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Waste materials contribute to a wide range of environmental and economic problems. To minimize their effects, a safe strategy for reducing such negative impact is required. Recycling and reusing waste materials have proved to be effective measures in this respect. In this study, an eco-friendly treatment is investigated based on using waste powdered glass (WGP) and EPS beads (EPSb) as mechanical and chemical admixers in soils. For this purpose, Atterberg limit, standard proctor, free swell, and unconfined compression tests are performed on soil samples with different ratios of waste materials at their optimum moisture contents. The obtained test results indicate that adding WGP to cohesive soils increases the unconfined compressive strength (UCS) and reduces free swell (FS). In contrast, using EPSb reduces both FS and UCS of the treated soil samples. An optimum combination of both waste materials is determined for the improvement of the properties of high plasticity clay used in this study. Furthermore, multiple linear regression (MLR) and artificial neural network (ANN) methods are used to predict the FS and UCS of the clayey soils based on the data obtained here and the experimental test results reported in the literature. Once the FS and UCS values of untreated soil and additive percentages are defined as independent variables, both methods are shown to predict the FS and UCS values of the treated soil samples on a satisfactory level with the coefficient of correlation ( R 2 ) values greater than 0.926. Additionally, when only the index properties (liquid limit, plastic limit, and plasticity index) of the soil samples with waste materials are used as dependent variables, the R 2 values obtained by the ANN method are 0.968 and 0.974 for FS and UCS, respectively. The results of the untreated soil samples' FS and UCS tests are known, and the linear regression and ANN techniques yield similar results. Lastly, the ANN method is used to predict the FS and UCS of the treated samples in accordance to the limited predictors (e.g., only the Atterberg limits of the soil sample). [ABSTRACT FROM AUTHOR]

In recent years, individuals have begun to pay more attention to non-traditional stabilizers due to the problems connected with traditional stabilizers. Traditional stabilizers have undergone extensive investigation, and the mechanisms by which they act are well understood. This paper presents findings of the effect of sugarcane vinasse wastewater (VI) and sodium alginate (SA) polymer on the compressibility behavior, and microstructural evolution of clay soil using mixing method. The premise of this paper is to eliminate waste material from nature and compare the performance of this material against the use of polymers that have recently been used in improvement. The additives were dissolved in water and then introduced to the dried stratified soil to produce improved soil samples using the mixing technique. Transported unconfined compressive strength (UCS) was examined for 1, 14, and 28 days of treatments with additive ranges of 3–15% for VI and 0.25–1.25% for SA. In clay with high plasticity, the findings show that VI significantly influences increasing the UCS. With the addition of 9% vinasse to the soil at the age of 28 days, the UCS has increased by 78.8%. Additionally, the introduction of 1.25% SA to the soil has increased by 261.9% for the 28-day treatment efficiency significantly. Microstructural and chemical examination revealed that the mineralogical and morphological contents of the stabilized soil were influenced due to the pozzolanic reaction. The results showed that waste by-product liquid was able to significantly increase the strength and compressibility of the clay soil. Using a large volume of waste by-product liquid to stabilize soil, the researchers discovered a straightforward application method. [ABSTRACT FROM AUTHOR]

Rainfall-triggered landslides pose a significant threat to both infrastructure and human lives, making it crucial to comprehend the factors that contribute to their occurrence. Specifically, understanding the relationship between these factors and the amount of rain that is necessary for triggering such events is essential for effective prediction and mitigation strategies. To address this issue, our study proposes a statistical modelling approach using machine learning, specifically the Random Forest algorithm, to investigate the connection between landslide predisposing factors and the daily rainfall intensity threshold necessary for the initiation of shallow landslides in Portugal. By leveraging a comprehensive dataset comprising historical landslide events, associated critical rainfall, and ten distinct landslide predisposing factors, we developed several models and used cross-validation technique to evaluate their performance. Our findings demonstrate that the Random Forest model effectively captures a relationship among landslide predisposing factors, critical daily rainfall intensity, and landslide occurrences. The models exhibit a satisfactory accuracy in assessing the spatial variation of critical daily rainfall intensity based on the predisposing factors, with a mean absolute percentage error (MAPE) of around 17%. Furthermore, the models provide valuable insights into the relative importance of various predisposing factors in landslide triggering, highlighting the significance of each factor. It was found that it takes higher rainfall intensity to trigger shallow landslides in the north region of Portugal when considering critical rainfall events of 3 and 13 days. Slope aspect, slope angle, and clay content in the soil are among the main predisposing factors used for defining the spatial variation of the daily rainfall intensity threshold. [ABSTRACT FROM AUTHOR]

Developing a geophysical test site (GTS) to a full target requires a lot of work in sequential order. This article presents the construction procedures and requirements for developing a GTS, field measurements, geophysical response analyses, and site descriptions. A GTS is an experimental site that contains several targets of known properties, materials, and parameters, buried at different locations, depths, and orientations. The 55 m × 55 m multi-purpose GTS was developed within the Ahmadu Bello University Geophysics Test Site (ABUGTS). The site was developed on a lateritic-clay soil within a shallow depth of 0.6–3 m to study the geophysical signature of various burial scenarios and replicate situations usually encountered in geophysical surveys, engineering, and environmental investigations. A pre-buried investigation with integrated geophysical methods was conducted to provide adequate information about the site condition. The integrated geophysical methods were also explored on a few buried targets for test runs alongside a laboratory test to determine the electrical and magnetic properties of the buried targets. The pre-burial study indicates that the site's electrical resistivity (ER) values decrease significantly from 1081 Ωm to 47 Ωm with depth due to the regional groundwater effect. The post-burial investigations show positive results, corresponding to the laboratory results. The post-burial results show that the subsurface resistivity of the burial terrain decreases from 200 to 0.1 Ωm due to the influence of the buried metallic target and increases from 1081 to 110,000 Ωm due to the influence of the buried non-metallic target, while the total magnetic intensity of the site increases from 44,500 to 48,000 nT. Seismic result shows distortion in subsoil layers after the buried target, confirming a significant influence of the natural geophysical signature of the site by buried targets. The implications of the GTS on economic growth and educational activities were discussed. Geophysicists, researchers, and institutions can now take advantage of the site to explore the existing and new geophysical techniques routinely employed in geophysical investigations. Geophysical equipment manufacturers and individuals can also use the site for instrument configurations. The site can provide an experimental site to appreciate the nature of subsurface anomalous generated by different buried targets. It can serve as a guide for modelling new GTSs while bridging the gaps between hypothetical teaching and real-life problems through effective field-based exercises. [ABSTRACT FROM AUTHOR]

Rapid urbanization has caused numerous construction solid waste landfills. Few studies have explored the impact of multi-source waste soils with remarkable spatial variability on the reliability of landfills. This study aims to characterize the site-specific spatial variability of stockpiled waste soils and perform a probabilistic stability assessment of a real-world landfill slope. An integrated probabilistic landfill analysis framework is developed, consisting of spatial variability characterization, random field modeling, and probabilistic slope stability analysis. Seventy-four groups of clayey waste soil parameters were obtained from a landfill in Hangzhou, China. The artificial mixing behavior makes the shear strengths of waste soils have high variability (coefficients of variation close to 0.5), a high positive cross-correlation (about 0.9), and bimodal marginal probability distributions. The spatial variabilities of the cohesion and friction angle of clayey waste soils are similar, with vertical and horizontal scales of fluctuation being 3.23 m and 34.32 m, respectively. The conditional random field modeling of clayey waste soils provides a more realistic slope stability assessment of the landfill and its impact on the failure probability highly relies on the strength and location of boreholes. More slope reinforcement measures should be adopted for safety management of the next stage of landfilling. [ABSTRACT FROM AUTHOR]

