Laserfiche WebLink
EXHIBIT 2 <br /> Santa Ana Boulevard Grade Separation <br /> September 13,2011 <br /> Page 4 <br /> Preliminary Retaining Wall Recommendations <br /> Earth 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 Earth Pressure: A static active lateral earth pressure of 36 psf per foot of depth is <br /> recommended for a free draining, level and compacted backfill. Materials placed behind the <br /> retaining wall should be Caltrans Structure Backfill. <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&E 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 (ksf). 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&E 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 backfilling, 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 backfill; if not, Caltrans Structure Backfill is recommended. <br /> Backfill 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 /> a Earth Mechanics,Inc. <br /> Geatechnical&Earthquake Engineering <br />