Linear Consolidation Research Articles

Novel Simplified Practical Method for One‐Dimensional Large‐Strain Consolidation

ABSTRACTA new simplified practical method for one‐dimensional nonlinear large‐strain consolidation of saturated homogenous soils is proposed. The derivation processes of the proposed method are introduced first, with a modification of Terzaghi's theory from a novel perspective to solve large‐strain consolidation problems. Verification checks of the proposed method with other solutions are then conducted. The proposed method is different from Lekha's solution because Lekha's analytical solution is based on the small strain theory. For linear consolidation, the proposed method shows excellent agreement with the Consolidation Settlement 2 (CS2) model. For nonlinear large‐strain consolidation, the new method is in good agreement with the CS2 model when Cc/Ck ≤ 1. After that, optimization of the proposed nonlinear solution is carried out for Cc/Ck > 1 with a more precise average constant coefficient of consolidation used in the simplified practical method, and good agreement is obtained between the solutions from the proposed method and the CS2 model. Overall, the proposed simplified method provides practical, reliable, and efficient solutions for analyzing linear and nonlinear large‐strain consolidation.

Air-boosted vacuum preloading method for land reclamation with vertical drains: Numerical and analytical solutions

As an emerging ground treatment technique, the air-boosted vacuum preloading method accelerates the consolidation process of soils with vertical drains and enhances the bearing capacity and stability of grounds. This improvement is achieved by augmenting the horizontal pressure differential between the drainage body and the surrounding soils. In the realm of existing theories, consolidation models are primarily established under the assumption of linear characteristics of soils. Nonetheless, for marine sedimentary soft soils characterized by high compressibility, the application of nonlinear consolidation theory becomes more appropriate. The well resistance effect of the drainage body over time is also considered in this study, and a comprehensive consolidation model tailored to soft soils with air-booster pipes and vertical drains is proposed. Subsequently, the analytical and numerical solutions for this consolidation model are derived, respectively. Comparisons are made with existing conventional linear consolidation models to substantiate the validity of the proposed consolidation model. This investigation delves into the influence of nonlinear compressibility and permeability of soils, variable well resistance, and drain spacing ratio, on consolidation behaviors. Particular emphasis is placed on the determination of the startup time for the air-boosted system. Finally, the proposed consolidation model is applied to the actual field prediction, affirming the accuracy and applicability of the developed consolidation model in practical soft soil treatments.

Determination of hydraulic parameters of non-linear consolidation clay layers by type curve method

The consolidation of clay layers is of great significance for groundwater environmental protection, groundwater storage utilization, and land subsidence. In this study, the governing equation for the excess pore water pressure during the non-linear consolidation process of clay layers under load conditions is obtained based on the one-dimensional non-linear consolidation theory. Analytical solutions are then derived for clay layers with single or double drainage caused by the dissipation of the excess pore water pressure. With these analytical solutions, the groundwater dynamics and deformation of the clay layer are analyzed. Correspondingly, a type curve method is proposed to calculate the hydraulic parameters of the clay layer through laboratory experiments, which verifies the reliability of the analytical solutions. The study results show that the deformation of the clay layer predicted by the non-linear consolidation theory is smaller than that predicted by the linear consolidation theory. The deformation of the clay layer increases with the increase in the thickness of the clay layer, the compressive index, and the overburden load, while it decreases with the increase in the initial void ratio and the initial effective stress. The stable time, at which the consolidation of the clay layer is completed, increases with the increase in the compression index and the thickness of the clay layer, while it decreases with the increase in the initial void ratio, the initial effective stress, and the initial hydraulic conductivity. It does not vary with the load pressure. Conclusively, the deformation prediction based on the non-linear consolidation theory is more accurate and applicable to further load pressures.

Diagnostic Accuracy of Chest Digital Tomosynthesis in Patients Recovering after COVID-19 Pneumonia.

