sites. Our geologic and engineering assessment for this recommendation aze presented in the following sections of this letter-report. SITE GEOLOGY Geologic maps of the area indicate that the site is underlain by tertiary volcanic: and/or sedimentary bedrock, and except for the valley floor, the rock is overlain by a mantle of Pleistocene Vashon Till. On the valley floor, recent Holocene Alluvium is mapped above the bedrock. Till is a non-sorted mixture of clay, silt, sand and gravel with sG~ttered cobbles and boulders that is deposited at the base of a glacier. The Vashon Till was overridden by the last glacial ice sheet that covered the region during the late Pleistocene. Due to the great weight of the ice, the till is overconsolidated typically to a very dense or hard state. The Holocene alluvium mapped in the bottom of the valley has been deposited by Rocky Brook and the Dosewallips River since the retreat of the last glacial i.ce and - typically consists of reworked sand, gravel, cobbles and boulders. W-7163-02 Mr. Don Knudsen SHANNON WILSON, INC. June i8, 1997 Page 3 The resence of the bedrock till and alluvium w p as confirmed during our site reconnaissance. Specifically, soft to medium soft sandstone was observed on lot 7 along the north side of the proposed envelope. Rock outcrops also form the cliffs along the west sides of lot 8 and 10. Till was observed on lot 10 above an elevation of approximately 600 feet (approximately the same location as the recommended revised building location shown on Figure 2}. Holocene allu~rium, consisting.of sandy gravel with cobbles and boulders was observed south and -west ©f the `>Oosewallips Road on lot 6. Sediments that appear to be present besides those indicated on geologic maps include deltaic, ~. lacustrine, ice contact and/or outwash sediments associated with the Vachon Stade glaciation. These sediments may have been deposited in Pleistocene Lake Russell (a lake that covered much of the Puget Lowland when continental ice sheets of the Vachon Stade blocked the existing drainage to the ocean through the Straight of Juan de Fuca) or along the sides or end of glaciers that were present in the valley. The lacustrine/ice contact/recessional deposits were observed on lots 2, 3, 4, 7, and 9 north and east of the Dosewallips road. These soils typically range from very stiff to hard, slightly gravelly, slightly -sandy, clayey silt to medium dense to very dense silty, sandy gravel. The deltaic sediments at the site are located along the east property line of lot 8 (along the top of the cliff) and are dense deposits of stratified, slightly silty to silty, sandy gravel with scattered cobbles and boulders. These soils appear to have been deposited in a delta, possibly into the Pleistocene Lake Russell or alongside remnants of glacial ice occupying portions of the valley. These coarse-grained deposits may be slightly cemented by iron oxide. ~_ Topsoil and colluvium have ~ developed above these geologic units. These relatively weak soils are typically only a few feet thick. Topsoil is derived from weathering and loosening W 7163-02 w M N y Mr. Don Knudsen SHANNON F~WILSON, INC. June 18,-1997 Page 4 of the underlying glacial deposits or rock. Colluvium is also weathered material but has reached its present location due to the forces of water and gravity. At each proposed building location, a level building pad had been developed by excavating into the hillside and filling on the down-slope side of the site with the excavated soil. Based on the topography surrounding each building site, the maximum fill thickness ranges from about 4 to 10 feet. The fill slopes are typically graded to about 50 percent (2 horizontal to 1 vertical} or less. SLOPE STABILITY AND PROJECT IlVIPACT Two areas of slope instability were observed during our site visit and are indicated on Figure 2. The first area of observed instability was along the east side of the Dosewallips Road in the cut on lots 3 and 4. The soils in the road cut appeared to be silt and clay with lesser amounts of sand and gravel. Seepage was observed along the cut, generally at the contact