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,- <br />~ <br />~ <br />I' <br />~' <br />;_ <br />Geotechnical Investigation <br />^ <br />Proposed Courthouse Square - Salem, Oregon <br />Seismic Site Coe~cient <br />6. Materials underlying the site are river alluvial deposits of dense to very dense sandy <br />and silty gravels. These materials extend to an approximate depth of 200 feet. <br />Underlying the alluvium is hard basalt bedrock. Based on this information, we <br />recommend a Seismic Site Coefficient of S, (S Factor = 1.0) for use in the design. <br />Site coefficients with corresponding subsurface conditions are presented in Table 23- <br />J of the Uniform Building Code. The soil profile at the site generally meets both the <br />(a) and (b) criteria of the S, profile. <br />Slabs-on-grade <br />~ 7. Slabs-on-grade should have a minimum of No.3 bars at 24 inches o.c.e.w. <br />Slab reinforcement shall be placed at mid-depth of slab. Minimum slab <br />~ thickness shall be 4 inches. Slabs on grade shall have a 4-inch granular <br />cushion of clean sand andlor gravel to prevent capillary rise. Winter time <br />ground water levels are expected to be 10 to 15 feet below grade. The deepest <br />' parking garage elevations are on the order of 20 feet below grade. Slab-on- <br />grade design should incorporate hydrostatic uplift pressures. The deepest <br />garage areas may be continuously below ground water levels. Water proofing <br />~ of basement slabs is critical to suitable performance of the slabs. In areas <br />outside o~the below ground garage, where floor coverings are anticipated, it <br />is recommended that the aggregate be overlain by a tough vapor proof <br />membrane to reduce the moisture in the slab and minimize moisture <br />~ condensation under floor coverings. <br />Retaining Walls <br />~ 8. For basement walls, constrained from top deflection, where the walls are <br />backfilled with import sand and gravel material, the walls should be designed <br />~ for an equivalent fluid lateral earth pressure of 55 pounds per cubic foot (pc~. <br />Where the ground water is 10 feet below grade and the basement wall height <br />~~~ <br />~ centurywest <br />ENGINEERING CORPORATION Q <br />~ March 7, 1997 40806.001.08 <br />' <br />