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Red clay as a special soil has a high liquid-plastic limit, water swelling and water loss shrinkage. To solve the problems red clay was modified by calcium carbonate produced in Hezhou, Guangxi. The Liquid-plastic limit, water loss shrinkage, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and consolidated drained (CD) triaxial shear test were carried out on the modified soils. The results show that when the calcium carbonate content is 20%, the plastic limit is 24.38 and the liquid limit is 38.67, which are reduced by 35.04% and 22.16%, respectively. The Montmorillonite content in the modified soil is reduced by 27.7%. The shrinkage coefficient decreased from 0.325 to 0.102. The NMR test shows that the content is 5% and 10% would lead to a decrease in the macropores and an increase in the micropores pores. The phenomenon is the opposite (15% and 20%). All contents led to the porosity increase. The calcium carbonate content of 5% was selected for triaxial shear tests to obtain the stress-strain curves. The Duncan-Zhang was used to predict the modified soil. The model has a large error in the prediction of the peak of the principal stress difference, but the overall trend is relatively consistent. Therefore, the correction coefficient related to the confining pressure was introduced. The corrected model fits the triaxial shear test well. The research provides a method for the liquid-plastic limits and shrinkage properties of modified red clay, explores the influence of calcium carbonate content on microscopic pores, and the correction of the model provides a theoretical basis for practical application. [ABSTRACT FROM AUTHOR]

Earthen materials have been used as economic building materials since ancient times and continue to be used today, particularly in our modern society that pursues sustainability. As a form of agricultural waste, straw stalks are reused in civil engineering to avoid being burnt, which not only saves costs but also avoids environmental impacts. In the following paper, we present an experimental study on the mechanical properties of rammed red clay reinforced by straw fibers. Straw stalks were cut into different lengths and mixed evenly with red clay in different proportions before being compacted. The compressive strength, flexural strength, and shear strength of the stabilized rammed straw were analyzed. The results show that straw stalks, as a single reinforcing material, can significantly improve the mechanical properties of rammed red clay. Straw stalks had varying effects on improving the mechanical indexes of rammed red clay. When the length of the straw stalks was 15 mm and the straw stalk content was 0 Sust.3%, the straw stalks had the best effect on improving the mechanical properties of rammed red clay. [ABSTRACT FROM AUTHOR]

Reutilisation of waste tire chips to improve red clay is of great significance to environmental protection. The mechanical properties of tire chip and cement stabilised red clay (TCCSRC) at different proportions were investigated through compaction, compression, unconfined compression strength (UCS), and direct shear tests. The UCS and shear strength of TCCSRCs with different proportions were tested and analysed at their optimal moisture content (OMC). The results indicated that the porosity ratio, UCS, shear strength, and cohesion of TCCSRC decreased with increasing tire chip content. The addition of cement increased the sample UCS and shear strength. When the content of tire crumb is 20% and the cement content is 5%, the specimens show good performance in all basic properties, including UCS can reach 1034.3 kPa; the shear strength can reach 46.7 kPa when the axial pressure is 150 kPa. [ABSTRACT FROM AUTHOR]

We report the production of concrete roof tiles using a red clay-based geopolymer binder with container glass waste and river sand as a concrete filler. Clear and colored container glass wastes were separately ground to powder and blended with low-grade red clay to achieve a SiO2/Al2O3 ratio of approximately 7.0. The powder blends were converted to geopastes with a solid-to-alkali solution ratio of approximately 0.8 using a 12-molar alkali activator solution containing a mixture of potassium hydroxide and sodium hydroxide. Rheological analysis showed that the geopaste binders with transparent and colored glass powders exhibited high shear thinning behavior. A higher viscosity was observed for the geopaste with colored glass powder due to the presence of colorants. Fine and coarse particles of river sand were prepared and mixed with different ratios of geopaste binder to river sand of 1:2.0, 1:2.5, and 1:3.0, respectively. All geopaste and river sand formulations were poured into acetate molds and heated in a metal chamber at 80 °C for 24 h, then aged at room temperature for 14 d. The highest flexural strength of 2.33 MPa was obtained from the formulation with a 1:2 ratio of geopaste with transparent glass powder and fine sand. The measured strength corresponded to an apparent porosity of 6.30% and a water absorption of 4.50%. The bulk density was approximately 1.16 g/cm³, which is classified as a lightweight material. A prototype geopolymer concrete roof tile was successfully produced with a sorption coefficient of approximately 0.170 mm/min1/2. This measured sorption coefficient and the physical properties indicate that the produced roof tile is a potential building material. [ABSTRACT FROM AUTHOR]

In order to investigate the dynamic mechanical properties of red clay under dynamic loading, the split Hopkinson pressure bar (SHPB) dynamic test system was utilized to conduct tests at water content levels of 5%, 7%, 9%, 11%, 13%, and 15%, and impact velocities of 6 m/ s, 8 m/ s, and 10 m/ s. A total of 18 sets of red clay samples with varying water content and impact velocity were examined to assess the dynamic characteristics of red clay under different water content and strain rate conditions. The findings indicate that the clay exhibits a noticeable strain rate dependency as the impact velocity increases. When subjected to impact loading, the dynamic stress-strain curve of lattice-clay displays two distinct curves corresponding to different loading strain rates, specifically brittle-plastic failure and brittle failure. As the strain rate rises, the failure mechanism of lattice-clay shifts gradually from plastic-brittle failure to brittle failure. Under the influence of impact velocity alone, the compressive strength and dynamic elastic modulus of terracotta increase with higher strain rates, while they initially decrease and then increase with rising water content. [ABSTRACT FROM AUTHOR]

