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

will likely occur. The tolerable magnitude of long-term settlement for the design of the structures and site improvements should be discussed with the structural engineer and included in the report, as well as appropriate mitigation measures. RESPONSE TO REVIEW COMMENT 10 The goal for the project is to limit static settlement to approximately 2 inches. We are proposing that a surcharge be used to induce approximately 90 percent of the settlement that would be caused by raising grades to final grades. We anticipate that settlement beneath buildings due to the decomposition of organic material will be minor. 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. The layer of hard silt that is occasionally present beneath the layer of soft to medium stiff silt is not susceptible to consolidation settlement. Seismic settlement is a separate issue related to life safety during an earthquake. We will discuss seismic settlement in our comprehensive geotechnical report for the project. Mitigation measures for static and seismic settlement, when applicable, will be discussed in our comprehensive geotechnical report for the project. REVIEW COMMENT 11 Page 4 of the report states that settlement monitoring should occur due to the highly variable nature of the fill. The report should describe the settlement monitoring plan recommended for this site, especially given the variable subsurface conditions in the fill and native soils. At a minimum, settlement plates should be placed along the alignment of all the major utility pipes and at the proposed building locations. Settlement plates would typically be read daily during placement of the surcharge (referring to statement on Page 7). RESPONSE TO REVIEW COMMENT 11 We have installed 16 settlement plates at the site,which corresponds to approximately 1 settlement plate per acre. This is the same settlement plate density that is being used at the nearby Polygon Simpson site. We installed settlement plates 4, 8, and 13 along the alignment of the City's 48-inch and 72-inch sewer lines. We installed the remaining settlement plates at various proposed building and roadway locations. In our opinion, the 16 settlement plates we have installed will be adequate for monitoring settlement at the site. We propose to take survey readings on the settlement plates at a rate of at least twice per week while fill or surcharge is being placed and for at least one additional month following the placement of fill or surcharge. After the additional month, settlement readings should be collected weekly. REVIEW COMMENT 12 Page 5. Please confirm that the crest of the surcharge should extend at least 10 feet beyond the limits of the building and pavement areas. G EODESIGN= 6 Polygon-128-01:081 1 15