Question

A series of consolidated, undrained triaxial tests were carried out on specimens of a saturated clay under no back pressure. The test data at failure are summarized:

Confining pressure kPa          Deviator stress kPa    Pore water pressure kpa

150                                                    192                                     80

300                                                    341                                     154

450                                                    504                                     222

1. Draw the mohr circles and find the cohesion and friction angle in terms of effective stresses.
2. Compute Skempton’s A-Parameter at failure for all three specimens
3. Is the soil normally consolidated or overconsolidated? Why?
4. Another specimen of the same clay that was consolidated under a cell pressure of 250kPa was to a consolidated , drained trial drained triaxial test. What would be the deviator stress at failure.

                             

A series of consolidated, undrained triaxial tests were carried out on specimens of a saturated clay under no back pressure. The test data at failure are summarized:

Confining pressure kPa          Deviator stress kPa    Pore water pressure kpa

150                                                    192                                     80

300                                                    341                                     154

450                                                    504                                     222

1. Draw the mohr circles and find the cohesion and friction angle in terms of effective stresses.
2. Compute Skempton’s A-Parameter at failure for all three specimens
3. Is the soil normally consolidated or overconsolidated? Why?
4. Another specimen of the same clay that was consolidated under a cell pressure of 250kPa was to a consolidated , drained trial drained triaxial test. What would be the deviator stress at failure.

  

Answer 1

Solution:-

Given that

confining pressure () kpa	Deviator stress () kpa	pore water (u) kpa
150	341	80
192	450	154
300	504	222

we know that

,

,   

,

In terms of effective stress

we know that

..........(i)

.......(ii)

......(iii)

.......(iv)

solving (iii) & (iv) equation

Substitute in eqn (iii)

b)

c)

As it has a cohesion intercept it is referred to as "Over consolidated day".

d)

we know that

676.34 = 250 +