Coir-geotextile plays a significant role in the reinforcement of red clay foundation. The present study was envisaged to investigate the effect of the length, reinforced depth, and embedment depth of the first layer of coir-geotextile as well as the vertical spacing of coir-geotextile on the bearing capacity and distribution of Earth pressure along the depth of a red clay foundation using plate loading tests and numerical simulation. The results revealed that the bearing capacity of the red clay foundation increased with an increase in the length of coir-geotextile and the reinforced depth of coir-geotextile. The bearing capacity of the red clay foundation was inversely proportional to the embedment depth of the first layer of coir-geotextile and the vertical spacing of the coir-geotextile. The optimal length, reinforced depth, and embedment depth of the first layer of coir-geotextile were found to be 3B , 2B , and 0.25B , respectively (B is the width of strip footing). The optimal vertical spacing of the coir-geotextile was found to be 0.25B. The Earth pressure in the red clay foundation reinforced with the coir-geotextile showed a gradual reduction along the depth of foundation. However, it dropped slowly within the reinforced depth of coir-geotextile due to the stress concentration caused by the coir-geotextile and dropped faster outside the reinforced depth of coir-geotextile. The red clay foundation reinforced with the coir-geotextile failed by punching. Based on the punching failure, the calculated values of the bearing capacity ratio of the simplified calculation method were observed to be close to the measured values in the model tests. The results obtained by the small-scale model tests in the present study can provide a reference for the bearing capacity and Earth pressure distribution of the red clay foundation reinforced by coir-geotextile under similar test conditions. [ABSTRACT FROM AUTHOR]

The physical and mechanical properties of red clay have a significant influence on the bearing characteristics of pile foundations. Therefore, this paper conducted model tests to study the influence of different red clay water content (16~−20%) and different compaction degrees (88~−92%) on the bearing characteristics of pile foundations. The results show that the load–displacement curves of the test pile generally exhibit a steep type. The ultimate bearing capacity of the test pile increases gradually with the compaction degree from 86% to 92%. However, the ratio of load borne by the side of the pile increases from 54.8% to 67.8%, while the ratio of load borne by the end decreases from 45.2% to 32.2%. The ratio of load borne by the pile end to that borne by the pile side also decreases gradually from 0.825 to 0.476. The ultimate bearing capacity of the test pile decreases gradually with the moisture content from 17% to 26%, showing a decreasing trend. However, the ratio of load borne by the pile side decreases from 69.5% to 51.9%, while the ratio of load borne by the end increases from 30.5% to 48.1%. The ratio of load borne by the pile end to that borne by the pile side also increases gradually from 0.439 to 0.927. This indicates that increasing the compaction degree or reducing the moisture content has a more significant effect on increasing the side resistance. In this paper, the ultimate bearing capacity of test piles are calculated by the Mohr–Coulomb criterion (M-CC) and Duncan–Chang hyperbolic model (D-CHM), respectively. The results show that M-CC and D-CHM methods can accurately calculate the bearing capacity of the pile foundation in red clay. The conclusion of this study can provide a reference for the design and construction of pile foundations in red clay areas. [ABSTRACT FROM AUTHOR]

[Objective] To master the deformation characteristics and the law of energy dissipation of Jiangxi red clay under the condition of shear loading-unloading. [Methods] The direct shear loading-unloading tests are finished, and the strength and deformation properties and the law of energy dissipation are studied. [Results] The mechanical behavior of red clay under various normal stresses, including shear stress, shear displacement, normal displacement and energy dissipation, are obtained. [Conclusion] The dissipation energy increase rate under shear loading and unloading is comparatively lower for low normal stress as compared to high normal stress. On the whole, the dissipation of energy has positive correlation with the normal stress, and the greater the normal stress, the greater the energy consumed by the plastic deformation. The dissipated energy under the same unloading conditions increases with the increasing of numbers of unloading the red clay exhibits shear shrinkage during unloading and loading in a direct shear test. Normal displacement increases during the unloading stage, followed by an increase and then decrease during reloading, resulting in shear expansion deformation. Shear expansion ends when the shear displacement reaches its value before unloading. Shear unloading will increase the normal displacement and the shear shrinkage of red clay, and this effect of unloading on the normal displacement becomes weaker with the increase of normal stress. [ABSTRACT FROM AUTHOR]

Freeze–thaw cycling has a significant impact on the energy utilization and stability of roadbed fill. Given the good performance of basalt fiber (BF) and plant fiber (PF), a series of indoor tests are conducted on fiber-reinforced red clay (RC) specimens to analyze the shear strength, thermophysical, and microstructural changes and damage mechanisms of the RC under the freeze–thaw cycle–BF coupling, meanwhile, comparing the improvement effect of PF. The results indicate that the RC cohesion (c) first increases and then decreases with the increasing fiber content under BF improvement, reaching the maximum value at the content of 2%, and the change in the internal friction angle (φ) is relatively small. As the number of freeze–thaw cycles increases, cohesion (c) first decreases and then gradually stabilizes. The thermal conductivity increases with increasing moisture content, and the thermal effusivity increases and then decreases with increasing moisture content and fiber content. The heat storage capacity reaches the optimum level at a moisture content of 22.5% and a fiber content of 1%. Microanalysis reveals that at 2% fiber content, a fiber network structure is initially formed, and the gripping effect is optimal. The shear strength of PF-improved soil is higher than that of BF at a fiber content of 4–6%, and the thermal conductivity is better than that of BF. At the same fiber content, the heat storage and insulation capacity of BF-improved soil is significantly higher than that of PF. [ABSTRACT FROM AUTHOR]

Abstract Red clay as a special soil has a high liquid-plastic limit, water swelling and water loss shrinkage. To solve the problems red clay was modified by calcium carbonate produced in Hezhou, Guangxi. The Liquid-plastic limit, water loss shrinkage, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and consolidated drained (CD) triaxial shear test were carried out on the modified soils. The results show that when the calcium carbonate content is 20%, the plastic limit is 24.38 and the liquid limit is 38.67, which are reduced by 35.04% and 22.16%, respectively. The Montmorillonite content in the modified soil is reduced by 27.7%. The shrinkage coefficient decreased from 0.325 to 0.102. The NMR test shows that the content is 5% and 10% would lead to a decrease in the macropores and an increase in the micropores pores. The phenomenon is the opposite (15% and 20%). All contents led to the porosity increase. The calcium carbonate content of 5% was selected for triaxial shear tests to obtain the stress-strain curves. The Duncan-Zhang was used to predict the modified soil. The model has a large error in the prediction of the peak of the principal stress difference, but the overall trend is relatively consistent. Therefore, the correction coefficient related to the confining pressure was introduced. The corrected model fits the triaxial shear test well. The research provides a method for the liquid-plastic limits and shrinkage properties of modified red clay, explores the influence of calcium carbonate content on microscopic pores, and the correction of the model provides a theoretical basis for practical application.

