Report 4 �
incr a1 y-00073
La VIELLE GEOTECHNICAL P.C. 2313 NE Alameda
Portland,Oregon 97212
(503)287-0511,Fax 282-7671
October13, 2014 14-2994.047
West Coast Homes Solutions. LLC
PO Box 1969
Lake Oswego, 97035
RE: AMENDED GEOTECHNICAL ENGINEERING EVALUATION
10006 SW 70th Place
Tigard, Oregon
Greetings:
At your request and authorization we visited the subject site on September 26, 2014 to
visually evaluate the geotechnical engineering aspects of the project. It is our
understanding that plans call for constructing the two story wood frame single family
home.
The proposed cuts are neat 10 feet at the rear of the house. The excavations have been
partially completed and standing at an inclination of five or six vertical to one horizontal.
The cuts are unsupported and appear to be standing well with no ground water seepage or
spalling, or ground cracks. The site is located on gentle west sloping hillside. The Oregon
department of geology h as mapped this area and found no significant evidence of existing
or past landslide activity.
Foundation should be designed to withstand major quakes from the Cascadian subduction
zone located about 200 miles offshore. This zone is expected to produce magnitude nine
earthquakes with prolonged shaking. In addition earthquakes in the range of 6.8 to 7.2
should be expected to occur on the Portland hills fault.
The soil exposed in the excavation is a stiff to hard, light brown, clayey silt. We looked for
but did not find any fill material.
Foundations
We recommend shallow conventional isolated or strip footings be used with a maximum
allowable bearing pressure of 2000 pounds per square foot. No fill should be placed
beneath foundations. The bearing surface should be protected from weather and foot traffic
by placing at least 1 inch of/4 inch minus crushed rock with in the formwork.
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October 13,2014
2 14-2944.047
Passive Lateral Resistance
We recommend a Passive Resistance of 200 pounds per square foot per foot of depth. The
first foot should be neglected.
Coefficient of Soil Friction
We recommend the coefficient of friction of 0.3.
Retaining Wall Loads
We recommend retaining walls be designed for active pressures of 35 pounds per cubic foot
if the back slope on the wall is horizontal and the soil supported by the wall is well drained.
If the back slope on the wall is used 2H:1V retaining wall should be designed for 55 pounds
for cubic foot.
Retaining wall backfill should be a clean free draining gap graded rock such as V2 to 2 inch
drain rock or 2 inch to 4 inch railroad ballast.
Excavation Slopes
It is our understanding that temporary excavations as high as 14 feet are expected. It is our
opinion that these walls can be completed without shoring if excavation site slopes are cut
no steeper than1H:4V, the footing and walls are cast before October 17th and the following
measures are taken.
Plan A:
The excavation side slopes are cut to maintain a 10 foot horizontal setback from the bottom
of the retaining wall to the property line. The contractor should walk the perimeter of the
excavation daily to look for evidence of slope instability.
Plan B;
If significant seepage should develop the excavation should temporarily stop and the
viability of completing the project should be discussed. New drainage collection methods
should be applied or the excavation backfilled
a
October 13,2014 3 14-2994.046
Plan C
If ground water seepage continues or increases alternative methods of shoring should be
designed. The excavation should be backfilled during that period and design and approval.
Sincerely,
LaVIELLE GEOTECHNICAL, P.C.
Craig C. LaVielle, PE/GE sego PRAteo a
cith t� X 14,805 `' ,