Consolidation Characteristics Research Articles

Effect of air-boost modes on clogging behavior for vacuum consolidation with prefabricated horizontal drain

The air-booster vacuum preloading method is considered a reasonable choice for alleviating clogging problems. However, research on the air-boost mode during the early consolidation stage is still lacking. In this study, a series of comparative experiments were designed to investigate the effects of applying different pressures and durations on the consolidation characteristics of dredged soil and clogging at two consolidation stages using indoor model tests and microscopic tests. The experimental results showed that the air-boost modes of low pressure and short duration should be adopted during the early consolidation stage, and as the continuous consolidation, the pressure and duration should be increased. Moreover, early gas injection had a more significant effect on alleviating clogging of the prefabricated horizontal drain (PHD), and the pore diameter of dredged soil was also smaller. The research results are an important guide for air-booster vacuum preloading to dewater high-moisture dredged soil.

Supply chain resilience and improving sustainability through additive manufacturing implementation: a systematic literature review and framework

Additive manufacturing (AM) is rapidly transforming supply chains across various sectors. This study explores the current academic literature on AM applications in the supply chain and practitioner literature to explore the application of AM across various sectors. It then identifies AM’s role in achieving supply chain resilience and environmental sustainability. Key themes addressed in the literature have also been discussed. TCM (Theory, Characteristics and Methodology) framework has been used to identify the research gaps and provide future research directions. The study also proposes a research framework and propositions based on AM characteristics and capabilities required to achieve supply chain resilience and environmental sustainability through AM. This study extends the AM literature to present an integrated approach towards simultaneously achieving resilience and environmental sustainability. The study reveals how the AM characteristics of design freedom, part consolidation and on-demand tool-less manufacturing aid in achieving the twin benefits. The research propositions could be taken by researchers interested in exploring the field further. The findings of this study will enable the decision-makers contemplating adopting AM, in making informed decisions and be better prepared.

Study on the Geotechnical Property Changes of Loess after Seismic Landslides—A Case Study of the Subao Loess Landslide in Ningxia, China

This study aims to explore the differences between the loess and landslide deposits, focusing on aspects such as particle distribution, consolidation characteristics, and the dynamic shear modulus. Through a series of experiments, the research reveals the similarities and differences between these two entities, yielding several key findings. Firstly, the process of landsliding disrupts the original structure of the loess, resulting in a reduction in porosity and a densification of the soil. Additionally, the movement and sorting of particles during the landslides cause variations in particle size distribution across different sections of the landslide deposits. Secondly, the landslide process not only alters the soil’s structure but also changes the particle sizes within the loess. Particle wear and sieving results in the transformation of larger particles into smaller ones, leading to a more uniform particle size distribution. This shift in the structure and particle size directly impacts the consolidation characteristics of landslide deposits, resulting in a substantial reduction in the compression coefficient. Despite undergoing consolidation for decades, the middle and lower sections of the landslide deposits still exhibit under-consolidation. Although the differences in the maximum dynamic shear modulus between the loess and landslide deposits at varying depths are relatively minor, differences in the porosity and consolidation characteristics lead to faster decay rates of the dynamic shear modulus for the latter. The study also highlights a reduction in the water sensitivity of the maximum dynamic shear modulus within the landslide deposits. Based on the experimental results, a predictive model is proposed, utilizing the A and m values to estimate the maximum dynamic shear modulus of both the loess and landslide deposits. In conclusion, this research uncovers the impact of landslide processes on the structure and properties of the loess, providing an insightful understanding into the disparities between these two entities.