between the topsoiUcolluvium and the underlying glacial deposit. it appears that the instability is confined to the topsoiUcolluvium, which is sliding over the more stable glacial deposits. While the presence of near surface groundwater is a contributing factor to the observed instability, it appears that the sliding is due primarily to over steepening of the bank caused by the road cut. The second area of instability noted at the site is on the south side of lot 10, near the common point with lots 8 and 7. This slide is located in topsoil/colluvium that has formed above the deltaic sediment. The slide is located above a cut for a logging road. No groundwater was observed at the location of the slide during our site visit. It appears that the sliding is due to removal of the toe of the slope when the logging road was initially constructed. In general, it appears that observed slope instability at the site is confined primarily to the topsoiUcolluvium in the upper few feet of the ground surface. Due to its relatively weak nature, topsoiUcolluvium will creep and occasionally slide down the hillside. The colluvium is particularly susceptible to movement where the slope is steepened (e.g., due to construction activities including road cuts) or when/where it becomes saturated (e.g., after W-7163-02 i~ ~~ Mr. Don Knudsen SHANNON WILSON, INC. 7urie iB, i997 Page 5 prolonged, heavy rainfall, or at the locations of seeps and rin son the slo We did not sP g Pe) observe indications of deep-seated slope instability. Based on the geologic conditions inferred from the geologic maps and from our site visit, it is our opinion that residences may be built on the proposed building sites {as indicated on 1994 to 1996 survey and shown on Figure 2) on lots 2, 3, 6, 7, and 9 and that the proposed ~~ ^ septic .drain field on lot i0 anay be constructed with 3ninimal impact on the stability of the slope, if the recommendations contained in this letter are implemented. Similarly, residences located in the recommended revised building locations on lots 4 and 10 (see Figure 2) may also be built with minimal impact on the stability of the slope, provided the recommendations in this letter are implemented. 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 line breaks/leaks, uncontrolled drainage, unwise development in adjacent areas, or other actions or events on a slope that may cause sliding. SITE DEYELOPMEl~1T RE~ONIlV~NDA~'IONS As indicated in scope of work, the purpose of the geologic assessment was to evaluate the slope and seismic stability with regard to the proposed long plat and building locations. Our scope of work did not include specific foundation design for each of the lots, which is more appropriate to complete once actual house dimensions; Layouts and other desired site developments (e.g., garages, outbuildings, landscaping) are determined by the future owners. The following provides general recommendations and conclusions regarding the location of the residences and site development so as to minimize the potential for slope and building movements. Building 7.ocations As previously indicated, it is our opinion that residential buildings can be constructed in the building envelopes for lots 2, 3, 6, 7, and 9 indicated on the 1994 to 1996 survey, which was provided. For lots 4 and 10, we recommend that the proposed building locations be revised as indicated on Figure 2. Due to the presence of the existing slides along the road cut along lot 4, we recommend that the house be located on the northeast portion of the W-7163-02 Mr. Don Knudsen SHANNON F~WILSON. INC. Tune 18, 1997 Page 6 property. We recommend that the building envelope on lot 10 be located on the relatively flat slope above approximately elevation 600 feet. Below this elevation, the slopes aze relatively steep and additional excavation in these soils could result in surficial slides similar to the one noted on the south side of the property (see Figure 2). Footings In general, we anticipate that the residences located in the proposed building locations may be supported on conventional spread continuous footing foundations