Transmission And Substation Foundations - Technical Design Manual (TD06088E)

Axial Compression Load (kip)

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80

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0.4

0.6

0.8

Axial Deflection (in)

1

LOAD TESTS

Type SS5 1-1/2" Square Shaft Screw Pile 10"-12" Lead Section 12'-0 Overall Length Installed Torque - 4,000 ft-lb

1.2

1.4

ASTM D1143 “Quick Test” Compression Plot Figure B-9

“blows per foot of set.” The subject of load tests and acceptance criteria are discussed by Crowther (1988) and may be referred to for a more complete treatment of the subject. Figure B-9 is a plot of results from a compression “quick test” per ASTM D1143-07 of a 12 ft long, 1-1/2” square shaft helical pile having 10” and 12” helix plates. It was installed in the residual fine grained soils of Roanoke, Virginia and tested immediately after installation. The load-displacement curve is completely below the elastic compression line, indicating no skin friction was acting on the shaft during the test. The load-displacement curve does not cross the PL/AE + 0.10D ave , which indicates the maximum test load is less than the ultimate geotechnical capacity of the helical pile. Figure B-10 is a plot of results from a tension “quick test” per ASTM D3689-07 of a 16 foot long, 1-1/2” square shaft helical anchor having 8”, 10” and 12” helix plates. It was installed in the residual fine grained soils of Centralia, MO and tested immediately after installation. The load-displacement curve is completely above the elastic tension line (red line), indicating no skin friction was acting on the shaft during the test. The load-displacement curve crosses the PL/AE + 0.10D ave line at approximately 41 kip. The average installation torque over the last three readings was 3,450 ft-lb. The torque correlation method (K t ) of capacity prediction says the ultimate geotechnical capacity is 3,450 x 10 = 34,500 lb (34.5 kip), using a K t of 10 ft -1 as outlined in Section 6. The tested ultimate geotechnical capacity based on 10% average helix diameter net displacement is 41 kip. Therefore, the K t based on the load test is 41,000/3450 = 11.9 @ 12.

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