   Chapter 12, Problem 12.18P 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

A clay sample was consolidated in a triaxial test under an all-around confining pressure of 15 lb/in.2. The sample was then loaded to failure in undrained condition by applying an additional axial stress of 22 lb/in.2. A pore water pressure sensor recorded an excess pore pressure of (Δud)f = 29 lb/in.2 at failure. Determine the undrained and drained friction angles for the soil.

To determine

Find the undrained and drained friction angles for the soil.

Explanation

Given information:

The confining pressure (σ3) is 15lb/in2.

The additional axial stress (Δσd) is 22lb/in2.

The excess pore pressure at failure (Δud)f is 9lb/in2.

Calculation:

Calculate the total major principal stress (σ1) using the following formula.

σ1=σ3+(Δσd) (1)

Here, (σ3) is total minor stress at failure and (Δσd)f is the deviator stress.

Substitute 15lb/in2 for σ3 and 22lb/in2 for (Δud)f in Equation (1).

σ1=15+22=37lb/in2

Find the undrained friction angles (ϕ) for the soil using the relation.

σ1=σ3tan2(45+ϕ2)σ1σ3=tan2(45+ϕ2)

(σ1σ3)12=tan(45+ϕ2)

tan1(σ1σ3)12=(45+ϕ2)ϕ2=tan1(σ1σ3)1245ϕ=2[tan1(σ1σ3)1245] (2)

Substitute 15lb/in2 for (σ3) and 37lb/in2 for σ1 in Equation (2).

ϕ=2[tan1(3715)1245]=2[tan1(1

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