bearing in undisturbed, dense/very stiff glacial soils or rock, or on densely compacted structural fill placed immediately above these materials. Footings should not bear in the existing fill placed on the down-slope side of the building pads, but should extend through the fill and bear in the geologic units previously outlined. Depending on the location of the buildings within the envelopes, this may require excavation through 10 to 12 feet of fill. Footings for building located adjacent to slopes steeper than 2 horizontal to 1 vertical {2H:1 V), should also be located below a hypothetical line extending from the base of the slope up to the building site at ZH:1V or at least 2 feet into very dense or hard native glacial soils. The risk posed to a residence by potential movement of the relatively loose, topsoiUcolluvium can be reduced by locating the footings in this manner. For example, the recommended revised building location on lot 4 is situated on top of an approximately 30- foot high slope that slopes down to the east at about 30 to 32 degrees (i.e., about 1.7H:1V to 1.6H:1V). Consequently, the footings for a building at the top of this slope should be located below a hypothetical 2H:1V line extending from the base of the slope up to the building site at or at least 2 feet into very dense or hard native glacial soils. Excavation and Site Grading It has been our experience that a slope cut to 2H:1V in the glacial soils will not ravel and maintain vegetation. Excavations in these soils will ravel if cut steeper than 2H:1V. Therefore, we recommend that permanent slopes cut steeper than 2H:1V into the glacial soils be protected. This protection may include rockeries or retaining walls, which would allow steeper excavation slopes. Atypical rockery construction detail is shown on Figure 3. In general, rockeries should be no higher than about 8 feet. Engineered walls may be required for steep cuts higher than 8 feet. Fill slopes should be sloped 2H:1V or flatter. W-7163-02 Mr. Don Knudsen SHANNON F~WILSON, INC. June 1$, 1997 Page 7 Drama e g Control of surface and subsurface water at the building sites will reduce the risk of slope movement. Consequently, we recommend footing drains be installed around the perimeter r of the buildings to.intercept and collect subsurface water. A typical footing drain installation is shown on Figure 4. Drains should also be installed behind rockeries and retaining walls to=intercept water flow. Roof drains should be installed to collect water.from roofs. All hazd surfaces around structures should be slope to away from the structures to catch basins and/or yard drains. Water collected in roof and yard drains should not be discharged into footing, rockery, or wall drains. Similazly, water that may be collected in footing, rockery, or wall drains should not be connected so that water can flow between these drains. At points where perforated pipes change to non-perforated pipes, a dam should be installed azound the pipe in the trench to force water in the trench into the non-perforated discharge pipe. The dam may be constructed by compacting clay soils around the pipe or slitting and placing sacks of concrete around the pipe. Water collected in drains should be routed via a tight line to a suitable discharge point (e.g., road ditch, drainage Swale, stream). Erosion Control Long term erosion control can be achieved through adequate control and dischazge of surface and subsurface drainage and re-vegetating disturbed azeas. Following the drainage recommendations contained in the pervious section of this report will reduce long-term erosion. For intermediate erosion control, cut and fill slopes may be re-vegetated with grasses. Some erosion may occur until the vegetation is established. The potential for erosion is typically the most severe during earthwork related construction, especially during wet weather. Wet weather generally begins about mid-October and continues through about mid-May, although rainy periods may occur at any time of the year. In"addition, groundwater levels are typically at there highest during -the wet weather months. Higher