1D elastic viscoplastic consolidation analysis of bi‐layered soft ground under time‐dependent drainage boundary and ramp load

AbstractThe elastic viscoplastic properties are non‐negligible factors of clays that cause the deviation between the theoretical and the measured values, which were rarely incorporated in layered consolidation problems. Thus, this paper extended a generalized bi‐layered one‐dimensional (1D) consolidation model for soft ground under ramp load, simultaneously incorporating elastic viscoplastic deformation, non‐Darcy flow (NDF), and time‐dependent drainage boundary (TDB) condition. The finite volume technique was employed to numerically solve the control equation. Then, the proposed method solutions were verified by comparing with degenerated cases, including oedometer experimental results, analytical and semi‐analytical solutions with different boundary conditions. Furthermore, parametric studies were conducted on the bi‐layered clay creep consolidation characteristics by investigating the effect of the loading rate, interface and flow parameters, and the relative soil layer properties. The results demonstrate that the entire dissipation rate of the excess pore‐water pressure (EPWP) and settlement rate in the bi‐layered ground become faster as the soil thickness with high permeability or low compressibility increases. When considering the viscosity of soft clay, the EPWP exceeding the overlying construction load value can occur in poorly drained locations. Neglecting loading rate, time‐dependent drainage boundary (TDB), and NDF can result in a significant overestimation of consolidation and settlement proceedings.

Primary and secondary consolidation characteristics of a high plasticity overconsolidated clay in compression and swelling

For a reliable prediction of the time-development of soil deformations, a detailed characterization of both primary and secondary deformations is required. Nevertheless, in the current engineering practice the estimation of the primary and secondary deformations relies on the assumption of a constant coefficient of consolidation and a constant creep index respectively. However, high plasticity overconsolidated clays have reportedly complex stiffness and permeability relationships that challenge the validity of those assumptions. Analytical solutions of the one dimensional consolidation have been proposed, accounting for variation in permeability and oedometer modulus. Nevertheless, the methods assume a simplified log-linear and linear relationship with void ratio and effective stress for the two parameters, respectively. One-dimensional oedometer and constant rate of strain testing were employed to investigate the time-deformation development of a particular high plasticity overconsolidated clay. A dependency of the time until the end of primary deformations on the stress path was observed, with the majority of the unloading steps extending well beyond the 24 h typical duration of a load increment. It was revealed that the coefficient of consolidation generally increases during consolidation, and it may vary by more than one order of magnitude at the early stages of the consolidation process. This variation has been attributed to a transient effect noticed in the permeability, which has not been previously reported. The linear relationship between primary and secondary deformation indices was confirmed as an upper bound. In an effort to better characterize the time dependent behaviour a new index, the primary time deformation index, was defined as the slope at the inflection point of the time-curves. This parameter was found to be linearly related to the creep index, presenting thus a potential of better predictions of the duration and magnitude of consolidation deformations for the engineering practice.

One-dimensional thermal consolidation analysis of saturated clay with variable compressibility and permeability considering partial drainage boundaries

The nonlinear consolidation characteristics of saturated clay will be markedly impacted by temperature. However, despite the ample progress of calculation methods for the one-dimensional consolidation of soft ground, theoretical investigations into thermal consolidation have not been thoroughly explored. Moreover, partially drained boundary is more consistent with the engineering practice, which is imperative to be involved to mitigate computational error when determining the consolidation behavior. In this context, a mathematical model is established to incorporate the temperature-dependent nonlinear characteristics of compressibility and permeability. Subsequently, the resulting governing equations and numerical solutions for the one-dimensional nonlinear thermal consolidation of saturated clay are obtained under partial drainage boundaries. Then the accuracy and reliability of the proposed model are validated by degradation analysis and simulation analysis with good agreements. Furthermore, the computed results of current study are adopted to conduct an in-depth assessment of the influence of several crucial parameters on the nonlinear consolidation behavior. The results demonstrate that increasing the temperature can remarkably accelerate the dissipation rate of excess pore water pressure, thereby promoting the consolidation process of saturated clay. The inclusion of partial drainage boundaries also has a significant influence on the consolidation performance, with a maximum difference in the dissipation rate of excess pore water pressure reaching up to 40 % when transforming a completely drained boundary into a completely undrained boundary. Additionally, the increment of pre-consolidation pressure will induce a gradual acceleration of consolidation rate.

