---
title: "Settlement of pile group in sand"
subject: "Foundation Engineering"
chapter: 8
key: "semester_5/foundation_engineering:pile-group-settlement-sand"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/pile-group-settlement-sand
site: BCT Engineering
---

# Settlement of pile group in sand

Foundation Engineering · Chapter 8: Pile Foundations

- Asked in: 2076 Chaitra, 3 marks
- Video: [Settlement of Pile Group | Soil Mechanics](https://www.youtube.com/watch?v=b2urYRtPylc) — APSEd
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/pile-group-settlement-sand
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-8

## Question

Describe the various methods of determining the settlement of pile group in sand.

## Short answer

Group settlement in sand is larger than single pile. Methods: Vesic's S_g = S √(B_g/D); Meyerhof's SPT formula S_g = 2 q √B_g I / N_bar with I = 1−L/(8B_g); equivalent raft method from a raft at 2/3 L depth with 2:1 spread; and elastic interaction methods.

## Answer

The settlement of a pile group in sand is greater than that of a single pile carrying the same load per pile, as a larger volume of soil is stressed. The main methods are:

1. **Vesic's method (empirical):**
$$
S_g = S\sqrt{\frac{B_g}{D}}
$$
where $S$ is the settlement of a single pile at the same working load, $B_g$ is the width of the group and $D$ the pile diameter.

2. **Meyerhof's SPT method:**
$$
S_g\ (\text{mm}) = \frac{2q\sqrt{B_g}\,I}{\bar N},\qquad I = 1 - \frac{L}{8B_g} \ge 0.5
$$
where $q$ is the net pressure on the group (kN/m²), $B_g$ is in metres, $L$ is the length of pile embedded in the bearing stratum and $\bar N$ the average SPT value within a depth $B_g$ below the tip (for CPT: $S_g = \dfrac{qB_gI}{2q_c}$).

3. **Equivalent raft method:** the pile load is assumed to act on an imaginary raft of the group size at a depth $\tfrac{2}{3}L$ from the top (for friction piles) with a 2:1 load spread, and the settlement of the raft is computed from elasticity or from SPT/plate test data.

4. **Elastic (interaction) methods** (Poulos): settlement from interaction factors between piles.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Group settlement compared with a single pile at the same load per pile is:
   A. Greater, as a larger soil zone is stressed
   B. Smaller
   C. Equal
   D. Zero
   Answer: A. Overlapping stress zones go deeper. (Key point: Group vs single)

2. Vesic's method gives Sg =
   A. S sqrt(Bg/D)
   B. S Bg D
   C. S/D
   D. S x n
   Answer: A. S is single pile settlement, Bg group width, D diameter. (Key point: Vesic)

3. In equivalent raft method for friction piles the raft is at:
   A. 2L/3 from top with 2:1 spread
   B. Pile head
   C. Tip
   D. Ground level
   Answer: A. Settlement of that raft is computed. (Key point: Equivalent raft)

4. Meyerhof's method uses:
   A. SPT value N-bar and net pressure q
   B. Load test only
   C. Hammer set
   D. Water content
   Answer: A. Sg = 2q sqrt(Bg) I / N-bar. (Key point: Meyerhof)

## Related in Foundation Engineering

- [Pile capacity in sand, group effect, load test](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-capacity-sand-group-load-test) — Foundation Engineering, chapter 8
- [Allowable load of 4×4 pile group, layered sand](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-group-4x4-figure-dcr) — Foundation Engineering, chapter 8
- [Negative skin friction on single pile and group](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Ansf-calculation-single-group) — Foundation Engineering, chapter 8, asked 2×
- [Pile group 4×4, two-layer clay, 2.4 m spacing](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-group-4x4-2-4m-layered) — Foundation Engineering, chapter 8, asked 2×
- [Single pile versus group action](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asingle-vs-group-pile-behaviour) — Foundation Engineering, chapter 8
- [Design pile group for 2000 kN](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-group-design-2000kn) — Foundation Engineering, chapter 8

## Related in other subjects

- [Primary settlement, sand over clay, 110 kPa](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aprimary-settlement-sand-clay-110kpa) — Soil Mechanics, chapter 9
- [Final settlement of clay, +30 kN/m²](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Afinal-settlement-sand-clay-30kpa) — Soil Mechanics, chapter 9
- [Settlement with preconsolidation 125 kPa](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aprimary-consolidation-settlement-preconsolidated) — Soil Mechanics, chapter 9