Many coastal areas have soft clay soils, characterized by high compressibility and low bearing capacity. There are several methods for improving soil characteristics, one of which is stone columns technique. This method can reduce the possibility for liquefaction, speed the consolidation effect, strengthen the soil, and lessen the compressibility of soft, loose, and fine-graded soils. In this study, unit cell stone columns with 50- and 75-mm diameters and the length of stone column to the depth of the soft clay (L/H) of 1 and 0.75, were subjected to laboratory experiments on soft clay soil with a cohesion of 7 kPa. Crushed asphalt, crushed concrete, crushed ceramic, dolomite, and treated concrete were tested as filler materials in the stone columns. In addition, tests were conducted on both unreinforced and geogrid-encased stone columns. The main objective is to identify the most effective filler material that improves in load-bearing capacity and minimizes the settlement. The behavior of stone columns was assessed by varying stress concentration ratio (n) and the load improvement factor (LIF). The results indicate that both n and LIF increase with increasing the settlement to the plate diameter ratio, reaching a stable value when that ratio reaches 10% or higher. Consequently, it can be inferred that using floating stone columns is more economically efficient than using end-bearing stone columns. Increasing the length and reinforcing the vertically encased stone columns improve both the bearing capacity and the stress concentration ratio. All the materials used in this study improved the bearing capacity and reduced settlement. It is observed that treated concrete yielded the best results in improvement, while crushed asphalt is considered the most economical option compared to the other materials used. [ABSTRACT FROM AUTHOR]

Soft soil concerns, due to high compressibility and low bearing capacity, prompted an investigation into stabilizing clay soil. Traditionally, binder including cement or lime has been used as stabilizers though a current requirement of alternatives is stem from environmental concerns. The study focused on the viability of using a novel binary activated blended binder composed of environmentally friendly materials, namely ground granulated blast furnace slag (GGBS) activated by cement kiln dust (CKD). The experimental work included investigating the impact of the developed binders on the Atterberg limits, standard Proctor compaction, California Bearing Ratio (CBR), unconfined compressive strength (UCS), and field-emission scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy. CBR tests were conducted after 7 days of curing or soaking, while UCS and SEM analyses were conducted after 7 and 28 days of curing. A fixed binder ratio of 9% was maintained, with GGBS blended at 25%, 50%, and 75% with CKD. For comparison, samples of untreated and treated soils with unary binders from GGBS and CKD were also prepared. Results indicated that activated binders notably decreased soil plasticity and maximum dry density, while elevating optimum moisture content, CBR, and UCS, especially in later stages of treated soil and unary GGBS binder. Unary CKD binder exhibited a similar trend to activated binders. The activating of 25% GGBS with 75% CKD provided the optimum binder which increased the mechanical strengths by about 6 times than untreated soil. SEM revealed substantial formations of C-S-H and C-A-H gel, along with ettringite, intensifying with time. This research provides viable outcomes for stabilizing clay soil using environmentally friendly binders, demonstrating significant improvements in soil properties, particularly when using the binary activated blended binder consisting of GGBS and CKD. [ABSTRACT FROM AUTHOR]

The adsorption retention of different antibiotics and the physical and chemical properties of soil can vary significantly, leading to differences in their retention ability in soil environments. To investigate the adsorption retention characteristics and transfer risk, as well as influential factors of spiramycin (SPI) in three different agricultural calcareous loess soils, which were studied by means of batch equilibrium method. The results show that the adsorption kinetics data can be well described by the pseudo-second-order model, and the sorption isotherms can be described by the Freundlich model. These model parameters indicate that soil organic matter (SOM) and cation exchange capacity (CEC) play a key role in the adsorption retention of SPI, while soil clay content and pH also exert some influence. Furthermore, the desorption amounts of SPI were consistently less than 35%, showing a high degree of irreversibility and a clear desorption hysteresis, making it prone to remaining retention in the soil. The adsorption amount changed little of pH value from 3 to 7. At a pH value of 7, adsorption is promoted by cation bridging between soil and SPI, and the existence of electrostatic attraction. The adsorption amount decreased when the pH value exceeded 7 dues to electrostatic repulsion. Compared with K+ and NH4+, the presence of high valence ions such as Ca2+, Mg2+ and ions with higher concentration has a significant inhibitory effect on adsorption. The FTIR spectral analysis of the adsorbents revealed that the adsorption retention was mainly governed by cation exchange, hydrogen bonding, and surface complexation. This study provides a scientific basis for assessing the retention ability and transfer risk of typical veterinary antibiotics in the soil environment. [ABSTRACT FROM AUTHOR]

Soil mineralogy and texture are directly related to soil carbon due to the physical properties of the clay surface. Traditional techniques for quantifying carbon in soil are time-consuming and expensive, making large-scale quantification for mapping unfeasible. The alternative is the use of soil sensors, such as diffuse reflectance spectroscopy (DRS), an economical, fast, and accurate technique for predicting carbon stocks. In this sense, this study aimed to (a) investigate the relationship of C with different soil mineralogical, chemical, and physical attributes for different geological and geomorphological compartments; (b) understand which spectral bands are most important for estimating C content; (c) estimate C content from diffuse reflectance spectroscopy using different mathematical techniques and indicate which one is the best for tropical soil conditions; and (d) map C contents in detail. The study area was the Western Plateau of São Paulo (WPSP), which covers approximately 13 million hectares (~ 48% of the State of São Paulo, Brazil). A total of 265 samples were collected in this area. The attributes clay, silt, sand, crystalline and non-crystalline iron, base saturation, soil density, total pore volume, total C, C stock, kaolinite/(kaolinite + gibbsite) and hematite/(hematite + goethite), hematite and goethite contents, and spectral curves were evaluated. The spectra were recorded at 0.5-nm intervals, with an integration time of 2.43 nm s−1 over the 350 to 2500-nm range (350–800 nm—visible—VIS and 801–2500 nm—near-infrared—NIR). The data were subjected to descriptive statistics, Spearman correlation, stepwise analysis, and cluster grouping for characterization purposes; partial least squares regression (PLSR) and random forest (RF) for estimation purposes; and geostatistics analysis for creation of spatial maps. Our results indicate that the highest C contents are associated with more clayey soils, oxidic mineralogy, higher total pore volume, and lower soil density in highly dissected basalt compartments. The random forest algorithm associated with the Vis–NIR spectral range is more efficient for estimating and mapping C contents. This suggests that integrating diffuse reflectance spectroscopy with machine learning techniques holds promise for shaping public policies related to land use, mitigating CO2 emissions, and facilitating the implementation of carbon credit policies in a rapid and economically efficient manner. [ABSTRACT FROM AUTHOR]

Soil degradation, marked by declining organic matter, threatens global food security. The impact of brewer's spent yeast (BSY) on clay and sand was analysed at varying application rates to assess its effectiveness in improving soil quality. A randomized complete block design with three replicates was employed. One kilogram of soil were mixed with BSY at application rates of 2 t/ha and 5 t/ha. The samples were incubated at 26 °C for 5 months with daily watering. We analysed pH, total nitrogen, organic carbon, total phosphorus, and electrical conductivity (EC); microbial activity (total heterotrophic bacteria, actinobacteria, and fungi) and soil enzyme activity (dehydrogenase, catalase, protease). BSY application improved soil quality, particularly in clay. Clay showed increased in pH, EC, N and C. BSY significantly boosted microbial populations (bacteria, fungi) in clay with a lesser effect in sand. Enzyme activity and a fertility index also improved in BSY-treated clay, while sand displayed increased activity of a different enzyme. Results suggest BSY holds promise as an organic fertilizer, especially for clay soils. Further research is needed to optimize application, understand long-term effects, and evaluate economic feasibility and social acceptance. This study contributes to the search for sustainable, local solutions to improve soil health and agricultural practices. [ABSTRACT FROM AUTHOR]

Although many commercial stabilizers are available for the treatment of poor soils; agricultural, agro-industrial, and environmentally friendly stabilizers are always encouraged. In this study, an attempt has been made to assess the effects of brewery spent grain ash (BSGA) on lime-treated clay for stabilization of an expansive clay to be used as road construction material. Brewery spent grain (BSG) is an agro-industrial solid waste product obtained during the brewing of beer. Through burning in an open cylinder, it is converted to BSGA. The clay was subjected to preliminary tests to classify and identify some required engineering properties of the sample. Initially, samples were thoroughly mixed with lime by weight of clay to determine the optimum amount of lime needed throughout the experiments. Through laboratory execution trials, 10% lime was determined to be the optimal amount. Following, BSGA was added to the treated clay, which was previously treated with 10% lime, at various percentages of 2, 4, 6, 8, and 10% BSGA by weight of clay. At 0% BSGA, the unsoaked and soaked California bearing ratio (CBR) rose from 13.56 and 8.24% to their greatest values of 14.99% and 9.3%, respectively, at 6% BSGA. Unconfined compressive strength (UCS) values rose from 112.63 kN/m2 at 0% BSGA to 130.31 kN/m2 at 6% BSGA, which is the highest value. Therefore, it was discovered that BSGA can be a beneficial addition to lime stabilization in clay soil. [ABSTRACT FROM AUTHOR]

