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• BHET treatment formed a flocculated bentonite matrix. • The flocculated bentonite matrix entraps water in its micropores. • BHET hydrogel constrained drainage path. • The hydroxyl groups of BHET retain a high amount of water. • The carbonyl and hydroxyl groups adsorb Pb2+. Polyethene terephthalate (PET) waste poses major environmental harm which can be minimized by reusing it in clay soil stabilization. In general, various polymers are known to reduce hydraulic conductivity and increase the shear strength of clays. However, the application of the effect of a chemically depolymerized form of PET, i.e., Bis (2-Hydroxyethyl) terephthalate (BHET) has not been performed as an additive in Compacted Clay Liners (CCLs) for landfills. This research focuses on the effect of the air curing period (1 and 28 days) on the hydromechanical behavior of BHET-treated SBM (0, 1, 2, 3, and 4 % by dry weight). Results from One Dimensional Consolidation tests showed that an increase in BHET content reduced both compressibility and hydraulic conductivity of SBM due to pore clogging mechanism of swollen BHET hydrogel, however, hydraulic conductivity reduced over 28 days of curing due to loss in re-swelling availability of the hydrogel, thereby allowing less tortuous paths to flow. Results from Consolidated-Drained Direct Shear tests showed that for 1 and 28-days curing, BHET treatment to SBM increased the cohesion (c') due to strong polymer interparticle bridging, however, polymer coating over the sand grains causes a reduction in its surface roughness to decrease the frictional angle (ϕ'). SEM (Scanning Electron Microscopy) and EDX (Energy-dispersive X-ray spectroscopy) analysis on BHET-treated specimens support the flocculation of bentonite, polymer bridging of sand and clay-sand polymer links. A significant Pb2+ removal capacity was also observed with BHET-treated SBM from the batch tests. FTIR (Fourier Transform Infrared Spectroscopy) analysis on batch sorption specimens confirms the role of the carbonyl groups (C = O) and hydroxyl groups (OH) present in the BHET structure indicating the possibility to adsorb Pb2+. The findings of the study suggested that a mechanism of interaction exists between sand-bentonite and BHET polymer and it can be adopted in CCLs design. [ABSTRACT FROM AUTHOR]

Stable isotope ratios of hydrogen (δ2H values) in local meteoric water correlate with those of nonexchangeable H (δ2H n) in bulk soil and organic matter, allowing for probabilistic spatial assignments to soil samples. We hypothesized that there is a similar correlation between the δ2H values of local meteoric water and the δ2H n value of soil clay fractions. The H pool of topsoil clay fractions is usually dominated by pedogenic clay minerals, which contain structural hydroxyl-H, preserving the δ2H values of ambient water at the time mineral formation. We applied a steam equilibration method with water vapors of known δ2H values to determine δ2H n values in soil clay fractions by eliminating the influence of easily exchangeable H. We collected topsoil samples from 24 locations on five continents with a wide variation in δ2H values of meteoric water. To calculate δ2H n values via steam equilibration, the equilibrium fractionation factor between exchangeable H in the clay fractions and equilibration waters (α ex–w) is needed, which is, however, unknown. We therefore assessed the effect of α ex-w values from 1 (no fractionation) to α ex-w = 1.08, which has been used in steam equilibration approaches of organic matter and bulk soil, on the δ2H n values of soil clay fractions. The δ2H n values of the clay fractions ranged from –167 ± SD1‰ for a northern Siberian sample to –44 ± 4‰ in western Kenya for α ex-w = 1 and from −191 ± 5 to –81 ± 5‰ for α ex-w = 1.08. The δ2H values of local meteoric water correlated significantly with the δ2H n values of the clay fractions (r = 0.85 for α ex-w = 1 and 0.65 for α ex-w = 1.08, p < 0.001). A multiple regression model including hillslope as a possible measure of the accumulation of clay minerals with a slightly different δ2H n value from nearby locations by eolian or aqueous transport in addition to the mean seasonal δ2H values of local meteoric water explained up to 89% of the observed variation in δ2H values of the clay fractions. Our results demonstrate that the δ2H n values of soil clay fractions are driven by the δ2H values of local precipitation on a global scale, irrespective of the used α ex–w value and influenced by the mineral type. Overcoming previous methodological limitations opens up opportunities for probabilistic spatial assignments of unknown organic matter-poor topsoil samples, applications to paleosoil problems or to experimentally track clay mineral neoformation in soils by tracer experiments. [ABSTRACT FROM AUTHOR]

• Soil thrust allows remotely operated vehicles to move forward. • Three failure modes are geometrically possible at the soil-track interface. • Upper-bound solutions for soil thrust are mathematically derived. • Resultant soil thrust is determined as the least upper-bound solution. • Proposed solution efficiently and accurately predicts the soil thrust. This study proposes a quick and reliable method for estimating the soil thrust in clay ground for a tracked vehicle based on limit analysis in three-dimensional conditions. With respect to the shape and location of failure surfaces in clayey ground, block, triangular wedge, and trapezoidal wedge failure modes were considered. Between the upper-bound solutions from the different failure modes, the least upper-bound solution was proposed as the soil thrust. To verify the proposed solution, it was compared to the model test and numerical simulations for a track system over model clay ground. The proposed upper-bound solution is expected to produce a reliable soil thrust quickly in real time, especially for submerged heavy-weight remotely operated vehicles (ROVs). [ABSTRACT FROM AUTHOR]

The impact of clay mineralogy on engineering properties relevant to road design, such as the strength and stiffness of road materials, has recently been the subject of intensive investigations, aiming at providing indirect measures of soil performance out of mineralogical data. This study deals with the effects of clay minerals on soil strength, expressed in terms of California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS), and stiffness, represented by the constrained modulus, which are commonly used as engineering properties for pavement materials. The study is performed on six clayey soils (S1-S6) of different geographic origins. Five of the six soils are highly plastic, potentially swelling, and one is kaolinitic soil. The mineralogical characteristics of the samples were analyzed through X-ray diffraction (XRD). The testing program included Atterberg limits, sieve analysis, CBR, UCS, and consolidation tests. The measured properties of the samples were compared in light of the mineralogical composition of the soils. The investigation showed that the kaolinite mineral is significantly more effective than the montmorillonite in reducing the plasticity of the clays. Higher strength indicators (CBR and UCS) were observed for samples with high kaolinite content (S4, S5, and S6). Moreover, the kaolinitic soil samples are characterized by a larger constrained modulus (E c) than the other samples. [ABSTRACT FROM AUTHOR]

The paper investigates the feasibility of using fine-grained soil as backfill material of geosynthetic-reinforced walls and slopes, through a laboratory study on pullout behavior of geogrids in granular layers. A series of pullout tests was carried out on an HDPE uniaxial geogrid in thin sand and gravel layers that were embedded in clay specimens. Aside from different soil arrangements, the influences of moisture content and overburden pressure on the geogrid pullout behavior is assessed and discussed. The tests were carried out at four different gravimetric water contents (GWC) on the dry and wet sides of the clay optimum moisture content (OMC), and overburden pressure values within the range σ v = 25–100 kPa. Particle Image Velocimetry (PIV) was used to capture digital images during the tests, which were processed to help with the interpretation and improved understanding of the soil-geogrid interactions at different GWC values. Results show that embedding geogrid reinforcement in layers of sand or gravel can significantly increase the pullout resistance in an otherwise moist clay backfill, and this improved pullout efficiency is greater at higher overburden pressures. The improvement in pullout capacity was observed in clay specimens compacted at both the dry and wet sides of the OMC. • Pullout performance of a uniaxial geogrid in different soils was studied. • Soils included clay, sand, gravel and clay specimens with single layers of reinforced sand or gravel. • The PIV technique was used to observe and interpret soil-geogrid interaction during the pullout process. • Factors examined included moisture content, particle size and thickness of granular layer, and overburden pressure. [ABSTRACT FROM AUTHOR]

• A unified gross traction algorithm is proposed for braked, towed, and powered wheels on clay. • The model is developed using the Database Records for Off-road Vehicle Environments. • The algorithm employs the ratio of average contact pressure to cone index. • The new equation can be implemented in off-road mobility models. A characteristic curve is presented for predicting gross traction of a wheel over a range of powered, towed, and braked modes on clay soils for slip ranging from positive 100% powered slip to negative 100% skid slip. The characteristic curve is a unified approach that relates the ratio of the contact pressure of the wheel to soil strength and predicts the gross traction coefficient over a continuous range of slip. The unified equation is defined by five inflection points: maximum/minimum traction, traction at zero slip, max change in traction with slip, and a shape factor coefficient. The inflection points aim to simplify the calibration of gross traction, slip, soil strength, and contact pressure by using functions adaptable to machine learning. The unified equation is comparable to historic traction equations but is unique in its ability to predict asymmetric braking and powered gross traction. The unified equation is supported and substantiated via error analysis by utilizing the Database Records for Off-road Vehicle Environments (DROVE) – a database constructed around the archived laboratory and field tests for wheels and tracks operating on different soils. The accuracy of the proposed model is assessed and compared to other conventional equations such as the Brixius equation and Maclaurin's extension of the Pacejka equation for off-road traction. [ABSTRACT FROM AUTHOR]

