Parameters are specified in the PLAXIS input in the following order:
Parameter 1 - critical state friction angle
Parameter 2 - - shift of the mean stress due to cohesion. The effective stress
used in the model formulation is replaced by
Non-zero value of is needed to overcome problems with stress-free state.
If , it will be replaced by a default value of 1 kPa. Any other value can be input by user (for basic hypoplasticity, set to very low number, e.g. ).
Parameters 3-5 - parameters of the basic hypoplastic model for clays , , .
Parameters 6 - Parameters of the basic hypoplastic model for clays (in place of the parameter of the Mašín (2005)  model, calibrated using the same procedure).
Parameters 7 - , ratio of horisontal and vertical shear moduli.
Parameters 8-10 - parameters of the model for clays with meta-stable structure (, and ).
Parameter 17 - bulk modulus of water for undrained analysis using the penalty approach with user-defined value of .
In drained analysis, consolidation analysis, and undrained analysis using PLAXIS option undrained should be set to 0.
Parameter 18 - Specifies vertical direction (set to 2 in PLAXIS2D, 3 in PLAXIS3D, 2 in SoilTest independently whether run from PX2D or PX3D).
Parameter 19 - Parameter (ratio of horizontal and vertical Young moduli). If set to zero, than calculated automatically from empirical formulation
Parameter 20 - Parameter
(ratio of horizontal and vertical Poisson ratios). If set to zero, than calculated automatically from empirical formulation
Parameter 21 - Parameter . Additional control of non-linearity inside state boundary surface. If set to zero, default value calculated from model parameters is used.
Parameter 22 - initial void ratio or overconsolidation ratio . If
, then .
Parameters 23-28 - initial values of the intergranular strain tensor
in Voigt notation (
Parameter 29 - initial value of sensitivity (model for clays with meta-stable structure). If , the basic model is used.
The routine uses 16 state variables:
State v. 1-6 - intergranular strain tensor
in Voigt notation (
State v. 7 - void ratio .
State v. 8 - Excess pore pressure for undrained analysis using user-defined value of . In undrained analysis using PLAXIS
option undrained this variable is equal to 0 end excess pore pressure may be found in standard PLAXIS menu.
State v. 9 - Effective mean stress.
State v. 10 - Number of evaluation of the constitutive model in one global time step (for postprocessing only).
State v. 11 - Mobilised friction angle
in degrees (for postprocessing only).
State v. 12 - Normalised length of the intergranular strain tensor
(for postprocessing only).
State v. 13 - Suggested size of the first time substep (for calculation controll).
State v. 14 - sensitivity (for model with meta-stable structure).
State v. 15 - overconsolidation ratio, defined as .
State v. 16 - 0 means model interation goes without problem. 1 means state boundary surface cut-off has been activated.
The hypoplastic model for granular materials is implemented via user defined subroutine usermod. To use the model in PLAXIS, copy the files UDSM_HPS.dll and UDSM_HPS64.dll into the PLAXIS installation directory. Then, select "user-defined model" from the Material model combo box in the General tab sheet (Fig. 4.1). After selecting the user-defined model, correct user-defined dynamic library (typically UDSM_HPS.dll) needs to be selected in the "Available DLL's" combo box under "Parameters" tab sheet. In the "Models in DLL" combo box, model with ID 2 (Hypoplas. - clay) must be selected. The parameters can then be input into the parameter table (Fig. 4.3).
Selecting clay hypoplasticity model in the "Parameters" tab sheet.
Parameters of the clay hypoplastic model for different soils have been evaluated by Mašín and co-workers. They are given in Table 4.3. Parameters of the model for clays with meta-stable structure are in Tab. 4.4 and typical parameters of the intergranular strain concept for fine-grained soils are in Tab. 4.5.
Table 4.3:Typical parameters of the hypoplastic model for clays.
For estimation of , see database from , here
for free download in the form of PDF preprint.
Table 4.4:Typical parameters of the model for clays with meta-stable structure (from )
Table 4.5:Typical parameters of the intergranular strain concept for clays