Intensified drought exacerbated by climate change aggravates the development of soil desiccation cracking, triggering several weakening mechanisms in surface soils and eventually causing various geohazards and environmental problems. This study investigates the effect and mechanisms of a bio-mediated approach based on microbially induced calcite precipitation (MICP) for remediation of desiccation cracks in soils with different layer thicknesses. We conducted 5 MICP treatment cycles on clayey soil samples to explore the influence of layer thickness on the water evaporation properties, desiccation cracking behaviors, and calcium carbonate content and distribution of MICP-treated soils. The results show that the MICP treatment can significantly decrease the water evaporation rate, the surface crack ratio, average crack width, and total crack length of all soil samples. The crack reduction ratio reaches over 90% after 5 MICP treatment cycles. The soil layer thickness has an obvious influence on the effectiveness of MICP for the clayey soil treatment. Thicker soil samples exhibit wider desiccation cracks, which, in turn, require more MICP treatment cycles for remediation. The calcium carbonate content and distribution of MICP-treated soils is governed by the original desiccation cracks, the wider cracks in thicker soil samples result in the higher calcium carbonate content of soil nearby the cracks, and the denser cracks in thinner soil samples lead to the more homogenous distribution of calcium carbonate. The remediation of soil desiccation cracks is mainly attributed to the coupling effect of the soil volume change and the accumulation of calcium carbonate crystal during MICP treatment. The findings of this study provide new insights into the mechanisms of the interaction between MICP-treated soil and drought climate and contribute to developing environmentally friendly approaches for soil improvement in regions subjected to droughts. [ABSTRACT FROM AUTHOR]

Background and aims: The accumulation of soil organic carbon (SOC) is a crucial process in mitigating climate change and ensuring soil quality. Subtropical plantations in China have shown high potential for enhancing SOC sequestration due to their high carbon sink capacity. However, the dynamics and compositions of SOC after long term afforestation are still poorly understood. Methods: We examined the dynamics of SOC and its fractions of different soil layers (0–5 cm, 5–10 cm, 10–20 cm, 20–40 cm, 40–80 cm, 80–100 cm) in a mixed broadleaf-conifer plantation (BCP), a Masson pine plantation (MP), and a Slash pine plantation (SP), and an enclosed forest (EF) in subtropical China. Both physical fractions (particulate organic carbon (POC), soil clay organic carbon (SOCclay), soil silt organic carbon (SOCsilt)) and chemical fractions (iron-aluminum-bound organic carbon (Fe/Al-OC), and calcium-bound organic carbon (Ca-OC)) were determined. Additionally, soil physicochemical properties were further analyzed. Results: Our results showed the SOC storage in the EF, BCP, MP, and SP in 2019 increased by 82%, 238%, 126%, and 103% respectively compared to 1984. The proportions of MAOC to SOC were respectively as follows: SP (65.9%) > BCP (64.9%) > EF (61.6%) > MP (53.9%). The mean proportions of SOCclay to MAOC were as follows: BCP (71.1%) > EF (66.9%) > MP (58.5%) > SP (51.0%). The mean proportions of Fe/Al-OC to MAOC were as follows: EF (53.3%) > SP (48.3%) > MP (47.9%) > BCP (39.8%). All these proportion increased with soil depth. RDA and PLS-SEM analysis revealed that soil nitrogen content and electrochemical properties (pH and EC) were the main factors that controlled SOC content and fractions. Conclusions: Subtropical plantations have significant soil carbon sequestration capabilities, but they are currently nearing saturation. Soil nitrogen content may be key factor limiting further enhancement of carbon sequestration. Due to the high proportion of MAOC and relative consistent SOC storage, BCP and SP are recommended as priorities for plantation regeneration in subtropical China. [ABSTRACT FROM AUTHOR]

Aims: Climate warming can potentially cause more plant-derived organic substrates into the surface soil. The newly produced carbon may accelerate or restrict native soil organic carbon (SOC) decomposition by priming effects (PE), so as to increase the uncertainty of the feedback prediction between climate change and soil carbon pool. However, it is controversial about the direction and driving factors of the PE of surface SOC in the warming world. Methods: In this meta-analysis, we investigated 1680 pairwise PE determined by 13C or 14C isotope labeling method in surface soils across cropland, grassland and forest from 39 warming experiments to generalize the direction and influencing factors of the warming effects on PE. Results: The meta-analysis showed that warming decreased PE across different ecosystems. The decrease was much greater in forest (effect size: -6.2) than in cropland (effect size: -2.6) and grassland (effect size: -1.7) and was more severe in simple substrates (effect size: -12.1), i.e., small molecules such as glucose and amino acid than that in complex substrates (effect size: -1.7), including plant tissues, residues and pyrolysis products, etc. The effect size of warming on PE was positively correlated with soil clay and pH, while negatively correlated with SOC content, total nitrogen, soil C/N ratio and warming intensity. Conclusions: These findings emphasize that warming will decrease the primed surface SOC loss, particularly in forest or organic matter-rich soils and larger warming intensity. [ABSTRACT FROM AUTHOR]

The degree of salinity, the freezing point, and the amount of unfrozen water are key factors in predicting the temperature, humidity, and mechanical behavior of saline permafrost soils used in construction as foundations for buildings. The results of the experimental studies are presented and a method for calculation of the amount of unfrozen water in saline soils is proposed. The calculated and experimental data show good convergence for both sandy and clay soils of different salinity and water content. [ABSTRACT FROM AUTHOR]

The undrained bearing capacity to eccentric and inclined loading of foundations resting on a two-layered clay soil is examined by 2D and 3D FE analyses. The ratio of the shear strength of two layers, the relative thickness of the uppermost layer in terms of the foundation width and the normalized values of eccentricity and horizontal loads are the key parameters of a comprehensive finite element study. Two cases of inhomogeneity referring to strength ratio higher or lower than unity, are separately examined, as they are associated with different failure mechanisms. The failure mode is examined in several cases, giving additional insight into the mechanics of the problem. Moreover, for a better visual understanding of how the overturning moment and horizontal force affect the ultimate capacity, the results are presented in terms of 3D, BC or sliding interaction diagrams. The 3D analyses of foundation resting on two-layered clay and subjected to combined M, V, H loading, the evaluation and presentation of the results as well, can support the contribution of the paper. [ABSTRACT FROM AUTHOR]

Soils containing swelling clays, such as montmorillonite, can develop significant pressures due to their water content, or can absorb significant surrounding water, leading to potentially dramatic volume changes. This work presents a generalized Terzaghi's stress principle that when rewritten in terms of measurable quantities, relates overburden pressure to volumetric change. In the limiting case of 100% clay it simplifies to the pressure-volumetric relationship developed by Phillip Low, and in the other extreme (no clay) Terzaghi's stress principle is obtained. The relationship is derived using Hybrid Mixture Theory, a multi-scale mixture theoretical framework, which allows for developing a more generalized mathematical model for multi-physics problems. The equation relating overburden pressure to volume incorporates the clay and water content, bulk liquid pressure, and four empirical constants. The resulting constitutive equation is validated against existing experimental data over a wide range of pressures and clay content. [ABSTRACT FROM AUTHOR]

