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Soil-improvement techniques with binders are used in several geotechnical engineering applications as a sustainable solution for the reuse of waste soils. Due to their inherent complexity and their mechanical behaviour, pyroclastic soils are generally considered waste geomaterials in their natural state. Lime treatment of pyroclastic soils can be considered a viable solution for their reuse in geotechnical applications. In this paper, some peculiar features of the chemo-physical evolution and mechanical behaviour of lime-treated pyroclastic soils are evidenced through a multi-scale experimental investigation. While, for clayey soils, the fine fraction is mainly responsible for ion exchange and pozzolanic reactions induced by lime, for pyroclastic soils, pozzolanic reactions are dominant processes due to the low quantity of clay minerals along with the abundance of aluminates and silicates as the main constituents of their amorphous phase. The link between the phenomena detected at the microscale level, the mineralogical composition, and the macroscopic behaviour of two lime treated pyroclastic soils of different origin is explored through a multiscale approach. [ABSTRACT FROM AUTHOR]

Mineralogical and geotechnical properties used to analyse the swelling potentials of Al-Hartha City. According to mineralogy, montmorillonite is a dominated clay mineral (33.61%) followed by montmorillonite-chlorite (33.34%), kaolinite (9.18%) and illite (5.38%). While calcite, Quartz, Feldspar, and dolomite are non-clay minerals that are also present. According to geotechnical analysis, the percent of clay range between 9-42% with an average of 25.5%, silt 55-80% with an average of 67.5% and sand 0-17% with an average of 8.5%. While liquid limits and plasticity index are, respectively, 10–25% with an average of 17.5% and 35%–51% with an average of 43%. According to the unified soil classification system (USCS), these soils are mainly low plasticity lean clay soils (CL) and 10% classified as medium stiff elastic silt (MH). According to activity values, soils are primarily inactive-(70%), normally active-(20%), active-(10%), and their consistency is plastic. according to an assessment of soil expansivity based on index properties and activity, a significant amount of the soil is expansive. Additionally, there is an agreement between the results of the mineralogical tests performed on these soils and the results of the measures of soil expansivity obtained from the evaluation of the swelling of the soil based on assessments of its index properties. [ABSTRACT FROM AUTHOR]

One of the potassium (K) sources for plant growth are the soil clay minerals (such as vermiculite) that have K element in their structure. The purpose of this research was the investigation of non-exchangeable K release from vermiculite clay soil to citric acid and calcium chloride extractants. Treatments included two vermiculite clay soil samples (with carbonatic (CV) and non-carbonatic (NCV)) and two extractants (0.01 M CaCl2 and citric acid). Thirteen successive extractions of K were done during 1, 2, 4, 6, 16, 24, 48, 72, 120, 168, 312, 384 and 552 h. Cumulative K release was determined and data was fitted to five kinetic equations. Results showed that there was a significant difference between treatments and extractants in K release. Cumulative K release to CaCl2 for CV and NCV was 3161 and 2935 mg kg−1, respectively while this was for citric acid 2172 and 1503 mgkg−1, respectively. The best kinetic models describing K release to CaCl2 and citric acid were Elovich (r = 0.98 and 0.80, p <.01) and power function equations (r = 0.96 and 0.76, p <.01). Maximum K release was observed in carbonatic vermiculite extracted with CaCl2 (1873 mgkg−1). Results of X-ray diffraction analysis showed that the peak intensity of vermiculite reduced with extraction time and no complete conversion were observed but its peaks showed the presence of mixed minerals such as mica-vermiculite and chlorite-vermiculite. Scanning electron microscopy analysis revealed that vermiculite clay soil structure was changed and more voids were observed in the mineral structure with extraction time. It's recommended that release experiment is done in longer time for better monitoring of vermiculite structural changes. The present study showed that vermiculite clay soil taken from Jiroft mine can be used as a natural source of potash fertilizer in sustainable agriculture. [ABSTRACT FROM AUTHOR]

The full behaviour of natural clay minerals in soil organic carbon (SOC) stabilization in the presence of oxides and external C inputs is yet unknown. Thus, an incubation experiment was conducted in a sand–clay mixture with different soil clay fractions (SCFs) obtained from Alfisol, Inceptisol, Mollisol, and Vertisol in the presence of wheat residues to compare their C stabilization capacity. The C mineralization rates were higher in 1:1 type dominated SCFs (Alfisol and Inceptisol) compared to 2:1 interstratified mineral dominated SCFs (Vertisol). Wheat residues as C source altered SCFs' abilities to stabilize SOC at only moderate dosages of application (3–12 g kg−1). C mineralization and microbial biomass carbon (MBC) fell by 40% and 30%, respectively, as the amount of clay increased from 7.5 to 40%. However, removing sesquioxides from the SCFs boosted C mineralization and MBC by 22% and 16–32%, respectively, which matched with higher enzymatic activities in the sand–clay mixture. The increased C stabilization capacity of Vertisol-SCF may be attributed to its greater specific surface area (SSA) (506 m2 g−1) and cation exchange capacity (CEC) [meq/100 g]. Regression analysis revealed that SSA, CEC, and enzymatic activity explained approximately 86% of total variations in C mineralization. This study highlighted the critical role of 2:1 expanding clay minerals and sesquioxides in greater stabilization of external C input compared to its 1:1 counterpart. It also implied that the role of mineralogy or texture and sesquioxides levels in different soils (Vertisol, Mollisol, Inceptisol, Alfisol) should be prioritized while adding crop residues to reduce C footprint and enhance sequestration. [ABSTRACT FROM AUTHOR]

The accurate prediction of swelling deformation and(or) swelling pressure if confined for expansive soils is essential for a better design and construction of a geotechnical structure that is built on or in an expansive soil. In this paper, we proposed a new method to quantify the swelling strain and(or) swelling pressure of expansive soils by considering the mineralogical components and their different swelling properties. The proposed multi-component model employs a tandem combination of different sub-molecular oedometers for different minerals, and the total swelling strain of soil was calculated by integrating the swelling strain of each mineral. A linear relationship between potential energy and swelling strain is identified based on molecular dynamics' simulation, which is then incorporated into the diffuse double-layer theory to calculate the relationship between confining pressure and swelling strain for each mineral. The numerical model was then validated by experimental results from the literature, which shows a good agreement with the experimental data in the literature. This model provides a cost-effective way to estimate the swelling behavior of expansive soil. [ABSTRACT FROM AUTHOR]

Light structures, roads, and pavements in semi-arid regions suffer from frequent damage due to expansive subsurface soils subjected to frequent wetting and drying. This research presents the distribution and characterization of expansive soil in a major semi-arid region. The characterization includes investigating the mineralogy and physical properties using X-ray diffraction and geotechnical testing methods. The mineralogical study is a key factor and is utilized to interpret and understand the geotechnical behavior of these soils. The X-ray diffraction showed that the mineralogy of clay is significantly variable for zones with different geological backgrounds. The influence of the minerals on the geotechnical properties of clay from different zones is viewed and reported. Non-sharp peaks above the background intensities were reported as a common feature within the zones of smectite clay minerals. The highly plastic clays showed clear peaks of minerals known for their high expansivity. The influence of high-intensity peaks of some clay minerals within the low ranges of 2θ may cause adjacent expansive mineral peaks not to appear. The flocculation of clays rich in expansive minerals and the cementitious bond between particles influence the magnitude of swelling and shrinkage in clays. [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]

Clay is a decomposed sedimentary rock consisting of aggregates of hydrated aluminum silicates, from the decomposition of rocks containing feldspar, such as granite. Clay has plastic properties, which means that by moistening it can be easily modeled. When dried, it becomes firm and when subjected to high temperatures, chemical reactions occur that, among other changes, cause the clay to become a permanently rigid material, called ceramics. Clays have wide use in the pottery industry, construction, and winemaking, among many other applications of economic and social importance. This research aims to classify clays according to different types of clays existing in the soils of Pucallpa, Peru, through the use of plithogenic sets. This novel theory was selected because it allows us to represent multiple attributes where each consists of different possible elements, including indeterminacy and vagueness. The classification of different types of clay is not simple; some of its physicochemical characteristics are common to more than one type of this mineral. To the knowledge of the authors, it is the first time that plithogenic sets are used in the classification of minerals. In this paper we provide a method based on plithogenic sets, such that 18 types of clays of Pucallpa can be classified. [ABSTRACT FROM AUTHOR]