Red clay soil in Guilin, characterized by a large pore ratio, high liquid-plastic limit, and high shrinkage, necessitates effective stabilization methods due to the region's seasonal flooding. This study employed enzyme-induced carbonate precipitation technology in conjunction with MgO and lignin fiber to stabilize the soil. The study aimed to elucidate the solidification mechanism of red clay and assess the effects of admixture dosage and curing age on unconfined compressive strength, carbonate formation, liquid-plastic limit, and fine particle content. The findings indicated that MgO significantly enhanced the unconfined compressive strength through a synergistic effect. The mineralization process of EICP technology facilitated CO2 production, promoting the carbonation of MgO, which, in turn, established an alkaline environment that further increased carbonate formation. The damage to the specimen was in the form of brittle damage. Conversely, conversely, the inclusion of lignin fibers enhanced the ductility of the soil matrix. The fibers interlaced within the soil matrix, preventing contraction and cracking under external forces and inhibiting the propagation of small fissures into larger ones, leading to plastic deformation. The dosage of MgO played a crucial role in the strength of stabilized red clay. At lower dosages, strength gains were primarily due to increased carbonate content, while higher dosages reduced water content, increasing inter-particle friction and soil densification. As strength increased, clay content decreased, and specific gravity rose. [ABSTRACT FROM AUTHOR]

As a typical special soil, red clay found in Guizhou Province, China, must be improved before it can be used for projects owing to its high plasticity. As a soil curing agent, the Consolid system is applicable to a wide range of soils, has good improvement effects and a simple operation, and is environmentally friendly. The effects of the dosage and curing age of the Consolid system on the unconfined compressive strength and shrinkage properties of the cured red clay–gravel mixture are studied. The results showed that both these properties of the red clay–gravel mixture were significantly improved by the Consolid System, and the higher the dosage of the Consolid system, the better the improvement effect. The thermal methods of thermogravimetric analysis and differential scanning calorimetry were used to determine that the bound water content was related to the amount of Consolid system admixture. With the increase in the dosage of the Consolid system, the weakly bound water content of red clay appeared to be reduced to different degrees, while the strongly bound water content was reduced to a lesser extent. The reduction in the weakly bound water led to an increase in the molecular gravitational force between the soil particles. This promoted the agglomeration of the soil particles to form a stronger agglomerate structure, thereby enhancing its mechanical properties. The physical phase analysis of cured soils with different amounts of Consolid system admixture was carried out by X-ray diffraction analysis. No chemical reaction occurred during improvement, but the crystal spacing was reduced. This phenomenon could be a factor improving the shrinkage properties. In addition, the shrinkage properties of the soil improved because of the low number of exchangeable cations on the mineral surface, allowing the cured soil to enter a charge equilibrium state quickly. [ABSTRACT FROM AUTHOR]

Red clay exhibits characteristics such as softening owing to water absorption and cracking because of water loss, which can lead to slope instability, road cracking, and compromised structural integrity when used directly in roadbed filling. Although the addition of industrial materials such as cement is a common engineering treatment, it severely impairs soil renewability. Lignosulfonate (LS) extracted from paper plant waste fluids is a natural bio-based polymer with promising applications as a soil improver. In this study, the boundary moisture content and mechanical properties of LS-treated red clay were investigated using Atterberg, unconfined compressive strength, and direct shear strength tests. Additionally, the LS-treated red clay modification mechanism was explored at multiple scales using zeta potential analysis, X-ray diffraction, scanning electron microscopy coupled with energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The results indicated that the LS dosage significantly affected both the water content and mechanical strength of the red clay boundaries. The optimal dosage of LS for red clay was 3 wt. %, at which the liquid limit was reduced by 32.97%, the plastic limit by 19.33%, and the plasticity index by 48.37%. The 28-day compressive strength of LS-treated red clay was increased by 378.4%, and the direct shear strength was increased by 136%. Analysis of the microstructure and mineral composition revealed that the LS-treated red clay did not form new minerals, but primarily filled pores and connected soil particles. Through the combined effects of hydrogen bonds, electrostatic interactions, and cation exchange, the LS-treated red clay reduced the size of the mineral particles and the thickness of the mineral double electric layer, resulting in increased structural densification. These results are of great scientific significance for the ecological modification of soils. [ABSTRACT FROM AUTHOR]

A triaxial test is a common method for studying the shear strength of soil. This test simulates actual engineering conditions; therefore, the evolution law of the shear band is universal. An in-depth study of this law will help reveal the shear failure characteristics of soil and promote the development of soil mechanics, geological disasters, and other disciplines. To implement directional research on the local deformation of soil samples and optimize the deformation measurement accuracy of soil samples, this paper combined digital image measurements with a triaxial test and used photogrammetry technology to improve this test without a large-scale transformation of the instrument. Taking the red clay soil in Guilin as the research object, the stress and deformation of soil samples on the entire surface were monitored throughout the test, and the accurate deformation data of 136 marked targets on the surface were collected. Based on these data, a three-dimensional reconstruction model of the soil samples was restored to study the overall and local stress–strain relationships, whereas the local strain characteristics were intensively analyzed. Depending on the deformation characteristics of the soil samples during the shear zone development, the evolution law of the shear zone from germination to complete formation was analyzed, and the evolution process was divided into four consecutive stages according to the proposed critical state discrimination method. The results of the study are as follows: (1) The outer and inner regions of the shear band on the soil sample surface have completely different deformation characteristics. In the outer region, the deformation is uniform, and the deformation extent tends to be stable. In the inner region, the deformation is nonuniform, and the deformation extent is continuously intensified. (2) According to the local strain difference between different regions on the surface of the soil samples, the critical state of shear band formation is determined: initial formation, stop expansion, and complete penetration. Moreover, a method is proposed to discriminate the stage of shear band development based on the localized strain on the sample surface. (3) Based on this method, the evolution process of the shear band is divided into four stages: compression deformation, surface expansion, extension penetration, and relative slip, and the different deformation laws and failure mechanisms of each stage are analyzed. The triaxial compression test of soil modified by the photogrammetry technique can obtain more accurate local intrinsic relationships and deformation characteristics, providing an accurate and economical research solution to investigate strain localization phenomenon.

