I am modelling sand slopes in Plaxis 3D using an HP model. I am using soil parameters from “Modelling of Soil Behaviour with Hypoplasticity” by David Masin (2019). During the models the phreatic surface is rising. The problem I am having with my models are that the total displacement I get with the model is extremely small. A very loose slope with a height of 20 m only settles about 10 mm during gravity loading. I want to know if anyone has had similar problems and whether they know how to fix it?
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Hi Arno, it is really hard to grasp what you are doing from this information. There are various parameter sets in the book you cite, at least two hypoplastic models (clay, sand), with and without intergranular strain concept…?? You speak about water rising, but then that the problem is in gravity loading stages. So water probably does not play any role there? It is impossible to reply to question which is formulated this way…
I apologise, I should clarify the problem. The ultimate goal of my model is to back analyse centrifuge models conducted at the Hong Kong University of Science and Technology. The slope is a homogenous slope and I am using the Toyoura sand parameters from “Modelling of Soil Behaviour with Hypoplasticity”. In the tests the groundwater started rising. That part of the model works fine. However, the issue I am having is that from the beginning of the model (from the initial phase which is gravity loading) the displacements in the model is extremely small. I am getting only a few mm displacement in a slope that is 20 m high, irrespective of which phase I am calculating. I have tried changing boundary conditions and even using different soil parameters (i.e. Hochstetten and Karlsruhe sand). I have checked all the parameters and units multiple times and the model conditions as well. No matter what parameters or conditions I use, I keep getting extremely small displacements during all phases of my calculations. When I use other types of models such as the Mohr-Coulomb model, I do not have any of the issues with the small displacements.
Hi Arno,
First of all, please use parameters validated using Hong-Kong centrifuge simulations, for example from
Ng, C. W. W., Boonyarak, T. and Mašín, D. (2013). Three-dimensional centrifuge and numerical modeling of the interaction between perpendicularly crossing tunnels. Canadian Geotechnical Journal 50, No. 9, 935-946.
This is more specific than generic parameters from the book (calibrated long ago in Karlsruhe).
Then, please try to calculate with and without intergranular strain concept, to see if there is any difference (this will let us understand where the problem was initiated).
David
Hi David
I checked with the parameters from that journal paper. Without the intergranular strain concept I get a bit better displacements during gravity loading (about 0.4 m for a slope with a 20 m height). However, for the rest of the phases the displacements are still small.
When I activate the intergranular strain concept I get strange errors in the model during the initial phase. I get errors with both the displacement and stresses in general. Please find a link to some screenshots I took of the errors I get.
https://drive.google.com/open?id=1tZbnmXYu9LYZlqubX-1O6BoxbBe5_8al
Arno