Chance Technical Design Manual

5.5 HELICAP HELICAL CAPACITY DESIGN SOFTWARE Hubbell Power Systems, Inc., engineers developed HeliCAP® he lical capacity design software to determine the bearing capacity of helical piles and anchors in soil. It has been revised several times to provide additional features such as side resistance for steel pipe piles and grouted-shaft helical piles. HeliCAP software is available to engineers and designers upon request. The soft ware uses the same theory of general bearing capacity as pre sented in Section 5.2 for deep foundations (depth ≥ 5B). A key feature of HeliCAP software is that it is designed to work with the information commonly available from soils reports. In North America, soil investigation usually includes a soil boring as de scribed in Section 2 of this manual. The most common informa tion available from the soil boring is the soil profile, groundwater location, and SPT blow count data per ASTM D1586. To utilize this data, the software includes blow count correlations for shear strength, angle of internal friction, and unit weight. These correlations are generally accepted as reasonable approxima tions given the available blow count data. The equations, factors, empirical values, etc., presented in this section are used in the HeliCAP v3.0 helical capacity design software. Using this software makes the selection of a helical pile/anchor much quicker versus using hand calculations. It al lows calculations to be made quickly while varying the differ ent parameters to arrive at the most appropriate solution. As with any calculations, the results from this software are no bet ter than the input data used to generate them. The software will assist in determining an appropriate helical lead configuration and overall pile/anchor length. It also pro vides an estimate of the installation torque. The helical lead configuration can vary by the number and sizes of helix plates required to develop adequate capacity. Helical pile/anchor length may vary due to the combined effects of the lead con figuration and soil strength. Generally speaking, the shorter the pile length for a given load, the better the performance will be in regard to deflection under load. HeliCAP® design software calculates ultimate capacity and must have an appropriate Factor of Safety applied to the re sults. The software has additional features that allow it to be used for other applications, but it is beyond the scope of this manual to present all facets of the software. For additional as

sistance, refer to the Help screen or contact Hubbell applica tion engineers. The image below is from HeliCAP v3.0 helical capacity design software. It shows a typical work page with the soil profile on the left and helical pile capacity on the right.

5.5.1 HELICAP SOFTWARE BEARING CAPACITY METHODOLOGY

As detailed earlier in this section, the individual plate bearing method states that the capacity of a single or multi-helix pile/ anchor is determined by summing the bearing capacities of the individual helix plates. Thus: Q t = S Q h where Q t = Total ultimate multi-helix pile/anchor capacity Q h = Individual helix ultimate capacity HeliCAP design software determines the ultimate bearing ca pacity of an individual helix with the following equation. An up per limit for this capacity is based on helix strength that can be obtained from the manufacturer. See Section 7 of this manual for the mechanical strengths of helix plates. EQUATION 5-32 Q h = A h (cN c + q’N q ) ≤ Q s where A h = Projected helix area Q s = Capacity upper limit = helix mechanical strength Design Examples 8-3 through 8-12 in Section 8 illustrate the use of the standard bearing equation to determine the bearing capacities of helical piles/anchors. These design examples are taken from actual projects involving residential and commer cial new construction, boardwalks, tiebacks, telecommunica tion towers, pipeline buoyancy control, etc. 5.5.1.1 SANDS ( φ ’ > 0; c = 0) HeliCAP design software determines the ultimate bearing ca pacity of a helix (Q h ) in a non-cohesive sand or gravel soil with Equation 5-33, which is derived from Equation 5-32 with the fine-grain (clay) term eliminated (also see Equation 5-19).

DESIGN METHODOLOGY

Page 5-22 | Hubbell Power Systems, Inc. | All Rights Reserved | Copyright © 2023