Extensive experimental studies have demonstrated the time-dependent mechanical behaviors of frozen soil. Nonetheless, limited studies are focusing on the constitutive modeling of the time-dependent stress–strain behaviors of frozen clay soils at different subzero temperatures. The objective of this study is to numerically investigate the time-dependent behavior of frozen clay soils at a temperature range of 0 °C to − 15 °C. The Drucker–Prager model is adopted along with the Singh–Mitchell creep model to simulate time-dependent uniaxial compression and stress relaxation behaviors of frozen sandy clay soil. The numerical modeling is implemented through the finite element method based on the platform of Abaqus. The constitutive modeling is calibrated by a series of experimental results on laboratory-prepared frozen sandy clay soils, where the strain hardening, the post-peak softening, and stress relaxation behaviors are captured. Our results show that both the rate-dependent model and creep model should be adopted to characterize a comprehensive time-dependent behavior of frozen soils. The rate-dependent stress–strain behaviors heavily rely on the rate- and temperature-dependent hardening functions, where the creep strain provides a very limited contribution. Nevertheless, the creep strain should also be adopted when a long-term analysis or stress relaxation behavior is involved. [ABSTRACT FROM AUTHOR]

This study proposes a constitutive model to simulate the clayey soil response to the external loads during soil-structure interaction, specifically in the context of pile installation and subsequent set-up. The model considers the alteration of soil structure during prolonged penetration and the gradual regaining of its thixotropic strength. The model is based on the disturbed state concept and critical state theory, with the Modified Cam-Clay model used to define the intact state response. The proposed model, referred to as the Critical State and Disturbed State Concept model, captures the elastoplastic behavior of both normally consolidated and over-consolidated soils. It was validated using triaxial test results and implemented in Abaqus software to simulate pile driving and the set-up phenomenon occurs after the end of pile driving. The model accurately predicts pile capacity and disturbance behavior in the soil, as demonstrated by field compression load tests. [ABSTRACT FROM AUTHOR]

Hard soils-weak rocks combine characteristics of soil behavior and rock behavior. Perhaps the most distinct among them is brittleness reducing shear strength significantly after failure with very little additional shear displacement combined with intense dilation. Several hard soils-weak rocks were tested under drained direct shear conditions following consolidation to various vertical stress values. All of them exhibited very high reduction of shear strength after rupture, ranging from 32 to 71% taking place in as little as 0.1 mm of additional shear displacement. This loss of strength resulted in very large decrease of cohesion intercept and for all soils significant decrease in the angle of shearing resistance. Dilation was abrupt during rupture and was as high as 1.2 mm for the coarsest of the soils. Dilation was exhibited for all vertical stress values applied, never switching to contraction even for the highest vertical stress applied except one point for one soil. Percentage loss of peak shear strength after failure remained very high even for the highest vertical stress values applied, with points of percentage loss of peak strength with vertical stress falling in a very tight region for all soils. This is in clear difference to both the position of points falling on the same plot for a preconsolidated clayey soil and the higher rate of strength loss decrease with increasing vertical stress compared to the hard soils-weak rocks tested. The test results presented add to the existing understanding of the behavior of hard soils-weak rocks under drained direct shear and constitute examples of behavior of very brittle hard soils-weak rocks. [ABSTRACT FROM AUTHOR]

The diversification of species for bioenergy silviculture in Amazonia will help several local and/or regional industrial segments. Thus, the expansion of knowledge on silvicultural practices of Tachigali vulgaris will support future commercial-scale plantations in Amazonia. This study aimed to evaluate possible differences in diameter, height, and wood volume of T. vulgaris trees grown under different nutritional doses, on two soil texture classes. In addition, we sought to determine the appropriate nutritional dose for the studied types of soil texture aiming at the production of energy wood. The study was conducted in two experimental areas of 1.6 ha each, located in the municipality of Almeirim – Pará, Brazil. Independent analyses were performed in both experimental areas at each age. The experiments were set up in a randomized block design with four blocks. A factorial scheme considering four phosphorus and three potassium doses were adopted, totaling 12 treatments. The diameter at 1.30 m (DBH), equivalent diameter, total height of the trees, and the commercial wood volume with bark per hectare (Vwb ha−1) were evaluated. A significant effect of nutrient doses was reported on DBH at the age of 2 years for the soil with a sandy loam texture. The Vwb ha−1 of the trees at 4, 5, and 6 years old was significantly affected by fertilization in clayey soils. Under the conditions of the present study, the nutritional doses of 0 kg ha−1 of triple superphosphate and 172 kg ha−1 of potassium chloride are recommended for the area with Oxisol of sandy loam texture and 195 kg ha−1 of triple superphosphate and 343 kg ha−1 of potassium chloride are recommended for the area with Oxisol of clayey texture. [ABSTRACT FROM AUTHOR]

Black wattle is a tree native to Australia and commercially planted in South Africa and Brazil. Replacement of exported nutrients by wood and bark harvesting, associated with the maintenance of harvest residues, increases productivity, thus maintaining production sustainability. Here, we review recent advances in soil nutrient dynamics, harvest residue management (HRM), and soil organic matter in black wattle plantations. Over the 7–11-year cycle of black wattle, N is the most exported macronutrient (458–1509 kg ha− 1), followed by K (200–766 kg ha− 1), Ca (270–717 kg ha− 1), Mg (62–128 kg ha− 1), S (29–57 kg ha− 1) and P (16–40 kg ha− 1). The average increase in bark yield to 20 kg P ha− 1 applications on sandy soils was 2.7–2.9 t ha− 1 and on clay soils from 2.8 to 8.7 t ha− 1. Sandy soils with low K are more responsive to fertilizer, and rates must consider the K content and cation exchange capacity. Ca and Mg addition responses are more likely when in the topsoil they are in low concentrations (< 0.75 and 0.41 cmolc dm− 3, respectively). Micronutrient fertilization reduces the occurrence of gummosis caused by Phytophthora spp, and B deficiency is the most common and can be supplied by fertilization or foliar application (1 g B L− 1). Few studies have evaluated the impact of black wattle HRM on soil organic matter (SOM) and its effects on production. However, conserving SOM should be considered an essential practice for the sustainability of black wattle production. [ABSTRACT FROM AUTHOR]

This study investigated the mechanical properties of a low-plasticity clay soil reinforced with polypropylene (PP) fiber in various contents (0.05%, 0.10%, 0.15%, and 0.20%) and lengths (6, 12, and 19 mm). The reinforced specimens were subjected to unconsolidated-undrained (UU) triaxial compression tests under three different confining pressures (50, 100, and 200 kPa). The optimum fiber contents in specimens reinforced with 6-, 12-, and 19-mm PP fiber were determined as 0.15%, 0.15%, and 0.20%, respectively. As a result, the highest values regarding deviator stress at failure (σdev), energy absorption capacity (EAC), and shear strength parameters occurred in specimens containing 0.20% PP (19 mm). As a result of the reinforcement process, the most remarkable improvements in the σdev, cohesion, internal friction angle, and EAC values of the natural soil are 59.95%, 21.80%, 63%, and 34.70%, respectively. Linear and nonlinear relationships between σdev and fiber length, fiber content, and confining pressure were investigated by multiple linear regression and artificial neural network methods. Equations were generated to predict σdev of a low-plasticity clay soil reinforced with PP fiber and were made available to geotechnical researchers. [ABSTRACT FROM AUTHOR]

A collection of feed forward neural networks (FNN) for estimating the limit pressure load and the according displacements at limit state of a footing settlement is presented. The training procedure is through supervised learning with error loss function the mean squared error norm. The input dataset is originated from Monte Carlo simulations for a variety of loadings and stochastic uncertainty of the material of the clayey soil domain. The material yield function is the Modified Cam Clay model. The accuracy of the FNN's is in terms of relative error no more than 10 - 5 and this applies to all output variables. Furthermore, the epochs of the training of the FNN's required for construction are found to be small in amount, in the order of magnitude of 90,000, leading to an alleviated data cost and computational expense. The input uncertainty of Karhunen Loeve random field sum appears to provide the most detrimental values for the displacement field of the soil domain. The most unfavorable situation for the displacement field result to limit displacements in the order of magnitude of 0.05 m, that may result to structural collapse if they appear to the founded structure. These series can provide an easy and reliable estimation for the failure of shallow foundation and therefore it can be a useful implement for geotechnical engineering analysis and design. [ABSTRACT FROM AUTHOR]