Soil erosion is a detrimental consequence of water flow that poses serious threats to the functionality/stability of earthen structures, dykes, river banks, canals, etc. Soil treatment/stabilization with additives remains a conventional and feasible technique to enhance soil erosion resistance. This study investigates the application of recycled concrete aggregates (RCA)- as a sustainable and environmentally-friendly additive- to lower the erosion propensity of clay soil. Jet Erosion Tests (JETs) were performed on treated soils comprising clay stabilized with 3 %, 5 %, 10 % and 15 % recycled concrete aggregates, and erosion parameters; namely, critical shear stress (τ c) and erodibility/detachment coefficient (k d) were measured. Laboratory findings elaborated that the increase in the RCA content and curing time of clay-RCA mixture significantly improved the erosion resistance as compared to the clay. The clay treated with 15 % RCA (after 28 days curing) demonstrated a 45 fold increase in τ c and 92 % decrease in k d , to the extent that the 'erodible' clay converted into the erosion 'resistant' clay-RCA blend. Concerning the practical implications, clay treatment with recycled concrete aggregates lowers the likelihood of concentrated leak erosion initiation and decelerates the progression of piping. [Display omitted] • Recycled concrete aggregate (RCA) is used as a stabilizer to decrease clay erodibility. • Jet Erosion Test (JET) is conducted to measure soil erosion parameters. • Stabilization with RCA turns the 'erodible' clay into an erosion 'resistant' mixture. • Clay stabilization with RCA reduces the possibility of erosion initiation. [ABSTRACT FROM AUTHOR]

Laboratory model tests were conducted to investigate the stability of the L-shaped caisson quay wall installed on the sandy soil with clay interlayer. A total of three L-shaped caisson models were cast to explore the effects of the loading position and the position and thickness of the clay interlayer on their stability under plate loading. The ultimate bearing capacity of the L-shaped caisson quay wall on clay interlayer foundation was reduced by a maximum of 41 % compared to sand foundation. The ultimate bearing capacity was significantly reduced when the distance of the clay interlayer to the rubble mound was less than 1/5 of the quay wall height. The applied surcharge made the lateral earth pressure coefficient higher than the active earth pressure coefficients and triangularly distributed along the L-shaped caisson wall. The modified Beton's method considered the effect of the toe length of the L-shaped caisson could more accurately predict the lateral earth pressure. The failure of the L-shaped caisson quay wall on the clay interlayer foundation has three forms Type-I, Type-II, and Type-Ⅲ which are influenced by the loading position, L-shaped caisson dimensions, and positions of the clay interlayer. [ABSTRACT FROM AUTHOR]

This study examines the application of nano-colloidal silica (NCS) in enhancing the mechanical properties of sandy clay soils. Consolidated undrained (CU) triaxial tests were performed on specimens containing varying percentages of NCS (0 %, 5 %, 10 %, and 20 %), which were then cured for different curing periods (1, 7, and 28 days) and subjected to three different confining pressures (50, 100, and 200 kPa). The findings revealed that the inclusion of 10 % NCS resulted in a significant 65 % increase in strength after 28 days compared to the untreated sample. However, higher NCS percentages, exceeding 10 %, led to a decline in strength as the excess NCS was not effectively utilized. The inclusion of NCS and increased curing time led to an increase in the brittleness of the soil and the application of confining pressure was able to reduce this brittleness.Furthermore, the use of 10% NCS and a curing period of 28 days significantly increased the stiffness and absorbed energy of the soil. Despite boosting the peak shear strength, NCS reduced the residual strength. Finally, polynomial modeling (Poly4) provided an excellent fit, enabling the characterization of the stress-strain and pore pressure-stain responses from the triaxial test. • A series of CU tests were conducted to investigate the strength behavior of sandy clay soil with NCS additive. • 10 % was the optimal content of NCS to modify sandy clay soil, which can improve strength. • The addition of NCS to the sandy clay soil enhances the strength and reduces the failure strain. • Empirical models were developed to predict and satisfactorily simulate q-ɛ and u- ε curves. [ABSTRACT FROM AUTHOR]

In this work, the mechanics of cone penetration during CPTu tests in Osaka clay, a natural structured silty clay, was investigated with the Particle Finite Element Method (PFEM). To describe the behavior of the soil, the FD_MILAN model, recently proposed by the Authors, was adopted. The model, based on the multiplicative decomposition of the deformation gradient, incorporates a scalar internal variable, the bond strength P t , to quantify the effects of structure. The macroscopic description of mechanical destructuration effects is provided by the hardening law of P t , according to which the bond strength decreases monotonically with accumulated plastic deformations. The brittle behavior resulting from the softening process associated to destructuration make the soil quite susceptible to the spontaneous development of strain localization in the form of shear bands. In order to deal with strain localization phenomena, the model is equipped with a non-local version of the hardening laws, incorporating a material constant – the characteristic length ℓ c – which provides the material with an internal length scale. The objective of this work was to get some insight on the effects of the characteristic length and of the initial degree of structure on: the kinematics of the soil deformation around the advancing cone tip; the evolution of soil structure with accumulated plastic deformations; the excess pore pressure field generated in the soil as a result of the hydro-mechanical coupling between the solid skeleton and the pore water, and the net cone resistance measured at the base of the cone. The results of the PFEM simulations show that the deformations around the piezocone are strongly affected by the characteristic length. For heavily structured soils, when ℓ c is relatively small with respect to cone radius, the accumulated plastic deviatoric deformation field is characterized by clearly visible shear bands while, as ℓ c increases, the detection of localized deformation regions becomes more difficult, if not impossible. This depends on the fact that, for large values of ℓ c , the shear band width may be of comparable size to the cone radius. In all cases, the soil around the advancing piezocone is subjected to a very strong destructuration process, which leads to the complete loss of bond strength in a large region around the cone tip and shaft. As a consequence, the use of conventional N c values from the literature in the interpretation of the CPTu test performed in heavily structured soils could provide undrained strength values closer to the ultimate undrained shear strength. At the same time, the use of empirical correlation to estimate the yield stress in oedometric conditions would lead to a significant underestimation of the overconsolidation ratio. [ABSTRACT FROM AUTHOR]

• The failure model of stiff-over-soft clay varying with soil parameter. • A new calculation method for ultimate bearing capacity of spudcan. A jack-up platform is prone to a 'punch-through' accident when working on the stiff-over-soft clay foundation. To assess the risk of punch-through, it is necessary to plot the bearing capacity-penetration curve for evaluating the penetration depth of the pile leg or to calculate the ultimate bearing capacity of the spudcan and compare it with the preload. However, accurate prediction of spudcan bearing capacity is not easy. In this paper, the failure mode about the stiff-over-soft clay under different geological conditions when punch-through occurs is discussed using coupled Eulerian lagrangian (CEL) method, varying the strength ratio between soft and stiff soil layers, the thickness of stiff soil relative to the spudcan diameter, and the non-homogeneity factor of soil strength. Based on the soil failure model with varying soil parameters, a new calculation method for ultimate bearing capacity of spudcan is proposed and then verified against existing centrifuge test results. The results show that the shape of soil shear plane in stiff clay is significantly affected by the strength ratio of soil layer and the non-homogeneity factor of soil strength. And the presented new method whose prediction errors compared with centrifuge test results are less than 5%, has better calculation accuracy than the ISO (International Organization for Standardization) method, which is valuable in guiding the calculation of the ultimate bearing capacity of the spudcan and ensuring the safe operation of the jack-up drilling units on stiff-over-soft clay. [ABSTRACT FROM AUTHOR]

The paper quantifies the uncertainty of material parameters of the hypoplastic model for clay resulting from the experimenter's choice about what laboratory data are utilised in the calibration process. The results of several 1D compression tests and undrained triaxial shear tests performed on twenty different fine-grained soils are considered in various combinations to yield a scattered set of material parameters for each soil. A hierarchical probabilistic model separating the variations and correlations of parameters within one soil from variations and correlations among different soils is formulated. The posterior distribution of the probabilistic model parameters is obtained by means of the Bayesian inference. The results allow for stochastic simulations on a structural level even when only point estimates of material parameters are available. • Material parameters of hypoplastic model for clay are determined for twenty soils. • Calibration uncertainty of the parameters is quantified for general fine-grained soil. • Covariance within one soil and between different soils is formulated separated. • Results are directly applicable in stochastic analysis with different clayey soils. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) is the largest terrestrial carbon (C) pool and is vulnerable to climate and land-use changes. Promoting the stabilization of SOC will reduce climate change-induced C losses. Mineral-associated organic carbon (MAOC), formed by the association of organic carbon with silt- and clay-sized minerals, is the major stabilized SOC fraction and key to sustaining soil health and mitigating climate change. However, the role of silt and clay in MAOC formation remains unclear in dryland ecosystems where microbes and plants are frequently under water stress. The current paradigm assumes that the main role of silt and clay is to adsorb and aggregate organic compounds. In a semi-arid environment, using a naturally occurring gradient of increasing soil silt and clay content partially due to aeolian dust inputs, we show that silt and clay also enhanced microbial decomposition of plant C inputs and microbial turnover, increasing microbial C inclusion into the MAOC pool. Finer-textured soils had higher soil water availability and higher volume of habitat available to microorganisms. The enhanced microbial processing interacted with changes in plant C inputs to further control the relative contribution of MAOC to SOC. Our results suggest SOC models should include soil textural effects on microbial activities and microbial C production in addition to physical protection of SOC. Our study also suggests that aeolian dust inputs can increase soil silt and clay contents and improve nutrient availability in dryland ecosystems, potentially mitigating the SOC loss under climate change and increasing the resilience of ecosystems to drought. • Silt and clay not only protect microbial carbon from decomposition but also enhance its production in dryland soils. • Silt and clay relieved environmental stress on microbes by increasing soil water content and pore spaces. • Microbial processing interacts with plant inputs to control the contribution of MAOC to SOC. • The effect of litter quality on the accrual of MAOC relative to SOC was negligible in drylands. [ABSTRACT FROM AUTHOR]

