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EXHIBIT 2 <br /> Santa Ana Boulevard Grade Separation <br /> September 13,2011 <br /> Page 2 <br /> General Subsurface Conditions <br /> According to the attached As-Built LOTB sheets for the nearby structures, a total of twelve auger <br /> borings were drilled between March and May, 1989. The deepest boring was advanced to about <br /> elevation+50 feet. Existing grade at the borehole locations at the time of the investigation ranged <br /> between elevations +130 feet and +168 feet. The existing grade at the subject site is about <br /> elevation+145 feet. <br /> At the nearby bridge site, the surficial material is embankment fill consisting predominantly of <br /> medium dense to dense silty sand with few interbedded very stiff to hard sandy silt. Thickness of <br /> this embankment fill varies from 10 to 25 feet. The embankment fill is underlain by about 40 feet <br /> of native deposits composed predominantly of loose to very dense silty sand and medium stiff to <br /> hard sandy silt with occasional silty clay and clayey silt interbeds. Below about elevation +105 <br /> feet, the stratigraphy included very dense silty sand, sand with gravel and cobbles, sandy gravel, <br /> and clayey gravel with some interbedded loose to medium dense silty sand and sand layers down <br /> to about elevation +80 feet. Very dense silty sand, sand with gravel and cobbles, sandy gravel, <br /> and clayey gravel layers were encountered below about elevation +80 feet down to the depth <br /> explored. <br /> Groundwater was not encountered in any of the borings that were drilled down to the deepest <br /> elevation of about+50 feet. <br /> Preliminary Seismic Recommendations <br /> It is our understanding that the Santa Ana Boulevard GS will be constructed using the American <br /> Railway Engineering and Maintenance-of-Way Association (AREMA) guidelines (AREMA, <br /> 2009). <br /> We performed a site-specific probabilistic ground motion analysis using FRISKSP (Blake, 2004 <br /> & 2000) computer program for the bridge site. The probabilistic analysis was performed using <br /> four attenuation equations published by Abrahamson and Silva (1997), Boore, et al. (1997), <br /> Campbell (1997), and Sadigh et al. (1997). These peak horizontal ground acceleration (PGA) <br /> values were obtained by averaging the results of the above-referenced attenuation equations and <br /> are provided in Table 1. <br /> Table 1. Seismic Design Parameters <br /> Ground Motion Level Return Period PGA = Site <br /> (Frequency) (g) = Coefficient, S <br /> 1 (occasional) 100 Years 0.214 <br /> ----------.. .................... <br /> 2 (rare) 500 Years 0.351 1.5 <br /> 3 (very rare) 2,400 Years 0.524 <br /> The structural engineer can use the data provided in Table 1 to develop the site-specific response <br /> spectrum following the procedure outlined in Section 1.4 of Chapter 9 of AREMA (2009). <br /> a Earth Mechanics,Inc. <br /> Geatechnical&Earthquake Engineering <br />