Variation of void ratio during primary consolidation test

[M. Tecle]

The following is a summary of a primary consolidation test on a silty clay with trace sand & gravel.


Load, psf Strain Void Ratio t50, min Cv, ft2/day

100 0.00 0.51 0.00 N/A
500 0.41 0.51 1.00 0.40
1000 0.90 0.50 6.25 0.06
2000 1.36 0.49 3.06 0.13
4000 0.58 0.50 2.72 0.15
8000 1.08 0.49 1.00 0.39
16000 2.06 0.48 0.81 0.48
32000 3.35 0.46 1.44 0.26
8000 3.01 0.47 1.00 0.37
2000 2.65 0.47 4.00 0.09
500 2.19 0.48 N/A N/A



Initial Final
Moisture Content, % 19.0 17.4
Wet Density, pcf 130.3 131.7
Dry Density, pcf 109.5 112.2

The above results show that there is an increase in void ration during the load increment to 4000 lbs. Can anyone tell me what could be the reason for that increase?

 

[M. Tecle]

Sorry for the confusing data shown in my previous post. Attached is a better presentation.

 

[LRJ]

It shouldn't have swelled. I wonder if the test specimen/equipment was altered in any way during the test?

 

[fattdad]

was this an undisturbed sample?
do you actually have data that shows it's a silty clay (i.e., cl-ml, per d2487)?
The plot is certainly gacked up! It's not just the 2tsf strain!

Not sure. . . It would help to know more about the sample depth, LL, PI, actual sand content, water content with respect to the LL, where's the water table and anything you know about the local formation.

Is this residuum? I ask because the depositional environment for an actual silty clay with trace sand and gravel seems glacial or residual. Doesn't seem marine. If interbedded it could be riverine?

Interesting. . .

f-d

ípapß gordo ainÆt no madre flaca!

 

[M. Tecle]

Thank you LRJ and f-d. Classification of the sample was verified using D2487 that it is Silty Clay. The sample was collected from below a river, undisturbed (using a shelby tube).

 

[aeoliantexan]

Excuse me for coming to this party so late. Plot void ratio or strain vs log pressure, cut the graph between the 2000 and 4000 psf points, and slide the second half of the graph straight down until it lines up with an extrapolation of the first half. Then it looks like a pretty good test. I think someone bumped or reset the dial gauge in the middle of the test. Seriously.

 

[LRJ]

That was my thought too: that the test equipment was knocked. However, such interpretations as you suggest shouldn't be applied: a re-test should be requested, at the expense of the contractor that performed this defective test.