HomeMy WebLinkAbout935100007 Geotech AssessmentS r
GeoResources, LLC
Ph. 253-896-1011 5007 Pacific Hwy. E,, Snits 20
_: _ , _l~. 25~-896-~~33 Fife, Washigntoa 98424.
._ --
;,
----- - January 17, 2005
Mr. Terry Ellingson ~ ~Y ~ ~ 2t~"^ ~
Ms. Elaine Morgan , .
____
5145 NW EI Camino Boulevard `
Bremerton, Washington 98312; . _ ..~_-___..____
Geotechnical Evaluation &
Design Report
Lot 8, Division 5, Bridgehaven
Thomdyke Road
Jefferson Courrty, Washington
Job No. EAingson.Thomdyke.01 RG
INTRODUCTION .and SCOPE
This geobechnical report presents the results of our geotec~nical evaluation of the above
referenced krt to provide geobechnical design criteria and recommendations for the proposed single-family
residential development at the above r+efenenced site. The project site is located at Lot 8, Division 5 of
Bridgehaven, in unincorporated Jefferson County, Washingthn. The site is generally situated in the South
Point area of Jefferson County, akmg Hood Canal, east of the intersection Finch Lane and Thorndyke
Road. The bcation of the site is shown on the Vidnily Map, Figure 1.
Our understanding of the project is based on our discussions with you, our sibs observations and
test pit, our experience in the area and our review of the data provided. We understand that the site
development will consist of a single famiy residence on the lot. Development at the sibs will induct the
typical associated utilities and driveway. Based on our site observations and discussions with you, grading
at the site will be assoaated with construction of the driveway and excavation of the foundatiorVdriveway
areas. The general. layout of the site is illustrated in the Site Plan, Figure 2.
The proposed residential structure will be situated to take advantage of the grade changes at the
site, which are well suited to conventional daylight basement construction. The site ~s bounded by
established residences bo the north and south, with Thomdyke Road terming the wesbem properly margin.
The site consists of a relatively level upland area where the residence is proposed. The upland area
abuts a steep slope area which descends th the east. Access to the proposed house site will be from
Thomdyke Road to a proposed garage which will be located below the proposed residence on the north
side of the residence.
Sbpes in the eastern portion of the site exceed 30 percent, with maximum relief well in excess of
10 vertical Beet. The purpose of our services is fn evaluate lire sibs soils and groundwater condations as a
basis for assessing the aidc:al areas, potential landslide, seismic and erosion hazards, at the site, and to
develop geotechnical recommendations and design criteria for the proposed site development.
Specifically, our scope of services for this project includes the foibwing:
1. Review the available surface and subsurface soil and ground wathr information. including the
existing geotechnical and per+o-hole data, Washington DOE maps and Jefferson County Soil
Conservation Service documents.
2. Visit the site and conduct a geologic reconnaissance to assess the site's slope, soil and ground
water conditions.
3. Evaluate the shallow subsurface conditions at the site by monitoring the excavation of best pits at
the building site.
4. Provide geobec~nicai recommendations for site grading inducting sith preparation, subgrarde
preparation, fiU placement criteria, suitabilit)r of on-site soils for use as stnx~ural fill, temporary and
permanent cut and fill slopes, drainage and erosion control measures.
EllingsoNMorgan-Triomdyke
January 17, 2005
Page 2
- - - 5. Provide recommendations and design criteria for foundaition and floor slab support, including
alk~nrable bearing capacity, subgrade modulus, lateral resistance values and estimates of
settlement.
6. Provide recommendations and design criteria for the design of conventional subgrade/retaining
(basement) walls, including backflll and drainage requirements, lateral design loads, and lateral
resistance values.
SITE CONDITIONS
SURFACE b GEOLOGIC CONDITIONS
The site is located in the South Point area of Jefferson County. The bt is an imegularrly shaped
pamel that measures 88-feet abng Thomdyke Road by 230 to 244-Beet Est to Mrest. The bt width tapers
to the and is only 52-feet wide at the eastern property margin. The steeper slopes in the eastern
portion of the site appear bo be related to sheep soils that formed on canyon slopes and oc~n bluffs. The
upland materials are deposits that likely formed in outwash and are somewhat excessivey drained, The
relative topography of the site area is shown on the Site Plan, Figure 2. Areas with slopes of 15 to 29
percent, and the local slope area in excess of 30 percent are illustrated on Figure 2.