Temporal changes in soil development were assessed on fluvial terraces of the Little River in the upper Coastal Plain of North Carolina. We examined five profiles from each of six surfaces spanning about 100,000 years. Soil-age relationships were evaluated with inter-surface clay mineral comparisons and regression of chemical properties versus previously reported optically-stimulated luminescence ages using the most developed subsoil horizon per profile. Bases to alumina (Bases/Al2O3) ratios have negative correlations with age, whereas dithionite-Fe (FeD) concentrations are positively correlated with time and differentiate floodplain (<200 yr BP) from terrace (≥10 ± 2 ka) soils and T4 pedons (75 ± 10 ka) from younger (T1-T3b, 10 ± 2–55 ± 15 ka) and older (T5b, 94 ± 16 ka) profiles. Entisols develop into Ultisols with exponentially decreasing Bases/Al2O3 ratios, reflecting rapid weatherable mineral depletion and alumina enrichment during argillic horizon development in the first 13–21 kyr of pedogenesis. Increasing FeD represents transformation and illuviation of free Fe inherited from parent sediments. Within ~80–110 kyr, a mixed clay mineral assemblage becomes dominated by kaolinite and gibbsite. Argillic horizons form by illuviation, secondary mineral transformations, and potentially, a bioturbation-translocation mechanism, in which clays distributed within generally sandy deposits are transported to surface horizons by ants and termites and later illuviated to subsoils. T5b profiles have FeD concentrations similar to, and gibbsite abundances greater than, those of pedons on 0.6–1.6 Ma terraces along Coastal Plain rivers that also drain the Appalachian Piedmont. This is likely because the greater permeability and lower weatherable mineral contents of sandy, Coastal Plain-sourced Little River alluvium favor more rapid weathering, gibbsite formation, and Fe translocation than the finer-grained, mineralogically mixed sediments of Piedmont-draining rivers. Therefore, recognizing provenance-related textural and mineralogical distinctions is crucial for evaluating regional chronosequences. [ABSTRACT FROM AUTHOR]

Unstable soil aggregates can easily be dispersed when mechanical energy is applied, denominated as readily dispersible clay (RDC) which is usually measured by turbidimetry. Faster methods that require minimum preparation at reduced costs are needed, such as the spectroscopy technique. Nevertheless, the technique has not yet been tested on soils. Electromagnetic radiation has strong interaction with soil physical elements (sand, silt, and clay) and with selective elements of the clay fraction, such as mineralogy. Thus, this study assessed the potential of 400–16,680 nm range (visible – Vis; near-infrared – NIR; short-wave infrared – SWIR; and medium infrared – MIR) spectroscopy to estimate RDC in some tropical soils. We also evaluated the wavelengths and regions that contribute to this prediction. We collected 68 samples from the underlying horizon of three different soils from three important states in Brazil The soil analyses were performed (physical and chemical) in the laboratory. RDC quantification was compared with the Vis-NIR-SWIR and MIR wavelengths models. The random forest (RF) algorithm was used to generate the prediction in the soil database. For RDC, the Vis-NIR-SWIR and MIR configuration presented a better relationship (coefficient of correlation (r) = 0.659 and root of the mean square error (RMSE) = 0.469%), although the results were similar when the regions were evaluated separately (Vis-NIR-SWIR – 350 to 2500 nm and MIR 2500 to 16,680 nm). RDC determination is more related to bands from 1980 to 2040, 6840 to 7360, and 7750 to 9820 nm. Spectroscopy showed its importance in RDC quantification, as it is fast and does not require soil preparations. The results show that spectral wavelengths are appropriate to assist on the estimative of RDC in the studied soils and may provide a basis for future research. [ABSTRACT FROM AUTHOR]

This paper describes key research on expansive soils and the methods employed to characterize them; fallacies in the current characterization of expansive soils are also explained. Novel swell characterization models that account for hydro, chemical, and mechanical behaviors of soils are introduced and used to demonstrate in case studies to improve expansive soil stabilization practices. The first two case studies present the results of expansive soils stabilized by incorporating clay mineralogy and soluble soil sulfate measurements. An innovative design method for successful stabilization of expansive soil is introduced in the first case study, which incorporated both basic clay mineralogy and unsaturated soil behaviors as well as performance-based durability studies. Sulfate soil stabilization works on medium-to-high sulfate soils, including rigorous laboratory and field validation studies, are presented in the second case study. The third case study, which involves a steep earthen embankment built with expansive clayey soils and experiencing recurring surficial slope failures and maintenance issues, is also discussed. Forensic studies explaining the causes of slope failures and their mitigation methods are also included. All case studies reveal the need for detailed data about soil chemistry, including clay mineralogy and sulfate studies, to improve the current field stabilization and infrastructure design on expansive soils. The last section summarizes recent innovations for better health monitoring and management of civil infrastructure built on expansive soils using unmanned aerial vehicle platforms and visualization tools, which will be valuable for validating the application of new materials, designs, and construction processes. [ABSTRACT FROM AUTHOR]

The mineralogical composition of nano-clays (NCs), and their potential implications in soil bulk properties of Indian Vertisols are unexplored. In this study, we have isolated NCs (<100 nm) from Deccan basalt (DB) alluvium derived Vertisols (Typic Haplusterts) of central India and characterized them for their mineralogy and crystalline behavior. The soils are clayey (>60%) in texture, rich in smectite mineral (60–80% in <2 μm fraction), alkaline (pH 7.8–8.5), calcareous, and contain <1.0% organic carbon. The clay fraction (<2 μm) is dominated by smectitic NC (40–60%) followed by hydroxy-interlayered vermiculite (HIV), pedogenic chlorite (PCh), kaolinite, and mica. The smectite is little hydroxy-interlayered (HIS), and hydroxy-interlayering is less pronounced in NC smectites than in the coarser clay smectites. The NC smectites are of smaller crystallite size (3.5–5.5 nm) and higher in crystal strain (15–22%) than coarser size clays because of its low lattice charge. The abundance of smectitic NCs considerably reduces the saturated hydraulic conductivity (<1 cm hr–1) of the soils due to high dispersion and swelling (COLE ≥ 0.20) of smectite clays even at the low level of exchangeable sodium percentage (ESP ≤ 5) and a moderate amount of exchangeable magnesium. The report on nano clays (<0.1 μm) highlights the unique role of nano smectites in some selected soil properties, as well as in the origin of SAT Vertisols of the Indian subcontinent. [ABSTRACT FROM AUTHOR]

In the present study, characterisation and quantitative microanalysis were identified for six expansive soils of which one is natural soil, i.e. black cotton (BC) soil and remaining soils were prepared by mixing of BC soil with different percentage of bentonite. The BC soil and prepared soil samples were characterised by the X-ray diffraction (XRD) and scanning electron microscope (SEM). The regular or irregular mixed layers of soils justified by SEM images. There are superstructures whose spacing can simply be described as the ratio of BC soil and prepared soil. d-Spacing was calculated by Bragg's formula (XRD) which was observed by joint committee on powder diffraction standards card and calculated by Bragg's equation for h-k-l plane for expansive soils and it was observed that d-spacing decreased with increasing prepared soil combination. Moisture content was taken below optimum moisture content, i.e. 15%, 17% and 20% to determine swelling and swelling pressure and found that montmorillonite mineral affects the swelling characteristics of expansive soils. [ABSTRACT FROM AUTHOR]

