2621 ROCKEFELLER AVE Geotech Report 2022-10-25

EXECUTIVE SUMMARY This report contains the results of our geotechnical engineering services for use in the design of the proposed Rockefeller Apartments building. The project consists of demolishing existing residences on the site and constructing a new four-and-one-half-story building with one level of below-grade parking. The parking level will daylight to the alley on the east with below-grade walls to the west. SUBSURFACE CONDITIONS The subsurface conditions at the site were evaluated by excavating six test pits in the footprint of the building. Based on our explorations,the near-surface soils generally consist of fill and loose weathered native soils overlying native glacial soils. The glacial till consists of dense to very dense silty sand with gravel and sand with silt. Groundwater was not encountered in the test pits. SEISMIC DESIGN In accordance with the 2003 International Building Code,the site is classified as Site Class C. REUSE OF ON-SITE MATERIALS The native glacial till is expected to be suitable for use as structural fill during the summer months and 11 may be used as fill in the wet weather months in areas needing only 90 percent compaction (ASTM D 1557) by utilizing good construction practices. We do not recommend using the native glacial till during wet weather when 95 percent compaction is required. We recommend exporting the 11 upper weathered till soils and loose native soils. If structural fill is needed at the site, we recommend reusing the dense native till from the deeper cut areas on the western portion of the site. 11 The existing fill containing debris or rubble is not suitable for reuse as structural fill. Loose fill exists along the east side of the building and should be removed from under planned foundations. The old fill should be partially removed from under the future garage slab. Recycled concrete from the existing foundations and sidewalks may be reused as structural fill. TEMPORARY CUT SLOPES I Excavations for the parking level will require cuts up to about 8 feet deep on the west side of the site and along the western portions of the north and south cuts. These cuts may be made as temporary open cut slopes depending on site constraints. Temporary unsupported cut slopes more than 4 feet high may be inclined at 3/4H:1V (horizontal:vertical) maximum steepness within the dense to 'very dense glacial till. The temporary cuts may be steepened to 0.5H:1 V in the dense to very dense till if evaluated during construction to be safe. Overlying loose native or fill soils should be inclined no steeper than 1.5H:1 V. FOUNDATION DESIGN 111 The building can be supported on conventional spread footings bearing on undisturbed dense to very dense glacial till or advance outwash, or on structural fill placed over these soils. Footings bearing on dense to very dense till and advance outwash may be designed using an allowable soil bearing value of 8,000 pounds per square foot (psf). Footings bearing on structural fill placed over undisturbed dense ' glacial fill may be designed using an allowable soil bearing value of 3,000 psf. The allowable bearing value may be increased by one-third for short duration loads such as wind or seismic events. File No.125 4 7-001-0 0 Page ES-1 GEOENGINEERS, February 3,2006 -