Consolidation Model Research Articles

Suction contribution to uplift capacity of suction buckets under serviceability conditions

Suction pressures induced inside buckets under tensile loads can greatly increase bucket uplift resistance. However, a considerable bucket upward displacement is required to mobilize a sizeable part of the suction pressure, which may not meet the serviceability requirements. To address this issue, this study emphasizes that suction buckets operate under compressive preloading conditions owing to their self-weight and potential ballasting, and that reduced compressive preloading can result in suction pressures at the underside of the bucket lid. The critical suction pressure, which refers to the suction pressure under the lid bottom at the instant at which the lid separates from the soil surface owing to tension, was identified and considered to contribute to the bucket uplift capacity. An axisymmetric consolidation model was developed to quantify the critical suction pressure. Analytical solutions were obtained using integral transformation techniques and verified using published data. A detailed parametric study was then conducted to explore the effects of bucket and soil parameters on the critical suction pressure. The results indicated that the critical suction pressure was robust despite significant variations in the soil permeability and boundary drainage conditions. This study provides new insights into the serviceability-driven design of suction buckets subjected to tensile loads.

Particularities of documenting the accounting events on intangible-asset acquisition, revaluation and write-off

Subject. This article deals with the issues of documenting the business operation items related to the recognition, revaluation and write-down of intangible assets. Objectives. The article aims to investigate and systematize the provisions that reveal the features of documenting transactions for the acquisition, creation, revaluation and write-down of intangible assets, as well as reveal the content and composition of the details of primary documents on the revaluation of intangible assets. Methods. For the study, we used the information retrieval, consolidation, and event modeling techniques. Results. The article proposes an author-developed primary document form for practical application, which records the results of the revaluation of intangible assets. The information contained in this document may serve as the basis for regulating the valuation of intangible assets by reflecting transactions for their revaluation and (or) write-down on accounts in accordance with the rules established by accounting standards. The versatility of the proposed document form makes it possible to use it in relation to the primary accounting of the results of the revaluation of fixed assets and other non-current assets. Conclusions. The quality of decisions made in the management system of the organization depends both on the professionalism of the managers and on the discipline of the performers who form the information base for decision-making and the subsequent reflection of the results of the accounting events in the reporting. Structuring the composition of the elements and their content contribute to improving the quality of not primary documents only, but also the entire system of accounting and analytical support for management and reducing the threat to economic security when performing transactions with intangible assets.

Nonlinear consolidation analysis for composite ground with combined use of impervious columns and prefabricated vertical drains under time-dependent loading

The technique of the combined use of soil-cement columns (impervious columns) and prefabricated vertical drains (PVDs) has been proposed and widely utilized in ground improvement projects. However, there are few theoretical investigations on the nonlinear consolidation behavior of this combined technique. To fill this gap, the logarithm models of e-lgσ and e-lgk are incorporated to describe the nonlinear consolidation characteristics of soils. Meanwhile, a mathematical model for the nonlinear consolidation of combined composite ground is established by considering the variation of the column-soil compression modulus ratio with consolidation. The governing equations and simplified analytical solutions for four types of loading schemes are obtained in consideration of the smear effects of both impervious columns and PVDs and the well resistance of PVDs. The calculated results of this paper are then compared with the proposed models and the impacts of various parameters on the nonlinear consolidation performance are investigated. The results show that ignoring the nonlinearity will overestimate the consolidation rate when the soil’s compressive indices are greater than the permeability indices. Besides, Cc/Ckv has little influence on the consolidation rate and can be ignored compared with Cc/Ckh. Furthermore, the increase in the stress increment within the ground due to the external loads leads to an acceleration of the consolidation when Cc/Ckh(v) > 1, and the dissipation rate of the excess pore water pressure increases by a maximum of 15 %. Finally, a field case study is conducted to verify the prediction ability of the current model.

Analysis of Consolidation by Vertical Drain with Vacuum Preloading Based on Axisymmetric Biot’s Consolidation Theory

A model of consolidation for a single-drain well under vacuum preloading, based on Biot’s axisymmetric theory and considering the “real strain” hypothesis, was established using the finite element method. Degenerating the consolidation equation of real strain yielded the Barron’s classical free strain and equal strain equations. The free strain and equal strain finite element models were derived by imposing boundary and constraint conditions on the real strain FEM model. The validation of the simulation process confirmed that the numerical model achieved consistent outcomes, with the theoretical values postulating its effectiveness. The real strain model revealed the Mandel–Cryer effect of soil near the vertical drain during the initial vacuum preloading consolidation process, causing the effective stress to increase more than the effective stress generated by the vacuum pressure and leading to a greater reduction in the void ratio. This phenomenon is one of the reasons for clogging during the vacuum preloading process. However, the free strain and equal strain models cannot produce this effect because they cannot describe the coupling between soil deformation and fluid flow. The parameter analysis of the real strain model showed that as Poisson’s ratio for soil decreased, the consolidation rate of soil also decreased, while the Mandel–Cryer effect of soil increased.

