SUPPLEMENTAL MATERIALS (6-19-17)

Geotechnical Investigation Capital Hill PUD Eugene, Oregon 5.2 Excavations Excavations in the site soils should stand near vertical to at least 5-feet in depth; some sidewall caving may occur due to varying soil types and the occasional presence of non-cohesive soil lenses or water seeps and springs. Heavy equipment should not be placed within 10- feet of an open trench. The site soils are classified as OSHA Type B. The Eugene Formation Sandstone expected to be encountered in excavations on the site is typically weathered to a degree that allows conventional construction equipment such as metal tracked excavators with toothed buckets to make excavations into the material although at a slower rate than fine grain soil. Occasionally tougher outcroppings of sandstone may be encountered which require rock hammers mounted to excavators in order to remove the material. 5.3 Cut and Fill Slopes Cut and fill slopes are expected to be required in order to widen portions of the existing Capital Hill Drive and construct the roadway across the existing gravel portion of the roadway. Proper benching and keyway excavation is critical to construct stable fill slopes. Keyway construction is described in Section 5.1 above and a Typical Fill Slope Detail is attached in Appendix B. Fill slopes shall be constructed in a manner that allows fill material to placed and compacted in horizontal lifts benched into the existing hillside. Fill slopes constructed of compacted earth shall not exceed a steepness of 1.5:1 (H:V). If steeper slopes are required, we recommend that structures such as retaining walls are considered. Cut slopes shall not exceed 1.5:1 (H:V) in steepness for excavation into the clay and weathered sandstone material. If tough sandstone is encountered in cuts requiring rock hammers for removal the geotechnical engineer may visit the site and approve steeper cuts to be constructed based on subsurface conditions. Surface water shall be directed away from the top of slopes and slope faces protected from erosion. 5.4 Drainage A complete storm drainage system is expected to be engineered for this project. Alteration of existing grades during project development will likely change near surface drainage patterns, but should not adversely affect adjacent properties. Foundation drains for all hillside structures such as residential foundations, retaining walls, and fill slopes should be installed based on the likelihood of seasonal springs and seeps. No infiltration testing was performed as part of our field investigation and rates favorable for the on-site disposal or storm runoff via infiltration facilities are not anticipated based on the relatively shallow depth to bedrock. Perimeter landscape and hardscape grades shall be sloped away from the foundations and water shall not be allowed to pond adjacent to footings during or after construction 5.5 Retaining Walls - Friction Coefficient and Earth Pressures The following parameters are provided for subsurface structures and retaining walls located within 10 feet of the existing ground surface. Based on an average in-situ unit weight of soil of 90 pcf: 1) The coefficient of friction of the clayey silt soil material is 0.30, 2) The passive earth equivalent fluid pressure is 220 psf/ft, and 3) The active earth equivalent fluid pressure is 37 psf/ft for unrestrained walls and, 52 psi/ft is sloping 2:1 above the wall. The at-rest pressure is 50 pcf for a restrained wall. These parameters assume there is no hydrostatic pressure, sloping backfill, or surcharge loads on the walls. Seismic loading on walls may be estimated as 4H', where H is the wall height and the resultant seismic force acts at a height of 0.6H above the base of the wall. For deep foundation systems, the soil coefficient of friction can be increased to 0.38 below a depth of 10-feet BGS and the passive pressure increased to 300 psf/ft. Branch Engineering, Inc. 10