Simulating soft soils in EDEM with the Soils Starter Pack

There are many different types of soils out there with different textures based on the amount of sand, silt and clay present and their moisture content. Soil is a material that can have different consistency and various level of stickiness and plasticity as well as different compressibility parameters.

Sand, silt and clay

This makes it difficult for engineers looking to understand the interaction of their equipment with soil and assess the impact that a specific type of soil might have on their design.

When it comes to modeling soil using the Discrete Element Method (DEM), the key to having confidence in simulation results is to choose the right parameters and material properties to ensure the simulation represents the real material behavior. For a complex material like soil determining those parameters represent a major challenge and a barrier for many engineers.

To overcome this, we have worked to develop a small selection of soil models and made them available in our EDEM software to enable users to start modelling soft soils easily.

Introducing the Soils Starter Pack

The Soils Starter Pack has been introduced as part of EDEM 2018. It includes 8 models of soils including different range of compressibility and stickiness. These models make use of different physics models inbuilt in EDEM to model a range of soils from gravels to soft compressible soils.

This resource is intended for users designing heavy equipment including off-road construction, agricultural & forestry machinery and vehicles which are handling, or in contact, with soft soils.  The Soils Starter Pack makes it possible to quickly and easily compare equipment designs with a range of different soils and test their performance for extreme conditions, for instance for a compressible, highly-sticky material such as mud and a free flowing one such as sand.

At the core of any DEM simulation is a contact model. Contact models consist of the different laws and equations that define the interaction between particles in a simulation. When a material shows stickiness and cohesion, is highly compressible or purely elastic, it is all down to the chosen contact model. In the Soils starter pack, 4 different contact models have been selected:

  • Hertz-Mindlin: This contact model is the default model used in EDEM due to its accurate and efficient force calculation. In this model the normal force component is based on Hertzian contact theory and tangential force model is based on Mindlin-Deresiewicz work.
  • Hertz-Mindlin with JKR: is a cohesion contact model that accounts for the influence of Van der Waals forces within the contact zone. It allows the user to model strongly adhesive systems, such as dry powders or wet materials.
  • Hysteretic Spring: The Hysteretic Spring contact model allows plastic deformation behaviors to be included in the contact mechanics equations, resulting in particles behaving in an elastic manner up to a predefined stress. Once this stress is exceeded, the particles behave as though undergoing plastic deformation
  • Edinburgh Elasto-Plastic Adhesion (EEPA) model: The Edinburgh Elasto-Plastic Adhesion Model (EEPA) captures the history dependence and the key characteristic behavior of cohesive solids. The model comprises a nonlinear hysteretic spring model to account for the elastic-plastic contact deformation and an adhesive force component that is a function of the plastic contact deformation.

Based on these contact models,  8 soil models were developed as listed below.

Soils_models_chart

Materials such as dry gravel and sand

  1. Non-compressible, non sticky soil

Materials such as wet gravel

  1. Non compressible, sticky soil
  2. Non compressible, very sticky soil

Materials such as freshly ploughed soil

  1. Compressible, dry soil
  2. Very compressible, dry soil

Materials such as clay and very wet sand

  1. Compressible, sticky soil
  2. Compressible, very sticky soil
  3. Compressible, soft, very sticky soil

The models can be accessed directly from within EDEM and are ready to be used in a simulation. This is part of our objective to make DEM simulation more accessible to engineers and to give them a starting point to using different physics models.

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