Pile Foundation Axial Capacity Calculator
Deep foundation engineering: Calculate ultimate compressive pile capacity (Q_ult), shaft friction (Q_s), tip end bearing (Q_b), and allowable geotechnical load (Q_all).
Pile Dimensions & Soil Stratum
Axial Geotechnical Capacity
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Frequently Asked Questions
What is the mobilization displacement difference between shaft friction and end bearing?
Full shaft skin friction mobilizes with very small pile head settlement—typically only 2 to 5 mm (0.5% to 1% of pile diameter). Conversely, tip end bearing in sand or stiff clay requires substantial displacement—between 5% and 10% of pile diameter (40 to 80 mm for an 800 mm pile)—to mobilize its ultimate capacity. In working load conditions, shaft friction carries the majority of structural load.
Why does the Alpha method cap adhesion in stiff, overconsolidated clays?
In soft clays (su < 30 kPa), the adhesion factor alpha is high (~1.0), meaning the clay bonds tightly to the pile shaft. However, in hard or heavily overconsolidated clays (su > 150 kPa), driven or bored piles induce micro-fracturing and shearing during installation. The adhesion factor drops to 0.40–0.50 because the disturbed soil remolds into a slickensided shear surface.
What is negative skin friction (down-drag) on deep piles?
When compressible soft soil layers (like peat or under-consolidated marine clay) settle downwards relative to the rigid pile shaft, the soil friction reverses direction. Instead of supporting the pile, the settling soil hangs from the shaft, adding massive downward vertical drag loads (down-drag) that can overstress the pile structural cross-section.