Consolidation Behavior Research Articles

Consolidation behavior of various types of slurry tailings co-disposed with waste rock inclusions: a numerical study

The co-disposition of mine tailings and waste rock in tailings storage facilities (TSFs) could contribute to increase the consolidation rate and decrease long-term settlement of tailings. Non-linear change of tailings properties during the filling process and interaction between tailings and waste rock inclusion (WRI) are critical to mechanical analysis but can, however, be complicated to simulate. The question of net volume gains or losses of tailings was also raised. In this study, fully coupled analysis which considered continuous variation of hydraulic conductivity and stiffness of tailings were performed to assess the evolution of consolidation of various tailings types in the presence of WRI. Effects of volume ratio of tailings over WRI on the net volume was investigated. Finally, effect of several practical aspects such as filling rates, and instantaneous filling assumption were considered. Results indicated that WRI could increase by 3.3 times the rate of consolidation of tailings. The zone of influence of WRI on tailings consolidation varied for each tailings. Using updated properties showed significant differences compared to models with constant values. The application of WRI can reduce volume available for the storage of tailings and net volumetric change due to settlement of the tailings with or without WRI could be estimated explicitly. Equations predicting evolution of net volume with the changes in the volume ratio of tailings and WRI were accordingly proposed. WRI effects were more pronounced with the increase of the filling rate. Finally, instantaneous filling assumption had little effect on the simulated rate of consolidation.

Compressibility Characteristics of Southwest Bangladesh Organic Soil Stabilized with Sand Column

This research investigates the characteristics of organic soil from southwest Bangladesh and the influence of sand columns on the void ratio (V0), consolidation coefficient (CC), and volume compressibility (CV) of stabilized soil. On the laboratory scale, cylindrical columns of varying diameters were extruded through organic soil samples and stabilized with 3%, 5%, 8%, 10%, and 23% sand in various geometries. After evaluating the engineering parameters, a series of 1-D consolidation experiments were performed to assess the effect of the sand column on stabilized soil samples. According to the Unified Soil Classification System (USCS), the organic soil used in this research is defined as organic silt (OH). According to the findings, the organic soil has a liquid limit of 118% and its particles pass through a 0.075 mm sieve. By incorporating sand columns, rapid consolidation was obtained, and the sample containing 77% organic soil and 23% sand exhibited the best consistent compressibility features. The effects of column number and geometry on the compressibility behavior of organic soil samples were also examined. The results for the 77% organic soil and 23% sand in a single column and the 82% organic soil and 8% sand in a double column are nearly identical. This study reveals that stabilization with sand columns may significantly enhance the physical and consolidation behavior of organic soil in southwest Bangladesh.

Experimental study on consolidation characteristics of deep clayey soil in a typical subsidence area of the North China Plain

Land subsidence is an important environmental problem in the North China Plain (NCP). A typical subsidence area mainly located on adjoining areas of Beijing and Hebei provinces was selected to study the consolidation characteristics of deep clayey soil. Clay samples were collected from 14 boreholes at different depths, and the compression and consolidation behavior of the soil was analyzed by high-pressure oedometer tests. Results show that the deformation amount and deformation stabilization time in the primary consolidation stage increase with the load but decrease with the sampling depth. The nonlinear compression model of e-log(p) does not fit well for deep normally-consolidated clayey soil, the log(e+ec)–logp model fit the shallow clayey soil better than the deep clayey soil, and the hyperbolic model fits almost all soil samples well. Based on statistical theory, the soil consolidation equation CE_NCP was established for calculating the relationship between the degree of consolidation and the time factor in subsidence areas. The equations were fitted with the data obtained from high-pressure consolidation tests to obtain three parameters a, b and c, which are applied to the consolidation calculations for soil samples at depths of 0–100 m, 100–200 m, 200–300 m and 300–400 m, respectively. The applicability of CE_NCP equation was evaluated by comparing it to the analytical solution of Terzaghi’s consolidation equation, results showing that CE_NCP equation is more suitable for the calculation of the consolidation in the study area than the Terzaghi’s analytical solution. Eventually, the CE_NCP equation was successfully used to estimate the degree of consolidation in a subsidence area of Lang Fang City in the NCP.