To study the engineering properties of red clay modified by sodium polyacrylate, the Liuzhou remodeled red clay cured by sodium polyacrylate was selected for the permeability test with variable head and triaxial shear test to analyze the permeability and mechanical properties of the modified red clay and to determine the optimum amount of sodium polyacrylate. The disintegration resistance and microscopic mechanism of the modified red clay were determined by the disintegration test and scanning electron microscope test, respectively. The results show that the permeability coefficient of the modified soil decreases gradually with the increase of sodium polyacrylate, and gradually stabilizes after reaching 3% with the permeability coefficient of 8.1379×10−7 cm/s, 90.78% lower than that of the plain soil. In contrast, the shear strength of the modified red clay shows an increasing trend firstly, then decreases, and then keeps stable at at 2%, which is 394.21% higher than that of the plain soil. The optimal dosage is 3%, and in such situation, the anti-disintegration performance of the modified soil is improved by 42.86%. The pores between the soil particles filled by polymer chains lead to the continuous fragmented granular red clay . The arrangement structure and denseness are better than those of the plain red clay. The impermeability, mechanical properties, and disintegration resistance of the red clay modified by sodium polyacrylate are significantly improved. This study can provide theoretical information for the practical engineering.

Copyright of Journal of Ground Improvement is the property of Journal of Ground Improvement Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Eolian sediments are extensively distributed across the Earth's surface, and their formation is intricately linked to climate change, tectonic activity, and topographic features. Consequently, the investigation of eolian sediments bears great geological significance. The northwest region of China is renowned for hosting the most extensive and thickest Late Miocene–Pliocene red clay deposits globally. Nonetheless, scholars have yet to reach a consensus regarding the precise formation processes of these red clays. The identification of the source region of the red clays is crucial for comprehending their formation mechanism. The correlation of zircon U-Pb age spectra is a frequently utilized method for determining the provenance of eolian sediments. In this study, we compared the previously published zircon U-Pb ages (n = 12,918) of the Late Miocene–Pliocene red clays in the Ordos Plateau with those from the potential provenance regions (n = 24,280). The analysis, supported by the tectonic and climatic background of the region, revealed that the Late Miocene–Pliocene red clay in the Ordos Plateau originates predominantly from the Yellow and Wei rivers, with a minor contribution from the weathering of bedrock in the western North China Craton. The transport of these detrital materials by the East Asian winter monsoon is impeded by the presence of the Qinling and Taihang Shan, resulting in their deposition on the flat surface of the Ordos Plateau. This development of red clay is consistent with the proximal accumulation model, illustrating how the hydrosphere, atmosphere, and lithosphere interacted to shape the red clay deposits during the Late Miocene and Pliocene periods in the Ordos Plateau. [ABSTRACT FROM AUTHOR]

Reflectance spectroscopy is rapid, inexpensive, and non-destructive and can provide important information about the mineralogy of rocks and sediments. We measured the reflectance spectroscopy of Miocene red clay deposits on the northeastern margin of the Tibetan Plateau, with the aim of developing a rapid methodology for detecting paleoclimatic changes. We obtained visible/near-infrared (VNIR) and short-wave infrared (SWIR) spectroscopy data from the red clay in the Jianzha Basin, and analyzed their relationship with independent paleoclimatic records, including mineral contents and environmental magnetic parameters. The results show that the VNIR parameters, including D500, D900, R500, and R900 (where D and R represent the depth and reflectance of the absorption peaks around 500 and 900 nm, respectively) are temperature-sensitive and correlated with the magnetic susceptibility, frequency-dependent magnetic susceptibility, and the marine δ18O record. The results of frequency-domain analysis of the VNIR parameters show that they reflect climate change on orbital timescales. SWIR parameters, such as AS1400, D1400/D1900 and D1900 (where AS represents the asymmetry of the absorption peaks around 1400 nm), are correlated with the illite and montmorillonite content, and they are sensitive to the weathering intensity. The spectral parameters of the eolian red clay in the Jianzha Basin reflect regional climatic changes caused by the uplift of the Tibetan Plateau at ∼8.5 Ma and global climatic cooling at ∼7.2 Ma, and thus they are applicable as both regional and global paleoenvironmental indicators. [ABSTRACT FROM AUTHOR]

