Coefficient Of Consolidation Research Articles

Insights into conditioning landfill sludge with freeze-thaw method: Effects on the physical-mechanical properties and micro characteristics

With the rapid increase of sludge production, large quantities of sludge with high water content (WC) are difficult to dispose of. It is necessary to evaluate sludge's physical-mechanical properties for waste sludge resource utilization and stability of landfills. In this study, freeze-thaw method is used to treat sludge. A series of tests, such as particle size analysis test, consolidation test, direct shear test, and SEM test, were carried out on the sludge treated by freeze-thaw. The influence of different refrigerating temperatures on the physical-mechanical properties is investigated. By analyzing the sludge morphology, particle distribution, pore change, consolidation and compression characteristics, shear characteristics, and microstructure, the influence mechanism of refrigerating temperature on sludge's physical-mechanical properties are revealed. The results show that after the freeze-thaw, the sludge particles gathered together, the water is easy to separate from solid particles. In addition, compressibility and void ratio of sludge decrease. At the same time, the permeability coefficient and consolidation coefficient increased by 1–2 orders of magnitude. When the freezing rate is slow, the sludge particles are pushed and squeezed by the ice layer, destroying the floc structure; when the freezing rate is high, the bound water can be better removed, which is conducive to forming a denser structure. Therefore, the cohesion of sludge decreases, and the internal friction angle increases after freeze-thaw treatment. Shear performance improved. The results of this study provide a reference for waste sludge resource utilization.

Compressibility of Fly Ash and Fly Ash-Bentonite Mixtures

Environmental protection, one of the most important issues nowadays, forces civil engineers to look for alternative solutions to the known ones. The use of substitute materials as an embankment fill or a ground material under the embankment instead of natural soil follows these trends. A great amount of fly ash is disposed of in landfills. It is a cost-effective material that can be used in construction instead of natural soil. The geotechnical properties of fly ash as a construction material in place of soil need to be examined. It includes laboratory tests to determine the chemical composition and geotechnical characteristics. In the present work, one-dimensional consolidation tests have been conducted to examine the compressibility behaviour of compacted fly ash and fly ash-bentonite mixtures used in the earth structures like road embankments. The analysis of the consolidation phenomenon is useful for predicting the magnitude and rate of settlement of the structure. Materials compacted at OMC to their MDD, according to Standard Proctor, were tested in Rowe-Barden type consolidometer on saturated and non-saturated samples. Coefficients of consolidation have been compared between values derived from log-time and square-root-of-time methods and direct hydraulic conductivity tests. Bentonite amount in fly ash-bentonite mixtures influences the vertical deformation of the sample.

Compressibility and cracking properties of soft soils treated with a polymeric stabiliser

The influence of polyacrylamide (PAM) on the mechanical and physical characteristics of two kinds of soft soils was investigated laboratory tests including consistency, standard Proctor compaction, incremental loading consolidation and desiccation tests were conducted on the untreated and treated soils. Based on results, addition of PAM caused a reduction in the soils' plasticity indices. Although adding PAM slightly increased the maximum dry density, it had a negligible impact on the optimum moisture content. An increase in PAM content reduced compressibility, initial void ratio, compression and swelling indices, coefficient of consolidation and permeability. Adding PAM caused the cracking potential of soils to decrease. Moreover, to have a better interpretation of the stabilisation mechanism as well as the microstructural changes induced by PAM, the field emission scanning electron microscopy and X-ray diffraction analyses were conducted on the soils. The results demonstrated that the PAM additive enables physical bonding between soil particles rather than chemical reactions. In other words, PAM does not change the soil in terms of the atomic structure of clay particles, rather it alters the whole structure of the clay mass by accumulating particles and creating a strong connection network between them by flocculating the aggregates.

Large-strain rheological consolidation analysis of multi-layered marine soft clays exhibiting natural structural characteristics

The destruction of marine soft clays’ macropore structure results in large-strain deformation during consolidation, as well as the potential to alter rheological deformation characteristics. A sectionalised regimes rheological model was adopted to describe the structural characteristics under the isotache framework, which led to a nonlinear variation of geometrical boundaries and material properties during consolidation. A semi-analytical theory combining numerical and analytical methods was developed, and the solutions for excess pore water pressure, degree of consolidation, and settlement were derived and computationally programmed. Using parametric analysis, the effects of rheological and structural characteristics on the consolidation behaviour of soft clay were discussed compared to the solutions of other theories. The coefficient of secondary consolidation in the transitional regime has an impact beginning in the middle of primary consolidation. The proposed solutions for degree of consolidation are smaller than the small-strain solutions during the early period of primary consolidation but change larger as consolidation progresses.

