Estimation of granular flow impact force on rigid wall using material point method

Landslides and avalanches cause loss of lives, as well as generate significant economic cost. Protection barriers help reduce the impact of such events. However, the design of the barriers requires the prediction of the landslide flow trajectory and the estimation of impact force. Material Point Method appears to have great potential for estimating those, since it can account for large displacement nature of sediment flows and their nonlinear behaviour. Therefore, it may be able to capture the complex interaction of landslides or avalanches with the ground and structures. This study focuses on simulating granular flows with Generalized Interpolation Material Point Method. The calculations use a constitutive model inspired by the Bagnold theory of granular flow [1] to model sand landslide / avalanche experiment [2] with sand treated as a linear elasto-plastic material. Shown simulations aim was to replicate the experiment. In particular, the paper focuses on estimation of the impact force of sand flow on a fixed rigid wall. Such force estimation is a first step to validate the Generalized Interpolation Material Point Method for use as a tool for the design of barriers defending against landslides and avalanches

Hydro-mechanical coupled dual domain material point method stabilized with a null-space filter

The Material Point Method (MPM) is a continuum-based numerical method especially suitable for solving large deformation problems. In this paper, we investigate the null-space errors present in MPM solutions. The paper establishes a null-space stability condition which is used to examine the null-space errors in different versions of the MPM. This analysis shows that a B-splines MPM satisfies the null-space stability condition and therefore reduces greatly the errors associated with the null-space. In contrast, the MPM, the Generalized Interpolation Material Point Method (GIMP) and the Dual Domain Material Point Method (DDMP) show non-trivial null-spaces in the mapping. To remove the null-space errors, this paper utilizes QR factorization method, which is similar to the Single Value Decomposition (SVD) method, but requires fewer computations. This paper simulates several problems with hydro-mechanical coupled Dual Domain Material Point Method (DDMP) formulation both with and without null-space error reduction. The simulations indicate that the null-space filter can improve significantly the accuracy of the pore water pressure for both gravity loading and consolidation in large strain simulation

A constitutive framework for the chemo-mechanical behaviour of unsaturated non-expansive clays

Both osmotic and matric suction changes have a significant influence on the mechanical behaviour of clays. Despite the different types of interactions at the microstructural level, both suctions havea relevant effect on the fabric of non-expansive clays. Starting from experimental observations at the laboratory scale, it is possible to identify some common features characterizing the mechanical response of non-expansive clays to salinity and degree of saturation changes. This paper presents an elastoplasticframework to reproduce the behaviour of unsaturated clayey soils upon changes in the salt concentration of the pore fluid. In particular, it presents a strategy to include osmotic suction induced by pore fluid salinity in BBM-like models [1]. The model was implemented in the Thebes code and it was calibrated on experimental data performed on Boom clay [2] and remoulded loess [3]

Estimation of granular flow impact force on rigid wall using material point method

Landslides and avalanches cause loss of lives, as well as generate significant economic cost. Protection barriers help reduce the impact of such events. However, the design of the barriers requires the prediction of the landslide flow trajectory and the estimation of impact force. Material Point Method appears to have great potential for estimating those, since it can account for large displacement nature of sediment flows and their nonlinear behaviour. Therefore, it may be able to capture the complex interaction of landslides or avalanches with the ground and structures. This study focuses on simulating granular flows with Generalized Interpolation Material Point Method. The calculations use a constitutive model inspired by the Bagnold theory of granular flow [1] to model sand landslide / avalanche experiment [2] with sand treated as a linear elasto-plastic material. Shown simulations aim was to replicate the experiment. In particular, the paper focuses on estimation of the impact force of sand flow on a fixed rigid wall. Such force estimation is a first step to validate the Generalized Interpolation Material Point Method for use as a tool for the design of barriers defending against landslides and avalanches

Modelling of sand column collapse with material point method

The paper shows numerical analysis of sand column collapse. The simulation was performed with the material point method and the results are compared to experiment. The problem considered involves extreme deformations and is difficult to model with more traditional numerical approaches like the finite element method. In the analysis, the sand is modelled with a rate-independent Mohr-Coulomb model. Despite the use of a simple constitutive model, the computed results agree with the experimental observations reasonably well. This agreement is satisfactory both during and after the collapse

An equivalent stress implementation of Barcelona Basic Model

The paper presents a novel implementation of the Barcelona Basic Model based on the equivalent stress concept. The Barcelona Basic Model may be regarded as an extension of the Modified Cam Clay model for use with partially saturated soils. This extension is achieved by changing the size of the yield locus in line with changes of suction. The paper presents an alternative way of implementing the Barcelona Basic Model, where the main yield surface remains unaffected by changes of suction, but the stress (alongside the stress-strain relationship) is modified instead. This approach is therefore called an equivalent stress approach. The presented model based on the equivalent stress approach offers the same capabilities and predicts the same soil behaviour as the Barcelona Basic Model; the only difference lies in the implementation of the model, though the end-user would not recognise that. However, equivalent stress offers a new interpretation of unsaturated soil behaviour. It follows that, with the help of the equivalent stress technique, a number of existing models for saturated soils can be easily enhanced to allow for modelling of unsaturated soils

Explicit stress integration with reduced drift for Barcelona Basic Model

The paper studies the effectiveness of a drift reduction method in integrating unsaturated soil models. The drift reduction is based on the NICE (Next Increment Corrects Error) method. The NICE method can be applied to any explicit stress integration method based on Runge-Kutta method. The performance of the stress integration enhanced by the NICE scheme is demonstrated with the Barcelona Basic Model. Numerical studies in this paper involve the integration of the Barcelona Basic Model with different numbers of strain increments and different sets of model parameters and initial conditions. The improved algorithm does not require any significant computations, thus the drift reduction is virtually accomplished without significant cost. The reduction in the yield surface drift appears to be rather significant, suggesting that under normal circumstances no additional drift correction method is required

Comparison of explicit and implicit integration schemes for the Barcelona Basic Model

The paper presents a comparison between a range of explicit and implicit stress integration schemes applied to the Barcelona Basic Model (BBM). The implicit algorithms tested are a general and an optimised return mapping algorithm for BBM. The latter is characterized by analytical integration of the hardening law and by solving only a single non-linear equation. This improves the stability and accuracy of the stress integration and reduces the required computing time. The explicit algorithms assessed include three Runge-Kutta algorithms with adaptive substepping and local error control and an extrapolation algorithm with substepping and global error control. A comparison of the algorithms accuracy and assessment of stability is presented based on tests with three sets of BBM material parameters and strain increments covering the range from zero to three percent of volumetric and shear strain

Impact of a spacing reduction in a fall cone test

The paper investigates an adjustment to the fall cone test, where the same soil sample is reused for four extra tests. The analysis shows that the fall cone test inaccuracies are much higher than the effect of reusing the sample. Therefore, the proposed procedure may help to establish the soil properties more accurately without much extra effort and reduce the number of samples needed for testing