19E - SANTA ANA GRADE SEPARATION PROJECT_Exhibit 2 in Color

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Santa. Ana Boulevard Grade Separation September 13, 2011 Page 4 Preliminary Retaining Wall Recommendations Earth retaining structures are proposed for the Santa Ana Boulevard Grade Separation Project. The retaining walls consist of Caltrans Standard Type 1 cantilevered retaining wall and Type SW cantilevered retaining wall. Lateral Earth Pressure: A static active lateral earth pressure of 36 psf per foot of depth is recommended for a free draining, level and compacted backfill. Materials placed behind the retaining wall should be Caltrans Structure Backfill. If applicable, a uniform lateral pressure due to vehicular traffic loading, equivalent to a vertical pressure produced by at least 2 feet of earth with a soil unit weight of 120 lb/fe, should be added to the above lateral earth pressure. Using an active earth pressure of 0.3, the recommended uniform lateral earth pressure due to traffic loading is 72 psf. In addition to the above loadings, the two railroad tracks will induce additional surcharge on the adjacent retaining wall located within the horizontal zone of influence. The uniform lateral earth pressure due to railroad surcharge and the extent of horizontal zone of influence will be determined during the PS&E phase using additional project information. Lateral Resistance: Resistance to lateral loads may be developed by a combination of friction acting at the base of the wall and passive earth pressure. A maximum passive equivalent fluid pressure of 370 psf per foot and a frictional coefficient of 0.4 between the soil -concrete interface can be used for preliminary design. We recommend 100% of the base friction for static loading. For seismic loading, we recommend combining 100% of the passive resistance and 100% of the base friction. Shallow Foundation Design: Using a maximum overexcavation depth (below the footing bottom) of three feet or less and some assumed footing bottom elevations, our calculations show that the allowable bearing capacity is about 3 kips per square foot (ksf). Using the 2006 Caltrans Standard Plan Sheets for Type -I walls, this implies that Type -I wall with a height of 12 feet or less can be supported on a spread footing. For Type -1 wall heights greater than 12 feet and Type - SW walls with bearing pressures greater than 3 ksf, we recommend using deep foundations. Foundation type for the retaining walls will be re -visited when site specific soil boring data become available during the PS&E phase. The horizontal limits of the overexcavation should begin one foot from each edge of the footing bottom and extending downward at a 45 -degree imaginary plane until the plane intersects the overexcavation depth. Prior to backfilling, the excavation bottom should be proof -rolled and after that the excavation bottom should be inspected by a qualified geotechnical engineer or technician to confirm the presence of an unyielding and competent surface. Onsite soils may or may not be suitable for use as backfill; if not, Caltrans Structure Backfill is recommended. Backfill should be compacted to a minimum relative compaction of 95% of maximum density as determined by Caltrans Test Method 216. Minimum footing embedment and offset (from a slope face) for retaining wall should be based on Section 4.4.5.1 of Caltrans Bridge Design Specifications (Caltrans, 2003). Earth Mechanics Inc. Geotechnical & Earthquake Engineering