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Santa Ana Boulevard Grade Separation <br />September 13, 2011 <br />Page 3 <br />Liquefaction Potential and Seismic Settlement Evaluation <br />The subject site is anticipated to have a low liquefaction potential due to the absence of <br />groundwater. Since the liquefaction potential at the bridge site is anticipated to be low, seismic <br />settlement of onsite soils is also anticipated to be low. A more detailed liquefaction assessment <br />will be conducted during the PS &E phase using site - specific soil boring data. <br />Scour Evaluation <br />The proposed structure does not cross a channel that conveys water; therefore, scour potential is <br />not anticipated to be a design issue. <br />Corrosion Evaluation <br />There is no corrosion test result included with the as -built plans. Site- specific soil corrosivity <br />will be investigated during the PS &E phase in accordance with Caltrans requirements. <br />Foundation Data of Nearby Bridges <br />The proposed GS is a new structure and therefore, no as -built foundation data specific to this <br />structure is available. However, the as -built plans for the nearby three structures (Bridge <br />Numbers 55 -671L, 55 -672, and 55 -675) that are located less than 0.3 mile from the proposed <br />railroad bridge were reviewed as part of this project. All of these structures are supported on <br />driven concrete piles with a service demand of 45, 70, or 100 tons. <br />Preliminary Bridge Foundation Recommendations <br />Bridge Configuration: The preliminary plan provided by the structural engineers indicates that <br />the Santa Ana Boulevard GS is a four -span steel plate girder bridge with a total bridge length of <br />about 247 feet and a total bridge width of about 40 feet. <br />Foundation Type: Due to the presence of weak near - surface site soils, deep foundation is <br />recommended for the proposed structure. The preliminary plans provided by the structural <br />engineers show that large - diameter Cast -In- Drilled -Hole (CIDH) pile extensions will be used at <br />the bents and driven steel HP piles will be used at the abutments. <br />Based on the information provided by the structural designers, the abutments are supported by <br />100 -ton steel HP piles (HP 14x89). For each 6 -foot diameter CIDH pile, a service load of 960 <br />kips is provided by the structural designers. Based on these axial demands, the preliminary pile <br />lengths are 70 feet and 55 feet at the abutments and the bents, respectively, for cost estimating <br />purposes. <br />As mentioned earlier, as -built foundation type for the three nearby Caltrans bridges is driven <br />precast - prestressed concrete (PCC) piles. We will evaluate the feasibility of using driven PCC <br />piles instead of the HP -piles during the PS &E phase when site- specific soil boring data become <br />available. <br />=Y e . 4 tics Inc. <br />-- - G Me aeII9,IaanfIg <br />