The upland portion of the sib is currently vegetated with scattered timber and locally. dense brush
undergrowth. The trees consist of a mix of evergreen and madr+ona. No evidence of erosion was
observed at the site at the time of our site observations, particularly where the vegetation is established.
The slope area below the proposed home sibs is densely covered with k~- brush. No shaik~w groundwater
seepage and/or surface flow was observed in the portion of the site where the home site is proposed.
Based on our data review (available geologic and geobechnical data), our geologic
reconnaissance of the stte area, our test pit excavations, review of pert best hole data provided to us, and
our experience in the arm, the shallow soils at the site likey consist of outwash sand with a trace gravel.
These soil ukey were deposited over glacially consolidated deposits (tit or hardpan and outwasn
material) and interglacial sediments.
Recessional outwash soils were deposited as the glaaal ice retreated and are typically medium
dense. These surfic:ial soils were deposited subsequent to the Fraser Glartiation, some 12,000 bo 15,000
years ago. Below the recessional deposits, glacialy consolidated sale are typically present. Vashon
glacial till was deposited at the base of the advancing glacial ice and is in a very dense condition where
undisturbed. Advance outwash material was deposited by mellwaber from the advanang glac'r~~l ice, and
subsequently over-ridden by the glaaal ice. The advance ouiw2rsh soils are likewise in a dense condition,
except where disturbed by weathering a previous grading activity. No significant intersecting geologic
contacts were observed in our test pit excavations or the open per+o•hdes at the site. Shaiksw
gr+a~ndwater and surface seepage was not observed in the test holes advanced in the building. or septic
drainfiekl areas. No evidence of surficial erosion was observed at the sibs at the time of our site visits,
particularly where vegetation is well established.
SITE SOILS
A review of the Soil Survey of Jefferson County (Sal Conservation Survey) indicates that the site
eels consist of Everett gravelly sandy loam (0 bo 15 per cent) in the upland area abutting Cassolary sandy
kram (30 bo 50 percent). The Everett sacs are generally derived from sandy glacial outwash eels and
consist of somewhat excessively well~lrained sands. Based on the SCS data, the Everett soils have a
slight bo moderate erosion hazard. The steeper Cassolary deposits have a severe erosion hazard.
SUBSURFACE EXPLORATIONS
Subsurface conditions at the site were evaluated by observing the exposed sacs in pert holes
excavated on site and observing 2 test pit excavated in the proposed building area, reviewing the available
geologic and geobechnical data for the sibs area and our site reconnaissance. The pert holes were
excavated in 4-locations west of the home in the proposed location of the on-sibs septic drainfield. Two
additional test pit was excavated near the proposed building area. The perc-holes extended b~ a
maximum of about 4-feet below ground surface (bgsj, while the best pits were extended to 6.5 to 7-teet
bgs. Uniform and favorable sale were disclosed at all locations explored. Site soils generally consist of a
layer of topsoil above moist red-brown grading ~ Ight brown fine bo medium sand. The light brown sand
EHingsoNl~Aorgsu~-Thomdyke
January 17, 2005
Page 3
-induded~a trace of gravel. _ _,. _
No groundwater was encountered within the depths explored, and the sidewalk of the best pit
were stable. Based on the conskbent nature of the soil conditions encountered in the pert holes and test
pit, and our previous experience in the area, it k our opinion that no additional excavations or borings are
required to d~aracterize the sibs soils or evaluate their stability.
The outwash soils were in a medium dense to dense condition, except where disturbed by
surficial weatiiering. No ground water seepage was observed in our explorations. Groundwater conditions
may vary wtih changes in preapitation, changes in site utilization, and other factors.
CONCLUSIONS
GENERAL
Based on the results of our sibs reconnaissance, data review, subsurface explorations and our
experience in the area, it k our opinion that the sibs k suitable for the proposed single-family residential
development. The construction of the daylight basement structure would provide additional stability in the
building areas with skoping surfaces. Grading at the site will generally occur in the wesbem and
southwesbem portions of the site associated with excavations for foundations and the driveway. Based on
the soils encountered and our understanding of the proposed site devebpment, conventional earthwork
and foundation support k feasible at the site. Conventional foundation support may be utilized for the
stnrdure. Pertinent conclusions and geobechnical recommendations regarding the design and
construction of the proposed. devek.prrrent are presented bek.w.