Simplified mathematical modeling to plane strain consolidation considering unsaturated and saturated conditions for ground with anisotropic permeability

Road embankment where the unsaturated soil layer lies above the saturated soil layer is often encountered in geotechnical engineering, but the analytical models for evaluating the plane stain consolidation characteristics of an unsaturated–saturated ground are limited. With a combination of the consolidation theories for saturated and unsaturated soils, this paper thus develops a plane strain consolidation model for exploring the transient behavior of unsaturated–saturated soils subjected to instantaneous loading. A semi-analytical solution, which is a simple tool for assessing unsaturated–saturated soil consolidation, is proposed by making use of decoupling strategy, Fourier expansion as well as Laplace transformation. Further, the proposed solution in this paper is validated by the published analytical or semi-analytical solutions in some specific cases. By implementing the proposed solution into a computation, the consolidation behavior of an unsaturated–saturated subgrade is presented, and the effects of important factors, including the anisotropic permeability ratio and interlayer permeability ratio, are studied. The anisotropic permeability ratio and interlayer permeability ratio are significant indexes to change the consolidation rate of lower soils so that the prefabrication of lateral drainage boundary on both sides of the unsaturated–saturated subgrade would accelerate its consolidation.

An Analytical Solution for 2D Plane Strain Consolidation in Unsaturated Soils with Lateral and Vertical Semipermeable Drainage Boundaries under Time-Dependent Loading

This paper has proposed a closed-form solution for two-dimensional (2D) plane strain consolidation in unsaturated soils with lateral and vertical semipermeable drainage boundaries under time-dependent loading. By using the eigenfunction expansion technique, the governing equations are expanded into coupled ordinary differential equations, and the final solution of pore pressures is obtained by the integral transform method. The degraded proposed solution is then verified with the existing solution. The results show full agreement with the solutions, which indicates the proposed solution and program are completely correct. Meanwhile, the comparison between the analytical solutions and the finite-element simulations also demonstrates the correctness of the proposed solution. Subsequently, the effect of semipermeable parameters and loading parameters on the consolidation behavior has been investigated through the obtained analytical solution. And the distribution of consolidation profiles along two different directions has also been studied. It can be concluded that time-dependent loading changes the dissipation process obviously compared with constant loading.

Cyclic loads induced consolidation deformation of PVD unit cells

Consolidation behaviors of a mini-PVD unit cell under cyclic loads were investigated experimentally and analytically. Two key influential factors investigated are frequency of a cyclic load and Δtl/T (T is period and Δtl is loading time increment during a cycle) ratio of an intermittent cyclic load. The test results indicate: (1) For continuous and fixed Δtl/T (>1/10) ratio intermittent cyclic loads, with the conditions tested (frequency < 2 Hz), frequency had no considerable influence on the consolidation rate as well as consolidation settlement of the mini-PVD unit cell; (2) for intermittent cyclic loads, the magnitude of consolidation settlement is a function of Δtl/T (<0.5). The smaller the Δtl/T, the smaller the consolidation settlement. A hand calculable method has been developed for calculating consolidation settlement curves induced by both continuous and intermittent cyclic loads. The calculated settlement curves generally agree well with the test results, and it is suggested that the method can be used in engineering design.

Consolidated Drained Triaxial Test on Treated Coastal Soil and Finite Element Analysis Using PLAXIS 2D

Coastal areas are susceptible to erosion and accretion; therefore, coastal soil mechanical properties and ability to withstand loads are important factors to consider. Coastal erosion is inevitable as the sand and silt particles move inexorably from place to place. This study investigates the primary consolidation behaviour of treated coastal soil by comparing the empirical data obtained from triaxial tests based on analytical calculations and FEM software, PLAXIS 2D. The aim is to propose an optimum mixture to improve coastal soil’s geotechnical properties, especially in shear strength and stiffness. Two different material models, including lime/RHA and cement/RHA, were utilized to compare the performance of advanced constitutive treated soil samples against the Mohr–Coulomb material model. 8% lime and rice husk ash (portions of 1 : 2) were chosen to be replaced with cement, as an application of waste material can reduce the cost and environmental impact. All the triaxial tests were conducted at effective confining pressures of 50 kPa, 100 kPa, and 200 kPa. While using PLAXIS 2D, the asymmetrical condition for modelling the triaxial test and 15 nodded triangular elements, as well as the Mohr–Coulomb model for soil properties, are used to simulate the empirical data to verify this study’s effectiveness. The modelling of 2-dimensional drain behaviour involves setting out the model geometry and boundary conditions. The results revealed that the deviatoric stress and volumetric changes of LRHA increased in a range of 4.5 to 5.2% and 72.18 to 141.79%, respectively, as compared to CRHA. The FE analysis results for peak deviator stress values reasonably agree with the experimental results. The variation was in the range of 1.22% to 4.10%. Eventually, the treated soil’s peak and maximum shear strengths are reported to allow flexible use in future projects.

