During the global coronavirus (COVID-19) pandemic, a huge amount of personal precautionary equipment, such as disposable face masks, was used, but further usage of these face mask leads to adverse environmental effects. Here, we evaluated the feasibility of using mask chips to reinforce clayey soil, testing this with static and impact loading, including uniaxial compression, diametral point load, and drop-weight impact loading tests. The concurrent influences of shape, size, and percentage of waste material were considered. Generally, the contribution of shredded face mask (SFM) was majorly attributable to its tensile reinforcement. As a consequence, the strength of the mixture, measured by the static tests, was increased. This property was enhanced by the addition of rectangular mask chips. We determined the optimum percentage of SFM, beyond which the uniaxial compression strength and the point load strength index decreased. An increase in the percentage of SFM in the soil produced a higher damping coefficient and lower stiffness coefficient, causing greater flexibility. This trend increased beyond 1.2% of SFM (by volume of clay soil). Generally, based on our results, 1-1.5% of SFM was the optimum content.

Geopolymers are recently recognized as superior sustainable alkali-activated materials (AAMs) for soil stabilization because of their strong bonding capabilities. However, the influence of freeze-thaw cycles (FTCs) on the performance of geopolymer-stabilized soils reinforced with fibers remains largely unexplored. In the current study, for the first time, the durability of polypropylene fiber (PPF) reinforced clayey soil stabilized with fly ash (FA) based geopolymer is investigated under FTCs, evaluating its performance during prolonged seasonal freezing. The effects of repeated FTCs (0, 1, 3, 6, and 12 cycles), different contents of alkali-activated FA (5 %, 10 %, and 15 %), varying PPF percentages (0 %, 0.4 %, 0.8 %, and 1.2 % with a length of 6 mm), and curing time (7 and 28 days) on the properties of stabilized samples have been determined through tests including standard Proctor compaction, unconfined compressive strength (UCS), mass loss, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The results revealed that a 0.4 % PPF concentration maximized strength in FA-based geopolymer samples by restricting crack propagation, irrespective of FA content, number of FTCs, or curing time. However, higher PPF contents lowered UCS values and Young's modulus due to fiber clustering and increased failure strain, respectively. Generally, an initial increase in UCS, Young's modulus, and resilience modulus (MR) of stabilized samples occurred with more FTCs because of their dense structure, delayed pore formation, and continued geopolymerization process and followed by a constant or decreasing trend in strength after 6 (or 3 in some cases) FTCs due to ice expansion in created air voids. Longer curing time resulted in denser samples with improved resistance to FTCs, especially under 12 FTCs. Moreover, samples with 10 % alkali-activated FA demonstrated the least susceptibility to FTCs. While initial FTCs caused no mass loss, subsequent cycles led to increased mass loss and remained below 2 % for all samples. Microstructural analysis results corroborated UCS test results. Although the primary chemical composition remained unchanged after 12 FTCs, these cycles induced morphological changes such as critical void formation and cracking within the gel structure. The stabilization approach proposed in this study demonstrated sustained UCS after 12 FTCs, promising reduced maintenance costs and extended service life in regions with prevalent freeze-thaw damage.

In cold regions, and considering the increasing concerns regarding climate change, it is crucial to assess soil stabilisation techniques under adverse environmental conditions. The study addresses the challenge of forecasting geotechnical properties of lime-stabilised clayey soils subjected to freeze-thaw conditions. A model is proposed to accurately predict the unconfined compressive strength (UCS) of lime-stabilised clayey soils exposed to freeze-thaw cycles. As the prediction of UCS is essential in construction engineering, the use of the model is a viable early-phase alternative to time-consuming laboratory testing procedures. This research aims to propose a robust predictive model using readily accessible soil parameters. A comprehensive statistical model for predicting UCS was developed and validated using data sourced from the scientific literature. An extensive parametric analysis was conducted to assess the predictive performance of the developed model. The findings underscore the capability of statistical models to predict UCS of stabilised soils demonstrating their valuable contribution to this area of study.

