Transmission And Substation Foundations - Technical Design Manual (TD06088E)

Table C-8 – SS175 Grouted Shaft in Soft Soils P2 Shaft Compression Strength

For example, an SS175 helical pile with a 5” diameter grout column more than doubles the ASD allowable compression strength of the P2 shaft. Larger grout columns increase the structural strength even higher. This is an example where torque correlation [Method 2] does not limit the (P4) geotechnical capacity. Base and side resistance [Method 1] calculated with HeliCAP® v2.0 Helical Capacity Design Software is often greater than strictly torque relationships. The helix strength (P3) is best determined directly by testing. The photos below (courtesy of CTL | Thomp- son) show how the helix strength can be determined. The load is applied through the shaft and resisted by the helix shaped fixture. The line of bearing is located at the average helix radius. The load is applied until the helix plate closes or the welds fail due to bending and shear. The test is stopped when the applied load begins to drop off. The maximum test load is considered the ultimate strength of the helix.

HELICAL PILES AND ANCHORS

Fig. C-1 – P3 Helix Strength Set-Up

Fig. C-2 – RS2875 14” Dia. Helix – Test Results

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