Non-uniform Consolidation Research Articles

Analytical solution on vacuum consolidation of flow mud considering radial non-uniform consolidation

Analytical solution on vacuum consolidation of flow mud considering radial non-uniform consolidation

Soil behavior near the PVD filter and interpretation of clogging during vacuum preloading

Clogging near the prefabricated vertical drain filter during vacuum preloading reduces the efficiency of ground treatment, and existing research has yet to agree on the cause. This study conducted a small model test to comprehensively examine the soil's water content and particle size distribution at different distances from the filter and tailwater for different preloading durations. The results showed that the particle size distribution of the soil at different selected points exhibited a slightly irregular difference. This indicates that no measurable migration of particles occurs, which was further confirmed by the particle size distribution of the soil after the one-dimensional consolidation test. The application of vacuum pressure did not significantly change the soil particle composition and, thus, its compressibility and permeability properties. The particle size distribution of tailwater revealed that a small number of fine particles with a mean size of 3–4 μm rapidly discharged with tailwater during the initial stage of vacuum preloading, which was much less than the mean size of the slurry and pore size of the filter. The decrease in water content and permeability indicates non-uniform consolidation, and the increase in the permeability coefficient ratio suggests the formation and development of the clogging zone.

Study of the Nonuniform Consolidation Characteristics of Soft Soils Using a Novel Model

The degree of soil nonuniformity consolidation varies continuously with the passage of consolidation time and is accompanied by nonlinear alterations in soil parameters. Existing theoretical models often assume a constant relationship between the parameters of the two soil layers, failing to consider the effect of nonuniform consolidation. This assumption does not align with real-world conditions and can lead to significant errors in calculation results. Hence, this study aims to investigate the dynamic changes in soil undergoing nonuniform consolidation and develop a mathematical model that accounts for this phenomenon. Based on the large-strain and double-layer models, an improved consolidation model was proposed, which considers nonuniform variations in consolidation with a vertical drain and corrections to calculations under the influence of the nonlinear relationships of soil parameters. The proposed improved model was validated by comparison with field test data, and the results were compared with those of the classical model. Finally, the effects of different consolidation parameters on consolidation behavior were investigated. The research is a reliable calculation method that incorporates the dynamic nonuniform changes in consolidated soil, enabling more accurate predictions of consolidation of foundations treated by vertical drains.

Non-uniform Consolidation of Soil and Influence of Corresponding Clogging Effect During Vacuum Preloading

Non-uniform Consolidation of Soil and Influence of Corresponding Clogging Effect During Vacuum Preloading

Effect of chemical additives on the consolidation behavior of slurries

A series of oedometer tests were conducted on slurries with three additives (NaCl, CaCl2, and FeCl3) of different concentrations in pore water (0.1–1.0 mol/L) to investigate the effect of the valency of cations and their concentration on the consolidation–compression behavior of slurries. Further laboratory model tests on the vacuum consolidation of a prefabricated vertical drain (PVD) unit cell were carried out to study the effect of the chemical additives on the performance of the unit cell. Based on the test results, it was found that the compression index and remolded yield stress of the soils increased with the concentration and cationic valence of the additives. For a given void ratio, the value of permeability deduced from the oedometer test results increased with the increase in the concentration and cationic valence of the chemical additives. In addition, the PVD unit cells with cationic chemical additives had a higher rate of consolidation and resulted in higher vacuum pressures in the model ground. Therefore, the chemical additives reduced the degree of apparent clogging induced by non-uniform consolidation of a PVD unit cell and increased the efficiency of vacuum consolidation.

Performance of a winged PVD (WPVD) for vacuum consolidation of soft clayey deposits

A new prefabricated vertical drain (PVD) with wings has been proposed, and its behaviour has been investigated using laboratory model tests and finite element analysis (FEA). The new PVD uses wings that are aligned perpendicularly to the surface of the PVD and is thus named WPVD. The wings increase the contact area of a WPVD with soil and serve as a horizontal drainage channel, and this can be more economic than a normal PVD with a larger diameter. Both the model test and FEA results show that, compared with a normal PVD, WPVD can increase the consolidation rate of a WPVD unit cell and, even, the final consolidation-induced settlement. The mechanism for the increase in the settlement is that WPVD can reduce the degree of non-uniform consolidation within a WPVD unit cell. The results also indicate that the effect of a WPVD depends on the total surface area of the wings per unit length of a PVD, as well as the ratio of the length (Ls) and width (Ws) of the wing (Ls/Ws). For a given surface area, the larger the Ls/Ws ratio is, the greater the effect of the wing is for increasing the rate of consolidation. Finally, an empirical equation has been established for evaluating the equivalent diameter of a WPVD, with which WPVD-induced consolidation can be analysed using existing PVD consolidation theories.

