Chance Technical Design Manual

PRACTICAL GUIDELINES FOR FOUNDATION SELECTION, TABLE 8-2

should have the right to load test the helical pile to determine if K t is greater than 10 ft -1 . Verification testing is often done in tension since it’s simpler and less costly to do than compres sion testing, and the compressive capacity is generally higher than tension capacity, which results in a conservative site-spe cific K t value. Estimate installing torque for field production control and specifying the minimum allowable without testing. EQUATION 8-19 Q ult = K t T, or T = Q ult /K t where Q ult = UC r in this example Interior columns: T = Q ult /K t = (58,000 lb/2 piles)/10 ft -1 = 2,900 ft∙lb ≅ 3,000 ft∙lb for the minimum average torque tak en over the last three readings. Perimeter grade beam: T = Q ult /K t = 48,000 lb/10 ft -1 = 4,800 ft∙lb for the minimum average torque taken over the last three readings. Note that the torque rating for the Chance Type SS5 product series is 5,700 ft∙lb – OK. STEP 10: PRODUCT SPECIFICATIONS See Section 7, Product Drawings and Ratings and Appendix C for Hubbell model specifications. STEP 11: LOAD TEST Since this is a small project with low loads in “normal” soils, it is acceptable to use the torque correlation method as the driving criteria and omit the “optional” load test.

ULTIMATE LOAD 1

DESIGN LOAD 2

HELICAL PILE PRODUCT SERIES

INSTALLATION TORQUE

kip kN kip kN

5,500

55 244 27.5 110

SS5

5,500

49.5 202 24.75 110 RS2875.203

7,000

70 312

35

156

SS150

8,000

72 320 36 160 RS2875.276

1 Based on a torque factor K series. 2 Based on a Factor of Safety of 2.

t = 10 for SS series and K t = 9 for RS2875

DESIGN EXAMPLES

For the 10”-12” configuration, the minimum depth of 18’-0 can be achieved by using a lead section, which is the first pile seg ment installed and includes the helix plates, followed by two or three plain extensions. For the 10”-12”-14” configuration, the minimum depth of 21’-0 can be achieved by using a lead sec tion followed by three or four plain extensions. The exact cata log items to use for a specific project are usually the domain of the contractor. Your Certified Chance Installer is familiar with the standard catalog items and is best able to determine which ones to use based on availability and project constraints. For your reference, helical piles with product descriptions are pro vided in Section 7 of this manual. The head of the helical pile is to be approximately 1’-0 below grade in the grade beam or cap excavation, which will put the twin-helix pile tip 18’-0 below the original ground level and the three-helix pile tip 21’-0. These are minimum depths, required to locate the helix plates at least 5’-0 into the bearing stratum. On large projects, it is advisable to add 3% to 5% extra ex tensions in case the soil borings vary considerably or if widely spaced borings fail to indicate differences in bearing depths. STEP 9: FIELD PRODUCTION CONTROL Use K t = 10 ft -1 for Chance® Type SS material if verification test ing is not done prior to production work. The minimum depth and minimum installing torque must both be achieved. If the minimum torque requirement is not achieved, the contractor

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