This paper presents a new finite element method (FEM) model to simulate the thermo-hydro-mechanical (THM) responses of water-saturated clay soils. The model can account for the effects of temperature variation on bound water dehydration and the corresponding thermo-poromechanical strains. The governing equations, including mass balance, momentum balance, and energy balance, are derived based on the principles of continuum mechanics for porous media. The impact of bound water dehydration on THM behavior is incorporated into the coupled THM equations. The model is equipped with an unconventional plasticity for more accurate description of elastoplastic behavior. To solve the nonlinear system of equations, a modified Newton–Raphson method is employed. The model is validated using laboratory tests on various clay soils with different geological origins, and reasonable agreement is achieved. The thermally induced contraction behavior of clay soils at a low overconsolidation ratio and thermally induced expansion behavior at a high overconsolidation ratio are well simulated. During heating, the effect of bound water dehydration on the generation of excess pore pressure in clay soils is highlighted in our numerical results. [ABSTRACT FROM AUTHOR]

Background and aims: The frequent occurrence of extreme rainfall events results in soils experiencing drying–rewetting (DRW) cycles. Such rewetting can lead to a surge in soil CO2 emissions; however, the main regulatory factors involved in this priming effect are unclear. Methods: In this study, we conducted a meta-analysis using data extracted from 43 published papers, to determine the direct regulatory factors involved in the priming effect of soil CO2. Results: The results indicated that the priming effect of rewetting on soil CO2 emissions was influenced by ecosystem type, soil properties, climatic factors, and the number of DRW cycles. The priming effect was the highest in cropland but the lowest in grassland when taking flux values observed before rewetting as the control group. It was also greater in acidic soils (pH < 6.5) and soils with a high clay fraction (clay ≥ 30%) than in other soils. The effect size (lnRR) of soil CO2 emissions was exponentially related to the mean annual precipitation (MAP), and decreased with increases in MAP. In DRW experiments, the priming effect of the first rewetting on soil CO2 emissions was the largest, an effect that gradually decreased with the number of DRW cycles, before disappearing completely. Most importantly, soil moisture influenced the peak time and the pulse time of the priming effect: the greater the change in soil moisture, the longer the peak time duration; the higher the maximum soil moisture content after rewetting, the longer the pulse time duration; and the lower the initial soil moisture content, the bigger the priming effect. Conclusion: Generally, physical mechanisms, especially soil moisture, directly regulate the CO2 priming effect during DRW cycles. Thus, this study provides a theoretical basis for assessing and predicting the impact of future precipitation changes on soil carbon cycling. Future studies should also carefully monitor any changes in soil microorganisms in response to changes in soil moisture during DRW cycles, because these appear to be significantly involved in CO2 release from soils. [ABSTRACT FROM AUTHOR]

Some soil characteristics, such as the shear wave velocity, the shear modulus, the Poisson ratio, and the porosity, affect how clay soils behave. The soil design parameters under loading, such as soil liquefaction induced by dynamic earthquake loading, employ the shear wave velocity and shear module with modest stress. In order to understand the pore saturation, the Poisson ratio and seismic velocity ratio are also utilized. Additionally, one of the most crucial physical characteristics for assessing permeability at the base of any engineering structure, resolving consolidation issues that may arise at the foundation of an engineering structure, and influencing the deformation behavior of soils is soil porosity. Predicting the porosity of clay soils is a crucial first step in tackling engineering and environmental issues that may arise in the soil after an earthquake or not. With the use of dynamic soil metrics such as seismic velocities, shear modules, bulk modules, seismic velocity ratios, and Poisson ratios, the current work aims to estimate soil porosity. Seismic refraction was used by various studies in the past to conduct in-situ geophysical research. The lithological characteristics of the soil (such as the grain size, shape, type, compaction, consolidation, and cementation of the grains) and the physical characteristics of the soil (such as porosity, permeability, density, anisotropy, saturation level, liquid–solid transition, pressure, and temperature), as well as the elasticity characteristics of the soil (such as shear modulus (G), bulk modulus (K), Young modulus (E), Poisson ratio (μ) and Lamé constants (λ )) all have an impact on seismic waves passing through a medium. [ABSTRACT FROM AUTHOR]

Expansive clayey soils often pose challenges for construction projects due to their low bearing capacity, swelling, and shrinkage properties. While previous research has explored additives to enhance these soils' properties, the potential of sand remains underexplored. This study investigates the impact of varying sand percentages on expansive clayey soils' consistency, compaction, and permeability. This study examines how adding different percentages of sand influences the physical properties of expansive clayey soils. Laboratory tests involved systematic testing of texture, compaction, and permeability. Findings reveal a notable improvement in the physical properties of the soil with the addition of sand. Results from the laboratory tests provided data for empirical equations that facilitate the prediction of soil properties based on the sand content. The enhancement in soil properties underscores the potential of sand as an additive for expansive clayey soils. The empirical equations presented here provide practical benefits to geotechnical engineers and practitioners engaged in construction projects involving these soils, offering them valuable insights into the benefits of sand additives to improve physical characteristics. The insights gained from this research hold promising prospects for improving construction practices and addressing the challenges associated with these soils. [ABSTRACT FROM AUTHOR]

This paper aims to propose a design method for energy piles using the results of in situ pressuremeter tests. The method is based on the incorporation of thermal effects through a numerical model of cylindrical cavity expansion. Pressuremeter profiles are generated by the numerical model, which represent the limit pressure at different temperature variations. The pile's bearing capacity is, subsequently, determined by following the standard procedure outlined in Eurocode 7 for the pile design, which is based on pressuremeter tests. Thus, relying on pressuremeter curves, the proposed method is enabled to provide the mobilized base resistance, shaft friction and the bearing capacity of an energy pile. In a second phase, a case study of an energy pile located in a clay soil is conducted in order to explain the different steps of the proposed method and to examine the impact of thermal effects on the bearing capacity. The study reveals an increase of the bearing capacity when heating which reaches 3% at Δθ = 40 °C and a decrease of 4% at Δθ = − 40 °C when cooling. This variation is non-linear and asymmetric because the decrease caused by cooling is not fully recovered during heating: A loss of 1% of the bearing capacity is observed. As a result, it is crucial to consider thermal effects in the design of geothermal piles. On the other hand, the proposed method could be a practical approach for engineers to design energy piles. [ABSTRACT FROM AUTHOR]

This article aims at presenting the results of an experimental study using limestone waste from a mining operation in order to reduce the swelling potential of clay soil. Initially, the physical and mineralogical characterization of the materials were conducted. Next, tests were carried out to assess the percentage of heave and swelling pressure. Oedometric compression tests were performed with flooding stress of 5 kPa, 60 kPa and 120 kPa. The tests were carried out in pure soil (S), waste (limestone powder—LP) and waste/soil mixtures at mass proportions of 40%LP/60%S, 60%LP/40%S and 80%LP/20%S. The results showed that pure clay soil exhibited high swelling potential and swelling pressure. On the other hand, the limestone powder shows no expansion. Swell pressure and percent of heave decrease with the increase of the residue content in the mixture. The results obtained demonstrate that the use of 60% waste can stabilize clay soil against swelling when submitted to a minimum stress of 62 kPa, and that incorporating 40% waste stabilizes the soil when submitted to stresses above 280 kPa. [ABSTRACT FROM AUTHOR]

Soil–cement mixtures have practical applications in geotechnical engineering. Peculiarities associated with the stiffness and strength gains over the curing time provided by cementation need to be investigated, especially for tropical soils. Few studies investigated mixtures of tropical soils and high early strength Portland cement, in order to understand the changes in physical and mechanical properties associated with mineralogical and microstructural alterations caused by artificial cementation. This work aimed to study the effects of cementation on a tropical clay soil using ultrasonic method and to correlate the results with those of other tests. The ultrasonic pulse velocity (UPV) was evaluated for the natural soil and mixtures of soil with different cement contents (1%, 2%, 3%, 5%, 7%), after different curing times, based on propagation of longitudinal ultrasonic waves. Mineralogical and microstructural analyses, geotechnical characterization, resilient modulus (RM) and unconfined compressive strength (UCS) tests, and physical–chemical investigation through volumetric variation were also developed. The ultrasonic response revealed direct effects of cementation on micromorphology, plasticity and granulometry. A microstructure with larger pores was transformed into a dense structure with particles bonded by cementitious compounds. This change provided new paths for the propagation of ultrasonic waves (UPV increases exceeded fourfold for a cement content of 7%) and greater mechanical resistance to the application of cyclic and static loads. Nearly linear increases in UPV, UCS and RM were observed with the addition of cement. A good linear relationship was observed between the values of UPV and RM (R2 > 0.8968) or UCS (R2 > 0.8925). [ABSTRACT FROM AUTHOR]

