Pile Capacity Calculator

In loose to medium sand, point bearing doesn't keep increasing indefinitely with overburden stress the way the raw Meyerhof formula suggests — beyond roughly 20 diameters of embedment, the effective stress at the tip levels off in practice. The calculator recreates this by capping the effective stress term at soilUnitWeight times min(20×D, pileLength), so for long piles in shallow soils the point capacity result reflects that limited depth rather than the full pile length.

The calculator adds a clay (alpha-method) term and a sand (beta-method) term together to estimate total skin friction, but running both mechanisms at full strength would double-count resistance for a soil that isn't purely one or the other. Halving the sand term (skinFrictionSand × 0.5) when frictionAngle is nonzero is a blending approximation so the combined result doesn't overstate capacity for mixed or intermediate soils.

Below the groundwater table, the calculator uses a buoyant (reduced) unit weight — soil unit weight minus 62.4 pcf for water — when computing the effective overburden stress (sigma_v) at the pile tip. That lowers both the point bearing and the average effective stress used in the sand skin-friction term, so a shallower water table reduces the calculated capacity for piles that extend below it.

2.5 is a commonly used static-analysis factor of safety for pile design when capacity is estimated analytically rather than confirmed by an actual load test; it accounts for the uncertainty inherent in the alpha/beta method assumptions. Projects that verify capacity with a field load test can sometimes justify a lower factor of safety, while highly uncertain soil conditions may warrant a higher one — this calculator applies a fixed 2.5 regardless.