Preliminary Geotechnical Engineering Report <br />Project No. 18-4986, 177 Day Island Road, Eugene, Oregon <br />NO " <br />Regardless of the dewatering system used, it should be installed and operated such that in-place <br />soils are prevented from being removed along with the groundwater. <br />Vibrations created by traffic and construction equipment may cause some caving and raveling of <br />excavation walls. In such an event, lateral support for the excavation walls should be provided by <br />the contractor to prevent loss of ground support and possible distress to existing or previously <br />constructed structural improvements. <br />PVC pipe should be installed in accordance with the procedures specified in ASTM D2321. We <br />recommend that trench backfill be compacted to at least 95% of the maximum dry density obtained <br />by Modified Proctor ASTM D1557 or equivalent. Initial backfill lift thickness for a %"-0 crushed <br />aggregate base may need to be as great as 4 feet to reduce the risk of flattening underlying flexible <br />pipe. Subsequent lift thickness should not exceed 1 foot. If imported granular fill material is used, <br />then the lifts for large vibrating plate-compaction equipment (e.g. hoe compactor attachments) may <br />be up to 2 feet, provided that proper compaction is being achieved and each lift is tested. Use of <br />large vibrating compaction equipment should be carefully monitored near existing structures and <br />improvements due to the potential for vibration-induced damage. <br />Adequate density testing should be performed during construction to verify that the recommended <br />relative compaction is achieved. Typically, one density test is taken for every 4 vertical feet of <br />backfill on each 200-lineal-foot section of trench. <br />Erosion Control Considerations <br />During our field exploration program, we did not observe soil types that would be considered highly <br />susceptible to erosion. In our opinion, the primary concern regarding erosion potential will occur <br />during construction, in areas that have been stripped of vegetation. Erosion at the site during <br />construction can be minimized by implementing the project erosion control plan, which should <br />include judicious use of straw wattles and silt fences. If used, these erosion control devices should <br />be in place and remain in place throughout site preparation and construction. <br />Erosion and sedimentation of exposed soils can also be minimized by quickly re-vegetating <br />exposed areas of soil, and by staging construction such that large areas of the project site are not <br />denuded and exposed at the same time. Areas of exposed soil requiring immediate and/or <br />temporary protection against exposure should be covered with either mulch or erosion control <br />netting/blankets. Areas of exposed soil requiring permanent stabilization should be seeded with an <br />approved grass seed mixture, or hydroseeded with an approved seed-mulch-fertilizer mixture. <br />Wet Weather Earthwork <br />Soils underlying the site are likely to be moisture sensitive and may be difficult to handle or <br />traverse with construction equipment during periods of wet weather. Earthwork is typically most <br />economical when performed under dry weather conditions. Earthwork performed during the <br />wet-weather season will probably require expensive measures such as cement treatment or <br />imported granular material to compact areas where fill may be proposed to the recommended <br />18-4986, 177 Day Island Road GRPT 7 GEOPACIFIC ENGINEERING, INC. <br />Version 1, August 27, 2018 <br />