One-Dimensional Consolidation Properties of Soft Clay under Multi-Stage Loading

The consolidation characteristics of soft clay under multi-stage loading and single-stage loading exhibit significant differences. In order to investigate the consolidation behavior of soft clay under multi-stage loading, one-dimensional oedometer tests were conducted on marine sedimentary soft clay from northern China. The results indicate that the overall time-deformation pattern of multi-stage loading is a cyclic nonlinear extension of that of single-stage loading. The final deformation between multi-stage loading and single-stage loading is approximately equal; however, the consolidation rate of single-stage loading is four times that of multi-stage loading. Furthermore, the coefficient of consolidation (Cv) decreases with increasing stress. Subsequently, the traditional Terzaghi one-dimensional consolidation equation was modified and a consolidation equation suitable for multi-stage loading is proposed in this study. The analysis of engineering applications demonstrates that the traditional theory provides more accurate predictions of consolidation rate and settlement when the load is small. However, when the load is large, the settlement predicted using the Terzaghi one-dimensional consolidation equation may have an error of 0–25% compared to that using the modified equation. The modified Terzaghi one-dimensional consolidation equation provides a more accurate representation of the actual consolidation of soft soil.

Geotechnical studies on cemented and untreated Behshahr loess and Amol clay of Iran

There has been little research into the effects of cement on the geotechnical properties of two types of fine-grained soil with roughly the same grain size. The cement percentages used in this investigation were 0, 4, and 8% by dry weight of soil. Compaction features, consolidation characteristics, unconfined compressive strength (UCS), and Atterberg limits were all determined in the laboratory. Furthermore, scanning electron microscopy (SEM) examinations were used to analyze the microstructures of cemented and untreated loess and clay. Notably, the MDD for loess and clay are 1.72 gr/cm3 and 1.57 gr/cm3 at CC = 0%, respectively, and 1.7 gr/cm3 and 1.55 gr/cm3 at CC = 4%. The OMC for loess and clay are 15% and 22% at CC = 0%, respectively, and 17% and 20% at CC = 4%. At CC = 0%, loess and clay have cohesion values of 25 kPa and 28.7 kPa, respectively, and 190 kPa and 140 kPa at CC = 8%. Internal friction degrees for loess and clay are 24 and 29 degrees at CC = 0%, respectively, and 36 and 34 degrees at CC = 8. The consolidation test findings demonstrated that increasing the cement proportion reduced cemented soils’ compressibility. The Plasticity Index (PI) rose as cement concentration increased. However, significant percentages of cement concentration reduced the plasticity index. Furthermore, adding cement agents resulted in significant improvements in elasticity modulus and UCS for both soils. The SEM results indicated that the cement-treated loess was denser and more homogenous than the cement-treated clay sample. Triaxial tests reveal that cement particles improve cohesiveness and internal friction angle.

Effect of smear zone on the consolidation characteristics under radial drainage

Vertical drains installed in soft clay deposits enhance the rate of consolidation in preloading projects. Using a mandrel to install the prefabricated vertical drains, its insertion and withdrawal will result in the remoulding of the soil zone surrounding it, called the smear zone. The extent of the smear zone is an important parameter that characterises the smearing effect. This paper describes this effect in terms of smear ratio (i.e. the ratio of the diameter of smear zone ds to the diameter of drain, dw) on the consolidation characteristics of soil with radial drainage. A series of radial consolidation tests with a predetermined smear zone in a model unit cell was conducted by varying the diameter of the smear zone. The experimental results show that beyond a smear ratio of 4, the soil behaves as if it is in a fully remoulded condition. The results were compared with some of the theoretical approaches reported in the literature. The analytical solution that predicts the time–settlement curve in a better way is identified. Also, it is observed that the gain in undrained shear strength due to the consolidation of soft clay decreases with the increase in the diameter of the smear.

