WorksheetsDeep Foundations: Pile Capacity Analysis
Total questions: 7
Worksheet time: 4mins
The ultimate axial capacity of a single pile is generally expressed as:
Qu = Qp only
Qu = Qs only
Qu = Qp + Qs
Qu = Qp – Qs
For downward axial loading, side (skin) friction along a pile shaft is typically fully mobilized at a relative pile–soil displacement on the order of:
A. 0.5–1% of pile diameter
B. 5–10 mm (driven 5 mm; bored ~10 mm)
C. 10–25% of pile diameter
D. 50–100 mm regardless of pile type
For point (end-bearing) resistance under downward load, full mobilization usually requires tip movement approximately:
0.5–1% of pile diameter
2–3% of pile diameter
10–25% of pile diameter
Equal to the embedment length
In sands (c' = 0), Meyerhof’s approach for pile point resistance in terms of effective overburden typically uses:
qp = q' Nq* up to a limiting value ql
qp = 9 cu
qp = su Nc (Nc = 5.14)
qp = γ' B Nγ
In saturated clays under undrained conditions (φ = 0), the commonly used expression for pile point resistance is:
Qp = Ap q' Nq*
Qp = 0.5 γ B Nγ Ap
Qp = 9 cu Ap
Qp = 0.4 pa N60 Ap
Coyle and Castello’s method for Qp in sand correlates Qp primarily with:
Undrained shear strength cu
Unit shaft friction profile along the pile
Effective overburden and an Nq* factor that depends on L/D and φ'
Elastic modulus of pile material
A practical upper bound (critical embedment ratio) for developing maximum point resistance in sands is often taken around:
L/D ≈ 4–8
L/D ≈ 8–20 (often ~15–20 depending on method)
L/D ≈ 1–2
L/D has no influence on qp
