Soft Clay Research Articles

Feasibility of biochar for low-emission soft clay stabilization using CO2 curing

Use of traditional lime-cement binders on stabilizing soft sensitive clays pose a significant challenge for the construction sector to reach Finland’s carbon neutrality goals by 2030. Traditional stabilization recipes consisting of cement as binders contributing significantly to CO2 emissions (≅ 500 kg CO2 eq./ton in deep mixing alone). This laboratory study explores the feasibility of achieving near carbon-negative stabilization of soft clay leveraging accelerated CO2 curing (ACC) in biochar (BC) enhanced cementitious composites. BC, a by-product of the biofuel industry, is used as partial replacement of cement (0 %, 10 %, and 50 % of binder) in developing precast cementitious piles. One non-carbonated treatment and two ACC treatments are employed to assess their uniaxial compressive strength, thermogravimetric properties and CO2 sequestration capacity. The results demonstrate that synergistic effects of using BC with ACC not only enhances the compressive strength of the composites but also promotes CO2 uptake due to formation of stable carbonates. BC due to its surface functional groups, honeycomb porous structure, and hydrophilicity facilitated uniform CO2 diffusion in the clay matrix and likely improved internal curing. In ACC treated composites, the replacement of 50 % of cement with BC resulted in sufficient load-bearing capacity (≥50 kPa as per Finnish Guidelines) for both shallow and deep clay layers, making a suitable subgrade media for many types of geotechnical applications. The measured bound CO2 increased gravimetrically from 2 % to 41 % when cement was partially replaced by BC. In case of non-carbonated samples, 10 % partial replacement of BC provided high strength (≥200kPa). Life Cycle Assessment (LCA) of a case study of utilizing BC stabilized clay in deep mixing operations can potentially reduce net carbon emissions to −50 kg CO2 eq./ton.

Fully coupled finite strain consolidation analysis for soft clay treated by prefabricated horizontal drain with vacuum and heat preloading

This paper established a one-dimensional fully coupled finite strain consolidation analysis for soft clay treated by thermal prefabricated horizontal drain under vacuum and heat preloading with the consideration of thermal elastic viscoplastic (TEVP) behaviors of soft clay. Firstly, the governing equations for finite strain consolidation, heat conduction, and heat convention process have been carefully derived based on the well-established Gibson’s large strain consolidation theory and TEVP constitutive model. Secondly, the accuracy and reliability of the numerical method have been verified with benchmark cases and three physical model tests. Then, improvement of consolidation efficiency rate (IER) was defined and used to study the effect of three variables on consolidation efficiency. Last but not least, a graphical user interface (GUI) was provided to support researchers and engineers in utilizing the proposed numerical method for conducting consolidation analysis of soft soil treated in the same or similar fashion.

Strength and Compressibility of Soft Clay Reinforced with Group Crushed Polypropylene Columns

Strength and Compressibility of Soft Clay Reinforced with Group Crushed Polypropylene Columns

Enhancement of Shear Strength Properties of Soft Clay Using Coir Fiber-Coconut Husk Ash-Wood Ash Mixture

Soft clay is a problematic type of soil because it has high water content, low shear strength, low bearing capacity, and high compressibility. This study explores the effectiveness of stabilizing soft clay using a combination of coir fiber, coconut husk ash, and wood ash. This research investigated the impact of incorporating 0.75% coir fiber and varying levels of a coconut husk ash-wood ash mixture (ranging from 0% to 10%) on the shear strength properties of soft clay. The study applied two different curing times: seven and 21 days. An unconsolidated-undrained triaxial test was conducted following ASTM D2850-03. The results demonstrated that combining coir fiber reinforcement with chemical stabilization through the ash mixture significantly enhanced the deviatoric stress, cohesion, internal friction angle, shear strength, and elastic modulus of soft soil. Specifically, an 8% ash content with a 21-day curing time achieved the highest deviatoric stress and shear strength. This highest shear strength value was 210% greater than soil solely reinforced with coir fiber.

