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 .