• Clay content and subfreezing temperature coupling affect soil FT deformation. • The clay aggregate evolution during FT accounts for the complex deformation. • Full-range evolution of soil structure is characterized via NMR and X-CT. • Quantitatively analyze contribution of micro/meso structure change to deformation. Climate change brought about significant freeze–thaw (FT) deformation of clayey soils distributed in cold regions, which resulted from soil structure evolution including pore size distribution change and crack development. However, the formation of clay aggregate that dominates the soil deformation behavior during FT remains unclear. This study investigated the effects of clay contents (5 %, 10 %, 15 %, and 20 %) and subfreezing temperatures (−5 °C, −10 °C, and −15 °C) on the soil FT deformation properties by isotropic isothermal FT tests. Meanwhile, the soil structure evolution was characterized via Nuclear Magnetic Resonance and X-ray Computed Tomography. The results indicated that the frost heave ratio (η) and thaw settlement coefficient (δ) non-linearly varied with clay content and subfreezing temperature. Specifically, the minimum η and δ were observed in the specimen with 10 % clay content, and the maximum η and δ were identified at −10 °C. This phenomenon can be attributed to the clay aggregate forming bimodal or unimodal pore size distribution (PSD) with different initial clay contents. The freezing characteristics of inter- and intra-aggregate pore water were determined by the solid-water interaction. Moreover, the FT action altered the structure of clayey soil by the change in PSD and the generation of cracks. The contribution of pore size change and crack development to the total volume change before and after FT was quantitatively analyzed. It demonstrated that pore size change was more important for the total volume change in specimens with lower clay content and higher subfreezing temperature, whereas crack development mainly contributed to the total volume change in the rest of the specimens. This study provides a deep insight into the deformation characteristics of clayey soils under different climate conditions in cold regions. [ABSTRACT FROM AUTHOR]

The Kahramanmaraş Earthquakes that occurred on 6 February 2023 resulted in extensive structural failures, including damages caused by soil liquefaction. This study focused on investigating the excessive settlements observed in buildings along Ataturk Boulevard in the Golbasi district, with a primary emphasis on the toppling failure of the Kayı Apartment. Field exploration, laboratory testing, and bearing capacity analyses were conducted to understand the failure mechanism. Since the foundation soil of Kayı Apartment predominantly consisted of clay, soil liquefaction alone could not explain the observed failure. Instead, the cyclic softening of clayey soil underground shaking was identified as a significant factor contributing to the damage. As one of the rare case histories documenting a failure caused by cyclic softening, the results of the study also shed light on the excessive displacements observed in nearby buildings with fewer stories that managed to withstand the earthquake without experiencing complete bearing capacity failure. [ABSTRACT FROM AUTHOR]

• The seepage of water in clay deviated from that predicted by Darcy's law. • Macropore and mesopore are the dominant pore types in clay. • The weakly bound water (outer layer) is the main type of water in clay. • The movable water content was closely related to the permeability of the clay. Water flow in saturated clay soil at low hydraulic gradients usually occurs via pre-Darcy flow. The occurrence of the pre-Darcy flow phenomenon is attributed to the adsorption of water on pore walls via surface forces. However, a clear understanding of the amount of water that is movable in saturated clay soil and the distribution of movable/immovable in the microstructure of clay soil is lacking. Furthermore, it is difficult to accurately evaluate the effect of water mobility on the seepage characteristics of clay soil. To investigate the effects of water mobility and pore microstructure on pre-Darcy flow in clay soil, nine clay samples were used to conduct constant head permeability experiments. The results showed that the seepage of water in clay deviated from that predicted by Darcy's law, and with increasing hydraulic gradient, the apparent water permeability first increased and then tended to remain constant. The porosity ϕ , average pore radius r p , sorting coefficient S p , mean pore radius D m , dry density ρ and tortuosity τ had major influences on the stable apparent water permeability k s. In contrast, the influences of maximum pore radius and median pore radius on k s were relatively weak. Macropores (>1.0 μm) and mesopores (100–1000 nm) were the dominant pore types in the clay and accounted for almost 80 % of the overall porosity. The water in saturated clay can be divided into four types according to interfacial forces. The results showed that weakly bound water (in the outer layer) was the main type of water in the clay. Among the four types of water, k s had the strongest correlation with the proportion of free water. The mobility of water was affected by coupling between interfacial forces and hydraulic gradients. The movable water content was closely related to the permeability of the clay. [ABSTRACT FROM AUTHOR]

This study examines the impact of incorporating sodium alginate (SA) biopolymer into soft clay using the deep soil mixing method (DSM). SA-stabilised samples were tested under high-moisture (A) and low-moisture (B) conditions to assess their mechanical properties, chemical attributes, freeze-thaw resistance, and microstructure. Results indicate that samples cured under condition A outperformed those in condition B, primarily due to enhanced biopolymer gel formation. In both conditions, increasing the SA content and curing time led to higher peak strength, stiffness, and pH. The higher SA ratio improved ductility in condition A but increased brittleness in condition B. At the 28-day mark, a 1.0% SA ratio and a pH range of 8.2–8.4 were crucial for specimen strength increase. Freeze-thaw cycles had minimal impact, with a modest reduction in compressive strength observed. Scanning electron microscopy showed face-to-face bonding between clay particles and the gel-like materials due to electrostatic attraction. After 14 days, ramifications occurred around the core structure, and after 28 days, high agglomeration structures appeared, attributed to clay particle flocculation. Energy-dispersive X-ray (EDX) analysis indicated an increase in the Si/Al ratio boosted sample strength, while X-ray diffraction (XRD) results showed no crystalline phase in SA-stabilised samples due to encapsulating clay minerals with gel-like materials. In summary, this study suggests that SA biopolymer offers an eco-friendly, sustainable option for enhancing soft clay with DSM. • The UCS and stiffness of stabilised clay soil increase with increasing sodium alginate and curing time. • The Ductility (D) significantly increases with increasing sodium alginate ratio. • High moisture conditions have a positive impact on expansion gelation. • The freezing-thawing cycles have minimal impact on sodium alginate stabilised clay. • Face-to-face bonding and electrostatic attraction occur between clay particles and gel-like materials. [ABSTRACT FROM AUTHOR]

Clays often have unfavorable geotechnical properties that limit construction applications on them. There is a need for sustainable soil improvement techniques to enhance the strength and stiffness of clays. While previous studies have explored clay stabilization with common supplements like cement, lime and fly ash, the utilization of sludge pond ash (SPA) as a sustainable additive has been limited and there is a lack of understanding of the interactive effects of SPA proportion, moisture content, and curing time on the mechanical behavior of clay. The objective of this study is to examine the mechanical properties of clay enhanced with SPA under different curing conditions. To achieve this, different proportions of SPA were mixed with the clay to obtain accurate findings on the efficacy of SPA addition on compaction and unconfined compressive strength (UCS) of the clay to determine mechanical properties. Scanning electron microscopy (SEM) provided imaging of clay improved with SPA to evaluate the microstructural changes in soil texture. Firstly, the sludge from a pond burned at 1000 °C (the optimal temperature determined by microstructural X-ray diffraction (XRD) analysis) was added to the mixture as 0, 2, 4, 6, 8 and 10% of the soil's dry weight, respectively. The studied samples were prepared with the same energy (equivalent to the standard Proctor test) at different moisture contents and were tested in a uniaxial device at 7, 28 and 56 days of curing. It was found that adding SPA to the base soil decreased the maximum dry unit weight (MDUW). On the other hand, it increased the optimum moisture content (OMC) of the compacted mixture. The study examined the combined effects of moisture content and curing time on the compounds, revealing that these factors induced a decrease and an increase in the UCS , respectively. The addition of SPA as an additive material to the clay mixture was found to exert a significant effect on the strength properties of the clay, with an optimal percentage of around 10%. Empirical correlations were also developed to predict the UCS of the SPA -improved clay with high precision. Furthermore, SEM analyses show that SPA acts as a glue gel between aggregate in the mixture and coat clay particles that changes the blend texture and alters weak bonding to aggregate-like particles. The results of both macro- and micro-scale analyses collectively confirm the superior efficacy of the optimal SPA replacement in enhancing various strength and stiffness properties of the clay. • Sludge Pond Ash (SPA) addition into the clayey soils lightens the specimens. • The optimum required SPA to activate pozzolanic reactions is 10%. • The addition of SPA to the soil enhances the UCS and reduces the failure strain. • Experimental data on the UCS can be effectively correlated using polynomial models. • From SEM , the SPA led to an increase in the amount of cement gels in the mixture. [ABSTRACT FROM AUTHOR]

The content of clay particles has a key influence on the physical and mechanical properties of microbial solidified granite residual soil. Microbial-induced calcite precipitation (MICP) treatment method of "mixing + grouting" was used to prepare microbial solidified granite residual soil samples with different clay contents and to explore the influence of clay content on the reinforcement effect of microbial solidified granite residual soil. A series of direct shear tests, disintegration tests, and microscopic observation tests was conducted to quantitatively analyze the influence of clay content on the shear strength and disintegration resistance of microbial solidified granite residual soil. The conclusions are summarized as follows: the shear strength and disintegration resistance of granite residual soils solidified by MICP treatment were remarkably improved, with the shear strength increasing by 9%∼16% when the clay content varied from 10%∼40%. The internal friction angle of the granite residual soil with different clay contents increased and then decreased with the increase in clay content. The cohesion of the microbial solidified granite residual soil increased with the increase in clay content, and the internal friction angle reached a minimum of 20% clay content (17.27°), which is 31.85% lower than that of 0% clay content (25.34°). The cohesion of the microbial solidified granite residual soil reached a maximum of 40% clay content (39.54 kPa), which is 8.69 times higher than that of 0% clay content (4.55 kPa). The MICP treatment technology is capable of effectively improving the shear strength and disintegration resistance of granite residual soils. The MICP treated process produces calcium carbonate precipitates that link the sand particles and fill the pores between the soil particles, increasing the number of larger agglomerates in the granite residual soil, which is the essential reason for the improvement in the softening and disintegration of the granite residual soil when exposed to water. • A novel microbial treatment method of granite residual soil was proposed. • The strength and disintegration mechanism of MICP treated granite residual soil was investigated. • The effect of clay content on MICP treated granite residual soil was studied. [ABSTRACT FROM AUTHOR]

