Glossary of symbols & terms
A quick reference for the symbols, soil parameters, and geotechnical terms used throughout PileCalc.
A quick reference for the symbols, parameters, and terms used across PileCalc. Each row links to the page where it is explained in full.
Symbols
| Symbol | Quantity | Typical units |
|---|---|---|
EI | Flexural rigidity (modulus × moment of inertia) | kN·m² |
b, B, D | Pile / footing width or diameter | m |
p | Soil reaction (force per unit length) in the p-y curve | kN/m |
y | Lateral deflection | m |
y₅₀ | Deflection at half ultimate resistance (= 2.5·ε₅₀·b for Matlock and Welch–Reese; ε₅₀·b for Reese stiff clay below water) | m |
pu | Ultimate soil resistance of a p-y curve | kN/m |
σ′v | Effective vertical stress | kPa |
φ (M–φ) | Curvature (note: also friction angle elsewhere) | 1/m |
My, Mp | Yield moment / fully-plastic moment | kN·m |
η | Group efficiency (block ÷ Σsingle) | — |
Soil parameters
| Symbol | Name | Notes |
|---|---|---|
γ, γ′ | Unit weight (total / buoyant) | Total above the water table, buoyant below it |
c, Su | Undrained shear strength of clay | Soft 12–25 · medium stiff 25–50 · stiff 50–100 · very stiff 100–200 kPa (FHWA NHI-06-088 Table 4-2, qu/2) |
φ | Friction angle of sand | (N₁)₆₀ 4 → 27–32° · 10 → 30–35° · 30 → 35–40° · 50 → 38–43° (AASHTO 2014, FHWA GEC 12 Table 5-5) |
ε₅₀ | Strain at 50% stress | Soft 0.020 · medium 0.010 · stiff 0.005 (COM624P Table 3.1) |
k | Subgrade modulus | Unit-dependent — match your unit system |
α | Adhesion ratio (Ca/Su) | 1.0 up to Su = 250 psf, falling to 0.33 (timber, concrete) or 0.19 (steel) at 4000 psf (NAVFAC DM-7.02 Fig. 2) |
qu | Unconfined compressive strength of rock | Reese (1997) weak rock: 0.5–5 MPa |
RQD | Rock Quality Designation | Length of core pieces ≥ 100 mm as % of the core run (Deere 1964) |
N | SPT blow count | Drives the FHWA sand methods |
Methods & codes
| Reference | Used for |
|---|---|
| COM624P (Wang & Reese, FHWA-SA-91-048) | The lateral p-y finite-difference governing equation |
| Matlock (1970) | Soft-clay p-y curves |
| Reese, Cox & Koop (1974); API / O'Neill–Murchison (1983) | Sand p-y curves |
| Reese (1997); Reese & Nyman (1978) | Weak-rock p-y curves |
| Georgiadis (1983) | Equivalent-depth method for layered soil |
| NAVFAC DM-7.02 | Axial side friction & end bearing |
| FHWA-IF-99-025 (O'Neill & Reese, 1999) | Drilled-shaft capacity |
| Vesić (1977, 1969) | Settlement; bearing factors; group settlement |
Terms
| Term | Meaning |
|---|---|
| p-y curve | Nonlinear soil-reaction (p) vs deflection (y) spring at a depth |
| t-z / q-w curve | Axial side (t-z) and tip (q-w) load-transfer springs |
| p-multiplier | Reduction applied to a row's p-y resistance from group shadowing |
| Block efficiency | Whether closely spaced piles fail as a block instead of individually |
| Critical depth | Embedment beyond which uplift breakout becomes local (deep mode) |
| Effective width | Reduced footing width B′ = B − 2e under an eccentric load |
| P-Δ | Second-order moment from axial load acting through lateral deflection |