Improved radial consolidation in soft clay using pervious concrete piles

The efficacy of a pervious concrete pile (PCP) in accelerating the rate of consolidation in unconsolidated soft clay deposits was explored. A series of laboratory consolidation tests was performed on PCPs, sand drains and stone columns in two different soft soils (clay with high compressibility (CH) and clay with intermediate compressibility (CI)) and their consolidation characteristics were compared. A novel annular setup was used to determine the consolidation characteristics of all three techniques employed. Compared with the sand drain and stone column, the PCP provided an extensive enhancement in consolidation characteristics such as the coefficient of compressibility and the coefficient of consolidation. The enhanced compression index obtained using the PCP implied a compelling scope for accelerating the radial consolidation of the surrounding soil, which was less in the case of the stone columns and sand drains. An improvement in the rate of consolidation in the radial direction was observed in both the CI and CH soils when a PCP was employed. The acceleration in consolidation was greater in the CH soil than in the CI soil.

CPT-based liquefaction resistance of clean and silty sands: a drainage conditions based approach

The cone penetration test-based simplified liquefaction triggering evaluations are largely based on linking liquefaction manifestations in the field to cone penetration resistance. These relationships are interpreted in such a way that for given penetration resistance, the liquefaction resistance increases as non-plastic fines content (FC) increases. However, several studies have indicated discrepancies in this relationship. Hence, there is a lag in rational scientific understanding of this observation. In this study, an experimental research program was undertaken to investigate the CPT-based liquefaction assessment by considering the effects of drainage conditions on the relationship between CPT resistance and liquefaction resistance. First, clean sand and silty sands having 5, 15, and 35% FC were tested at different relative densities by stress-controlled cyclic direct simple shear (CDSS) tests to investigate cyclic resistance of silty sand with varying amounts of non-plastic fines. Then, a set of tests involving piezocone penetration (CPTu), seismic CPTu (SCPTu), and direct push permeability (DPPT) were undertaken in a large-scale box filled with the same soils used in the CDSS tests. The large-scale test results quantified the effect of drainage conditions (coefficient of consolidation) on cone penetration resistance. Finally, by combining the CDSS and CPTu test results, an alternative CPT-based liquefaction resistance relationship was proposed by considering the effects of drainage conditions.

Determination of the coefficient of consolidation by piezocone tests under partially drained conditions

Dissipation tests after piezocone penetration are used widely to estimate the consolidation behaviour of cohesive soils. Interpretation of dissipation tests is complicated in intermediate soils, such as in silts and silty clays, since the accumulated pore pressures and the subsequent dissipation response are affected by the partially drained conditions. The influence of partial drainage on dissipation response is investigated using a large-deformation finite-element approach within the framework of effective stress analysis. The numerical approach is validated by comparison with the existing centrifuge tests where dissipation tests were performed after undrained and partially drained penetrations. The numerical results provide insights to quantify the effects of drainage conditions, including distribution of pore pressures prior to dissipation and then the operative coefficient of consolidation, ch, against various penetration velocities. The time corresponding to a given degree of dissipation is found to be increased with reducing normalised penetration velocity, as the gradients of normalised pore pressures are reduced in the radial direction before dissipation. The ratio between ch and the coefficient of consolidation can be described through a unique backbone curve. A new approach estimating the coefficient of consolidation from a dissipation test following partially drained penetration is proposed for practical applications.

