7505 SEAWAY BLVD Geotech Report 2022-10-25

November 11, 2016 HWA Project No. 2014-117-21 4.6 SIGNAL POLE FOUNDATIONS We understand six new cantilever traffic signals are proposed for this project. We understand all signals will consist of a cantilever signal pole conforming to the WSDOT Standard Plans. Three cantilever traffic signals are proposed near the eastern transit entrance, to facilitate access from the transit facility to 75th Street SW, and three cantilever traffic signals are proposed at the intersection of the PUD driveway and 75th Street SW. The numbering designation and the location of each signal pole is presented on Figure 3, Signal Designation and Location Plan. Based on the soil information obtained in our explorations and the existing topography in the vicinity of the signal poles,we have divided the foundation design of signal poles into three separate cases. Case I: Based on our explorations BH-3 and HH-5, located in the vicinity of the Signal Poles 1 and 6, WSDOT standard plan foundations will be appropriate at these locations. For Standard Plan foundation design, required signal standard foundation depths and diameters will be a function of the total "XYZ"value of each mast arm, and the allowable lateral bearing stress of the surrounding soil. For Signal Poles 1 and 6, allowable lateral bearing pressures of 1,500 psf should be used for the signal pole foundations. We recommend 3 or 4-foot diameter drilled shafts be used. Case II: Our exploration indicate that WSDOT Standard Foundation Plans will not be applicable at the location of Signal Poles 2 and 3; as very loose soils were encountered from the ground surface to a depth of 12.5 feet, as indicated by the boring log for BH-5,presented in the Appendix A, Figure A-6. Therefore, a non-standard signal pole foundation design is required. We understand that the design team desires to use conventional p-y method of lateral analysis (i.e., LPILE)to estimate shears, moments and deflections of the signal pole foundation. Soil parameters for use in LPILE analyses are provided in Figure 4. The soil parameters provided in Figure 4 may be used with LPILE for lateral structural analyses and design of the signal pole foundations. Parameters are provided for static and seismic, non-liquefied analyses. Since the signal poles are to be supported on single drilled shafts, group action in not a design consideration of lateral capacity of the drilled shafts. Case III: The soil information obtained from BH-6,presented in Appendix A, Figure A-7 suggests that WSDOT standard plans can be utilized to design foundations of Signal Poles 4 and 5. However, the close proximity of these signal poles to the top of the slope on the north side of the 75th Street SW requires special consideration for these signal poles. For Standard Plan foundation design,required signal standard foundation depths and diameters will be a function of the total "XYZ"value of each mast arm, and the allowable lateral bearing stress of the surrounding soil. For Signal Poles 4 and 5, an allowable lateral bearing pressure of 1,000 psf should be used for the signal pole foundations. Due to the close proximity of the slope on the north side of these signal poles, we recommend that the signal foundation be embedded one shaft diameter deeper than what is recommended in WSDOT Signal Standard Foundation Plans. We 2014-117 Final Geotechnical Report 11 HWA GEOSCIENCES INC.