Settlement <br />An allowable bearing pressure of 2,500 psf is recommended for design. New <br />footings will bear on a thin layer of Select Fill followed by relatively stiff alluvium <br />and shallow gravel, or on compacted fill. The structures will have a finished floor <br />elevation of ± El. 402.8 (i.e., 1 foot above a base flood elevation of ± El. 401.8). <br />Therefore, a maximum (net) fill depth of ±3 feet is anticipated (in addition to the <br />slab and base rock thicknesses). <br />A formal settlement analysis was not performed. However, given the observed <br />stiffness of the foundation soils, the limited thickness of fine-grained soils <br />underlying the site and the anticipated building loads, we recommended assuming a <br />total foundation settlement of ± 1 inch or less. Differential settlements are <br />expected to be ±'/a inch or less. <br />On-site Disposal of Storm Water <br />No infiltration tests were run on the surficial soils. However, the field exploration <br />indicates the near-surface soil typically consist of medium to high plasticity silt <br />(MH) or clay (CL). Based on plasticity indices (PI) of 16 and 23, we expect these <br />soils will have relatively low permeability. The sand that underlies some of the <br />eastern portion of the site contains ±40% fines. Therefore, the sand is also <br />expected to have a relatively low permeability. <br />The alluvial gravels are relatively shallow within the western and central portions of <br />the property. These gravels are expected to have relatively high permeability, as <br />evidenced by the rapid infiltration noted in TP-2, TP-4, TP-7 and T=10. However, <br />the alluvial gravel is expected to have good hydraulic connection with the nearby <br />river. Therefore, ground water levels in the alluvium beneath the property are <br />expected to respond relatively quickly to fluctuations in river levels. During <br />flooding, the hydrostatic pressures in the gravels are expected to reflect the river <br />level. <br />As a result of the above considerations, it is our opinion the native soils are not <br />suitable to dispose on-site storm water. Furthermore, the underlying gravels will <br />also not be suitable material to dispose of storm water because of the hydraulic <br />connection with the river (during flooding). <br />Pavement Analysis and Design <br />A new parking area will be constructed along the western side of the development. <br />The pavement improvements include construction of a new section of Portland <br />cement concrete (PCC) pavement (connecting Oakleigh Lane to the parking lot), <br />new asphaltic concrete (AC) pavement for the parking stalls, a PCC trash/recycling <br />pickup and a Grasscrete fire turnaround. <br />Oakleigh Meadows Cohousing - February 12, 2013 <br />1 4 5 0 Geotechnical Investigation Project 2131004 <br />Eugene, Oregon 5. Willard C. Dixon Architect, LLC <br />