CPR grouting is a technique used to improve soft clayey soils through vertical drains and the injection of low mobility grout. CPR grouting still faces limited acceptance among certain practitioners, primarily due to the doubtful process of soil consolidation induced by grout injections. The aim of this study is to investigate the behavior of soft clays subjected to CPR grouting, attempting to enhance the theoretical understanding of the technique and evaluating the related consolidation process. The technique is studied using a special laboratory apparatus, in which a latex membrane is inflated within a soil specimen to simulate the grout injection. In this paper, we introduce the modified equipment, its components, describe the experimental procedure, outline the sample preparation, and present the experimental results. The key findings of this study suggest that injection pressure appears to be unrelated to the expanded volume, the peak injection pressure is similar across all tests, and larger injected volumes does not necessarily produce higher amount of soil consolidation. Although laboratory conditions are not identical to field conditions, laboratory tests indicate that grout injection does lead to consolidation in the soft clay, offering a valuable empirical guidance for a more cost-effective grouting design plan. [ABSTRACT FROM AUTHOR]

Aims: Soil organic carbon (SOC) storage is mainly governed by inputs from plant and microbial sources. How the relative contributions of these two sources in forest soils vary along broad-scale environmental gradients is poorly understood. The contributions of these two carbon sources in different soil layers are also elusive. Methods: We used amino sugar and lignin phenol as biomarkers to indicate microbial- and plant-derived soil carbon. The concentrations of amino sugar and lignin phenol in topsoil (0–10 cm) and subsoil (30–60 cm) of major forest types along a latitude gradient in China were investigated. Results: The concentration of soil amino sugar decreased along the latitude in topsoil, which is mainly controlled by the variations in mean annual temperature and soil nitrogen. The concentration of lignin phenols decreased along latitude in topsoil, mainly controlled by soil carbon/nitrogen ratio. The microbial-derived carbon was mainly composed of fungi-derived in topsoil, while bacteria-derived dominated in subsoil. Climate and soil properties are primary factors controlling the persistence of microbial residues and lignin phenols in topsoil, and soil clay is the crucial factor in the subsoil. Conclusions: Both microbial residuals and lignin phenols in topsoil showed a decreasing trend with increasing latitude, but controlled by different sets of environmental factors. Subsoil microbial residues and lignin phenols showed no trend along the latitude and are mainly influenced by soil clay content.These findings provide new insights on how climate and vegetation affect soil carbon persistence, revealing significant distribution patterns of forest soil microbial residuals and lignin phenols along a latitude gradient. [ABSTRACT FROM AUTHOR]

The definition of soil stabilization is a method to enhance the engineering properties. Polyurethane grout is one of the least expensive methods and can be used in construction. Polyurethane injection resin systems for crack injection, slab lifting, soil stabilization, leak sealing, and structural crack repair have been used for the last two decades. Polyurethane foam hasn't been used or understood as a loaded structural element in soils like as embedded piles. In this piece of work, a trial was made to numerically study the behavior of polyurethane foam when used as piles embedded in the clay and sand soils. Plaxis 3D software was adopted to carry out this study. Polyurethane piles of varying diameters and lengths were modelled as embedments in the clay and sand soil, and then incremental loads were applied. Moreover, the study involved the behavior of polyurethane piles when the clay strength was increased. The results indicated that embedded pile resistance to loading increased with the increase in length and pile diameter. When the loading results of polyurethane foam embedded in loose sand are compared with the loading results of piles in soft clay, the ultimate capacity of piles in loose sand, was much higher than that in soft clay. The results also indicated that the polyurethane pile load-carrying capacity increased when L/D ratio decreased for both soft and stiff clay. In this study concrete piles in clay and sand soil were modelled to examine the percentage of loading capacity of concrete piles to that of polyurethane piles for clay and sand soil. [ABSTRACT FROM AUTHOR]

This investigation examines the effect of clamshell ash (CSA) and lime additives on the physico-mechanical characteristics of kaolinite clay soil stabilized at the optimum silica fume content. Laboratory tests were performed to assess plasticity, shrink-swell characteristics, compaction characteristics, unconfined compressive strength (UCS), shear strength characteristics, mineralogical and morphological microstructure characteristics of stabilized soil specimens. The kaolinite clay soil was stabilized at its optimum silica fume content (6%) to produce the highest strength and was altered with three non-identical proportions of clamshell ash and lime (3%-9%). Cylindrical soil specimens, 76 mm in height and 38 mm in diameter, were moulded and treated for curing periods of 1, 7, 14, and 30 days to examine the strength of the altered soil. The findings revealed that, adding clamshell ash and lime significantly alters the plasticity, shrink-swell, maximum dry unit weights, and optimum moisture contents of the silica fume-stabilized soil. In terms of strength, the beneficial effects of CSA and lime additives were found to be more significant with more extended curing periods. Incremental increases in curing periods resulted in further enhancements in UCS, cohesion, and internal friction angle, indicating continued strength development over time. Microstructural analysis using field emission scanning electron microscopy and X-ray diffraction provided insights into the interparticle bonding mechanisms and microstructural changes induced by the addition of CSA and lime. The emergence of cementitious phases and pozzolanic responses between soil particles and stabilizers contributed to the densification and strengthening of the stabilized soil matrix. The findings of this study provide valuable insights into the potential of clamshell ash and lime additives to enhance the engineering properties of kaolinite clay soil stabilized with silica fume. These results have implications for sustainable soil stabilization practices, offering a promising approach to improve the performance of soils for various engineering applications, including construction and geotechnical projects. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) is a crucial medium of the global carbon cycle and is profoundly affected by multiple factors, such as climate and management practices. However, interactions between different SOC fractions and land-use change have remained largely unexplored in karst ecosystems with widespread rock outcrops. Owing to the inherent heterogeneity and divergent response of SOC to land-use change, soil samples with close depth were collected from four typical land-use types (cropland, grassland, shrubland, and forestland) in the karst rocky desertification area of China. The aim of this study was to explore the responses of SOC dynamics to land-use types and underlying mechanism. The results showed that land-use type significantly affected SOC contents and its fractions. Compared with cropland, the other three land uses increased the total organic carbon (TOC), microbial biomass carbon (MBC), and non-labile organic carbon (NLOC) contents by 6.11–129.44%, 32.58–173.73%, and 90.98–347.00%, respectively; this demonstrated that a decrease in both labile and recalcitrant carbon resulted in SOC depletion under agricultural land use. Readily oxidized organic carbon (ROC) ranged from 42 to 69%, accounting for almost half of the TOC in the 0–40-cm soil layer. Cropland soil showed significantly higher ROC:TOC ratios than other land-use types. These results indicated that long-term vegetation restoration decreased SOC activity and improved SOC stability. Greater levels of soil exchangeable calcium (ECa) and clay contents were likely responsible for higher stabilization and then accumulation of SOC after vegetation restoration. The carbon pool index (CPI) rather than the carbon pool management index (CPMI) exhibited consistent variation trend with soil TOC contents among land-use types. Thus, further study is needed to validate the CPMI in evaluating land use effects on soil quality in karst ecosystems. Our findings suggest that land-use patterns characterized by grass or forest could be an effective approach for SOC-sequestration potential and ensure the sustainable use of soil resources in the karst area. [ABSTRACT FROM AUTHOR]