Effect of mineralogical composition and chemical properties on the consolidation behaviour of clay soils

ABSTRACT Consolidation characteristics like coefficient of consolidation (cv ) and compression index (cc ) are greatly influenced by the clay mineralogical composition of the soil. For the purpose, 20 clay soil samples collected from various locations of Tamil Nadu were subjected to one-dimensional consolidation test, and the clay minerals like montmorillonite, illite, and kaolinite were quantified using soil chemical properties. From the test results, it is observed that cv varies with consolidation pressure σ due to varied mineralogical composition. cv -σ trend decreases for soils with montmorillonite percentage (%M) greater than 42% and increases for soils with illite (%I) and kaolinite (%K) percentages greater than 42% and 41% respectively. The paper also focuses on the effect of CEC and SSA on cv and cc of the clay soil samples. A new correlation for cc in terms of clay mineral percentages and chemical properties (CEC, SSA) has been developed using regression analysis.

Effects of initial compaction condition and temperature on swelling characteristics of compacted bentonite

Given that isolated high-level radioactive waste repository cannot be modified during operation, understanding the influence of the buffer's initial conditions is critical. This study investigates the influence of the initial dry density and water content on the swelling pressure and consolidation characteristics of Korean bentonite, which is a buffer candidate in the engineered barriers of the repository. In order to consider the high temperature repository condition, samples of various dry densities and water contents were tested at different temperature. Prediction models were developed using the test data and the models were used to analyze the effects of initial conditions. The research findings indicate that the influence of dry density, water content, and temperature on swelling pressure is not absolute and can show different tendencies depending on the case. In terms of consolidation behavior, the compression index and pre-consolidation pressure differ with dry density and temperature, while recompression is unaffected. The study's results align with prior research on compacted expansive clays, with the double structure of clay serving as a suitable explanation for the swelling phenomenon's dependence on the initial compaction condition.

Secondary consolidation characteristic of bentonite by long-term consolidation tests of 2.7, 3.7 and 4 years

Secondary consolidation characteristic of bentonite by long-term consolidation tests of 2.7, 3.7 and 4 years

A case study on the variability of the coefficient of consolidation and its design reliability

The consolidation characteristics of cohesive soils are estimated using established relationships between the coefficient of consolidation (cv) and index tests, as well as laboratory oedometer tests. While the design cv is preferred from the field dissipation tests, the conversion from a horizontal to vertical value needs to be considered. A trial load was used to verify the consolidation parameters during a Queensland Road upgrade, which involved both road widening and raising of the existing embankments over compressible soils. Construction was done in 4 stages, and with preloading and surcharging in selected areas. Settlement monitoring and Asaoka plots were used to validate the design, and “moderately conservative” design values were adopted. This case study is used to show the large variability of the cv by the various test methods. While 99% of the site settlement was within the magnitude and time predicted during design, a 25 m length was not consistent with the data and performance of the rest of this site within the flood plain. The back-calculated cv was below the lowest test value and even data from nearby settlement plate monitoring from adjacent stages. In situ tests were located within 25m of this unconforming area and given that stratigraphy was consistent then the cv value adopted may not be representative. The lessons learnt show the various verification and validation process required to envelope risks, but all conditions with a “moderately conservative” design may not be covered.

Shrinkage and Consolidation Characteristics of Chitosan-Amended Soft Soil—A Sustainable Alternate Landfill Liner Material

