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Micro-scale characterization of fluid flow in a uniform particle pack using coupled discrete element-lattice Boltzmann method
Get PDFParticle scale investigation of geo-mechanical phenomena using numerical simulations has increasingly attracted the attention of researchers stimulated by recent advances in computational capacities. In this paper, the pore scale characteristics of flow in a particulate soil pack is investigated. A randomly distributed pack of uniform particles is created using a discrete element simulation of 500 particles with 9mm diameter settling freely into a box. Then the lattice-Boltzmann method is utilized to simulate a constant flow passing through the particle pack with a wide range of Reynolds numbers from 10-4 to 18. Subsequently, the pressure loss occurred in the flow when it passes through the particles is studied to characterize the transformation of flow conditions from laminar to turbulent mode. The pore scale characteristics of the flow, e.g. fow tortuosity, are then compared to those of pack scale, e.g. fluid pressure difference between base and top of the particle pack to acquire more understanding on transforming from laminar to turbulent flow in micro (pore scale) and macro (pack) levels. Furthermore, the effects of flow rates demonstrated by Reynolds numbers are examined on the drag forces applied on particles. Discussions on the micro-scale behaviour of flow in porous media based on the results obtained from numerical simulations are provided
Feed-back on the development of a small scale Contact Erosion Test in the laboratory (characteristic size ~ 30 cm)
Get PDFTo determine the hydraulic load requested to initiate contact erosion process, tests are performed with an apparatus called the “Contact Erosion Test”. This device originally results from research carried out by Grenoble University, Électricité de France and Compagnie Nationale du Rhône, at the scale of ~60 cm. It has been adapted to a smaller scale in geophyConsult laboratory to conduct tests on samples extracted from core drilling. The instrumentation was improved to enable a better control of the hydraulic loading and avoid biases. The test protocol was modified, especially to better constrain the soil density at the interface. From the first series of test, we drew conclusions on the test repeatability and on the influence of parameters of the soil state. Discrepancies with previous results obtained at the scale of ~60 cm were identified. Therefore, a new erosion test campaign was planned to confirm and determine the reasons for these differences
Lime treated soil erodibility investigated by EFA erosion testing
Get PDFErosion is susceptible to reduce the overall stability of a structure under hydraulic and static loads, but also can lead to the development of a fast breach. In parallel, dikes and levees builders and designers have not so many ways to improve initial properties of materials available on site, for the construction or restoration of hydraulic embankments. In this context, soil treatment with lime is a relevant procedure that is reported to improve the mechanical properties and erosion behavior of silty and clayey soils.
This study focuses on the changes induced by lime treatment on the erosion resistance of a silty soil, and the evolution of relevant erosion parameters with curing time. EFA (Erosion Function Apparatus) tests on a silty soil from Marche-les-Dames (Belgium) were performed on the native soil, and after 2.5 % lime addition at several curing times (1, 7 and 28 days). After 1 day curing time, a slight increase in the soil erosion resistance is recorded, whereas after seven days submitted to a water flow velocity above 3 m/s, the soil passes from a medium to a low erodibility level. After 28 days, the soil has a very low erodibility for the same water velocity
Local mechanisms of cohesive soil erosion
Get PDFThe present study provides an experimental contribution to a better understanding of erosion mechanisms, based on a parametric analysis with different model materials. Such model soils allow for a controlled variation of physical properties, as well as the particle size and shape, and even the cohesion and bonding strength which can be quantified by specific mechanical testing devices. In parallel, the soil’s resistance against erosion can also be somehow quantified by means of experimental procedures such as the JET test (Hanson and Cook 2004). The goal of the investigations presented here is to determine the soil’s mechanical properties having a strong impact on the erosion resistance, and thus being required in an efficient erosion model. The useful case where the model material is also transparent enables, with adapted optical equipment, the time-space monitoring of single soil particles during erosion and thus a local analysis of erosion and soil’s detachment. Experimentally, this condition is achieved by using an oil mixture as eroding fluid and a model soil made out of glass beads possibly bonded with a very viscous liquid, all phases having approximately the same refractive index. Coupling then this refractive index matching technique with the planar laser-induced fluorescence, as already used by Philippe & Badiane (2013), makes it possible to observe the mechanisms by which the fluid flow removes single particles from the cohesive material
The importance of permeability in granular filter design and control
Get PDFGranular filters are required to perform two basic functions in embankment dams: (a) prevent the migration of base soil particles, and (b) allow drainage of seepage water. Traditionally, retention function (a) has been evaluated using Particle Size Distribution (PSD) and drainage function (b) using Permeability (kf), but usually permeability have been also correlated with PSD, so the permeability criterion have been expressed in terms of D15b of the base soil and D15f of the granular filter. Only few authors have used filter permeability for the assessment of retention function and there is no general agreement with them, but permeability should be a very important variable because it takes into account not only the whole PSD of the filter, (instead of just several representative diameters), but also other important characteristic such as compaction, porosity, density and particle shape. Based on a literature review and research experience at the University of Granada, this paper analyses the importance of filter permeability in the design and control of granular filters in embankment dams, even with dispersive base soils
