1810 104TH ST SE A T AND T WIRELESS ANTENNA 2022-12-02

Geotechnical Engineering Fart Irerracon SN4924—Silver Lake North Cell Tower Everett, Washington October 24, 2014 Terracon Project No. 81145043 The horizontal subgrade reaction values presented in the table above are applicable to static loads up to one-third of the ultimate lateral capacity of the shaft. For cyclic loads induced by wind or seismic forces, we recommend that 25 percent of the constant of horizontal subgrade reaction or coefficient of horizontal subgrade reaction be used to calculate lateral deflections to depths of 10 feet bgs. We recommend that 50 percent of the constant of horizontal subgrade reaction or coefficient of horizontal subgrade reaction be used to calculate lateral deflections below depths of 10 feet bgs. We recommend that the ultimate lateral resistance of the soils be evaluated as part of the drilled shaft design, in addition to deflection. The constants of horizontal subgrade reaction are based on a 1 foot square loaded area; reduction of these values for wider loaded areas may be appropriate. 4.3.2 Drilled Shaft Construction Considerations We recommend that the foundation construction be observed on a full-time basis by a Terracon representative in order to verify that the soils encountered are consistent with the recommended design parameters. Drilling into the very dense silty sand soils may present difficult drilling conditions. Geologic mapping indicates the potential presence of scattered large cobbles or boulders and constructability of a drilled shaft foundation may be hindered if encountered during construction. Based on the density and fines content of the soils observed in our exploration, in our opinion a drilled shaft foundation could likely be drilled without casing; however the contractor should be prepared to utilize means and methods of maintaining an open hole and stable shaft sidewalls during drilling and placement of reinforcing steel and concrete. The use of temporary casing and/or bentonite slurry may be required to maintain stability of the shaft sidewalls. Groundwater conditions encountered during construction may differ from those observed in our boring and may increase the chance of caving soils. Construction of drilled shafts should only be performed by contractors experienced in construction of this type of foundation, and in the use of temporary casing and/or slurry. If casing is used, reinforcing steel should be placed inside the casing. The casing should be pulled as the concrete is placed to provide final contact between the soil and the concrete. A minimum head of 5 feet of concrete should be maintained above the lower edge of the casing as it is pulled to prevent intrusion of soil during extraction. Following completion of drilling, soft, loose or disturbed soil should be removed from the bottom of the shaft prior to placement of concrete. We recommend that concrete be placed into the excavation through a tremie pipe extending to the bottom of the excavation. Concrete must not be allowed to free fall into the excavation or be placed through water or slurry without the use of a tremie if groundwater is present. An uninterrupted supply and placement of concrete should be performed to produce a monolithic pier/foundation. Use clean, watertight tremie pipes large enough in diameter to allow the free flow of concrete. The tremie pipes should be placed within one foot above the bottom of the excavation prior to the commencement of concrete placement. Maintain a minimum 5 feet embedment of the tremie pipe into the concrete during placement to Responsive■ Resourceful■ Reliable 7