SEISMIC -LIQUEFACTION
According to the Seismic Zone Map of the United States contained in Fgure 16-2 of the 1997
UBC (Uniform Building Code), the project site k located within Seismic Risk Zone 3. Based on the
subsurface conditions observed at the site, we interpret the site conditions to oomespond bo a seismic Soil
Profile type Sp, for Dense Sal, as defined by Table 16-J (UBC), or as Site Class'D' in the 2003 IBClIRC
building code documents, in acxordance with Table 1615.1.1. This k based on the inferred range of SPT
(Standard Penetration Test) bkriv courts relative bo test pit excavation progress and probing with a i4-inch
diameter steel probe rod. The shallow sal conditions were assumed to be representative for the site
conditions beyond the depths explored.
Based on our review of the subsurface conditions, we conclude that the site soik are not
susceptible bo liquefaction. The near-surface sa'k bek>ar the upper weathered sak are generaly in a
medium dense to dense condition, and are likey underlain by very dense gkaedy overridden sotis, and
the static water table k located well bek.w the sibs. Shaking of the already medium dense soil k not apt to
produce a denser configuration and subsequently excess pore water pressures are not likey to be
produced. Calection of the shaik.w perched groundwater in the south and west central portions of the site
will improve overall stability at the site.
LANDSLIDE HAZARD
CiassiAcatlon
Portions of the project site are bcabed in an area mapped as'Unstable" by the Washington State
Department of Ecology in the Coastal Zone Atlas. In addition, based on the proximity of the steep slope to
the east, and previous repeated landslide activity ~ with retaining wa8 construction on a nearby
property, we understand that Jefferson Courrty has designated the project vicinity as a landslide hazard
overlay area. The writer was involved in the forensic evaluation of the previous landslide activity which
oaxrmed several properties north of the subject property. Based on that work, the landslide activiitr at the
nearby site was triggered by the construction of a bin wall which was bc;abed bek.w the residence and on
the steep descending slope bebw the home. That kocalized slide area was repaired by the construction of
a series of short timber walk extending full height up the slope which restored the sk>pe and k intended to
profiect against further erosion and loss of ground.
The sak in the flatter portion of the site where. the residence will be constructed are mapped by
the SCS (Jefferson County Soil Caoservation Survey) as Everett graveNy sandy loam. The limitations for
home site relate to the rrroderabey sheep th steep soik. Based on the above, we conclude that the site
does the meet the technical criteria for a landslide hazard area.
Euingson/Morgan-Thomdyke
January 17, 2005
Page 4
EROSION HAZARD
The building site on the subject lot is looted in an area mapped by the Soil Conservation Service
as Everett gravelly sandy loam. The erosion hazard for these soils is slight tD moderate. However, the
stepper Cassolary soils comprising the slope below the home are rafted as a severe erosion hazard.
It is our opinion that the potential erosion hazard of the site is not a Nmiting factor for the proposed
residential development The proposed-new home would be set bads from the edge of the steep slope by an
appropriate buffer (greater than 30fieet). Removal of natural vegetation should be minim¢ed and limited to the
active oonstnx~ion areas, except for the removal of hazard trees in proximity b the break in slope. Temporary
and permanent erosion contrd measures should be installed and mcntained during oa>stnxition or as soon as
practical thereafter tD Umit the additional influx oft wafter bo exposed areas and probed potential receiving waters.
Erosion control measures should include but not be limited th berms and swales with cf>ecc dams to
channel surface water runoff, ground cover/protection in exposed areas and silt fences. Graded areas
should be shaped th avoid concentrations of runoff onth cut or fill slopes, natural slopes or other erosion-
sensitive areas. Temporary ground ever/protection such as jute or excelsior matting, wood chips or plastic
sheeting should be used until permanent erosion protedaon is established.As pt~wiarsly discussed,
weathering and erosion are natural processes that affect steep slope areas. As Hated, no evidence of surfidal
raveling or sloughing was observed on site. To manage and reduce the potential risk for these natural
processes, we r+eoornrrrend the foAowing:
• No drainage of concentrated surface wafter or sgnificant sheet flow onto or near the slope area.
• Replanth~egetabe distrirrbed slope areas outside of the building omits with deeply rooted low vegetation.
• Install erosion control measures (as described above) as soon as practical in the disturbed building area.
We expect this will include conventional moping and erosion pr+oberfion.
