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seismic coefficient of 0.0. This approach is <br />consistent with historic observations of <br />soil nail wall performance subjected to <br />ground accelerations as large as 0.7g and <br />with centrifuge tests performed on <br />reduced -scale models of soil nail walls <br />producing similar results. These <br />observations and test results are <br />attributed to the flexibility and design <br />redundancy of soil nail walls." <br />In response to Comment 3, Section <br />1803.5.12(1) likely was intended for rigid <br />and semi -rigid retaining walls such as <br />cantilever concrete, soldier pile, tieback, <br />and sheet pile where the an active earth <br />pressure wedge is developed behind the <br />facing of the wall. For walls where there is <br />a significant component of soil structure <br />interaction, like a soil nail wall, <br />determining the seismic action on internal <br />stability is not as straight forward. Soil nail <br />walls have been observed to perform very <br />well during seismic events despite not <br />having explicitly being designed for <br />seismic loading due to the walls ductility <br />(NCHRP 611, 2008). <br />NCHRP Report 611 which is states: "In a <br />number of areas it was apparent that <br />significant deficiencies exist with current <br />design methodologies. These deficiencies <br />reflect the complexity of the overall soil - <br />structure interaction problem that occurs <br />during seismic loading. The nature of <br />these deficiencies is such that for several <br />of the wall types (for example, MSE, <br />anchored, and soil nail) independent <br />research efforts involving specific model <br />and prototype testing will be required to <br />fully understand the mechanisms involved <br />in seismic loading." <br />Page 4 of 7 <br />