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The use of prefabricated horizontal drains (PHDs) with combined surcharge and vacuum preloading is an effective improvement approach for dredged clayey slurries. However, there is no large-strain analysis method for PHD-induced consolidation of high-water-content sludge, even though it is a typical large-strain problem. This study develops a two-dimensional plane strain model based on Gibson's large-strain theory, considering horizontal and vertical flows, nonlinear hydraulic conductivity, and compressibility during the consolidation process. The alternative direction implicit (ADI) difference method is used to solve the governing equation. The proposed model is verified by the data from an analytical one-dimensional (1D) large-strain model and from field measurements. Compared with the improved small-strain models, the proposed model produces a slower consolidation of sludge. Furthermore, the analyses incorporating geometrical and mechanical nonlinearities show that, in comparison with the external load and the horizontal permeability, the spacing of the PHDs (horizontal and vertical) and the vertical permeability are more crucial factors significantly impacting consolidation efficiency. Specifically, smaller PHD spacing and greater vertical permeability lead to a more efficient consolidation. [ABSTRACT FROM AUTHOR]

Lime treatment combined with vacuum preloading has been used in the treatment of dredging slurry for many years. Previous studies have indicated that particle grading, which is one of the essential properties of slurry, could affect the pore-size distribution and compression characteristics of slurry and thus affect the efficacy of the lime treatment and vacuum preloading. However, the effect of particle grading has not yet been examined quantitatively. This study investigated the compressibility of lime-treated slurries with different particle gradings using a one-dimensional oedometer for compression testing. A series of laboratory model tests were carried out to examine the effect of particle grading on the efficacy of lime-treated slurry with vacuum preloading. The results showed that particle grading significantly influences optimal lime content. For clay or low-plasticity silt, the optimum lime content for lime treatment combined with vacuum preloading was found to be 2%. When slurry contains increased silt and sand grains, more lime is required to achieve effective lime treatment. However, excessive lime would reduce the efficacy of lime treatment on the compressibility and permeability of the soil. [ABSTRACT FROM AUTHOR]

A series of one-dimensional incremental load consolidation–hydraulic conductivity tests was performed on reconstituted clays. Based on these tests, together with the test data compiled from the literature, the quantitative interrelation between the variation of hydraulic conductivity in the vertical direction with void ratio and the compression behaviour is established. It is found that the hydraulic conductivity in the vertical direction can be expressed as a function of void index, initial void ratio and void ratio at the liquid limit. The effects of initial void ratio and void index on hydraulic conductivity in the vertical direction for a given clay with a given void ratio at the liquid limit can be comprehensively attributed to the effect of void ratio on hydraulic conductivity in the vertical direction. These two findings introduce the point that the hydraulic conductivity in the vertical direction is a function of void ratio and void ratio at the liquid limit. Empirical equations are proposed to determine the hydraulic conductivity in the vertical direction using void ratio and void ratio at the liquid limit or using effective vertical stress, initial void ratio and void ratio at the liquid limit. These two empirical equations are correlated based on the concept of intrinsic compression. [ABSTRACT FROM AUTHOR]

Abstract: Based on Gibson’s governing equation for one-dimensional finite-strain consolidation of a saturated thick soil layer, a simple semi-analytical method is developed to solve the problem of one-dimensional consolidation by taking into account the varied compressibility of soil under cyclic loadings. The solution in the transformed domain is obtained using the method of Laplace transforms. Thereafter a numerical inverting procedure is applied to study the behaviors in the time domain. The variation of soil compressibility during compression and rebound is paid special attention, and a computer program has been written that enables this facet of soil behavior to be accounted for. The technique used is numerically stable and has proved accurate in predicting consolidation settlements and the distribution of void ratios within soil layers. [Copyright &y& Elsevier]

Abstract: Eight series of falling head hydraulic conductivity tests were performed on both undisturbed and remolded specimens of four clays from China using a modified oedometer to investigate the change of hydraulic conductivity during compression. Similar to their compression behavior, the undisturbed specimens showed the curves of hydraulic conductivity versus effective vertical stress lying above those of the remolded specimens. Past studies showed that the compression curves of remolded clays could be unified into a unique line using the void index. However, such unification between the void index and the hydraulic conductivity for remolded clays was not found in this study. The relationship between the void index (or void ratio) and the hydraulic conductivity for undisturbed specimen was almost identical to that of the remolded specimen. The relationship between the void ratio and the hydraulic conductivity on a logarithm scale was nearly linear with a slope of 0.5 times the initial void ratio at strains <20%, and became concave upwards within the full range of strains during compression. Similar to the oedometer test data, the relationship between the specific volume and the hydraulic conductivity could be expressed by a straight line in a bilogarithmic plot within the full range of strains during compression. [ABSTRACT FROM AUTHOR]