Clay soil samples from the Afo-Okpella and Okpekpe in parts of the southern Niger Delta were analyzed for their geochemical composition, mineralogical and geotechnical characteristics. X-ray fluorescence analysis, x-ray diffraction analysis and index property tests were carried out to determine elemental composition, mineralogical nature and geotechnical attributes of the clay. The XRF reveals that SiO2 and Al2O3 are the predominant oxides. The XRD analysis shows that kaolinite is the predominant clay mineral with varying amount of quartz also traces of illite, smectite. The geotechnical index test shows that the clay soil samples studied also contains considerable amounts of silt-size particles (18%-70%) which makes them unsuitable in their raw state for use as fillers, raw materials in the paint industries. The clays were generally of medium to high plasticity and medium to high compressibility, however the classification of degree of expansion as regard to percentage linear shrinkage places the entire clay bodies studied in the critical degree of expansion. The study reveals that they are good for the production of quality bricks, ceramics and other industrial usage such as rubber, paper and paint industries. [ABSTRACT FROM AUTHOR]

The soil-water characteristic curves (SWCCs) for soils are important for geotechnical engineers in the prediction of clay behavior in case of partially saturated conditions. In the wastewater and waste containment industry, variable clay content is considered. It is not practical to run a time-consuming test several times to obtain the soil-water characteristic curves for every proportion. This study is aimed at introducing a practical procedure to predict the response of clay of known mineralogy and geological setting when clay content within a liner is variable. Fitting curves were performed using Fredlund and Xing's (1994) equations. The general trends were established for selected clay of known high content of smectite minerals. Obtained curves were examined, and areas under the suction curve were integrated from the starting point to the inflection point for clay-sand material with 5%, 10%, 15%, 30%, 60%, and 100% clay content. This area can be used to estimate the profile of the SWCC for higher or lower clay content based on an area factor determined for a specific clay type or clay of known mineralogy. Other clay of similar nature, but not typical mineralogy, were compared in order to observe and validate the use of the area method in predicting the SWCC for similar soils. [ABSTRACT FROM AUTHOR]

The 1 M ammonium acetate (NH4OAc) (AA) is the most widely used method for soil-test potassium (K), but other methods have been also suggested to estimate crop available K. The accuracy of these extractants may be influenced by soil texture and clay mineralogy. This study evaluated the relationships among AA, Mehlich-3 (M3), and sodium tetraphenylboron (TPhB) methods using soils differing in texture and clay minerals from the agricultural area of Uruguay. The M3 and AA extractable K concentrations were highly correlated (R2 > 0.97) across soils, although AA extracted slightly higher amount of K than M3. The TPhB method extracted more K than AA and M3, indicating that extracted K from different pools. The slopes of the relationships between TPhB and AA or M3 varied among soils being higher in fine-textured and illitic soils than in coarse soils. These results would be useful for evaluating the feasibility of incorporating M3 into a test program using the existing calibrations of the AA method. In addition, TPhB could be considered a complementary tool to improve the interpretations of the extractants to estimate soil-test K along with other characteristics such as the texture and clay mineralogy. [ABSTRACT FROM AUTHOR]

The current research was done to investigate the effect of wetting-drying cycles, time, and clay mineralogy on K fixation capacity of highly calcareous soils. In order to conduct the study, eight soil samples were collected. The samples were treated with different concentrations of K including 200 (K1), 400 (K2) and 800 mg kg−1 (K3) and 8 different incubation time including 6 h (t1), 24 h (t2), 72 h (t3), one week (t4), two weeks (t5), one month (t6), two months (t7) and three months (t8). Also, a wetting-drying treatment was done (td) in order to simulate the effect of irrigation and soil drying on K fixation. The results showed that for all K levels addition, the percentage of fixed K was increased with time. The K fixation content was increased with the increase in the added K from K1 to K3, while K fixation percentage was decreased. The results also showed that there was a significant difference between soils with wetting-drying treatment (td) and soils with three-month incubation (t8) in K fixation capacity, so that the fixation of K by the soils was increased with wetting-drying cycles. [ABSTRACT FROM AUTHOR]

The hysteretic behaviour of the dry region (<−1.5 MPa) of the soil water characteristic, which is of the essence for accurate characterization and modelling of bio‐physicochemical soil processes under dry conditions, is well documented. However, knowledge about how to best quantify water vapour sorption hysteresis and about the effects of soil properties on dry‐region hysteretic behaviour is limited. To overcome this knowledge gap, we proposed a new method for quantifying sorption hysteresis and evaluated its applicability based on measured sorption isotherms of four source clay minerals and 147 soil samples. Furthermore, the effects of clay mineralogy, clay content, soil organic carbon (SOC) and cation exchange capacity (CEC) on the magnitude of sorption hysteresis were investigated. For the clay minerals, kaolinite did not exhibit hysteretic behaviour, illite showed some hysteresis, whereas Na‐ and Ca‐smectite exhibited strong hysteretic behaviour. The average hysteresis, corrected for clay and SOC contents, was strongly reflective of the dominant clay mineralogy of the soil samples. For the soil samples with low SOC content, the average hysteresis significantly increased with increasing clay content (R2 = 0.92), except for the kaolinite‐rich samples (R2 = 0.35). The SOC‐rich samples that exhibited illitic clay mineralogy and similar soil texture showed a significant increase in average hysteresis with increasing organic carbon content (R2 = 0.93). For all soil samples combined, the CEC was the strongest indicator for the magnitude of water vapour sorption hysteresis. Highlights: A new index for quantification of soil vapour sorption hysteresis was proposedLarge SOC and clay content increased sorption hysteresisFor soil samples, dominant clay mineralogy controlled the magnitude of hysteresisCation exchange capacity was the best predictor of hysteresis for all soil types [ABSTRACT FROM AUTHOR]

Purpose: The aims of this study were to investigate the composition of clay minerals in soils derived from different parent materials and to elucidate how parent materials and pedogenic environment affect the distribution of clay minerals and reveal the implications for pedogenetics and taxonomy in Stagnic Anthrosols. Materials and methods: Clay mineralogy and physicochemical properties of the Hydragric horizon of Stagnic Anthrosols derived from granite (GR), plate shale (PS), quaternary red clays (QRC), limestone (LS), purple sandy shale (PSS) and fluvial-lacustrine deposit (FLD) located in Hunan Province of China were analysed to explore the relationships between the conditions influencing the formation of the soil and the composition of clay minerals. Results and discussion: Results indicated that the composition of clay minerals is closely related to both parent material and type of Stagnic Anthrosols: the soils derived from GR, PS and QRC, which are mostly classified as Fe-accumulic-Stagnic Anthrosols, are dominantly 1:1 type kaolinite and vermiculite and illite/vermiculite mixed layer minerals of widespread distribution. However, soils derived from LS, PSS and FLD were mainly classified as Hapli-Stagnic Anthrosols and are mainly composed of 2:1 type illite/smectite mixed layer minerals, where chlorite is commonly found. Illite is widely distributed and its content varies the least among different parent materials. An extremely significant relationship between pH and kaolinite, chlorite and mixed layer minerals was noted, and the two kinds of mixed layer minerals showed highly significant negative correlation. Conclusions: This study revealed that the types and quantities of clay minerals in the soil are closely related to the types of parent material. This reflected better direction and degree of development in Stagnic Anthrosols, which is related to the physicochemical properties of parent material and can be used as one of the bases for the classification of soil groups and subgroups within the soil family for Stagnic Anthrosols in Chinese Soil Taxonomy. [ABSTRACT FROM AUTHOR]