Building Setritirck
Jefferson County requires a building setback and buffer area fran aU landslide and erosion hazard areas.
The butler distance i s calculated based on the vertical height of the slope. Albemativey, a stnrctural setback
may be recommended by a licensed geobechnik:ad engineer. Vegetation in the buffer may be enhanced, if
approved or required. Cl~ring, grading and Bing within the setback area is alieowed if ti can be demonstrated
that the buffer vegetation wiU not be adversely impacted, or if the anpads can be mitigated.
Based on our geobedrnik~l evaluation of the site, we reoommerrd a Structural Setback of 30 Beet
where footings wUl be fourxled in the medium dense native soils. The Stuctural Setback maybe measured
horizontally from the bottom of the footing to the face of the slope where slopes are 30 percent or steeper, as
described in the "Buyer Modification' section of this report.
Buffer Modifkatlon
Where necessary, the Structural Setback may be measured from the bottom of the footing to the
face of the steep skape, in accordance with UBC/ IBC. Where the Setback tlAodific~tion is utilized, the.
foundation elemenrts should be extended vertically th meet the recommended setback criteria. This
modification is based on the foundation elements extending m and being founded in medium dense th dense
soils. Maintaining the prescribed setback in this manner provides the conventional 2 m 1 bearing prism. A
schematic section is provided as Figure 6.
Roadways and driveways are exempt from the Building Seti~adk criteria. Conventional eartlrnroric
guidelines should be utilized with the recommended geobachnical design criteria for cuts and fills in the
roadway and driveway areas, as described in the "Earthwork Section" of this report.
As previously discussed, weati~ering, erosion and the resulting surficc sloughing and shaNow
IandsUd'atg are nature prokx that affect steep sops areas. As noted, lok eviderroe of surfik~al
raveling and riling were not observed in the steeper portions of the sibs owing bo the dense ground oov~. To
mitigate and neduoe the potential for these natural processes to became exacerbated, we recommend the
fdbwing: No drainage of concentrated surface water or significant sheet flow onto or near the slope area.
Drainage from the roof and driveway area should be collected and tighti~ted ib the site's on-sibs infiltration
system, or sheet flowed to densely vegetated portions of the site.
ENingsonlAAorgsn-Thomdyke
January 17, 2005
Page 5
__ _
`~ No' png within the sefbadk zone unless retained by engineered retaining wars or as a
monitored and engineered fill.
• No penalation of surface water within 30 feet of the top of the steep slope unless the seepage rate is
controlled tp a slow seep (s~nnilar bo septic systems).
FJIRTHWORK
Site Preparation
Grading at the site is expected to be limited to and generally associated with construction of the
driveway and excavation for the garage and residence. Depending on site grades, we anticlpate the
garage floor will be constricted below existing sibs grades, requiring the construction of
retaining/basement walls around the perimeter of the garage. The house would be constructed one story
above the garage elevation. All areas to be graded/excavated should be cleared of deleterious matter
including any existing stnxrtures, foundations, abandoned utility lines, debris and vegetation. Graded
areas should be stripped of any forest duff and organic-laden soils.
Based on our explorations, we estimate that stripping on the order of 5 to 8 inches will be
necessary to remove the root zone and surfic:iaal soils containing significant organic materials. Areas with
deeper, unsuitable organics should be expected in the viclnity of depressions, steep slopes or heavy
vegetation. Stripping depths of up to 2.5 feet may ocx+ur in these areas. These organic materials may be
stockpiled and later used for erosion control and landscaping/revegetation. Materials that cannot be used
for landscaping or erosion control should be removed from the project sibs.
Existing areas of uncontrolled fill material, if present, below proposed final grades of the future
home site or project improvement areas, should be removed and recompacted in accordance with the
recommendations provided in this report.
Where placement of fill material is required, the exposed subgrade areas should be oompaded to
a firm and unyielding surface prior th placement of any fill. We recommend that trees be removed by
overturning in fill arms so that a majority of the roots are removed. Excavations for tree stump removal
should be badcfiRed with stnx~ural fill compacted to the densities described ~ the "Sducturai Fiil"
section of this report.
Any soft, loose or otherwise unsuitable areas delineated during proofroliing or pn~bing should be
reoomparbed, if practical, or overexcavated and replaced with structural fiN, based on the
recommendations of our sibs representative.
