Freeze-thaw vacuum treatment of landfill sludge: Mechanism of uneven frost heaving and dewatering performance
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Keywords:
Oedometer test
Consolidation
Dewatering
Frost heaving
Abstract The consistency of very soft sediments prevents the conventional oedometer test from being applied to study their compressibility and permeability characteristics. The hydraulic consolidation test in existence requires sophisticated instrumentation and testing procedures. The present paper proposes a seepage-force-induced consolidation testing procedure for studying the compressibility and permeability behavior of soft sediments at low effective stress levels. The good agreement that has been observed between the results obtained from the proposed method and the conventional oedometer test at overlapping effective stress levels indicates that the proposed method can be used to study the compressibility and permeability characteristics of soft sediments at low effective stress levels satisfactorily.
Oedometer test
Consolidation
Effective stress
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Abstract Traditionally, there have been two approaches to the modelling and prediction of the extent and rate of dewatering of particulate networks: consolidation theory and filtration theory, developed by geotechnical engineers and physical scientists, respectively. The physical situations and governing equations for Terzaghi's consolidation model (Terzaghi and Peck 1967) and Landman and White's filtration model (Landman and White 1997) are essentially the same. However, their methods of determining the relative dewatering parameters differ. The consolidation method matches experimental data from oedometer testing to the theoretical predictions of the model in order to determine the coefficient of consolidation, cv. The filtration method determines a solids diffusivity coefficient, D, based upon the experimental data from a filtration rig, which is then used in modelling to make predictions. This work aims to highlight the similarities between the two approaches, initially by demonstrating the theoretical relationship between the two parameters, cv and D, and then through experimental determination. The material characteristics of a kaolin sample undergoing one-dimensional (zero lateral strain) compression are determined using both oedometer and filtration testing and equated using the developed theoretical relationship. The results indicate that the two testing methods are essentially the same, and that their relevant analysis techniques give similar outcomes. Consequently, geotechnical engineers can use filtration methods and physical scientists can use consolidation methods.
Terzaghi's principle
Consolidation
Oedometer test
Dewatering
Biot number
Soil Mechanics
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The treatment of cyanobacterial dewatering and reduction has become a new issues in lakesimprovement. The essence of dewatering of cyanobacterial is a process of consolidation and drainage; therefore,the investigation of the consolidation behavior of cyanobacterial byconsolidation experiment is important to the enhancement of dewatering effects. Based on the improvement of oedometer by setting additional piezometer and displacement sensor,one type of cyanobacterial and one type of dredged materials were studied for their difference of consolidation characteristics. The results indicated that consolidated time of cyanobacterial was very long and the excess pore water pressure dissipated very slowly. The coefficient of consolidationand coefficient of permeability of cyanobacterial is extremely low,and have great changed in the consolidation process. Meanwhile,the main reason of long time consolidating and extremelyslow for drainage is a large number of organic matter cells in cyanobacterial.
Dewatering
Consolidation
Oedometer test
Piezometer
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The piezocone is one of the most widely used in-situ tools with which to characterise the soil profile, distinguishing different types of sediment, and to provide quantitative data on the soil strength and consolidation characteristics. For fine-grained soils where penetration occurs under nominally undrained conditions, consolidation characteristics are obtained from dissipation tests conducted with the piezocone brought to rest. Dissipation testing is interpreted to yield a coefficient of consolidation, by comparison of the excess pore pressure decay with theoretical solutions. It is generally acknowledged that the coefficient of consolidation derived from in-situ dissipation tests will be greater, by a factor of perhaps 2 to 10, than values derived from oedometer tests on samples recovered from the corresponding depth. Apart from potential differences in horizontal and vertical permeability, differences arise from the influence of the rigidity index on the initial excess pore pressure field and the more complex stress paths undergone by soil elements surrounding the piezocone by comparison with an oedometer test. In order to advance the science underlying interpretation of dissipation testing, a careful parametric study has been undertaken using finite-element analysis, with the soil modelled as modified Cam Clay. The aim has been to derive an ‘operative' coefficient of consolidation, linked to the consolidation and swelling parameters of the soil model, thus allowing quantitative treatment of the difference in coefficients of consolidation derived from laboratory oedometer or in-situ dissipation testing. The effect of partial consolidation during the penetration phase is also considered.
Oedometer test
Consolidation
Penetration test
Stress path
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Laboratory consolidation tests for a two-layer soil system under oedometer conditions were conducted under both vacuum pressures and surcharge loads. The effects of the order of soil layers on the behaviour of vacuum consolidation of the two-layer soil system have been investigated by comparing vacuum pressure and surcharge load induced consolidations. Under one-way drainage conditions, for both a surcharge load and a vacuum pressure, the order of soil layers only influences the rate of consolidation but not the final settlement. When a layer with a relative lower value of hydraulic conductivity (k) is located immediately adjacent to the drainage boundary, the consolidation rate is slower. However, for vacuum pressure applied under two-way drainage conditions, the order of the soil layers not only influences the rate of consolidation but also the magnitude of settlement.
Consolidation
Oedometer test
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Oedometer test
Consolidation
Subsoil
Soil test
Poisson's ratio
Effective stress
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Citations (26)