---
title: "Sand compaction piles and stone columns"
subject: "Foundation Engineering"
chapter: 10
key: "semester_5/foundation_engineering:sand-compaction-piles-stone-columns"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/sand-compaction-piles-stone-columns
site: BCT Engineering
---

# Sand compaction piles and stone columns

Foundation Engineering · Chapter 10: Foundation Soil Improvements

- Asked in: 2081 Bhadra, 2 marks; 2074 Chaitra, 2 marks; 2076 Asoj, 1 marks (asked 3 times)
- Video: [Sand Compaction Pile Tips, Sand Pile, SCP Tips](https://www.youtube.com/watch?v=v0tc0TujOAc) — Civil Engineer Mizan
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/sand-compaction-piles-stone-columns
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-10

## Question

What are sand compaction piles and stone columns?

## Short answer

Sand compaction piles are sand columns installed by driving and compacting sand in stages, densifying soil and acting as drains. Stone columns are compacted crushed stone columns formed by vibro-replacement, improving bearing capacity through lateral confinement; their capacity depends on passive soil resistance.

## Answer

**Sand compaction piles** are columns of compacted sand formed in loose sandy or soft clayey soil. A casing is driven or vibrated into the ground, filled with sand, and withdrawn in stages while being re-driven to compact the sand. The surrounding soil is densified, and the sand pile increases the strength and acts as a drain, reducing settlement and liquefaction potential. They are also used in soft clay.

**Stone columns** are vertical columns of compacted crushed stone or gravel (size 20 to 75 mm) installed in soft clay or loose silty soil, usually by **vibro-replacement** (a vibrator is jetted into the ground and the hole is backfilled with stone in lifts) or by a driven casing (rammed stone column). Diameters are 0.6 to 1.0 m, spaced at 1.5 to 3 m in a triangular or square grid.

**Functions:** they increase the bearing capacity, reduce settlement, speed up consolidation by acting as drains, and reduce the liquefaction potential. The capacity of a column depends on the lateral confinement given by the soil: $q_{ult} \approx \sigma_{r}K_p$, where $\sigma_r$ is the limiting radial stress in the soft soil (bulging failure) and $K_p$ is the passive earth pressure coefficient of the stone.

## Check yourself

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

1. How is a sand compaction pile formed?
   A. Cement grout is pumped into drilled holes
   B. Casing is driven, filled with sand and withdrawn in stages while re-driving to compact the sand
   C. A heavy weight is dropped from a crane
   D. Soil is mixed with lime
   Answer: B. The casing is filled with sand and withdrawn in stages while being re-driven to compact it. (Key point: Forming sand compaction piles)

2. What are stone columns and how are they commonly installed?
   A. Concrete piles cast in place
   B. Columns of compacted crushed stone installed by vibro-replacement or rammed casing
   C. Columns of lime-treated clay
   D. Steel tubes driven to rock
   Answer: B. Stone columns are compacted crushed stone or gravel placed in lifts after a vibrator or casing makes the hole. (Key point: Stone column material and installation)

3. What governs the capacity of a stone column?
   A. The strength of the stone only
   B. The length of the casing
   C. The colour of the soil
   D. The lateral confinement of the surrounding soft soil, with bulging failure
   Answer: D. q_ult is about sigma_r times Kp, where sigma_r is the limiting radial stress in the soft soil. (Key point: Capacity of stone column)

## Related in Foundation Engineering

- [Preloading and stone columns](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apreloading-stone-columns) — Foundation Engineering, chapter 10

## Related in other subjects

- [Compaction curves of sand and clay](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Acompaction-sand-vs-clay) — Soil Mechanics, chapter 5
- [Road compaction specification, sand cone](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aroad-compaction-sand-cone-check) — Soil Mechanics, chapter 5
- [Materials for 5 m³ stone masonry 1:6](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Amaterials-stone-masonry-5m3) — Estimating and Costing, chapter 4