Sb~uctural Fill
All fill materiaVtrerx;h backfill should be placed as structural fill. The struc~trral fill should be placed
in horizontal lifts of appropriate thickness bo allow adequate and uniform compaiction of each liftft. Fill
should be compacted th at least tlt5 percent of MDD (maximum dry density as determined in acxordance
with ASTM D-1557).
The appropriate bft thidkness will depend on the fill characteristics and carrrpaction equipment
used. We recommend that the appropriate lift thickness be evaluated by our field representative during
construction. We recommend that our representative be present during site grading activities th observe
the work and perform field density tests.
The suitability of material for use as structural fill will depend on the gradation and moisture
content of the soil. As the amount of fines (material passing US No. 200 sieve) increases, soN becomes
increasingy sensitive to smaN changes in moisture content and adequate compaction becomes mare
difficult th achieve. During wet weather, we recommend use of weq~raded sand and gravel with less than
5 percent (by weight) passing the US No. 200 sieve based on that fracion passing the 3/4-inch sieve. If
prolonged dry weather prevails during the earthwork and foundation installation phase of construction, a
somewhat higher (up to 10th 12 perti;ent) fines content will be acceptable.
Material placed for structural fiN should be free of debris, organic matter, trash and cobbles
greater than 6 inches in diameter. The moisture content of the fill material should be adjusted as
necessary for proper compaction
ENingsonlMagan-Thorndyke
January 17, 2005
Page 6
SuitaWifiy ofi On-Silts lilsrterials as Ffll _ ___ _,,.,,, ,_ _ ._
During dry weather construction, any nonorganic on-site soil may be considered for use as
structural fiN, provided it meets the criteria described above in the structural fill section and can be
compacted as recommended. If the material is over-optimum moisture content when excavatied, it will be
necessary fA aerate or dry the soil prior to plaoernent as structural fill. Many of the soils encountered in
our test pits appeared near optimum moisture content
The woricability of material for use as slnxx~ural fill will depend on the gradation and moisture
content of the soil. As the amount of fines increases, soil becomes increasingly more sensitive to small
changes in moisture content and adequate compaction becomes more difficult or impossible th achieve.
The soils at the site generally consist of fine th medium sand with trace gravel. These soils are
comparable to Class A "pit run' material and will be suitable for use ~ strtrctrual fdl provided the moisture
content is appropriate. Any organic the soils should be stockpiled and treated in a similar manner as the
topsoil strippings.
All fill material in the budding and driveway areas should be placed as described in the
"Structural Fill" section of this report and compacted to at least 95 per+oent of the MOD. If fiN material is
imported to the sibs for wet weather constnrction, we recommend that it be a sand and gravel mbcture such
as huh qualify pit run with ass than 5 peroent fines.
CUT AND FILL SLOPES
AN job sibs safety issues and precautions are the respatsibility of the contractor providing
services/work. Temporary cut slopes will likely be necessary during grading operations or utility
installation. As a general guide. temporary slopes of 1.5 to 1 (horizontal to vertical) or flatter maybe used
for temporary cx~ts for the site sods in a medium dense condition. Should ground water seepage be
encountered, such as in proximity to the drainage swale, flatter temporary slopes may be required.
These guidelines assume that aN surface loads are kept at a minimum distance of at least one
hall the depth of the cut away fr+an the top of the slope and that significant seepage is not preserrt on the
slope face. Flatter cut slopes will be necessary where significant raveling or seepage occurs.
We recommend a maximum slope of 2 bo 1 for permanent cut and fdl sbpes in areas of medium
dense sand and gravel. Where 2 to 1 slopes are not feasible in these soils, retaining structures should be
considered. Where retaining stnx~utes are greater than 4feet in height (bottom of footing th top of
stnx~ure) or have slopes of greater than 15 peroent above them, they should be engineered. In areas of
dense bo very dense undisturbed glaaad till, permanent cut slopes of 1.5 to 1 may be constnx~ed. It
should be recognized that sbp~ of this nature do ravel and require occasional maintenance. Where
raveNng or maintenance is unacceptable, vre recommend that fiatber slopes or retaining systems be
considered. -
Fill placed on slopes that are steeper than 5 to 1 should be "keyed" into the undisturbed native
soils by cutting a series of horizontal benx~es. The benches should be 1 ~4 times the width of equipment
used for grading and a maximum of 3 Beet in height. Subsurface drainage may be required in seepage
areas. Surface drainage should be directed away from all slope faces. Sane minor raveling may occur
with time. All disturt~ed areas should be vegetated or otherwise protected as soon as practical to facilitate
the devebpment of a protective vegetative layer or establishment of a permanent erosion protection.
