---
title: "Normally vs over consolidated soil"
subject: "Soil Mechanics"
chapter: 9
key: "semester_4/soil_mechanics:normally-vs-over-consolidated"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/normally-vs-over-consolidated
site: BCT Engineering
---

# Normally vs over consolidated soil

Soil Mechanics · Chapter 9: Compressibility of Soil

- Asked in: 2076 Baisakh, 2 marks; 2073 Bhadra, 2 marks (asked 2 times)
- Video: [Over Consolidated Soil and Normally Consolidated Soil | OCR | Elementary Engineering](https://www.youtube.com/watch?v=xzc8MoLcu4c) — Elementary Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/normally-vs-over-consolidated
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-9

## Question

Differentiate between normally consolidated and over consolidated soil deposits.

## Short answer

Normally consolidated soil has never sustained pressure greater than present overburden (OCR=1), is highly compressible and settles more. Overconsolidated soil experienced higher past pressure (OCR>1), is stiffer, less compressible, and has higher strength.

## Answer

| Point | Normally consolidated (NC) | Over consolidated (OC) |
|---|---|---|
| Definition | Present effective overburden pressure is the maximum it has ever experienced | Present effective overburden is less than the maximum past pressure |
| Pre-consolidation pressure $\sigma'_c$ | $\sigma'_c = \sigma'_0$ | $\sigma'_c > \sigma'_0$ |
| OCR | $OCR = 1$ | $OCR > 1$ |
| Compressibility | High (steep virgin line) | Low (flat recompression curve) |
| Settlement | Large | Small |
| Strength | Lower | Higher, stiffer |
| Cause | Deposition under normal geological loading | Erosion, removal of ice, desiccation, water table fluctuation |

## Check yourself

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

1. A normally consolidated soil is one in which
   A. present effective overburden is the maximum it has ever experienced
   B. past pressure was greater than present
   C. the soil is dry
   D. OCR is greater than 1
   Answer: A. For NC soil, sigma'c = sigma'0 and OCR = 1. (Key point: NC definition)

2. For an over-consolidated soil, OCR is
   A. equal to 1
   B. less than 1
   C. greater than 1
   D. zero
   Answer: C. sigma'c > sigma'0, so OCR > 1. (Key point: OCR)

3. Compared with NC clay, OC clay generally has
   A. higher compressibility and larger settlement
   B. lower compressibility, smaller settlement and higher stiffness
   C. the same compressibility
   D. no strength
   Answer: B. OC clay follows the flat recompression curve, so it is stiffer and settles less. (Key point: Settlement behaviour)

## Related in Soil Mechanics

- [Average permeability of layered soil](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Alayered-soil-average-permeability) — Soil Mechanics, chapter 6
- [Triaxial advantage over direct shear](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Atriaxial-advantages-over-direct-shear) — Soil Mechanics, chapter 10
- [NC/OC clay, e-log p, preconsolidation](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aconsolidated-clay-e-log-p-preconsolidation) — Soil Mechanics, chapter 9
- [Clay over sand, effective stress at depths](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aclay-sand-profile-effective-stress-depths) — Soil Mechanics, chapter 6
- [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
- [Drained and CU tests on two samples](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Adrained-and-cu-two-samples-parameters) — Soil Mechanics, chapter 10

## Related in other subjects

- [Simple vs compound interest; number of deposits](https://www.bctengineer.com/question.md?key=semester_6%2Fengineering_economics%3Asimple-vs-compound-deposits-20-lakh) — Engineering Economics, chapter 2
- [Soil and rock types of Himalayan zones](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Asoil-and-rock-types-of) — Engineering Geology I, chapter 7
- [Balanced, under, over sections with strain diagrams](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Abalanced-under-over-sections-with-strain) — Design of RCC Structure, chapter 4
- [Allowable load of 400 mm pile, layered soil](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-400mm-layered-soil-chart) — Foundation Engineering, chapter 8