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Sanisand

*Mechanical = Sanisand  
p_atm [F/A], e_0 [-], lambda_c [-], xi [-], M_c [-], M_e  [-], m [-],  G_0 [-] 
nu [-], h_0 [-], c_h [-], n_b [-], A_0 [-], n^d [-], z_max [-], c_z [-]

The material parameters of Sanisand are given in the following.

  • \(p_{atm}\) [F/A] is the atmospheric pressure usually given by 100 kPa.
  • \(e_0\) is the critical void ratio at zero mean effective stress and can for instance be obtained from (several) undrained monotonic triaxial tests reaching the critical state. It will be in the range of \(e_{c0}\) used by the hypoplastic model. The parameters are not identical, however.
  • \(\lambda_c\) and \(\xi\) define the relation between critical void ratio and mean effective stress. Again, they can for instance be obtained from (several) undrained monotonic triaxial tests reaching the critical state.
  • \(M_c\) and \(M_e\) are the critical stress ratios for compression and extension, respectively. They can be calculated using the critical friction angle.
  • \(m\) defines the elastic range of the model. Conventionally, it is chosen to 0.05.
  • \(G_0\) and \(\nu\) are the elastic parameters of the model.
  • \(h_0\) and \(c_h\) are obtained from the fitting of monotonic triaxial tests. They have no physical meaning.
  • \(n_b\) influences the peak in the \(q\)-\(\varepsilon_1\) plot. Again, it has no physical meaning.
  • \(A_0\) and \(n^d\) influence the dilatancy. They also have no physical meaning.
  • \(z_{\max}\) and \(c_z\) are the parameters influencing the cyclic mobility effect. They are obtained by fitting of cyclic triaxial test data.

State variables

From the state variables of Sanisand, only the void ratio can be initialised analogously to the procedures described for the hypoplastic model. The initial back stress tensor is always defined such that the initial stress state is in the centre of the elastic range of the model.

Additional output variables

The following additional output variables are available in the *Output command:

  • Void ratio: void_ratio
  • Back stress tensor: alpha_11, alpha_22, alpha_33, alpha_12, alpha_23, alpha_13.
  • Stress projection: proj. Flag that indicates if the stress correction is active (see Theory Manual). proj takes the value of 0 if the stress projection is inactive.
  • Plastic strain: eps_plas
  • Value of the yield surface: F_yield. Should always be less than zero. For values close to zero, the model will most likely produce plastic strain.
  • Convergence of return mapping algorithm: no_conv. Greater than zero if return mapping algorithm failed.