Transmission And Substation Foundations - Technical Design Manual (TD06088E)

The value of α is usually obtained from any one of a number of published charts and is typically related to the absolute value of the undrained shear strength of the clay. Figures 4-6 and 4-7 give typical plots of α vs. undrained shear strength for a number of cases in which f S has been back calculated from actual pile load tests. Generally it is sufficient to select an average value of α for a given undrained shear strength for use in design. The total shaft resistance is then obtained from: Q S = (f S )( π )(d)(L) Equation 4-22 where:

Q S = Total Shaft Resistance d = Diameter of Central Shaft

DESIGN METHODOLOGY

Figure 4-7 Variation in Adhesion Factor with Undrained Shear Strength of Clays (from Murthy 2003).

Figure 4-8 Variation in Adhesion Factor fromAmerican Petroleum Institute [fromASCE (1993b)].

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