---
title: "Application of UU, CU, CD tests"
subject: "Soil Mechanics"
chapter: 10
key: "semester_4/soil_mechanics:uu-cu-cd-practical-application"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/uu-cu-cd-practical-application
site: BCT Engineering
---

# Application of UU, CU, CD tests

Soil Mechanics · Chapter 10: Shear Strength of Soil

- Asked in: 2077 Chaitra, 3 marks
- Video: [UU, CU and CD Tests | Soil Mechanics](https://www.youtube.com/watch?v=Cg_NBvLL4Ng) — APSEd
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/uu-cu-cd-practical-application
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-10

## Question

Describe briefly the practical application of UU, CU and CD triaxial tests.

## Short answer

UU test gives undrained strength for short-term stability of foundations and embankments on soft clay. CU test provides parameters for cases like rapid drawdown after consolidation, using total or effective stress. CD test yields drained parameters for long-term stability of slopes, retaining walls, and for sands.

## Answer

**UU test (unconsolidated undrained)**

- Gives $c_u$ with $\phi_u \approx 0$ for saturated clay.
- Used where loading is fast and the clay has no time to drain: **stability of foundations and embankments on soft clay at the end of construction**, bearing capacity in the short term, and temporary excavations in clay.

**CU test (consolidated undrained)**

- Gives $c_{cu}$ and $\phi_{cu}$ (total stress) and, with pore pressure measurement, $c'$ and $\phi'$ (effective stress).
- Used where soil is first consolidated and then loaded quickly: **rapid drawdown of an earth dam** after steady seepage, stage-constructed embankments, and sudden loading of already-consolidated clay under a structure.

**CD test (consolidated drained)**

- Gives $c_d$ and $\phi_d$ (about equal to $c'$, $\phi'$).
- Used for **long-term stability** when excess pore pressure has dissipated: natural slopes and cuttings, retaining walls and drained foundations, and for sand and gravel, which drain quickly.

## Check yourself

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

1. Which field situation is best modelled by the UU test?
   A. Long-term stability of a natural slope
   B. Stability of an embankment on soft clay at the end of construction
   C. Rapid drawdown of an earth dam after steady seepage
   D. Drained stability of a retaining wall in sand
   Answer: B. Loading is fast and soft clay cannot drain, so the undrained UU strength (c_u, phi_u = 0) applies. (Key point: UU application)

2. The CU test is most suitable for which case?
   A. Rapid drawdown of an earth dam after steady seepage
   B. End-of-construction stability on soft clay
   C. Long-term stability of a cutting
   D. Slope in clean gravel
   Answer: A. Soil is first consolidated under seepage and then loaded quickly, which is the consolidated-undrained condition. (Key point: CU application)

3. Why is the CD test used for long-term stability and for sand and gravel?
   A. Pore pressure is at its maximum so total stress parameters are needed
   B. Loading is so fast that no drainage occurs
   C. The soil is assumed to have phi = 0
   D. Excess pore pressure has dissipated, so drained parameters c_d and phi_d (about c', phi') govern
   Answer: D. Long-term or free-draining conditions have no excess pore pressure, so the drained parameters apply. (Key point: CD application)

## Related in Soil Mechanics

- [Triaxial tests by drainage; UCS vs cu](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Atriaxial-tests-by-drainage-ucs) — Soil Mechanics, chapter 10
- [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
- [Three triaxial tests, Mohr circles, φ](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Amohr-circle-three-triaxial-tests-friction) — Soil Mechanics, chapter 10
- [CU tests on overconsolidated clay](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Acu-overconsolidated-effective-parameters) — Soil Mechanics, chapter 10
- [UCS as special case of UU test](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aucs-special-uu-triaxial) — Soil Mechanics, chapter 10

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