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Santa Ana Boulevard Grade Separation <br />September 13, 2011 <br />Page 4 <br />Preliminary Retaining Wall Recommendations <br />Barth retaining structures are proposed for the Santa Ana Boulevard Grade Separation Project. <br />The retaining walls consist of Caltrans Standard Type 1 cantilevered retaining wall and Type SW <br />cantilevered retaining wall. <br />Lateral Barth Pressure: A static active lateral earth pressure of 36 psf per foot of depth is <br />recommended for a free draining, level and compacted backflll. Materials placed behind the <br />retaining wall should be Caltrans Structure Backflll. <br />If applicable, a uniform lateral pressure due to vehicular traffic loading, equivalent to a vertical <br />pressure produced by at least 2 feet of earth with a soil unit weight of 1201b/ft3, should be added <br />to the above lateral earth pressure. Using an active earth pressure of 0.3, the recommended <br />uniform lateral earth pressure due to traffic loading is 72 psf. <br />In addition to the above loadings, the two railroad tracks will induce additional surcharge on the <br />adjacent retaining wall located within the horizontal zone of influence. The uniform lateral earth <br />pressure due to railroad surcharge and the extent of horizontal zone of influence will be <br />determined during the PS &B phase using additional project information. <br />Lateral Resistance: Resistance to lateral loads may be developed by a combination of friction <br />acting at the base of the wall and passive earth pressure. A maximum passive equivalent fluid <br />pressure of 370 psf per foot and a frictional coefficient of 0.4 between the soil - concrete interface <br />can be used for preliminary design. We recommend 100% of the base friction for static loading. <br />For seismic loading, we recommend combining 100% of the passive resistance and 100% of the <br />base friction. <br />Shallow Foundation Design: Using a maximum overexcavation depth (below the footing bottom) <br />of three feet or less and some assumed footing bottom elevations, our calculations show that the <br />allowable bearing capacity is about 3 kips per square foot (kst). Using the 2006 Caltrans <br />Standard Plan Sheets for Type -1 walls, this implies that Type -1 wall with a height of 12 feet or <br />less can be supported on a spread footing. For Type -1 wall heights greater than 12 feet and Type - <br />SW walls with bearing pressures greater than 3 ksf, we recommend using deep foundations. <br />Foundation type for the retaining walls will be re- visited when site specific soil boring data <br />become available during the PS &B phase. <br />The horizontal limits of the overexcavation should begin one foot from each edge of the footing <br />bottom and extending downward at a 45- degree imaginary plane until the plane intersects the <br />overexcavation depth. Prior to backfllling, the excavation bottom should be proof- rolled and <br />after that the excavation bottom should be inspected by a qualified geotechnical engineer or <br />technician to confirm the presence of an unyielding and competent surface. Onsite soils may or <br />may not be suitable for use as backflll; if not, Caltrans Structure Backflll is recommended. <br />Backflll should be compacted to a minimum relative compaction of 95% of maximum density as <br />determined by Caltrans Test Method 216. <br />Minimum footing embedment and offset (from a slope face) for retaining wall should be based <br />on Section 4.4.5.1 of Caltrans Bridge Design Specifications (Caltrans, 2003). <br />=Y . oics Inc. <br />-- - G Mee ae119,1aanf1g <br />