I am working with weathered granite laying on hard granite on Plaxis 2D v20. The problem is I used RocLab to get the closest fit to Mohr Coulumb just to make sure of the hoek brown results. What is VERY weird is that mohr coulumb input reach an overall factor of safety of 2 , while hoek brown model is more reinforced and reaches FS= 1.2 ...
Another question on plaxis, in hoek brown model Erm is defined in the manual as modulus of rock mass and you can easilty calculate it. What value E' should I input into plaxis mohr coulumb model? Do I use the same E=Erm?
The value E' as input into plaxis is similar to E of the mohr coulomb model into rocklab.
The value determined for the rock mass can be used, but a certain range can be obtained by taking the UCS values lower in the design for more altered zones.
Check the stress level you used in RockLab. If the confining stresses in RockLab in the region of interest are different from the stresses in your Plaxis model, the distance from linear M-C shear strength envelope to curved H&B shear strength envelope may be significant, affecting plastification.
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