A construction site is underlain by clay soil (an overconsolidated deposit). A 9-in.-diameter steel pipe pile that was driven to a depth of 35 ft as a test pile is load tested. The failure load (test load where large settlement commences) is 80 kips. Because of the small tip area, assume the pile end bearing is negligible and the pile functions as a friction pile. Perform a back analysis to determine the value of the alpha coefficient (α) to use with a total stress method of analysis (result will be used when estimating the capacity for various different length production piles to be installed at the site). The unit weight of the clay soil and the total stress shear strength of the clay (c, cohesion value) is uniform throughout the depths planned for the piles (unit weight is 115 pcf, cohesion value, c, is 1800 psf).
A construction site is underlain by clay soil (an overconsolidated deposit). A 9-in.-diameter steel pipe pile that was driven to a depth of 35 ft as a test pile is load tested. The failure load (test load where large settlement commences) is 80 kips. Because of the small tip area, assume the pile end bearing is negligible and the pile functions as a friction pile. Perform a back analysis to determine the value of the alpha coefficient (α) to use with a total stress method of analysis (result will be used when estimating the capacity for various different length production piles to be installed at the site). The unit weight of the clay soil and the total stress shear strength of the clay (c, cohesion value) is uniform throughout the depths planned for the piles (unit weight is 115 pcf, cohesion value, c, is 1800 psf).
Given data:
Diameter of the pile (d) = 0.9 in.
Depth of driven (D) = 35 ft.
Failure load or test load on the test pile = 80 kips.
Unit weight of the clay = 15 pcf.
Cohesion of the clay (c) = 1800 psf.
Calculating the value of α:
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