Apparent clogging effect in vacuum-induced consolidation of dredged soil with prefabricated vertical drains

The improvement efficiency of a dredged slurry by vacuum preloading is greatly affected by the apparent clogging effect arising during the consolidation process, where the apparent clogging effect refers to the combined impacts of filter clogging and particle blinding around the drain due to particle migration and non-uniform consolidation. Three laboratory model tests with different types of soils were performed to investigate the apparent clogging effect. First, the filter clogging effect was investigated by scanning electron microscopy and cross-plane permeability tests. Second, changes in the particle size distribution due to particle migration were analysed at the micro- and macro-levels, and the particle migration induced blinding effect was assessed through the results of the compressibility and permeability tests. The test results indicated negligible particle migration in pure clay and relatively higher blinding effect in mixture soils. Finally, the effects of blinding due to particle migration and non-uniform consolidation on the overall consolidation rate were theoretically quantified. Both the analytical and tests results implied that the apparent clogging effect is predominantly by non-uniform consolidation rather than the particle migration-induced blinding effect, especially for cohesive marine clay.

Behaviour of a PVD unit cell under vacuum pressure and a new method for consolidation analysis

Abstract The behaviour of a prefabricated vertical drain (PVD) unit cell with clays of high initial water content has been investigated by laboratory model tests and finite element analysis (FEA). The results indicate that there is considerable horizontal soil movement towards the PVD. The soils in the zone near the PVD are in horizontal compression, and the other zones are in horizontal tension. The surface settlements are not uniform, and the soil at the periphery of the unit cell settles more than the soil near the PVD. The model test results indicate that the phenomenon of soil particle separation does not occur, and it implies that the main mechanism of apparent “clogging” is due to non-uniform consolidation. The results of the FEA indicate that at the end of vacuum consolidation, the soil adjacent to the PVD has a higher effective vertical stress as well as undrained shear strength, but the stress state is very close to the critical state line. Then, a new explicit consolidation analysis method has been established/verified for considering the variations of consolidation properties, including apparent clogging during the consolidation process.

Prefabricated Vertical Drain (PVD) and Deep Cement Mixing (DCM)/Stiffened DCM (SDCM) techniques for soft ground improvement

Soft ground improvement techniques have become most practical and popular methods to increase soil strength, soil stiffness and reduce soil compressibility including the soft Bangkok clay. This paper focuses on comparative performances of prefabricated vertical drain (PVD) using surcharge, vacuum and heat preloading as well as the cement-admixed clay of Deep Cement Mixing (DCM) and Stiffened DCM (SDCM) methods. The Vacuum-PVD can increase the horizontal coefficient of consolidation, Ch, resulting in faster rate of settlement at the same magnitudes of settlement compared to Conventional PVD. Several field methods of applying vacuum preloading are also compared. Moreover, the Thermal PVD and Thermal Vacuum PVD can increase further the coefficient of horizontal consolidation, Ch, with the associated reduction of kh/ks values by reducing the drainage retardation effects in the smear zone around the PVD which resulted in faster rates of consolidation and higher magnitudes of settlements. Furthermore, the equivalent smear effect due to non-uniform consolidation is also discussed in addition to the smear due to the mechanical installation of PVDs. In addition, a new kind of reinforced deep mixing method, namely Stiffened Deep Cement Mixing (SDCM) pile is introduced to improve the flexural resistance, improve the field quality control, and prevent unexpected failures of the Deep Cement Mixing (DCM) pile. The SDCM pile consists of DCM pile reinforced with the insertion of precast reinforced concrete (RC) core. The full scale test embankment on soft clay improved by SDCM and DCM piles was also analysed. Numerical simulations using the 3D PLAXIS Foundation finite element software have been done to understand the behavior of SDCM and DCM piles. The simulation results indicated that the surface settlements decreased with increasing lengths of the RC cores, and, at lesser extent, increasing sectional areas of the RC cores in the SDCM piles. In addition, the lateral movements decreased by increasing the lengths (longer than 4 m) and, the sectional areas of the RC cores in the SDCM piles. The results of the numerical simulations closely agreed with the observed data and successfully verified the parameters affecting the performances and behavior of both SDCM and DCM piles.

