# 15.7. Kayenta Model

Note, many parameters of this model are undocumented.

    BEGIN PARAMETERS FOR MODEL KAYENTA
      B0        = <real> b0
      B1        = <real> b1
      B2        = <real> b2
      B3        = <real> b3
      B4        = <real> b4
      G0        = <real> g0
      G1        = <real> g1
      G2        = <real> g2
      G3        = <real> g3
      G4        = <real> g4
      RJS       = <real> rjs
      RKS       = <real> rks
      RKN       = <real> rkn
      A1        = <real> a1
      A2        = <real> a2
      A3        = <real> a3
      A4        = <real> a4
      P0        = <real> p0
      P1        = <real> p1
      P2        = <real> p2
      P3        = <real> p3
      CR        = <real> cr
      RK        = <real> rk
      RN        = <real> rn
      HC        = <real> hc
      CTPSF     = <real> ctpsf
      CUTPS     = <real> cutps
      CUTI1     = <real> cuti1
      T1        = <real> t1
      T2        = <real> t2
      T3        = <real> t3
      T4        = <real> t4
      T5        = <real> t5
      T6        = <real> t6
      T7        = <real> t7
      J3TYPE    = <real> j3type
      A2PF      = <real> a2pf
      A4PF      = <real> a4pf
      CRPF      = <real> crpf
      RKPF      = <real> rkpf
      FAIL0     = <real> fail0
      FAIL1     = <real> fail1
      FAIL2     = <real> fail2
      FAIL3     = <real> fail3
      FAIL4     = <real> fail4
      FAIL5     = <real> fail5
      FAIL6     = <real> fail6
      FAIL7     = <real> fail7
      FAIL8     = <real> fail8
      FAIL9     = <real> fail9
      PEAKI1I   = <real> peaki1i
      STRENI    = <real> streni
      FSLOPEI   = <real> fslopei
      PEAKI1F   = <real> peaki1f
      STRENF    = <real> strenf
      FSLOPEF   = <real> fslopef
      SOFTENING = <real> softening
      IEOSID    = <real> ieosid
      DILATLIM  = <real> dilatlim
      NU        = <real> nu
      YSLOPEI   = <real> yslopei
      YSLOPEF   = <real> yslopef
      CKN01     = <real> ckn01
      VMAX1     = <real> vmax1
      SPACE1    = <real> space1
      SHRSTIFF1 = <real> shrstiff1
      CKN01     = <real> ckn02
      VMAX1     = <real> vmax2
      SPACE1    = <real> space2
      SHRSTIFF1 = <real> shrstiff2
      CKN01     = <real> ckn03
      VMAX1     = <real> vmax3
      SPACE1    = <real> space3
      SHRSTIFF1 = <real> shrstiff3
    END [PARAMETERS FOR MODEL KAYENTA]

Kayenta is an outgrowth of the Brannon-Fossum-Strack isotropic geomaterial model that includes features and fitting functions appropriate to a broad class of materials including rocks, rock-like engineered materials (such as concretes and ceramics), and metals. Fundamentally, Kayenta is a computational framework for generalized plasticity models. As such, it includes a yield surface, but the term “yield” is generalized to include any form of inelastic material response including micro-crack growth and pore collapse. Kayenta supports optional anisotropic elasticity associated with ubiquitous joint sets. Kayenta supports optional deformation-induced anisotropy through kinematic hardening (in which the initially isotropic yield surface is permitted to translate in deviatoric stress space to model Bauschinger effects). The governing equations are otherwise isotropic. Because Kayenta is a unification and generalization of simpler models, it can be run using as few as 2 parameters (for linear elasticity) to as many as 40 material and control parameters in the exceptionally rare case when all features are used. Isotropic damage is modeled through loss of stiffness and strength. If ever you are unsure of the value of a parameter, leave it unspecified so that Kayenta can use an appropriate default. See [[1]] for a full description of the model, inputs, and output variables.

The command block for a Kayenta material starts with the line:

    BEGIN PARAMETERS FOR MODEL KAYENTA

and terminates with the line:

    END [PARAMETERS FOR MODEL KAYENTA]

In the above command blocks, the following are valid parameters for the Kayenta material model. If ever you are unsure of the value of a parameter, leave it unspecified so that Kayenta can use an appropriate default.

