Soil test - Triaxial (HSM)

Question

Hello, 
 
 I have a question regarding the Eur parameter of the HSM, which is the rigidity of unloading / reloading of the drained triaxial test.

Unfortunately, I have the drained triaxial test data (without unloading and reloading) it's a loading increment until a 14% of axial deformation, so what I can get is the data "E50" and I am unable to calculate the Eur, on the other hand I have data from the oedometric tests contain unloading and reloading, can I obtain a Eur rigidity from the oedometer data and use it as Eur in the HSM parameters? 
 
 Best regards.

Stefanos Papavasileiou · Answer

Dear Adnan, 
 It is possible to use the unloading/reloading stiffness from the oedometer test instead. We know that based on Hooke's law you can correlate the Eur,oed to the Eur,triax and for a low Poisson's ratio (vur) these are Eur,oed ~ 1.1 * Eur,triax In any case, you will probably need to do a calibration with SoilTest for the Eoed,ref, therefore, you can also directly use the Eur,oed and see if that matches the laboratory data you have. 
 Regarding the different reference pressure, you can use the equations in our Material Models manual that define the E50, Eur and Eoed based on the reference pressure you have (&sigma;'3 for triaxial test or &sigma;'1 for oedometer test) and the power m parameter. In our latest manuals, i.e. CONNECT Edition V20 Update 2, these are equations 6.3, 6.5 and 6.16, respectively 
 Typically for sand m=0.5, so, for example, you can calculate E50,ref = E50 * sqrt(pref/&sigma;'3) in which pref = 100kPa and &sigma;'3 is the reference pressure you have.