Chapter 12, Problem 12.22P

### Principles of Geotechnical Enginee...

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

Chapter
Section

### Principles of Geotechnical Enginee...

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

# Undisturbed samples from a normally consolidated clay layer were collected during a subsoil exploration. Drained triaxial tests showed that the effective friction angle was ϕ ′ = 25 ° . The unconfined compressive strength, qu, of a similar specimen was found to be 133 kN/m2. Find the pore pressure at failure for the unconfined compression test.

To determine

Find the pore pressure at failure for the unconfined compression test.

Explanation

Given information:

The effective angle of friction (ϕ) is 25°.

The compressive strength is (σ1) is 133kN/m2.

Calculation:

Show the equation of the major effective principal stress (σ1) as follows

σ1=σ1(Δud)f

Here, (Δud)f is the pore water pressure developed in the specimen at failure.

Show the equation of the minor effective principal stress (σ3) as follows

σ3=σ3(Δud)f

σ1=σ3tan2(45+ϕ2)σ1σ3=tan2(45+ϕ2)

Substitute σ1(Δud)f for σ1 and σ3(Δud)f for σ3.

σ1(Δud)fσ3(Δud)f=tan2(45+ϕ2) (1)

Consider the normal stress (σ3) at initial point is 0

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