Irrigation water containing appreciable amount of magnesium (Mg) is increasingly used in farming. However, studies on the effect of Mg on soil permeability and structural stability are limited and the results are contradicting. In this study, four soils of different dominant clay mineralogy, specifically kaolinite, illite and montmorillonite, were used to investigate the effect of Mg on saturated hydraulic conductivity (K sat), interaction with organic carbon and soil clay dispersion and to compare to the effect of Ca. The soils were packed in columns and leached with four groups of either Ca-Ca, Ca-Mg, Mg-Mg or Mg-Ca solutions at the successive concentrations of 0.5, 0.25, 0.1, 0.05, 0.025, 0.01, 0.005, 0.001 and 0.0001 M, and finally with deionised water. K sat was measured and leachates were assessed for dissolved organic carbon (DOC) and dispersion as turbidity. The leached soils were tested for aggregate stability, mechanical dispersion and zeta potential. This study showed that Mg had a disaggregation effect on soil structural stability. As compared to Ca, K sat on Mg treated cores were lower over a wide range of concentrations, desorption of DOC and turbidity from Mg clay surface was higher, although the dispersion in leachates was insignificant under both Mg and Ca treatments. The effect of Mg treatment was more pronounced on smectic and illitic soils. The decrease in K sat was related to Mg induced disaggregation, due to intra-crystalline swelling and/or the inter-crystalline swelling in Mg treated soil clays. • Mg had a disaggregation effect on soil structural stability. • Mg reduces K sat as compared to Ca. • DOC from Mg leached samples is greater than that from Ca leached samples. [ABSTRACT FROM AUTHOR]

Lemon (Citrus limon), a species of the genus Citrus, is an economically significant crop and extensively cultivated in Iran, especially in Fars Province. Very little information is currently available on the changes in the different forms of soil potassium under the influence of lemon tree plantations or the associated mineralogical changes. The objective of this study was to investigate the status of different forms of K and the transformation of K-bearing minerals in the rhizosphere in lemon orchards of varying ages. Results demonstrated that the amounts of soluble, available, exchangeable, and nonexchangeable K in the control were higher than those in the lemon orchards of all the age range studied. The highest reduction in the different forms of soil K was measured for the 50-year-old orchard. The nonexchangeable K was significantly lower in the 20- and 50-year-old lemon orchards as compared with the control soil. Soil potassium concentration was observed to decrease with increasing soil depth. Our findings also indicated that vermiculitization of illitic clay minerals occurred due to both root potassium uptake and root activities in the rhizosphere of lemon trees. Shallower soil depths in the orchards were found to contain a higher illite content, while the vermiculite and interstratified I/S content increased with depth, except in the case of the 5-year-old orchard. Our findings also show that soils under lemon orchards of different ages exhibit differences in their K availability and, further, that vermiculitization might take place as a result of long-term cultivation despite the application of potassium fertilizers. [ABSTRACT FROM AUTHOR]

Abstract Clayey soils are considered as problematic soils for geotechnical engineering. They are characterized by poor geotechnical properties because of their high plasticity and water absorption properties. The consisting treatment by substituting a fraction of these soils by an inert sand is approached. However, if some conclusions are common to these works, they could not be generalized. Very often, the results obtained depend on the nature and intrinsic properties of the soils considered. The aim of the present study is to investigate clayey soil (from the region of Medea, Algeria) treatment effect by using dune sand on geotechnical, structural and mineralogical properties. Atterberg limits, compaction and unconfined compression tests are performed on clay soil and for mixtures with different dune sand percentages. In addition, triaxial tests and free swelling oedometric tests are carried out on the mixture corresponding to the optimal dune sand content. The mineralogical properties are determined using X-ray diffraction (XRD). X-ray diffraction patterns have showed that the dune sand addition in clay soil introduces only a change in quartz intensity. In addition, it is observed that the treatment provides a substantial improvement in the mechanical properties, especially for the 30% dune sand mixture. Nevertheless, this optimal with 30% dune sand mixture does not solve the problem of swelling, because the latter is important than untreated clay soil. Highlights • Clayey soil treatment with dune sand. • Dune sand addition impact on the geotechnical characteristics of clayey soil. • Dune sand addition effect on the mineralogical properties of clayey soil. [ABSTRACT FROM AUTHOR]

Abstract Argillites that strongly luminesce under UV radiation were detected in the Bazhenov Shale Formation (BSF) of the West Siberian Basin during routine core examination and found to be persistent over a wide lateral area. The mineralogy and fabric of these luminescent layers were characterized by optical and fluorescence microscopy, SEM, TEM, XRD and IR methods. Optical and fluorescence microscopy showed that the luminescent layers were to a large extent derived from volcanic ash falls and could be described as meta-tuffites, although normal detrital sedimentation continued at the same time. The layers have a thickness of several mm to a maximum of 3–4 cm and can be defined as a clay-rich regional horizons extending for over 500 km. XRD showed that two principal clay minerals were predominant, namely a kaolinite group minerals, (kaolinite-rich) and a mixed-layer illite-smectite (I/S) similar to that found in K-bentonite. Total organic matter in the luminescent layers is much lower than that in the enclosing BSF clayey-silty siliceous sediments above and below as shown by pyrolytic analyses. Evidence is presented that the luminescent characteristic of the argillites is related to their clay mineralogy, specifically to their content of kaolin minerals, although a contribution from nitrogenous organic matter cannot be entirely discounted. In some ways the luminescent argillites can be compared with bentonites associated with ash transformations or with tonsteins in coal beds, which are also derived from volcanic ash falls and contain highly crystalline kaolinite. However, tonsteins originate at or near land surface whereas the argillites were apparently formed in the deep ocean. But just as tonsteins can be used for detailed stratigraphic studies and are valuable in the context of coal exploration, so may the luminescent argillites prove to be significant both stratigraphically and in the search for economic hydrocarbon deposits, bearing in mind that their clay mineralogy may be sensitive to temperature and depth of burial and related to their placement in the oil and gas window. Graphical abstract Image 1 Highlights • Luminescent layers in the Bazhenov Shale Formation occur over a wide area of the West Siberian Basin. • The luminescent layers are clay-rich and originate from alteration of volcanic ash in a deep ocean environment. • The mineralogy of the luminescent layers is dominated by kaolinitic minerals and mixed-layer illite-smectite. • The luminescent layers are kaolinitic meta-tuffites, similar to tonsteins and K-bentonites. • These layers could be possibly used as lithostratigraphic markers. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate and relate the geotechnical parameters with the mineralogical properties of the Miocene and Plio-Quaternary (Pliocene to Quaternary) lacustrine and fluvial sediments, particularly clayey soils in the Orta County, Çankırı. The study area is located about 110 km northeast of Ankara which is the capital city of the Republic of Turkey and Orta is a small county of Çankırı. The study area is a structural depression in the northern part of the Orta plain which is filled by fault-controlled continental sedimentation. In order to correlate the geotechnical and mineralogical characteristics and to establish a relation between these properties, comprehensive geotechnical laboratory studies have been performed. For correlation purposes, disturbed and undisturbed soil samples were collected from twenty-two locations of the study area. On these samples, mineralogical (i.e., methylene blue absorption, specific surface area determination, X-ray powder diffraction (XRD) and scanning electron microscope (SEM-EDAX)) analysis and geotechnical (i.e., sieve analysis, hydrometer, Atterberg (consistency) limits, oedometer and swelling) tests were implemented. By the aid of the statistical analysis, cross-correlation of the soil properties was established by the regression analyses performed. In particular, the plasticity index was correlated with cation exchange capacity, specific surface area, clay content, percent of fines, smectite and smectite/kaolinite ratio (SKR). There was a direct relationship between PI and smectite percentage as well as between PI and SKR. Additionally, the liquid limit was correlated with the clay content and the effect of the specific surface area on the swelling characteristics was studied. The effects of the mineralogical properties of the Orta clays together with the geological history on geotechnical parameters were investigated by considering the relationships mentioned. The results of the study revealed that the mineralogical characteristics had a significant effect on the geotechnical behavior of clayey soils of the Orta County which was demonstrated by regression analyses. Finally it was identified that the geotechnical properties of clayey soils can be approximated and more reliably determined if the mineralogical character and composition of clay is accurately investigated and well developed. [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]

Observations from past earthquakes have shown that subway tunnels can suffer severe damage or excessive deformation due to seismic shaking. This study presents the results of finite element analyses on subway tunnels installed in normally consolidated clay deposits subjected to far-field ground motions. The clay strata were modelled by a hyperbolic-hysteretic constitutive model. The influences of three factors on the seismic response of the clay-tunnel systems were examined, namely ground motion intensity, tunnel wall thickness and clay stiffness. Furthermore, the computed racking deformations of the tunnel were compared with several analytical estimations from the literature, and the relationship between racking ratio and flexibility ratio for rectangular tunnels installed in normally consolidated clay deposits was proposed. The findings may provide a useful reference for practical seismic design of tunnels. [ABSTRACT FROM AUTHOR]

