GEO-26

Pile α shaft friction

Qs = α cu As. α falls as cu rises (API, Tomlinson).

Reading speed

PilesAPI αTomlinson

Governing equation

Q_s=\alpha\, c_u A_s

where

\alpha: Adhesion α (—)
c_u: Undrained strength (kPa)
D: Diameter (m)
L: Embedded length (m)
Q_s: Shaft resistance (kN)

Lecture brief

Historical brief

Soil mechanics became a quantitative laboratory after Karl von Terzaghi’s 1925–1943 work on effective stress, consolidation and bearing. These sheets still size shallow foundations, retaining walls, piles and drainage in SI. This sheet (GEO-26 — Pile α shaft friction) is the form associated with API α · Tomlinson. Working symbols: $\alpha$ , $c_u$ , $D$ , $L$ $\rightarrow$ $Q_s$ . Total-stress shaft resistance in clay. α ≈ 1 at cu = 25 kPa, ≈ 0.5 at 75 kPa.

Purpose

Purpose: compute

Q_s

from

\alpha

c_u

D

L

in Geotechnical engineering via

Q_s=\alpha\, c_u A_s

Qs = α cu As. α falls as cu rises (API, Tomlinson). Use it when a real geotechnical engineering question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

\alpha = 0.550\,\mathrm{—}

c_u = 50.000\,\mathrm{kPa}

D = 0.600\,\mathrm{m}

L = 18.000\,\mathrm{m}

, the governing relation

Q_s=\alpha\, c_u A_s

yields

Q_s = 933.1\,\mathrm{kN}

. A pile, a clay sleeve, a skin-friction arrow. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Adhesion α \alpha0.55 —Undrained strength c_u50 kPaDiameter D0.6 mEmbedded length L18 m

Outputs

Shaft resistance Q_s933.1 kN

Reading speed

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Narration of this film

A pile, a clay sleeve, a skin-friction arrow.

Total-stress shaft resistance in clay. α ≈ 1 at cu = 25 kPa, ≈ 0.5 at 75 kPa.

Reading speed

Watch on YouTube