A numerical model that accounts for fully coupled long-term large strain consolidation and heat transfer provides a more realistic analysis for various applications, including geothermal energy storage and extraction, buried power cables, waste disposal, groundwater tracers, and landfills. Despite its importance, existing models rarely simulate fully coupled large-strain long-term consolidation and heat transfer effectively. To address this research gap, this study presents a numerical model, called Consolidation and Heat Transfer (i.e., CHT), designed for one-dimensional (1D) coupled large-strain consolidation and heat transfer in layered soils, with the added capability to account for thermal creep. The model employs a piecewise-linear approach for the coupled long-term finite strain consolidation and heat transfer processes. The consolidation algorithm extends the functionality of the CS-EVP code by incorporating thermally induced strains. The heat transfer algorithm accounts for conduction, thermomechanical dispersion, and advection, assuming local thermal equilibrium between fluid and solid phases. Heat transfer is consistent with the spatial and temporal variation of void ratio and seepage velocity in the long-term consolidating layer. This paper details the development of the CHT model, presents verification checks against existing numerical solutions, and demonstrates its performance through several simulations. These simulations illustrate the effects of seepage velocity, thermal boundary conditions, and layered soil configurations on the coupled heat transfer and consolidation behavior of saturated compressible soils.

Fly ash, a by-product of coal combustion, enhances the geotechnical properties of soil, primarily through its two types: class F and class C, known for their pozzolanic and cementitious properties, respectively. Numerous studies have explored the benefits of both types offly ash in stabilizing problematic expansive soils, which are characterized byweak strength, high compressibility, and significant volume changes that can damage infrastructure. However, direct comparisons between class F and class C fly ashes in improving expansive soils are limited. This study aims to fill this gap by conducting a critical review of research from the past 20 years, focusing on the impact of class F and class C fly ashes on the geotechnical properties of expansive clayey soils. Key parameters examined include Atterberg limits, free swell, unconfined compressive strength (UCS), and California bearing ratio (CBR). The findings indicate that both fly ash types reduce liquid limits and plasticity indices of clayey soils, with class C fly ash showing more pronounced effects. Additionally, class C fly ash significantly reduces soil swelling and enhances UCS and CBR, especially due to its higher CaO content. The study provides novel formulas to aid future researchers in predicting the behavior and performance of clayey soils stabilized with these specific fly ash types, offering a comprehensive examination of their geotechnical parameters.

This study investigates the impact of Washingtonia palm biomass on clayey soil shear strength using experimental and statistical approaches. The research examines the effects of Washingtonia filifera leaf powder, trunk fibres, and biochar derived from the rachis (pyrolyzed at 400 degrees C) on the properties of reinforced soil. Factors investigated include additive percentage (1%, 3%, 5%), sodium hydroxide (NaOH) solution concentration (2%, 5%, 8%), and immersion time (1 h, 4 h, 7 h). A Box-Behnken experimental design with 15 trials was employed to prepare soil-powder, soil-fiber, and soil-biochar composites. Direct shear tests were conducted on reinforced and unreinforced specimens to determine shear strength, cohesion, and friction angle. Results showed significant improvement in shear strength for all additives under normal stresses of 100, 200, and 300 kPa. Increasing additive content enhanced both cohesion and friction angle. Biochar-reinforced soil yielded the highest cohesion of 112 kPa, followed by fiber-soil with 70 kPa and powder-soil with 69 kPa, compared to 15 kPa in unreinforced soil. Additionally, soil mixed with powder, fiber, and biochar exhibited friction angle improvements of 57%, 93%, and 110% respectively, from an initial 13.5 degrees in unreinforced soil. Regression models were developed for shear stress responses using the Response Surface Methodology, and the influence of each parameter on the models was determined using ANOVA analysis. Using a combined approach of response surface methodology (RSM) and the desirability function, optimal values (5% of additives, 5% NaOH concentration, and 1 h of immersion time) were determined. These optimal values agreed well with the experimental results. It can be concluded that the inclusion of the three additives has positive benefits on the mechanical properties of the reinforced soil, with biochar demonstrating the most significant improvements.

The substantial development of desiccation cracks profoundly impacts the mechanical and hydraulic properties of clayey soils, potentially leading to various engineering challenges such as slope failures. Therefore, identifying the soil's cracking potential is crucial for guiding engineering design and construction processes. The aim of this study was to propose a method for cracking potential classification for clayey soils. To this end, standard cyclic wet-dry tests, capable of maximizing the soil's cracking potential, were proposed based on an analysis of the cracking behavior of lateritic soils under different wet-dry conditions. Subsequently, the cracking characteristics of several typical clayey soils (i.e., lateritic soil, kaolinite, bentonite, and attapulgite) were examined by standard cyclic wet-dry tests. Finally, a novel method for cracking potential classification of clayey soils was proposed incorporating the entropy weighting method. The results show that the most significant degree of cracking in lateritic soil is observed under vacuum saturation and 60 degrees C oven-drying, which is identified as the standard wet-dry condition. When the crack development stabilizes after multiple standard wet-dry cycles, the cracking potential of the soil is characterized by parameters such as the total crack length, maximum crack width, surface crack rate and the fractal dimension of the cracks. On this basis, a classification method is proposed to categorize the cracking potential of clayey soils into five levels: extremely weak, weak, medium, strong, and extremely strong. The cracking potential of different clayey soils was evaluated using this method, revealing that bentonite exhibited the highest cracking potential, classified as extremely strong.

