3400 RIVERFRONT BLVD Geotech Report 2022-10-25 (2)

ground shaking on a site this close to the river could be large enough to affect the project feasibility or life-safety of the buildings. No seismic related evaluations or analyses were mentioned in GeoDesign's draft report. RESPONSE TO REVIEW COMMENT 5 Our comprehensive geotechnical report for the project will address seismic hazards, including liquefaction, seismic settlement, and lateral spreading. REVIEW COMMENT 6 Page 2 of the report states "the soil beneath a depth of approximately 35 feet bgs consists of dense to very dense sand or hard silt and will not be susceptible to consolidation settlement." This statement may be accurate for consolidation settlement of the upper compressible soils, but soils susceptible to settlement caused by liquefaction likely extend deeper. The borings included in ESNW's report indicate that the loose and soft materials extend beneath 35 feet. Boring B-102 suggests loose sand to a depth of 40 feet bgs and then the last sample driven at 40 feet may also be in potentially liquefiable sand deposits. The last sample taken in Boring B-103 was also terminated in potentially liquefiable soils, and the last recorded blow count(45) may not be an indication of dense sand, but rather gravel or some other obstruction. RESPONSE TO REVIEW COMMENT 6 We agree that seismic settlement will extend deeper than static settlement. Our comprehensive geotechnical report for the project will address seismic hazards, including liquefaction and seismic settlement. REVIEW COMMENT 7 Pages 2 and 3 of the report discuss the difficulty of predicting settlement in the fill, especially due to variability of organic silt and wood debris. The potential risk to the site improvements, foundations, and structures due to the variable nature of the fill and wood debris must be addressed in the report. How will the risk of long-term settlement be mitigated, as it relates to decomposition of organic materials? RESPONSE TO REVIEW COMMENT 7 We recommend that building footings be supported on soil that has been adequately improved or that additional explorations be performed to confirm that organics are not present in the fill layer beneath footings that could cause long-term settlement. REVIEW COMMENT 8 Page 3 of the report presents consolidation parameters from "site consolidation data or published correlations." Please provide references for the information used. Site consolidation data(consolidation curves) and other laboratory tests used in the analyses should be included in the report as supporting documentation. G EODESIGN= 4 Polygon-128-01:0811 15