Which type of lime is commonly used in soil stabilisation to improve the engineering properties of clay soils and enhance their load-bearing capacity?
Try it first: pick an option, then read the explanation.
Asked in SSC JE 05/06/2024 (Morning)
Detailed Explanation
Adding lime to a clay changes it chemically. Calcium ions replace the sodium and other ions on the clay particles (cation exchange), so the particles flocculate and the soil becomes more friable, less plastic and less prone to swelling. Over time, lime also reacts with silica and alumina in the clay (pozzolanic reaction) to form cementing compounds that raise strength.
Why “Hydrated lime or Quicklime” Is Correct
The two forms of lime used for stabilisation are quicklime (CaO) and hydrated lime (Ca(OH)2). Quicklime is more concentrated and also dries wet soil as it hydrates; hydrated lime is easier and safer to handle and is the most common. Option (b) names both, so it is the best answer.
Note: the commission cancelled this question, because hydrated lime is the same thing as slaked lime (option a), so two options were effectively correct. Remember the content rather than the key: hydrated (slaked) lime and quicklime are both used.
| Method | How it works | Best for |
|---|---|---|
| Mechanical | Blend soils to a good grading and compact | Granular bases and sub-bases |
| Cement | Cement hydrates and binds particles | Sandy and low-plasticity soils |
| Lime | Cation exchange and pozzolanic reaction cut plasticity and swelling | Clays, black cotton soil |
| Bitumen | Coats grains, waterproofs and binds | Sandy soils |
| Chemical / other | Calcium chloride, sodium silicate, geotextiles, heat | Special cases |
Why the Other Options Are Wrong
- A. Slaked lime: Slaked lime is hydrated lime, so it is also used — this overlap is why the question was cancelled.
- C. Fat lime: ‘Fat lime’ is a classification of building lime by purity; it is not the term used for stabilisation lime.
- D. Dolomitic lime: Dolomitic lime contains magnesium oxide and is used less often; calcium-rich lime is preferred.
Key Point
Lime stabilisation uses quicklime (CaO) or hydrated/slaked lime (Ca(OH)₂); best suited to clays.
Key Concepts for Students
- Usual lime content is about 2–8% by dry weight of soil.
- Lime reduces plasticity index and swelling of black cotton soil.
- Cement stabilisation suits sandy soils better than heavy clays.
Practice more: this is question 1 in Soil Stabilization MCQs – Part 1. Try the whole set and check every answer instantly.