Kuttanad is a region that lies in the southwest part of Kerala, India, and possesses soft soil, which imposes constraints on many civil engineering applications owing to low shear strength and high compressibility. Chemical stabilizers such as cement and lime have been extensively utilized in the past to address compressibility issues. However, future civilizations will be extremely dependent on the development of sustainable materials and practices such as the use of bio-enzymes, calcite precipitation methods, and biological materials as a result of escalating environmental concerns due to carbon emissions of conventional stabilizers. One such alternative is the utilization of biopolymers. The current study investigates the effect of chitosan (biopolymer extracted from shrimp shells) in improving the consolidation and shrinkage characteristics of these soft soils. The dosages adopted are 0.5%, 1%, 2%, and 4%. One-dimensional fixed ring consolidation tests indicate that consolidation characteristics are improved upon the addition of chitosan up to an optimum dosage of 2%. The coefficient of consolidation increases up to seven times that of untreated soil, indicating the acceleration of the consolidation process by incorporating chitosan. The shrinkage potential is reduced by 11% after amendment with 4% chitosan and all the treated samples exhibit zero signs of curling. Based on the findings from consolidation and shrinkage data, carbon emission assessments are carried out for a typical landfill liner amended with an optimum dosage of chitosan. In comparison to conventional stabilizers like cement and lime, the results indicate that chitosan minimized carbon emissions by 7.325 times and 8.754 times, respectively.

Experimental investigation on geopolymer-stabilized expansive soil

Expansive soils pose serious issues because to their insufficient bearing capacity and trivial deformation characteristics. These soils must be made suitable for engineering projects by soil improvement in the present scenario due to non availability of appropriate sites. The addition of industrial by products to locally expansive soils has gained popularity due to low carbon emissions and low incurring cost for improving soil properties. At present excellent bonding properties of geopolymers have been recognised as superior sustainable Alkali activated binders for soil stabilization. The paper discusses the effect of addition of Ground Granulated Blast furnace Slag(GGBS) with Geopolymer in combination to a selected high expansive nature soil properties varying GGBS proportions from 5% to 20% and Geopolymer solution from 0.6 Molarity to 1.0 Molarity (0.6 M to 1.0 M). Series of tests were conducted for Plasticity characteristics, Compaction characteristics, Unconfined Compressive strength test and Consolidation characteristics. From the test results optimum amount of GGBS is 10% and Geopolymer is 1.0 M, at this combination the Unconfined Compressive strength was found to enhance by 238% and swelling pressure decreased by 90% and Compression index reduced by 58%.

Mechanical properties of a high plasticity clay mixed with sand and low-plastic silt

It is of fundamental importance in geotechnical engineering practice to have a comprehensive understanding of how the mechanical properties of widespread alluvial soils are affected with varying concentration of sand, silt, and clay particles. Moreover, among the available methods of chemical and mechanical stabilization of high plasticity cohesive soils, mixing this soil with sand and/or non-plastic silt still brings a cost-effective and environment friendly solution. In this study, clay-sand and clay-silt mixtures were prepared by adding sand and silt to the clay samples in different proportions to explore geotechnical properties of sand-clay and silt–clay mixtures and develop empirical correlations for Atterberg’s limits, compaction properties, unconfined compression strength, and consolidation characteristics for these soil mixtures. It was observed that for additive contents of up to 50%, the liquid limit and plasticity index of high plasticity clay sample decreased by 36% and 55% (with silt) and 47% and 58% (with sand), respectively. The reduction in undrained shear strength determined from unconfined compressive strength tests was about 37% with silt and 59% with sand contents. The compression index decreased by almost 13% with silt and 39% with sand. Likewise, it was also observed that the coefficient of consolidation increased with addition of silt and sand by 57% and 87%, respectively. As the increase in silt and sand content transformed the soil into a compact mass which ultimately should lead to a decreased total settlement as well as the rate of settlement of such soils. The statistical models proposed in this study have high coefficient of determination which depicts the reliability of these models in predicting the mechanical properties of sand-silt–clay mixtures.

