The Duncan-Chang material model is used to simulate soil. It assumes a hyperbolic stress-strain relation and was developed based on tri-axial soil tests. The model accommodates the variation of Poisson's ratio by means of stress-dependent Poisson's ratio (E-v model) or stress-dependent bulk modulus (E-B model).
Refer to the following page, Duncan-Chang Theoretical Description, for additional clarification and equations in which the material properties are used.
General tab:
- Cohesion Intercept (c) This is the strength parameter c used in the Mohr-Coulomb criterion for the failure of the soil. The input must be greater than or equal to 0.
- Friction Angle (phi) This is the strength parameter φ used in the Mohr-Coulomb criterion for the failure of the soil. The input must be in the range of 0 (inclusive) to 90 degrees.
- Cohesionless Soils Activate this option if the soil is considered cohesionless, in which case the Mohr failure criterion is based on the friction angle.
- Friction Angle (dphi) This value,Δφ
0
, is the reduction in the strength parameter φ for a 10-fold increase in the minor principal stress σ
3
. The input must be in the range of 0 (inclusive) to 90 degrees.
- Failure Ratio (Rf) The failure ratio relating the stress intensity range (σ
1
-σ
3
) for failure to the ultimate. The typical range is 0.75 to 1, but values between 0 and 1 (inclusive) are acceptable.
- Modulus Number (K) Modulus number used to define the initial modulus. This value must be greater than 0.
- Modulus Number (Kur) Modulus number when the model has been unloaded. The stress intensity range (σ
1
-σ
3
) is less than the historical maximum. This value is greater than or equal to the modulus number K.
- Modulus Exponent (n) Modulus exponent used to define the initial modulus.
- Formulation Choose the formulation to use to account for the variation of Poisson's ratio.
- E-B is the stress-dependent bulk modulus method
- E-v is the stress-dependent Poisson's ratio method
- Bulk Modulus Number (Kb) Bulk modulus number used with the E-B formulation. The value must be greater than 0.
- Bulk Modulus Exponent (m) Bulk modulus exponent used with the E-B formulation.
- Poisson's Ratio Parameters (G) Material parameter used with the E-v formulation.
- Poisson's Ratio Parameters (F) Material parameter used with the E-v formulation.
- Poisson's Ratio Parameters (D) Material parameter used with the E-v formulation.
- Atmospheric Pressure The default is based on 14.696 psi, converted to the same units as the model.
Advanced tab:
The following material properties are used to stabilize the analysis at time zero and if the minor principal stress (σ
3
) become less than or equal to zero. Values for time 0 (and before failure) and after failure are entered.
- Elastic Moduli at Rest: Young's Modulus: A reasonable default is 0.01*K*Pa, where K is the Modulus Number and Pa is the atmospheric pressure (both entered on the General tab).
- Elastic Moduli at Rest: Poisson's Ratio: Enter the Poisson's Ratio for the soil in the rest condition.
- Elastic Moduli at Failure: Young's Modulus: A reasonable default is 0.001*K*Pa, where K is the Modulus Number and Pa is the atmospheric pressure (both entered on the General tab).
- Elastic Moduli at Failure: Poisson's RatioEnter the Poisson's Ratio for the soil in the failed condition.