Effects of fracture grouting with sodium hydroxide during electro-osmosis on clay

ABSTRACTElectro-osmosis is a foundation treatment method for clay that is not widely used because of its nonuniform consolidation effect and high cost. To overcome these limitations, this study investigates fracture grouting. To determine the optimal grouting method, anode grouting, polyurethane grouting, and fracture grouting were first compared in one-dimensional electro-osmosis consolidation tests using self-made model boxes under an equal electric potential gradient, and then different solution concentrations were tested. By comparing the current, drainage rate, and coefficient of energy consumption during the electro-osmosis process, as well as moisture content, electrical conductivity, and shear strength after the tests, the moisture and shear strength of clay after electro-osmosis were found to be significantly improved by adding chemical reagents at the fracture. In addition, the optimum concentration of fracture grouting was determined to be 1.5%, and the shear strength after testing of clay that had been treated with sodium hydroxide was found to be higher than that of the control group. However, the effects of fracture grouting in the early stage were clearer than the effects of fracture grouting at later stages.

Method for Considering the Effect of Nonuniform Consolidation

Method for Considering the Effect of Nonuniform Consolidation

Equivalent ‘smear’ effect due to non-uniform consolidation surrounding a PVD

This paper investigated the effect of non-uniform consolidation within a prefabricated vertical drain (PVD) unit cell on the average degree of consolidation through laboratory model tests and finite-element analysis. By considering the permeability (k) changing with the void ratio (e), the results of the finite-element analysis showed that the effect of non-uniform consolidation has a considerable effect on the average degree of consolidation of a PVD unit cell. Further laboratory model tests of a PVD unit cell were conducted, and analyses of the model test results confirmed the effect of non-uniform consolidation. Finally, a method of considering the effect of non-uniform consolidation for the analysis of PVD-induced consolidation was established with an equivalent ‘smear’ effect concept.

Experimental research on the marine hydrodynamic action on the consolidation process of the sediments in the Yellow River Estuary

Based on the in-situ measurements, the impact of the marine hydrodynamics, such as wave and tide, in the rapidly deposited sediments consolidation process was studied. In the tide flat of Diaokou delta-lobe, one 2 m×1m×1 m test pit was excavated. The seabed soils were dug and dehydrated, and then the powder of the soil was mixed with seawater to be fluid sediments. And an iron plate covered part of the test pit to cut off the effect of the marine hydrodynamics. By field-testing methods, like static cone penetration test (SPT) and vane shear test (VST), the variation of strength is measured as a function of time, and the marine hydrodynamics impact on the consolidation process of the sediments in the Yellow River estuary was studied. It is shown that the self-consolidated sediments’ strength linearly increases with the depth. In the consolidation process, in the initial, marine hydrodynamics play a decisive role, about 1.5 times as much as self-consolidated in raising the strength of the sea-bed soils, and with the extension of the depth the role of the hydrodynamics is reduced. In the continuation of the consolidation process, the trend of the surface sediments increased-strength gradually slows down under the water dynamics, while the sediments below 50 cm are in opposite ways. As a result, the rapidly deposited silt presents a nonuniform consolidation state, and the crust gradually forms. The results have been referenced in studying the role of the hydrodynamics in the soil consolidation process.

Lines of dense nanoparticle colloidal suspensions evaporating on a flat surface: Formation of non-uniform dried deposits

Line evaporation of dense nanoparticle suspensions is studied theoretically and experimentally. The 2-D lines are drawn by a pen-like nozzle continuously dispensing a commercially available concentrated organic suspension (50 wt%; 4.3 vol%) of 5 nm gold nanoparticles in toluene solvent. Such particle-containing lines show promise for industrial applications where circuits are inkjet-printed and heat-treated to dry off the organic solvent and sinter the nanoparticles, thus producing a continuous electrically conducting path. The employed nanosuspension displays spontaneous thickening upon contact with a solid surface in the ambient atmosphere, and thus does not dry according to the well-established coffee-stain forming mechanism applicable to dilute particle suspensions. In the present work, model lines (∼1 mm width) are studied to elucidate the drying peculiarities of such nanoparticle slurries. These scaled-up lines allow detailed spatial measurements of their topography throughout their prolonged evaporation period, and make possible direct comparisons between experiment and theory. The results show the particle deposits formed by evaporative drying of these lines to be of non-uniform thickness with a dent in the middle of the lateral cross-section. Formation of this practically undesirable landscape is attributed to the highly non-uniform evaporative character of sessile or pendent liquid lines, which results in a non-uniform consolidation of the porous phase formed upon contact with the solid surface. The formulated description of the shape changing process, as done in the framework of the consolidation theory, yields predicted deposit speck shapes that compare favorably with the temporally resolved experimental data.

