Chance Technical Design Manual

For example, an SS175 helical pile with a 5” diameter grout column more than doubles the ASD allowable compres sion 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) geotech nical capacity. Base and side resistance [Method 1] calculated with HeliCAP® Helical Capacity Design Software is often great er than strictly torque relationships. The helix strength (P3) is best determined directly by testing.

The photos in Figures C-1 and C-2 (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 ra dius. 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 con sidered the ultimate strength of the helix.

HELICAL PILES & ANCHORS

FIG. C-1 – P3 HELIX STRENGTH SET-UP

FIG. C-2 – RS2875 14” DIA. HELIX – TEST RESULTS

TABLE C-10 – SS175 P3 HELIX STRENGTH

NOMINAL, LRFD DESIGN & ASD ALLOWABLE STRENGTHS OF SS175 HELIX PLATES FOR SHAFT AXIAL TENSION & COMPRESSION 1

ASD Allowable Strength, kip (kN)

Helix Diameter in (mm)

Nominal Strength, kip (kN)

LRFD Design Strength, kip (kN)

Thickness in (mm)

6 (150)

0.5 (13)

123.3 (548.5)

92.5 (411.4)

61.6 (274)

8 (200)

0.375 (9.5)

84.5 (375.9)

63.4 (282)

42.3 (188.2)

10 (250)

0.375 (9.5)

66.1 (294)

49.6 (220.5)

33.1 (147.2)

12 (300)

0.375 (9.5)

57.5 (255.8)

43.1 (191.9)

28.7 (127.7)

14 (350)

0.375 (9.5)

51.8 (230.4)

38.9 (172.8)

25.9 (115.2)

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