We have studied soils of the western coast of the Chivyrkui and Barguzin bays on the Svyatoi Nos Peninsula, which is the largest peninsula of Lake Baikal in the Republic of Buryatia. Morphogenetic characteristics of soils on the main types of coasts of the peninsula—low abrasion with isolated lagoons, low abrasion, accumulative, and ingression—are given. Rocks in the basis of the coasts of the bays are an important factor of soil formation. It is shown that the genesis of soils depends on the distance from the lake and the altitude, resulting in the difference in their structure and properties. The soils are not directly affected and flooded by lake water due to high mountainous coasts, which are often rocky with steep slopes. Soil formation beyond the floodplain regime is also typical for soils of the closest to the lake level: soddy podzols, which occupy low shores of accumulative types. The particle-size composition of the studied soils varies widely from loose sand to light clay. The common properties of soils include acid and weakly acid reaction, the regressive-accumulative type of humus distribution, and differentiation of bulk oxides along the profile. The revealed evidences of podzolization in Al–Fe-humus soils and of clay accumulation in brown soils are related to sufficient moistening of the coasts and the warming effect of the lake water mass. The research results may be used in landscape planning in territorial organization and monitoring work in recreation areas. [ABSTRACT FROM AUTHOR]

Granite residual soil is a widely encountered clayey soil with unique microscopic soil structures. Its soil structures mainly stem from the presence of interparticle cementation by iron oxide. An attempt is made herein to experimentally quantify the impact of interparticle iron oxide cementation on soil's mechanical properties, particularly in the high suction range. The amount of interparticle cementation is artificially generated by mixing soil samples with varying mass fractions of iron hydroxide colloid. The mechanical behavior of these soil samples in the full suction range is measured via the drying cake test. Preliminary experimental results demonstrate that interparticle iron oxide cementation can significantly decrease soil shrinkage (by up to 52%), and substantially increase soil elastic modulus (by up to 1.83 times) and negative suction stress change (by up to 0.82 times). [ABSTRACT FROM AUTHOR]

In this investigation, the structural strength of a clayey soil compacted at three different dry densities (1.7, 1.6 and 1.5 Mg/m3) and three different compaction water contents (20%, 16% and 12%) was studied by using a micropenetrometer. The penetration curves at various water contents during the drying and wetting cycle were analyzed. The maximum unit penetration strength and the penetration stiffness were used to represent the structural strength. Experimental results show that the structural strength increases with decreasing water content. At a given water content, the larger dry density, the larger structural strength and the smaller hysteresis loop induced by the drying-wetting cycle. At a higher dry density, the structural strength increases and the drying-wetting cycle induced hysteresis loop becomes smaller. Specimens compacted on the wet side of optimum water content exhibit a dispersed structure and those compacted on dry side of optimum water content have an aggregated structure. For soils with a dispersed structure, the structural strength increases with decreasing water content and the growth rate is gradually accelerated. However, for soils with an aggregated structure, when dried to water content lower than 8%, the structural strength increases by a small degree or even decreases. Moreover, the hysteresis loop of the soil specimens with dispersed structure is much smaller than those with an aggregated structure. [ABSTRACT FROM AUTHOR]

There are three main electrochemical factors affecting the electroosmotic flow in clay soil: the voltage loss at the clay/electrode interface, the type of current carriers in the soil, and the ion composition change in the clay due to voltage application. Appropriate evaluation of these factors is important to cost effectively implement electroosmosis for in situ soil consolidation projects. In this study, three different experimental systems were developed and used to investigate electrochemical reactions occurring in reconstituted and natural marine clay during electroosmotic consolidation. The results of polarization tests show that the voltage loss at the clay/electrode interface is different depending on the combination of the clay material and electrode material. The results of electroosmotic element test also show that electroosmotic dehydration does not increase if large current–voltage value is applied and that an optimal current–voltage value for causing electroosmosis depends on the cohesive soil composition. If the clay contains a lot of oxidizable ions, such as sodium, these ions affect electrophoresis and chemical reactions that occur in the soil. Therefore, the optimal configuration to apply electric current also differs depending on the clay. The results of laboratory-scale electroosmotic dehydration tests, arranged in a realistic in situ layout, are performed to study the relationship between soil dehydration, consolidation, and surface crack generation. [ABSTRACT FROM AUTHOR]

Information on microbial biomass carbon (MBC) is crucial to assess their stocks and role for plant nutrient release in soil. Next to fumigation-extraction, molecular methods are routinely used to estimate the contribution of fungi, bacteria, and archaea to the soil microbial community. However, more information on the links between these different indices would deepen the understanding of microbial processes. The current study is based on 11 datasets, which contain MBC and MBN data obtained by fumigation-extraction and information on bacterial, archaeal, and fungal gene abundance, totalling 765 data points from agricultural, forest, and rangeland soils. Some of these datasets additionally provide information on double-stranded deoxyribonucleic acid (dsDNA) and fungal ergosterol. MBC varied around the median of 206 µg g−1 soil. MBN followed with a median MB-C/N ratio of 4.1. Median microbial gene abundance declined from bacteria (96 × 108) to archaea (4.4 × 108) to fungi (1.8 × 108). The median ratio of MBC/dsDNA was 15.8 and that of bacteria/dsDNA was 5.8 × 108 µg−1. The relationships between MBC and dsDNA as well as between bacterial gene abundance and dsDNA were both negatively affected by soil pH and positively by clay content. The median ergosterol/MBC and fungi/ergosterol ratios were 0.20% and 4.7 (n × 108 µg−1), respectively. The relationship between fungal gene abundance and ergosterol was negatively affected by soil pH and clay content. Our study suggests that combining fumigation-extraction with molecular tools allows more precise insights on the physiological interactions of soil microorganisms with their surrounding environment. [ABSTRACT FROM AUTHOR]

Evaluating the liquefaction capacity of saturated loose sandy and clayey soils is an important task to be completed in the course of implementing new construction projects in seismic areas. This article addresses the main characteristics and input parameters of three soil models, including HS small, UBC3D-PLM, and PM4Silt. The behavior of the "soil base–pile foundation–structure" system is examined by using these models to simulate the soil behavior during an earthquake. The results demonstrate the main differences between these models and draw attention to the importance of the choice of a soil model for seismic analysis, particularly when soil liquefaction is considered. [ABSTRACT FROM AUTHOR]

Laboratory experiments on clayey soils under dynamic triaxial compression were conducted to establish a nonlinear relationship between the dynamic modulus of soil deformation and the frequency of impact. The most significant increase in the dynamic modulus of soil deformation is observed under an increase in frequency from 5 to 10 Hz. In comparison with fluvioglacial soils, the dynamic deformation modulus in glacial loams grows slower under an increase in frequency. This confirms the dependence of the obtained relations on the genesis of soils. The research results were used to develop vibration protection systems for high-precision equipment in high-tech industries. [ABSTRACT FROM AUTHOR]

Coir is a promising natural fiber that can be used for soil stabilization through fiber reinforcement. In this paper, weight gain, reduction in water absorption, and single-fiber tensile strength tests are performed to evaluate the application of different natural agents such as neem oil, kerosene, and cashew nutshell liquid (CNSL) in improving the mechanical properties and durability of coir fibers. Tri-axial tests are performed on soil specimens cured for 3, 28, and 180 days to determine the improvement in their shear strength when reinforced with coir fibers treated with different agents. The fiber reinforcement led to an increase in the shear strength of the soil by improving cohesion and friction angle. Among the different agents used, the CNSL is found to be the most effective agent for coir fiber treatment. [ABSTRACT FROM AUTHOR]

In this study, fast-growing poplar reclaimed from abandoned homestead in Xixian New District, Xi'an City, Shaanxi Province, was used as the research object to explore the multi-fractal characteristics of soil particle size distribution under different management modes of abandoned land (control), irrigation, fertilizer irrigation and mixed fertilizer irrigation. The results showed that the mean values of soil clay, silt and sand in abandoned land were 14.58%, 81.21% and 4.22% respectively, 14.08%, 79.92% and 5.99% under irrigation, 15.17%, 81.19% and 3.64% under fertilizer irrigation, and 16.75%, 80.20% and 3.05% in mixed fertilizer treatment. From 40 cm, with increasing soil depth, soil clay particles increase under irrigation, fertilizer irrigation, and mixed fertilizer irrigation modes. The single fractal dimension of soil particle size distribution (D) in each treatment ranges from 2.721 to 2.808. At 60–100 cm, D shows fertilizer irrigation > mixed fertilizer irrigation > irrigation > abandoned land, indicating that fertilization and irrigation can increase the fine-grained matter of deep soil particles and reduce soil roughness. Compared with abandoned land, under irrigation, fertilizer irrigation and mixed fertilizer modes the capacity dimension (D0), entropy dimension (D1), correlation dimension(D2), shape characteristics of the multifractal spectrum (Δf) and overall inhomogeneity of the soil particle size distribution (D0–D10) indicate an uneven distribution of soil particle size; fractal structure characteristics of soil (D−10–D0) indicate a simplified soil structure, and degree of dispersion of soil particle size distribution (D1/D0) indicates that soil particle size is distributed in dense areas. Pearson correlation analysis showed that D was significantly correlated with clay, sand, D0–D10, soil organic matter (SOM) and soil available phosphorus (SAP) (P < 0.05). Stepwise regression analysis showed that clay was the main controlling factor of D and D0–D10 changes. The research results can provide some potential indicators for the quality evaluation of abandoned homestead reclamation. [ABSTRACT FROM AUTHOR]