Due to the high degree of weathering, the red clay slope has low anti-disintegration performance, and the clay easily becomes wet and disintegrates after soaking in water. It causes geological problems such as slope collapse caused by soil softening. To study the disintegration characteristics of modified red clay, the disintegration test of red clay modified by using lignin fiber, clay particles and lime was carried out, analyzing the disintegration characteristics of improved red clay from physical and chemical perspectives and analyzing the improvement mechanism of three modifiers with the scanning electron microscopy test. The analysis results show that the water-holding capacity and disintegration resistance of soil mixed with lignin fiber decrease; the disintegration time of reshaped red clay increases with the increase in clay content; and the average disintegration rate of the soil decreases with the increase in clay content. With the increase in lime content, the soil cement increases. The integrity of the soil is enhanced, and its anti-disintegration ability is improved; the saturated moisture content of reshaped red clay increases with the increase in lignin fiber and clay content, while the saturated moisture content of soil decreases with the increase in lime content. The damage analysis shows that the larger the damage factor of soil, the worse its anti-disintegration ability, and the easier the soil disintegrates. The purpose of this paper is to explore the essence of the soil disintegration phenomenon, and on this basis, using high-quality improved materials, to improve the soil, which easily disintegrates. This move aims to significantly enhance the anti-disintegration ability of the soil, thereby improving its resistance to softening and disintegration, thereby effectively improving and maintaining the ecological environment. At the same time, the improved soil will help to improve the utilization rate of the slope and foundation soil, thereby reducing the economic cost of maintenance engineering. Against the current background of sustainable economic, social, and ecological development, it is of great strategic significance to ensure the sustainable availability of land resources in specific areas and maintain their productivity and ecological stability for a long time. The research into this subject not only helps to deepen the understanding of soil disintegration, but also provides strong technical support for the rational utilization of land resources and the protection of the ecological environment. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Guilin is a famous karst area, and currently the view that the disintegration of red clay will cause soil cave collapse is increasingly recognized. In order to study the influence of the coupling effect of moisture content and void ratio on the disintegration of red clay, different moisture contents and void ratios of Guilin red clay were placed on a self-made disintegration apparatus to record the real-time disintegration amount and observe the disintegration phenomenon. Images of the structural characteristics of soil were obtained by a scanning electron microscope (SEM). Additionally, nuclear magnetic resonance (NMR) was applied to analyze the distribution of water in both natural and saturated states. The results show that the disintegration rate of red clay decreases as the initial moisture content increases, but increases with the increase of void ratio. Both moisture content and void ratio affect the structural characteristics of red clay. When the moisture content remains constant, the soil changes from a three-peak to a two-peak structure as the void ratio increases. The total area and secondary peak area of the T2 spectrum increase, while the starting T2 value of the main peak shifts to the right and the area decreases. Meanwhile, the starting T2 value of the secondary peak shifts to the right and the area increases. When the void ratio remains constant, the starting T2 value of the main peak gradually shifts to the left and the area decreases as the moisture content increases. However, the starting T2 value of the secondary peak shifts to the right and the area decreases or first decreases and then increases. The disintegration rate does not exhibit a significant relationship with either pore volume or macropore volume. The combined water saturation shows a bilinear relationship with both the moisture content and void ratio, where it increases as the initial moisture content increases, but decreases as the void ratio increases, with a correlation coefficient of 0.9929. The disintegration rate has an exponential relationship with the combined water saturation, and it decreases as the combined water saturation increases, with a correlation coefficient of 0.9934. [ABSTRACT FROM AUTHOR]

This work focused on removing iron with oxalic acid from red clay samples collected from Kapasia Upazila, Gazipur District, Bangladesh. To characterize the red clay, the study employed several techniques: particle size analysis, WDXRF (wavelength-dispersive X-ray fluorescence), AAS (atomic absorption spectroscopy), XRD (X-ray diffraction), TGA (thermogravimetric analysis), and FESEM (field emission scanning electron microscopy). Additionally, leaching experiments were conducted with varying concentrations of oxalic acid, temperatures and times. After leaching, the red clay composition changed significantly: SiO₂ increased from 53.6 % to 63.13 %, Fe₂O₃ decreased from 17.1 % to 3.64 %, Al₂O₃ remained relatively stable at 18 %–18.22 %, and other oxides showed minor variations. 78.71 % of the iron was removed at optimal leaching conditions (1.0 M oxalic acid, 100 °C, 150 min, and 250 rpm). Mineralogically, the red clay samples are composed of illite, kaolinite, quartz, feldspar, hematite and chlorite. Thermal analysis showed significant weight loss at temperatures between 300 and 600 °C. Ceramic trials were conducted at firing temperatures of 900 °C and 1100 °C to evaluate the mechanical properties of tiles. The results obtained showed significant improvements in red clay quality for ceramics. Being a low-cost and eco-friendly process, this becomes a very prominent alternative to conventional iron removal techniques and helps produce high-quality ceramic tiles, contributing towards economic growth in Bangladesh.

The partial replacement of conventional natural coarse aggregate (NCA) with artificial light weight aggregate (LWA) manufactured from local clay and solid waste to develop a lightweight aggregate concrete (LWAC) for the structural use was studied in this paper. Red clay and Savar clay were used individually with solid wastes like rice husk ash (RHA) and waste glass to produce LWA. The suitability of raw materials and LWA was evaluated by investigating various properties. The mechanical, thermal and durability properties of manufactured LWAC were explored. The results of physical, chemical, thermal and geotechnical properties revealed that Red clay is better than Savar clay for the preparation of LWA. All the physical and mechanical properties of LWA prepared from Red clay are suitable for the preparation of LWAC compared to Savar clay. The test results demonstrated that the concrete manufactured by replacing 30 % of NCA with LWA produced a concrete of lightweight properties. The compressive strength of LWAC for 7 and 28 days was observed as 28 and 48 MPa, respectively. The results of modulus of elasticity, splitting tensile strength, flexural deformation, and creep test of LWAC revealed that these mechanical properties meet the requirements for the structural concrete. The RCP test proves that chlorine permeability of LWAC is comparable with NCA. It was observed that the superior performance of LWAC can be achieved only when the optimized mix designed is followed strictly. The suitability of the replacement of natural aggregate by LWA may be helpful for Bangladesh due to the scarcity of natural coarse aggregate and reusability of solid waste materials.

