Data part, material properties

start_define
phi 0.349065
end_define
start_define
tanphi 0.3639
end_define

start_define
c 10.0
end_define

First we define the soil friction angle $\phi=0.349065$ in radians (so 20 degrees), and the cohesion $c = 10.0 \frac{kN}{m^2}$.

group_type 1 -materi
group_materi_memory 1 -total_linear
group_materi_density 1 2.0
group_materi_elasti_young 1 1.e5
group_materi_elasti_poisson 1 0.3
group_materi_plasti_tension_direct 1 10.0
group_materi_plasti_mohr_coul_direct 1 phi c 0.0

When we made the mesh with GID, all elements were assigned to group 1. Here we define the material properties of group 1. The group_type is set to -materi which means that material strains, stresses, etc. will be solved. With group_materi_memory set to -total_linear you specify a classical geometrically linear (small deformations) approximation for the soil; this is sufficient for almost all typical calculations. The soil density is set to $2. \frac{1000. kg}{m^3}$ in the data record group_materi_density. The Young's modulus and Poisson's ratio are $1.e5 \frac{kN}{m^2}$ and $0.3$, as set in the records group_materi_elasti_young and group_materi_elasti_poisson respectively. For shear failure the Mohr-Coulomb yield surface is used; the record group_materi_plasti_mohr_coul_direct specifies the friction angle $\phi$, the cohesion $c$ and zero dilatancy. To include tension failure (limitation of tensile stress in soils), you explicitely need to include group_materi_plasti_tension_direct in the input file; here the maximum tensile stress is set to $10.0 \frac{kN}{m^2}$.

change_dataitem 10 -group_materi_plasti_mohr_coul_direct 1 0 -use
change_dataitem_time 10 0.0 tanphi 1.0 tanphi 2.0 0. 1.e20 0.0
change_dataitem_time_method 10 -tangent
change_dataitem 20 -group_materi_plasti_mohr_coul_direct 1 1 -use
change_dataitem_time 20 0.0 c 1.0 c 2.0 0.0 1.e20 0.0

The change_dataitem and change_dataitem_time records take care that the friction angle and cohesion are lowered in the calculation, so that we find the minimum friction angle and cohesion for stability. The ratio of the start values and the minimum values will define the safety factor.

The change_dataitem 10 record specifies for the group_materi_plasti_mohr_coul_direct record with index 1 (so group 1) and 'number 0'. With 'number 0' the first value in the group_materi_plasti_mohr_coul_direct is meant, thus the friction angle. The diagram in change_dataitem_time 10 specifies that at time $0.0$ the friction angle is the predefined word phi (thus $0.349065$), at time $1.0$ it is again the predefined word phi, at time $2.0$ it is $0.0$ and at time $1.0e20$ it is $0.0$. Between the specified time points the value will be linearly interpolated. The -use specifies that the given values should actually be used (as opposed to other options, see the users manual).

Similarly the cohesion is varied in time with change_dataitem 20 and change_dataitem_time 20.