rr~ <br />Table 2. Summary of DCP Test Results <br />Location <br />Initial Test <br />Soil Description <br />'DCP <br />'Average <br />'Corrected <br />Depth <br />(mm/blow) <br />Mr <br />Mr <br />(inches) <br />(psi) <br />(psi) <br />8.4 <br />Medium stiff, low to medium <br />97.6 <br />8,213 <br />2,710 <br />TP-12 <br />plasticity silty CLAY <br />24 <br />Stiff, medium plasticity clayey SILT <br />76.8 <br />9,018 <br />2,976 <br />7.2 <br />Medium stiff, low to medium <br />111.0 <br />7,811 <br />2,578 <br />TP-13 <br />plasticity silty CLAY <br />12 <br />Stiff, medium plasticity clayey SILT <br />53.8 <br />10,362 <br />3,419 <br />7 <br />2 <br />Medium stiff, low to medium <br />97.0 <br />8,233 <br />2,717 <br />TP-14 <br />. <br />plasticity silty CLAY <br />3 3.2 <br />Stiff, medium plasticity clayey SILT <br />54.5 <br />10,305 <br />3,401 <br />Notes: 1. DCP (mm/blow) based on the average readings at and below the anticipated subgrade elevation. <br />2. M, based on average DCP values at the test depth and correlation: M, = 49022.76(DCP)-o.31 <br />(ODOT Pavement Design Guide, 2011). Values may vary slightly due to rounding. <br />3. Corrected M, value is based on the ODOT recommended correction factor of 0.33 for fine-grained <br />soil. <br />ENGINEERING ANALYSIS <br />Bearing Capacity <br />Based on the test pits logs and the site layout shown in Figure 2A, we anticipate <br />the foundations for Buildings 1, 3, 5 and 6, and the Common House will bear on <br />medium stiff to stiff silty clay (typically followed by shallow gravel). Building <br />Units 2, 4 and 7 will bear on imported fill placed over predominantly stiff silt and <br />sand. The surface of the gravel beneath these units typically lies at a depth of <br />11 feet below the current ground surface. These anticipated conditions were used <br />to estimate the bearing capacity and settlement (discussed below). <br />The allowable bearing capacity was estimated for spread footings and continuous <br />(strip) footings placed ± 1 .5 to 2 feet below the ground surface on a minimum of <br />6 inches of Select Fill underlain by stiff alluvium (i.e., clayey silt to silty clay) or <br />imported granular fill. If properly compacted, imported granular fill should have a <br />shear strength higher than the underlying native alluvium. Therefore, the strength <br />of the native soils will typically govern the bearing capacity. <br />Field vane measurements near the anticipated foundation elevation indicated <br />undrained shear strengths ranging from ±0.45 to 0.95 tons/ft2 (tsf). An allowable <br />bearing capacity was calculated using an assumed undrained shear strength of <br />0.5 tsf. The calculation suggests an allowable bearing pressure of 2,500 Ib/ft2 (psf) <br />using a typical factor of safety of 3. This assumes the footings will be underlain <br />by a minimum of 6 inches of compacted Select Fill, as defined in the <br />Recommendations section below. <br />Oakleigh Meadows Cohousing February 12, 2013 <br />Geotechnical Investigation Project 2131004 1 449 <br />Eugene, Oregon 4• Willard C. Dixon Architect, LLC <br />