1707 SCENIC DR SNO CO PUD Geotech Report 2022-10-25

� Allowable Bearing Pressure Provided that foundations are supported as recommended above, an allowable bearing value of 3,000 psf may be used for foundations supported on structural fill. The two transformer mat foundations will be supported on structural fill. A subgrade modulus of 75 pci may be used for the design of mat foundations supported on structural fill. A bearing value of 4,000 psf may be used for foundations supported on undisturbed medium dense to dense glacial till. A subgrade modulus of 100 pci may be used for the design of mat foundations supported on undisturbed medium dense to dense glacial till. These allowable bearing pressures appiy to the total dead and long-term live loads and may be increased up to one-third for short-term live loads such as wind or seismic forces. Settlement Provided all loose and soft soil is removed, including existing fill, and the subgrade is prepared as recommended, we estimate that the total settlement of mat foundations founded on dense glacial till will be on the order of 1/2-inch. The settlements will occur rapidly, essentially as loads are applied. Differential settlements are expected to be less than 1/2-inch. Mat foundations supporting light-weight equipment and founded on at least 2 feet of structural fill over existing fill will likely experience settlement on the order of 1h to 1 inch. However, additional settlement may be realized in localized areas depending on the depth of the existing fill, composition of the fill, and the presence of water. Lateral Resistance Lateral foundation loads may be resisted by passive resistance on the sides of foundations and by friction on the base of the foundations, as previously recommended for the Control Building foundation design. Drilled Piers The proposed dead end structures and bus structures may be supported on drilled piers for resistance to overturning. We understand that the drilled piers will be designed by others using the CAISSON program. Dense glacially consolidated soils are expected at various depths, as summarized in Table 1. Loose to medium dense soil,fill, or structural fill is anticipated above the dense till after the site is graded. Drilled piers located in the 115kV yard should extended through existing fill soils and be embedded in dense native soils. We recommend that the embedded portion of the drilled piers extend a minimum distance of 5 feet into the dense glacial till deposits. The axial capacity of the drilled pier must resist downward components of applied loads. We recommend using an allowable end-bearing value of 50 kips per square foot (ksf) for piers supported on the dense to very dense glacial till. The allowable end bearing value should be applied to the base area of the drilled hole into which the reinforcement is placed in concrete. This value includes a factor of safety of about 3. The allowable capacity may be increased by one-third for short- term loads, such as seismic forces. A side resistance value of 800 psf can be used for the bottom of the piers located in the native till deposits. A passive pressure of 350D psf may be used in design of the piers(where D is the depth below the ground surface, excluding the upper 2 feet). The passive resistance acts over two times the diameter of the pier and includes a factor of safety of 1.5. Table 3 presents recommended input parameters for the CAISSON computer program for design of the drilled piers. GEOENGINEERS� October24,2014 Page 15 Fle Na.0482-027-02