Chapter 12, Problem 12.17P

### 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

# Consider the triaxial tests in Problem 12.16. a. What are the normal and shear stresses on a plane inclined at 33° to the major principal plane for specimen I? b. What are the normal and shear stresses on the failure plane at failure for specimen II? 12.16 The results of two consolidated-drained triaxial tests on a clayey sand are given here.Calculate the shear strength parameters of the soil.

(a)

To determine

Find the normal and shear stress on a plane inclined at 33° to the major principal plane for specimen I.

Explanation

Given information:

Specimen I:

The chamber pressure σ3 is 70kN/m2.

The deviator stress is (σ1σ3)f is 155kN/m2.

The inclined angle with major principal plane θ is 33°.

Specimen II.

The chamber pressure σ3 is 140kN/m2.

The deviator stress (σ1σ3)f is 265kN/m2.

Calculation:

For specimen I:

Find the major principal effective stress at failure (σ1) as shown below:

(σ1)=σ3+(Δσd)f (1)

Substitute 70kN/m2 for σ3 and 155kN/m2 for (Δσd)f in Equation (1).

(σ1)=70+155=225kN/m2

Find the normal stress (σf) on a plane inclined at 33° to the major principal plane for

specimen I using the equation.

σf=σ1+σ32+σ1σ32cos2θ (2)

Here, σ3 and σ1 minor and major effective principal stress, ϕ is angle of friction, and c is cohesion

(b)

To determine

Find the normal and shear stress on the failure plane at failure for specimen II.

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