Level I Investigation Report Eugene Riverfront Development <br />City of Eugene Eugene, Oregon <br />The 2014 OSSC methodology defines six soil categories that are based on average shear-wave velocity in the <br />upper 100 feet (30 m) of the soil column. The shear-wave velocity is the speed with which a particular type of <br />ground vibration travels through a material, and can be measured directly by several techniques. The six soil <br />categories are Hard Rock (A), Rock (B), Very Dense Soil and Soft Rock (C), Stiff Soil (D), Soft Soil (E), and <br />Special Soils (F). Based on these criteria, the site corresponds to Site Class D. <br />4CONCLUSIONS AND RECOMMENDATIONS <br /> <br />4.1Summary of Subsurface Conditions <br /> <br />Subsurface conditions at the site generally include zones of fill, clay/silt/sand, and gravel, underlain by very <br />stiff silt (Eugene Formation). Groundwater is likely hydraulically connected to the adjacent Willamette River <br />and based on previous monitoring at the site by others, is present at depths of 15 to 20 feet bgs. <br />4.2Summary Geologic and Seismic Hazards <br /> <br />The fill at the site is variable in content and thickness, but in several locations consists of gravel without debris. <br />However, based on previous development and historic activity at the site, fill that includes construction debris <br />such as brick, concrete, metal, plastic, etc., should be anticipated, particularly in the upper 10 to 15 feet. <br />Zones of soft silt and clay may be compressible under moderate to high loads and should be evaluated on a <br />site-specific basis, depending on the proposed development. Based on the soils encountered in the <br />explorations completed to date at the site and those completed by others, the risk of encountering expansive <br />soils at the site is low. <br />Based on the type and relatively density of site soils and the depth of groundwater at the site, the risk of <br />liquefaction and lateral spreading following a code-based earthquake is low. <br />The site is located outside the 100-year flood plain. <br />4.3Geotechnical Design Considerations <br /> <br />The subsurface conditions at the site generally consist of gravel fill over silt and fine- to coarse-grained sand <br />and gravel underlain by Eugene Formation. Based on our observations and analyses, conventional foundation <br />support of lightly loaded park-type structures on shallow spread footings appears feasible. Similarly, support <br />of at-grade hard surfaces such as paths, walkways, courtyards, and vehicular pavements are feasible. <br />Excavation with conventional equipment is feasible at the site. <br />The grading and final development plans for the project had not been completed when this report was <br />prepared. Once completed, PBS should be engaged to review the project plans and update our <br />recommendations as necessary. <br />Development will likely include multi-story and mid-rise structures. Previous development of the site includes <br />several structures that were supported on piles that terminated with limited embedment into the Eugene <br />Formation. Depending on the type, size, location, and foundation loads associated with future development of <br />portions of the site, foundation support on piles may be necessary. <br />4.4Additional Explorations <br /> <br />PBS is currently under contract with the City of Eugene to provide a geotechnical engineering report for the <br />proposed development infrastructure. These services include the recent completion of an additional eleven <br />geotechnical borings to depths of up to 25 feet bgs (shown on Figure 2), installation of piezometers to <br />April 4, 2019 <br />4 PBS Project 73368.001 <br /> <br />