Effect of salt permeants on the consolidation and hydraulic behaviour of fibre treated black cotton soil for landfill application

Clay liner functions as an impermeable barrier between leachate and groundwater in landfills. In this work, naturally available black cotton (BC) soil is adopted as a liner material due to its high swelling and low hydraulic conductivity, which helps to eliminate the risk of groundwater pollution by preventing pollutant mobility. The liner's potential is threatened by two issues: shrinkage cracks and chemical attacks. BC soil induces desiccation cracks and high compressibility due to its high shrinkage potential upon drying, which severely impacts its hydraulic conductivity behaviour. In recent years, fibres have been used as reinforcing materials to control compressibility and shrinkage cracks of the liner. In this investigation, waste tire fibres, which were used as a reinforcing material, mixed with BC soil in the proportion of 5, 10 and 15% by their dry weight. Since the essential parameters of liner would change due to the interaction of chemicals in leachate, hence, this study examined the consolidation and hydraulic properties of fibre mixed BC soil in the presence of two inorganic salt permeants (NaCl and CaCl2) of two concentrations (0.1 and 1N) to mimic the leachate effect. The results revealed that when salt solutions were utilised as saturating pore liquids, the time to achieve the 90% of consolidation (t90) of fibre-treated BC soil was decreased, thereby increasing the coefficient of consolidation (cv). These changes were more significant at higher concentrations of pore liquids. The t90 value for 15% fibre-treated soil with DI water is 27.0 min, and it decreased drastically to 0.8 min (97.0% reduction) for 1N NaCl solution and 0.6 min (97.8% reduction) for 1N CaCl2 solution at the higher consolidation pressure of 784.5 kPa. Compression index (Cc) and void ratio (e) were reduced with the salt permeants irrespective of the fibre content. Finally, it was shown that salts substantially impact the hydraulic conductivity values of fibre-treated soil and that up to 10% fibre content is appropriate for landfill liner application.

Consolidation Properties of Soil/Modified Bentonite Backfill in Salt Solution

The consolidation properties of soil-bentonite (SB) backfills containing 20% of the weight of sodium-hexametaphosphate-modified calcium bentonite (SHMP-20CaB) and prepared with 0 mM to 1000 mM calcium chloride (CaCl2) solution were evaluated. The results indicated that both consolidation stress and CaCl2 concentration had significant effects on the consolidation behaviors of the SHMP-20CaB backfill. In general, an increase in consolidation stress resulted in a decrease in the void ratio (e) and in the coefficient of volume change (mv), alongside an increase in the coefficient of consolidation (cv). The increased CaCl2 concentration yielded a dropped void ratio, and a nonlinear decreased compression index (Cc) and rebound index (Cs), respectively, from 0.18 to 0.13 and from 0.022 to 0.010, and a nonlinear increase cv. A threshold CaCl2 concentration of 100 mM was observed at the inflection points of the Cc, Cs, and cv. In contrast, the mv was insensitive to the CaCl2 solutions. The deterioration in e, Cc, and Cs and the increase in cv were the result of a compressed diffuse double layer of the bentonite by the CaCl2 solution, which thus exerted certain negative effects on the consolidation behaviors of the SHMP-20CaB backfill.

Measuring strength and consolidation properties in lacustrine clay using piezocone and self-boring pressuremeter tests

As a result of the growing population in Switzerland, new infrastructure is increasingly founded in areas of extremely soft clays, which are challenging to build on. Reliable characterization of such sediments is, therefore, essential to facilitate efficient and economical designs. For various reasons, it is often beneficial to measure soil properties in situ, using probes like the piezocone or self-boring pressuremeter. The main objective of this study was to explore the key differences of these two site investigation techniques in terms of measuring undrained strength and consolidation characteristics in varved lacustrine clay. Experimental data from a field-testing campaign carried out in Switzerland demonstrate that both probes yield comparable results. The quality of the predictions was further assessed by comparing the field measurements to results from laboratory tests and existing empirical relationships. Additionally, a new method based on Monte Carlo simulations was presented, to provide context to the disparity between the consolidation coefficients estimated in the field ( ch) and laboratory ( cv), and to aid prediction of field values of ch from laboratory measurements.