Purpose: To assess the diagnostic accuracy of traditional chest X-ray (CXR) and digital tomosynthesis (DTS) compared to computed tomography (CT) in detecting pulmonary interstitial changes in patients having recovered from severe COVID-19. Materials and Methods: This was a retrospective observational study, and received local ethics committee approval. Patients suspected of having COVID-19 pneumonia upon emergency department admission between 1 March and 31 August 2020, and who underwent CXR followed by DTS and CT, were considered. Inclusion criteria were as follows: (1) patients with previous SARS-CoV-2 infection proven by a positive RT-PCR on nasopharyngeal swabs performed upon admission to the hospital, and with complete clinical recovery; (2) a diagnosis of SARS-CoV-2-related ARDS, according to the Berlin criteria, during hospitalization; (3) no recent history of other lung disease; and (4) complete imaging follow-up by CXR, DTS, and CT for at least 6 months and up to one year. Analysis of DTS images was carried out independently by two radiologists with 16 and 10 years of experience in chest imaging, respectively. The following findings were evaluated: (1) ground-glass opacities (GGOs); (2) air-space consolidations with or without air bronchogram; (3) reticulations; and (4) linear consolidation. Indicators of diagnostic performance of RX and digital tomosynthesis were calculated using CT as a reference. All data were analyzed using R statistical software (version 4.0.2, 2020). Results: Out of 44 patients initially included, 25 patients (17 M/8 F), with a mean age of 64 years (standard deviation (SD): 12), met the criteria and were included. The overall average numbers of findings confirmed by CT were GGOs in 11 patients, lung consolidations in 8 patients, 7 lung interstitial reticulations, and linear consolidation in 20 patients. DTS showed a significantly higher diagnostic accuracy compared to CXR in recognizing interstitial lung abnormalities—especially GGOs (p = 0.0412) and linear consolidations (p = 0.0009). The average dose for chest X-ray was 0.10 mSv (0.07–0.32), for DTS was 1.03 mSv (0.74–2.00), and for CT scan was 3 mSv. Conclusions: According to our results, DTS possesses a high diagnostic accuracy, compared with CXR, in revealing lung fibrotic changes in patients who have recovered from COVID-19 pneumonia.

Pulmonary Artery Filling Defects in COVID-19 Patients Revealed Using CT Pulmonary Angiography: A Predictable Complication?

Purpose This study is aimed at assessing the prevalence of pulmonary artery filling defects (PAFDs) consistent with pulmonary artery embolism (PAE) in patients with SARS-CoV-2 infection and at investigating possible radiological or clinical predictors. Materials and Methods Computed Tomography Pulmonary Angiographies (CTPAs) from 43 consecutive patients with a confirmed COVID-19 infection were retrospectively reviewed, taking into consideration the revised Geneva score and the D-dimer value for each patient. Filling defects within the pulmonary arteries were recorded along with pleural and parenchymal findings such as ground glass opacities, consolidation, crazy paving, linear consolidation, and pleural effusion. All these variables were compared between patients with and without PAFD. The predictive performance of statistically different parameters was investigated using the receiver operating characteristics (ROC). Results Pulmonary embolism was diagnosed in 15/43 patients (35%), whereas CTPA and parenchymal changes related to pulmonary COVID-19 disease were evident in 39/43 patients (91%). The revised Geneva score and the mean D-dimer value obtained using two consecutive measurements were significantly higher in patients with PAFD. The ROC analysis demonstrated that a mean D-dimer value is the parameter with the higher predictivity (AUC 0.831) that is a cut‐off value > 1800 μg/l which predicts the probability of PAFD with a sensitivity and specificity of 70% and 78%, respectively. Conclusions This single centre retrospective report shows a high prevalence of pulmonary artery filling defects revealed using CTPA in COVID-19 patients and demonstrates that the mean value of multiple D-dimer measurements may represent a predicting factor of this complication.

High-resolution CT features of COVID-19 pneumonia in confirmed cases

BackgroundCoronavirus (COVID-19) pneumonia emerged in Wuhan, China, in December 2019. It was highly contagious spreading all over the world, with a rapid increase in the number of deaths. COVID-19 is characterized by fever, fatigue, dry cough, and dyspnea with variable chest imaging features which have been detected.In our study, we shared our experience of CT findings in proven cases of COVID-19 to recognize the different CT patterns to help in proper and accurate diagnosis.ResultsThe most common CT features detected in COVID-19 cases were ground glass patches (93.3%) followed by subpleural linear abnormality (53.3%), air bronchogram (23.3%), and consolidation patches (23.3%), as well as bronchial wall thickening (16.7%), crazy paving pattern (13.3%), and discrete nodules surrounded by ground glass appearance (10%). Only one case had pleural effusion (3.3%). No cavitary lesions or specific lymph nodes were detected in any of the examined patients. The lung lesions showed typical diffuse, basal, and subpleural involvement with less affection of the upper lobes.ConclusionCT imaging findings of COVID-19 can help in early and accurate diagnosis of COVID-19 and proper assessment of the severity of the disease.

