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3 <br />The consideration of seismic surcharges in the soil nail wall <br />In response to the comment issued by <br />design was issued as a comment in April 2017; the response <br />Sabrina Fandler of the City of Everett <br />indicated that is was not applicable. It is noted that IBC <br />Public Works Department during a permit <br />Section 1803.5.12(1) requires seismic lateral earth pressures <br />review conducted in 2017 which <br />to be considered concurrent with other soil pressures on <br />questioned using a seismic coefficient of <br />retaining walls; this section does not limit the types of <br />zero for internal stability, KLF issued the <br />retaining walls required to comply with this loading. The <br />following response: <br />seismic loading should be considered for the design of all <br />walls, or commentary should be provided substantiating that <br />"The IBC requires a factor safety <br />the loading is not required. <br />h <br />of 1.1 against seismic failure in the sliding <br />against <br />a <br />and overturning modes of failure, which <br />was considered. However, it does not <br />provide guidance regarding internal <br />stability. Hence, we referred to the 2015 <br />FHWA Geotechnical Engineering Circular <br />No. 7, which does provide guidance <br />regarding internal design for seismic <br />conditions. <br />Section 6.8 of the 2015 FHWA <br />Geotechnical Engineering Circular No. 7 <br />states that seismic design is not <br />mandatory for MSE and soil nail walls in <br />AASHTO-defined Seismic Zone 3 <br />(0.30<SD1<0.50) or for walls at sites <br />where the site -adjusted, design PGAD is <br />less than 0.4g provided the soils behind <br />the wall do not liquefy or sustain <br />significant strength degradation (mainly <br />fine-grained soils) during dynamic loading. <br />At this site, the AASHTO-defined SD1 is <br />0.46g and PGAD is 0.40g, both of which <br />meet the above stated criteria. The <br />geotechnical report characterizes the site <br />as having "low susceptibility to <br />liquefaction" and the site soils are silty <br />sand glacial till, which do not sustain <br />significant strength degradation. <br />Based on the FHWA design standard and <br />the site characterization, we applied a <br />Page 3 of 7 <br />