Phase transition mechanism of high-silica fluxed pellets during consolidation

ABSTRACT An in-depth study of the consolidation behaviour of high-silica fluxed pellets will help promote the development of a high-proportion pellet smelting process suitable for China’s resource structure. Lime, slaked lime, and limestone were used as calcium-containing additives to prepare high-silica fluxed pellets, and the suitable calcium-containing additives were lime and limestone. Compared with acid pellets, the suitable preheating temperature of high-silica fluxed pellets is higher (1100°C). The phase transformation during preheating consists mainly of the thermal decomposition of CaCO3 and Ca (OH)2 and the reaction between the solid phases.The roasting temperature of high-silica fluxed pellets should be controlled within a small range (1250°C–1280°C). The phase transition during the roasting of mainly lies in the generation and migration of the liquid phase. The Fe2O3 consolidation, the pore distribution law, and the liquid phase formation jointly determine the consolidation properties of the pellet.

Theoretical analysis and experimental verification of large deformation electro-osmosis consolidation treatment of dredged slurry

Electro-osmosis (EO) can be used to rapidly treat large areas of dredged slurry. At present, the theory of electro-osmosis consolidation (EOC) needs to be further developed to fit actual dredged slurry treatment scenarios. In this study, governing equations of EOC considering the large deformation constitutive relationship were derived with excess pore water pressure (EPWP) as a variable, and a concise EOC model was established for dredged slurry. Together with boundary conditions and initial conditions, the numerical method was adopted to obtain the finite difference solution for the EOC model. Then, EO experiments with different voltage stages were conducted using a self-designed and large-diameter EOC device, where the variations in current, drainage volume, EPWP, water content and vane shear strength were measured. Moreover, the phenomena of soil cracks, heat release, and electrode corrosion as well as the formation of Fe(OH)3 were recorded during the EO process. Additionally, nonlinear variation laws for effective stress, hydraulic permeability coefficient (HPC) and electro-osmosis permeability coefficient (EOPC) with void ratio of dredged slurry were obtained through indoor tests, in which a self-designed device for testing EOPC was used. Finally, the correctness of the proposed EOC model was verified by comparison with the results of the experiments and Esrig's analytical solution considering the small-strain constitutive relationship, where the consolidation characteristics were analyzed. In conclusion, the large deformation EOC model deduced in this paper could provide a more accurate prediction of the consolidation behavior of dredged slurry.

Experimental investigation of local chemo-mechanical behaviour and temporal development of osmotic consolidation in expansive clay

A series of one-dimensional cation infiltration tests under different drainage/infiltration conditions, infiltration times, ion concentrations (Na+), and vertical stresses were performed to comprehensively understand the osmotic consolidation of bentonite. The local behaviour of the specimen was captured on a digital camera through a transparent acrylic oedometer ring by tracking the movements of the marker sands on the side of the specimen. The Na+ concentration of the pore fluid throughout the specimen was measured after the test to investigate the spatiotemporal relationships between consolidation behaviour and cation infiltration. In the initial period of infiltration, the pore water pressure measured at the undrained bottom increased. A local swelling behaviour inside the specimen was observed during osmotic consolidation. The low permeability of expansive soils obstructs osmotically induced water drainage from the interlayer space of the expansive clay mineral, especially in regions far from the drainage boundary. This transition of pore water pressure affects the local mechanical behaviour; the dissipation of pore water pressure is followed by settlement. Therefore, the process of osmotic consolidation is totally longer than that of pure mechanical consolidation.

One-Dimensional Solar Energy Thermal Consolidation Model Testing and Analytical Calculation for Marine Soft Clays

There are significant energy and financial expenditures associated with the current thermal drainage consolidation approach used to treat the marine soft clay foundation. Especially for some reclaimed lands in remote areas where a large amount of stable electricity is not readily available. In view of the problem, this paper aims to investigate a novel treatment method by using solar energy thermal consolidation. The model testing was conducted to assess the treatment effect of the foundation. Results from two groups of one-dimensional surcharge preloading consolidation model experiments, conducted under conditions of both solar heating and ambient temperature, were presented. The advantage of the solar heating approach was demonstrated by a comparison of the two tests. An analytical calculation method was proposed for predicting the consolidation behavior on the basis of the temperature variation caused by solar energy in the marine soft clays, and good agreement was observed. The outcomes reveal that solar heating can improve the consolidation effect of soil deep in the foundation. The foundation temperature can be raised by 15 °C in winter, and the variation range can exceed 10 °C. The settlement increases by 16% compared with the ambient temperature group.

