Chapter 12, Problem 12.14P

### 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

# Following are the results of consolidated-undrained triaxial tests on undisturbed soils retrieved from a 4-m thick saturated clay layer in the field (γsat = 20.7 kN/m3). a. Estimate graphically the Mohr-Coulomb shear strength parameters c' and ϕ'. b. Estimate the shear strength in the middle of the clay layer.

(a)

To determine

Find the Mohr column shear strength parameters c and ϕ by graphical method.

Explanation

Given information:

The saturated unit weight (γsat) 20.7kN/m3.

The thickness (t) of clay layer is 4m.

The chamber pressure, deviator stress, and pore pressure at failure for tests 1, 2, and 3 is given in the Table.

Calculation:

Consider Test 1:

Find the effective minor principal stress (σ3) at failure for test 1 using the relation:

σ3=σ3(Δud)f (1)

Here, σ3 is chamber pressure and (Δud)f is pore water pressure at failure.

Substitute 75kN/m2 for σ3 and 11kN/m2 for (Δud)f in Equation (1).

σ3=75(11)=86kN/m2

Find the effective major principal stress (σ1) at failure for Test No 1 using the relation as follows:

σ1=σ3+(Δσd)f (2)

Here, σ3 is effective minor principal stress and (Δσd)f is deviator stress at failure.

Substitute 86kN/m2 for σ3 and 166kN/m2 for (Δσd)f in Equation (1).

σ3=86+166=252kN/m2

Similarly calculate the effective minor principal stress (σ3) and effective major principal stress (σ1) for remaining Test 2 and 3

(b)

To determine

Find the shear strength in the middle of the clay layer.

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