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Report 114cr aoiii-OW702 La VIELLE GEOTECHNICAL P.C. 2313 NE Alameda Portland,Oregon 97212 (503)287-0511,Fax 282-7671 September 29, 2014 14-2994.047 West Coast Homes Solutions. LLC PO Box 1969 Lake Oswego, 97035 RE: AMENDED GEOTECHNICAL ENGINEERING EVALUATION 10048 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 3/4 inch minus crushed rock with in the formwork. /Mr v70111—‘66)702 September 29,2014 2 14-2994.047 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:1 V 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 '/2 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 10 feet are expected. It is our opinion that these walls can be completed without shoring if excavation site slopes arc cut no steeper than1H:4V 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 Ms i ,zare(-07a September 29,2014 3 14-2994.047 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 ( *4-......\\ IL "Gl"T7V �<i. �7 Pte_.