Laserfiche WebLink
r <br />� AirTouch Cellular <br />3 Octaber 7997 <br />�_ <br />L. <br />`I <br />C. <br />l <br />7-91 M-11905-0 <br />PaBe 8 <br />detailed analyses are available, either the simplified passive earth pressure method or the <br />subgrade reaction method is typically used to deterrc:ne the pier diameter and depth <br />required to resist groundline reaction forces and moments. 'fhese methods are described <br />below. <br />• P_assive Earth Pr ur M thod: The passive earth pressure method is slightly <br />conservative by neglecting the redistribution of shear forces that develop near <br />the bottom of the pier. Our recommended passive earth pressures for the soil <br />layers encountered at this site are presented in Table 4. These values are <br />expressed as an equivalent fluid unit weight (WP) to reflect the linear increase <br />with depth and may be assumed to act over an area measuring tw� Rier <br />diameters wide by eight pier diameters deep. A lateral deflection at the ground <br />surface equal to a6out 0.002 times the pier length would be required to mobilize <br />the full allowable passive pressure presented below. The values listed in Table <br />4 incorporate a safety factor of at least 1.5, which is commonly applied to <br />transient or seismic loading conditions. <br />TABLE 4 <br />RECOMMENDED ALLOWABLE PASSIVE EARTH PRESSURES <br />Depth Interval yyP <br />(feet) (pcf) <br />Oto5 p <br />5 to 12%: 250 <br />7 2'/: to 28 300 <br />28 to 40 350 <br />• Subo�ade Reaction Method: The subgrade reaction method is slightly more <br />complex ttian the passive pressure method and is typically used to compute <br />lateral desic�n loads based on allowable lateral deflections. Using this method, <br />the soil reaction pressure (p) on the face of the pier is related to the Iaterai <br />displacement (y) of the pier and the coefficient of horizontal subgrade <br />reaction (kh); this relationship is expressed as p=khy. The calculation of kh <br />depends primarily on the constant of horizontal subgrade reaciion, the pier <br />diameter, and the soil type as detailed below: <br />7�B 1 M�11 BO6�0 <br />► SAND ana ooft CLAY: For soil layers consisting of sand or soft clay <br />deposits, the coefficient of horizontal subgrade reaction ;kh) increases <br />linearly with depth and is derived from the constant of h��rizontal <br />