2710 14TH ST BLDG A Geotech Report 2023-12-29

' also observed in TIP-14, above the localized clean sand layer. The fill/weathered glacial till soils thickness varied across the three sites. At Site 1 the soils ranged from 2.5 to 6.5 feet deep; at Site 2 from 3 to 6 feet ' deep; and at Site 3 from 4 to 5.5 feet deep. These soils may consist of reworked glacially consolidated soils (fill) that were graded during the original site development or weathered glacially consolidated soils. ' 3.3.1.3. Glacial Till Glacial till was encountered below the fill/weathered till in all of the test pits completed at Sites 1 and 3, and in TP-5 at the south end of Site 2. When encountered, the glacial till extended to the depths explored. ' The glacial till generally consists of dense to very dense silty sand with variable gravel and cobble content. 3.3.1.4. Glaciolacustrine Deposits ' Glaciolacustrine deposits were encountered below the fill/weathered glacially consolidated soils in the northern three -fourths of Site 2 (test pits TP-1 through TP-4). The glaciolacustrine deposits consisted of medium stiff to hard silt and clay and typically exhibited oxidation staining near the top of the unit. When ' encountered, the glaciolacustrine deposits extended to the depths explored. Although not encountered in our test pits, boulders are common in glacially consolidated soils and should be anticipated during construction. 3.3.2. Groundwater Conditions ' Groundwater and groundwater seepage were not encountered during our test pit excavations. It should be noted however, that perched groundwater should be expected to vary as a function of season, precipitation and other factors. Seepage zones should also be expected to develop in the fill material, perched above ' the dense glacial till and glaciolacustrine deposits. ' 4.0 CONCLUSIONS AND RECOMMENDATIONS Based on the results of our subsurface exploration program, geotechnical laboratory testing, analyses, and ' experience on other similar projects, we conclude thatthe proposed Baker Heights Redevelopment project can be constructed satisfactorily as planned with respect to geotechnical elements. The primary geotechnical considerations for the project are summarized below: ' ■ The site is classified as Site Class C, in accordance with the 2015 International Building Code (IBC). ' ■ Shallow foundations can be constructed on the glacially consolidated soils. Allowable bearing pressures of 6,000 and 4,000 pounds per square foot (psf) may be used for footings bearing on native undisturbed dense to very dense glacial till and stiff to hard glaciolacustrine deposits, respectively. An ' allowable bearing pressure of 3,000 psf may be used where imported structural fill is placed below footings, if needed, that extends to the native glacially consolidated soils. Glacial till can be expected over most of Site 1 and glaciolacustrine deposits can be expected over much of Site 2. ' ■ Conventional slabs -on -grade are considered appropriate and should be underlain by a 6-inch-thick layer of capillary break consisting of clean crushed rock with negligible fines and sand content. ■ Below -grade walls and retaining structures should be evaluated using an equivalent fluid density of 35 pounds per cubic foot (pcf) provided that the walls will not be restrained against rotation when backfill is placed. If the walls will be restrained from rotation, we recommend using an equivalent fluid density of 55 pcf. GEOENGINEER� October 30, 2019 Page 4 He No. 21288-002 00