Preliminary Geotechnical Engineering Report <br />Project No. 18-4986, 177 Day Island Road, Eugene, Oregon <br />NO " <br />The above foundation recommendations are for dry weather conditions. Due to the high moisture <br />sensitivity of engineered fill and native soils, construction during wet weather is likely to require <br />over-excavation of footings and backfill with compacted, crushed aggregate. As a result of this <br />condition, we recommend foundation excavations be observed to verify subgrade strength. <br />Concrete Slabs-on-Grade <br />Preparation of areas beneath concrete slab-on-grade floors should be performed as recommended <br />in the Site Preparation section. Care should be taken during excavation for foundations and floor <br />slabs, to avoid disturbing subgrade soils. If subgrade soils have been adversely impacted by wet <br />weather or otherwise disturbed, the surficial soils should be scarified to a minimum depth of 8 <br />inches, moisture conditioned to within about 3 percent of optimum moisture content and <br />compacted to engineered fill specifications. Alternatively, disturbed soils may be removed, and the <br />removal zone backfilled with additional crushed rock. <br />For evaluation of the concrete slab-on-grade floors using the beam on elastic foundation method, a <br />modulus of subgrade reaction of 150 kcf (87 pci) should be assumed for the fine-grained soils <br />anticipated to be present in the upper four feet at the site. This value assumes the concrete slab <br />system is designed and constructed as recommended herein, with a minimum thickness of 8 <br />inches of 1 %2"-0 crushed aggregate beneath the slab. The total thickness of crushed aggregate will <br />be dependent on the subgrade conditions at the time of construction and should be verified visually <br />by proof-rolling. Under-slab aggregate should be compacted to at least 90 percent of its maximum <br />dry density as determined by ASTM D1557 (Modified Proctor) or equivalent. <br />In areas where moisture will be detrimental to floor coverings or equipment inside the proposed <br />structure, appropriate vapor barrier and damp-proofing measures should be implemented. A <br />commonly applied vapor barrier system consists of a 10-mil polyethylene vapor barrier placed <br />directly over the capillary break material. Other damp/vapor barrier systems may also be feasible. <br />Appropriate design professionals should be consulted regarding vapor barrier and damp proofing <br />systems, ventilation, building material selection and mold prevention issues, which are outside <br />GeoPacific's area of expertise. <br />Permanent Below-Grade Walls <br />Lateral earth pressures against below-grade retaining walls will depend upon the inclination of any <br />adjacent slopes, type of backfill, degree of wall restraint, method of backfill placement, degree of <br />backfill compaction, drainage provisions, and magnitude and location of any adjacent surcharge <br />loads, as well as depth to ground water. If below grade walls are planned, then the depth to high <br />ground water should be determined. At-rest soil pressure is exerted on a retaining wall when it is <br />restrained against rotation. In contrast, active soil pressure will be exerted on a wall if its top is <br />allowed to rotate or yield a distance of roughly 0.001 times its height or greater. <br />If the subject retaining walls will be free to rotate at the top, they should be designed for an active <br />earth pressure equivalent to that generated by a fluid weighing 35 pcf for level backfill against the <br />wall. For restrained wall, an at-rest equivalent fluid pressure of 55 pcf should be used in design, <br />18-4986, 177 Day Island Road GRPT 10 GEOPACIFIC ENGINEERING, INC. <br />Version 1, August 27, 2018 <br />