Clinical characteristics of connective tissue disease-related interstitial lung disease: an analysis of 186 cases

Objective To analyze the clinical characteristics of connective tissue disease related interstitial lung disease (CTD-ILD). Methods The demographic data, clinical manifestations, blood gas analysis, lung function, chest high resolution CT (HRCT), histopathology of 186 patients with CTD-ILD admitted in Jinhua Central Hospital from January 2013 to December 2017 were retrospectively analyzed. Results In 186 patients with CTD-ILD,70 were males and 116 were females, with a mean age of 56.22±12.27. Among them, 61 cases were polymyositis/dermatomyositis (DM/PM)-ILD, 44 cases were rheumatoid arthritis (RA)-ILD, 26 cases were interstitial pneumonia with autoimmune features (IPAF), 16 cases were systemic sclerosis (SSc)-ILD, 14 cases were Sjogren syndrome (SS)-ILD, 11 cases were overlap syndrome (OS)-ILD, 7 cases were systemic lupus erythematosus (SLE)-ILD, 5 cases were undifferentiated connective tissue disease (UCTD)-ILD, and 2 cases were mixed connective tissue disease (MCTD)-ILD. The incidence of respiratory symptoms was higher than that of systemic symptoms, and the incidence of systemic symptoms was higher than that of skin symptoms. Cough was the most common symptom of respiratory system, and arthralgia was the most common symptom of systemic symptoms, accounting for 54.9% (101/186) and 48.9% (91/186) respectively. Blood gas analysis showed that hypoxemia accounted for 56.5% (83/147) and type Ⅰ respiratory failure accounted for 26.5% (39/147) . The proportion of restrictive ventilation dysfunction in pulmonary function tests was 70.9% (105/148) and the diffuse dysfunction was 81.1% (120/148) . The manifestations on HRCT were reticular linear shadow (44.1%), ground-glass opacity (54.3%), consolidation (23.1%), nodules shadow (20.9%) and cystic low density shadow (9.1%) . The histopathological diagnosis mainly was non-specific interstitial pneumonia (NSIP, 43.0%) and usual interstitial pneumonia (UIP,40.0%). Conclusion The arterial blood gas analysis, lung function and chest HRCT screening, and lung histopathological examination are important for early identification and diagnosis of CTD-ILD. Key words: Connective tissue diseases; Lung diseases, interstitial; Blood gas analysis

A Finite Element Method with Strong Mass Conservation for Biot’s Linear Consolidation Model

An H(div) conforming finite element method for solving the linear Biot equations is analyzed. Formulations for the standard mixed method are combined with formulation of interior penalty discontinuous Galerkin method to obtain a consistent scheme. Optimal convergence rates are obtained.

Intensifying solar-thermal harvest of low-dimension biologic nanostructures for electric power and solar desalination

High-efficiency solar harvest and solar-thermal conversion have been targeted in modern sustainable energy science for diverse potential applications. However, broad applications with inorganic nanomaterials as solar-nanoheaters have suffered from low conversion efficiency, potential noxiousness and complicated synthesis procedures. Meanwhile, living organisms rely on delicate bio-synthesis of bio-macromolecules to produce organic bio-melanins with optimal nanostructures and solar-thermal properties for survival from harsh environments. Followed by this inspiration, alginate, one marine polysaccharide, is used to alter the polydopamine nanostructures, one artificial bio-melanin, from nanoparticles to high-aspect-ratio nanofibrils (diameter ~ 40 nm and aspect ratio up to 120 nm). During polymerization, alginate not only increases structural order (e.g. π-π conjugation) of polydopamine oligomers within their protoparticles, but also leads to linear consolidation of protoparticles. Polydopamine nanofibrils are found to exhibit super absorbance and high solar-thermal conversion efficiency (~ 86%) in full-range solar spectrum, being superior to conventional polydopamine nanoparticles and comparable to graphene and carbon nanotubes. Thus these biological nanofibrils may offer a promising platform for high-efficiency solar-energy harvest applicable in solar evaporative desalination, solar electric power etc.

MODERN MOLECULAR-GENETIC APPROACH TO INCREASE EFFICIENCY OF SELECTION PROCESS IN ANIMAL BREEDING OF UKRAINE

MODERN MOLECULAR-GENETIC APPROACH TO INCREASE EFFICIENCY OF SELECTION PROCESS IN ANIMAL BREEDING OF UKRAINE

Characterizing land displacement in complex hydrogeological and geological settings: a case study in the Beijing Plain, China