Effect of chemical additives on the consolidation behaviours of mini-PVD unit cells –from macro to micro

The mechanism of adding NaCl, CaCl2 and small amounts of cement/lime (1–4% by dry weight) into clay slurry for mitigating the effect of apparent clogging around PVDs during vacuum consolidation was investigated by mini-PVD unit cell consolidation tests as well as microstructure observations via scanning electron microscopy (SEM) imaging. The consolidation test results indicated that for the specimens with CaCl2, cement and lime additives the rate of consolidation increased considerably, while the effect of the NaCl additive was limited. The SEM images show that for the specimen without additive, there were obvious localized deformation-induced microstructure anisotropies. For specimens with CaCl2 and cement/lime additives, the microstructures of the soils tended to be isotropic. The additives tested reduced the thickness of the diffusive double layer around the clay particles and promoted the formation of a more stable flocculated microstructure, therefore mitigating the effect of apparent clogging.

Nonlinear consolidation analysis of multilayered soil with coupled vertical-radial drainage using the spectral method

The nonlinear variation of soil compressibility and permeability with void ratio (i.e., e-log σ′ and e-log k) has been included in the consolidation theory to accurately predict the behavior of soft soil stabilized by vertical drains. However, most current nonlinear consolidation models incorporating the coupled radial-vertical flow are based on some simplified assumptions, while including some features such as the complex implementation of multilayered computations, time-dependent loading and stress distribution with depth. This study hence introduces a novel approach where the spectral method is used to analyze the nonlinear consolidation behavior of multilayered soil associated with coupled vertical-radial drainage. In addition, time- and depth-dependent stress and soil properties at each soil layer are incorporated into the proposed model. Subsequently, the solution is verified against experimental and field data with comparison to previous analytical solutions. The results show greater accuracy of the proposed method in predicting in-situ soil behavior. A parametric study based on the proposed solution indicates that the ratio between the compression and permeability indices (ω = Cc/Ck) has a great impact on the consolidation rate, i.e., the greater the ω, the smaller the consolidation rate. Increasing the load increment ratio and the absolute difference between unity and ω (i.e., |ω − 1|) can exacerbate prediction error if the conventional simplified methods are used.

Spatial variation of permeability and consolidation behaviors of soil using ordinary kriging method

The present study is aimed at finding out spatial distribution of permeability characteristic of soil using ordinary kriging method at any location using the data from a few boreholes at NIT (National Institute of Technology) Patna Bihta campus. Kriging is also popularly known as BLUE (i. e. Best Linear Unbiased Estimator) which can be used to interpolate the data obtained from a few locations to get an estimate of any parameter at other locations throughout the study area. In the present work, soil samples collected from eight boreholes have been tested to obtain various geotechnical properties including liquid limit (LL), plastic limit (PL), plasticity index (IP), coefficient of volume compressibility (mv) etc. These values have been used as inputs in an Ordinary Kriging model to calculate coefficient of consolidation (Cv) and coefficient of permeability (k) throughout the NIT Patna, Bihta campus and build contour plots of (Cv) and (k) over the NIT Patna campus to show their spatial variation. The novelty of the current work lies in the first time proposed method for developing the spatial distribution of(Cv) and(k). Markov correlation matrix has been used to develop the correlation behavior of the parameters considering different values of correlation length. In the present study, it is found that the coefficient of consolidation Cv of soil ranges 10−8 (m2/sec). The Kriged values of k are in the range of 10−11 to 10−10 (m/s). Finally, semi-variogram have been shown to display the auto-correlation of the measured data points and cross-validation of data set which establish that the Kriged data are reasonably correlated. Also, various error estimators such as Mean Error, Root Mean Square Error, Average Standard Error, Root Mean Square Standard Error, Mean Standard Error have been calculated using the Kriged data points over the entire area and, it is found that the error level in the predicted Kriged data are reasonably small.

One-dimensional consolidation of unsaturated–saturated soil system considering pervious or impervious drainage condition induced by time-dependent loading

Since the ground with unsaturated soil layer and saturated soil layer is very common in most areas, a more comprehensive analytical solution is essential for the accurate prediction of ground consolidation behavior. In this paper, the one-dimensional consolidation theories for unsaturated and saturated soils are introduced to simulate the consolidation characteristics of the different soil layers, and the hypothetical soil interface of two layers that only allows pore water to flow is supposed in this model. After using the decoupling and Laplace transformation techniques to the coupled governing equations, the general Laplace-domain solutions are proposed under the permeable or impermeable surface for ground consolidation that an unsaturated–saturated ground with finite thickness subject to arbitrary time-dependent loading. The results in the temporal domain for the excess pore pressures and soil settlement are numerically obtained by Crump’s algorithm. The methodology and proposed solution are validated by some published solutions in the literature. Based on the proposed solutions under the three representative boundary conditions, the temporal behavior of ground subjected to ramp loading is explored. The results show that boundary condition would significantly affect the evolutions of excess pore pressures and further change the ground settlement.