The red clay of the Chinese Loess Plateau (CLP) is an important geological archive for understanding the variability in the late Neogene East Asian monsoon. The periodicity of the summer monsoon of the red clay on the eastern CLP is dominated by eccentricity cycles within the constraints of the palaeomagnetic chronological framework, whereas global climate change characteristics represented by the deep-sea oxygen isotope record at that time show a dominating obliquity cycle. Here, we analyzed the East Asian summer monsoon proxies from the Shilou red clay section with the cyclostratigraphy method. The results show that the summer monsoon variation was dominated by obliquity, the optimum deposition rate was 4.451 cm/kyr, and the floating age of the Shilou red clay section was ca. 1.7 Ma. The late Neogene East Asian summer monsoon inferred from the eastern CLP was thus paced by the obliquity cycle, which is consistent with global change.

Under the background of climate warming in the Qinghai-Tibetan Plateau (QTP), frequent freeze–thaw cycling (FTC) brings about great geological disasters such as subgrade failure, landslides, and mudslides, which is closely related to the strength reduction caused by the structural damage of soils. In this study, to explore the association between macro shear strength and microstructure evolution of soils subjected to FTC, the red clay distributed widely in the QTP was chosen and used to conduct a series of triaxial shear and nuclear magnetic resonance (NMR) tests in the range of 1 to 7 FTCs. Triaxial shear test results reveal that the shear strength reduction of specimens mainly occurs within five FTCs, and the trend of peak deviator stress with increasing FTCs can be described in three stages: rapid descent (FTCs less than three), slow descent (FTCs between three and five), and stabilization (FTCs greater than five). NMR tests show that the T2 spectrum curves exhibit a distinct bimodal distribution characteristic, corresponding to macropores and micropores. Part of the micropores gradually develop into macropores with increasing FTCs, especially within five FTCs. The increase in macropores proportion leads to a loose soil structure, which is consistent with the deterioration of the shear strength of specimens. Finally, based on the experimental results and classical Mohr–Coulomb theory, a new shear strength model with structural damage for red clay has been proposed by introducing a damage factor expressed by T2 spectral area. [ABSTRACT FROM AUTHOR]

Red clay is widely distributed globally and is closely related to human production and life. The middle reaches of the Yellow River basin in China are characterized by complex geological structures, concentrated rainfall periods. The soluble salts such as sodium sulfate enter the red clay particles along with the infiltrating water, forming a red clay-like saline soil. In order to study the effects of water and salt on red clay soils, this paper uses red clay in the Heyang of Weinan with different ratios of distilled water (10–20%) and Na2SO4 (0–4%), and obtains the resistivity of red clay soils at different frequencies (100 Hz–100 kHz) using an inductance, capacitance and resistance digital bridge tester. The results show that the resistivity of red clay is negatively correlated with water and salt content. With the increase of water content, the increase of conductive paths in the pore water improved the electrical conductivity of the red clay; while when the concentration of Na2SO4 increased, the free moving anions and cations in the pore water increased, the electrical conduction efficiency increased and the resistivity decreased. The high frequency increased the conductivity of red clay by contributing to electrical double layer deformation, whereas the electrode polarization led to inhibition of conductivity under low frequency. A negative power exponential relationship exists between the resistivity of red clay and the test frequency. This study may provide a valuable reference for the rapid identification of the physical properties of red clay and its internal structure. [ABSTRACT FROM AUTHOR]

Red clay is a special soil that loses water and shrinks easily, which causes expansion and contraction and leads to the generation and development of cracks, weakening the strength and engineering properties of the soil. This investigation analyzed the mechanism of crack evolution and patterns of strength decay in red clay under dry–wet cycles and established a relationship between strength and crack ratio by employing image processing techniques and conducting direct shear tests on red clay with various initial moisture contents and humidification times. The results show that the crack ratio increases with the number of dry–wet cycles and eventually tends to be stable after the fourth dry–wet cycle, and the stress–displacement curve of red clay changes from weak hardening to hardening. With the progress of the dry and wet cycles, the shear strength indexes of red clay decrease extensively, displaying a negative association with the sample's initial moisture content and the duration of humidification. Based on the experimental result, a quadratic function was established to model the relationship between soil cracking ratio and shear strength, which can predict the shear strength of red clay from the cracking ratio. [ABSTRACT FROM AUTHOR]

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• Calibration of red clay with different water contents based on EDEM software. • The Hertz-Mindlin with JKR Cohesion model was used to model red clay soil's physical properties. • Experimental studies provide insights into the impact of soil moisture content on its properties. • Technical references for future research on soil-tool interactions were provided. Distinct physical properties of red clay soil in hilly and mountainous regions of southwest China, including high adhesiveness and density, challenge the operation of agricultural machinery. A scarcity of accurate discrete element simulation parameters for this soil type restricts computational modeling. The study was focused on red clay soil with a moisture content of 12.50% ± 1% and a measured repose angle of 35.54°. The soil's inherent physical properties were identified through experimental assessments. Soil contact mechanical parameters were obtained from the GEMM database, and optimal contact parameter ranges were determined using Steepest Ascent Experiments, with the simulated soil particle repose angle serving as the response value. A second-order regression model was developed using a quadratic regression rotation orthogonal combination test. By taking the actual repose angle as the optimization criterion, parameters were optimized. The optimal contact mechanical parameters in EDEM simulations were identified as: JKR surface energy at 8.981 J/m2, recovery coefficient at 0.474, dynamic friction coefficient at 0.196, and static friction coefficient at 0.45. The model yielded a repose angle of 36.21°, closely corresponding with the observed value, with a relative error of 1.80%. The parameters calibrated in this study offer a valuable reference for future soil-tool interaction studies and tillage implement optimization in these regions. [ABSTRACT FROM AUTHOR]

Red clay in Lijiang River basin of Guilin with different cadmium ion concentrations subjected to dry-wet cycles at 40 °C is taken as the research object in this paper. Triaxial test is conducted to study the effects of cadmium pollution and dry-wet cycles on the deformation and shear strength characteristics of red clay. The results show that the horizontal shrinkage rate, vertical shrinkage rate and volume shrinkage rate of red clay is increased with time in an “S” shaped curve under different cadmium concentrations. The peak shear stress of red clay is increased with dry-wet cycles under different cadmium concentrations. With the increasing of dry-wet cycles, the cohesive force of cadmium-contaminated red clay tends to increase first and then decreases. Cadmium finishes its damage to the structure of red clay before the dry-wet cycles, so that the internal friction angle reaches the limit value, and the more increased of cadmium concentration, the more obvious the mechanical characteristics of the damage. [ABSTRACT FROM AUTHOR]