Characterization of land displacement induced by long-term overexploitation of groundwater is necessary to ensure sustainable water supply in Beijing, China. The northern part of the Beijing Plain is an important water source area and is also designed for groundwater recharge from South-to-North Water Diversion Project. We aim to depict the process of characterizing land displacement under complex hydrogeological and geological context in the region using remote sensing and geographic information system. Interferometric synthetic aperture radar time-series analysis was used to detect land displacement from 2003 to 2010. Statistic linear regression equations between groundwater level and land displacement were built based on linear consolidation principle. The spatial difference of Pearson correlation coefficient (R) and slope (k) were discriminated to quantify the response of land displacement to groundwater level change. The results show that there are two major displacement cones with annual rates up to −40 and −24 mm year−1. R and k had a negative and positive correlation with increasing land displacement, respectively. A larger R reflects that the groundwater level has a closer relation with the occurrence of land displacement. The weak correlation is due to the delay in the propagation of the pressure drawdown in the fine-sediment layers or lens from the pumped aquifers where the pressure is measured. Thick compressible layer has more potential for land displacement. Results of this study are necessary to clarify the land displacement characteristics, to make full use of abundant spatial–temporal dataset, and ultimately to support hazard prevention and mitigation decisions.

Consolidation of a poroelastic sphere: Numerical investigations of Cryer's problem

AbstractIn geomechanics the consolidation of a fluid‐saturated soil is of great interest and many theories have been proposed in the recent years. A special case is the consolidation problem in a porous, fluid‐saturated sphere under drainage and hydrostatic pressure. For this configuration Cryer [2] discussed the special effect of pore pressure response. We increase the complexity of the classical approach, taking into account a modified sphere with an undrained layer. This modification is an expansion of the original problem towards more realistic situations of a poroelastic rock which contains a heterogeneity (modified Cryer problem). It results in nearly effective drainage for the heterogeneity and significant differences in momentary stress state. The interaction between the skeleton and the pore fluid of the porous sphere is implemented numerically with Biot's theory of linear consolidation in an us‐p‐formulation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Development of negative skin friction on single piles: uncoupled analysis based on nonlinear consolidation theory with finite strain and the load-transfer method

The development of negative skin friction (NSF) on single piles is investigated based on an uncoupled method of analysis with the Mikasa (1963) generalized nonlinear consolidation theory in terms of finite strain and the nonlinear load-transfer method. Predicted results are compared with results based on the conventional linear consolidation theory with infinitesimal strains. It is found that predicted development of dragload using the conventional consolidation theory is slightly greater and conservative compared to that using the nonlinear consolidation theory based on effective stress (β method). Effective stress predictions using the conventional theory are larger due to the faster dissipation of excess pore pressures, with the assumption of constant coefficient of consolidation and permeability. However, since the relative displacements required to mobilize the ultimate skin friction are small, and piles are usually installed near the final stages of soil consolidation, the differences in the predictions for the development of dragload on piles between the two consolidation theories are overshadowed. Using the uncoupled model for pile NSF, it is therefore found that the most significant factor for the estimation of dragload and downdrag is the proper selection of the β value rather than the consolidation theory used.

Evaluation of monotonic and non-monotonic dissipation test results

The dissipation test evaluation method presented here employs: (i) a point-symmetric, linear, coupled consolidation model with a new boundary condition and a new time factor, (ii) an automatic and mathematically precise, non-linear, inverse problem solver which includes some reliability testing methods and a kind of regularization technique, and (iii) a method to identify the initial condition. The evaluation method is equally applicable to pore water pressure data displaying monotonic or non-monotonic time variation, with the only difference that the initial condition is identified differently during the inverse problem solution. The necessary testing time is very short provided that the pore water pressure is measured well above the tip. This is attributed to the ability of the one-dimensional, linear consolidation model to account for the geometry and the unloading effects that occur when steady penetration of the static cone penetrometer ceases.

Comparison between Coupled and Uncoupled Consolidation Analysis of a Rigid Sphere in a Porous Elastic Infinite Space

Linear consolidation analyses are usually treated either by means of Terzaghi-Rendulic uncoupled theory or Biot's consolidation theory. In this note, the problem of consolidation displacements around an axially loaded sphere was considered. It is demonstrated that both the uncoupled analysis and the coupled analysis give the same governing equation for pore fluid pressure dissipation with time. A simplified procedure for deriving transient strain components is illustrated. A general solution for time-dependent displacements is obtained using uncoupled consolidation analysis. Close agreement is evident between the new approximate uncoupled analysis solution and the existing coupled analysis solution with a maximum error of less than 0.5%.

