Materials

This page outlines how to define soil and structural materials in STEM and highlights practical tips for choosing parameters.

Soil materials

Soil materials are defined by combining a soil formulation, a soil law, and a saturation law. Hereby an example of how to define two soil material layers and how to add them to the model. Further details about the soil formulation can be found in Linear elastic material.

from stem.soil_material import OnePhaseSoil, LinearElasticSoil, SoilMaterial, SaturatedBelowPhreaticLevelLaw

ndim = 3

soil_formulation_1 = OnePhaseSoil(ndim, IS_DRAINED=True, DENSITY_SOLID=2650, POROSITY=0.3)
material_1 = SoilMaterial(
    "soil_1",
    soil_formulation_1,
    LinearElasticSoil(YOUNG_MODULUS=30e6, POISSON_RATIO=0.2),
    SaturatedBelowPhreaticLevelLaw(),
)

soil_formulation_2 = OnePhaseSoil(ndim, IS_DRAINED=True, DENSITY_SOLID=2550, POROSITY=0.3)
material_2 = SoilMaterial(
    "soil_2",
    soil_formulation_2,
    LinearElasticSoil(YOUNG_MODULUS=30e6, POISSON_RATIO=0.2),
    SaturatedBelowPhreaticLevelLaw(),
)

model.add_soil_layer_by_coordinates([(x1, y1, z1), (x2, y2, z2),(x3, y3, z3), (x4, y4, z4)], material_1, "soil_layer_1")
model.add_soil_layer_by_coordinates([(x5, y5, z5), (x6, y6, z6),(x7, y7, z7), (x8, y8, z8), (x9, y9, z9)], material_2, "soil_layer_2")

Practical tips

Units: SI (N, m, kg, s, Pa).
Names: keep material names unique—used for mapping to physical groups and IO.
Drainage assumptions: In STEM for railway induced vibrations all the layers should be one-phase drained. This means that to simulate saturated layers the Poisson ratio should be set to 0.495. Please refer to formulation for further details.