groundwater levels will increase the potential for groundwater to seep into site excavations and cause erosion and local slope instability. The groundwater would need to be intercepted by drainage ditches, trench drains, or otherwise removed. In addition, the till and the lacustrine/ice contact deposits typically contain sufficient silt and plastic fines to produce a cohesive, unstable erodible mixture when wet. Therefore, it would be the most. advisable to perform earthwork during the normal dry weather months of mid-May through W 7163-02 e Mr. Don Knudsen June i8, i997 Page 8 SHANNON F~WILSON, INC. mid-October. The following recommendations are applicable if earthwork is to be accomplished in wet weather or in wet conditions: a. 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 crushed rock. The size or type of equipment may have to be limited to prevent soil disturbance; b. 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. This soil would likely need to be imported to the site; c. The ground surface in the construction area should be sloped and sealed with a smooth-drum roller to promote the rapid runoff of precipitation, to prevent surface water from flowing into excavations, and to prevent ponding of water. d. No soil should be left uncompacted and exposed to moisture. A smooth-drum 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; e. Excavation and placement of structural fill 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; and f. Covering of work areas, soil stockpiles, or slopes with plastic; sloping; ditching; installing sumps; dewatering; and other measures should be employed, as necessary, to permit proper completion of the work. Straw bale and/or geotextile silt should be aptly located to control soil movement and erosion. Additional Engineering and Construction Monitoring We recommend that once the final building size, location within the building envelope, and layout are determined for lot 7, additional explorations and geotechnical engineering recommendations be formulated for development on this site. Structural engineering services may also be required for design of basement walls. These additional design-phase engineering services will be required due to the steep slope at the site and the presence of W-71b3-02 Mr. Don Knudsen June 18, 1997 Page 4 SHANNON Z;WILSON. INC. the road and potential traffic loading on adjacent retaining basement walls. In addition, depending on the location of the house or potential retaining walls, seepage observed along joints in the exposed sandstone may require particular drainage considerations and design. For the remaining lots (lots 2, 3, 4, 6, 9, and 14), we recommend that as a minimum, an engineering review of the individual building .plans be performed as they are developed to confirm that the plans and specifit~tions are °consistent -with the recommendations in this report. If retaining walls, extensive regrading, or other significant geotechnically-related construction is proposed as the sites are developed, additional design phase engineering services (including subsurface explorations} may be required. The advisability of additional engineering work should be evaluated when individual building plans are reviewed: We also recommend that earthwork be monitored by a qualified geotechnical engineer or his/her representative. LIlVIITATIONS 1 The conclusions and recommendations in -this letter are based on site conditions observed during our site visit and assume that observed conditions are representative of the subsurface conditions throughout the site; i.e., the subsurface conditions are not significantly different from those observed during our site reconnaissance or indicated on geologic maps. If, .during subsequent site activities (e.g., construction), subsurface conditions different from those inferred in this letter aze 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 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. This report was prepared for the use of the owner, engineer, and 7efferson County in the design and development of structures on the sites. With respect to future 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 geologic maps, site reconnaissance, and discussion of geologic and subsurface conditions included in this report. Please note that the scope or our services did not include any investigation for the presence or absence W-7163-02 Mr. Don Knudsen June 1~, 1997 Page 10 SHANNON F~WILSON, INC. of hazardous or toxic material in the soil, surface water, groundwater, or air on or below or azound this site. 