Pile Group Capacity Calculator

Complete Guide to Pile Group Capacity and Design

The Pile Group Capacity Calculator determines ultimate load, efficiency, and settlement for pile groups. Essential for high-rise buildings, bridges, and offshore structures. Use with Single Pile Capacity and Settlement tools.

Why Pile Groups?

Single piles limited in capacity. Groups transfer load to deeper strata via:

• Skin friction (clay)
• End bearing (sand/rock)
• Block action

Group Capacity Formula

\[ Q_g = \eta \cdot n \cdot Q_s \]

η = efficiency (0.7–1.0)

Efficiency Factors

• Clay: η = 0.7 (s = 3D)
• Sand: η = 1.0
• s < 2.5D → block failure

Block Capacity (Clay)

\[ Q_b = 9 c_u B_g L_g + \gamma B_g^2 L_g \]

Settlement Analysis

Group settles less than single pile due to stress overlap. Use equivalent raft method.

Step-by-Step Design

1. Compute Q_s
2. Select n, s, layout
3. Apply η
4. Check block failure
5. Estimate settlement

Example: 3x3 Group in Clay

Q_s = 800 kN, s = 3m, D = 0.6m:

• η = 0.75
• Q_g = 9 × 0.75 × 800 = 5400 kN
• FS = 2.5 → Allowable = 2160 kN

Efficiency Table

Pile Spacing Rules

• Minimum s = 2.5D
• Preferred s = 3–4D
• Maximum s = 8D

Negative Skin Friction

Add downdrag in compressible fill:

\[ Q_{nsf} = p \cdot \pi D \cdot L_f \cdot \beta \]

Best Practices

• Use cap thickness ≥ 0.5D
• Align piles with load
• Test piles in group
• Check lateral capacity

Common Mistakes

• Ignoring group efficiency
• Insufficient spacing
• Neglecting settlement
• Assuming η = 1.0 in clay

Advanced Topics

• P-y curves for lateral
• Seismic pile response
• Micropiles in groups
• CFD modeling

Conclusion

Accurate pile group capacity ensures foundation safety. Our calculator delivers instant results for friction, end-bearing, and block mechanisms. Optimize spacing and layout for cost-effective deep foundations. Build on solid ground!

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