Cutting – Discover Dredging

Interpore 2026: The Cutting Of Clay in A Herschel-Bulkley Model

Proudly holding my poster for the Interpore conference

This week, I’ll be in Nantes at the Interpore 2026 conference1. This is an academic conference on everything porous, ranging from catalysts, to food, to foams, to biology and even soil mechanics. And that is a topic where my research fits in. I submitted an abstract for a poster on the work done by our intern Prasanna Ramadurai2 on the applicability of Herschel-Bulkley fluid modelling for the simulation of the cutting of clay. The accompanying presentation can be found here.

The elemental physics of clay deformation with the rate process theory

As a refresher, clay is a funny substance. The constituent particles of various minerals that form small plates, that are electrostatically charged. Due to these charges, they tend to cling together. When you deform the mass, there develops a shear plane. The particles move over each other with alternating repelling and attracting electric fields. This discrete path is reminiscent of how in particle physics moving steps are only possible when there is enough energy to push the particle past an activation threshold. This was initially postulated by Boltzmann3 and subsequently formalised by Arrenius and Glasstone in the rate process theory. Miedema further applied this to the deformation of clay4. Depending on the amount of water present, it can behave like the clay can behave like thick water or soft rock. Both captured by the same equations. Eventually the resulting shear stress curve is very similar to a Herschel-Bulkley fluid.

Shear stress model by Miedema and comparable fluid models

The work of Prasanna focused on exploring a workflow to simulate the deformation of clay using Ansys Fluent for CFD. This package does not support the deformation model as described by Miedema. But, as the resulting behaviour should be similar to the Herschel-Bulkley model, the H-B viscosity could be used. As previously described here, Prasanna managed to find the appropriate settings and setup to achieve credible results.

Result of the experiments and the simulation compared

As Fabian Kruis5 has previously done experiments in the soil bin test rig, we do have reference data from actual measurements. Fabian has recorded the deformation and analysed the internal movements with PIVlab. The vector field from PIVlab is very similar to the vector field calculated by Ansys Fluent with the Herschel-Bulkley viscosity model. However, translating the deformation to stresses and ultimately to the cutting forces on the blade is still to be improved. The results from Ansys overestimate the measured forces.

Next to the poster, I also prepared a presentation. This presentation can be accessed through the conference portal, or directly from here. Off course, when you are at the conference, you can approach me there. Or through the contact details her on this website.

Resulting shear plane angles from PIVlab and Ansys

References

ISFOG 2025: Commissioning The Test Rig And Reporting To Academia

Fully covered cutter head in sticky clayThis week, I will be presenting my paper1 about the initial experiments on the test rig at the 5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG 2025)2. I will be there in the breaks to explain my poster3 in the lunch breaks. For my audience not present at the symposium, I can highlight the most interesting parts here. I presume, most of you are aware of the operation of a Cutter Suction Dredge and also know about its problems when working in clay. The clay will adhere to the teeth and arms and clog the cutter head. This leads to interruption of the project and in consequence: time and cost overruns. Also, the production itself is difficult to calculate. This is why we at Damen Dredging Equipment started the CHiPS project with the TU Delft4 to investigate the process, improve the estimation model and optimise the design of the cutter head for operation in clay.

Forces involved in the cutting of clay

Forces involved in the cutting of clayFor this purpose, we constructed a linear cutting test rig. Last post about the graduation of Fabian Kruis has more on the results of his thesis5. In the ISFOG article, we wrote about the design and performance of the rig and the opportunities it provides for further research. The design criteria for the rig as was laid down in the assignment for Ines Ben M’hamed were6:

Identifying the main parameters influencing the cutting forces and the cutting regime.
Designing general arrangement for testing linear cutting models.
Capture the signals for force and deformation.