• RCA-clay mixture can be a reliable and eco-friendly alternative as subgrade layers. • Recycled concrete aggregate (RCA) inclusion in expansive clay subgrade leads to higher strength and resilience modulus. • The optimum proportion of Clay-20 %RCA-9 %GBS mixture is found to be strong enough to be used as subgrade/subbase layers. • The model proposed by MPDGE provides a good prediction for the M r values of treated expansive clay subgrade. • This paper can encourage and further promote the use of recycled concrete aggregate in the road construction industry. In urban areas, due to urban development and lack of space, roads may be built on the expansive clay subgrade. Expansive clay soils increase in volume when in contact with water and shrink by losing water. Recycled concrete aggregates (RCA) are one of the components of construction and demolition (C&D) wastes that can be used instead of natural resources in road construction projects. In this research, a combined method of mechanical and chemical stabilization was used to evaluate the use of RCA as a mechanical stabilizer and granulated blast furnace slag (GBS) as a chemical stabilizer to improve the strength and resilience characteristics of expansive clay subgrade. Laboratory results showed that adding RCA wastes to expansive clay subgrade reduced atterberg limits (LL, PL, and PI) and optimum water content (OWC) and increased the maximum dry density (MDD), California bearing ratio (CBR), and uniaxial compression strength (UCS). Expansive clay subgrade with 20 % RCA was treated with GBS chemical stabilizer in order to achieve a minimum 7 days target strength of 1.7 MPa for subbase application. A series of repeated load triaxial (RLT) tests were performed according to the AASHTO T307 procedure and resilient modulus (M r) values of the stabilized clay subgrade specimen were evaluated at different curing times under cyclic loading. Also, the proposed Mechanistic-Empirical pavement design Guide (MEPDG) model was used to predict M r values in different confining and deviator stresses which showed a good correlation with the measured M r values. Finally, the improvement of the clay subgrade stabilized with RCA and GBS was also supported by SEM analysis. The results obtained from this research showed that the use of RCA, in addition to reducing disposed waste and environmental pollution, can improve the physical and mechanical characteristics of expansive clay Subgrade layers. [ABSTRACT FROM AUTHOR]

Silicon (Si) is an abundant element in terrestrial ecosystems and makes essential contributions to agricultural crops, environments, and industries; however, current knowledge of Si speciation in soil systems is based primarily on crystalline mineral types with limited information about the effect of Si-adsorbed species on the most chemically reactive clay fraction. Herein, we investigated Si speciation in the clay-sized fraction of tropical soils. Silicon K-edge X-ray absorption near edge structure (XANES) spectra of clay samples, together with a wide range of reference compounds varying in clay and Fe/Al oxide mineralogy, showed the predominance of Si in a beidellite structure and of Si adsorbed to montmorillonite and to kaolinite. Unique features, including a pre-white-line feature, white-line position and intensity, and post-edge numbers and positions of Si reference spectra, could differentiate most Si reference standard spectra. Silicon adsorbed to goethite, Si-ferrihydrite-natural organic matter complexes, and Si in the structure of biotite, illite-smectite, chlorite, quartz, and Si nanoparticle, variously occurred in different samples. The CaCl 2 extraction data revealed that extracted Si was below the limits of Si deficiency in one-half of the total soil samples and accounted for only 0.02% of total soil Si. Soil extractable Si had a positive correlation with pH, organic matter, and clay. Our results present a novel application of Si K-edge XANES as a tool for identifying Si speciation in natural clays that are the most chemically reactive phase of Si retention and release in terrestrial and aquatic systems. [Display omitted] • Reference spectra of silicon sorbed to clay mineral and Fe/Al oxides are presented. • Si-ferrihydrite-natural organic matter complexes have been synthesized and proposed. • White-line and post-edge features of Si reference spectra can identify most Si standards. • Structural Si in beidellite and Si sorbed to montmorillonite/kaolinite dominated Si species. • Si nanoparticles could form in clay-sized fractions of soil systems. [ABSTRACT FROM AUTHOR]

This study investigates the replacement of conventional stabilizers with eco-friendly alternatives, with a specific focus on enhancing pavement subgrade applications. This research aims to evaluate the impact of lime-zeolite treatment on the properties of clayey subgrades and its potential to outperform traditional stabilization methods. Various tests, such as Proctor compaction, Atterberg limits, swelling, and unconfined compressive strength (UCS), were performed considering the plasticity index variation. Optimal zeolite replacement led to significant improvements in the clayey soils' behavior. It reduced the plasticity index by up to 9.4% and almost eliminated swelling. Furthermore, unconfined compressive strength (UCS) values were enhanced by up to 7.56 times when compared to untreated soil. Ultrasonic pulse velocity (UPV) tests indicated substantial increases in primary wave velocity (V p) and constrained modulus (M v), reaching values of 2650 m/s and 9600 MPa, respectively, representing improvements of around 6.5 times and 50 times over untreated clay. The results highlight the remarkable efficacy of lime-zeolite substitution, particularly at a 25% replacement level. The improvements in plasticity, swelling, and strength characteristics signify the potential of this eco-friendly approach in pavement subgrade enhancement. The significant increases in UPV parameters provide insights into the improved structural integrity of the treated soils. This innovative approach offers valuable contributions to pavement subgrade design by addressing plasticity, swelling, and strength issues in clayey soils, ultimately leading to more sustainable and effective infrastructure projects. • Lime-zeolite treatment controls the soil plasticity and swelling potential. • Lime-zeolite treatment improves the primary wave velocity and constrained modulus. • Zeolite accelerates the chemical and pozzolanic reactions in lime-treated clays. • Lime-zeolite treatment provides a dense medium with strong interparticle forces. • Subgrades with expansive or soft clays can be well-modified using lime and zeolite. [ABSTRACT FROM AUTHOR]

• This study showed that PVC aggregates stabilized with cement improve the mechanical characteristics of clay soils. • Development of response models for each test (MDD, OMC, C, φ, and UCS) as a function of three factors, i.e. B, C, and PVC. • Experiments and modeling allowed estimating the values of MDD, OMC, C, φ, and UCS for non-laboratory formulated mixtures. The present research work aims to use the mix design approach to develop some models that can predict the mechanical properties of clayey soil. For that, the proctor compaction test, direct shear test, and uniaxial compression test were performed on bentonite (B) and other mixtures incorporating different proportions of polyvinyl chloride (PVC) aggregates stabilized with cement (C). The experimental and modeling results indicated that a good correlation existed between the three factors (B, C, and PVC) and the values of the maximum dry density, cohesion, and compressive strength responses. It was also found that the majority of models gave relatively good correlation coefficients (R2 ≥ 0.90) for all the responses under study. The results obtained indicated that this bentonite had a compressive strength 180.24 kPa, with a cohesion 64.71 kPa, and a maximum dry density equal a 1.571 gr/cm3. In addition, the experimental and modeling findings showed that the mixture including C (55% ± 10%), PVC (35% ± 10%), and B (10% ± 10%) exhibited a quite high cohesion of 103 kPa (more than one and half times that of unreinforced samples), while the highest compressive strength of 445 kPa (two and half times more than that of unreinforced samples) was obtained for the mixture comprising of C (50% ± 10%), PVC (25% ± 10%) and B (25% ± 10%). In addition, it turned out that these results are very encouraging in terms of environmental protection because this technique allows recycling and valorizing huge quantities of PVC waste produced throughout the world. It has been revealed that PVC wastes can be utilized in the geotechnical field to improve the mechanical behavior for clay soils, and to assess the values of maximum dry density, cohesion, and compressive strength of mixtures not made in the laboratory using the derived statistical models. [ABSTRACT FROM AUTHOR]

• CEB are alternative to fired clay bricks in regions with low energy coverage. • By-products of the road industry allow to stabilize very clayey soil for production of CEB. • Vegetable aggregate can be used to produce earth-based materials, just like other biosourced materials. • Biosourced CEBs have the erodibility performances 10 times higher than the normative recommendations. In developing countries such as Benin, the use of clay soils to produce fired clay bricks can be confronted with the problems of availability of the energy required for firing. The present study assesses the possibility to use these clay resources to produce compressed earth blocks (CEB) as alternative to fired clay. CEBs were produced by physically stabilizing a highly clayey soil with 0/5 granite dust, followed by chemical stabilization with 8 w t % cement and the incorporation of 0 to 1.5 w t % quackgrass straw. This resulted in dimensional stability of CEB, despite a slight swelling of 16.33 mm/m upon immersion observed only on CEB containing 1 and 1.5 w t % straw. The coefficients of resistance to abrasion are well improved above the standardized minimum threshold of 2 cm 2 / g , i.e. 29.7 to 7.72 cm 2 / g for straw contents of 0 to 1.5 %. Moreover, the maximum erosion depth of the CEB of 32.6 m m / h , is well below the limit of 120 m m / h , despite using a water pressure 10 times higher than the standard pressure of 50 k P a. These results testify to the durability of stabilized CEB. However, the dry and wet compressive strength decreased from 5.1 to 2.84 M P a and from 3 to 1.02 M P a , respectively, with the straw content of 0 to 1 %. This does not hinder the use of these CEB for sustainable building construction, as the values of their compressive strength in dry and wet conditions were respectively above the required values of 2 M P a and 1 M P a. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive investigation of torpedo anchors penetrating into sand-overlying-nonhomogeneous clay deposit, with the main objective of predicting the anchor embeddment depth after it penetrates through the top sand layer. The behavior of the torpedo anchor and soil failure mechanisms during the installation process are analyzed using large deformation finite element (LDFE) methods. To validate the numerical models, comparisons are made with data from existing centrifuge and field tests. An extensive parametric study is then conducted, exploring a wide range of soil properties, soil layer thickness, anchor velocities, and parameters related to torpedo anchor geometry. Two intriguing findings emerge from the analysis. Firstly, there is an evolving soil failure, with the strain-softening region expanding in the clay near the boundary between the two soil layers. Secondly, the velocity profile during both the acceleration and deceleration stages varies with different sand layer thicknesses, displaying a nonlinear relationship with the anchor's final embedment depth. Based on the findings, a simple design procedure is developed to account for the influencing factors on the anchor installation depth. This procedure is expected to be valuable for engineers seeking to estimate the behavior of torpedo anchor installations in sand-overlying-nonhomogeneous clay soil deposits. • The installation of torpedo anchors in sand-overlying-nonhomogeneous clay is explored through the CEL analyses. • The installation depth, velocity profiles and failure patterns of the anchor are studied through parametric analyses. • A design procedure is proposed for predicting the anchor penetration depth in sand-overlying-nonhomogeneous clay deposit. [ABSTRACT FROM AUTHOR]

