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CPT Model Generator

The CPT FEM Tool is a compact graphical application for creating, running, and evaluating axisymmetric cone penetration test (CPT) models with numgeo. It guides the user from the geometry and mesh definition to the generated numgeo input files and the evaluation of the calculated CPT response.

  • Download for Windows

    The standalone executable contains the graphical tool and its Python dependencies.

    Download CPTFEMTool.exe

  • Requirements

    A working numgeo installation is required to run the generated model. Simulations with friction additionally require a working Intel oneAPI Fortran environment.

Demonstration

The following video demonstrates the basic workflow, from defining the model to generating the numgeo input files.

Main functions

The graphical interface supports the following parts of a CPT model:

  • definition of the CPT and soil-domain geometry, including the initial embedment and the part of the CPT above the ground surface;
  • structured axisymmetric mesh generation with a graphical preview;
  • horizontal soil layers with layer-specific state and hydraulic parameters;
  • hypoplastic or Mohr-Coulomb soil behaviour;
  • surcharge, initial stress ratio, penetration settings, and hydrostatic conditions for drained analysis;
  • separate friction coefficients for the CPT body and the measurement sleeve, as well as a user-defined sleeve length;
  • generation of the soil mesh, CPT mesh, master input file, evaluation script, and the contact user routine when friction is active;
  • direct start of numgeo with a user-defined number of processors; and
  • evaluation and export of tip resistance \(q_c\), sleeve friction \(f_s\), friction ratio \(R_f\), and the corresponding force components.

Always inspect the results in ParaView

Inspect every simulation in ParaView before using its results. Check the deformed mesh, the evolution of element distortion, the contact behaviour, and the relevant displacement, stress, and pore-pressure fields for physical plausibility. Tip resistance and sleeve-friction curves from the graphical interface should be interpreted together with these field results. Completion without an error message is not sufficient evidence that the results are physically meaningful.

Typical workflow

  1. Select the output directory and enter a model name.
  2. Define the CPT geometry, soil dimensions, mesh resolution, and soil layers.
  3. Select the constitutive model and enter the material and analysis parameters.
  4. Use Generate & Plot Mesh to inspect the mesh before writing any files.
  5. Use Write Input Files to create the complete numgeo model in the selected output directory.
  6. Use Run numgeo to start the calculation.
  7. After the calculation has finished, use Plot results or Export results for the CPT evaluation.

The run command first searches for a local executable whose name contains numgeo in the calculation directory and next to the CPT tool. If none is found, it calls numgeo.exe or numgeo through the system PATH.

Friction and sleeve evaluation

A friction coefficient greater than zero automatically activates the contact user routine. numgeo compiles this routine when the analysis starts, which requires a functioning Intel oneAPI Fortran environment. The CPT-body and sleeve coefficients can be specified independently; setting the body coefficient to zero applies friction only to the measurement sleeve.

The sleeve-friction result is evaluated only over the specified measurement sleeve. The friction ratio is calculated from the simulated sleeve friction and tip resistance. The interface warns when either friction coefficient exceeds 0.2, because large friction values may cause substantial mesh distortion during penetration.

Generated files

For a model named <model>, the tool writes the principal files below to the selected output directory:

  • <model>_mesh_soil_part.inp
  • <model>_mesh_cpt_part.inp
  • <model>_master.inp
  • <model>_master_evaluation_shaft.py
  • user_contact_properties.f90 when friction is active

Numerical difficulties and limitations

The CPT FEM Tool is a first version for setting up highly nonlinear penetration analyses. The graphical interface automates model generation, but does not establish that every combination of geometry, mesh, material parameters, contact properties, and analysis settings defines a suitable numerical model. Successful completion cannot be guaranteed for all combinations of input parameters.

Large element distortions can develop during penetration, particularly near the cone and along the contact surfaces. Excessive distortion is a major potential cause of convergence problems and premature termination of the calculation. Mesh resolution, penetration increments, contact parameters, and material behaviour should therefore be assessed together when investigating an unsuccessful analysis.

The Zipper method also involves simplifying assumptions and modelling uncertainties. These limitations must be considered when interpreting the calculated CPT response and comparing it with measurements. A converged solution alone does not demonstrate that the model adequately represents the physical penetration process.