Bottom-initiated radial cracking is a special phenomenon for soil as it is subjected to desiccation. This study aims to simulate the initiation and propagation of radial cracks in soil using both experimental and discrete-element method (DEM) approaches. Under controlled conditions of constant temperature and humidity, a laboratory desiccation test of clayey soil samples with bottom-constrained boundary conditions was carried out to illustrate the soil bottom-initiated radial desiccation cracking behavior. The evaporation characteristics as well as the development of radial cracking initiating from the subsoil were captured. To simulate this phenomenon, a desiccation model based on discrete-element method was used in DEM. Based on the laboratory testing results, appropriate parameters are selected for the numerical simulations. The DEM approach was calibrated by reproducing the experimental results of radial desiccation cracking. Subsequently, the initiation and propagation mechanisms of this typical soil cracking phenomenon was analyzed and discussed. With the constraint of the bottom boundary, the initiation of radial desiccation cracking was associated with the arched distribution of inter-particle tensile force in the soil samples. The propagation direction of the cracks was perpendicular to the inter-particle tensile forces. Finally, the effects of basal friction, evaporation gradient and shrinkage parameter on the bottom-initiated radial cracks in the simulation were analyzed. The size of the bottom particles and interface bonding factor played a significant role in the effect of basal friction. Compared with the samples under uniform water loss conditions, the bottom shrinkage rate was relatively low for the sample under a gradient water loss. In addition, an increase in the shrinkage parameter of the soil particles led to a greater extent of crack propagation. [ABSTRACT FROM AUTHOR]

Understanding the efficacy of alternative phosphorus (P) sources in tropical soils is crucial for sustainable farming, addressing resource constraints, mitigating environmental impact, improving crop productivity, and optimizing soil-specific solutions. While the topic holds great importance, current literature falls short in providing thorough, region-specific studies on the effectiveness of alternative P sources in Brazilian tropical soils for maize cultivation. Our aim was to assess the agronomic efficiency of alternative P sources concerning maize crop (Zea mays L.) attributes, including height, shoot dry weight, stem diameter, and nutrient accumulation, across five Brazilian tropical soils. In greenhouse conditions, we carried out a randomized complete block design, investigating two factors (soil type and P sources), evaluating five tropical soils with varying clay contents and three alternative sources of P, as well as a commercial source and a control group. We evaluated maize crop attributes such as height, dry weight biomass, and nutrient accumulation, P availability and agronomic efficiency. Our results showed that, although triple superphosphate (TSP) exhibited greater values than alternative P sources (precipitated phosphorus 1, precipitated phosphorus 2 and reactive phosphate) for maize crop attributes (e.g., height, stem diameter, shoot dry weight and phosphorus, nitrogen, sulfur, calcium and magnesium accumulation). For instance, PP1 source increased nutrient accumulation for phosphorus (P), nitrogen (N), and sulfur (S) by 37.05% and 75.98% (P), 34.39% and 72.07% (N), and 41.94% and 72.69% (S) in comparison to PP2 and RP, respectively. Additionally, PP1 substantially increased P availability in soils with high clay contents 15 days after planting (DAP), showing increases of 61.90%, 99.04%, and 38.09% greater than PP2, RP, and TSP. For Ca and Mg accumulation, the highest values were found in the COxisol2 soil when PP2 was applied, Ca = 44.31% and 69.48%; and Mg = 46.23 and 75.79%, greater than PP1 and RP, respectively. Finally, the highest values for relative agronomic efficiency were observed in COxisol2 when PP1 was applied. The precipitated phosphate sources (PP1 and PP2) exhibited a similar behavior to that of the commercial source (TSP), suggesting their potential use to reduce reliance on TSP fertilization, especially in soils with low clay contents. This study emphasized strategies for soil P management, aimed at assisting farmers in enhancing maize crop productivity while simultaneously addressing the effectiveness of alternative P sources of reduced costs. [ABSTRACT FROM AUTHOR]

Identifying strength parameters under drained conditions is crucial for monitoring and evaluating long-term soil deformations caused by structures built on or in soils. Geotechnical engineers carry out direct shear tests (DSTs) and triaxial tests (TAs) in the laboratory to identify strength parameters under such conditions. However, it can take considerable time to ascertain the failure envelope of even a single soil in the TA tests commonly used to evaluate drained conditions. This study explores whether the effective internal friction angle (ϕ′)—as one of the drained shear strength parameters of remolded soils—can be identified with a vane shear test (VST) at very low (down to 0.001/min) rotation speeds, which is easy to implement and takes a relatively shorter time. For this aim, 18 different remolded soil samples with a wide range of plasticity were prepared using static compaction in the laboratory. DST tests were conducted under drained conditions to evaluate the drained shear strengths of the remolded soil samples. VST results indicate that the peak shear strength decreases with the rotation speed as expected. Shear strengths obtained from the slowest VSTs were correlated with ϕ′s from DSTs. While the results were not encouraging, it was observed that the results of VSTs still could be used in a predictive equation for ϕ′ which, as a function of LL and total density as well as VST strength parameter, the regression coefficient rose to 0.92. Some effective cohesion intercepts were observed during DSTs, which in turn somewhat reduce the predicted ϕ′s. [ABSTRACT FROM AUTHOR]

Low-volume roads are anticipated to have less traffic and provide access to socio-economic activities in rural areas. The present study deals with the stabilisation of soil with locally available waste materials, i.e. low calcium fly ash (FA) and brick dust (BD). These two wastes are available abundantly and lead to an increase in pollution levels. Initially, lime was added to make the silty clayey soils plastic-free. The initial consumption of lime was found to be 5%. Then, the soil was stabilised with cement fly ash and cement brick dust techniques for strength, durability and shrinkage evaluation. The cement was varied from 2 to 8% with FA and BD by fixing the ratio to 1:3 as per AASHTO guidelines. The unconfined compressive strength (UCS), indirect tensile strength test and California bearing ratio were conducted for strength evaluation. The wetting and drying cycles were evaluated for durability analysis. The linear shrinkage cracking was evaluated after the curing period of 28 days. It was observed that there was a magnificent increase in strength and durability values. The maximum UCS attained value was so high that it could act as a replacement for the granular sub-base layer in the pavement structure. The linear shrinkage evaluated at fixed relative humidity was significantly reduced. The statistical analysis reported that there was a significant difference between the two admixtures. The utilisation of these wastes not only enhances strength, but also deficits the cost of construction along with reducing the pollutants in the environment. [ABSTRACT FROM AUTHOR]

Electrokinetics has gained importance as a sustainable soil modification and remediation method for improving problematic sites. The formation of cracks during the electrokinetic treatment is an important concern during the field implementation of the process. Therefore, considering this, this study investigated the impact of a voltage gradient on the performance evaluation of electrokinetic consolidation clayey soil after adding a lime. The performance was evaluated regarding cumulative discharge, surface settlement, power consumption, reducing water content, alteration in soil pH, and crack formation. The surface settlement increases by 50% for the applied voltage gradient of 1.00 V/cm compared to that of 0.25 V/cm. The power consumption in the case of 1.00 V/cm after the addition of lime is 3.67 times compared to that without lime; however, the difference is insignificant for 0.50 V/cm. Further, the pH near the cathode increases to 10.94 from 7.81 after the addition of lime in the case of 0.50 V/cm. Finally, adding lime helps drastically reduce the surface crack formed during the electrokinetic treatment. [ABSTRACT FROM AUTHOR]