Transmission And Substation Foundations - Technical Design Manual (TD06088E)

DESIGN EXAMPLE 10 FOUNDATION EARTH PRESSURE RESISTANCE SYMBOLS USED IN THIS DESIGN EXAMPLE

PCF..............................................................POUNDS PER CUBIC FOOT 7-50 K A ....................................ACTIVE EARTH PRESSURE COEFFICIENT 7-50 K P ..................................PASSIVE EARTH PRESSURE COEFFICIENT 7-50 P A ............................................................................................ACTIVE LOAD 7-51 P P ..........................................................................................PASSIVE LOAD 7-54

Project A CHANCE ® helical type SS5 1-1/2” square shaft helical anchor is proposed as part of a pier and beam foundation for a residential structure (see Figure 8-31). The top of the helical anchor is fixed in a concrete grade beam that extends 4’-0 below grade. The surface soils are loose sands. Determine the lateral capacity of the grade beam using the Rankine earth pressure method. Assumptions • The lateral capacity of the 1-1/2” square shaft helical anchor is limited based on shaft size. It is generally not assigned any contribution to the lateral capacity of a foundation • The effective length of the grade beam for lateral resistance is 25’-0 • Assume a unit weight of 95 pcf • The water table is well below the bottom of the grade beam

DESIGN EXAMPLES

• There are no surcharge loads • From Table 8-9, K a = 0.2, K p = 3

Earth Pressure on a Grade Beam Figure 7-33

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