Pile Capacity
Shaft friction and end bearing of bored and driven piles in layered clay and sand, and the length a load needs.
Calculates the axial compression capacity of a single bored or driven pile through any sequence of clay and sand layers with the methods used in practice: the α-method in clay, the β-method in sand with limiting values, and end bearing at the tip. It shows the friction and the cumulative capacity with depth, the capacity against pile length, the allowable load with the chosen factor of safety and the shortest pile that carries a given working load.
Overview
Where soft alluvial clay overlies a firmer layer, as under much of Baghdad and Basra, heavy structures and bridges are founded on piles. The tool turns the borehole log into the capacity profile that guides the choice of diameter and length before load tests confirm it.
Every layer keeps its own parameters, and the contribution of each layer is listed, so the engineer sees where the capacity comes from.
What you enter · What you get
What you enter
- Installation method, diameter, length, water table and factor of safety
- Soil layers: thickness, unit weight, cu for clay, φ′ and N60 for sand
- Optional working load
What you get
- Shaft resistance, end bearing, ultimate and allowable capacity
- Friction and cumulative capacity with depth
- Capacity against length and the required length
- Contribution of each layer (CSV)
How it works in the field
Method and equations
Clay
Driven piles: α = 0.5ψ^−0.5 for ψ = cu/σ′v ≤ 1 and 0.5ψ^−0.25 above (API RP 2A), end bearing 9cu. Bored piles: α = 0.55 for cu/pa ≤ 1.5, reducing to 0.45 at 2.5, no friction in the top 1.5 m, end bearing 6(1 + 0.2 L/D)cu ≤ 9cu (O’Neill & Reese 1999).
Sand
Driven closed-ended piles: fs = K σ′v tan δ with K = 1.0 and the API (2000) limiting friction and end bearing for δ = φ′ − 5°. Bored piles: β = 1.5 − 0.245√z between 0.25 and 1.2, reduced by N60/15 in loose sand, fs ≤ 200 kPa, and qb = 57.5 N60 ≤ 2.9 MPa.
Capacity
Friction is integrated over 0.25 m steps around the perimeter; end bearing acts on the full tip area. The allowable load is the ultimate capacity divided by the factor of safety.
Accuracy and error limits
- Static capacity formulas predict measured pile capacities with a typical scatter of ±30–50 % (coefficient of variation 0.3–0.5); they are a design estimate, not a measurement. Bored pile capacity depends strongly on construction quality: soft toe debris can remove most of the end bearing.
- Not included: negative skin friction, group efficiency and group settlement, cyclic and lateral loading, the structural strength of the pile and the settlement needed to mobilise end bearing (about 5–10 % of D).
- To reduce the error: run static or dynamic load tests on trial piles (they allow FS = 2.0), measure cu with field vane or triaxial tests, use corrected SPT or CPT data in sand, and clean the base of bored piles before concreting.
Who uses it
Standards and references
- American Petroleum Institute (2000). Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms — Working Stress Design, API RP 2A-WSD, 21st ed.
- O’Neill, M.W. & Reese, L.C. (1999). Drilled Shafts: Construction Procedures and Design Methods. FHWA-IF-99-025, Federal Highway Administration.
- Tomlinson, M. & Woodward, J. (2015). Pile Design and Construction Practice, 6th ed. CRC Press.
- Fellenius, B.H. (2023). Basics of Foundation Design. Electronic edition.
- Peck, R.B., Hanson, W.E. & Thornburn, T.H. (1974). Foundation Engineering, 2nd ed. Wiley.
At a glance
- Category
- Engineering & geotechnics
- Runs on
- Phone, tablet and desktop browser
- Export
- Depth profile and capacity–length chart as PNG, JPG and PDF; depth table as CSV; full PDF report
- Access
- Free
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