General Observations of Constant Flow Rate Filter Pressing

Consolidating powder compacts to a uniform and high particle packing density is a central aspect of ceramic processing. Experiments on the formation of powder compacts from slurries of differing properties and filter pressed under different conditions are presented. The influence of (1) piston velocity, (2) the solid content of the slurry, and (3) slurry viscosity are discussed. A simplified theory of nonuniform cake growth is developed. This theory is based on the assumption that the cake profile is time independent in a reference plane moving with the cake/slurry interface. Classical theory assumes uniform cake density, while more difficult finite element methods are required for calculating nonuniform cake growth conditions. This theory simplifies nonuniform cake consolidation mechanics and allows simple spread-sheet-type calculations on cake uniformity. Cake uniformity is an important goal in processing. Piston stress-displacement behavior can be reasonably simulated from the fundamental cake properties (permeability and yield curve). The inverse, estimating the fundamental cake properties from piston stress-displacement behavior, appears to provide only rough estimates of these characteristic parameters. The Kozeny-Carman equation appears to reasonably fit the permeability behavior of these filter cakes.

The Continuous Curing Process for Thermoset Polymer Composites. Part 2: Experimental Results for a Graphite/Epoxy Laminate

A new composite manufacturing method called continuous curing has been developed to alleviate problems in the processing of thick composites such as long manufacturing cycle times and material degradation due to thermal spiking. A 10 cm-thick graphite/epoxy (AS4/3501-6) laminate was fabricated using the continuous curing method. The thermal distributions were measured during the process and the final cure distribution was obtained by DSC testing. The mechanical performance of the laminate was analyzed by destructive testing of 16-ply mechanical test specimens removed from the bulk laminate. These specimens were distributed at five locations across the thickness of the laminate. Results for longitudinal compressive strength, transverse tensile strength, and interlaminar shear strength show some degradation. An attempt to quantify the factors contributing to the lower measured strengths is presented. Optical microscopy and image analysis was performed to obtain void and fiber volume distributions across the laminate thickness. Longitudinal layer waviness was measured by optical microscopy. The degradation in strength can be attributed to the high degree of layer waviness, nonuniform consolidation, and excessive voids. These manufacturing defects are attributed to less than optimal processing parameters chosen for the demonstration experiment.

Staged curing of composite materials

In this paper the composites processing technique stage curing is developed. Stage curing is especially suited for the fabrication of thick composites in which thermal spiking and non-uniform consolidation are problematic. It is also useful for assessing the effects of lengthy lay-up times on mechanical integrity for large, complex composite structures. The effects of stage curing on the mode I interlaminar fracture toughness and interlaminar shear strength were investigated by double cantilever beam and interlaminar shear strength testing. From the results of these tests, no degradation was found for the staged cure cycles investigated. Additionally, the feasibility of reducing void content by stage curing was demonstrated. The interruption of the cure cycle with an intermediate cooldown under pressure before gelation results in shrinkage and collapse of voids. Subsequent gelation of the resin can give materials with reduced void content compared with conventional curing.

Deformation of foundations during freezing of a clay foundation bed

The deformation is discussed of the foundations of an unfinished 2-story building, which was caused by the freezing and heaving of the soils in the foundation bed. In the spring, after thawing of the entire stratum of seasonally frozen soils, the unfinished building began to be deformed. Between the concrete blocks of the two foundation walls which were left uncovered during the winter, gaping vertical cracks tapering downward were seen. The concrete base course and foundation blocks were probably laid on previously frozen clay, which by the time of building the foundations had already undergone heaving in the presence of a small surface load. The accumulation of moisture around the sand lens promoted heaving of the clay. Subsequently freezing continued through the concrete blocks and into the warming earth heap, which also proved to be inadequate. The porosity and water content of the clay subjected to heaving was determined. Nonuniform consolidation of the clays led to uneven settlement of the foundations and to cracking. The total displacement of the deformed foundation wall relative to the monolithic part exceeded 2cm. The lost load-bearing capacity of the clays was gradually restored with time, the ground was compressed and compacted and deformations of the structure which were pronounced during the initial period died out.