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1. Pile Dimensions

2. Soil Stratigraphy (Layers)

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About

Deep foundations rely on piles to transfer structural loads to stronger soil layers deep underground. This calculator estimates the Ultimate Bearing Capacity (Qu) of a precast driven concrete pile by summing two components: Skin Friction (Qs), derived from the adhesion of soil along the pile shaft, and End Bearing (Qb), the resistance at the pile tip.

Users can construct a digital bore log by adding multiple soil layers (Sand, Clay). The tool applies the Alpha (α) Method for cohesive soils (Clay) and frictional analysis (β or N-values) for cohesionless soils (Sand), providing a total static capacity estimate essential for preliminary foundation design.

pile foundation geotech skin friction end bearing soil mechanics

Formulas

Total Ultimate Capacity (Qu) is:

Qu = Qskin + Qtip

For Clay layers (Alpha Method):

Qs = layers α cu Asurface

For Sand layers (simplified stress method):

fs = K σv tan(δ)

Reference Data

Soil TypeInteraction TypeKey ParameterTypical Values
Clay (Soft)Adhesion (α)Cohesion (cu)10 - 25 kPa
Clay (Stiff)Adhesion (α)Cohesion (cu)50 - 100+ kPa
Sand (Loose)FrictionAngle (φ)28° - 30°
Sand (Dense)FrictionAngle (φ)35° - 40°
Concrete PileMaterialDensity2400 kg/m3

Frequently Asked Questions

The Alpha method is an empirical approach used to calculate the skin friction of piles in clay. The factor alpha (typically 0.5 to 1.0) accounts for the reduction in soil strength due to the disturbance caused by driving the pile.
Piles in clay rely heavily on skin friction. While there is some end bearing, significant settlement is required to mobilize it, which often exceeds structural limits. In contrast, piles driven into dense sand or rock rely heavily on end bearing.