How does PileCalc analyze pile groups?

Vertically, it computes single-pile, equivalent-block and governing ultimate resistances, then reports ASD allowable, optional LRFD factored resistance and service-load settlement separately. Laterally, it applies the FHWA GEC 9 row p-multipliers to the p-y curves so trailing-row shadowing is captured explicitly.

Is this a full 3D group program like Ensoft GROUP?

No — GROUP models large 3D battered-pile systems under combined loading with flexible-cap FEM, and remains the tool for that. PileCalc covers the far more common cases: vertical efficiency/block checks and lateral p-multiplier runs, in the browser, at a fraction of the cost.

What p-multipliers does it use?

FHWA GEC 9 (2018) Table 7-1: at 3B spacing the row 1/2/3+ values are 0.8/0.4/0.3; at 5B they are 1.0/0.85/0.7, with linear interpolation between. Requests outside 3B–5B fail instead of extrapolating.

FHWA GEC 12 / GEC 9 · USACE EM 1110-2-2906

Pile groups: efficiency, block failure and p-multipliers.

Vertical ultimate/block resistance, explicit ASD/LRFD design values and service-load sand settlement; lateral response with FHWA GEC 9 row p-multipliers.

Try it free Try the free group efficiency calculator

Vertical group resistance compares summed single-pile ultimate resistance with the equivalent-block ultimate mode, then reports ASD allowable and optional LRFD factored resistance separately. Settlement is evaluated at the service load you specify.

The USACE settlement factor applies to cohesionless profiles — clay, rock and mixed profiles are rejected explicitly rather than approximated. Lateral rows use the FHWA GEC 9 Table 7-1 p-multipliers over their published spacing range.

Efficiency & block checks

Both computed on every run; the governing mechanism is reported, not assumed.

Row-by-row p-multipliers

Spacing-dependent front and side factors, with the full per-row response visible.

Service-load settlement

USACE sand-group factor at your working load, with convergence evidence reported on every run.

One tool with the rest

The same pile flows between single-pile lateral, axial and group runs — no re-entry, no separate license.

Validated against published benchmarks

Every figure below is produced by the engine on the cited published problem — closed-form solutions, design-manual tables, or independent codes — and reproduced by the test suite on every release.

p-multiplier (row-shadowing) deduction factors

Quantity	PileCalc	Reference	Agreement
In-line (front) p-multiplier at 3D / 6D / 8D spacingAllPile Table 8-4 / FHWA-NHI-05-042	0.40 / 0.80 / 1.00	0.40 / 0.80 / 1.00	exact
Side-by-side p-multiplier at 1D / 2D / 3D spacingAllPile Table 8-5 / FHWA-NHI-05-042	0.30 / 0.60 / 1.00	0.30 / 0.60 / 1.00	exact

See the full per-tool validation report

The numbers, published

PileCalc's engine is checked term-by-term against the reference codes. A representative sample of the benchmarks — every intermediate value is visible in the app so you can reproduce them yourself.

Benchmark

Quantity

PileCalc

Reference

Agreement

Free-head pile (EI 1.43×10⁶, D 1 m, L 24.4 m)Liang et al. (2014) exact solution / RSPile

Max moment

792.2 kN·m

792.1 kN·m (exact)

within 0.1%

Fixed-head pile (EI 1.43×10⁶, D 1 m, L 24.4 m)Liang et al. (2014) exact solution / RSPile

Head moment

−581.1 kN·m

−581.0 kN·m (exact)

within 0.1%

Cantilever pile (EI 320, D 0.1 m, L 5.25 m)Liang et al. (2014) exact solution / RSPile

Head deflection

8.75 mm

8.750 mm (exact)

within 0.1%

Cantilever pile (EI 320, D 0.1 m, L 5.25 m)Liang et al. (2014) exact solution / RSPile

Max moment

2.335 kN·m

2.334 kN·m (exact)

within 0.1%

Circular pile, API sand (D 0.5 m, L 10 m, H 100 kN)RSPile verification manual

Deflection & moment profile

RSPile 2018 problems #1/#2/#8/#15

chart-reading tolerance

within 1–3%

Steel pile, multi-layer slope stabilization (17 m)RSPile / TZPile / LPile

Lateral resistance

607 kN

582 kN

within ~4%

Read how we validate — and why against two independent codes

Pile groups: common questions

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