Previous use in SOPALE varied phi to take account of lambda_pore_prs implicitly, i.e. by choosing phi_effective such that
sin(phi_effective) = (1.0-lambda_pore_prs)*sin(phi)This method can still be used in which case all inputs for lambda_pore_prs should be set to 0 and the input values of phi are interpreted as effective internal angles of friction.
Alternatively, the input phi's are true material properties, e.g. compatible with Byerlee's Law (30-40 degrees) and the lambda_pore_prs values are effective pore pressure ratios associated with each material. Note fluid pressures are not calculated separately/dynamically in this version. Lambda_pore_prs is specified as a material property and should be chosen to reflect the fluid pressure environment envisioned for this material.
| lambda_pore_prs | Fluid pressure environment |
|---|---|
| 0.0 | dry rock environment, no fluid pressure |
| 0.3-0.4 | hydrostatic fluid pressure - depends on the density distribution of the model material |
| close to 1.0 (but not equal to 1.0) | lithostatic conditions, strongly overpressured conditions |
Note that the theory used here is the most simple form. It hides the underlying problem of the best measure of the solid pressure in lambda_pore_prs. The solid pressure may not be lithostatic. This is likely the case in frictional-plastic materials (see Petrini and Podladchikov, J.Met.Geol.v.18, p.67-77, 2000).