# Consolidated drained triaxial test

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1. May 13, 2017

### fonseh

1. The problem statement, all variables and given/known data
This is the problem regarding with Consolidated drained triaxial test .
I have uploaded some photos here . The first photo is from my notes . While the 2nd until the 3rd photo are from my refernce book .

2. Relevant equations

3. The attempt at a solution
In the first photo , I dont understand why the σ1' = σ1 ?
Since the water is drained from the soil , so i think the first red circled is incorrect ..The shear stress at step 1 should be σ1 only .

For the green circle part , why σ3 = σ3 ' ? Shouldnt it = σ'3 = σ3 + Δσ ( pressure due to drainage) ?
In 641,jpg , we can see that the effective stress at failure is σ3 + Δσ . But , i don't understand why it's σ3 = σ1 .

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• ###### 641.png
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Last edited by a moderator: May 13, 2017
2. May 14, 2017

### Staff: Mentor

The sample starts out with the compressive stress components equal in all directions, and zero pore pressure. Then, the axial stress is increased, while the transverse stress is held constant (and water is allowed to seep out, so that the pore pressure remains zero). The only question is, why doesn't the transverse stress increase as a result of the Poisson effect. Maybe, by the nature of the test, the transverse stress is held constant.

3. May 14, 2017

### fonseh

Do you mean in the case in the 638.PNG , the transverse stress is held constant ?
While in the 639-641 , the tranverse stress is allowed to increase ?

4. May 15, 2017

### Staff: Mentor

639 doesn't say anything about the transverse stress. But in 640 and 641, yes.

5. May 18, 2017

### fonseh

Do you mean in the case in the 638.PNG , the transverse stress is held constant ?

6. May 18, 2017

### fonseh

do you mean in 639- to 641 , all the shear stress( in all direction) is allowed to increase ? But in 638 , the tranverse stress is kept constant ?

7. May 18, 2017

### Staff: Mentor

Sure.

8. May 18, 2017

### Staff: Mentor

We are dealing with the principal stresses here, so there are no shear stresses in these directions.

9. May 18, 2017

### fonseh

One more question , why σ1' = σ1 ? and σ1 ' = σ1 + Δσ ???

10. May 19, 2017

### Staff: Mentor

Because the pore pressure is zero.

11. May 19, 2017