Marl was treated with Mg-rich lime to evaluate the effectiveness of lime stabilization for this expansive, clay- and carbonate-rich material. XRD and TEM analyses revealed very limited dissolution of expandable clay minerals and neoformation of Mg-enriched smectites. C-(A)-S-H phases formed and initially cemented clay particles. However, they experienced decalcification and decomposition over time, leading to disaggregation of clay particles and deterioration of some of the marl's geotechnical properties. Results question the effectiveness of lime stabilization for marls, especially using Mg-rich lime. Modifications to commonly used treatment protocols in order to overcome these shortcomings are discussed. [ABSTRACT FROM AUTHOR]

Heavy clay soils are globally widespread but their poor drainage and poor aeration limit their use for agriculture. This study was designed to test the effect of the amendment of biochar (BC) from woody shrubs on drainage/saturated hydraulic conductivity (Ksat), soil aeration/air capacity, available water capacity and biomass and grain yields of maize. In a field experiment, BC from Gliricidia sepium was applied in planting basins or rip lines at 2.5% and 5% w/w in addition to a control without BC. The maize biomass and grain yields were higher in BC treated plots compared to control (p<0.05) during the 2012 and 2013 seasons. There was no significant difference in the yields between 2.5% and 5% BC treatments (e.g. grain yield were 6.6 and 8.1 t ha-1 in 2012 and 9.3 and 10.3 t ha-1 in 2013 compared to control with 4.2 and 6.7 t ha-1 in 2012 and 2013, respectively). Soil from the same field site was also mixed with a similar woody shrub BC from Eupatorium adenophorum in the laboratory at rates of 2.5%, 5% and 10% BC w/w and a control without BC. The mixtures were then incubated and subjected to two wet-dry cycles for two weeks. Core samples were taken from the incubated soil and tested for bulk density, Ksat and pF measurements. Total porosity and moisture at field capacity and wilting point were 72.3%, 43.7% and 23.7%, respectively, and not affected by BC amendment (p>0.05). In contrast, bulk density decreased linearly by 0.011±0.002 g cm-3 per percent BC added (p<0.001). Ksat and air capacity of the soil were 288 cm day-1 and 30.9%, respectively falling within the generally accepted optimal range. Both Ksat and air capacity followed a significant quadratic relation (p<0.05) upon BC addition, decreasing at low BC doses, reaching a minimum at 3–5% BC and increasing at higher doses. Results allowed a partial attribution of the yield increases to changes in soil physical properties such as changes in bulk density and not clearly to Ksat and air capacity. [ABSTRACT FROM AUTHOR]

Since the discovery of oil and gas in Oloibiri, an onshore oilfield located in Oloibiri in Ogbia Local Government Area of Bayelsa State, Nigeria on Sunday 15th January 1956 by Shell Darcy, hundreds of oil wells have been drilled and not a single of these oil wells was drilled without the use of bentonite. This work is aimed at evaluating the rheological properties of raw and beneficiated Nigerian clays to ascertain their worth for use as drilling mud in oil and gas well drilling. This will save foreign earnings used in the importation of bentonite by the oil and gas development companies, create employment opportunity and open a new frontier for solid mineral development. Five clay samples from Pindiga Formation in Benue Trough, northeastern Nigeria were collected and subjected to elemental, rheological and other physical properties tests and analysis, while another portion of same samples were beneficiated using sodium carbonate, gum Arabic and poly-anionic cellulose for rheological enhancement then subjected to same cycle of tests and analysis above. Results obtained indicates that wet beneficiation as adopted in this study has proved to be more effective in Ca and Na ionic exchange. The rheological and other physical properties of the clays attained the standard that is required for use in oil and gas well drilling after addition of 12% sodium carbonate and 1.5 g poly-anionic cellulose. It was also discovered that when the formulation was allow to age (stay for 24 h), it attained optimum rheological requirement with 12% sodium carbonate and just 0.8 g poly-anionic cellulose. The clays studies do not require addition of weighing additive such as barite because of their high iron content which made their density attain the require standard even without additives. [ABSTRACT FROM AUTHOR]

Soils exhibit undesirable volume changes when exposed to high concentrations of acids, which is manifested most frequently in the beds of foundations of industrial establishments associated with their production or use. However, control of this phenomenon has received less attention than it deserves. This paper aims to investigate the mineralogical and micro-structural changes occurred during the volume change behavior of phosphogypsum treated clayey soils contaminated with sulfuric acid and phosphoric acid solutions. Oedometer test results showed high swelling and low compressibility for acid contaminated soils than that of water. The change in microstructure towards flocculated fabric along with mineralogical transformations are responsible for the volume changes in soils. The mineralogical changes that affected the volume change behavior are discussed with FT-IR, XRD and SEM analysis. Phosphogypsum treatment was found to be effective in controlling volume changes in soils with phosphoric acid, whereas in the case of sulfuric acid found to be futile. [ABSTRACT FROM AUTHOR]

• Adhesion behavior of clayey soils are investigated through experimental tests. • Adhesion increases firstly and decreases thereafter with increasing water content. • Clay fraction and mineralogical composition significantly influenced the adhesion. • The updated semi-empirical diagram considering compositional factors is proposed. Clogging is common for tunnel boring machines, especially in clayey soil, and when it happens, the cutter heads or even the entire tunnelling device can become completely clogged, causing low excavation efficiency and high project costs. Because clogging stems from the adhesion of the excavated geomaterials, a better understanding of soil adhesion is required if clogging is to be avoided. Reported here are piston pull-out tests conducted to investigate the adhesion of natural clayey soils and artificial soils prepared using pure kaolin, montmorillonite, and silica sand, thereby enabling consideration of the effects of compositional factors (e.g., clay fraction, and mineralogy). The results show that with increasing water content, the adhesion stresses of the studied samples increased initially and then decreased. With increasing clay fraction, the adhesion stresses increased linearly because of the larger real contact area of the interface between the soil and a foreign object. With the addition of montmorillonite, the soil adhesion also increased significantly because of its microstructural properties. An updated semi-empirical diagram is proposed that allows the effects of compositional factors on clogging potential to be evaluated qualitatively. The measured maximum adhesion stresses of the studied samples occurred in the region of strong clogging in the semi-empirical diagram, showing the feasibility of using adhesion stress as an index for assessing the clogging of tunnel boring machines. This study provides valuable experimental data on soil adhesion and a better understanding of the adhesion behavior of clayey soils. [ABSTRACT FROM AUTHOR]

Effective pretreatment of spectral reflectance is vital to model accuracy in soil parameter estimation. However, the classic integer derivative has some disadvantages, including spectral information loss and the introduction of high-frequency noise. In this paper, the fractional order derivative algorithm was applied to the pretreatment and partial least squares regression (PLSR) was used to assess the clay content of desert soils. Overall, 103 soil samples were collected from the Ebinur Lake basin in the Xinjiang Uighur Autonomous Region of China, and used as data sets for calibration and validation. Following laboratory measurements of spectral reflectance and clay content, the raw spectral reflectance and absorbance data were treated using the fractional derivative order from the 0.0 to the 2.0 order (order interval: 0.2). The ratio of performance to deviation (RPD), determinant coefficients of calibration (), root mean square errors of calibration (RMSEC), determinant coefficients of prediction (), and root mean square errors of prediction (RMSEP) were applied to assess the performance of predicting models. The results showed that models built on the fractional derivative order performed better than when using the classic integer derivative. Comparison of the predictive effects of 22 models for estimating clay content, calibrated by PLSR, showed that those models based on the fractional derivative 1.8 order of spectral reflectance ( = 0.907, RMSEC = 0.425%, = 0.916, RMSEP = 0.364%, and RPD = 2.484 ≥ 2.000) and absorbance ( = 0.888, RMSEC = 0.446%, = 0.918, RMSEP = 0.383% and RPD = 2.511 ≥ 2.000) were most effective. Furthermore, they performed well in quantitative estimations of the clay content of soils in the study area. [ABSTRACT FROM AUTHOR]