Incorporation of three different creep models into large-strain consolidation analysis of a clayey tailings deposit

Soft soils and clayey tailings deposits can exhibit substantial creep during consolidation. Creep can strongly influence the consolidation and strength development of tailings deposits but is rarely considered in existing large-strain consolidation analyses for design purposes. This paper presents an analysis of a 13 m high deposit of soft clayey tailings using large-strain consolidation coupled with three alternate creep formulations: the Yin–Graham, Vermeer, and overstress formulations. Predictions of settlement and excess pore water pressure using all three consolidation–creep models have better agreement with the measured data compared to predictions from a large-strain consolidation model without creep. The overstress model is more difficult to calibrate for young soft soils in an initially normally consolidated state, owing to the strong dependency on the initial ratio between an unknown small preconsolidation stress and the initial small effective stress. The models calibrated to the pilot study were then used to extrapolate the full-deposit behavior, and the implications of using such consolidation–creep models and their limitations are discussed.

Analysis of Using the Empirical Model of Organic Soil Consolidation to Predict Settlement

Abstract The paper describes two models for determining the constrained elasticity modulus of organic soils based on the settlement of an overloading embankment. In these methods, based on the settlement of the embankment of the load exerted on the subsoil, using the inverse problem, it is possible to determine the constrained modulus. A parameter determined in this way can also be determined during consolidation. Changes in the settlement at successive stages of consolidation can be used to determine the constrained modulus of the organic soil at a given point in time. Assuming a “temporarily stable” (quasi-stationary) state at each analysed stage of consolidation. The constrained elasticity modulus was determined for the settling at a given moment. constrained modulus tests of organic soils were carried out for two embankments previously described in the literature. In this case, the modulus was also analysed during consolidation. These embankments are founded on peat and peat-gyttja substrates. In both cases, the layer of organic soil was 4 m. The presented methods with the assumption of a one-dimensional state of deformation, despite the state of spatial stress, can be used during construction using the “design and build” technology. The constrained modulus determined from the embankment overload will represent the actual deformations – volumetric deformations (including other deformations that actually occurred) during the consolidation period. The paper was concluded with several conclusions.

Large-Strain Consolidation of Sludge in Multiple-Drainage Geotextile Tubes

This paper presents a profound solution for a novel method of dewatering dredged sludge using a combined geotextile tube and vacuum-assisted prefabricated horizontal drains. Firstly, an analytical model was proposed to provide a basis for the design of the proposed approach. This two-dimensional plane-strain consolidation model was based on Gibson’s large-strain theory, incorporating the horizontal and vertical flows with consideration of the self-weight, nonlinear compressibility, and hydraulic conductivity of soil. Secondly, the numerical solution obtained using the alternative direction implicit method was compared with the existing one-dimensional model for verification. Thirdly, a field trial was carried out to evaluate the performance of the proposed approach and analytical model. Finally, the effects of various major design parameters on the consolidation efficiency of the tube system were also investigated through a parametric study to establish an optimal design. This study showed that a higher consolidation efficiency and an earlier optimal efficiency point could be achieved when decreasing the horizontal drain interval and increasing the tube height. Furthermore, surcharge preloading induces a more significant effective stress increment in soil than vacuum preloading of the same magnitude.

Discussing the Negative Pressure Distribution Mode in Vacuum-Preloaded Soft Foundation Drainage Structures: A Numerical Study

The aim of this paper is to clarify the negative pressure distribution in drainage structures of soft foundations reinforced by vacuum preloading. The focus of this study was an actual engineering project, the Beijing–Shanghai high-speed railway; four different soil consolidation models were established using FLAC3D to consider various loading conditions. The consolidation process of the soft foundation was calculated and analyzed in detail. The results show that (1) the settlement developed rapidly within the first 30 days, slowed during the period between 20 and 30 days, and finally stabilized. (2) The settlement curves obtained from the four different models were highly consistent with the site monitoring curve for the first 5 days, after which point significant differences appeared. (3) During the first 20 days, the pore water pressure decreased noticeably within the depth range of 0–18 m. Between days 20 and 30, the rate of pore water pressure decrease slowed down, and after the 30th day, the pore water pressure remained constant at all depths. (4) Vacuum preloading affected the soil to a depth of approximately 16 m. A concave or linear distribution of negative pressure in the drainage structure was found to be a reasonable assumption, providing a reference for the numerical analysis of vacuum preloading.