Red clay, a widely distributed soil, weakens significantly when exposed to water. This poses challenges for using it as a foundation for urban infrastructure, as rainwater scouring, infiltration, and external loads can cause uneven settlement and landslides, compromising structural integrity. To address this issue, we propose the use of a green highly permeable water-soluble polyurethane material (PSP) as an alternative to conventional curing agents. We conducted a series of tests to evaluate the efficacy of PSP in improving the mechanical properties of red clay. Acoustic emission tests were used to examine the failure mode of PSP-stabilized red clay, while scanning electron microscopy provided microscopic insights into clay stabilization mechanisms. The triaxial test results establish empirical relationships between strength, stiffness, toughness, and control parameters (PSP content, moisture content, and confining pressure) of the stabilized clay. We found that PSP-stabilized soils exhibit ductile failure and strain hardening, with PSP curing agents effectively enhancing clay strength and stiffness within a 3-day curing period. Univariate analysis reveals positive correlations between peak energy absorption values, peak stress rates, and PSP content, while showing a negative correlation with moisture content. Confining pressure variations have relatively little effect on peak stress ratios of PSP soils, and PSP soil stiffness minimally influences confining pressure as PSP content increases. Importantly, PSP treatment significantly increases ductility compared to untreated clay soils, distinguishing PSP soils from hydric soils. • Microscopic strengthening mechanism of PSP-treated red clay soils. • The relationship between failure mode, mechanical properties, PSP content and moisture content is analyzed. • The empirical formulas for estimating peak stress, initial tangent modulus and failure ratio are established. • A solution for the rapid trenchless curing of clay is presented. [ABSTRACT FROM AUTHOR]

The paper proposes a rigorous analytical approach to predict interaction between torsionally loaded piles and saturated clay soils. The soil deformation mechanism around the pile is determined using the non-associated and anisotropic constitutive model, SANICLAY, along with the axisymmetric condition, equilibrium equation, and boundary conditions. By solving the derived governing equations, the hoop shear stress against rotation curve is obtained, including elastic, elastoplastic, and critical state processes. Taking advantage of the finite-difference method, the torque-rotation behavior of the pile and the stress-strain state of the soil around the pile are figured out. The proposed approach is compared with a FEM simulation and a parametric analysis is conducted to investigate the effect of overconsolidation ratio and in-situ coefficient. Model pile tests and field tests are used to manifest the validity and capacity of the model. The results demonstrate that the present approach can well predict the torque-rotation response of the pile and can reflect some important phenomena observed in pile tests. • This paper presents an approach for predicting soil-pile interaction of torsionally loaded piles in saturated soils. • The soil mechanism around the pile is determined using the non-associated and anisotropic constitutive model, SANICLAY. • The stress-rotation curve is derived by considering axisymmetric condition, equilibrium equation, and boundary conditions. [ABSTRACT FROM AUTHOR]

The aim of the paper is to simulate the response of a deep excavation supported by sheet pile walls and lime-cement columns. The application of the deep mixing technique using lime-cement products in deep excavations changes the initial state of the natural soil and creates substantial displacements associated with the installation effects. In this paper, the influence of lime-cement stabilisation was investigated using the finite element method for an instrumented braced excavation. The 2D finite element analyses were performed with advanced constitutive models for both natural clay and stabilised soil, exploiting the laboratory test made on both field mixed and laboratory mixed stabilised clay samples. The numerical results show that taking account of installation effects provides realistic predictions of deformation, excess pore water pressure evolution, as well as the structural forces in the struts. [ABSTRACT FROM AUTHOR]

Earth pressure balance shield (EPBS) has become the mainstream construction method for metro tunnels in China, which inevitably generates a large amount of discharged soil, putting enormous pressure on the environment and the cost. In order to realize the resource utilization of shield dregs, this paper explored the feasibility of recycling the waste silty clay as a soil conditioner in EPBS tunnel construction. Mixtures of bentonite, wasted silty clay, carboxymethyl cellulose (CMC), and tap water in different ratios were prepared. Defining the substituted ratio as the mass ratio of silty clay to (bentonite + silty clay), the effect of the substituted ratio on the apparent viscosity, flow curve, rheological model and physical stability of bentonite-silty clay composite slurry were investigated. Furthermore, the relationship between slurry microstructures and macroscopic rheological properties was revealed by scanning electron microscopy (SEM). The results show that the constitutive relationship of bentonite slurry (0% substituted ratio) can be well described by Herschel-Bulkley model. The silty clay has a deteriorating effect on the rheological behavior and physical stability, and changes the flow pattern of the composite slurry. Microscopically, CMC makes the clay particles in slurries form agglomerates with larger particle sizes, and can absorb excess free water from the slurry, thus significantly increasing the yield stress and apparent viscosity. The recycling scheme proposed in this study can not only greatly reduce the procurement cost of raw materials, but also eliminate the transportation and disposal costs of discharged soil, which has significant environmental benefits and promising application prospects. [ABSTRACT FROM AUTHOR]

• C:N ratios in soils and particle-size fractions were assessed in tropical highlands. • Sand C:N ratios increase with depth, whereas silt and clay C:N vary little. • C:N ratios decrease with increasing Ca and Mg contents, CEC, and clay activity. • N-enrichment in clays is likely controlled by mineralogy. • R-NH 3 + sorption onto clays can be critical to organic matter stabilization. Factors affecting soil organic carbon (SOC) retention in the tropics are relatively well known, but this is not the case for N retention and thus C:N ratios, a common proxy for organic matter stability. Recent data suggest that SOC and N concentrations vary with climate, whereas soil C:N ratios depend on particle-size fractions contents. However, such knowledge is still incipient for tropical soils, native vegetations and deeper soil layers, which are critical to understand how land use and climate change affect C and N fluxes. We assessed SOC, N and C:N ratios in bulk soils and sand, silt and clay fractions, and their correlations with other soil properties under native tropical forests in the highlands near Lavras, Brazil. Soil samples were collected to 1-m depth in soils of contrasting texture and mineralogy, formed on quartzite, sericite-schist, gabbro, itabirite, ironstone, meta -limestone, gneiss, and phyllite. Mean SOC and N concentrations were generally high, whereas mean soil C:N ratios varied from 9.5 to 18.7 among parent materials, and only in three soils C:N ratios varied considerably with depth. Enrichment factors (EFs) were generally < 1 in the sand and silt fractions for SOC and especially N. Conversely, EFs for clay were mostly > 1 for SOC and even higher (up to 6.58) for N. Such trend indicates that SOC and N are concentrated in clays, and more importantly, that N sorption is favored compared with SOC, and likely dependent on clay mineralogy. Soil C:N ratios decreased with increasing values of exchangeable bases, due to higher N in the most fertile soils, suggesting that a mechanism of R-NH 3 + cationic sorption is likely involved. Our results suggest that soil N is a critical component of the overall stabilization of soil organic matter onto clays of tropical soils, deserving further investigation also under temperate climate and other zones. [ABSTRACT FROM AUTHOR]

• The combination of MgO and fly ash effectively solidifies salt-bearing clay in areas subjected to seasonal freeze–thaw cycles. • The substitution of conventional solidifying materials with fly ash constitutes a sustainable and ecologically responsible approach to consolidating clay soils. • The cementation of soil particles is efficiently accomplished by the carbonate compounds generated from magnesium and calcium. This paper presents an innovative method for improving the strength of salt-bearing clay under freeze–thaw cycles. The active magnesium oxide (MgO) and industrial waste fly ash were employed as primary solidifying materials in the seasonal freezing soil reinforcement process, and the reinforcement effect is achieved through carbonate crystals generated through carbonization tests. The solidification effect was investigated with varying ratios of solidifying materials, salt content, and freeze–thaw cycles. The experiment results revealed that the combination of active MgO and fly ash effectively enhances the strength of salt-bearing clay. Specifically, compared to unsolidified soil, the soil solidified with 8 % active MgO (8M0F) and a combination of 4 % active MgO and 4 % fly ash (4M4F) demonstrated a significant increase in ultimate strength by 14 and 12 times, respectively. Moreover, the number of freeze–thaw cycles exhibited a negative correlation with ultimate strength, whereas the salt content demonstrated a similar negative correlation. Microscopic analysis revealed that the 8M0F sample produced mainly magnesium carbonates and hydrogen and oxygen compounds, whereas the 4M4F sample generated primarily magnesium and calcium carbonates. The resulting compound crystals efficiently filled the internal pores and cemented the soil particles, leading to a substantial increase in strength. Overall, these results indicate that the active MgO combined with fly ash solidifying method can offer a viable and sustainable solution for improving the strength of salt-bearing clay in areas with seasonal freeze–thaw cycles. [ABSTRACT FROM AUTHOR]