To investigate the influencing factors and mechanisms of shear strength of red clay with a high liquid limit, which was selected at different milepost locations based on the Nanning Bobai Nabu Section Project of the Nanning Zhanjiang Expressway, the basic physical properties of red clay were determined using a liquid plastic limit test, compaction test, inductively coupled plasma optical emission spectrometer (ICP-OES), and X-ray fully automatic diffractometer (XRD). Red clay with a high liquid limit was selected. Furthermore, the direct shear test was used to study the effect of different water contents and compaction degrees on the shear strength. The experimental results demonstrate that under the same compaction degree, the shear stress of the soil sample increases significantly with an increase in normal stress, and the greater the water content, the smaller the shear stress of the soil sample. At 200 kPa, the shear strength of soil samples with 24% water content is 57%, 46%, and 35% of the shear strength of soil samples with 15% water content under different compaction degrees(K) of 86%, 90%, and 93%, respectively. Under the same moisture content, the shear stress of the soil sample shows an increasing trend with an increase in the degree of compaction, and the greater the compaction degrees, the greater the shear stress of the soil sample. The cohesion c and internal friction angle φ of soil samples increase with an increase in the compaction degree, but the increase in cohesion c is also affected by the water content. Under the condition of low water content, the cohesion c of soil samples can be increased by 1.06 times when the water content is 15% and by 0.47 times when the water content is 18%. Under the condition of high water content, the cohesion c of soil samples with 21% water content only increases by 0.3 times, and that with 24% water content only increases by 0.35 times. [ABSTRACT FROM AUTHOR]

This study investigates the modification of red clay with calcium carbonate. The pore distribution was obtained using a combination of mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) techniques. The influence of calcium carbonate content, density, confining pressure, and shear strain on the pores was studied. Introducing pore classification to assess the extent of the damage under different conditions and the relationship between different types of pores. The results show that the content of added calcium carbonate has little effect on pore distribution when the density is low (1.4 and 1.5 g/cm3). The content of calcium carbonate has an influence on pore distribution when the density is high (1.6 g/cm3). With the density increases, the number of macropores and mesopores between soil particles decreases, while the small pores increase. The confining pressure results in the preferential drainage of free water from macropores. The porosity decreases as the confining pressure increases. Under the same confining pressure, as the shear strain increases, the large pores decrease while the small pores increase. Based on the analysis of damage degree, the shear strain is positively linearly related to the damage degree of intragranular mesopores, which forms a convex function relationship with intragranular macropores and intergranular mesopores (except under a confining pressure of 100 kPa). [ABSTRACT FROM AUTHOR]

The thermal conductivity of backfill soil is one of the important factors affecting the load capacity of direct buried cable. In order to explore the influence law of various factors on the thermal conductivity of modified red clay, samples with different sand content, dry density and water content were prepared. Under the condition of constant temperature and airtight, the transient hot-wire method was used to test the thermal conductivity of samples, and the influence law of sand content, dry density and water content on the thermal conductivity of modified red clay was analyzed. The results show that the copper tail sand has a better effect on the thermal conductivity of red clay, and the thermal conductivity of the improved soil increases linearly with the sand content and water content. With the increase of dry density, the increase trend of thermal conductivity of improved soil is phased. When the dry density of improved soil is greater than 1. 65 g / cm 3, the growth rate of thermal conductivity decreases obviously. The effect of copper-tail sand on the thermal conductivity of modified soil is that a large amount of quartz improves the heat transfer efficiency between solid frames. The influence of moisture content and dry density on the thermal conductivity of improved soil is mainly due to the change of the three-phase heat transfer mode of improved soil. Based on the test results, a new model for predicting the thermal conductivity of the improved soil is established, which can better predict the thermal conductivity of the improved soil. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Desiccation cracking is a common phenomenon for red clay due to alternating wet and dry weathers. The presence of cracks definitely affects the strength of the soil; however, characterizing the development of desiccation cracks inside the soil has been a challenge. The purpose of this study was to propose a method to quantify the volumetric crack rate (VCR) of red clay and investigate the influence of VCR on the unconfined compressive strength (UCS) of red clay. First, the relationship between wave speed and VCR was quantified by a prefabricated crack method to obtain the equivalent VCR (EVCR). Then, the EVCR was compared with the surface crack rate (SCR) to determine the reliability of the method. Finally, unconfined compression tests were carried out to explore the relationship between EVCR and UCS. The results show that the relationship between the prefabricated VCR and wave velocity can be described by a logarithmic equation. The calculated VCR by this equation is linearly correlated to the SCR of red clay, indicating that the logarithmic equation is effective to quantify the VCR of red clay caused by wet and dry cycles. The UCS and residual strength of red clay containing cracks reduce following an exponential function with increasing EVCR. Gray relational analysis showed that the correlation between UCS and EVCR is better than that between UCS and SCR, suggesting that it is more reliable to express the crack rate by EVCR when studying the UCS of red clay. [ABSTRACT FROM AUTHOR]

In order to explore the creep characteristics of red clay under different pressures, the stress–strain curve and stress–strain–time curve of red clay under different pressures were obtained, and the triaxial shear and creep characteristics of red clay under different pressures were analysed. A triaxial shear test and creep test were carried out on red clay from Guilin as the research object under different pressures. The results show that: ➀ the cohesion and the angle of internal friction of red clay from Guilin, obtained from a triaxial shear test, are 57.20 kPa and 22.47°, respectively; ➁ according to the physical meaning of the parameters of the Burgers creep model, a simple and practical parameter inversion method is proposed, which can be used to obtain the parameters of the Burgers model for red clay under different perimeter pressures and differing deviatoric stress; and ➂ when comparing the calculation results with the test results, the correlation coefficients R2 of the two are above 0.9, with a good fitting effect, so the model can accurately describe the creep characteristics of red clay from Guilin. This study can provide a theoretical basis and technical support for engineering construction in the red clay area of Guilin. [ABSTRACT FROM AUTHOR]