In the Cangzhou area of China, groundwater over-exploitation has led to serious land subsidence, and the creep deformation of aquitards has been monitored and found to be closely related to the development of land subsidence. The objective of this paper is to develop a computational model to reflect the creep deformation of aquitards in this area. Firstly, creep tests were conducted on clayey soils with burial depths ranging from 65.7 to 121.7 m. The results show that the total strain consists of three parts: instantaneous strain, primary consolidation strain and creep strain. Creep-time curves and isochronous creep stress-strain curves under stepwise loading were obtained by using the Boltzmann superposition principle, and both types of curves were characterized by nonlinearity, and the creep curves as a whole showed a trend of stable development. Secondly, on the basis of analyzing the advantages and disadvantages of the classical rheological models for clayey soils, a nonlinear creep model of NCE_CS that can take into account the influence of primary consolidation is proposed. The model contains five parameters, which can be solved by using genetic algorithm, and then a simple determination method of the parameters is proposed. Finally, by comparing with the test data and the calculation results of four classical creep models, it is confirmed that the NCE_CS model can fit the creep curves better. The NCE_CS model was also successfully used to estimate the creep behavior in another subsidence area located in Renqiu City in northwest of Cangzhou. This study will provide a basis for quantitative calculation of creep of clayey soils in the Cangzhou area.

Reclaimed brick masonry makes up a noteworthy portion of construction and demolition waste (CDW), totaling approximately 31%, even exceeding concrete waste. This study proposes using reclaimed brick masonry to enhance the micro- and macro-properties of clayey soil. Extensive laboratory testing was conducted to evaluate the performance of reclaimed brick powder (BP) along with 5% cement content. The cement was used to generate chemical bonds with BP and soil grains. Micro-testing like XRF, XRD, EDAX, and SEM analyses confirmed the formation of CSH and CAH compounds which strengthened soil structure and enhanced its brittleness. However, after 10% BP, the addition of coarser grains converted the soil structure from dense to porous. Macro-properties assessment confirmed that 10% BP with 5% cement content is an optimum combination for selected soil. The addition of BP reduces the required amount of cement for soil stabilization, making it an eco-friendlier solution. The addition of the optimum combination decreased the wL, IP, FSI, wopt, and Cc and increased the gamma dmax, qu, CBR value, and sigma y significantly. It is also confirmed by the specimen's failure morphology analysis that BP with cement in clayey soil curtailed cement generated brittleness and enhanced ductility.

The unconfined compressive strength and shear strength represent the basic mechanical properties of clayey soil. If the soil in its natural state does not have sufficiently good mechanical properties, in engineering practice, it can be improved by chemical stabilisation of the soil. The stabilisation procedure involves adding reagent(s) to the soil with the aim of permanent improvement in the mechanical properties of the soil. In this study, the individual effects of seven different chemical stabilisers (traditional and alternative) on the mechanical properties of clayey soil were analysed. In the first stage of the research, comprehensive analyses were conducted on the effect of each of the selected stabilisers on the compressive strength of the soil. Each of the selected stabilisers was considered with three different content percentages in the soil mixture, with the aim of determining the optimal stabiliser content. Unconfined compressive tests were conducted to determine the unconfined compressive strength (UCS) of the soil. In the second stage of the research, extensive analyses of the effects of each of the selected stabilisers alone on the improvement in soil shear strength parameters (cohesion and internal friction angle), were carried out with the optimal content of each of the stabilisers. The shear strength parameters were determined by direct shear tests. Both stages of the research were conducted at three different time intervals after the chemical stabilisation (3, 14, and 28 days) in order to determine the long-term efficiency of the chemical treatment of clayey soil. Based on detailed comparative analyses, it was determined that all the selected stabilisers contributed to a lesser or greater extent to a significant improvement in the analysed mechanical properties of clayey soil. A statistical analysis of the obtained results was also conducted using the method of analysis of variance (ANOVA), on the basis of which the individual effect of each selected stabiliser on improving the mechanical properties of clayey soil was validated and quantified.