HomeMy WebLinkAboutPermit Field Test & Inspection Report 2005-8-22
August 22, 2005
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Mr. Gordon Brei Evans
Aristocrat Homes
84865 Ridgeway Road
Pleasant HIll OR 97455
RE: GEOTECHNICAL ASSESSMENT TL 3200, NW 1/4, NW 1/4, Sec. 2, T 18S, R 3W
Dear Mr. Evans:
I am writing this letter to present the findmgs of our assessment of slope stabilIty and foundatIOn
conditions at the residential lot known as Tax Lot 3200, in the NW 1/4 of the NW 1/4 of SectIOn 2,
T 18S, R 3W, WIllamette Baseline and Meridian. The approximate site location is shown on Figures
1 and 2. The lot is proposed to be developed with a smgle-family residence, which is expected to
be constructed with a daylight-basement garage.
The site was visited on August 16,2005. The site IS located southe?lst of the cul-de-sac off Glacier
:9rive and nod Street. The site is vegetated with grasses, scotch broom, ivy, some blackberries and
'.dRugl5!,~'fir and big leaf maple trees. The overall slope is to the NW at appro~imately 25 %. A
sectio'n~Mras measured upslope from the cul-de-sac, approximately through the center of the property
(figure: '2) ,)f;
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"~;;:E~avation backfill present near the NE property comer at the cul-de-sac indIcate that partly
- dJcomp'6sed rock unit RU-402 (fine-grained sandstone) is located within the depth of that
excavation. A hand auger hole, mstalled in the north-central portIOn of the property (Figure 2),
encountered 2 25 feet of slope wash deposits (SU-B and -C) over completely decomposed RU-402.
Both SU-B and SU-C conSIst of clayey sand WhICh has high to very high dry strength, high toughness
and no dilatancy. From 4.6 to 4.75 feet below grade, a few portIOns of RU-402 were encountered'
which could not be remolded with finger pressure.
1,
Douglas fir trees at the site are mostly straight or have trunks with long down-slope swept lower "
portions (see site photos, attached). No evidence of previous, large-scale slope movement (c1osed- ' "
contour depressions, low-sloping benches, back-rotated trees, sag ponds, disrupted drainage,
etc.) was observed at the site or in the immediate vicinity.
Based on the dry strength and toughness properties of SU-B and the matrix of SU-C, it is probable
that the fines consist of fat clay (CH) and that these SOlI units are expanSIve. The curved lower
sections of the fir trunks are consistent WIth this assessment. As a result, it is recommended to
remove these units from beneath all areas which will be used for bearing or placement of structural
/'
fill.
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,/'
"
P.O. Box 2238, Eugene, OR 97402
(541) 607-5700 FAX: 607-5701
CCB # 127073
Mr. Bret Evans
August 22, 2005
Page 2
RU -402 IS sUItable for placement of shallow spread footings. In the absence of further mformation
regarding strength of the material, footings should be designed for bearing pressures of no more than
1,500 psf. It is probable that significantly higher beanng capacity is available on partly decomposed
RU-402, but thIS would need to be venfied after completion of at least a partial foundation
excavation
Due to the probable expansive properties, SU-B and -C should not be utilized for structural
fill. It may be possible to utilize excavated RU-402 as structural fill, but this optIOn is limited to dry-
weather construction
Permanent cut slopes in SU-B and -C, and in CDS RU-402 should be sloped at no steeper than 2H
: 1 V, and the tops should be rounded to prevent mmor sloughing. Temporary cut slopes in all these
units can be sloped at 1 H : 1 V. Permanent cut slopes in partly decomposed RU -402 (where less than
50 % of the material can be remolded with finger pressure) can be sloped at 1.5 H : IV.
Because shallow groundwater is expected to be perched on RU-402 during the wet season, it is
recommended to install foundation drainage on the up- and side-slope sides of the foundation. Such
drainage should consist of a trench excavated into the perimeter of the foundation pad, at least 6
inches below the level of the rest of the cut, sloped to drain, lined with filter fabric and backfilled
with open rock A rigid, perforated pipe with glued Joints should be placed in the bottom of the
trench. The trench should be backfilled WIth open rock to within 12 inches of the finished grade, and
the filter fabric draped over the rock The trench can then be backfilled to grade with soils suitable
for landscaping. The drainage pipe can eIther be day-lighted down-slope or directed to the cul-de-sac
and storm drainage system.
If you have any questions regarding this matter, please do not hesitate to contact me at 607-5700.
Sincerely,
GeoSCIence, Inc.
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/ Gunnar Schlieder, Ph.D, CEG
att: Location Map, Site Map, Field-Developed Section, Hand
170 E
Name SPRINGFIELD
Date 8/22/2005
Scale 1 lOch equals 2000 feet
Location 044002' 104" N 122053' 37 9" W
Caption Figure 1 Location Map
Copynght (C) 1997, Maptech, Inc
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Figure 2: Site Map and Section Location
Portion of Tax Lot Map. Not to Scale
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.I." u 1/41'1" 1/4 Sec. 2, T 18S, R3W, TL 3200
Figure 3: Field - Developed Geologic Section
Scale (ft.) as Shown
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