HomeMy WebLinkAboutPermit Field Test & Inspection Report 2003-10-10
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K & A Engineering, Inc.
P.O, Box 23624, Eugene, OR 97402
521 Market St., Suite B, Eugene, OR 97402
(541) 684-9399 Voice
(541) 684-9358 FAX
engineering
October 10, 2003
Project: 134.03
Stapleton Timber and Excavation
38141 Place Road
Fall Creek, OR 97438
Subject: Geotechnical Site Evaluation
458 So. 72"d St.
Springfield, OR
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PURPOSE AND SCOPE
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As requested, K & A Engineering, Inc. has evaluated the subject residential building site for suitability to
construct a conventional concrete cast-in-place strip and spread footing foundation supporting a conventionally
wood-framed one or two-story single-family residence. This evaluation includes recommendations for
preparation of the foundation soils to support the foundation.
INVESTIGATION AND FINDINGS
General
Our investigation was conducted at the beginning of excavation operations for foundation preparation. The site
is located on a north-facing slope at the end of a cul-de-sac. The natural ground slope varies between 15 and
20%. There are no indications of slope movement on this lot or other residential lots (most of which are
presently occupied) adjacent to the site.
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Subsurface Soils
Foundation soils revealed in the excavator consisted of 2 to 4-feet of unspecified loose fills (mostly silts and
gravelly silts) over the original ground surface. Soils below the original ground surface consisted of 1 to 3-feet
of moist, moderately stiff, brown plastic silts or tan, saturated, highly plastic clays. Soft, weathered tuff
underlies the plastic silts and clays
Groundwater was not encountered in the excavation, which ranged from 3 to 7 -feet [n depth.
SUMMARY AND RECOMMENDATIONS
General
The existing soils at the site are not suitable for supporting the proposed foundation. The loose fills do not
provide a consistent allowable bearing capacity. The underlying native soft plastic silts and clays are highly
expansive and would likely present a significant hazard associated with consolidation (settlement) over time.
K & A Engineering, IDe,
Foundation Preparation
To make the site suitable for construction of the proposed foundation, we make the following recommendations.
1. The unspecified fill should be removed from the foundation area. These soils are suitable for
landscaping and final grading around the foundation after construction is complete.
2. The underlying plastic sitts and clays should be removed from the site entirely. The site should be
prepared so that the underlying weathered tuff is smooth and undisturbed. Benched excavation is
acceptable to accommodate the natural slope as long as the benches are horizontal and uniform in
grade and width.
3. The foundation area should be brought to the proper grade by placing a coarse select granular fill on the
undisturbed weathered tuff to within 6 to 12-inches of final grade, and covered with a fine select
granular fill to footing grade.
4. A perimeter footing drain should be installed around the back (uphill) and sides of the foundation to
intercept water and route it away from the foundation.
5. We recommend that a crawlspace drain be installed underneath the foundation. This should be
installed at the time that the foundation is constructed.
Specifications
Coarse Select Granular Fill
Coarse select granular fill can consist of a well-graded silty-sandy-gravel pit run or a 3 to 5-inch open graded
crushed quarry rock.
Well-graded pit run should have less than 15% of the material (by weight) passing the no. 200 sieve and no
fragments larger than 4-inches. Well-graded pit run should be placed in layers not exceeding 12-inches and
compacted with a heavy steel-wheeled vibratory drum roller until there is no significant deflection along the
sides of the roller. Moisture content of the pit run should be at or near optimum to avoid pumping of fines from
the material and to promote maximum dry density.
Quarry rock should consist of durable crushed basatt rock having a uniform gradation in the 3 to 5-inch range.
Crushed quarry rock should have 100% fractured faces. Quarry rock should be placed in layers not exceeding
12-inches and well-seated in place with the back of the excavator bucket.
Fine Select Granular Fill
Fine select granular fill should consist of clean, durable, well-graded material with a maximum particle size of 1
1/2-inches and a maximum of 10% passing the no. 200 sieve. Select granular fill shall be placed in layers not
to exceed 12-inches (loose) and mechanically compacted to a dry density exceeding 95% of maximum as
determined by ASTM 0698.
Footing Drain
The footing drain should consist of a 3-inch diameter, continuous perforated pipe placed at the outside of the
bottom of the footing. The perforated pipe should be covered on the sides and top with a minimum of 12-
inches of %-inch to 1 lh-inch clean drain rock covered with a non-woven geotextile. The footing drain should
be routed to the storm drain system and should not be connected to the roof drain system.
Project: 134.03 458 So. 72nd St., Springfield, OR
Client: Stapleton Timber and Excavation
Page 2 of 2
October 10,2003
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K & A Engineering, Inc.
Crawlspace Drain
A minimum of one 3-inch diameter schedule 40 PVC or ABS solid pipe should be placed undemeath the footing
at a low point along the front (north) footing to drain any water that may collect in the crawlspace. The
crawlspace drain may be connected to the footing drain system north of the foundation.
Non-woven Geotextile
Geotextile used to separate the native soils from the footing drain should consist of a light to medium-weight
needle-punched, non-woven polypropylene fabric having an ADS of 70. The fabric should not have any tears or
punctures. Lap the fabric a minimum of 12-inches at the top of the drain rock and at splices.
LIMITATIONS OF THIS REPORT
This report has been prepared for the exclusive use of Stapleton Timber and Excavation and its design
consultants for the subject proposed structure.
This geotechnical investigation, analysis, and recommendations meet the standards of care of competent
geotechnical engineers providing similar services at the time these services were provided. We do not warrant
or guarantee these recommendations, site surface, or subsurface conditions. Exploration test holes indicate
soil conditions only at specific locations (i.e. the test hole locations) to the depths penetrated. They do not
necessarily reflect soiVrock materials or groundwater conditions that exist between or beyond exploration
locations or limits.
The scope of our services does not include construction safety precautions, techniques, sequences, or
procedures, except as specifically recommended in this report. Our services should not be interpreted as an
environmental assessment of site conditions.
Thank you for the opportunity to be of service. Please call us if you have questions or need further assistance.
Respectfully,
EXPIRES
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Michael Remboldt, P.E.
Principle, K & A Engineering, Inc.
Project: 134.03 458 So. 7200 St., Springfield, OR
Client: Stapleton Timber and Excavation
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October 10,2003