Exchangeable sodium ions are widely reported to be the principal reason for the dispersivity of soils. From fundamental theoretical considerations, several other factors such as pH, cation exchange capacity, mineralogy, electrolyte concentration, and dissolved salts can affect the attractive/repulsive forces in soils and hence are considered to have a significant role in assessing the dispersivity of soils. To assess the influence of these parameters, a known dispersive soil was treated with sodium hydroxide and lithium hydroxide and the dispersivity was assessed. It was confirmed that the effects of these factors on dispersivity are manifested through the amount of hydration of the adsorbed monovalent cations. Because the inner hydration shell of adsorbed monovalent cations is larger than those of higher-valency ions, dispersivity is related to the presence of monovalent cations alone. It was also established that within the monovalent cations, the size of hydrated ions can vary and can influence the dispersivity of the soil. The dispersivity of soils increased with a reduction in the size of the ions. The increase in repulsive force (causing dispersion) due to the reduction in the size of the cation is explained through diffuse double layer theory. A complete philosophy of dispersion is proposed in light of the current experimental results. [ABSTRACT FROM AUTHOR]

Clayey marl from four localities in the Neogene basin of Jijel (NE Algeria) were studied by mineralogical and physico-chemical characterization in order to evaluate their potential suitability as raw materials in ceramic applications. X-ray diffraction (XRD) and Fourier Transform-Infrared (FT-IR) spectrometry are used to establish the mineralogical composition. Chemical and physical properties were carried out by XRF and particle size distribution, consistency limits, calcimetry of Bernard and density of solid particles, respectively. Quartz, clay and calcite were present as dominant mineral phases associated with feldspars, plagioclase and dolomite. The clay minerals prevail in all samples, with kaolinite and illite being the dominant phase and interstratified 10–14 Å and chlorite, comprising the rest of the clay components. The chemical compositions indicated that SiO 2 (42–54%), Al 2 O 3 (12–19%) and CaO (2–17%) are major elements while Fe 2 O 3 is less abundant (4–8%). The classification of the clays using appropriate ternary diagrams suggests their possible use in the production of red products like tiles and masonry bricks. [ABSTRACT FROM AUTHOR]

The Bazhenov Shale Formation (BSF) of the west Siberian Basin is considered to be a promising unconventional hydrocarbon reservoir, acting as a source, store and seal of the oil and gas contained therein. It has a high content of organic matter, ranging from 2 to 20% (average 8–12%), and was deposited in a marine environment at an average water depth of 2220 to 2500 m where depositional conditions were of an intensely reducing nature. Deposition took place over a period of 8 to 10 million years mainly during Upper Jurassic times. This study reports the mineralogy of 83 core samples representative of the clayey-silty siliceous rocks of the Bazhenov Shale Formation (BSF) taken from six wells in the south-east of the west Siberian Basin. The mineralogy of most samples was found by X-ray diffraction (XRD) to be strikingly similar with most being dominated by quartz, and with albite, mica-like minerals (illite plus mixed-layer illite/smectite (I/S)) and pyrite commonly occurring in subsidiary amounts. Kaolinite and chlorite occur intermittently, usually in no great quantity. Throughout all six wells, plagioclase feldspar (albite) predominates over K-feldspar which is only of sporadic occurrence. The clay (< 2 μm) fraction of available core samples largely consists of illitic material comprising a combination of true illitic mica and mixed-layer I/S with R 3 stacking. Both optical microscopy and scanning electron microscopy (SEM) show the BSF to be composed of a mixture of detrital and authigenic minerals. Thus, quartz occurs as a detrital mineral and as the crystallized product of radiolarian tests subsequent to deposition. The micaceous (muscovitic) material seen in thin section is clearly of terrigenous origin but the fine-grained illitic material is considered to be at least partly diagenetic . With regard to feldspars, although thin sections show some to be detrital, it is considered that albite is also likely to be a diagenetic mineral, as it is in many sandstone reservoirs. In many of the core samples albite is the only feldspar detectable and it is improbable that provenance could yield feldspar detritus consisting only of pure albite over such an extended period of time. Other minerals in the BSF must also be regarded as diagenetic rather than detrital. This is certainly true of the carbonate minerals and pyrite, and the book-like aggregates and euhedral morphology of kaolinite observed by SEM and TEM are also indicative of a diagenetic origin. Finally, the illitic clay mineralogy of the BSF is considered in a general way in the context of their permeability, particularly as it relates to their anisotropic structure and pore water chemistry. It is also suggested that the siliceous nature of the Bazhenov shale makes it a suitable candidate for the creation of enhanced permeability through hydraulic fracturing technology, although matrix permeability may be adversely affected by reactions involving the external basal surfaces of the illitic clays exposed in slit-like pores. [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]

• 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]

The shrinkage and swelling phenomena of certain clay soils cause differential settlement manifested by disorders that affect mainly the individual frame. The objective of this research was to create a map related to these phenomena especially in the area of Algeria N’gaous (figure 1). The approach of the study is primarily based firstly on the interpretation of a geological map at a scale 1 : 50 000 and on the other part from existing literature and observations on a synthesis of a large number of geotechnical information to determine susceptibility to the phenomenon of clay or marl formations. This approach consisted in the establishment of a synthetic departmental mapping of these formations that have been identified from a hierarchy as to their susceptibility according to the shrinkage and swelling phenomenon. This classification was established on the basis of three quantifiable main features: the dominant lithology of formations, the mineralogical composition of their clay fraction (proportion of swelling minerals) and geotechnical behavior (primarily assessed from the blue value and the plasticity index). [ABSTRACT FROM AUTHOR]

• Mechanical and microstructural behavior of a clayey soil stabilized by an alkali-activated binder composed of two residues. • Experimental design to analyze the mechanical behavior of soil-alkali activated binder, and soil-Portland cement mixtures. • Porosity/binder content index as a reliable parameter when evaluating soil stabilization. This paper evaluated the mechanical and microstructural behavior of a clayey soil stabilized by an alkali-activated binder composed of two residues (sugarcane bagasse ash and hydrated eggshell lime) and sodium hydroxide. The sugarcane bagasse ash, an agro-industrial waste, contains high aluminosilicates content (64.74 % silica and 13.25 % alumina), needed for alkali-activation processes; calcium additions from the lime (72.90 % calcium oxide) allow curing at room temperatures. An experimental design analyzed the mechanical behavior of soil-alkali activated binder, and soil-Portland cement mixtures. Unconfined compressive strength (UCS), tensile strength (STS), stiffness (G 0), durability (accumulated loss of mass, ALM), and matric suction tests, and XRD and SEM-EDS investigations were performed. Statistical analysis showed a higher influence of the dry unit weight over the binders' mechanical results. In addition, binders presented similar mechanical results for mixtures cured in room temperature (23 °C) (e.g., UCS around 5 MPa for high density-high binder content samples with 30 % moisture content, and STS around 0.6 MPa for high density-high binder content samples with 28 % moisture content). For both binders, the lowest ALM was 1.63 % for high density-high binder content samples. The porosity/binder content index was a reliable parameter when evaluating soil stabilization. XRD and SEM analysis of alkali-activated samples showed, respectively, an amorphous hump attributed to disordered structures (C S H and (C,N)-A S H) and soil particles embedded in a cementitious matrix. Higher temperature (40 °C) and curing period (28 days) resulted in a denser structure. [ABSTRACT FROM AUTHOR]