Expression of Transposable Elements in the Brain of the Drosophila melanogaster Model for Fragile X Syndrome.

Fragile X syndrome is a neuro-developmental disease affecting intellectual abilities and social interactions. Drosophila melanogaster represents a consolidated model to study neuronal pathways underlying this syndrome, especially because the model recapitulates complex behavioural phenotypes. Drosophila Fragile X protein, or FMRP, is required for a normal neuronal structure and for correct synaptic differentiation in both the peripheral and central nervous systems, as well as for synaptic connectivity during development of the neuronal circuits. At the molecular level, FMRP has a crucial role in RNA homeostasis, including a role in transposon RNA regulation in the gonads of D. m. Transposons are repetitive sequences regulated at both the transcriptional and post-transcriptional levels to avoid genomic instability. De-regulation of transposons in the brain in response to chromatin relaxation has previously been related to neurodegenerative events in Drosophila models. Here, we demonstrate for the first time that FMRP is required for transposon silencing in larval and adult brains of Drosophila "loss of function" dFmr1 mutants. This study highlights that flies kept in isolation, defined as asocial conditions, experience activation of transposable elements. In all, these results suggest a role for transposons in the pathogenesis of certain neurological alterations in Fragile X as well as in abnormal social behaviors.

The Influences of Vacuum–Surcharge Preloading on Pore Water Pressure and the Settlement of a Soft Foundation

Vacuum–surcharge preloading is widely used in soft soil foundation reinforcement projects. To study the characteristics of the changes in pore water pressure and settlement of the soft soil foundation as a result of the effect of vacuum–surcharge preloading, in this paper, a consolidation model was established for large–sized sand–drain fluid–solid coupling along the depth direction while taking the sequence of the actual surcharge and vacuum into consideration by using FLAC3D, and a soft foundation’s consolidation process was calculated and analyzed in detail. The results showed the following: (1) the sand drain could be used as a load boundary condition and a vacuum load could be realized by adjusting the pore pressure at the nodes. (2) For the effect of a single vacuum, the settlement and pore water pressure were evenly distributed on the horizontal plane, and the maximum calculated value of the surface settlement was 90.92 cm, but the phenomenon of a “pot–bottom shape” of the settlement and pore pressure gradually became obvious with the increase in the surcharge, and the maximum calculated value of the surface settlement was 153.01 cm. (3) In the numerical calculations, it was found that the pore pressure and settlement distinctly fluctuated once each level of surcharge was applied. The changes in the settlement were basically consistent with the measured values after the adjustment of positive and negative pressure, and the variation trend of the pore pressure was consistent with the measured value. (4) The depth affected by the vacuum could reach at least 16 m. All of these findings are expected to provide references for the calculation of consolidation in vacuum–surcharge preloading.

Plane‐strain model for large strain consolidation induced by vacuum‐assisted prefabricated horizontal drains

AbstractVacuum‐assisted prefabricated horizontal drain (PHD) can be used to accelerate the consolidation process of dredged mud slurry with high water content, and this method exhibits advantages over traditional treatment methods that use prefabricated vertical drain (PVD). However, large‐strain model that can simulate soil consolidation induced by vacuum‐assisted PHDs is missing in the literature, although the large‐strain models for PVD‐induced radial consolidation are abundant. This study presents a piecewise‐linear plane‐strain model for large‐strain consolidation induced by vacuum‐assisted prefabricated horizontal drains. The model is called PCS, abbreviation for Plane‐strain Consolidation Settlement. PCS model can account for complex conditions including large strain, multiple layers of PHD boards, staged filling of soil layers, varying spacing of PHD boards, time‐dependent surcharge and/or vacuum loading, soil self‐weight, nonlinear compressibility, and hydraulic conductivity during the consolidation process, vertical and horizontal flows, and non‐Darcian flow. The PCS is validated using the two‐dimensional Terzaghi's consolidation theory (small strain) and a large‐scale laboratory model test (large strain), which involves multiple soil layers filled in stages, multiple PHD layers, and different horizontal spacings of PHD boards. Lastly, the proposed model is applied to a case study conducted at Shimokita Peninsula (Aomori Prefecture, Japan), where vacuum‐assisted PHDs have been used to treat the dredged mud slurry for a duration of 330 days.