FOUNDATION SUPPORT
We recommend that spread footings for any residence be founded on medium dense or denser
native soils or on structural fitll that extends bo suitable native soils. The soil at the base of the excavations
should be disturbed as little as possible. Ali loose, soft or unsuitable material should be removed or
recompac~ed, as appropriate. A representative from our firm should observe the foundation excavations
to determine ff suitable bearing surfaces have been prepared, particxrlariy in the areas where the
foundation will be situated in fill material. We rerxammend that daylight basement structures be
considered for the site. All exterior footing elements should be embedded at least 18 inches bek~r grade
for frost protection. Where foundation elements are located near slopes of 15 peroent of more, the
footings should be located a minimum of 2 times the footing width from the slope farce (trorizontaly), and
founded in medium dense or denser native soils or property prepared structural fill.
We recommend a minimum width of 2 feet for isolated footings and at least 16 inures for
continuous wad footings. Footings founded as described above can be designed using an allowable soil
EHingsoNMorgan-Thomdylce
January 17, 2005
Page 7
ng capacity , _ _.
ri of 2000 psf (pounds per square foot) for combir~d dead and bng-teim-live roads. The
weight of the footing and any overlying backfill may be neglected. The allowable bearing value may be
ink:reased by one-third for transient loads such as those induced by seismic events or wind loads.
Lateral loads may be resisted by friction on the base of footings and floor slabs and as passive
pressure on the sides of footings. We recommend that an allowable coefficerrt of friction of 0.35 be used
to cakwlate frik~ion between the concrete and the underlying soil. Passive pressure may be determined
using an alkwYable equivalent fluid density of 300 pcf (pounds per cubic foot). Factors of safety have been
applied to these values.
We estimate that settlements of footings designed and construted as recommended will be less
than 1 inch, for the anticipated load conditions, with differential settlements between oorrrparably kraded
footings of 1/2 inch or less. Most of the settlements should occur Hy as loads are being applied.
However, disturbance of the foundation subgrade during constnaction could resuR in larger settlements
than pr+edicbed.
FLOOR SLAB SUPPORT
Slabs-on~rade (garage or fbor) should be supported on medium dense or denser native soils or
on structural fill prepared as described in the Sbuctural FIII section of this report. We recommend that
floor slabs be directly underlain by a minimum flinch thickness of coarse sand and/or gravel containing
less than 3 percent fines. The drainage material should be placed in one lift and compacted to an
unyielding condition.
A syntl~edc vapor barrier is r+scommended for the control of moisture migration through the
slab, in particular where adhesives are used to arxthor carpet or file fio the slab. A thin layer of sand may
be placed over the vapor barrier and immediately bekriv the slab to protect the liner during steel and/or
concrete placement.
A subgrade modulus of 400 kcf (kips per cubic foot) may be used for floor slab design. We
estimate that settlement of the floor slabs designed and constructed as recommended, will be 1/2 inch or
less over a span of 50 feet.
SUBGRADE AND RETAINING WALLS
The lateral pressures acting on subgrade and retaining (basement) walls will depend upon the
nature and density of the soil behind the wall. ff is also dependent upon the presence or absence of
hydrostatic pressure. If the walls are backfilted with granular weh-drained soil, the design active pressure
may be taken as 35 pcf (pounds per cubic foot) equivalent fluid density. This design value assumes a
level badkskape and drained conditions as deskxibed bek>w. The design for ak~ive pressure assumes the
walls can yield 0.001 times=the wall height Stiffer walls, or walls restrained from movement by
diaphragms or floors, should be designed to resist at-rest pressures of 50 pcf.
Positive drainage, which controls the development of hydrostatic pressure, can be accomplished
by placing a zone of coarse sand and gravel behind the walls. The granular drainage material should
contain less than 5 percent fines. The drainage zone should extend horizontally at least 18 inches from
the back of the wall. The drainage zone should also extend from the base of the wall to within 1 foot of the
top of the wall. The drainage zone should be compacted to approxirnatiely ti0 percent of the MDD. Over-
compaction should be avoided as this can Ind to excessive lateral pressures.
