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

# Preloading and stone columns

Foundation Engineering · Chapter 10: Foundation Soil Improvements

- Asked in: 2078 Bhadra, 3 marks
- Video: [Design and Construction of Stone Columns: A Method of Ground Improvement Technique](https://www.youtube.com/watch?v=pkfIlWgoKF4) — Geotechnical Engineering Consultancy
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/preloading-stone-columns
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-10

## Question

In order to increase the engineering properties of soils, soil stabilization is done. Briefly explain the preloading and stone columns for foundation soil improvements.

## Short answer

Preloading places temporary surcharge fill on soft clay to induce consolidation settlement before construction, often with vertical drains. Stone columns are compacted crushed stone columns installed by vibro-replacement, increasing bearing capacity, reducing settlement and providing drainage.

## Answer

Soil stabilization improves the strength and reduces the settlement of weak soils. Two common ground-improvement methods are given below.

#### Preloading

Preloading means placing a temporary load (surcharge fill) on the site before construction, so that most of the consolidation settlement of soft clay occurs beforehand.

- The fill is kept in place until the expected settlement is achieved, then removed, and the structure is built.
- Vertical **sand drains** or prefabricated vertical drains (PVD) are often provided to shorten drainage paths and speed up consolidation.
- Settlement is monitored with settlement plates and piezometers.
- It is suitable for soft clays, silts and organic soils where time is available. Disadvantage: it needs time and space.

#### Stone columns

Stone columns are vertical columns of compacted crushed stone (gravel) installed in soft clay or loose silty soil.

- A hole is made by a vibrating probe (vibro-replacement) or by driving a casing, then filled with stone in lifts and compacted.
- The stiff columns carry most of the load and also act as drains.
- They increase bearing capacity, reduce settlement and reduce liquefaction potential.
- Typical diameter is 0.6-1.0 m at 1.5-3 m spacing.

## Check yourself

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

1. Why is surcharge placed before construction in preloading?
   A. So most consolidation settlement of soft clay occurs beforehand
   B. To stop all drainage
   C. To make the clay swell
   D. To lower the water table
   Answer: A. Settlement is brought forward, so the structure then settles little. (Key point: Purpose of preloading)

2. What is the main disadvantage of preloading?
   A. It needs a vibrating probe
   B. It increases liquefaction
   C. It reduces bearing capacity
   D. It needs time and space
   Answer: D. Consolidation takes time and fill material and space are required. (Key point: Limitation of preloading)

3. How do stone columns improve soft ground?
   A. Stiff columns carry most load and act as drains, reducing settlement and liquefaction potential
   B. They act only as anchors
   C. They only waterproof the soil
   D. They loosen the soil
   Answer: A. Compacted stone is stiffer than the soft soil and also drains water. (Key point: Stone column action)

## Related in Foundation Engineering

- [Sand compaction piles and stone columns](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asand-compaction-piles-stone-columns) — Foundation Engineering, chapter 10, asked 3×
- [Soil stabilization by admixture](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aadmixture-stabilization) — Foundation Engineering, chapter 10, asked 2×
- [Methods of soil stabilization](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asoil-stabilization-methods) — Foundation Engineering, chapter 10, asked 2×
- [Preloading](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apreloading) — Foundation Engineering, chapter 10, asked 3×
- [Purposes of foundation soil improvement](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asoil-improvement-purposes) — Foundation Engineering, chapter 10
- [Bituminous stabilization](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Abituminous-stabilization) — Foundation Engineering, chapter 10

## Related in other subjects

- [Soil stabilization methods and lime stabilized road](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-methods-lime-road) — Transportation Engineering II, chapter 3
- [Soil stabilization, equipment, mass haul characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-definition-equipment-mass-haul) — Transportation Engineering II, chapter 3
- [Soil stabilization methods; soil cement construction](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-methods-soil-cement-road) — Transportation Engineering II, chapter 3
- [Soil stabilization factors; mechanical; cement-soil base](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-factors-mechanical-cement-soil) — Transportation Engineering II, chapter 3