One-dimensional large strain electro-osmotic consolidation model based on multi-field coupling

Current electro-osmotic consolidation theories and numerical models usually ignore the variation of chemical fields and are applicable to soft clay soils with a single chemical composition. In this paper, a numerical model, called EC4, is presented for one-dimensional large strain electro-osmotic consolidation with coupled electrical-hydro-chemical fields. The algorithm accounts for non-linear variation of soil parameters, ion transport and a variety of chemical reactions, including ionization-neutralisation reactions, ion adsorption–desorption reactions and electrolytic water reactions at electrodes. The laboratory electro-osmotic consolidation tests on kaolin samples with different NaCl concentrations were conducted. The laboratory results were used to verify the accuracy of EC4. Then EC4 was implemented to example problems to investigate the effect of important chemical characteristics on the electro-osmotic consolidation. The effects of electrical voltage and initial pH on settlement, degree of consolidation, excess pore pressure and energy consumption of multi-field coupled electro-osmotic consolidation were further analyzed.

Drawdown‐induced consolidation of aquifer systems considering water‐table decline

AbstractBoundary condition is an important factor in estimating land subsidence induced by groundwater withdrawal. In previous analytical studies, the upper boundaries are commonly assumed to be constant‐head, which could fail to reflect the declines in groundwater table during groundwater pumping. A one‐dimensional (1‐D) consolidation model of aquifer systems due to groundwater drawdown is considered in this study, in which the water‐table decline is taken into account. A mathematical model, which incorporates Neuman's model of unconfined flow into Terzaghi's theory of consolidation, is first presented. The analytical solutions for both hydraulic head drawdown and subsidence are developed in the Laplace domain. A more explicit solution to the elastic, single‐layered model is also derived. The validation of the presented solutions is verified by comparing with existing solutions in degenerated cases. The results show that the presented hydraulic drawdown solutions can be used to describe the water table decline. Moreover, the subsidence solutions are notably different from solutions based on the commonly‐used constant‐head boundary, and these previous models could severely underestimate the subsidence. The influences of specific yield, compressibility of the pore water, hydraulic conductivity, and viscosity of soil skeleton on the water table decline and long‐term deformation are also investigated using the presented solutions.

Analytical solutions for consolidation of soft soil improved by air‐boosted vacuum preloading considering clogging effect

AbstractAir‐boosted vacuum preloading is a newly emerging soft soil‐improving technology and increasingly draws attention of researchers and engineers. However, few analytical theories are available in the literature to facilitate the design and calculation of it in practice. To fill this gap, an analytical model for the consolidation of soft ground improved by air‐boosted vacuum preloading is proposed based on the assumption of equal volumetric strain and Darcy's law. Moreover, a time‐dependent clogging effect is taken into consideration to describe the gradual reduction in the drainage capacity of prefabricated vertical drains (PVDs) during the consolidation process. In addition, the smear effect is also considered due to the installation of PVDs. An air booster pipe and the surrounding PVDs are introduced into the unit cell for analysis based on the principle of equal cross‐sectional area, and analytical solutions under two typical time‐dependent horizontal loading are then developed. A comparison is made with the existing analytical model of conventional vacuum consolidation, which indicates that air‐boosted vacuum preloading can promote the consolidation of soft soil more effectively than conventional vacuum preloading. Furthermore, the obtained solution under instantaneously loading is used to investigate the influence of several parameters on consolidation behavior. Finally, to verify the accuracy of the analytical model with or without clogging effect, a comparative study is carried out with a field test.