A perforated PVC pipe with a minimum diameter of 4 ink~es should be placed in the drainage
zone abng the base of the wall to direct accumulated water to an appropriate discharge location. We
recommend that a non woven geatextile finer fabric be placed between the drainage material and the
remaining wall backfill to reduce silt migration into the drainage zone. The infiltration of silt into the
drainage zone can, wdh time, reduce the permeability of the granular material. The filter fabric should be
placed such that it fuly separates the drainage material and the backfiN, and should be extended over the
top of the drainage zone.
Lateral loads may be resisted by friction on the base of footings and as passive pressure on the
sides of footings and the buried portion of the wall. We recommend that an allowable coefficient of friction
of 0.35 be used th cak:ulate friction between the conkxete and the underlying soil. Passive pressure may
be determined using an allowable equivalent fluid density of 300 pcf. Factors of safety have been applied
to these values.
ENingsonl~Aorgan-Thomdyke
January 17, 2005
Page 8
PAVEMENT or DRNEWAY SUBGRADE
We recommend that pavement and/or driveway slab subgrades be prepared in accordance with
the previously described site preparation and stnidural fill nrcommendations. The upper 2 feet of
roadway subgrade should have a density of at least 95 percent of the MDD (ASTM D-1577).
SITE DRAINAGE
Ali ground sur'faoes, pavemerrts and sidewalks should be sbped away from the r+esidenoe and
assoaabed structures. Surface weber runoff should be controlled by a system of curbs, beans, drainage
swales, and or catbch basins, and dispersed into vegetated auras, or conveyed m the site's sliorrrnwaber
infiltration system. We reoornmend that conventional roof and footing drains be instaged for aN structur+es.
Drains should be provided behind all retaining waNs. The roof drain should not be connected th the footing
drain unless an adequate gradient wfil prevent a surnharge of the tvobng drain. Coed stortrnWaber should
be directed bo the site's stomnNater system. The system bcation has yet th be determined. IdeaYy, scam
water should be tightiined to the base of the hiN side. However, that wdl result in some disturbance bo the
sensitive slope area below the proposed home. Altentativey, as discxassed earlier, sborrnwater may be
infiltrated. No drainage of concentrated surface weber or sgnific;arrt sheet flow onto or aver the slope area
should be albwed. Drainage from the driveway area should be sheet flawed th the adjacent vegetated
portions of the site. No peroolation of surFace water within 30 feet of the top of the sheep sbpe uMess the
seepage rate is controlled b a sbw seep (similar to septic systems).
EllingsonAlAorgan-Thomdyke
January 17, 2005
Page 9
uMfTa~nofvs
We have prepared this report for use by Mr. Terry Ellingson and Ms. Elaine Morgan, and
members of their design team, for use in the design of a portion of this project The data used in
preparing this report and this report should be provided to prospective contractors for their bidding or
estimating purpcees only. Our report, conclusions and interpretations are based on data from others and
limited site reconnaissance, and should not be construed as a warranty of the subsurface conditions.
Variations in subsurface conditions are possible between the expbrations and may also occur
with time. A contingency for unanticipated conditions should be included in the budget and schedule.
Sufficient monitoring, testing and consultation should be provided by our firm during construction th
confirm that the conditions encountered are consistent with those indicated by the expbrations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether earthwork and foundation installation activities compy with contract
plans and specifications.
The scope of our services does not include services related to environmental remediation and
construction safety precautions. Our recommendations are not intended to direct the oontractor"s
methods, techniques, sequences or procedures, except as specificaly described in our report for
consideration in design.
If there are any changes in the kaads, grades, kx~tions, configurations or type of facll'Ities to be
constructed, the conclusions and recommendations presented in this report may not be fully applicable.: If
such changes are made, we should be given the opportunity to review our recommendations and provide
written modifications or verifications, as appropriate.
Within the limitations of scope, schedule and budget, our services have been executed in
accordance with generally accepted practices in this area at the time this report was prepared. No other
conditions, express or implied, should be understood.