Parametric optimization of Cement-based solidification combined with vacuum-assisted filtration

This study delves into the parametric optimalization of cement-based stabilized soft clays (CBSC) combined vacuum-assisted filtration (VAF) technique on for engineering applications, focusing on the influence of the retarder, calcium source and intermittent time etc. Key findings include VAF benefiting CBSC’s strength for water discharge from the paste, where the UCS of CBSC treated with VAF can increase more than ten times higher than the untreated samples (e.g., 767 kPa versus 60 kPa). The added retarders extend the initial setting time, thus facilitating the removal of excessive water, that the 0.2 % addition of calcium lignosulfonate causes 6.5 % increment of dewatering mass. Especially, calcium lignosulfonate, working as a versatile agent of imparting significant improvements in the rheological properties of cement mixtures and augmenting the structural integrity of clayey soils, was found to significantly enhance the VAF efficiency and the UCS, of which 28-day’s UCS further increases comparing to referential group after VAF. The study also reveals that calcium sources, such as desulfurized ash and lime, are also vital in replenishing calcium ions lost during VAF and maintaining a strong alkaline environment, significantly contributing to the strength enhancement. Additionally, the intermittent timing is also critical to the filtration efficiency, where the intermittent time was recommended within two hours post-mixing. These findings offer valuable insights for the practical application of CBSC by the VAF assistance, particularly involving soft clays with high water content.

Oedometer Study Regarding the Consolidation Behavior of Nanjing Soft Clay

Ground settlement resulting from consolidation may lead to tilted buildings, cracks in the pavement, damage to underground utilities, etc. Therefore, it is crucial to understand the consolidation behaviors (including primary consolidation and secondary compression) of the soil of the subgrade. There is a large amount of soft clay deposited in Nanjing, located in the Yangtze River Basin. The consolidation behavior of Nanjing soft clay can significantly affect foundation design and the cost of construction. In this study, experimental measurements of the consolidation behavior of Nanjing soft clay were conducted, and parameters (such as pre-consolidation pressure, secondary consolidation index and secondary consolidation ratio) related to consolidation were assessed. The concept of simulated over-consolidation ratio (OCRs) was proposed, and the close relationship between primary consolidation and secondary compression settlement and the OCRs of Nanjing clay was investigated.

SIMULATION OF DISPOSAL SLOPE DESIGN USING THE SPENCER METHOD IN THE SOFT MATERIAL AREA OF PT XYZ, BERAU, EAST KALIMANTAN

PT XYZ is a coal mining company utilizing an open-pit mining system, currently serving as the subject of this research. Every mining activity requires a disposal area to place the residual materials covering the mineral deposits. This study aims to analyze the disposal slope's stability in accordance with KEPMEN ESDM No.1827 Tahun 2018. The slope design simulations were conducted using limiting variables, like the bench angle of 35°, bench heights of 5 meters and 10 meters, and bench widths of 10 meters, 20 meters, and 30 meters. Input data comprised material properties such as unit weight, cohesion, and internal friction angle for materials including soft clay, dense clay, bund wall, and waste. The data was obtained by tests on basic physical properties and triaxial compression tests. The conditions assumed the slope was saturated groundwater level while considering the earthquake coefficient. This research employed the Spencer method for slope stability analysis, resulting in a safe and volumetrically efficient slope design with bench angle angle of 35°, bench heights of 5 meters, and bench widths of 30 meters with the safety factor 1,11.

Layered seabed effects on buried pipeline response to ice gouging

In ice gouging analyses, the seabed is often simplified as a uniform material domain, over-looking the potential complexities inherent in layered seabed formations, which are wide-spread in numerous Arctic regions. This study investigates the pipeline response into the distinct seabed configurations, including layered soft over stiff clay, layered stiff over soft clay, and uniformly soft and uniformly stiff compositions, to ice gouging. This was achieved through comprehensive large deformation finite element (LDFE) analysis, employing a Coupled Eulerian Lagrangian (CEL) algorithm. Incorporation of the strain-rate dependency and strain-softening effects involved the development of a user-defined subroutine and incremental update of the undrained shear strength within the Abaqus software. The pipeline is explicitly incorporated into the model, allowing for a detailed investigation of its response to ice gouging phenomena within these layered seabed scenarios. This research demonstrates that simplifying a layered seabed into a uniform can be misleading. Such an approach can lead to significant errors, potentially overestimating or underestimating pipeline response to ice gouging. By incorporating these complexities, engineers can develop more optimized designs with enhanced safety margins in Arctic environments prone to ice gouging phenomena.