The interaction of similar soil forming factors with different parent materials determines soil chemical weathering, influencing soil processes and properties. In the coastal temperate rainforests of southeast Alaska, Spodosols is the dominant soil order in well-drained parent materials regardless of the lithology. Yet, the role of lithology on chemical weathering, base cation depletion, and mineral transformation during pedogenesis remains elusive. Here, we established a lithosequence comprised of soils derived from tonalite, phyllite, slate, and metavolcanic rocks to test the hypothesis that despite the soils in southeast Alaska presenting similar taxonomy and morphology, the influence of lithology in chemical weathering intensity and mineralogy can be detected. We evaluated physicochemical properties, clay mineralogy, Fe-Al oxides, chemical weathering, and elemental mass balance on eleven Spodosols sampled along the lithosequence. We also propose a new weathering index, the Weathering Index for Spodosols (WISP), suitable to evaluate the weathering degree of soils with Al mobility and base-rich parent materials. This index fills a gap in traditional weathering indices that uses Al as an immobile element and/or does not evaluate the leaching of main base cations. We found the pedons across the lithosequence expressed similar physicochemical properties, with predominantly thick profiles, presenting andic properties, relatively thick spodic horizons, and thin E horizons. Podzolization imposed similar mineral transformation trends, mainly dissolution of chlorite, mica alteration to interstratified mica-vermiculite, and formation of smectite in E horizons. Kaolinite was detected in the soils from all lithologies, but only in trace amounts in phyllite soils. Fe oxides depth distribution was similar but with a higher concentration in the slate (44.5 ± 4.2 g/kg), followed by metavolcanic (31.6 ± 4.0 g/kg), phyllite (27.9 ± 3.8 g/kg), and tonalite soils (19.9 ± 5.7 g/kg) and predominantly as organometallic complexes (extracted by Na-pyrophosphate). The stronger weathering of chlorite and mica in the E horizons was reflected in larger losses of Mg and K, while Ca and Na were more depleted in the spodic horizons, suggesting plagioclase weathering. Slate soils were the most depleted in base cations, followed by phyllite, tonalite, and metavolcanic soils. The more depleted status of slate soils was supported by the higher WISP values (WISP = 62), followed by phyllite (WISP = 55), tonalite (WISP = 53), and metavolcanic soils (WISP = 45). Our results demonstrated that lithology controlled elemental depletion intensities, Fe oxide concentrations, and partially the clay fraction mineralogy in addition to podzolization acting as a dominant pedogenic process across all sites. These findings advance our understanding of the role of lithology on soil mineralogy/geochemistry that impacts critical soil functions, such as the soil carbon cycle, elemental fluxes, organo-mineral interactions, and solid-solution reactions. [ABSTRACT FROM AUTHOR]

Dispersive soil has poor physical properties, which reduce porosity, air and water movement. These properties can reduce crop production and create problems with soil stability under buildings and infrastructure. Traditionally, clay dispersion has been related to the exchangeable sodium percentage ( ESP) of soil or to the sodium adsorption ratio ( SAR) of soil solutions. However, the roles of the other exchangeable cations, potassium and magnesium, in clay dispersion have been debated in the literature and their importance is unresolved. Based on the relative dispersive and flocculating powers of sodium, potassium, magnesium and calcium, a new concept for describing dispersive soil is proposed. This defines the net dispersive charge as the difference between the dispersive charge, calculated from the concentration of exchangeable cations measured at a given soil pH and their dispersive powers, and the flocculating charge, calculated from the concentrations of cations in dispersed solutions and their flocculating powers. The net dispersive charge of a soil determines the clay dispersion. Clay disperses when the net dispersive charge is positive and does not disperse when it is zero or negative. This new concept resolves controversies in the literature caused by the roles of organic matter, clay mineralogy, exchangeable cation composition and electrolyte concentration in relation to clay dispersion. Experimental confirmation of this concept is provided by the analytical data of 96 soil samples collected from different parts of South Australia and Victoria in Australia and from previously published data. Possible methods of estimating net dispersive charge from soil solutions are discussed. Highlights Examined the role of different exchangeable cations in inducing clay dispersion., The long-debated issue of the importance of different cations in dispersive soil is resolved., The net dispersive charge in soil is related to the amount of dispersed clay., Reclamation of dispersive soil requires the net dispersive charge to be zero. [ABSTRACT FROM AUTHOR]

Shield tunnel drives in both, overconsolidated clays soils and sedimentary rock with clay minerals, frequently suffer extremely from hindrance due to clogging. The problem of clogging can have varying degrees, from locally blocked disk cutter housings to completely clogged excavation chambers with a blocked cutterhead. The clogging risk depends on multiple mineralogical and soil-mechanical parameters. The authors have more than 15 years of experience in practice and scientific research with the problem of clay clogging of TBMs. The paper shows the occurrence and risk for clogging in varying ground types and for different machine components, summarizes the available characterization methods for the stickiness of the ground, discusses a variety of laboratory tests for the assessment of clogging potential, explains a recently developed diagram for the assessment of clogging risks for all types of tunnelling machines, and introduces a new testing scheme for the evaluation of sedimentary rocks regarding clogging. [ABSTRACT FROM AUTHOR]

ABSTRACT Development of rock physical properties in well-sorted and poorly-sorted unconsolidated mono-quartz sands and sand-clay mixtures as a function of effective stress in both dry and brine-saturated conditions is assessed in this study. The tested samples were prepared with full control on their mineralogy, grain size, grain shape, sorting, and fabric. The experiments were performed in a high-stress uniaxial oedometer up to a maximum of 30 MPa vertical effective stress. Sand-clay samples were a mixture of sand grains and clay particles (kaolinite or smectite) in different proportions. The maximum clay volume fraction used in the experiments was at most 30%. The initial bulk density of the tested sand-dominated samples was adjusted to be close to the maximum index density expected for natural sediments (sand-clay mixtures) during deposition. In pure sand samples, finer grained sand show higher initial porosity than relatively coarser grained sands. Moreover, sand-clay mixtures have lower initial porosity than pure sands. Porosity decreases as a function of increasing clay content. The poorly-sorted sand samples are less compaction prone than the well-sorted sand samples. Among well-sorted sand samples, coarser grained sands are more compressible than finer grained sands. At a given effective stress level, sand-clay mixtures are more compaction prone compared with their sand component alone. Pure sands and clay-poor sand-clay mixtures (either sand-kaolinite or sand-smectite) show almost the same degree of compaction when tested in both dry and brine-saturated conditions. In contrast, clay-rich sand-kaolinite and sand-smectite mixtures (clay volume >20%) are significantly more compact in brine-saturated condition. The Vp values of brine-saturated sand-kaolinite mixtures shows a positive correlation with the kaolinite content, whereas Vp starts to decrease substantially when the volume fraction of smectite exceeds 10% of the whole sand-smectite samples. Saturated bulk moduli estimated by Gassmann's fluid substitution agree with measurements for brine-saturated clay-poor sand samples. However, the model does not yield proper predictions for sand-clay samples containing 20% clay volume and above, particularly when the clay is mainly smectite. The acoustic and physical properties derived from experimental compaction of pure sands and sand-clay mixtures show a good agreement with rock properties derived from well logs of mechanically compacted pure sands and shaly sands in progressively subsided basins such as Viking Graben in the North Sea. Thus, the outcome of this study can provide reliable constraints for rock physical properties of sands and shaly sands within the mechanical compaction domain and contribute to improved basin modelling and identification of hydrocarbon presence, overconsolidation, and/or undercompaction. [ABSTRACT FROM AUTHOR]