The developed test rig was inspired by the model described by Hatamura and Chijiiwa7. The blade is attached to a linear moving trolley, cutting through a block of clay mounted in a frictionless moving soil bin. The reaction forces on the box are measured. and images of the grid printed on the side of the clay block are captured with a GoPro camera of later evaluation with PIVlab®. A set of 30 experiments was defined according to the Buckingham-PI method as presented at the CEDA Dredging Days last year8.

General arrangement of the linear cutting test rig

Next to the cohesion and adhesion, the tensile strength of the clay had to be measured to obtain a consistent result. We could confirm the linear relation between cutting depth and the cutting force as predicted by existing models from literature. As we were using modern techniques for capturing images, we were able to accurately measure the displacements with the PIVlab® application. The good results are due to the novel printing technique developed by Fabian Kruis, to apply a grid on the side of the clay sample. One remarkable result is, that most models for the calculation of the sliding forces, only take adhesion into account, but measurements indicate that the external friction cannot be neglected. This appeared in the measured shear angle, which was much lower than the shear angle predicted by existing models.

Captured deformations in a vector field. Note the differences in shear angle

The experiments yielded a treasure trove of measurements, we are still analysing them. e.g. We noticed some strange reversal of the vertical cutting forces. And we are interested in the transition from one cutting regime to another. Those results will be presented in my next journal paper. In the mean time I am watching all those captured movies over and over again. To me it’s very inspiring and I like to share an example.

A slow motion movie of a clay cutting experiment (ASMR)

References

Graduation Fabian Kruis: Modelling Friction In Clay

Fabian Kruis presenting his graduation research

Fabian Kruis graduated on his master thesis at the Delft University of Technology on a project for my PhD research1. He investigated the cutting behaviour of plastic clay. As it was the first time we are now actually using the test rig designed by Ines2, he first had to do was a lot of trouble shooting for commissioning the test rig. Spoiler alert: the cutting forces were much higher than expected and the linear drive was not strong enough to cover the whole range of experiments we’ve wanted to do.

The cutting forces involved with cutting of clay are acting on all four sides of the simplified chip. On the outside, there is the barometric pressure of the surrounding water. On the far end, there is an unknown and hard to determine force from the rest of the chip that is not in contact with the blade anymore. At the shear plane, there are the normal force, the internal friction and the cohesion. At the blade, there are the normal force, the external friction force and the adhesion. The sum of these last three forces will give the cutting force we are looking for, as they make up the required cutting power on the drive. But they can only be calculated, once the other forces are known.

Overview of all the forces involved with the cutting of clay, acting on the chip

Fabian’s assignment was to have our own experience with the cutting of clay and check whether the models used in the dredging industry have any reliability in predicting the cutting forces. checking whether all assumptions and simplifications were justified. e.g. Plastic clay does have similar properties and behaviour as a fluid. And a fluid does not have an internal friction. Consequently, clay should not have an internal friction also. Right? When there is no internal friction, there can’t be an external friction either. Right, right? Fabian tested these assumptions by actually performing shear tests on internal and external planes.3

Explanation of internal friction for solids, fluids and clay

At least for the clay we used in this research, he already found that the assumption for ‘no friction in clay’ is not valid. Consequently, this had knock on effects on the rest of the cutting force calculation. We did find a different behaviour, the shear plane was off and the cutting forces were indeed much higher than expected. It is now up to me to use Fabians results and model modifications to implement into my own research. As a matter of fact, I used part of his thesis to write an article and hope to present this soon. I’ll keep you update on those developments.
As we are very satisfied with Fabian’s work and him as a person himself, we offered him a position in our team at Damen Dredging Equipment in Nijkerk, which he happily accepted. So, next to progress for my research, we have a new colleague. Welcome Fabian, thank you!

Fabian signing his MSc. certificate. — Fabian signing his MSc. certificate sitting in the ‘dredging chair

Tag: Cutting

Interpore 2026: The Cutting Of Clay in A Herschel-Bulkley Model

References

See also

ISFOG 2025: Commissioning The Test Rig And Reporting To Academia

References

See also

Graduation Fabian Kruis: Modelling Friction In Clay

References

See also