Pile Group Efficiency Calculator
A 3 × 3 group of 400 mm piles at 1.2 m spacing has an efficiency of 72.689 %.
72.6889647067822 %
Full answer, then cut to fewer decimals (not rounded):
- 72.6889647067822 %
- 72.688964706782 %
- 72.68896470678 %
- 72.6889647067 %
- 72.688964706 %
- 72.68896470 %
- 72.6889647 %
- 72.688964 %
- 72.68896 %
- 72.6889 %
- 72.688 %
- 72.68 %
- 72.6 %
- θ = tan⁻¹(d/s)
- 18.43494882 °
- Number of piles
- 9
- Group capacity η × N × Q
- 3271.003412 kN
Step-by-step solution
- θ = tan⁻¹(0.4/1.2) = 18.43494882°
- η = 1 − θ[(n − 1)m + (m − 1)n] / (90 m n) = 1 − 18.43494882 × 12 ÷ 810 = 0.7268896471
Pile Group Efficiency Formula
η = 1 − θ[(n − 1)m + (m − 1)n] / (90 m n)
θ = tan⁻¹(d/s) in degrees; m rows, n piles per row
Worked Example
A 3 × 3 group of 0.4 m piles at 1.2 m spacing:
- θ = tan⁻¹(0.4/1.2) = 18.43494882°
- η = 1 − θ[(n − 1)m + (m − 1)n] / (90 m n) = 1 − 18.43494882 × 12 ÷ 810 = 0.7268896471
Number of piles: 9 · Group capacity η × N × Q: 3271.003412 kN
GATE tip
For piles in clay, also check block failure: the group capacity is the smaller of η × N × Q and the capacity of the block of soil enclosing the piles.
More Geotechnical Engineering Calculators
-
Consolidation Settlement Calculator
Sc = Cc H/(1 + e₀) log₁₀((σ′₀ + Δσ)/σ′₀), t = Tv d²/cv
Tv = (π/4)U² for U ≤ 60 %, else 1.781 − 0.933 log₁₀(100 − U%)
Example: A 4 m doubly drained clay with Cc = 0.3, e₀ = 0.9, σ′₀ = 100 kPa and Δσ = 50 kPa: Final consolidation settlement Sc = 111.216 mm.
-
Shear Strength Calculator
τf = c + σ tan φ; σ₁ = σ₃ Nφ + 2c√Nφ
Nφ = tan²(45° + φ/2); failure plane at 45° + φ/2
Example: A soil with c = 10 kPa and φ = 30° under σ = 100 kPa: Shear strength τf = 67.735 kPa.
-
Terzaghi Bearing Capacity Calculator
qu = cNc + γDf Nq + 0.5γBNγ
square: 1.3cNc + qNq + 0.4γBNγ; circular: 1.3cNc + qNq + 0.3γBNγ
Example: A 2 m strip footing at 1.5 m depth in sand with φ = 30° and γ = 18 kN/m³: Ultimate bearing capacity qu = 950.645 kPa.
-
Soil Phase Relationship Calculator
Se = wG, γ = (G + Se)γw/(1 + e)
n = e/(1 + e), γd = Gγw/(1 + e), γsat = (G + e)γw/(1 + e), γ′ = γsat − γw
Example: A soil with G = 2.65, e = 0.7 and S = 80 %: Bulk unit weight γ = 18.5236 kN/m³.
Frequently asked questions
Why is group efficiency below 100 %?
Stress zones of closely spaced friction piles overlap, so the group carries less than the sum of the individual piles.
What is the usual minimum pile spacing?
About 2.5 to 3 times the diameter for friction piles (IS 2911).
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Pile Group Efficiency Calculator. Retrieved October 29, 2026, from https://scientificconverters.com/calculators/pile-group-efficiency-calculator/
IEEE
Scientific Converters, "Pile Group Efficiency Calculator," scientificconverters.com. Accessed: Oct. 29, 2026. [Online]. Available: https://scientificconverters.com/calculators/pile-group-efficiency-calculator/