Influence of drainage conditions on piezocone penetration mechanism in offshore clays

ABSTRACT CPTu (piezocone penetration test) is widely used in engineering practice to determine various parameters of clays under partially drained conditions. However, most existing research is based on undrained or fully drained conditions for clays, leading to underestimation or overestimation of soil strength. By applying the Eulerian-Lagrangian large deformation finite element method to analyse the water-soil interaction, the CPTu driving mechanism in offshore saturated soft clays under different drainage conditions is revealed. An advanced hypoplastic constitutive model for clays is used to simulate the nonlinear behaviour of kaolin under different drainage conditions. The generation, accumulation, and dissipation of excess pore water pressure under different drainage conditions are analysed, as well as the influence of excess pore water pressure on cone tip resistance and the effective stress of the soil during the CPTu penetration process.

Effect of Glass Fiber Reinforcement on Bearing Capacity and Settlement of Foundations on Soft Clay

Effect of Glass Fiber Reinforcement on Bearing Capacity and Settlement of Foundations on Soft Clay

Electrokinetic Remediation of Cu- and Zn-Contaminated Soft Clay with Electrolytes Situated above Soil Surfaces.

Electrokinetic remediation (EKR) has shown great potential for the remediation of in situ contaminated soils. For heavy metal-contaminated soft clay with high moisture content and low permeability, an electrokinetic remediation method with electrolytes placed above the ground surface is used to avoid issues such as electrolyte leakage and secondary contamination that may arise from directly injecting electrolytes into the soil. In this context, using this novel experimental device, a set of citric acid (CA)-enhanced EKR tests were conducted to investigate the optimal design parameters for Cu- and Zn-contaminated soft clay. The average removal rates of heavy metals Cu and Zn in these tests were in the range of 27.9-85.5% and 63.9-83.5%, respectively. The results indicate that the Zn removal was efficient. This was determined by the migration intensity of the electro-osmotic flow, particularly the volume reduction of the anolyte. The main factors affecting the Cu removal efficiency in sequence were the effective electric potential of the contaminated soft clay and the electrolyte concentration. Designing experimental parameters based on these parameters will help remove Cu and Zn. Moreover, the shear strength of the contaminated soil was improved; however, the degree of improvement was limited. Low-concentration CA can effectively control the contact resistance between the anode and soil, the contact resistance between the cathode and soil, and the soil resistance by increasing the amount of electrolyte and the contact area between the electrolyte and soil.

Cyclic response of floating geosynthetic-encased steel slag columns in soft clay

Geosynthetic-encased stone column (GESC) technology for strengthening soft clay offers significant advantages in terms of cost-effectiveness, environmental sustainability, and engineering applicability. It is widely applied in treating soft foundations for railways, bridges, and embankments. This study evaluates the cyclic response of the geosynthetic-encased steel slag column (GESSC) composite foundation employing three-dimensional nonlinear finite element analysis. A numerical study is conducted to assess the cyclic response of floating GESSC considering the influence of key design variables, including cyclic load amplitude, loading frequency, geosynthetic encasement stiffness, and length-to-diameter ratio. Results show that both cyclic load amplitude and frequency affect the cumulative settlement and excess pore pressure within the GESSC foundation. Within specified limits, increasing the encasement stiffness and column length can significantly improve the GESSC load-bearing characteristics. The parametric study suggests an optimal geosynthetic encasement stiffness for the field prototype columns within the range of 4480–5760 kN/m and a critical steel slag column length of 10 times the column diameter.