The effect of variable soil moisture, which is found in natural field conditions, is the single most limiting aspect that limits proximal implementation of VisNIR spectroscopy for predicting soil properties using dried-ground spectral libraries. Though the external parameter orthogonalization algorithm (EPO) has shown promise in removing the effect of soil moisture on soil spectra of intact-field moist soils without having to know the soil moisture, EPO has not been widely tested and has not been tested on soils with highly weathered mineralogy (oxides and kaolinite). Thus, the objective of this work was to test the effectiveness of EPO on intact field moist soil spectra and a dried-ground spectral library from highly weathered soils located in Brazil and to use this diverse dataset to assess the sensitivity of the EPO-PLS parameterization and performance to changes in the structure of the calibration spectral dataset. A dried-ground spectral library of 1515 soils collected from Piracicaba and Sao Paulo State, Brazil was transformed using the EPO P-matrix from 80 surface and subsurface soils collected independently of the library and scanned at field-moist intact and at dried-ground condition. Results show that EPO can remove the effect of soil water from field-moist spectra for tropical soils with kaolinitic and ferritic mineralogies. Predicted clay content improved from 320 to 120 g kg − 1 for spectra before and after EPO, respectively. Bootstrapping analysis was performed to assess the sensitivity of the EPO-PLS procedure to changes in the structure of the calibration spectral dataset. All EPO-PLS parameterizations were constrained to a small set of values and small changes to EPO-PLS parameterization had little observed effect on model performance. Large spectral libraries, those developed at the national or continental level, will contain soils of varying mineralogy. While research has shown that EPO is effective on smectitic soils as well as on kaolinitic soils, it is still unclear to what extent mineralogy controls EPO effectiveness. [ABSTRACT FROM AUTHOR]

Mineralogical and geochemical investigations have been done on the hydromorphic clays (pseudogley soils and recent alluvial clastic sediments) in the Sanaga Maritime region (Southern Cameroon). Pseudogley soils are developed on gneisses from the Yaoundé Group. They have a dark brown to greyish brown color, with silty clay texture. Their mineral assemblage is made up of kaolinite, goethite, quartz, smectite, rutile, muscovite–illite and feldspars. The alluvial clastic sediments are characterized by variable colors (purple yellow, greenish, dark brown and purple brown) and sandy clay to clay texture. The mineral assemblage of alluvial clays is similar to that of pseudogley soils. SEM observations confirm the presence of kaolinite, smectite, quartz and muscovite–illite. Infrared data show that kaolinite is more orderly in pseudogley than in the alluvial clastic sediments. The Ngog-Lituba gneisses have moderate contents in SiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, CaO, Na 2 O, K 2 O and several trace elements including REE. High element depletion is noticed in the pseudogley soils except Cr, V, Zr, Pb and REE. However, the alluvial clays are marked by a strong mobilization of LILE (Na, K, Ba, Rb and Sr) and REE, relative to the parent rock and pseudogley soils. The chondrite-normalized REE patterns are homogenous and parallel with Ce-anomalies. The (La/Yb) N shows that the REE fractionation increase from the parent rock to the alluvial clastic sediments. The mineralogical and geochemical features show that the clastic river sediments are derived from the erosion of the neighboring pseudogley materials before hydraulic sorting. [ABSTRACT FROM AUTHOR]

The strip of Pand north of heavy crude oil represents the main source of Cuban hydrocarbons. About the reservoirs several thickness of clayey sediments are reported. Such sequences of these rocks characterize the base of Vega Alta formation providing a sealing character. Recently scanning electron microscopy with X ray microanalysis have been used as part of a methodology of analysis, developed for clayey seal rock characterization in thouse strip of land. This methodology consisted on the integration of the morphological and chemical information. These techniques were applied to drilling cores and outcrop samples. The results of the analysis allowed to get information about the nature of the seal rocks, which is important aspect to take into account for the hydrocarbon exploration. With the application of these techniques, clays belonging to the complex mixture illite, smectite were determined. The spectra obtained by x-ray fluorescence, corresponding to clayey rocks. The chemical composition evidence the nature of these rocks, where the major elements are silicon, aluminum, calcium and magnesium. These studies allowed a better characterization of the oil seal, and allowed more detailed studies, not only in the strip of land north and also in other areas, aspect which is the main objective of the present research. [ABSTRACT FROM AUTHOR]

Silty sands and clayey silts taken from a landslide in the Agri Valley have been analysed in order to study the role of sediment composition in the slope stability and the development of a slip zone. A geognostic hole was used to collect samples and monitor movements. A slip zone at a depth of about 14 m was identified. Compositional and physical--mechanical characterisation of samples was carried out. Some compositional characters, such as a 32-2µm grain-size fraction, clay mineral content, cation exchange capacity and total nitrogen, increase in the slip zone. Some correlations have been found between geotechnical properties (residual shear strength and residual friction angle) and the same compositional characters, which can therefore be considered possible factors influencing slope stability. [ABSTRACT FROM AUTHOR]

Five clayey materials from two quarries located in the Amezmiz region (Morocco) were sampled and investigated for their physical, chemical, mineralogical and thermal characteristics to evaluate their potential suitability as raw materials in various ceramic applications. Physical properties were identified by particle size distribution, consistency limits and total organic content. Chemical, mineralogical, and thermal properties were investigated by XRF, XRD, and TG/DTA techniques, respectively. A common raw material in pottery manufacturing of Morocco was used as reference sample (REF). Results show that the main oxides in the samples were SiO 2 , Al 2 O 3 , and Fe 2 O 3 , whereas the other oxides were present only in small quantities. Quartz, illite and vermiculite were present as dominant mineral phases and the minor phases of kaolinite, calcite and smectite also appeared in the samples. The results showed that two of the studied clayey materials have adequate characteristics for the production of structural ceramics. However, for the two other clays it is necessary to add more plastic clays to enhance the workability. [ABSTRACT FROM AUTHOR]

Abstract: The red clay soils which are widespread in China are known to be highly sensitive to drought during the dry season but the origin of this high sensitivity to drought remains unclear. Several red clay soils were selected in the Hunan province for study. We studied their basic physico-chemical properties and clay mineralogy, their structure and shrinkage properties, as well as their water retention properties. Results show that the amount of water available between −330 and −15,000hPa water potential is consistent with that recorded in many other clay soils from different parts of the world and thus cannot explain the high sensitivity of the red clay soils to drought. This high sensitivity to drought might be related to the high proportion of poorly available water which was characterized by the amount of available water between −3,300 and −15,000hPa water potential. Comparison with clay soils located in different parts of the world and for which the sensitivity to drought was not identified showed that this proportion of poorly available water is indeed much higher in the red clay soils studied than in clay soils representing a large range of both clay content and mineralogy. This specific behavior of the red clay soils studied is thought to be related to the history of their parent materials: these materials are continental sediments which may have been submitted to great hydric stress, thus leading to strongly consolidated soils with consequences such as a high proportion of poorly available water, strong aggregation and weak shrinkage properties. [Copyright &y& Elsevier]

This study aims to follow the effect of the diagenetic transformations on the clayey fraction and the organic matter of the Tunisian southern sub-surface. 61 samples from oil well named NWA-1 were recuperated for series of analyses. This study follows a comparative approach between the mineralogical, geochemical and petrographic studies. To discuss results from a statistical viewpoint, the Principal Component Analysis (PCA) was applied in order to find out any correlation between different components. The associated minerals quartz, feldspar, calcite, pyrite, anhydrite, gypsum, dolomite and olivine are also detected. These associated minerals remove by-products by the illitization reaction. The Index of Crystallinity (IC) of illite shows that, except some anomalies, the studied samples are between the epizone and the anchizone. Downward, samples show the effect of diagenetic processes and weak signs of low-grade metamorphism. As regards to the organic matter, values of Tmax range between 333°C and 463°C. On the other hand, potential hydrocarbon compounds (S2) show low values compared to those of (S1); but they maintain a similar variability from 0.63 to 21.12. SEM observations and X-ray microanalyses supported the formation of authigenic micro-quartz. The PCA of clay minerals, chemical components, and the depth shows three different populations. Feldspar, chlorite and quartz make up a population positively correlated with the depth. The second population seems to be indifferent to depth variation; it is made up of two sub-populations: the population of illite, gypsum and anhydrite, which is obtained by a counter clock rotation of depth population; and the population of pyrite, kaolinite, olivine phyllosilicate, which is obtained by an anticlockwise rotation of depth population. Third, the population of smectite, calcite and dolomite is inversely proportional to the depth variation. On the other hand, the PCA of TOC, Tmax, HI, S1, S2 and the depth make up a homogenous statistical population following the depth evolution. [ABSTRACT FROM AUTHOR]