Transmission And Substation Foundations - Technical Design Manual

SECTION 7: DESIGN EXAMPLES

Design Example 3

Helicap Final Run Figure 7-9 b

With a final ultimate capacity known, it is time to determine the installation requirements. With the helix configuration being a 10/12/14/14, the length of the lead is 11 ft. Therefore the grout will start 11 ft from the tip of the pile. From the Helicap® report, it is known that in the 28 ft length, 6.8 kips of ultimate friction were developed a the estimated friction bearing capacity per foot is .242 kip/ft. Therefore, for every

foot the pile is longer than 11 ft, it will require 0.242 kips less capacity per foot. So for example at 39 ft, it will only require 78.2 kip of bearing capacity. Being as torque to capacity ration Kt is 10:1, therefore, only 7,900 ft-lbs of torque is required instead of the 8,500 had friction not been included. With this known, it is possible to plot the required torque on a chart vs. depth as seen in Figure 7-13.

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