Can a time varying external load applied to a saturated soil mass generate excess pore pressure when using Mohr-Coulomb in a coupled fluid-mechanical analysis?

FLAC3D
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Hello @everyone, @itascaYang @isaac @itsmoho_sen @ITE @itascaYang @itasca @dafo407_itasca @ddegagne @dblanksma @itmam

I am running a coupled fluid–mechanical FLAC3D model using the Mohr-Coulomb constitutive model. I have assigned fluid properties such as permeability, porosity, Biot coefficient/fluid modulus, and initialized the pore-pressure field.

My current approach has been based on the standard coupled-flow formulation using:

  • Biot fluid coupling
  • Fluid modulus
  • Porosity and permeability
  • Fluid-flow calculations using model fluid active on
  • Flow convergence using model solve fluid ratio-flow
  • Evaluation of characteristic fluid time scales and fluid-flow time totals following the ITASCA recommendations for coupled analysis.

The general workflow I have been using is:

  1. Establish the initial phreatic surface and steady-state pore-pressure field.
  2. Perform mechanical adjustment to obtain equilibrium under the generated pore-pressure distribution.
  3. Activate coupled fluid–mechanical analysis.
  4. Apply a time varying external loading to the model and monitor pore-pressure and excess pore response within the soil.

My loading is not an earthquake loading problem. The objective is to investigate pore-pressure generation within the soil mass due to externally applied mechanical loading on the structure.

My question is:

Can the standard Mohr-Coulomb model in FLAC3D generate excess pore pressure due to external mechanical loading in a coupled fluid–mechanical analysis? In other word, in a fully coupled Mohr-Coulomb analysis, can excess pore pressure be generated through poroelastic compression caused by an external load, and if so, how does this differ from the excess pore-pressure generation mechanisms implemented in Finn, Roth, or P2PSand models?

Or is Mohr-Coulomb only able to respond to assigned/flow-generated pore pressures, while contraction-induced or cyclic excess pore-pressure generation requires a special constitutive model such as Finn or P2PSand?

Any recommended ITASCA examples or documentation explaining this difference would be very helpful.

Thank you.