Percolation Behavior of Soft Clay under Vacuum Suction

Percolation Behavior of Soft Clay under Vacuum Suction

Revisiting mixing uniformity effect on strength of cement-based stabilized soft clay

Despite the fact that mixing uniformity (i.e. the consistency of binder distribution) significantly influence the quality of ground improvement during in situ soil mixing projects, its quantitative evaluation was rarely concerned due to the difficulty of measurement from an engineering perspective. A methodology was proposed to quantitatively evaluate the mixing uniformity of stabilized soil using handheld X-fluorescence spectrometry (XRF), which is helpful to elucidate the significance of mixing uniformity on strength. In other words, the calcium content was monitored to ascertain the distribution of cement within the matrix, and a quantitative index was subsequently established. It was observed that an increase in mixing uniformity resulted in a transition in the behavior of the stabilized clay from a plastic to a brittle failure mode, and from a localized failure to a global shear failure under unconfined compression. Subsequent observation of the destruction process revealed that cracks were more readily formed in the low cement zones and then bypass the high cement zones. Furthermore, the effect of mixing uniformity on strength is likely to be amplified with prolonged curing periods. The enhancement of uniformity would increase the volume of the high binder zones, thereby enhancing the overall high-strength performance. The proposed methodology is capable of characterizing the discreteness between the tracked element's measured and theoretical contents, thusing avoiding the uncertainty associated with other indirect indicators. The convenience of the portable handheld XRF apparatus was confirmed, as it can be readily deployed in situ or ex situ to track calcium content within the stabilized mass after borehole sampling.

Sustainable ground improvement of soft clay using eggshell lime and rice husk ash

Stabilization of clay using lime or cement is conventionally accepted practice. Although it is effective, they impose several implications on the environment. Hence, it is high time that an alternate sustainable binder needs to be investigated. Eggshell, a waste from food industry, is an alternate source for calcite and can be considered to produce eggshell lime (EL). Also, rice husk ash (RHA), an agricultural waste product, is a silica rich source which is a pozzolanic material. In the current study, the efficiency of both the materials in stabilizing the soft soil is investigated and the results suggests that the plasticity and the strength characteristics of soft clay can be significantly improved by the addition of EL. After adding optimum concentration of 3 % EL, the liquid limit decreased from 74 % to 53 %, plastic limit increased from 27 % to 46 % and shrinkage limit increased from 8 % to 44 %. On increasing the EL content, the swelling got reduced from 88 % of virgin clay to 17 % in case of 3 % EL and finally to zero with 5 % of EL. Also, the addition of combination of EL and RHA to the soft clay has improved the strength characteristics significantly. As the curing days increased, slight variation was only seen in the plasticity characteristics which may be due to rapidity of cation exchange. But strength characteristics increased suggesting the occurrence of pozzolanic reactions and formation of gel. The 28th day strength of the clay treated with 3 % EL increased to as high as 757 kPa. The strength characteristics showed that as we increase the percentages of EL and RHA combination, the strength would increase tremendously much better than the treatment with eggshell lime alone. This is because of the supply of CaO and SiO2 sources. For 5 % of EL and 15 % of RHA, the 1 day curing strength was near to 500 kPa. With less concentration of eggshell lime and RHA, the treated soil was appearing to be more porous in SEM while when the binder concentration was increased, the pores were filled and presence of C-S-H gel was also detected. XRD test results also showed the presence of C-S-H gel.

Enhancement effect of calcium carbide residue and rice husk ash on soft soil: Small-strain property and micro mechanism

The resource utilization of calcium carbide residue (CCR) and rice husk ash (RHA) is helpful to save resources and alleviate environmental pollution. In this research, CCR and RHA were used to modify soft clay, and the resonant column test was conducted to explore its small-strain dynamic characteristics. The micro-mechanism of CCR-RHA modified soft clay (CRSC) was investigated by using scanning electron microscopy, X-ray diffraction and mercury intrusion tests. The findings demonstrated that the dynamic shear modulus of the CRSC increased with the increase of RHA content and confining pressure, but decreased with the increase of shear strain. In contrast, the damping ratio presents the opposite change law. The Hardin-Drnevich (H-D) model was used to fit the dynamic shear modulus/maximum dynamic shear modulus (G/Gmax)-shear strain γ and the damping ratio D-shear strain γ. As confining pressure increased, Gmax increased but Dmax dropped in CRSC specimens with the same RHA content. The changes of the fitted G/Gmax-γ curve could be divided into progressively decrease stage and rapid decrease stage, while the changes of the fitted D-γ curve could be separated into linear stage and slow stage, with the same turning point γ = 10−4. Microscopic tests revealed that the incorporation of CCR and RHA helped to promote the hydration reaction, and the generated hydration products such as calcium silicate hydrate were able to enhance the integrity and compactness of the CRSC. The results of this research putfward solid foundation for the application of CCR-RHA in the modification of soft soil.

