Principles of Geotechnical Enginee...

9th Edition
Braja M. Das + 1 other
ISBN: 9781305970939



Principles of Geotechnical Enginee...

9th Edition
Braja M. Das + 1 other
ISBN: 9781305970939
Textbook Problem

Consider the clay sample in Problem 12.11. A consolidated-undrained triaxial test was conducted on the same clay with a chamber pressure of 10 lb/in.2. The pore pressure at failure was (Δud)f = 4.2 lb/in.2. What would be the major effective principal stress, σ 1 , at failure?

12.11 In a consolidated-drained triaxial test on a normally consolidated clay, the specimen failed at a deviator stress of 27 lb/in.2. If the effective friction angle is known to be 23°, what was the effective confining pressure at failure?

To determine

Find the major effective principal stress, σ1 at failure.


Given information:

The pore water pressure at failure (Δud)f is 4.2lb/in2.

The effective friction angle (ϕ) is 23°.

The chamber pressure (σ3) is 10lb/in2.


Show the expression of major effective principal stress as shown below:

σ1=σ3tan2(45+ϕ2)+2c(45+ϕ2) (1)

Here, σ3 and σ1 minor and major effective principal stress and c is cohesion.

For normally consolidated clay, cohesion is equal to zero.

Substitute 0 for c in Equation (1)

σ1=σ3tan2(45+ϕ2)+2(0)(45+ϕ2)=σ3tan2(45+ϕ2) (2)

Substitute (σ3Δud(f)) for σ3 and 23° for ϕ in Equation (2)

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