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 3 Subsurface Conditions On March 26, 1998, an exploratory test boring was drilled to a depth of approximately 30 feet below the existing ground surface. The location of the boring, designated as B-I, is shown on Figure 2. Surficial soils encountered at the boring location consisted of about 10 feet of fill soils above glacial till. The fill soils were comprised of clayey sand, with organics such as wood debris, and a variable gravel content. The fill soils below about 6-fecyt were a heterogeneous mixture of silt, sand and gravel. The materials below the f0-foot depth are very dense and interpreted to have been glacially overridden. These soils have been compressed by the weight of thousands of feet of glacial ice and are considered to be relatively incompressible. At the time of drilling, minor perched groundwater was encountered about 10 feet below the ground surface. Groundwater was also noted to occur within occasional water bearing gravel lenses within the till. Perched conditions develop when the presence of a relatively impermeable soils unit, which serves to impede the infiltration of surface water. It should be recognized that groundwater levels could fluctuate due to factors such as seasonal changes,precipitation or future site utilization. Seismic Conditions According to the Seismic 'lone Map of the United States contained in the 1994 Uniform Building Code, the project site lies within Seismic Risk Zone 3. Based on our analysis of on-site explorations, we interpret the subsurface site conditions to correspond to a seismic soil profile type S-2, as defined by Table 16-J of the 1994 Uniform Building Code. Soil Profile type S-2 applies to a profile consisting of predominantly medium-dense to dense, or medium-stiff to stiff soil conditions. CONCLUSIONS AND RECOMMENDATIONS Current development plans call for construction of a 100-foot tall monopole and associated equipment building or cabinets. Based on the subsurface conditions encountered in our boring, we recommend that the proposed tower be supported on a drilled pier foundation. Design criteria for compressive, uplitt and lateral support of drilled pier foundations are presented below. Normally, a conventional mat foundation could also be used to support a to vLr of this type. Because of the depth of fill present on this site, the mat would need to penetrate at least 10-feet I,,achieve adequate bearing soils. In addition, we understand that Western Wireless prefers to utilize drilled piers for tower foundation as a construction expedient. We should be contacted to provide foundation design recommendations for a mat foundation, if desired, for this site. Our specific recommendations conceming site preparation, equipment pad foundations, tower foundations, and structural fill are presented in the following sections: