6107 BERKSHIRE DR 2018-01-02 MF Import

ADaPT Engineering, Inc. Western Wireless Corporation ADaPTJob No, WA98-992 April I, 1998 Page 3 Subsurface Conditions On March 26, 1998 an exploratory test boring was drilled to a depth of approximately 29 feet below the existing ground surface. The location of the boring, designated as B-1, is shown on Figure 2. Surficial soils enaumtered at the boring location consisted of 2 feet of brown, clayey topsoil with some gravel overlying 4.5 feet of tan/brown, damp, dense to very dense, silty gravelly sand, interpreted to be weathered glacial till. Native soils below the weathered glacial till consisted of tan/brown, damp, very dense, silty gravelly sand, interpreted to he unweathered glacial till that extended to the full depth explored (up to approximately 29 feet below ground surface (bgs)). The materials below the 2-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 ire and are considered to be relatively incompressible. At the time of drilling, groundwater was encountered about 21 feet below the ground surface, which we interpreted to be perched groundwater. Perched conditions develop when the presence of a relatively impermeable soil 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 Zone 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 -silo explorations, we interpret the subsurface site conditions to correspond to a seismic soil profile type S-2, as defined by Iable 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 130-foot tall monopole (North American Pole) and associated equipment building or cabinets. Based on the subsurface conditions encountered in our boring, %%e recommend that the proposed tower hi: supported on a drilled pier foundation. Design criteria for compressive, uplift and lateral support of drilled pier foundations are presented below. Normally, a conventional mat foundation could also be used to support a tower of this type. However, we understand that West ern Wireless prof ;s to utilize drilled piers for tower foundation as a construction expedient. We should he contacted t0 provide foundation design recommendations for a mat foundation, if desired, for this site. Our specitic recommendations concerning site preparation, equipment pad foundations, tower foundations, and structural fill are presented in the following sections: