HomeMy WebLinkAboutPermit Correspondence 1997-5-1
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GEM CONSULTING, INC.
Geologic. Environmental, & Mineral Resource Consulting
P.O. Box 23635, Eugene, OR 97402-0430
(541) 686-1227, Fax 686-2411
May 1, 1997
Mr. Kevin Hare
Hammertime Construction
5729 Main Street #335
Springfield OR 97478
RE: SOILS INVESTIGATION, 683 CASCADE, SPRINGFIELD, OR.
Dear Kevin:
This letter serves to report the findings and recommendations regarding the placement of
the residential home foundation at 683 Cascade in Springfield. Our work consisted of
inspection of two test pits in the planned location of the footings. The materials exposed
in the test pits were field classified according to the Unified Soil Classification System and
in-place unconfined' compressive strength measurements were taken using a pocket
penetrometer.
Two test pits were excavated and inspected on April 30, 1997. The soil materials exposed
in the pits were similar indicating the subsurface soil profile is consistent across the. site. The
test pits were approximately 2.5 to 3 feet deep. The materials encountered in the test pits
consisted of about 1 foot of dark brown top soil. The top soil unit, referred to as Soil Unit
A, was moist to wet, soft in consistency, above the plastic limit, and field classified as a MH,
Sandy Silt. Below Soil Unit A was a brown silty gravel with sand (GM), referred to as Soil
Unit B. Soil Unit B was moist, hard in consistency, with stained state igneous rock,
fragments ranging in size from a few inches to a few feet in diameter. The matrix was below
the plastic limit. Soil unit B was present from about 1 foot below the surface to the bottom
of the test pits. Groundwater was not encountered in the test pits, however, surface puddles
had formed due to recent rains.
Readings of unconfined compressive strength in Soil Unit B, obtained using a pocket
penetrometer, varied from a low of 4,000 pounds per square foot (pst) to greater than 8,000
psf, indicating that buildings placed on Soil Unit B can be designed for an allowable bearing
capacity of 1,500 psf. Differential settlement due to variations in bearing strength within Soil
Unit B is expected to be insignificant.
Buildings should be founded in Soil Unit B. We recommend that the trenches for the
footings be excavated into Soil Unit B (Soil Unit A is not Suitable for foundation
placement). Therefore, the depth of the trenches should be about 1.5 to 2 feet below the
existing grade. The disturbed material in the base of the trenches should be removed or
compacted prior to placement of the footings. A compacted leveling course of gravel should
be placed in the trenches (4-6 inches should be sufficient).
Surface runoff and shallow groundwater should be directed away from the footings to avoid
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Mr. Kevin Hare
Hammertime Construction
May 1, 1997
Page 2
degradation of the subgrade, excessive settlement, shrink-swell reactions, erosion, and
damage to the foundations., This can be accomplished with surface control and diversion,
adequate subsurface drainage b,ehind footing walls, and water proofing the foundation walls.
Subsurface drainage Will be required behind footing walls. To be effective, subsurface drains
should be constructed as close to the outside of the foundation as possible. The bottom of
the drain should be at or immediately below of the 'bottom of the footing. The subsurface
drain should consist of trenches with a minimum width of 12 inches. The trenches should
be lined with an acceptable filter fabric. A 3- or 4-inch diameter perforated pipe with glued'
joints should be placed in the trench and the trench backfilled with permeable graveL The
gravel should be cover.ed with filter fabric prior to' placement of other backfill. To avoid
accumulation of)subsurface water in the trenches, trenches should be graded to drain and
day-lighted.
Surface drainage should be directed away from the building foundation by grading to ensure
that the ground surface slopes away from the foundation to a suitable area down-slope.
Ponding should be prevented in the entire area. Downspouts and all surface and subsurface
drains should be discharged in a piping system that carries the roof runoff directly into the
City's stormwater system or other acceptable areas such as drywells. The crawl space should
be graded with a slight slope to prevent water from ponding in the crawl space and enabling
water to flow toward one or more designated low areas where the water could be collected
and discharged from beneath the foundation. Vapor t~ansmission in the crawl space can be
blocked by covering the space with visqueen.
This report was prepared for the exclusive use of Hammertime Construction and their
authorized agents. Professional services' were " perlormed, and our, recommendations
provided in accordance with generally accepted principles and practices. The analyses,
conclusions, and recob:1inendations in this report are based upon site conditions as they
presently' exist and assume that the limited number of points investigated are generally
representative of subsurface conditions. If, during construction, conditions are found which
. differ significantly from those presented here, GEM must be advised at once so these
conditions and our recommendations can be reviewed and revised, if necessary.
If you have any questions, please do not hesitate to contact'n
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