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Policy brief “Soil quality in spatial planning”
Traditional spatial planning does not consider soil quality sufficiently. Soil quality is an account of the soil's ability to provide ecosystem and social services through its capacities to perform its functions under changing conditions. Land and soil are finite resources facing growing pressures and conflicts over their use. Land use planning and soil management should balance the supply of ecosystem services with society’s demands. This policy brief (funded by the European Commission, DG Environment) explains the topic, gives examples, main barriers and recommendations for action.
Tidal wave propagation along The Mekong deltaic coast
A two-dimensional, barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the South China Sea with a particular interest for its characteristics along the Mekong deltaic coast. The study indicates that tidal waves propagate from the Pacific Ocean into the South China Sea mainly through the Luzon Strait (LS), where the K1 diurnal tide dominates due to a quarter wavelength resonance in this semi-enclosed basin, and that the incoming tidal waves from the Celebes open boundary play a more important role than those from the Andaman and Flores open boundaries. Previous studies have not explained why both adjacent seas including the South China Sea and the Gulf of Thailand are dominated by a diurnal tide, while a semidiurnal tide dominates along the eastern Mekong deltaic coast. By means of Green's law, continental shelf tidal resonance theory and standing wave theory, this study clarifies that the large amplified M2 semidiurnal amplitude leading to a prevailing mixed semidiurnal tide is caused not only by the shoaling effect and the continental shelf oscillation resonance phenomenon but also by the position on the standing wave anti-node line. Moreover, the finding of radial tidal currents occurring along the southern Mekong estuarine coast has not been revealed in earlier studies. Based on a number of numerical, geometrically schematised experiments, we suggest that the interaction between the large amplified amplitude near the shoreline associated with the adjacent low amplitude band system, causing convex hydraulic gradients of tidal amplitude due to basin geometry as well as sloping topography, is the mechanism for developing these radial tidal current systems. The results reveal that wind monsoon climate could cause either damped or amplified tidal amplitudes around the Mekong deltaic coast of which approximately 2–3 cm is due to the changing atmospheric pressure, the tangential stress of wind over the water surface and wind enhanced bottom friction. Also, this study suggests that the tidal generating forces should be considered to achieve accurate model results depending on the geographical region of interest. Findings achieved from this study contribute to a deeper insight of tidal wave propagation from a deep ocean to a shallow flat basin similar to the South China Sea and its Mekong deltaic coast.
Calibration of hypoplastic parameters using an MPM model of a CPT
MPM can be used to model cone penetration tests (CPT). This study aims at showing how inverse analysis can be employed to calibrate the MPM model of a CPT, and in particular the input parameters of an advanced constitutive model, using field data. The considered CPT test was carried out in sandy soil. The selected constitutive model belongs to the class of hypoplasticity. A gradient-based optimization algorithm is used to simultaneously calibrate 5 of the 13 hypoplastic input parameters. The inverse analysis of the MPM model successfully converged after few iterations.
MPM-analysis of landslide propagation observed in flume test
In this paper a controlled failure of a loose sandy soil in a flume laboratory experiment was simulated. The slope deformation process was analyzed and compared to the results of Material Point Method (MPM) analyses, performed through the Anura3D code. The objective of the paper is to outline the role of some key factors from the failure onset until the final slope configuration. Particularly, the effect of soil stiffness, hydraulic conductivity and dilatancy angle on the final shape of the slope was addressed and discussed. The paper highlights the importance of considering the correct value of these mechanical parameters, when a complex large deformation analysis is conducted.
Implementation of non-trivial boundary conditions in MPM for geotechnical applications
This paper describes current work on the implementation of non-trivial boundary conditions (BCs) for improving the general applicability of the Material Point Method (MPM) to geotechnical boundary values problems. It summarises novel boundary treatments (non-trivial BCs) in MPM for (i) flow conditions, as well as (ii) the application of a surface traction on a moving boundary for solid materials. Both treatments are required, for example, to estimate the consequence of slope failure in geotechnical engineering. The flow condition BCs have been used to simulate a subcritical flow and the surface traction BC has been applied on top of aslope leading to failure. Both examples show that these new treatments are useful in solving practical problems.
Comparison between Material Point Method and meshfree schemes derived from optimal transportation theory
Both the Material Point Method (MPM) and meshfree schemes based on optimal transport theory have been developed for efficient and robust integration of the weak form equations originating from computational mechanics. Although the methods are derived in a different fashion, their algorithms share many similarities. In this paper we outline the close resemblance of MPM and Optimal Transportation Meshfree (OTM) schemes. Aside from a theoretical analysis, the methods are compared numerically using a one-dimensional benchmark.
Simulation of seepage and overtopping induced dam failures
In this paper, we describe three applications of the two-point two-phase formulation of the Anura3D MPM computational package to the soil/water interaction problems. In the model, the behaviours of the soil and water are analysed in a single framework, and the interactions between soil and water are fully dynamic. The three case studies concern the seepage flow through soil embankment, overtopping-induced dam failure and the solitary wave impact on a rubble mound breakwater, respectively. These case studies highlight the advantage of the meshfree methods for investigating the instability mechanisms and the post-failure processes simultaneously. The two-point two-phase formulation of the Anura3D MPM software is shown to be capable of studying the complicated interactions between the fluid flow and the deformation of the granular materials.
Geometric and material non-linear wave propagation with the material point method
This paper presents the numerical modelling of one-dimensional wave propagation with the material point method, considering geometric and material non-linearity. Geometrical non-linearity corresponds to the non-linear relation between strain and displacements due to large deformations, whilst material non-linearity is caused by the non-linear relation between stress and strain. In this study, a finite solid column will be used as an example to illustrate the effect of both non-linearities in the overall response.
Proceedings of the 2nd International Conference on the Material Point Method for Modelling Soil-Water-Structure Interaction - MPM 2019 (Cambridge, 8-10 January 2019))
Passive dosing of organic substrates for nitrate-removing bioreactors applied in field margins
Denitrifying bioreactors are dependent on organic matter supply as a substrate for effective NO3 removal. In this study, the difference in removal efficiency and side effects when using different organic matter sources and dosing strategies was tested in two field experiments. The organic matter sources tested were woodchips and ethanol. The effect of woodchips was tested using woodchip-enveloped drains. Ethanol was supplied to a flow-through reactor by passive dosing by diffusion through silicone tubing. The woodchip-enveloped drains showed a removal efficiency of 80% during the first year of application, but this rate decreased during the second and third years of application, coinciding with a decrease in dissolved organic C and an increase in redox potential. The removal efficiency was higher and remained higher over a longer period of time when the drains were installed more deeply. The flow-through reactor with ethanol could lead to a higher removal efficiency (up to 95%) at higher hydraulic retention time (HRT, 0.1 d) than the woodchip-enveloped drains (HRT = 5 d). Passive dosing of organic substrates is simple, needs little maintenance and no energy, and can be performed independent of electricity. A denitrifying bioreactor with a controlled drainage inlet and outlet is a promising setup for optimizing N removal and minimizing side effects.