Soil calculations

Soil calculations using elastic spring

The most simple way to model soil layers is by using an elastic spring, also called the “Winkler model or Winkler theory”. This theory assumes that the reaction exerted by the soil is proportional to the soil settlement:

   

with

• the reaction of the soil
• the layer constant, a spring contant
• the settlement

Even if we would manage to find an acceptable value of the layer constant , there are some flaws in the Winkler model:

• according to Winkler-theory, if the slab is uniformly subject to a load, it sinks into the soil without stress;
• the load of a slab has no influence on the settlement of a neighbouring slab.

In models where settlement is important, we prefer the iterative soil layer model (see below) over the Winkler theory.

Soil calculations using iterative equilibrium model

In this approach, you enter the properties of the different soil layers in Diamonds. However, Diamonds cannot calculate with the literal soil layers. It will translate the soil layers into spring functions (similar to a stiffness diagram) in such a way that the deformation of the plate loaded with the loads = deformation of the soil loaded with the reactions of the plate. Determining the spring functions is an iterative process that is illustrated in the diagram below.

with:

• z the depth of the layer
• C or A compression or recompression constant (for CPT-test, more info)
• Δh thickness of the layer
• σ initial stress due to the loads of the soil
• Δσ_z(i) increase of the stress due to the added loads
• α_k structural coefficient of the soil layer k (for Ménard test, more info)
• E_MK compression modulus of the soil layer k (for Ménard test, more info)

The composition of a ground/ terrain profile can be defined in the geometry configuration (see Supports on surfaces).