Determination of collapse and consolidation behavior of cohesionless soils

Determination of collapse and consolidation behavior of cohesionless soils

Analytical solution for consolidation of sand‐filled nodular pile (SFNP) foundation and its engineering application

AbstractThe sand‐filled nodular pile (SFNP) foundation is newly proposed to improve the bearing capacity and accelerate consolidation settlement of foundations installed in soft clay soil. By filling sand while driving the nodular pile into the soft clay soil, the SFNP foundation provides an extra drainage path with the aid of the nodular segment, while maintaining the high modulus reinforcement body at the core of the composite foundation. The performance of the SFNP foundation is greatly influenced by its consolidation behaviour. This study develops a generalized model for the SFNP foundation, and a closed‐form solution is then established considering the smear and well resistance effects. The developed model and the associated analytical solution are employed to investigate the consolidation rate and load distribution of the SFNP foundation. Finally, the analytical solution is utilized to evaluate the performance of SFNP foundation for an expressway project located in Zhejiang, China. The predicted dissipation of the excess pore water pressure employing the developed analytical solution agreed well with measured response from the field test, which further confirmed the advantages of the SFNP foundation and the reliability of the developed solution.

Special features of microbial cake under high pressure conditions in microfiltration

Here, cell separation from microbial suspensions (gram-negative bacterium Escherichia coli, gram-positive bacterium Lactococcus lactis, and yeast Saccharomyces cerevisiae) was performed by dead-end microfiltration. From the results of three types of experiments, namely constant-rate and constant-pressure filtration, and constant-pressure consolidation, it was revealed that the microfiltration behaviors of microbial suspensions can be described on the basis of the pressure dependences of the average void ratio and specific resistance of the microbial cake. However, under high-pressure conditions, we found that the cake structure of Escherichia coli was changed, and the calculations were inconsistent with constant-rate filtration data. The data, such as constant-rate filtration behaviors, spectra of filtrate, electron micrographs of filter cake, and constant-pressure consolidation behaviors, indicated the possibility of cellular destruction of Escherichia coli under pressures above 700 kPa. In contrast, this phenomenon was not observed at pressures of up to 1000 kPa in yeast with different cell envelope compositions. Cellular destruction affected the filtration performance, and since intracellular water was discharged, the dehydration characteristics of the cake changed significantly. The findings on the properties of microbial cakes under high pressure obtained in this study are useful for improving the efficiency of filtration operations for microbial suspensions and dehydration operations for biological sludge.

Modeling consolidation of soft clay by developing a fractional differential constitutive model in conjunction with an intelligent displacement inversion method.

Studying the constitutive relation of soft clays is of critical importance for fundamentally understanding their complex consolidation behavior. This study proposes a fractional differential constitutive model in conjunction with an intelligent displacement inversion method based on the classic particle swarm optimization for modeling the deformation behavior of soft clay. The model considered the rheological properties of soft clay at different consolidation stages. In addition, statistical adaptive dynamic particle swarm optimization-least squares support vector machines were implemented to identify the model parameters efficiently. The accuracy and effectiveness of the model were validated using available experimental results. Finally, the application results showed that the proposed model could efficiently simulate coupling properties of soft clay’s primary and secondary consolidations.

Investigation of One-dimensional Consolidation of Fractional Derivative Model for Viscoelastic Saturated Soils Caused by the Groundwater Level Change

The Fractional calculus theory is introduced into the Merchant model to study the mechanical characteristics of saturated soils. Laplace transform is applied to the 1D consolidation and the fractional derivative Merchant model constitutive equations of saturated soils. In the transform domain, the analytical solutions of effective stress and settlement are obtained by solving the simultaneous equation. The Crump's method is used to the numerical inversion of Laplace transform, and the semi-analytical solution of the one-dimensional consolidation is obtained. A series of parameters, such as the fractional order, compression modulus, coefficient of viscosity, permeability coefficient and the variation models of groundwater level, are studied. Considering the continuity conditions, the 1D consolidation equation of single-layer saturated soil is generalized to multi-layer soils, and then the influence of different boundaries on several kinds of consolidation behavior was analyzed.