====== EP-ROCK ======
===== Description =====
Constitutive law for layered rocks at constant temperature

==== The model ====
This law is only used for elasto‑plastic constitutive law for mechanical analysis of layered rocks, with only one family of parallel joints.  Rocks are elastic and joints have a COULOMB rigid plastic behaviour.
==== Files ====
Prepro: LROCK.F \\
Lagamine: ELP1.F (2D), ELP3DT.F (3D)
===== Availability =====
|Plane stress state| NO |
|Plane strain state| YES |
|Axisymmetric state| NO |
|3D state| YES (?) |
|Generalized plane state| NO |
===== Input file =====
==== Parameters defining the type of constitutive law ====
^ Line 1 (2I5, 60A1)^^
|IL|Law number|
|ITYPE| 10 |
|COMMENT| Any comment (up to 60 characters) that will be reproduced on the output listing|
==== Integer parameters ====
^ Line 1 (I5) ^^
|NINTV|number of sub‑steps used to integrate numerically the constitutive equation in a time step.|
==== Real parameters ====
^Line 1 (6G10.0)^^
|E|Young's elastic modulus|
|ANU|Poisson's ratio|
|CO|material cohesion between layers|
|FI|friction angle (in degrees) between layers|
|ST|stratigraphy angle (in degrees), that is the angle of the layers with respect to an horizontal plane|
|PSI|dilatancy angle (in degrees)|
===== Stresses =====
==== Number of stresses ====
= 6 for the 3-D state \\
= 4 for the other cases.
==== Meaning ====
The stresses are the components of CAUCHY stress tensor in global (X, Y, Z) coordinates.
For the 3-D state :
|SIG(1)|$\sigma_{xx}$|
|SIG(2)|$\sigma_{yy}$|
|SIG(3)|$\sigma_{zz}$|
|SIG(4)|$\sigma_{xy}$|
|SIG(5)|$\sigma_{xz}$|
|SIG(6)|$\sigma_{yz}$|
For the other cases :
|SIG(1)|$\sigma_{xx}$|
|SIG(2)|$\sigma_{yy}$|
|SIG(3)|$\sigma_{xy}$|
|SIG(4)|$\sigma_{zz}$|


===== State variables =====
==== Number of state variables ====
2
==== List of state variables ====
|Q(1)|= element thickness (t) in plane stress state|
|:::|= 1 in plane strain state|
|:::|= circumferential strain rate ($\dot{\varepsilon}_\theta$) in axisymmetrical state|
|:::|= 0 in 3‑D state|
|:::|= element thickness (t) in generalized plane state.|
|Q(2)|= 0 if the current state is elastic|
|:::|= 1 if the current state in elasto‑plastic (i.e., sliding between joints has occurred)|