The effect of PVD layout on the consolidation characteristics of dredged slurry under vacuum preloading

Vacuum preloading coupled with prefabricated vertical drains (PVDs) has been widely used to improve the property of the dredged slurry. However, the effect of PVD layout on slurry consolidation characteristics remains poorly understood. This study conducted two vacuum preloading model tests—with single and dual PVDs. Particle image velocimetry (PIV) was used to directly observe the slurry displacements and strain paths. The test results revealed that the slurry consolidation characteristics were similar under different PVD layouts in the early stage of vacuum preloading. However, in the mid-stage, the effect of dual PVDs led to a significant reduction and increased dispersion of the slurry horizontal displacement. This, in turn, resulted in a thinner clogging zone and a subsequent decrease in vacuum pressure loss. Consequently, the slurry near the PVDs experienced an extended period of consolidation deformation. During the later stage, the single PVD model test exhibited a distinct zone of both vertical and horizontal compression in the slurry, while under dual PVDs, the slurry primarily underwent vertical compression and horizontal extension. The study also provided the relationship between the clogging zone thickness and time, which provided a reference for theoretical consolidation calculations.

Effect of chemical regulation combined with mechanical filtration on deep dewatering and consolidation characteristics of sludge.

To reveal the mechanism underlying deep dewatering of municipal sludge, this paper investigated the sludge characteristics from the perspective of soil mechanics, and analyzed the sludge physical and mechanical properties, stress as well as dewatering behavior during the dewatering process. Before and after cationic polyacrylamide (CPAM) and chitosan (HACC) conditioning, the pressure filtration dewatering time of treated sludge was shorter than that of raw sludge, and the water removal rate was greater than 70% at the 6 MPa pressure. However, with the increase in filter pressing time, the filtration resistance coefficient of sludge increased, and the water pressure in sludge pores rose up, and a longer time was needed for dissipation at the larger pressure, resulting in the slowdown of sludge consolidation. In addition, based on the three-stage Terzaghi Voigt model, when the pressure rose from 2 to 6 MPa, the time from filtration stage to compression stage of raw sludge was shortened, and the second stage played the most important role in the dewatering process. Compared with the raw sludge, the sludge filtration stage was shortened after CPAM or HACC conditioning, and the main dewatering mechanism changed from the second compression stage to the first compression stage, which means the bound water in sludge flocs was transformed into free water. This was also the reason why the dewatering, compression and consolidation rate of the conditioned sludge was faster than that of the raw sludge.

Compression and consolidation characteristics analysis of waste tire powder bed during gas pressurization

Pressurized conveying of waste tire powder was one of the key challenges in the feeding process. In this paper, the characteristics of powder bed compression behaviors during gas pressurization were studied by a visualization tank. Compared with the pulverized coal, the higher compressibility of waste tire powder bed revealed the serious consolidation problem in the high-pressure hopper. The source of bed consolidation was fluid dynamic force and constrained space. The intrusion probe was applied to the consolidation test of the compressed powder bed. The results showed that the gas pressurization enhanced the consolidation and the consolidation distribution existed along the axial direction. The maximum relative intrusion resistance was located at the compaction height of bed from 10.2 % to 22.2 %. This study was helpful in further optimizing the operation of pressurized conveying in the dry-fed gasification process of waste tire powder.

Nonlinear consolidation model of composite foundation with partially penetrated stone column

A nonlinear consolidation model for composite foundation with partially penetrated stone column is established based on the piece-linear finite difference method. This model allows for consolidation analysis of composite foundation with partially penetrated stone column under both free strain and equal strain conditions, while accounting for self-weight of stone column and soil layer, smear zone, well resistance effect, attenuation of additional stress along the depth direction, and the nonlinear variation of compressibility and permeability during the consolidation process. A calculation program was developed in Fortran, and the model was validated. The numerical solution of the average degree of consolidation obtained from the present model under equal strain condition is slightly smaller than the existing analytical solution, but overall it agrees well with the FEM result and the simplifying solution. Under both free strain and equal strain conditions, the numerical solutions of the excess pore water pressure obtained from this model and the FEM results are in good agreement. The nonlinear consolidation characteristics of composite foundation under different strain conditions were investigated, and the influence of penetration ratio, Cc/Ck and column diameter ratio on the average degree of consolidation and average settlement were further analyzed through numerical examples.