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- 12 - <br />• <br />undergo some differential movement and should be designed using a minimum <br />dead load pressure to reduce heave potential. <br />FOUNDATION DESIGN CRITERIA <br />Straight-Shaft Piers:- Straight-shaft piers drilled into the claystone <br />bedrock will derive theft bearing capacity both from end bearing and <br />from skin friction. The following design and construction details <br />should be observed: <br />(1) Piers drilled Into the unweathered bad rock may be designed for a <br />maximum end pressure of 35,000 psf. ') <br />(2) Piers may also be designed fora maximum skin frlctlon of 3,500 psf ~ <br />for that portion of the pier in bedrock (darkened portion of Logs <br />• of Exploratory Noles). ~ <br />(3) Piers should be designed for a minimum dead load pressure of '" <br /> 15,000 psf based on the end area of the pier only. <br />(4) Piers may be designed for uplift based on their skin frlctlon and <br /> the surcharge weight of a truncated cone from the bottom of the ;~ <br /> <br /> pier to the ground surface on a 25° angle from the vertical. ~ '-~~ <br /> ~~ <br />(5) The pier should penetrate a minimum of 4 feet Into the unweathered <br /> bedrock and have a minimum total length of at least 8 feet. Where 9 <br /> minimum dead load pressures are not feasible, a minimum penetration <br /> of 6 feet should be used. <br /> } <br />(6) A 4-lnch void should be provided beneath any grade beams to prevent i <br /> uplift on the grade beams and to concentrate the load,.on the <br />~. piers. t <br />,i <br /> <br /> <br />,~ <br />b <br />s <br />:~ <br />