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. If you. have any questions regarding the observations, conclusions, or recommendations, please call us. We appreciate the opportunity to be of service. Sincerely, SHANNON & WILSON, INC. E°~~ OREGON 650 ~~~~~ LOGS William J. Perkins, R.P.G. Senior Geologic Engineer WJP:IiHD/v'JP ~ ~~8 !5 ? Herman H. (Tex) Druebert, P.E. Enclosures: Figure 1 -Vicinity Map Figure 2 -Site Plan Figure 3 -Typical Rockery Detail Figure 4 - Subdrai.nage and Backfilling Important Information About Your Geotechnical Report cc: Ryan Tillman, Tillman Engineering, Inc. W7163-02.LTR/W7163-1kd/dgw W-7163-02 E%PIRE3 7/2ij ~1 ~~ .z- - i i w M ^ M ^ 1 Kit ~~~~~~~~= . ~ ~~ N f ~~ ~6~ Sao 9p, ~~. 1 ~~ ~~ ?60p \\\ ~`~ --__~J~ O ~~ ~,`0 ~' ° PROJECT ~ a°° ~ LOCATION .~ .. I ~. --~'-aoo 00 , ~'~~ SEygpL S ~r~ r, '\ ~ \~- 600 ~. SSd i ~ ~ ~` ~ coo _ ~ _=~=J _ ---- - ~O r6 ar~~ - I -- ___ -80 ~ •~ 4 ~, ~ I• 1~ I I ~~. .~o r ~ s ~ ~ o ' _ N a~ » '- m~ I ~+ 34 i ~ r I ~° v~ I /• . BOO o ~ * ,~ ~ 1/2 1 Knudsen Long Piat Brinnon, Washington Scale in Miles NOTE VICINITY MAP Map taken from 124,000 USGS topographic June 1997 W-7163-02 map of+Brinnon, WA quadrangle, dated 1953, photorevised 1985. SH~ON &£~UNIN~C. FIG. 1 ^ a ~ i i ~ t ~ ~ ~Nz07 ~ g .. ~ ~~,~~ . o 3 ~ ~ ~ ~ m -, r ~ ~ o a a~ NO p ~ p* u°, n w rn °D ~ ~ ~ `~. c m °' a o c Z lO s . m g' ° n ~ a ~ ~ o ~~ m ~ s ca a ' z ° -n ,~ ~° ~ ~. ~ ~ ~ o 0 ~ ~~ v ,~ a o .~ ~ ~ o ~ V W ~ . ? ~ O N f0 ~ ,-. C ~ fQ C p N N N O ~ ~ CS ~ _ . (D = `G 5 8~• ! 8'a2" tr za. ~~ ~, _~ t at ~. as c ~ ~ '~~ . ' ~~ ~ .~ ~ ~ "' r. O {;'ti . t.. ~ j ~~ ~7 "' (p o . - z tai 0 0 (move) r Z oa ' o "'~ - "~ ~ , t N B5• t °m o L2N31•:. pov L~N~1 , , N s ''~ N La N c"8• ~3 ~* ~ rn r '' ...~.N.~.I.!- ' ` ~ 3 ~'~ 8+ IELD 1)RA 1N~ O ..o A~N~F 17 0~' Tt7A ~r 't.c.: m 3 ~:~ .a THE M ~. (~, ,~~; ~,: ~, ~ ^~ ~ o'ff'" \ ~~ ~~9 ~ . .ti. ~'; ~ '~"~ g:i• I ~4'~i5' E '~ 42~^.t;~.n,~ s~ C:,14> 4d9. S~ ` a~.~ AC. ~''• .; DRR 1 Nl' ! EL t3 ^~•.,. \ \ ts+~t~w ;..... ,,u \?~ `\ ,, stx.-nom s7~c E5M`T. ~0}~ ~k. ~ \y~,."rl, sa' x 21' ~ w rn ~~. : O t?! rNtr ~trNF~' t r ~. sue„ ....... ~ ~ ~ . a Ra. .. ~ 7~ ~ ~' ~r; ...... UT t L 17' l 1r5. 5CE u,, `~`\ a.2 AC, ~~= :'~}1 ham" ,~, AF N0. 2717'3. ~ 7+ w ~ ~ t 5g ~i - t a. pQ:....: M ~ 1 ....: ,~~ S C AC ..... ~,~ ,Q~~~•. '+r ' . b~ r, ~' •. ~ ., . 'Fa~~. ~~~~~ ~` fi~ ,h~i 4 '~~ \~. M /~2 et' N s '~. ~ = C a ~ Z ..a ~. ~Z V .~ 0 z z an 'T1 v >r I ~ N N V) ~ a m ~~ 'p ~ r r ~~ a ?~ Z O . ti 4' ~ ~ ~~ e d ~ Cti / ,~~p. s. ~ na. h N ~~ ~ t~~ ~ / ovel ~ a ~ sue. r} ~ ~ m ~~ 63~ ~~ 5~ ,' ~ ~9~ ~ N 1y ~ ~ ~;t ..:....:............ N~ \; _ D ate. ~ AC. G ~ ,~~ (~ -~ ~ N ~yyO ~r ~, y~yryry t~q ~ ~ x taOC p l,.Y~~.,~ r,~~ S" ~ ".w~ J+G. 747 0 ~ LC~ ~~,~ :.:11 (.f v' Rive ,,~ N r~ ~ ~~' "~^-,.~ ~ ~ . ~ ~'`` x'~`~'' t~ ~' ~~ ,5,~ ~, dip ~`" O 5. 1 Ac. _ _-n tD ~ &. ~p ry x ',J .} N 138• a~6' ~5' W ~J~~. ~~ ± N t lJ ~l f~.J * ii ~ .7 [i'~. a~.l ~, 151.3&' ~ o ' 4~~ ~ ' ~ } 1 "x ;' ~~~ $" Compacted Native-Snit (Impervious Surface Layer) 12" Min. W3 Min. Width _ I for Base Rock ~ I Maximum slope behind rockery is 3H to 1 V for a horizontal distance equal to the height of the rockery. 3 1 (-_~~ Stable Excavation Slope in Dense Native Soil (Contractor's Responsibility) Openings Chinked with Quarry Spalls l3ackfill Clean, well-graded sand & gravel or crushed rock, 2` max. size, 40 fo 60% gravel, less than 5% fines (passing #200 sieve). Fines shall be non-plastic. Compact in 6" lifts with min. of 4 coverages 6yhaod-operated tamper. Compact to at least 92% of Modified Proctor maximum dry density (ASTM D-1557-70). Bac~ll and rock placement should be built up fogether. 