   Chapter 12, Problem 12.8P Principles of Geotechnical Enginee...

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

Solutions

Chapter
Section Principles of Geotechnical Enginee...

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

Refer to the triaxial test on the silty clay specimen in Problem 12.6.a. What is the inclination of the failure plane with the major principal plane?b. Determine the normal and shear stress on a plane inclined at 30° with the major principal plane at failure. Also, explain why the specimen did not fail along this plane.12.6 Consider the silty clay soil in Problem 12.4. If a consolidated drained triaxial test is conducted on the same soil with a chamber-confining pressure of 105 kN/m2, what would be the deviator stress at failure?

(a)

To determine

Find the inclination of the failure plane with the major principal plane.

Explanation

Given information:

The diameter (d) of clay sample particle is 63.5mm.

The height (h) of the clay sample is 32mm.

The angle of friction ϕ is 30°.

Calculation:

Calculate the area of specimen (A) as follows:

A=πd24 (1)

Substitute 63.5mm for d in Equation (1).

A=π(63.5)24=12,661.264=3,165.32mm2(1m103mm)2=0.00316m2

Find the normal stress (σ) using the formula as follows:

σ=NA (2)

Here, N is the normal force and A is the area of specimen.

Substitute 0.00316m2 for A and 84N for N in Equation (2).

σ=840.00316=26,582.27N/m2(1kN1,000N)=26.58kN/m2

Similarly calculate the normal stress (σ) for remaining Tests as shown in Table 1.

 Test no Normal force, N(N) Normal stress (σ′)(kN/m2) 1 84 26.58 2 168 53.16 3 254 80.38 4 360 113.92

Find the shear strength (τf) of the failure as follows:

τf=SA (3)

Here, S is shear force.

Substitute 28.9N for shear force and 0.00316m2 for A in Equation (3).

τf=28.90.00316=9,145.5N/m2(1kN1,000N)=9

(b)

To determine

Find the normal and shear stress on a plane inclined at 30° with the major principal plane at failure.

Explain why the specimen did not fail along this plane.

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