943 research outputs found

    Constitutive modelling of municipal solid waste

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    Design of landfills must consider both stability and integrity of the lining system. Therefore, stresses and strains in both mineral and geosynthetic lining materials must be controlled. Interaction between waste and barrier system is of particular importance for assessing the stability and structural integrity of steep non-self supporting barrier systems. The most appropriate approach to assess the interaction is the use of numerical modelling techniques, and therefore an appropriate constitutive model for waste material is required to represent its mechanical behaviour. In a literature review the key aspects of mechanical behaviour of municipal solid waste (MSW) were investigated, including the influence of compressible and reinforcing particles on compression and shear behaviour of MSW were identified. Constitutive modelling of both MSW and soil material were reviewed, based on which the methodology for this study have been developed. In addition, requirements of an appropriate constitutive model for MSW have been suggested from the numerical modelling experience, and a framework to develop a constitutive model for MSW was produced. A one-dimensional compression model was developed by including the influence of compressible particles on MSW compression behaviour. One-dimensional compression tests on both real and synthetic waste samples were modelled and the results have shown that the compression model can reproduce the measured behaviour. A fibre reinforcing model was developed by including the influence of reinforcing particles on MSW shear behaviour. A triaxial compression test on fibre reinforced sand was modelled and the results have shown that the reinforcing model can predict its shear strength. A constitutive model for MSW has been developed by combining the Modified Cam-Clay with the one-dimensional compression and the fibre reinforcing models. Typical MSW triaxial compression tests have been modelled and the results have shown that the MSW model can reproduce the stress-strain behaviour in specific strain ranges. The constitutive model for MSW has been coded into a non-linear elasto-plastic finite element method program. Comparisons between the finite element analysis results and the analytical solutions have been performed and good agreements have been obtained

    Development and evaluation of a phase relationship for MSW

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    Compression is one of the most important mechanical aspects of behaviour of municipal solid waste (MSW) which concerns stability, deformation and structural performance in a landfill. Previous studies have shown that compressible particles play a significant role in MSW compression. Definition of the void ratio in classical soil mechanics theory may no longer be applicable for MSW material since high non-linearity between void ratio changes and vertical stress changes have been identified in compression tests. A new phase relationship for MSW has been developed to include the volume loss of compressible particles and this has been evaluated using onedimensional compression test data. The comparison between analytical and test results has demonstrated that the MSW phase relationship is capable of analysing the volume losses originated from inter-and intra-void ratio changes, in addition to the total volume loss of the MSW sample under different vertical stresses. Since it can isolate the volumetric change of compressible particles from the total volume loss, the MSW phase relationship is important when developing a constitutive model for MSW assuming elasto-plastic material behaviour, which couples the volumetric and shear behaviour

    Landfill capping stability: tapered solution with seepage

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    The capping system is one of the major structural elements in modern landfills. When using artificial sealing materials (e.g. a geomembrane) as the capping liner, the stability of the cover soils and integrity of the geosynthethics need to be assessed. Traditional design methods only consider uniform cover soil thickness with different degrees of saturation and seepage build-up (i.e. parallel submergency ratio). This paper proposes an analytical method which includes the seepage build-up in the stability analysis for the capping slope with a tapered cover soil profile, that is when cover soils become thicker from top to bottom. Both the parallel (modified) and horizontal seepage force build-up patterns have been considered and analysed. The proposed analytical methods are applied to a design case in which uniform thickness cover soils are considered. The results are comparable to those of the traditional methods and therefore they are verified. Parametric analyses have confirmed the tapered profile can effectively improve the capping slope stability and indicated that the interface shear strength (between the cover soil and the underlying geosynthetic) and cover soil shear strength have the most significant effects on the capping slope stability

    Experimental investigation of flow and heat transfer characteristics on matrix ribbed channel

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    The effect of the rib width to height ratio t/e and width to pitch ratio t/p on the local heat transfer distribution in a rectangular matrix ribbed channel with two opposite in line o 45 ribs are experimentally investigated for Reynolds Numbers from 54000 to 150000. The rib height to channel height ratio e/H is 0.5, t/p and t/e both varies in range of 0.3-0.5. And to simulate the actually situation in turbine blades, and provide useful direct results for turbine blade designers, the parameters are same with the blade. The experiments results show that, in comparison to fully developed flow in a smooth pipe of equivalent hydraulic diameter, the Nusselt number inside the matrix-ribbed rectangular channel is increased up to 5 to 9 times higher, while total pressure drop is enlarged by up to significant magnitude. The Nusselt number ratio increases with t/p and t/e increased. Semi-empirical heat transfer is developed for designing of cooling channel

    Landfill side slope lining system performance: a comparison of field measurements and numerical modelling analyses

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    Low permeability engineered landfill barriers often consist of a combination of geosynthetics and mineral layers. Even though numerical modelling software is applied during the landfill design process, a lack of data about mechanical performance of landfill barriers is available to validate and calibrate those models. Instrumentation has been installed on a landfill site to monitor multilayer landfill lining system physical performance. The lining system comprises of a compacted clay layer overlaid by high density polyethylene geomembrane, geotextile and sand. Data recorded on the site includes: geosynthetic displacements (extensometers), strains (fibre optics, Demec strain gauges, extensometers) and stresses imposed on the liner (pressure cells). In addition, temperature readings were collected by a logger installed at the surface of the geomembrane, at the clay surface using pressure cell thermistors and air temperature using a thermometer. This paper presents readings collected throughout a period of three years and compares this measured performance with the corresponding numerical modelling of the lining system for stages during construction. Numerical modelling predictions of lining system behaviour during construction are comparable with the measurements when the geosynthetics are covered soon after placement, however, where the geosynthetics are left exposed to the sun for an extended period of time, in situ behaviour of the geosynthetics cannot be replicated by the numerical analysis. This study highlights the significant influence of the effect of temperature on geosynthetics displacements. A simple thermal analysis of the exposed geosynthetics is used to support the explanation for observed behaviour

    Closeness centrality and betweenness centrality ranking changes of key countries in potassium salt trade from 2000 to 2021.

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    Closeness centrality and betweenness centrality ranking changes of key countries in potassium salt trade from 2000 to 2021.</p

    Potassium salt trade quantity from 2000 to 2021(a) and cumulative distribution of PTN in 2000, 2005, 2010, 2015, and 2021(b).

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    Potassium salt trade quantity from 2000 to 2021(a) and cumulative distribution of PTN in 2000, 2005, 2010, 2015, and 2021(b).</p

    Node centrality of top 10 countries from 2000 to 2021.

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    Node centrality of top 10 countries from 2000 to 2021.</p

    The roles of 13 major countries in 2000,2010, and 2021.

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    The roles of 13 major countries in 2000,2010, and 2021.</p

    Top 5 countries by five different indicators in 2000, 2010, and 2021.

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    Top 5 countries by five different indicators in 2000, 2010, and 2021.</p
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