- The initial elastic bulk modulus is defined with the `B0` command line.

- The high pressure coefficient in nonlinear elastic bulk modulus function is defined with the `B1` command line.

- The curvature parameter in nonlinear elastic bulk modulus function is defined with the `B2` command line.

- The coefficient in nonlinear elastic bulk modulus to allow for plastic softening is defined with the `B3` command line.

- The power in bulk modulus softening is defined with the `B4` command line.

- The initial elastic shear modulus is defined with the `G0` command line.

- The coefficient in shear modulus hardening is defined with the `G1` command line.

- The curvature parameter in shear modulus hardening is defined with the `G2` command line.

- The coefficient in shear modulus softening is defined with the `G3` command line.

- The power in shear modulus softening is defined with the `G4` command line.

- The joint spacing is defined with the `RJS` command line.

- The joint shear stiffness is defined with the `RKS` command line.

- The joint normal stiffness is defined with the `RKN` command line.

- The constant term for meridional profile function of ultimate shear limit surface is defined with the `A1` command line.

- The curvature decay parameter in the meridional profile function is defined with the `A2` command line.

- The parameter in the meridional profile function is defined with the `A3` command line.

- The high-pressure slope parameter in meridional profile function is defined with the `A4` command line.

- One third of the elastic limit pressure parameter at onset of pore collapse is defined with the `P0` command line.

- One third of slope of porosity vs pressure crush curve at elastic limit is defined with the `P1` command line.

- The parameter for hydrostatic crush curve is defined with `P2` command line.

- The asymptote of the plastic volumetric strain for hydrostatic crush is defined with the `P3` command line.

- The parameter for porosity affecting shear strength is defined with the `CR` command line.

- The triaxial extension strength to compression strengt ratio is defined with the `RK` command line.

- The initial shear yield offset [non negative] is defined with the `RN` command line.

- The kinematic hardening parameter is defined with the `HC` command line.

- The tension cut-off value of I1 is defined with the `CUTI1` command line.

- The tension cut-off value of principal stress is defined with the `CUTPS` command line.

- The relaxation time constant 1 is defined with the `T1` command line.

- The relaxation time constant 2 is defined with the `T2` command line.

- The parameter no longer in use. [set to zero] is defined with the `T3` command line.

- The parameter no longer in use. [set to zero] is defined with the `T4` command line.

- The relaxation time constant 5 (stress) is defined with the `T5` command line.

- The relaxation time constant 6 (time) is defined with the `T6` command line.

- The relaxation time constant 7 (1/stress) is defined with the `T7` command line.

- The type of 3rd deviatoric stress invariant function is defined with the `J3TYPE` command line.

- The potential function parameter 1 (default=A2) is defined with the `A2PF` command line.

- The potential function parameter 2 (default=A4) is defined with the `A4PF` command line.

- The potential function parameter 3 (default=CR) is defined with the `CRPF` command line.

- The potential function parameter 4 (default=RK) is defined with the `RKPF` command line.

- The failed speed is defined with the `FSPEED` command line.

- The peak I1 hydrostatic tension strength is defined with the `PEAKI1I` command line.

- The peak (high pressure) shear strength is defined with the `STRENI` command line.

- The initial slope of limit surface at PEAKI1I is defined with the `FSLOPEI` command line.

- `PEAKI1F` is the same as PEAKI1I, but for failed limit surface.

- `STRENF` is the same as STRENI, but for failed limit surface.

- `FSLOPEF` is the same as FSLOPEI, but for failed limit surface.

- The `SOFTENING` command line allows transition of limit surface from intact description to failed description.

- The amount of time that passes with the stress state at the limit surface before the limit surface collapses (i.e., softens) is defined with the `TFAIL` command line.

- The upper limit on plastic volume strain is defined with the `DILATLIM` command line.

[1]

R.M. Brannon, A.F. Fossum, and O.E. Strack. Kayenta: theory and user’s guide. Technical Report SAND2009-2282, Sandia National Laboratories, Albuquerque, NM, 2009.