920 MILLWRIGHT LOOP S BASE FILE Geotech Report 2023-12-29

very loose to medium dense, fine to medium sand with variable silt content containing shell fragments and significant wood debris at some locations. Interbedded soft silt layers were encountered within the fill. Recent deposits were encountered below the fill and generally consist of very loose to medium dense, fine sand with variable silt content, and very soft to medium stiff sandy/clayey sift. Interbedded soft clay layers were encountered within the recent deposits. Glacially consolidated soils were encountered below the recent deposits and generally consist of dense to very dense send with variable silt and gravel contents and hard sandy silt, extended to the depths explored. Glacially consolidated soils are considered as competent bearing soils. The locations of the standard penetration lest (SPT) and cone penetration test (CPT) borings that were reviewed and used in our analyses are shown in the Site Plan (Figure 2). The corresponding SPT and CPT logs are presented in Appendix A, Previous Subsurface Investigations. 2.3. Groundwater Conditions Based on the reviewed information, the design groundwater level was assumed at Elevation 0.00 feet on the water side in front of the bulkhead and at Elevation t12.00 feet on the land side behind the bulkhead. 3.0 DESIGN CROSS SECTION Cross Section A -A', the location of which is shown in Figure 2, was selected for use in our geotechnical analyses. The soil delineation for Cross Section hA' is presented in Figure 3. Due to the lack of subsurface exploration Information on the water side, according to the nearby projects along the bulkhead segments; A, B, and C, we assumed marine area fill being backfilled at the toe of the bulkhead to achieve the 2.5H:SV slope from Elevation 0.00 feet to Elevation -9.00 feet. The soil profile behind the bulkhead was horizontally extended to the water side. 4.1. ASCE 7.16 Seismic Design Information The projectsite is classified as a Site Class F duetothe presence of the liquefiable soils belowlhe proposed buildings. Based on our discussions with PND, it is our understanding that the building vibration period will be less than 0.5 seconds. Consequently, the project can be completed usingthe codebased seismic design per American Society of Civil Engineers (ASCE) 7-16; and a site -specific response analysis Is not required. Based on the previous SPT and CPT borings completed at the site and within the site vicinity, the project site is best characterized as a Site Class D per ASCE 7-16, consistent with the nearby projects along the bulkhead segments A, B, and C (as stated in our draft geotechnical report for Parcels AS, Al2, and A7 dated July 28, 2020) and the Hotel Indigo project, which is approximately 300 feet away from the project site. We recommend the use of the following ASCE 7-16 mapped parameters for Site Class, short Period mapped MCEn spectral response acceleration (S.), 1-second period mapped MCEn spectral response acceleration (Si), and seismic coefficients (FA and Fv) for the project site (Table 1). GEGENGINEEkS.0 Dawtar20 2Ow osrcoge s