313 76TH ST SE WESTERN WIRELESS CORPORATION Geotech Report 2018-01-02 MF Import

ADaPT Engineering, Inc. Western Wireless Corporation ADaPT Job No, WA98.993 April I, 1998 Page 8 Modulus of Subgradc Reaction Method: Using this method, the pier is designed to resist lateral loads based on acceptable lateral deflection limits. For sandy soils, the coefficient of horizontal subgrade reaction (kh) is considered to be directly proportional to the depth along the pier. The formula to determine kh is kh= nhx, where x is the depth below the ground surface in inches. We recommend using the value for the constant of horizontal subgradc reaction (nh) for the various soil types presented in Table 4 below. Table 4 Constant of Horizontal Subgrade Reaction (nh) Depth(feet) nh(pci) 02 0 2-10 25 10.30 60 Construction Considerations: At this site, the upper 10-feet of soils is comprised o: loose to medium dense fill soils. Wood debris was noted in the fill soils. In addition, a perched groundwater condition was encountered at a depth of about 10-feet below file ground surface. Localized zones of water bearing gravel were noted in the underlying native deposits. The foundation drilling contractor should be prepared to case the excavation to prevent caving of the pier shaft sidewalls. In our opinion, considering the predominantly fine-grained nafurc of the site soils, dewatering of the drilled shaft will not likely be required. Should unanticipated heavy groundwater inflows be encountered during drilling, it may be necessary to pump the accumulated ground%kater prior to pier concrete placement. Alternatively, the use of bentonite slurry could be utilized to stabilize file drilled pier excavation. Additionally, the drilling contractor should be prepared to clean out the bottom of the pier excavation if loose soil is observed or suspected, with or without the presence of slurry or groundwater. As a minimum, we recommend that the drilling contractor have a cleanout bucket on site to remove loose soils and/or mud front file bottom of the pier. If groundwater is present and abundant within the pier hole, we rer-ommend that the foundation concrete be trernied from the bottom of the hole to displace the water and minimize the risk of contaminating the concrete mi,v. The Drilled Shaft Manual published by the Federal I lighway Administration recommends that concrete be placed by tremie methods if more than 3 inches of water has accumulated in the excavation.