HomeMy WebLinkAboutEvaluation of Subgrade Conditions - GEO General - 10/31/2006 Bradley-Noble Geotechnical Services
E A Division of The Bradley Group, Inc.
PO Box 12267, Olympia WA 98508-2267
Phone 360-357-7883 • FAX 360-867-9307
31 October 2006 ' D
OCT 31 2006
Mr. Don Tryon MASON COUNTY
1223 Ridge Street SE
Lacey, Washington 98503
Subject: Evaluation of subgrade conditions at your new home site, Lot 103 in the
Lake Limerick Development, Mason County Tax Parcel Number
321275100103.
Dear Mr.Tryon:
As requested by your site work contractor First Choice Excavation, I visited the above
site. At the time of my site visit, the septic tanks had been installed, rebar was laid on
the ground in the proposed footing lines, and the site cleared and leveled. In the
excavation for the septic tanks, we were able to observe the site soil profile. We find
about two feet of granular Vashon recessional outwash soils over Vashon subglacial till.
These soils are suitable for support of standard spread footings supporting building loads
typical of residential type of construction.
We did note that the surface of the soils seemed to be loose, probably from the fine
grading work used to prepare the building pad. We recommend that these soils be re-
densified to a firm and non-yielding surface prior to casting of the foundation. This re-
densification work can be accomplished by either the use of a small self-propelled
vibrating drum compactor or by static compaction using a loaded dump truck wheel
rolling the building pad. The compaction effort should extend at least five feet outside
of building lines to improve lateral soil support.
To aid in ensuring a dry crawl space a footing drain system must be installed. We
recommend the use of rigid plastic pipe for this system as it is more resistant to
crushing and displacement during backfilling of the foundation wall. Roof rain leaders
are to be connected into a separate tightline collection system isolated from the footing
drain system. We recommend the use of rigid plastic pipe with glued watertight joints
for this system. Collected water should be conveyed to the area drainage for disposal
and not allowed to pond around the structure or drain field.
Placement of backfill is to be in conformance with 1803.2 placement of backfill in the
International Building Code (IBC). Site grading to maintain a positive slope away from
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the foundation must be constructed as specified in 1803.3 site grading of the IBC. This
is to prevent ponding of water against the foundation walls. We also recommend that a
minimum vertical space of 3 inches be maintained between bottom of crawl space vents
and top of landscape soil. This is to prevent the vents from becoming a conduit for
water entry into the crawl space and to promote good ventilation.
With the area topography draining towards this area and the thin layer of permeable
soils on the impermeable subglacial till, attention to general site drainage is required to
ensure a dry crawl space.
If you have any additional questions, or if we may be of further assistance to you on this
project, please contact us at our Olympia office.
Cordially,
BRADLEY-NOBLE GEOTECHNICAL SERVICES ct Wash;
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David C. Strong, L.E.G.
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DAM C. STRONG