Liming with 'structure lime', comprising approximately 80–85% ground limestone and 15–20% slaked lime, has been promoted in subsidised environmental schemes in Sweden since 2010 to increase clay aggregate stability and mitigate particulate phosphorus losses to surface waters. To date, approximately 65,000 ha have been structure-limed. Apart from stabilising aggregates, liming may also improve other physical properties, such as soil strength. This study examined the effect of increasing application rate (0–16 t ha-1) of structure lime on soil strength, approximated by horizontal (draught requirement) and vertical (penetrometer resistance) measurements, in eight field soils (clay content 26–38%) to which structure lime had been applied two, three, four or six years previously. Draught requirement when cultivating with a multipurpose cultivator significantly decreased (by 11%) with the highest application rate of structure lime (16 t ha-1) compared with an unlimed control. This reduced the wheel power requirement by 7.1 kW and diesel consumption by 1.2–1.4 L ha-1, and lowered CO 2 emissions by 3–4 kg ha-1. To clarify the general effect of structure liming, the mean value of all limed treatments was compared with that of the unlimed control. This showed that structure liming in general significantly reduced the draught requirement (by 7%). However, penetrometer resistance measurements revealed no significant effects of structure liming and no relation between draught requirement and penetrometer resistance measurements. Overall, the results indicate that structure liming can reduce fuel consumption, due to easier soil tillage, and thus lower CO 2 emissions. • Cultivator draught requirement was measured in structure limed field trials. • A towing eye with sensors that can measure forces in three directions was used. • Structure liming reduced horizontal draught requirement by 7%. • Reductions corresponded to decreases of 1.2–1.4 L diesel ha-1 and 3–4 kg CO 2 ha-1. • Structure liming did not affect penetrometer resistance in this study. [ABSTRACT FROM AUTHOR]

• Effect of salinity in grout on the performance of soilcrete was evaluated. • Seawater has no effect on long-term UCS of soilcrete contains inactive clays. • In active clay at cement <15 %, curing time had a negative effect on the strength. • The change in LL and UCS with salinity is similar. S oil-cement columns created by the injection of grout into the soil are common in practice for stabilizing soft soil in coastal areas. The behavior of clay-cement under marine conditions, especially considering the effect of both the clay mineral type and water salinity, has been less considered. The current study investigated the effects of high salinity grout on the mechanical and the physical behavior of cement-stabilized marine clay at a range of cement contents and water-to-cement ratios. The performance of the cement-stabilized marine clay was compared with those of kaolinite as an inactive clay and bentonite as an active clay. The results showed that, when saline water was used in the soil–cement mixtures containing kaolinite or marine clay, there was no decrease in strength and the cement content had no effect on the results. For active bentonite at 5% and 10% cement contents, the curing time had a negative effect on the strength; over time, the strength of the mixtures decreased. In practice, there should be no concern about the use of saline water to create grout at cement contents greater that 15%. However, if the clayey soil contains active minerals, a cement content of less than 15% is not recommended. [ABSTRACT FROM AUTHOR]

• Thermal conductivity for frozen soil is higher than that of unfrozen soil. • Higher thermal conductivity of frozen and unfrozen soils at higher clay content. • Current models cannot predict correctly thermal conductivity of frozen sandy soil. Thermal conductivities of five sandy soils subjected to freezing-thawing and drying-wetting cycles were determined. Specimens were prepared at five different clay contents of 0, 5, 10, 15, 20% prior to compaction at the Proctor maximum dry density. Soil specimens were saturated prior to freezing-thawing and drying-wetting experiments. During a freezing-thawing cycle, soil's thermal conductivity and unfrozen water content were measured at different temperatures ranging from -3 °C to 0 °C. During a drying-wetting cycle, soil's thermal conductivity was measured at different water contents. The experimental results were then compared with predictions by two of the most appropriate existing models, namely De Vries's and Johansen's models, in order to provide insights into the effects of clay content on soil thermal conductivity at (saturated and unsaturated) unfrozen and frozen states. [ABSTRACT FROM AUTHOR]

Fluoride, a naturally occurring chemical element, is largely insoluble in soils. More than 90% of the fluoride in soil is bound to soil particles and is unable to be dissolved. As part of the soil, fluoride is predominantly located in the colloid or clay fraction of the soil, and the movement of fluoride is strongly affected by the sorption capacity of the soil, which is affected by pH, the type of soil sorbent present, and the salinity. The Canadian Council of Ministers of the Environment soil quality guideline for fluoride in soils under a residential/parkland land use scenario is 400 mg/kg. In this review, we focus on fluoride contamination in soil and subsurface environments, and the various sources of fluorides are discussed in detail. The average fluoride concentration in soil in different countries and their regulations for soil and water are comprehensively reviewed. In this article, the latest advances in defluoridation methods are highlighted and the importance of further research addressing efficient and cost-effective methods to remediate fluoride contamination in soil is critically discussed. Methods used to mitigate fluoride risks by removing fluoride from the soil are presented. We strongly recommend that regulators and soil chemists in all countries explore opportunities to improve defluoridation methods and consider adopting more stringent regulations for fluoride in soil depending on geologic conditions. [Display omitted] • Fluoride in soil and subsurface environments are discussed. • Sources of fluoride in soil/water and their effects are overviewed. • Soil quality parameters for residential land use in various countries are summarized. • Recent advances in defluoridation methods in soil are highlighted. • Globally organized various mitigation programs are presented. [ABSTRACT FROM AUTHOR]

A systematic study was performed in laboratory model tests to assess the response of cement-improved reinforced monopiles to lateral monotonic and cyclic loading in clay. The overall load‒deflection behavior and profile of the bending moment was fully studied in monotonic tests, in addition to the p - y curves of the reinforced and unreinforced piles. Cyclic loading tests were carried out at different cyclic magnitude values and load ratios, and the cement-improved soil reinforcement range was also varied. This study provides several insights into the ongoing development of the deflection, unloading stiffness and bending moment of cement-improved soil reinforced piles as cycling progresses, which can provide empirical design recommendations for cement-improved soil reinforced monopiles subjected to lateral cyclic loading. Based on the typical p - y curve models of pile in soft clay and stiff clay, by considering the proportion of soil resistance shared by cement-improved soil and soft clay around a pile under lateral load, the modification factors of two parameters p u and y 50 are derived, and then a modified p - y curve model of cement-improved soil reinforced piles in soft clay is established. • A systematic study for the monotonic response of the cement-improved soil reinforced piles have been fully studied. • Several fresh insights into the ongoing development of deflection, unloading stiffness and bending moment of reinforced pile as cycling progresses are provided. • The modification factors of two parameters p u and y 50 are derived, and a modified p - y model of cement-improved soil reinforced pile in clay is established. [ABSTRACT FROM AUTHOR]

In order to analyze the change of static pressure pile characteristics in silt and silty clay with the penetration depth, two PHC pipe piles were penetrated in the field in the actual project, and the research was based on the full section test technology and FBG test technology. The results show that the pile pressure increases with the increase of the pile penetration depth; The change of pile tip resistance is affected by the soil layer hardness; When the pile tip is in the transition stage, the pile tip resistance increases significantly; In the process of pile penetration, the hardness and brittleness of the soil layer will be affected by the pile penetration, and the different soil layers will have different effects on the pile tip resistance of the two piles; When the pile goes deep into the soil, the pile side resistance will change slowly, but it will usually increase. This fluctuation is related to the difference of the soft and hard layers of the soil layer, and will also be subject to performance constraints; The pile end resistance ratio in hard soil will be smaller than that in soft soil, which will further affect the load sharing ratio of the test pile. The test results can provide support for practical engineering technology. • For the purpose of analyzing how jacked pile properties in silty soil and silty clay vary with penetration depth based on full-section test technique and FBG test technique. • Through the test, using the total cross-section test technology continuously collecting the whole process of penetration of pile end resistance, analyses the change rule. • Compared with the traditional test methods and test components, the technology in this paper is more advanced, the data has higher accuracy. [ABSTRACT FROM AUTHOR]

Thermal desorption technology can effectively remediate fuels-contaminated clayey soil. However, the microscopic mechanism for the contaminant desorption on clay is still unclear, especially with the existence of water on clay surfaces. In this study, a combination method including TGA experiments, multi-phase and multi-component kinetic models, and MD simulation was proposed to reveal the thermal desorption mechanism of n -dodecane in unsaturated clay. Results showed that the thermal desorption behavior of the free nonaqueous phase liquid (NAPL) and the adsorbed phase of n -dodecane or water could be identified by the multi-phase and multi-component kinetic models based on the desorption process rate obtained by thermogravimetric analysis (TGA) experiments. The activation energy of the NAPL phase (49–69.9 kJ/mol) was lower than the adsorbed phase (90 kJ/mol). The activation energy of the NAPL phase had the same linear relationship with its mass on kaolinite and montmorillonite, while adsorbed phase only existed on the kaolinite surface. MD simulation showed that water demonstrated competitive adsorption with n -dodecane on montmorillonite surfaces and prevented the formation of the adsorbed phase while having little influence on the n -dodecane adsorption on kaolinite surface, which agrees well with the kinetic analysis of the TGA experiments. With the combination of macroscopic experimental analysis and microscopic molecular simulation, it can be concluded that the mass of the NAPL phase limited the desorption behavior, while the interaction between the clay mineral surface and n -dodecane was the key factor that dominated the thermal desorption behavior of the adsorbed phase. The presented results provide new insight into the desorption mechanism of hydrocarbon on clay minerals, which is of significance for the design of thermal desorption remediation. [Display omitted] • Kinetic model for thermal desorption can identify n -dodecane and water on clay. • Adsorbed water prevent adsorbed n -dodecane formation on highly hydrophilic clay. • Mass of the NAPL phase is the rate-limiting factor of its desorption behavior. • Adsorbed n -dodecane desorption depends on its interaction with mineral surface. [ABSTRACT FROM AUTHOR]