4" Diameter Slotted ABS Pipe Bedded in washed 3/8"pea gravel (6"cover around pipe), sloped to drain and connected by tightline to storm drain outfall. No fabric around pipe. Aft loose to medium dense soil at rockery foundation should be overexcavated down to dense or hard soil and replaced with compacted bac~l! as described above. The excavation shalt be kept free of water. The prepared rockery foundation shat! be evaluafed by a soils engineer prior to placement of rock. MINIMUM WEIGHT OF ROCK _. . ~-;,,,. Not to Scale Portion of wall below 6 feet, 2400 Ib. ("8-man") rock. Portion of wall above 6 feet, 1800 Ib. ("4-man") rock. H=8' Max. 4 I l M Sloped to Drain Away From Structure Wall ~-- Pavement or 10" to 15'-~ Impervious Soil Backfill Meeting Gradation _ Requirements for Structural Fill {See Note 2} Excavation Slope ~ Contractor's .~__ Respons~'lity 6` Min. Cover of Pea Gravel (6"Min. on Sides of Pipe) Subdrain Pipe Not to Scale MATERIALS Drainage Sand & Gravel with the Following Specifications: Passing Sieve Size by Weight 1-1/2" 100 3/4" 90 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) Drainage Sand & c e Gravel or Washed Pea Gravel 18" o 0 Min. Damp Proofing Weep Holes Vapor v (See Note 1) Barrier '9 Fkx>rSlab °' ° ~ O~~ - , ~0 ' e ~"° ~ O ° ~ ~ p ~~ ~~ 18" Min. ~ . D . e T "O o 2" to 4" 4" minimum diameter perforated or slotted pipe; fight joints; sloped to drain (6"/100' min. slope); provide clean-outs. Washed Pea Gravel NOTES 4" Min. 1. Drainage gravel beneath floor stab should be hydraulically connected to subdrain pipe. Use of 2" ., d"~ameter weep holes as shown is one applicable method. 2. 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 Na. 200 sieve (by wet sieving) with no plastic fines. 3. Bac~ll 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. 4. A11 backfill should be placed in layers not exceeding 4" loose thickness and densely compacted. Beneath paved or sidewalk areas, compact to at least 95% mortified Proctor maximum density (ASTM: D1557-70, Method C). Otherwise compact to 92% minimum. 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. W-7163-02 SHANNON & WILSON, INC. ~ Geotechnical and Environmental Consultants .~ Attactuneat to Report Pa®e 1 of 2 Dared: June i8. 1997 ~: Mr. Don Knudsen Shelton, Washington Important Information About Your Geotechnical/Environmental Report CONSULTIl~TG SERVICES ARE PERFORMED FOR SPECIFIC P(JRPOSES AND FOR SPECH'IC CLIII~ITS. Consultants prepare reports to meet the specific needs of specific individuals A report prepared for a civil engineer may not be adequate fin a construction contractor or even another civil engineer: Unless indicated otherwise, your c~sultant prepared your mport expressly iior you and expressly for the Purposes you indicated. No one other than you shoultlapply::this. ru~ort for its intended purpose without first coafetring with the consultant. No party should apply this report for any purpose other than that orrgmally contemplated without first conferring with the consultant. T~ CONSEJLTANT'S REPORT 1'<S.BAS® ON PROJECT-SPECIFIC FACTORS. A geotechnicallenvironmental report is based on a subsurface exploration plan designed to consider a unique set of project- apecific fracture. Depending on the project, these may include: the general nahue of the strudute and property involved; its sire and configuration; its historical use and practice; the location of the structure on the site and its orientation; other impra~vements 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 haw any factors that change subsequent to the date of the report may affect the rdations Unless yourr consultant indicates otherwise, yuwr .