Screening methodology for bank erosion estimation at pipeline watercourse crossings
Get PDFA screening level model was developed to estimate bank erosion at pipeline watercourse crossings to provide estimates of the probability of pipeline exposure resulting from various extreme flood events. The model uses estimates of flood duration and maximum water velocity during flooding to predict the amount of bank erosion that would occur and compares the results to the horizontal “setback” distance. When the predicted horizontal erosion is equal to horizontal distance between the pipeline and the bank position, the probability of that flood occurring is equal to the probability of pipeline exposure due to bank erosion. The results of the bank erosion calculation can then be compared to: the probability of the flood causing exposure by scour and/or avulsion; regulatory acceptance criteria for pipelines; and company integrity objectives to assess the need for additional investigation or proactive mitigation
National scale multivariate extreme value modelling of waves, winds and sea levels
No full textIt has long been recognised that extreme coastal flooding can arise from the joint occurrence of extreme waves, winds and sea levels. The standard simplified joint probability approach used in England and Wales can result in an underestimation of flood risk unless correction factors are applied. This paper describes the application of a state-of-the-art multivariate extreme value model to offshore winds, waves and sea levels around the coast of England. The methodology overcomes the limitations of the traditional method. The output of the new statistical analysis is a Monte-Carlo (MC) simulation comprising many thousands of offshore extreme events and it is necessary to translate all of these events into overtopping rates for use as input to flood risk assessments. It is computationally impractical to transform all of these MC events from the offshore to the nearshore. Computationally efficient statistical emulators of the SWAN wave transformation model have therefore been constructed. The emulators translate the thousands of MC events offshore. Whilst the methodology has been applied for national flood risk assessment, it has the potential to be implemented for wider use, including climate change impact assessment, nearshore wave climates for detailed local assessments and coastal flood forecasting
Numerical analysis of bed elevation and bank line changes at the confluence of Nakdong and Geumho Rivers in Korea
Get PDFThe river confluence forms complex flow pattern because of different inflow discharges from the main stream and tributary. Complex flow feature at the confluence affects geomorphological changes. Especially rapid and continuous flow changes produce unstable condition in the channel geometry. Therefore, it is important to analyze geomorphological changes such as bank erosion and deposition as well as bed changes at the confluence channel for river maintenance and management, especially before and after the construction of river structures like weirs and bridges. Progressive erosions including headcutting and bank erosion are expected in the confluence in Nakdong River and Geumho River, Korea because a large weir (Gangjeong-Goryeong Weir) has been constructed in the upstream channel during Four Major Rivers Restoration Project. Therefore, flow changes, bed elevation changes, and bank-line changes have been simulated in this study using the 2-dimensional numerical model of CCHE2D (Center for Computational Hydroscience and Engineering 2-Dimension) to analyze variations after the weir construction. The largest flood event before and after the weir construction is selected for hydraulic condition in the model. The measured data for flow and sediment discharge at the Dongchon Station in the Geumho River and Waegwan Station in the Nakdong River have been used for boundary conditions. Numerical simulations of this study reproduce similar variation to the actual condition regarding geomorphological changes in the river confluence. The study results should provide fundamental information to establish many countermeasures for channel stability against excessive erosion and deposition of bed and bank at the confluence section
Scour of soil with dynamics interactions among soil-water induced by jet flow
Get PDFThe present study attempted to explicate the scouring mechanism due to overflow focusing on the tractive force and the pore water pressure in the ground by using several geomaterials. For example; In the case of sandy soil, the scour profile has same profile as proposed by Yeh et al (2006), and the excess pore water pressure was generated. Especially, the excess pore water pressure was severely increased and it increased with the depth of sedimentation ground increased due to jet flow. As a result, the effective overburden pressure became zero, and a fluidization/liquefaction-like phenomenon occurred. Moreover, we investigated the mechanics of generate the excess pore water pressure in the ground induced by jet flow by using SPH method. As a simulation results, we found that the generating excess pore water pressure in the porous rigid ground was lower than the 1g-field model test
The hydrodynamics of a recirculating (O-tube) flume
Get PDFAn O-tube flume is a horizontal closed-circuit flume that can be driven by an inline impellertype pump to produce steady and/or oscillatory flow over a mobile seabed. An O-tube has the ability to reproduce large combined wave and current conditions near the seabed, typical of (cyclonic) storm conditions. In this paper, we investigate the hydrodynamics of an O-tube and show applications of this technology. First, we derive a dynamic equation to explain the coupling between pressure and flow rate within the O-tube. This result can be thought of as an extension of the classical hydrodynamic equations developed for U-tubes and allows for improved control of the flow within the O-tube by providing a prediction of the non-linear interaction between steady flow (i.e. currents) and unsteady flow (i.e. waves). We demonstrate this improved control by comparing measurements of flow rate taken from an O-tube with the dynamic equation. Secondly, we present velocity measurements to give a detailed description of the flow field within the O-tube, including mean flow profiles and seabed shear stress. Finally, we conclude the paper by providing two example applications of the facility to study sediment transport and scour