SCALANIE GRUNTÓW JAKO INSTRUMENT GOSPODAROWANIA PRZESTRZENIĄ NA OBSZARACH WIEJSKICH

Since its introduction in Poland in 1923, land consolidation has continuously been an instrument for improving the farmland planning, thus creating the best possible production conditions in agricultural areas. The aim of the paper is to evaluate the current regulations on land consolidation, in particular to answer the question whether and to what extent this solution serves the efficiency of land management in rural areas, and to what extent it fulfils the objectives set by the legislator in relation to: land management in rural areas, taking into account their production capacity for agriculture and other use; improvement of spatial organization; enabling sustainable development of rural areas and protection of natural resources. The study refers to the guides of the Food and Agriculture Organization of the United Nations (FAO) for national legislators designing legal solutions for land consolidation. In conclusion, the author calls for the work to be initiated on a new model of land consolidation or, more broadly, a regulation relating to the management of rural areas

Model of Non-Isothermal Consolidation in the Presence of Geobarriers and the Total Approximation Properties of its Finite Element Solutions

Model of Non-Isothermal Consolidation in the Presence of Geobarriers and the Total Approximation Properties of its Finite Element Solutions

A model for one-dimensional consolidation of clayey soils with non-linear viscosity

A model for the one-dimensional consolidation of saturated clayey soils, considering creep, is proposed, based on the consolidation mechanism idealized by Terzaghi (1941). The effective vertical stress is divided into two parts: one corresponding to the “solid” contacts, and other relating to the “viscous” contacts, the void ratio changes being caused by variations solely in the solid portion. Based on experimental evidence, a non-linear viscosity law was adopted, described by a hyperbolic function, in addition to its dependence on the void ratio. The resulting differential equation system is solved through the Finite Difference Method. The main “secondary effects of time” – experimental deviations from the classical Terzaghi (1925) theory – were able to be reproduced using the model, as well as experimental results that support other categories of consolidation models, such as the isotache- and Cα/CC-based models. A good fit was obtained for the results of long-term laboratory tests in clays from different parts of the world that reached the end of secondary consolidation. A good prediction was also reached for the evolution of settlements from the experimental embankment on the soft soils of Lilla Mellosa, monitored since 1947 in Sweden.

Consolidation by Vertical Drains Considering the Rheological Characteristics of Soil under Depth and Time-Dependent Loading

Vertical drains have been widely used in soil improvement projects to accelerate consolidation and improve the strength of soft soil. Previous consolidation models are mainly based on instantaneous loading, which cannot reflect the actual time-variable loading condition. This paper presents a set of analytical solutions for consolidation with vertical drains under depth and time-dependent loading, involving one-step loading, multi-step loading, and cyclic loading. A four-element model, which is a combination of the Merchant model and Maxwell model, is introduced to consider the rheological characteristics of the soil. By simulating the results of a consolidation test, it is found that the four-element model is more accurate than the Merchant model in predicting the changes in pore pressure and settlement during the clay consolidation process. Based on the solutions obtained, several factors affecting consolidation behavior are investigated. It has been shown that the rheological behavior becomes more and more obvious at the later stage of consolidation with the decrease both in the modulus of the spring in the Kelvin body and the viscosity coefficient of the independent dashpot. With the increase in the viscosity coefficient of the dashpot in the Kelvin body, the rate of consolidation becomes faster at an initial stage but slower at a later stage. For cyclic loading, the consolidation degree in each cycle reaches a maximum at the end of unloading and reaches a minimum at the beginning of the loading.

Fully Coupled Model for One-Dimensional Large-Strain Consolidation and Heat Conduction in Saturated Clay

The consolidation characteristics of soils are affected by both mechanical loading and ambient temperature. However, research on this coupled theory is lacking. In this study, a fully coupled model for one-dimensional large-strain consolidation and heat conduction is established, where the influences of temperature on the physical-mechanical properties of saturated clay are considered. Based on the finite difference method, the numerical solutions for the coupled model are developed. Moreover, the correctness is validated by comparing the calculational results of the proposed model with those of the COMSOL simulation (a finite element software simulation) and the classical analytical solutions, respectively. Finally, the effects of different factors on consolidation behaviors are discussed. It is found that the increase in temperature increment ΔT generally accelerates the dissipation rate of excess pore-water pressure (EPWP) and increases the final settlement. The settlement is gradually reduced with an increasing effective yield stress σcR. A larger permeability coefficient kvr,R leads to an increasing EPWP dissipation rate. Furthermore, it is observed that the influence of σcR on the settlement is slightly enhanced with an increasing ΔT, while the effect of kvr,R on the dissipation rate of EPWP becomes less remarkable under a higher ΔT. In conclusion, the proposed coupled model can properly describe the large-strain consolidation behaviors of saturated clay when the effect of heat conduction is incorporated.

A locking-free and mass conservative H(div) conforming DG method for the Biot's consolidation model

A locking-free and mass conservative H(div) conforming DG method for the Biot's consolidation model