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 umrefrigerated one, or chemicals are discovered oa or near the site); (Z) when the sia, elevation, or configuration of the proposed project is altered; {3) when the location or orienta- tion of the proposed project is modified; (4) whey -there is a change of ownership; or (~ for application to as 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. SDBSURFACE CONDTITONS CAN CHANGE. Subsurface conditions may be affected as a result of naUrral processes or human activit}t Because a geotechmcal/environmental =:" report is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a 4-' report whose adequacy may have been affected by times 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/eavimnmental report. The consultant should be kept apprised of a~ such events, and should be consulted to determine if additional tests are necessary. MOST RECOMIISENDATIONS ARE PROFESSIONAL JUDGMENTS. surface and subsurface conditions onl at those ruts where samples are taken. The Srte exploration and testuug rdentrfies actual Y Po data were extrapolated by your consultant, who then applied judgmcet to reader an opinion about overall subsurface conditions 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 is 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- lions can be particulazly beneficial in this respect. Page 2 of 2 A REPORT'S CONCLUSIONS ARE PREI-Il4i~tARx The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that condi- tions revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual subsurface conditions can be discerned only during eartlrKOrk; therefore, you should retain your consultant to observe actual conditions and to pra+ide conclusions Only the consultant who prepared ~ reP°rt is frilly familiar with the background information needed to determine whether or not the report's recommendations based oa those conclusions are valid and whether or not the contractor is rt cannot assume responsr'br7ity or liability for abiding by applicable recommendations. The consultant who developed Your rope the adequacy of the report's recommendations if another party is retained to observe construction. THE CONSULTANT'S REPORT LS SUBJECT TO ON. Costly Problems can occar when other design Professionals develop their plans based on misinterpretation of a geotechaicaUenvir- ormoeatal report. To help avoid these problems, the consultant should be retained to work with other project design professionals ~ _ ~~ : geological, brydrogeoy~gcal, .and environmental findings, and to review the adequacy of their plans and specifications relative to these issues. BORING LOGS AND10R MONITORING WELL DATA SHOULD NOT BE SEPARATET) FROM THE REPORT. F~ ~~ 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 geotechnic~Ueaviron~~ mP°~' These final logs should not, under any circumstances, be redrawn for inclusion in ~ or other design drawings, because drafters ~Y c:ommit errors or omissions is the transfer process. - To reduce the likelihood of boring log or monitorigg well misinterpretation, contractors should be given ready access to the /metal report prepared or authorized for their use. If access is provided only to the complete geotechnrcal engmeenng that a contractor was not one of the report P for you, yon should advise contractors of the report's limitations, assuming specific persons for whom the report was prepared, and that developing construction cost 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 -ooatractor should discuss the report with your consultant and perform the additional or alternative wrn~k believed necessary to obtain the data specifically appropiate for construction cost estimating pittposes. Some clients hold the mistalaea 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 RESpONSIBH,TTY CLAIISFS CLOSED Because geotechnical/eavironmental engiaeerirg ~ based extensively oa judgment and opinion, it~nsultants. To helt p prevent design disciplines This situation has resulted is wholly unwarranted claims being edged against this problem, consultants have developed a number of clauses for use is 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 recog- nise their individual responsibilities and talae appropriate action. Some of these definitive clauses are lil~ly to appear m Y°»r report, and you one encouraged to read them closely. Your consultant will be pleased to give full and frank ansv~+ers to your questions. The preceding Paragraphs are based oa information provided by the ASFElAssociation of Engineering Firms Practicing in the Geosciences, Silver Spring, Maryland fJ p ^ ^ P i~ a i „o ~