Respectfuly submitted,
~`. G~
. I~r.~t,r,
~`~~,.~
E7eP~+.~ 1{(0 ! ~
Brad P. Biggerstaff, RPG Kurt Groesch, PE
Princlpat Principal
BPB:KG:kwwO
DoGD:Ellingson.Thomdyke..01 RG
Attadtmerns
G~ADLEY P. ~1GG~RSTAF~
GeoResources, LLG
5007 Pacific Highway Fist, Sure 20
Fife, W~hingUon 98424
Phone: 253-896-1011
Fax: 253-596 2633
Figure 1: Site vicinity Map
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JEFFERSON COUNTY AREA, WASHINGTON - SHEET NUMBER 62
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s fc ~ ~ o :~
5000 4000 3000 2000 1000 0 :~-3G -.
c..'~..~ . ~mm~
Figure 3: USDA SCS Map
SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS GROUP GROUP NAME
SYMBOL
GRAVEL CLEAN GW WELL-GRADED GRAVEL, FINE TO COARSE GRAVEL
GRAVEL
COARSE GP POORLY~RADED GRAVEL
GRAINED Moro than 5096
SOILS Of Costae fraction GRAVEL GM SILTY GRAVEL
R
t
i
d WITH FINES
on
e
a
ne
No. 4 Sieve GC CLAYEY GRAVEL
SAND CLEAN SAND SW WELL-GRADED SAND, FINE TO COARSE SAND
M
th
50%
oro
an
Retained on
No. 200 Sieve
SP
POORLY-GRADED SAND
Moro than 50%
OF Coarse Fradan SANG SM SILTY SAND
Passes WITH FINES
No. 4 Sieve SC CLAYEY SAND
SILT AND CLAY INORGANIC ML SILT
FINE
GRAINED ~ CLAY
SOILS Liquid Limit
Less than 50 ORGANIC OL ORGANIC SILT, ORGANIC CLAY
SILT AND CLAY INORGAWIC MH SILT OF HIGH PLASTICITY, ELASTIC SILT
Note than 50%
Passes CH CLAY OF HIGFt PLASTICITY, FAT CLAY
No
200 Sieve
. ~~ LJmk
50 or moro ORGANIC OH ORGANIC CLAY. ORGANIC SILT
HK3HLY ORGANIC SOILS PT PEAT
NOTES:
1. Field classification is based on viwal examinatbn of soil
in general aoc~rdanoe with ASTNI D2488-90.
2. Soil classification uekq laboratory bells is based on
ASTM D2487~0.
3. Description of soY density a cortsistierxy sro based on
interpretation of blow count data. viswl appearance of
soils and or best data.
SOIL MOISTURE MODIFIERS:
Dry- Absence of moisWro, dry to the Much
Moist- Damp, but no visible weber
Wet- Visible free weber or saturated, usualy mil is
obtaMed from below weber table
GeoResourCes, LLC SOIL CLASSIFICATION SYSTEM
5007 Paafic Hwy. E, Ste 20
Fife, Washington 984242648
Ph.253-896-1011
Fx. 253-896-2633 FIGURE 4
TEST PR LOGS _
MORGANIELLNVGSON RESIDENTIAL SRE
LOT 8, DMSION 5 BRfIDGEHAVEN, OFF THORNDYKE RD
JEFFERSON COUNTY, WASHINGTON
TEST PR 1 -See Fgure 2
R) Sad T
0.0 - 1.0 Topsoil
1.0 - 2.5 SP Rd/Bm SAND w/ silt and occ gravel (boss tD med dense, moist)
2.5 - 6.0 SP Bm SAND w/ occ gravel (hose to med dense, moist)
6.0 - 7.0 SP Bm SAND w/ occ gravel (med dense, moist) (small roots do 2.5')
No caving observed
No groundwater seepage observed
TEST PR 2 - See figure 2
DeMh (ft1 Soil Type Description _...
0.0 - 1.0 Topsoil
1.0 - 2.0 SP RdBm SAND w/ silt and ooc gravel (hose to med dense, moist)
2.0 - 5.0 SP Bm SAND w/ ooc gravel (hose ~ med dense, moist)
5.0 - 6.5 SP Bm SAND w/ occ gravel (med dense, moist) (small roots do 4')
No caving observed
No groundwater seepage observed
Conven#ionai Footing
,~
~ ~ i R~ridontlai
~, S~
Siop+~ Qnsa~er : ~ ~ ~ Fe~undsgon
Than 3(1 Peru gk p ~ ~ ~ Ets~r~nt-
Footing Exfnnston or Pile Support
. (~ Restdei'ttlal
~~
SIoPe:GneebeN`
Than 3o P
~.
G~oRssources
'~ Footing a: c3rads-n~: .
Footing or Pilitt~
Extension
STRUCTURAL SETBACK
FIGURE 6