Some Applications of Linear Viscoelasticity to Problems of Consolidation under Variable Loading

The main purpose of this paper is to present a general method to derive closed form solutions for one-dimensional consolidation problems under time dependent loading using the Linear Viscoelasticity theory. A review of the basic concepts of this theory is initially presented and, mainly for illustration purposes, the method is applied to three consolidation problems, leading to relevant solutions for Geotechnical Engineering. In the first application, considering Terzaghi’s and Barron’s solutions, creep functions are determined for vertical and radial drainage, allowing derivation of expressions for one-dimensional consolidation under a number of linear loads for these drainage conditions. Using Carrillo’s equation, the creep function for combined vertical and radial drainage is obtained, leading to corresponding solution for linear variable loading. Partial submersion of embankments on soft soils is another consolidation problem under time dependent loading solved by means of Viscoelasticity. Classical approximate solutions are used in this second application to establish creep functions for vertical drainage and exact Barron’s solution to establish creep function for radial drainage. An expression for late stages of consolidation is also derived for combined vertical and radial drainage condition. The third application considers the problem of load transfer from a consolidating deposit of soft clay to a pattern of drain columns of finite stiffness. Diagrams concerning a case of consolidation under linear variable three-step loading and consolidation with partial submersion of the fill are provided to illustrate the solutions obtained.

Stress Analysis of a Borehole in Saturated Rocks Under in situ Mechanical, Hydrological and Thermal Interactions

A novel approach is developed to represent coupled thermal-hydraulic-mechanical (THM) behavior of porous systems that incorporates the non-isothermal free and forced convection of a single component fluid in a non-boiling thermoelastic medium. The three-way simultaneous coupling between the THM triplet is currently linear, but no restriction is placed on incorporating material nonlinearities. The coupled PDEs are solved in space by grid-adaptive finite elements. The model is validated against solutions for linear non-isothermal consolidation of a column. We demonstrate the utility of the model by analyzing the behavior of a deep wellbore in a themoelastic medium circulated by a pressurized, but chilled fluid. Model results illustrate the significant importance of the cross-couplings between individual THM processes for the evaluation of wellbore stability.

New Fast Convolution Algorithm in Boundary-Element Methods for Two- and Three-Dimensional Linear Soil Consolidation Analysis

Over the last 25 years , the time domain boundary element formulations for the linear consolidation theory of Biot involving fully coupled governing differential equations of flow through porous media and those of elastic deformation of porous skeleton have been fully developed and implemented for both single-region and multiregion two-dimensional plane strain, axisymmetric and three-dimensional problems. However, this storage-based convolution method used in those developments was not found to be suitable for solving large practical problems because of the substantial computer disk space requirements. In order to find a better alternative, an accurate integration-based scheme was developed by the present writers and co-workers, in which, the storage was eliminated by accurately recalculating the summation (involved in the time convolution) of the right-hand side at each step during the time marching process. Although this work was not published in any literature, by using this type of approach, solving l...

Study on one-dimensional consolidation of soil under cyclic loading and with varied compressibility

This paper presents as semi-analytical method to solve one dimensional consolidation problem by taking consideration of varied compressibility of soil under cyclic loading. In the method, soil stratum is divided equally inton layers while load and consolidation time are also divided into small parts and time intervals accordingly. The problem of one-dimensional consolidation of soil stratum under cyclic loading can then be dealt with at each time interval as one-dimensional linear consolidation of multi-layered soils under constant loading. The compression or rebounding of each soil layer can be judged by the effective stress of the layer. When the effective stress is larger than that in the last time interval, the soil layer is compressed, and when it is smaller, the soil layer rebounds. Thus, appropriate compressibility can be chosen and the consolidation of the layered system can be analyzed by the available analytical linear consolidation theory. Based on the semi-analytical method, a computer program was developed and the behavior of one-dimensional consolidation of soil with varied compressibility under cyclic loading was investigated, and compared with the available consolidation theory which takes no consideration of varied compressibility of soil under cyclic loading. The results showed that by taking the variable compressibility into account, the rate of consolidation of soil was greater than the one predicted by conventional consolidation theory.

Numerical solution of a non-linear model for self-weight solids settlement

The present study proposes a 1D model that describes the solids consolidation process occurring in a saturated sediment column due to its own weight. The governing consolidation equation, a second order non-linear transient partial differential equation of the parabolic type with the effective stress as the dependent variable, is solved by using the finite element and finite difference methods. In the spatial discretization of the problem, the Petrov–Galerkin method is used to obtain the weak form of the equation. For the model's time discretization, two timing step schemes are used for the sake of comparison: the Crank–Nicolson and the backward-difference schemes. The contribution of the non-linear terms is determined by employing the standard Newton–Raphson iteration method. The present formulation and numerical approach are examined by using the results of two consolidation tests, an attapulgite solids column and a mixture of kaolin–bentonite solids column. The comparison shows that the consolidation rate and the distribution of the volume fraction of solids within the columns can be accurately predicted by the present model. In addition the results of the non-linear model are compared with those of the corresponding linear consolidation model. It is shown that the linear model significantly overpredicts the rate of consolidation. Finally, the effect of the initial conditions on the model predictions is also examined.