9910 EVERGREEN WAY SPRINT ANTENNA 2018-01-01 MF Import

' • LSI Adapt medium dense, wet, gray, silty sand with gravel. Soils encountered between 18.5-f:et bgs and the full explored depth of the soil boring were logged as dense to very dense, wet, silty sand with gravel. Groundwater was encountered at about 12.0-feet bgs at the site during drilling. We interpret site condiuons to be conducive to development of "perched" groundwater. The groundwater level would fluctuate due to factors such as seasonal v�riations in precipitation, changes in site utilization, or other factors. Seismic Conditions According to the Seismic Zone Map of the United States contained in Figure 16-2 of'the 1997 Unifortn Building Code (UBC), the project site lies within Seismic ftisk Zone 3. Based on our subsurface exploration, we interpret the site conditions to correspond to a seismic Soil Profile type Sd, as defined by 7able 16-J of the 1997 Uniform Building Code. This soil profile is characterized by dense soil with an average SPT blowcounts between 15 and 50 b]ows per foot within the upper 100 feet bgs. We have discounted the recorded SPT vxlues for the purpose of seismic site characterization owing to the pres;,nce of gravel and oversized materials. Current (1996) Nationa! Seismic Flazard Maps prepared by the U.S. Geological Survey indicate that a peak bedrock site acceleraticn coefficient of about 0.30 is appropriat^ for an earthquake having a 10-percent probability of exceedance in 50 years (corresponding to a retum interval of 475 years). For purposes of seismic site characterization, the observed soil conditions were extrapolated below the boring termination depth, ba,ed on a review of geologic maps and our knowledge of regional geology. CONCLUSIONS AND RECOMMENDATIONS Current development plans call for the r4eplacement of an existing wooden light pole by the conswction of a communications tower, ihe installation of and associated equipment building or cabinets in the Froposed lease arca. Based on the subsurface conditions encountered in our boring, and in order to limit site disturbance, as a construction expedient we recommend thc proposed to��•er be supported r�n a drilled pier foundation. Design criteria for compressive, uplift and lataral support of drilled pier Soundations are presented below. From a geotechnical standpoint, mat foundation support for the proposed tower would be feasible, but would likely result in greater site disturbance, possible extending beyond tl�e limits of the lease area. Our specific recommendations concerning site preparation, equipment building or cabinet foundations, to�ver foundations, access driveway and structural fill are presented in the following sections. Site Preparation Site preparation will involve the removal 01' sparse grass and eround cover and near surface soils, site excavation, and preparin� suberades. The fbllowing comments and recommendations apply to this site preparation: Spnnt PCS � August 4, ?IX13 ii/ Adapt Prujcct No. WA03-97?0 Page 3 /7