A new interpretation of the constant rate of strain consolidation test for determining the coefficient of consolidation

A new interpretation of the constant rate of strain consolidation test for determining the coefficient of consolidation

Some parameters of the interior and productivity of young beef cattle

The paper presents the study results of the indicators of individual development of Ukrainian gray, Ukrainian meat, and light Aquitaine breeds, biochemical indicators of blood serum, and also calculated the level of correlations between traits. The research was carried out at the State Enterprise “Experimental Farm “Polyvanivka” and the Animal Husbandry Laboratory of the State Institution “Institute of Grain Crops of the National Academy of Sciences of the Russian Academy of Sciences”, as well as the testing center of the Institute of Animal Husbandry of the National Academy of Sciences of the Russian Academy of Sciences. The work was carried out following the program of scientific research No. 31, “Genetic improvement of agricultural animals, their reproduction and preservation of biodiversity. (Genetics, preservation, and reproduction of biological resources in animal husbandry)”, the task “To identify population-genetic regularities of the biological diversity of the isolated gene pool of the autochthonous gray Ukrainian breed of cattle”. The evaluation of young cattle of the specified breeds was carried out taking into account the following indicators: live weight at the time of birth, at the age of 6 and 12 months, average daily increase in live weight for the following periods: time of birth – 6 months, 6 months – 12 months. The “formation intensity” index was calculated according to this method of Yu. K. Svichin (1985), biometric processing of the research results – according to the methods of V. P. Kovalenko and others. (2010), S. S. Kramarenko and others. (2019). Total protein content, the activity of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase were studied in blood serum. It has been established that the biochemical parameters of blood serum in bulls of Ukrainian gray, Ukrainian meat, and light Aquitaine breeds correspond to the physiological norm of clinically healthy animals. According to the indicators of the live weight of Ukrainian gray, Ukrainian meat, and light Aquitaine breeds of bulls at the age of 12 months, the minimum requirements of the elite class prevail by 2.2–4.8 %; at the age of 6 months, this indicator ranges from -3.8 (gray Ukrainian bulls) to +7.2 % (light Aquitan bulls). The average daily gain in live weight in animals of the studied breeds during the period of rearing from birth to 6 months of age and from birth to 12 months of age varies from 830.1 to 1052.4 g. The “formation intensity” index of Ukrainian Gray Bulls is 0.899 ± 0.0210, Ukrainian meat – 0.961 ± 0.0393 and light Aquitaine – 1.008 ± 0.0417 points. The coefficients of phenotypic consolidation of gray Ukrainian, Ukrainian meat, and light Aquitaine bulls vary from +0.241 (K1, live weight of Ukrainian beef bulls at birth) to +0.838 (K2, live weight of light Aquitan bulls at 12 months of age ). The coefficient of pairwise correlation between biochemical parameters of blood serum and live weight of Ukrainian gray, Ukrainian meat, and light Aquitaine breeds ranges from –0.921 ± 0.1377 to +0.738 ± 0.2384. This indicates the possibility of using total protein content, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activity for the early prediction of the live weight of animals of the studied genotypes.

Geotechnical properties of some tidal flat sediments of Khor-Abdullah coast, southern Iraq

This research involves geotechnical studies for some tidal flat sediments of Khor-Abdulla coast in the southern Basra city. This area has an important strategic location in future, the Iraqi Government intending to establish large engineering projects such as a big Basrah port. Sediment samples have been taken at a depth of 1.25 m to study the physical, chemical, and engineering properties of this region’s sediment. The investigation results reveal that its average high natural moisture was 37.5 %, Liquid Limit LL 45.5 %, Plastic Limit PL 26.5 %, Plasticity Index PI 19%. Hence, these sediments show high clay percentages (85-65%). It can be classified as Silty Clay sediments with low plasticity. Engineering tests resulted in average Compression Strength of 206 kN/m2, Max. dry density 1.63 g/cm3 while consolidation coefficient 0.15 m2/year, consolidation index (0.28) with initial consolidation 35.5 kN/m2, and swelling index 0.071. These factors indicate a week sediment with low plasticity. Chemical tests results reveal high concentrations of sulfates chlorides, and organic matters. TDS were 30666 mg/l, CaCO3 41 mg/l, sulfate 2987 mg/l, Mg 600 mg/l, Ca 46.6 mg/l, and chlorides 1334.2 mg/l. while EC 44.5 mmhos/cm, pH 7.7.
 

