HomeMy WebLinkAboutBLD2005-00557 Geotechnical Report •
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NORTHWESTERN TERRITORIES, INC.
A JLS GROUP COMPANY
717 SOUTH PEABODY STREET,PORT ANGELES,WA 98382
NTI Engineers Land Surveyors Geologists
Construction Inspection Materials Testing
(380)452-8491 FAX 452-8498 www.nii4u.com E-Mail:info@nti4u.com
JLS GROUP,
INC.
Au, 2
July 7, 2005
Gary & Betty Greene r c „ ; c , r bt
c/o Finne Architects —
217 Pine St.
Seattle, WA 98101
Re: Geotechnical Observations of Hand Dug Test Pits for Foundation Design, Tax Parcel #'s
821151005 & 821151006, Located in Section 15, T28N, R1E, W.M. Jefferson County,
WA
Dear Mr. & Mrs. Greene:
Per our proposal letter dated April 21, 2005, we have completed the geotechnical inspection.
and staking of the house, garage and bridge. The location of the garage was moved to the
south side of the property after the surveyors had been to the site and staked it at the north side
of the property, thus the garage stakes are no longer accurate. The test pit for the garage was
located approximately by pacing off of existing features shown on the site plan.
Five hand-dug test pits were excavated to a maximum depth of 4' using posthole diggers in the
proposed location of the house, garage and bridge abutments. The test pits were very similar,
with about one foot of topsoil over sandy soil. The upper two to three feet of soil contained roots
and rootlets. The soil became harder at about three feet. There was some mottling of the soil
suggesting seasonal perched water, and there was water at a depth of—2.4' in the garage test
pit which was dug near the east side of the garage, which is an area of fill according to the site
plan. The postholes were left open and stakes were placed in the holes for future reference if
needed.
To prepare the site to receive foundations, we recommend stripping off vegetation, topsoil, roots
and other deleterious material. The subgrade should be in a firm and unyielding condition.
Loose areas should be compacted to a firm unyielding condition or over-excavated and
replaced with properly placed and compacted structural fill or otherwise stabilized in order to
achieve the desired condition.
The on site sandy soil can be used for structural fill provided that deleterious material is
removed. Preparation for placement of structural fill should include the removal of vegetation,
topsoil and other deleterious material under the proposed fill areas.
Imported structural fill should conform to the specifications for Gravel Backfill for Foundations
listed in Section 9-03.12(1) of the 2004 WSDOT Standard Specifications, or similar material
subject to approval of the engineer. Structural fill should be placed in horizontal lifts not to
exceed 8"thick, with each lift being compacted to at least 95% of the modified proctor value, at
1
near optimum moisture content. Compaction testing should be performed in order to verify that
proper compaction i.s being achieved. NTI can perform this service if requested.
For spread and continuous footings, the recommended allowable foundation pressure for the
native sandy soil is 2000 pounds per square foot (psf) at a minimum depth of 12 inches below
finish grade and a minimum footing width of 12". Local codes should be checked for required
footing depth for frost protection. The lateral bearing of this soil is 150 lbs. psf/ft of depth below
natural grade. These values may be increased by 1/3 when considering load combinations,
including wind or earthquake loads. The lateral sliding coefficient of this soil is 0.25, to be
multiplied by the dead load.
It is also recommended that the ground around the house be sloped to drain away from the
structure. Footing drains are also recommended, but should not be connected to roof drains.
Limitations
This report has been prepared exclusively for your use in conjunction with the above referenced
project. The report has not been prepared for use by others or for other locations. Others may
use it only with the express written permission of the Engineer.
Within the limits of scope, schedule and budget, this report was prepared in general accordance
with accepted professional engineering and geological principles and practices in this or similar.
localities at the time the report was prepared. No other warranty, expressed or implied, is made
as to the conclusions and professional advice included in this report.
The observations, conclusions and recommendations presented in this report were based on
our visual observations of the subject property at the time of our site visit; no laboratory tests
were performed. Soil and geologic conditions can vary significantly between test holes and/or
surface outcrops. If there is a substantial lapse of time, conditions at the site have changed or
appear different than those described in this report, NTI should be contacted and retained to
evaluate the changed conditions and make modifications of this report if necessary.
Sincerely,
NORTHWESTERN TERRITORIES, INC. groN;° of wasyy cy
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Robert A. Leach, P.E., MBA ��a, ,�F�1sT�%'441 777/CS
Principal Engineer ssio EN°
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/�.� Po EXPIRES 12/30/2006
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Bill Payton, L.E.G. . ,.e " "�' '.�,
Engineering Geologist
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!William C. Payton Jr..i
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