The 'unconfined compression test' (UCT) gives the undrained shear strength (Su) of clay as:
Choose the correct answer
Su = qu (full compressive strength)
Su = qu/2 (half the unconfined compressive strength, for φ=0 saturated clay)
Su = 2qu
Su cannot be found from UCT
Correct Answer
B. Su = qu/2 (half the unconfined compressive strength, for φ=0 saturated clay)
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UCT: no cell pressure (σ3 = 0). Axial load applied until failure. qu = unconfined compressive strength. Since σ3 = 0 and σ1 = qu, Mohr circle has diameter qu. For φ = 0 condition (saturated clay, undrained): Su = qu/2. Test is quick, simple; valid for saturated clays only. Not for sands (need confinement).
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