HomeMy WebLinkAboutBuilding Miscellaneous 2005-1-6
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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
l'nglnel'ring
January 6, 2005
ProJect: 74.04
Hayden Homes
2464 SW Glacier Place, Suite 110
Redmond, OR 97756
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Subject General Foundation Drainage Recommendations
Jasper Meadows Subdivision - 201 Addition
Springfield, Oregon
PURPOSE AND SCOPE
Tl1is letter provides additional recommendations for drainage for the construction of single-family residences at
the subject new subdivision. Tl1ese are intended to supplement recommendations provided in the original
geotechnical report provided by Boire Associates, which included general construction criteria for development
of the project site.
SITE CONDmONS .
As documented in our summary report of September 20, 2004, the gently sloping site had from 1 to 3-feet of
gray plastic silts over weathered yellow!lan tuffaceous sandstone.
Excavation for the foundation pads consisted of benches cut into the slope with cuts as high as 4-feel K & A
Engineering, Inc. witnessed excavation and provided on-site recommendations so that all foundation cuts were
made to suitable subgrade soils or bedrock.
After excavation and grading of subgrade to undisturbed soilS/rock, 10 to 24-inches of granular fills were placed
on the foundation subgrade and compacted.
Groundwater was not encountered in any of the excavations except at the lower elevation of the project in the
road subgrade.
FOUNDATION DRAINAGE RECOMMENDATIONS
Since a significant amount of low penneability, dense granular fill will support foundation loads on the
underlying native soils and rock, if groundwater were present above the excavation grade it is likely that the
granular fill could trap and isolate water in the foundation excavation. Conventional footing drains would not
remove this water because it would be below the footing grade.
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K & A Engineering, Inc.
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As a precaution to avoid the possibility of trapping water below the foundation, we recommend that low point
drains be installed in the crawlspaces with the inlet at subgrade level. Tl1is will effectively drain the entire
foundation. Tl1is low point drain can replace the recommended conventional footing drains.
Tl1e low point drain should be constructed at the base of a small well excavated in the granular fill. The sides of
the well should be unifonn with a slope not exceeding 2 horizontal to 1 vertical. Tl1e inlet pipe should be
covered with some sort of grate or galvanized screen to prevent fines from entering into the drain system. Tl1e
low point drain should be located in the crawlspace as close to the downhill side of the foundation as possible.
Additionally, we recommend that the final grading at the surface between houses slope to a gentle swale that
routes surface runoff away from the foundation to the street or to an approved stonn drain collector. Tl1e swale
should have a total drop of at least 1-foot.
Tl1ank you for the opportunity to be of service. Please call if you have any questions.
Sincerely,
Michael Remboldt, P.E.
K & A Engineering, Inc.
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Project 74.04 Jasper Meadows Subdivision Phase II, Springfield, OR
Client Hayden Homes
Page 2 of 2
January 6, 2005