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zaqqaz (Geotechnical) (OP)
10 Jul 07 15:27
Hello everybody,

Does anybody have experience with consolidation test using constant rate of loading (CRL)? How comparable are the results to the regular testing methods.

I appreciate any advise on the required equipment as well.

Thanks
jdonville (Geotechnical)
16 Jul 07 17:50
zaqqaz,

What's your situation that you need to do something other than the standard 1-D oedometer test?

Jeff
Helpful Member!  rockiologist (Geotechnical)
18 Jul 07 7:41
zaqqaz,

If you have access to ASTM D4186 V.04.09 please read. The biggest advantage to the CRS test compared to the incremental is speed. With a CRS test a sample can be completed in as little as two (2) days sometimes sooner. The biggest limiting factor is the permeability of the soil. YOU have to keep a pore pressure ratio between 3-15% according to ASTM. The biggest downfall is the cost of the equipment. ASTM D 4186 states that you must use data aquisiton software due and that type of automated equipment is not cheap. I hope this helps.

rockiolgist
zaqqaz (Geotechnical) (OP)
18 Jul 07 9:45
Hi,

As rockiolgist mentioned the most attracting thing with CRS and CRL methods is their speed.  Further, if you have triaxial machine with minimal additional cost you can run the CRS test.  

My only problem is with the validity of the results and how comparable are they with the regular 1D test.

Thanks
moe333 (Geotechnical)
18 Jul 07 11:59
Chuck Ladd's 2003/2004 Arthur Casagrande lecture discusses the interpretation of CRS test results and compares them with 1D tests.  Google Charles Ladd Panamerican conference.
oldestguy (Geotechnical)
18 Jul 07 20:53
It may not be ASTM, but if you are in a hurry and exactness is not needed, add the new load increment at hourly intervals.  On most material I have tested that is sufficient for reasonable accuracy.   Unloading the same but fewer steps.
moe333 (Geotechnical)
19 Jul 07 13:03
Besides the advantage of speed in the CRS test, it also  provides a much better definition of the consolidation curve and the pre-consolidation pressure since the data is  almost continuuous.  You have to be a little lucky to evaluate the virgin and recompression curves, and the pre-consolidation pressure accurately with the odometer test.  Ladd aslo recommends plotting each of the points at the end of primary compression (approximately 1 hr.) since a 24 hr. test will include significant secondary compression.   
BigH (Geotechnical)
19 Jul 07 21:17
moe333 - plotting strain and log(p') on log-log paper gives you a fairly decent estimate of the preconsolidation break in the curve.  Oldestguy has a point - in that the curves at various "times" whether 1 hour, 6 hours, 1 day, 10 days, etc. are fairly parallel - so can get a decent estimate if you are pressed for time of the Cc value.
moe333 (Geotechnical)
20 Jul 07 12:15
My point is that if your loading increments are not close to the preconsolidation pressure, your estimate of pc can be off by a relatively significant amount.  With the odometer test, you need a little luck in order to choose a load that corresponds closely with the actual pc in order to be accurate.  This is not an issue with the CRS test.  The 2003/2004 paper by Ladd discusses this aspect in detail and is a very good (and long) read.     

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