PHC pipe pile cooperated with jacked method is widely used in recent years. The excess pore water pressure of pile-soil interface caused during jacked PHC pipe driving would produce important effect on jacked pile construction and bearing characteristics. Two full scale jacked-in piles are penetrated into the clayey soil and studied by monitoring the law of generation and dissipation of excess pore water pressure. The law of excess pore water pressure with penetration depth and time is also analyzed. From this test results, excess pore water pressure of the pile-soil interface increases to the peak and then begins to decrease, but it remains large. The excess pore water pressure of S1 test pile pile-soil interface decreases from 201.4 kPa to 86.3 kPa, and decreases from 374.1 kPa to 114.3 kPa for S2 test pile. The excess pore water pressure of pile-soil interface rises first at the initial stage of consolidation, and it dissipates when the hydraulic gradient between pile-soil interface and soil around the pile disappears. The dissipation degree of excess pore water pressure reaches from 75% to 85%. The proposed solution provides certain engineering significance for jacked pile construction and bearing capacity design in the clayey foundation. • Through on-site monitoring of the distribution and dissipation of excess pore water pressure at the pile-soil interface, the stress characteristics of the pile-soil interface during the PHC pipe pile sinking process were studied. • The maximum ratio of excess pore water pressure of pile-soil interface to effective pressure of overlying soil is 1.08, and gradually decreases along the pile. • The excess pore water pressure at the pile-soil interface caused by pile sinking is approximately linearly increased with the depth of the soil. • Studying the generation and dissipation of excess pore water pressure at pile-soil interface is helpful to reveal the important characteristics and bearing capacity of pile-soil interface during pile-sinking. [ABSTRACT FROM AUTHOR]

The need for the efficient remediation of soils impacted by per- and polyfluoroalkyl substances (PFAS) is substantially growing because of the notable upsurge in societal and regulatory awareness of this class of chemicals. To remediate PFAS-contaminated soils using mobilization approaches, the choice of appropriate techniques highly depends on the soil's composition, particularly the clay content, which significantly affects the soil's permeability. Here, we investigated the PFAS mobilization efficiency from soils with different clay contents by using two techniques: electrokinetic (EK) remediation and hydraulic flushing. Artificial kaolinite was added to a loamy sand soil to prepare four soil blends with clay contents of 5, 25, 50, and 75%, each contaminated with perfluorooctanoic acid (PFOA) and perfulorooctanesulfonic acid (PFOA) at 10,000 μg/kg. EK remediation was conducted by applying a low voltage (30 V) with a current of 100 mA, and hydraulic flushing was carried out by applying a hydraulic gradient (HG) with a slope of 6.7%. Results show that, with a 14-day treatment duration, the EK-mobilization efficiency was enhanced substantially with the increase of clay content (removal of PFOS increased from 20% at 5% clay to 80% at 75% clay), most likely due to the increase of electroosmotic flow due to the higher content of particles having a zeta potential (i.e., clay). For HG, increasing the clay content significantly suppressed the mobilization of PFAS (removal of PFOS decreased from 40% at 5% clay to 10% at 75% clay) due to a notable decrease in the soil's permeability. Based on the results, applying hydraulic flushing and washing techniques for mobilizing PFAS would be appropriate when treating permeable soils with a maximum clay content of about 25%; otherwise, other suitable mobilization techniques such as EKs should be considered. [Display omitted] • PFAS mobilization from soils with different clay contents was investigated. • PFAS adsorption to soils increases at higher clay contents. • The clay content in soils substantially affects the mobilization efficiency of PFAS. • PFAS removal from soils by electrokinetics increases with higher clay content. • Hydraulic flushing works best for mobilizing PFAS from permeable soils. [ABSTRACT FROM AUTHOR]

• Evaluating different unstudied Easter Moroccan clayey materials for potential industry usage. • The impact of raw materials' properties and industrial processing on the characteristics of the final product. • Investigation of mineralogical, chemical, and physical properties of the raw materials. • Experimental measurement of the thermal and mechanical properties of the produced bricks. • Comparative study between laboratory and industry scale bricks. This study aims to the valorization of soil materials (unfired and fired) for sustainable buildings in eastern Morocco. To make this study more representative, four clay soils from different areas were considered in this investigation (i.e., Zaio, Oujda, Lota, and Midar). Geotechnical tests revealed that all samples exhibit a high clay content and medium plasticity. X-ray diffraction, thermal gravimetric analysis and energy dispersive X-ray spectroscopy of the soils showed the presence of quartz, calcite and several clay minerals. The significant clay content and the high density of the bricks (1589–1713 kg.m−3) have an effect on the properties of the unfired solid clay brick. Experimental results have shown that the thermal conductivity and compressive strength of the unfired solid clay brick vary between (0.77–1.07 W.m−1K−1) and (1.7–2.4 MPa) respectively. The cavities and firing process for fired hollow clay bricks contributed to the increase in thermal and mechanical resistance of the bricks by (0.19–0.4 W.m−1K−1) and (2.9–5 MPa) respectively. After identification of all the samples, the authors' justified choice was to use the soil collected from the Lota site for the ANSYS-Fluent hybrid wall case studies. In comparison to the other cases, the configuration (Mortar/Fired hollow clay brick and unfired solid clay brick/Mortar) demonstrated a 2 h improvement in time lag and a considerable decrease in the amplitude of the temperature fluctuation. Therefore, unfired solid clay bricks and fired hollow clay bricks may be used in combination to provide thermal comfort for a sustainable building. [ABSTRACT FROM AUTHOR]

There is a clear nonlinear characteristic of the seepage velocity of clay; however, its existing prediction models are mostly empirical, and the prediction accuracy needs to be improved. In this paper, the soil–water retention curve is considered an indirect indicator reflecting the scale distribution of the soil seepage channel to calculate the initial hydraulic gradient of the microscopic seepage channel, based on which a nonlinear seepage velocity prediction model for clay soils was established in combination with the Tao-Kong model. To verify this model, the saturated seepage velocity of three dry densities of Hunan clay under different hydraulic gradients was measured with a GDS permeameter. Using the new model, the saturated seepage velocity under different hydraulic gradients was predicted and compared with experimental results and prediction results from existing models. The comparison showed that the new model has the highest accuracy. Both the prediction and experimental results showed that seepage in Hunan clay exhibits a nonlinear behavior and has an initial hydraulic gradient. When the seepage pressure is small, the permeability coefficient is small; as the seepage pressure increases, there is a steep increase in stair, and the larger the dry density is, the larger the initial hydraulic gradient. [ABSTRACT FROM AUTHOR]

• Contribution of organic carbon (OC) to total specific surface area (SA) is unclear. • EGME SA correlated with water sorption SA, except for OC-rich soils. • OC contribution to SA depended on clay mineralogy and OC content. • OC contribution ranged from 7.5 to 13.9 m2/g per %C depending on clay mineralogy. • For samples rich in montmorillonite, OC negatively contributed to total SA. Soil specific surface area (SA) reflects the quantity and quality of the soil mineral and organic fractions. For soil samples that have similar clay mineral types, clay content and or organic carbon (OC) contents are good predictors of SA. However, the magnitude of the OC contribution to SA for different soil types is unclear, particularly since SA varies depending on which method or probe molecule is used to measure it. Consequently, we set out to (i) quantify the contribution of soil OC to total SA for soils with varying clay mineralogy, and (ii) assess the effect of probe molecule (EGME or H 2 O) and water sorption direction on the contribution of OC to the total SA. We utilized 330 soil samples (clay = 1 to 89 %; silt = 2 to 78 %; OC = 0.03 to 34.9 %) that were grouped according to clay mineralogy and OC content. The total SA was measured using EGME adsorption (SA E) and water adsorption and desorption (SA H2O). The contribution of OC to SA was examined using regression and partial correlation analyses that combined clay, silt, and OC as explanatory variables. Results showed that SA E values were strongly correlated to SA H2O , except for OC-rich soils where SA E was significantly lower than SA H2O. Apart from montmorillonite-rich samples, OC contribution to SA E was smaller than for SA H2O. Organic carbon had a positive contribution to desorption SA H2O for all sample groups, except for montmorillonite-rich samples; OC contribution was 7.5, 10.7, and 13.9 m2/g per %C for illite-rich, kaolinite-rich and OC-rich samples, respectively. There was no significant effect of water sorption direction on the OC contribution to SA H2O. Partial correlation analyses that accounted for clay and silt contents confirmed a negative contribution of OC to SA E or SA H2O for soil samples dominated by montmorillonite clay minerals. We can conclude that for the soil types investigated here (except montmorillonitic soils), OC has a positive contribution to total SA, and the magnitude of the contribution depends on the clay type. [ABSTRACT FROM AUTHOR]

• Na- and Ca-montmorillonite contents of the clay mixtures were estimated using visible-near-infrared (Vis-NIR) spectra. • Partial least square regression (PLSR) models well estimated Na- or Ca-montmorillonite contents of the clay mixtures. • PLSR models estimated Na- or Ca-montmorillonite content of bentonite samples. • PLSR models performed better than single regression (SLR) and multivariate (MLR) regression models. The aim of this study was to evaluate whether Na- and Ca-montmorillonite and the swell-indicating properties (i.e., free swell index, water uptake capacity, and cation exchange capacity (CEC)) of clay mineral mixtures can be estimated using visible-near-infrared (Vis-NIR) spectral features. The data regarding four types of reference clay minerals (KGa-1b, kaolinite; IYd, illite; SWy-3, Na-montmorillonite; STx-1b, Ca-montmorillonite) and binary and ternary mixtures of the reference clay minerals (SWy-3/KGa-1b/IYd, and STx-1b/KGa-1b/IYd) with specific mass percentage ratios were used as a calibration dataset. The absorption spectral features could be correlated well with changes in the clay mineral content of the mixtures. The leave-one-out cross-validation results showed that the partial least square regression (PLSR) calibration models produced the best prediction in the following order: Na or Ca-montmorillonite, kaolinite, and illite amounts in the mixtures. The calibration models produced better predictions in the ascending order of CEC, free swell index, and water uptake capacity, regardless of the multivariate statistical methods and type of exchangeable cations in montmorillonite. Validation using an independent dataset indicated that the PLSR model predicted the Na- and Ca-montmorillonite content in clay mineral mixtures and bentonite samples. The results of this study provide the possibility of using Vis-NIR absorption spectral features as a screening tool for predicting the montmorillonite content with different interlayer cations in relatively pure clay soils (e.g., bentonite), if the calibration model is developed using the specific montmorillonite contained in the clay soil of interest. [ABSTRACT FROM AUTHOR]

