Question

For the clay with an OCR of greater than 4 in a CD test, the A-factor at failure will be. 
1. Zero
2. Positive (less than 1)
3. Negative
4. Positive (more than 1)

Answer 1

Correct Answer - Option 3 : Negative

Concept:

Over Consolidation Ratio:

Over Consolidation Ratio ( OCR ) is defined as the ratio of maximum pressure experienced in the past

( Preconsoildation pressure ) to the present overburden pressure.

\({\bf{OCR}} = \frac{{{\bf{Maximum}}\;{\bf{pressure}}\;{\bf{in}}\;{\bf{past}}}}{{{\bf{Present}}\;{\bf{overburden}}\;{\bf{pressure}}}}\)

OCR > 1 ⇒ It is Over consolidated soil

OCR = 1 It is Normally consolidated soil

OCR < 1It is Under consolidated soil

Calculation:

OCR of clay = 4

Since the OCR of the given soil is greater than 1, it is overconsolidated clay.

A – factor is a function of the over-consolidation ratio in the case of overconsolidated clay.

For OC clays, A = f (OCR)

For heavily overconsolidated clay A < 0, the typical value of A are –0.2 to –0.3