Fracture effect on the hydro-mechanical behaviour of Callovo-Oxfordian claystone

Excavation of the galleries for the geological disposal of radioactive waste can induce an excavation damaged zone (EDZ), which can have consequences on the long-term safety of the repository. In this study, intact Callovo-Oxfordian (COx) claystone taken from the Meuse/Haute-Marne Underground Research Laboratory in France was artificially fractured in different directions, and the hydro-mechanical behaviour was investigated by performing high pressure oedometer test and hydraulic conductivity test. Comparison between the fractured and intact COx samples allows identification of the effects of fracture in terms of swelling, compression, hydraulic conductivity and creep. It appears that the presence of fracture decreases the swelling strain and this phenomenon depends on the infiltration path and the orientation of fracture. In particular, the infiltration path affects the global swelling rate of fractured claystone. The self-sealing of fracture is mainly attributed to the swelling of COx claystone grains in the fracture zone. Lower compression coefficient a, higher compression index Cc* and higher secondary consolidation coefficient Cα are observed for the fractured claystone, indicating a higher compressibility and creep than the intact one. The compression and creep behaviours depend on both the orientation of fracture and the stress level. Comparison of hydraulic conductivities between fractured and intact claystone indicates that the hydraulic conductivity can be partially recovered due to the collapse of macro-pores in the filled fracture zone. This is also confirmed by analysing the evolution of consolidation coefficients cv with stress. Beyond a stress level about 16 MPa, the fracture effect can be neglected, but the compressibility increases further due to grain breakage. Interestingly, this stress is close to the in-situ stress before excavation.

Identification of preferable method for the precise estimation of coefficient of consolidation (Cv) for coal ash

The exact determination of settlement and the time required to complete that settlement is very important from the safety point of view. There are several methods available to find the rate of consolidation that is highly dependent on the settlement versus time curve. Here, it has been attempted to identify the suitable method for the determination of the rate of consolidation of coal ash. After analyzing the value of the coefficient of consolidation (Cv) estimated from various methods, the rectangular hyperbola method (RH method) is found to be in best linear correlation between the measured Cv and calculated Cv. The coal ash shows an increment in Cv with the increase in effective pressure. The Cv obtained from the RH method is higher than the Cv obtained from Taylor’s and Casagrande method that helps in close approximation with field Cv. The precise determination of Cv helps in better prediction of the time required for the consolidation settlement that will increase the performance of the structure.

PREDICTION OF ROAD CLEARANCE

One method of handling soil that can be done to speed up the consolidation process is to add a Pre-Loading embankment on top of the plan embankment. In addition, this handling is also carried out to achieve a reduction by the design load, so that the settlement of embankment after the construction period still meets the required criteria and standards. This study was conducted to obtain a comparison of the prediction of embankment settlement with the empirical method using CPT data and the prediction of settlement using the Asaoka Method. In addition, the results of the consolidation coefficient will also be compared which can be used to determine the right time for Pre-Loading excavation during the construction period. The data used are CPT test data in the field as well as laboratory test data and measurement data for the settlement plate settlement closest to the position of the CPT test. From the analysis carried out, it is obtained that the prediction of decline using the Asaoka method is smaller than the prediction of decline using the empirical method using CPT data. In addition, from the analysis, it was found that at locations HB-04 and SP 70, as well as HB-07 and SP 91, showed laboratory consolidation coefficient values (cv-Lab.) which were close to the consolidation coefficients of the Asaoka Method (cv-Asa.), while in HB -05 and SP 79 and HB-06 and SP 85 show a large difference in values. The average comparison of the cv-Lab. consolidation coefficients and CV-Asa. is 58.5%.

Compaction and consolidation characteristics of chemically treated expansive soil of Jamshoro

The Jamshoro soil is a weak and expansive soil. The construction of infrastructure on such soils has resulted severe damages and huge maintenance costs. Thus, it needs treatment to enhance its geotechnical properties. This research work investigates the effects of chemical stabilizers such as lime, fly ash, and silica fume on the compaction and consolidation characteristics of expansive soil of Jamshoro. The stabilizers were added individually in different proportions (5%, 10%, 15%, and 20%) in the soil. The results show that maximum dry density decreased, while optimum moisture content increased with the increase of the stabilizers’ content in the soil. The compression index and swelling index of lime treated soil significantly decreased than that of soils treated with silica fume and fly ash. On the other side, the coefficient of consolidation and permeability of fly ash treated soil considerably increased than that of soils treated with silica fume and lime.

