Capacity vs length
Sweep the embedded length and read off the pile length required for a target axial capacity — the NAVFAC method run at every length.
“How long does the pile need to be?” is usually the first axial question — and answering it one run at a time is slow. The capacity vs length tool sweeps the embedded length across a range, re-running the axial resistance and t-z/q-z service response (the same methods as the axial tool) at every length, and plots ultimate and allowable downward capacity, service settlement, and ultimate uplift against embedment.
How the sweep works
The pile is rebuilt at each swept length and the full static capacity is re-evaluated — side friction integrated over the new shaft, and end bearing at the new tip depth:
Because the whole calculation repeats per length, layer transitions matter: the curve steepens when the tip enters a stronger bearing layer and flattens past the critical-depth caps. A tip exactly on an interface bears in the stratum below. Each station also runs at half resolution; any resistance or service-settlement difference above the declared tolerance fails the request instead of publishing a mesh-sensitive curve.
Pile inputs
The pile is the axial tool's uniform pile without a length — diameter, modulus, unit weight and the driven/bored switch; the sweep supplies the length. The soil profile, groundwater, service load, factors of safety, limiting-depth/K settings, and numerical controls are explicit inputs. The soil fields otherwise follow axial capacity. Make the profile extend below the maximum swept tip so its bearing stratum is defined.
The length sweep
The shortest embedded length to evaluate — the left end of the curve.
The longest embedded length to evaluate. Extend it comfortably past the length you expect to need so the required-length interpolation lands inside the curve.
Number of lengths evaluated, evenly spaced from min to max (2–50). More points trace layer transitions more finely.
Required length
Enter the service load. The engine evaluates its settlement at every length; the UI also draws that same action on the allowable-resistance chart and interpolates the shortest length whose allowable resistance reaches it. Changing the service load re-runs the scientific batch because it changes every reported service state.
If the KPI reads “> max”
Reading the results
- Allowable down is the design curve — capacity after FStip / FSside. The required-length KPI reads off this curve.
- Ultimate down is the unfactored plunging load; jumps mark the tip entering a stronger layer.
- Ultimate uplift (side friction + effective self-weight) grows almost linearly with length — useful for tension piles, where length is bought purely for friction.
- Service settlement is the converged t-z/q-z displacement at the declared service action, not a capacity-derived proxy.
Use the station convergence record and method metadata when selecting a length. A separate project-specific settlement criterion can still govern even when the resistance ratio is below one.