Total stress model of clay considering small strain characteristics

Saturated soft clay has the characteristics of high compressibility, low strength, and high structural sensitivity. Its small strain characteristics have a significant impact on the deformation development and long-term bearing capacity of ocean engineering foundations. A total stress model for undrained cyclic loading of clay considering small strain characteristics was created based on the Overlay model. The proposed model was used to simulate the static or dynamic triaxial test results of over consolidated Chicago clay, remoulded normally consolidated Georgia kaolin, and normally consolidated clay Malaysia kaolin, respectively. The results verified that the model can simulate the static shear characteristics of clay. The model can also simulate the weakening of soil strength and strain accumulation under cyclic loading, and is suitable for analyzing the response of ocean engineering foundations under long-term cyclic loading.

Strain characteristics of reinforced soft clay around tunnel under metro loads

This study investigates the Strain characteristics of reinforced soft clay surrounding a tunnel subjected to cyclic loading, employing the Global Digital Systems cyclic triaxial test on the saturated reinforced clay near Shanghai Metro Line 4’s Hailun Road station. Initially, the study examines the impacts of frequency, dynamic stress amplitude (DSA), and loading cycles on cumulative plastic strain. Following this, the orthogonal design method was employed to organize tests, and an evaluation method for assessing soil strain was developed through mathematical statistical analysis. The results indicate at the constant vibration frequency, cumulative plastic strain increases with an increase in DSA and decreases with as load frequency increases. DSA is the primary factor influencing the axial deformation of subway tunnels, whereas the interaction between load frequency and vibration frequency is negligible. The findings suggest that measures to prevent and control subway tunnel settlement should concentrate on DSA during the early stages of subway operation.

Numerical Analysis of Creep Effects on the Settlement of PHC Pipe Pile in Soft Clay Treated by Deep Mixing Method

Numerical Analysis of Creep Effects on the Settlement of PHC Pipe Pile in Soft Clay Treated by Deep Mixing Method

Experimental investigation of the roughness, freezing temperature and normal stress on the shear mechanical action of frozen saturated clay-rock interface

Recently, with the increase in global temperature, the permafrost degradation trend has intensified, and the soil-rock binary slope in permafrost regions has become more unstable. Therefore, this paper focuses on the shear strength of the clay-rock interface in the binary slope. The three-dimensional roughness, freezing temperature, and normal stress are key factors affecting the shear strength of the clay-rock interface. The influence of freezing temperature can be further quantified by using the unfrozen water content (UWC), which was measured by nuclear magnetic resonance (NMR) technology. By analyzing experimental results, it can be concluded that the three-dimensional roughness can effectively improve the shear strength of the clay-rock interface under freezing conditions, and the shear strength increases with the growth of the climbing angle (ic). The influence of temperature can be attributed to the effect of UWC on the internal friction angle and cohesion of saturated clay. Compared with the internal friction angle, the cohesion of saturated clay decreases faster with the increase of UWC. In addition, the shear strength of the clay-rock interface rises linearly as the normal stress increases, therefore the Mohr-Coulomb criterion also can be used to characterize the shear strength of the clay-rock interface. An interesting finding is that significant tensile cracks will appear in the clay part around the large bulge under low normal stress and high roughness. It further confirmed the contribution of large bulges to the prevention of shear slides of soft clay. The quantification understanding of the shear mechanical action of the clay-rock interface can provide a reference for scientific disaster reduction in cold regions.