2312 W CASINO RD COMMUNITY TRANSIT Geotech Report 2022-10-25

The proposed vault can be satisfactorily supported on the very dense glacial till encountered in our borings or on a minimum 2-foot thickness of structural fill. An allowable bearing pressure of 3,000 psf may be used in design of vault foundations supported on structural fill. This value can be increased to 8,000 psf where footings will be supported on undisturbed dense to very dense glacial till (anticipated below a depth of about 10 feet based on the 1979 as-built of the existing stormwater pipe and subsurface conditions encountered in boring B-3). We recommend placing a minimum 6-inch-thick layer of crushed rock beneath the vault slab to provide a level foundation and prevent disturbance of the subgrade. The effects of buoyancy under empty vault conditions should be considered in design. Buoyancy effects can be resisted by the weight of the concrete structure, the weight of zones of soils which are located above the slab floor which protrude beyond the walls, and soil friction along the sides of the walls. We recommend temporary cut slopes be inclined at 1H:1V (horizontal to vertical) or flatter depending on localized sloughing. Slope inclinations may need to be modified by the contractor if localized sloughing occurs. Steeper slopes up to 3/4H:1V may be feasible in the very dense glacial soils provided the geotechnical engineer confirms soil conditions are consistent and evaluates stability of the slopes during construction. ill The existing fill and native glacial till soils consist of moisture-sensitive silty soils that will become easily disturbed when wet. Re-use of the excavated soils will not be practical during wet weather or if the soils are more than about two points above the optimum moisture content. Based on the moisture content of the samples obtained in the borings, portions of the on-site soils may be suitable during dry weather provided they are properly conditioned. ri Perched groundwater was observed at 71/2 feet and 141/2 feet in boring B-3. Based on our experience, it is likely that utility excavations may be dewatered using a series of sumps and pumps from within the excavations. 4.1. Earthquake Engineering We evaluated the site for seismic hazards including liquefaction, lateral spreading, fault rupture and earthquake induced landsliding. Our evaluation indicates that the site does not have liquefiable soils present and therefore also has no risk of liquefaction induced lateral spreading. In addition, the site has a low risk of fault rupture and earthquake induced landsliding. 4.1.1.2015 IBC Seismic Design Information We recommend the following IBC 2015 parameters for Average Field Standard Penetration Resistance, Site Class,short-period spectral response acceleration(Ss), 1-second period spectral response acceleration (Si), and Seismic Coefficients FA and Fv. TABLE 1.2015 IBC SEISMIC PARAMETERS 2015 IBC Parameter Recommended Value Average Field Standard Penetration Resistance >50 Site Class C Short Period Spectral Response Acceleration,Ss(percent g) 144 1-Second Period Spectral Response Acceleration,Si(percent g) 56 GEOENGINEERS_5 November 14,2019 Page 4 File No.2095-019-07