5828 GLENWOOD AVE CINGULAR WIRELESS ANTENNA Geotech Report 2022-10-25 (2)

Adapt Engineering • Sub grade Reaction Method: The subgrade reaction method is typically used to compute lateral design loads based on allowable lateral deflections. Using this method, the soil reaction pressure(p)on the face of the pier is related to the lateral displacement(y)of the pier by the horizontal subgrade modulus(kh); this relationship is expressed as p=khy. Because soil modulus values are based on small scale, beam load test data, and are usually reported as a vertical subgrade modulus(k„),they must be converted to horizontal subgrade modulus values representative for larger scale applications (such as large pier diameters) by means of various scaling factors, as discussed below. In addition to the scaling and loading orientation, the soil-pier interaction governing kh is also affected by the soil type,as follows: • SAND and Soft CLAY: For cohesion-less soils (sand, non-plastic silt) and soft cohesive soils (clay, cohesive silt), the horizontal subgrade modulus (kh) increases linearly with depth (z). This relationship is expressed as kh=nhz(1B), where nh is the coefficient of horizontal subgrade reaction and(1/B)is the scaling factor. • Stiff or Hard CLAY: For stiff or hard cohesive soils (clay, cohesive silts), the horizontal subgrade modulus (kh) is essentially the same as the vertical subgrade modulus (kg) and is considered constant with depth. This relationship is expressed as kh=k41(ft)/1.5B], where [1(ft)/1.5B] is the scaling factor (B is expressed in feet). Our recommended values for the coefficient of horizontal subgrade reaction (nh) and the vertical subgrade modulus(kg)for the soil layers encountered at this site are presented in Table 4 below. These values do not include a factor of safety since they model the relationship between contact pressure and displacement and are ultimate values. Therefore,the structural engineer or monopole manufacturer should select an appropriate allowable displacement for design, based on the specific requirements of the communication equipment mounted on the tower. AT&T Mobility do General Dynamics October 10,2016 Adapt Project No.WA16-20654-GEO •