Experimental Study for the Effect of Additives Silica Fume on the Properties of the Synthetically Contaminated Soil

This paper aims at studying the impact of the reaction that occurs between contaminants present in the soil and silica fume added on the chemical, physical and mechanical properties of the soil. The soil samples were contaminated in the laboratory with nickel nitrate (Ni(NO3)2). Silica fume (SF) was added to three different ratios (3%, 5%, and 10%). Several laboratory experiments were conducted to study soil characteristics before and after adding silica fume to the contaminated soil. The results revealed that the increment percentage of liquid and plastic limits was obtained with an increase in the percentage of silica fume additive to the nickel-contaminated soil. Notably, the maximum dried densities were decreased by increasing silica fume ratios to the nickel-contaminated soil, while the optimum water content increased with increasing silica fume ratios to the nickel-contaminated soil. The value of organic matter for soil samples was roughly equal numbers ranging from 3.33% to 4.07% (i.e., no change in the organic matter for soil samples mixed with different ratios of silica fume). The coefficient of consolidation (Cv) increased from 0.0026 in a soil sample that was contaminated with nickel ions at a concentration equal to 750 mg/kg without adding silica fume to 0.0755 in a soil sample contaminated with nickel ions at a concentration of 750 mg/kg mixed with silica fume at a ratio of 5% and then decreased to 0.00531 in a soil sample contaminated with nickel ions at a concentration of 750 mg/kg mixed with silica fume at a ratio of 10%.

CONSOLIDATION CHARACTERISTICS OF LATERITIC SOIL TREATED WITH RICE HUSK ASH

Lateritic soil was treated with 0, 4, 8, 12 and 16% rice husk ash (RHA) by dry weight of soil to determine its consolidation properties. Test carried out include; particle size distribution, specific gravity, compaction test with varying compactive efforts (British Standard Light (BSL), West African Standard (WAS) as well as British Standard Heavy (BSH)) and consolidation test. Samples for consolidation test were compacted and then cured for 7, 28 and 56 days; then subjected to one dimensional consolidation testing to observe the influence of curing period and compactive effort on its consolidation characteristics. Index tests showed improved geotechnical properties. The maximum dry density (MDD) for BSL compaction decreased with a rise in RHA content from 1.72 to 1.42 Mg/m3 while optimum moisture content (OMC) increased from 16.5 to 27.3% with rise in RHA doses from 0 up to 16%. Similar trend was observed for WAS and BSH energies. The Pre-consolidation pressure rise with increment in RHA content and also with increase in both compactive efforts and curing period with few exceptions. At 12% RHA content, the Pre-consolidation pressure increased from 65 to 66.5kN/m2 at 7 days and 56 days respectively. Increase in RHA content caused a decrease in Compression Index (Cc) and Swelling Index (Cs). Compression Index also decreased with increase in both compactive efforts and curing period. There was no observed trend in the Swell Index with curing period. As the compactive efforts increased, the swell index decreased. The RHA reduced the Coefficient of Volume Compressibility (Mv) and the Coefficient of Consolidation (Cc). Curing period and compactive effort have no effect on Mv and Cc. Based on the results obtained, curing period of atleast 28 days using up to 12% RHA compacted at energy level of BSH improved the properties of the treated soil and can be use for geotechnical engineering applications like embankment or rural roads.

Numerical Simulation of Thermal Conductivity of Stainless Steel and Al-12Si Powders for Additive Manufacturing

Abstract A three-dimensional model of a partially melted powder bed with particles stochastically distributed in size and space coordinates has been developed. Numerical simulation of temperature distributions in stainless steel AISI 316 L and Al-12Si powders in vacuum, air, and argon has been performed to analyze unsteady heat transfer in a porous medium. The numerical model demonstrates a large effect of heat transfer through the gas phase in case of powders with low thermal conductivities like stainless steels. At the porosity level of 65% and above, the mechanism of heat transfer drastically changes and a linear dependence of thermal conductivity on porosity frequently used in literature becomes incorrect. The effects of the consolidation coefficient and size distribution on effective heat transfer in powders are discussed. The obtained dependencies of the effective thermal conductivity on porosity and the consolidation coefficient could be used in additive manufacturing applications.