The applications of helical piles have grown significantly and they have become more popular for construction, especially as a potential offshore foundation system in recent years, owing to their distinct benefits over alternative systems. Helical piles may be installed in groups to support heavy loads; therefore, a reliable design requires an accurate assessment of their behavior. The present study used finite element modeling to extensively analyze the uplift and lateral behavior of group piles installed in soft clay soil. The problem was modeled using Plaxis 3D software, and the model was validated using laboratory scale model test data. The validated model is then utilized to investigate the group effect for three distinct configurations, namely rectangular, triangular, and square patterns, with helical piles placed at varied center-to-center spacing's. The term "group efficiency" is used to describe the group effect of each group on the ultimate capacity. The findings showed that the group efficiency is significantly influenced by the number of piles, center-to-center pile spacing, and the failure criteria assumed to interpret test data. The load-transfer mechanism was also investigated and reported for varying group configurations. Finally, for the assumed failure criteria, the provision of an optimum spacing ratio is suggested for both tensile and laterally loaded group helical piles. • Assumed failure criteria substantially affect group behavior and predicted performance. • The group effect becomes insignificant under uplift and lateral loading when the pile spacing exceeds 3D. • As the group size increases, the uplift and lateral group capacities also increase. • The displacement contours are significantly affected by the helical pile spacing ratio (S g /D) and configuration types. [ABSTRACT FROM AUTHOR]

This paper presents the results of a centrifuge study in which swell of an expansive clay profile was induced in the centrifuge. A factor which has previously hindered such research is the time required to induce significant swell in-flight, within a reasonable time frame. In this study the use of an artificially fissured fabric together with geotextile layers allowed for a significant magnitude of swell to be achieved within a matter of hours. Measurements of matric suction and water content throughout testing highlight the potential difficulties associated with such measurements in a fissured profile. The suction in clay along the interfaces of fissures can be significantly reduced almost instantaneously with the ingress of water. In contrast, elements closer to the centre of intact masses may take significantly longer to respond, illustrating the role of the dual processes (and hence dual scaling laws) of moisture ingress along fissures, followed by diffusion associated with swelling of the clay. A comparison of the magnitude of swell induced in this centrifuge model with that of conventional oedometer swell tests indicated gross overpredictions from the oedometer testing. In this comparison, the severe limitation of oedometer tests reducing a sample to a point of zero suction is emphasised. Finally, it is illustrated how an understanding of the rate of swell throughout an expansive profile can provide insights into the validity of the predictions from oedometer swell tests. • A centrifuge study of an artificially fissured expansive clay profile is presented. • A significant magnitude of swell was achieved in-flight in a short timeframe. • Suction, water content and penetration resistance were measured in-flight. • Swell in the model was compared with results of conventional oedometer tests. • Limitations of conventional oedometer testing are presented. [ABSTRACT FROM AUTHOR]

• The effect of different polystyrene (PS) fractions added to laboratory standard soil particle sizes was evaluated using MIR spectra. • MIR absorbances from binary soil-PS mixtures were different. • MIR absorbances depend on the combination of the soil physical fraction and PS particle size. • No linearities were observed depending on the fraction analysed. As the volume of plastics produced, used, and discarded around the world continues to increase, the environmental pollution presented by these polymers and their by-products continues to be impacted. Different methods and techniques have been proposed to evaluate plastics in environmental samples, including soils. However, in most cases, the effect of variables such as plastic particle size, soil physical fractions, and interactions between them, was not evaluated or not well understood. The aim of this study was to evaluate the effect of different polystyrene (PS) fractions added to laboratory standard soil particle sizes (clay, sand, and silt) on the attenuated total reflectance (ATR) mid-infrared (MIR) spectra of the samples. Additive-free PS was sieved in four particle sizes, namely fraction 1 (∼500–251 µm), fraction 2 (∼250–181 µm), fraction 3 (∼180–107 µm) and fraction 4 (∼106–46 µm). The PS fractions were used to spike four physical soil fractions such as clay, loam, sand and sandy and analysed using ATR-MIR spectroscopy (4000–400 cm−1). The results of this study indicated that the MIR absorbances at specific frequencies of the binary soil-PS mixtures are different and depend on the combination of the soil physical fraction and PS particle size. Overall, no linearities were observed depending on the fraction analysed. This is of importance as the data indicates a different behaviour on the MIR spectral properties of the sample. Although further validation is needed, these results might have a direct effect on the development of robust protocols to monitor MPs in complex matrices such as soil using MIR spectroscopy. [ABSTRACT FROM AUTHOR]

Scour is ubiquitous in offshore wind farms and threatens the stable state of the natural frequency of offshore wind turbines. The foundation of offshore wind turbines is a layered seabed, which mainly consists of clay, silt, and fine sand layers. However, little published literature can be found on the natural frequencies of monopiles in layered foundations with scour. The objective of this study was to reveal the influence of scour in layered foundations on the natural frequencies of monopoles and study its mechanism based on the dynamic characteristics of layered foundations. Therefore, based on an actual layered seabed, three typical layered foundations were established, and the first natural frequency of the monopile in terms of sensitivity to scour as well as the ability to resist continuous scour in the layered foundations were revealed. Moreover, the experimental results were analysed based on the stiffness and damping variations of the layered foundations under scour conditions. Importantly, a competitive relationship between the stiffness and damping of the layered foundations on the variation of the first natural frequency with scour was found and elaborated for the first time. The competitive relationship was influenced by the proportion of clay in the layered foundation. • The first natural frequencies of monopiles in different layered foundations present different responses to scour and different resistance to continuous scour. • The stiffness characteristics and damping characteristics of the layered foundations present a competitive relationship in the response of first natural frequency of monopile to scour. • The competition relationship between the stiffness characteristics and damping characteristics is influenced by the proportion of sandy soil and clay in the layered foundations. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic not only poses an unprecedented threat to global health but also severely disrupts the natural environment and ecosystems. Mitigating the adverse impacts of plastic-based personal protective equipment (PPE) waste requires the cooperation of professionals from various fields. This paper discusses a novel, cleaner approach to soil stabilisation by repurposing the nitrile gloves into a sustainable road material to improve the mechanical properties of expansive clay soil as pavement subgrade. For the first time, extensive geotechnical testings, including standard compaction, unconfined compressive strength (UCS), unsoaked California bearing ratio (CBR), repeated load triaxial (RLT), and swelling-shrinkage tests, were carried out to investigate the engineering performance of different proportions of the shredded nitrile gloves (SNG) (e.g., 1%, 1.5%, 2%) were blended with expansive clay (EC). In addition, surface roughness, scanning electron microscopy (SEM), and X-ray micro-CT analyses were conducted, and images were obtained to study the microstructural modification of the EC-SNG mixtures. The experimental results indicated that the blend of expansive clay with SNG helped in increasing the compressive strength, resilient modulus, and CBR and assisted in reducing the swelling and shrinkage of the soil. SEM and surface roughness analyses indicated the interaction between the soil matrix interface and the rough surface of the SNG. The main reasons for increasing the strength and stability of clay soil could be attributed to the high tensile strength of the SNG and the formation of the three-dimensional grid, and friction between the soil particles and SNG. According to the X-ray micro-CT test results, the incorporation of SNG led to an increase in closed porosity. [Display omitted] • An innovative approach to mitigate the problem of medical waste generation associated with COVID-19 is presented. • A cleaner and sustainable subgrade was developed by using discarded nitrile gloves. • The addition of 1.5% SNG to the soil provided the highest strength properties. • SNG reduced the swelling and shrinkage of the expansive clay subgrade. [ABSTRACT FROM AUTHOR]

[Display omitted] • RTPF and RCA have been used for clay reinforcement/stabilization. • The strength of clay-fiber-RCA composites is significantly higher than clay. • Porosity/volume relations have been explored for clay-fiber-RCA composites. • Composites with 0.5%RTPF and 10%RCA are suited as subbase of flexible pavements. The application of recycled materials for soil improvement is advantageous from the viewpoint of lowering construction costs, preventing depletion of natural resources, and reducing environmental pollutions. This experimental study investigates the application of recycled concrete aggregates to enhance the strength properties of clay soil reinforced with recycled tire polymer fibers and glass fibers. Unconfined compression and indirect tensile tests were performed on composite soils comprising clay reinforced with 0.5 % fibers and stabilized with 5 %, 10 % and 15 % recycled concrete aggregates. Laboratory findings elaborated that the increase in the RCA content and curing time would significantly improve the unconfined compressive and tensile strengths as compared to the clay. Moreover, the approximate ratio of tensile to compressive strength is a constant value for the composite soils, irrespective of fiber type, RCA amount and curing duration. Concerning the practical implications, the clay reinforced with 0.5 % fibers and stabilized with 10 % recycled concrete aggregates is strong enough after 28 days of curing to fulfill the strength requirements of subbase layers in both flexible and rigid pavements. [ABSTRACT FROM AUTHOR]