Hi,
My geotech team is using PLAXIS 2D to predict the settlement from 100-ft deep soft soil. During our check on input parameters, we found that the Poisson's Ratio for Unloading and Reloading (Vur) considerably affected the settlement amount in soft soil. We used Soft soil model for the ground.
PLAXIS reference recommends use Vur=0.2 if there is no other evidence from laboratory testing. I would like to ask you 1) How the Poisson's ratio can be determined from laboratory testing, and 2) Why using Vur=0.2 is recommended and reasonable.
I attached a graph showing the rate of settlements in soft soil condition, and the graph presents that using smaller value for Vur considerably reduced the settlement from both two difference models.
Thanks in advance.
Jinho Park
1) The Poisson's ratio can for instance be measured from a drained triaxial compression test on overconsolidated soil. Plot volume strain as function of axial strain and the initial incliniation of that plot is (1 - 2*nu).
2) When measuriing it from laboratory tests Poisson's ratios found are in the range 0.15-0.25, but generally concentrated around 0.2. Values above 0.25 are not realistic.
With kind regards,
Dennis Waterman
Thank you Dennis.
Do you have a formula or graph showing how to get the Poisson's ratio for Unloading and Reloading?
I could not get sense from "Plot volume strain as function of axial strain and the initial incliniation of that plot is 1-2*nu".
What does nu mean?
Thank you.
Best regards,
Jinho
Dear Jinho,
"nu" obviously is the Poisson's ratio which is denoted with the Greek letter "nu" ...
See the graph below: