With reference to the picture, I am assuming that STAAD.Foundation relates cohesive soil only to undrained condition and cohesionless soil only to drained condition.
Unless there's something I technically misunderstand, according to BS 1377-7:1990, cohesive soil can undergo drained AND undrained tests while cohesionless soil can only undergo drained tests. Accordingly, it is not right to tie the parameters of cohesive soil types only to undrained parameters.
For your reference, in the next image I tabulated from BS 1377-7:1990 the type of test (which is the clause number in the first column) stating the specimen condition in the second column, and which soil type is permitted to be tested for each type of test (third splitted column). Written in pencil is the clause number for reference of the extracted information.
Another question, 'shear strength' is the term that is interpreted by cohesion c and angle of shearing resistance ɸ. That being said, what value am I expected to enter in the shear strength field if cohesionless soil was chosen?
Thanks in advance
Some background.
The terms
Cohesionless SoilCohesive soilCohesionShear Strength
are used only for calculating the resistance to uplift forces. If there is a footing under uplift for one or more load cases, and one or more of these terms is switched on, the contribution to the uplift resistance will come from three terms:
the selfweight of footing and pedestal (if any)the weight of soil on the footingthe frictional resistance along the side faces of the footing if Cohesion or Shear Strength are provided. This resistance is reported in the output under the heading "Effect due to adhesion".
If you still need the details of how adhesive forces are calculated, we have to get back to you after an investigation.
In SFA, Cohesive soil takes Cohesion value and Cohesion-less soil takes Shear Strength value. You are right in the statement that Cohesion-less soil can only go to drained shear test (Not un-drained). So, we must modify the statement here.
Now, SFA uses Cohesion value for cohesive soil or shear strength value for cohesion-less soil only for two reasons-