Settlement Equations
Settlement Equations
(OP)
I have a book by Das that shows the primary settlement for overconsolidated soils equation being based on Cs (swell index).
I have a book by Coduto that shows the exact same equation except it uses Cr(recompression index) instead of Cs.
Which one is correct?
I have a book by Coduto that shows the exact same equation except it uses Cr(recompression index) instead of Cs.
Which one is correct?





RE: Settlement Equations
DAS: S=Cs H/(1+eo)log(pf'/po')
Coduto: S=Cr H/(1+eo)log(pf'/po')
RE: Settlement Equations
RE: Settlement Equations
I see in the Coduto book I have, it says "that the recompression and rebound curves have nearly equal slopes, but the rebound curve is more reliable because it is less sensitive to to sample disturbances". Coduto goes on to use the recompression index specifically where Das uses the swell index.
So it doesn't matter which one you use, since they are supposed to be the same slope?
RE: Settlement Equations
I happen to like to report the recompression index and compression index as the recompression and compression ratios - in these, you can obtain from a strain-log p curve or conversely, divide the Cr, Cc by 1+e0.
RE: Settlement Equations
RE: Settlement Equations
What is being described is a method for estimating the amount of settlement that will occur if a load is applied to an overconsolidated soil mass and the magnitude of the load does not exceed the "maximum load" that the soil had experienced in the past. It is a little more complicated than that in reality but for the purposes of discussion, the above statement will suffice.
Cracks in sheet rock are generally caused by differential movements of the foundation. These can be due to settlements or do to heaving or some combination of the two.
Settlements of overconsolidated soils are generally quite small and hence a probably not responsible for your cracking.
RE: Settlement Equations
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.
RE: Settlement Equations
RE: Settlement Equations
If the test is run "properly" by incorporating an unload/reload cycle as a part of the consolidation test, you don't have to worry about sample disturbance.
Choice of CR or CS will affect your answer, unless you choose a "representative" value that essentially represents both -
What are you analyzing?
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.
RE: Settlement Equations
RE: Settlement Equations
Focht3 is right that there is some curvature on the rebound/reload - but sometimes, too many take it to far back in this area (viz., too much rebound). For estimating the appropriate level of rebound (then reloading), I'd look at the approximate difference in the existing effective pressure and the preconsolidation pressue - then control the rebound value to this basic difference. It might give a better (straighter) line on both rebound and reload.