Geochemical analyses of trace elements in the ocean water column have suggested that pelagic clay‐rich sediments are a major source of various elements to bottom‐waters. However, corresponding high‐quality measurements of trace element concentrations in porewaters of pelagic clay‐rich sediments are scarce, making it difficult to evaluate the contributions from benthic processes to global oceanic cycles of trace elements. To bridge this gap, we analyzed porewater and bulk sediment concentrations of vanadium, chromium, cobalt, nickel, copper, arsenic, molybdenum, barium and uranium, as well as concentrations of the major oxidants nitrate, manganese, iron, and sulfate in the top 30 cm of cores collected along a transect from Hawaii to Alaska. The data show large increases in porewater concentrations of vanadium, manganese, cobalt, nickel, copper, and arsenic within the top cm of the sediment, consistent with the release of these elements from remineralized organic matter. The sediments are a sink for sulfate, uranium, and molybdenum, even though conditions within the sampled top 30 cm remain aerobic. Porewater chromium concentrations generally increase with depth due to release from sediment particles. Extrapolated to the global aerial extent of pelagic clay sediment, the benthic fluxes in mol yr−1 are Ba 3.9 ± 3.6 × 109, Mn 3.4 ± 3.5 × 108, Co 2.6 ± 1.3 × 107, Ni 9.6 ± 8.6 × 108, Cu 4.6 ± 2.4 × 109, Cr 1.7 ± 1.1 × 108, As 6.1 ± 7.0 × 108, V 6.0 ± 2.5 × 109. With the exception of vanadium, calculated fluxes across the sediment–water interface are consistent with the variability in bottom‐water concentrations and ocean residence time of the studied elements. Key Points: Porewater transition metal concentrations vary by up to an order of magnitude in aerobic pelagic clay sedimentsMost variability in porewater concentrations is observed in the top 5 cmCalculated benthic fluxes of most transition metals agree with estimated fluxes based on water column concentrations [ABSTRACT FROM AUTHOR]

Objective The content and existence form of bound water have an important influence on the physical and mechanical properties of red clay, and macroscopic shrinkage of red clay leads to microstructure changes of soil particles, pores and bound water, which in turn may cause soil surface cracking, triggering infiltration, destabilization, and other engineering geological problems. Methods Thermogravimetric analysis tests, BET tests, scanning electron microscopy (SEM) and zeta potential tests were conducted to study the variation characteristics of bound water during the shrinkage of undisturbed red clay. The structural model of spherical and lamellar clay particles based on the uniform distribution of bound water film was established, and the formula for the calculation of bound water film thickness was derived. Results The results showed that most of the water in undisturbed red clay exists in the form of bound water and the loss of weakly-bounded water continues throughout the shrinkage process of red clay. During the process, the zeta potential, specific surface area and the thickness of the bound water film decreased continuously. Conclusion The results reveal the intrinsic mechanism of water loss and shrinkage of red clay, which can provide theoretical support for solving environmental engineering geological problems.

The physical and mechanical properties of red clay have a significant influence on the bearing characteristics of pile foundations. Therefore, this paper conducted model tests to study the influence of different red clay water content (16~−20%) and different compaction degrees (88~−92%) on the bearing characteristics of pile foundations. The results show that the load–displacement curves of the test pile generally exhibit a steep type. The ultimate bearing capacity of the test pile increases gradually with the compaction degree from 86% to 92%. However, the ratio of load borne by the side of the pile increases from 54.8% to 67.8%, while the ratio of load borne by the end decreases from 45.2% to 32.2%. The ratio of load borne by the pile end to that borne by the pile side also decreases gradually from 0.825 to 0.476. The ultimate bearing capacity of the test pile decreases gradually with the moisture content from 17% to 26%, showing a decreasing trend. However, the ratio of load borne by the pile side decreases from 69.5% to 51.9%, while the ratio of load borne by the end increases from 30.5% to 48.1%. The ratio of load borne by the pile end to that borne by the pile side also increases gradually from 0.439 to 0.927. This indicates that increasing the compaction degree or reducing the moisture content has a more significant effect on increasing the side resistance. In this paper, the ultimate bearing capacity of test piles are calculated by the Mohr–Coulomb criterion (M-CC) and Duncan–Chang hyperbolic model (D-CHM), respectively. The results show that M-CC and D-CHM methods can accurately calculate the bearing capacity of the pile foundation in red clay. The conclusion of this study can provide a reference for the design and construction of pile foundations in red clay areas.

Eolian sediments are extensively distributed across the Earth’s surface, and their formation is intricately linked to climate change, tectonic activity, and topographic features. Consequently, the investigation of eolian sediments bears great geological significance. The northwest region of China is renowned for hosting the most extensive and thickest Late Miocene–Pliocene red clay deposits globally. Nonetheless, scholars have yet to reach a consensus regarding the precise formation processes of these red clays. The identification of the source region of the red clays is crucial for comprehending their formation mechanism. The correlation of zircon U-Pb age spectra is a frequently utilized method for determining the provenance of eolian sediments. In this study, we compared the previously published zircon U-Pb ages (n = 12,918) of the Late Miocene–Pliocene red clays in the Ordos Plateau with those from the potential provenance regions (n = 24,280). The analysis, supported by the tectonic and climatic background of the region, revealed that the Late Miocene–Pliocene red clay in the Ordos Plateau originates predominantly from the Yellow and Wei rivers, with a minor contribution from the weathering of bedrock in the western North China Craton. The transport of these detrital materials by the East Asian winter monsoon is impeded by the presence of the Qinling and Taihang Shan, resulting in their deposition on the flat surface of the Ordos Plateau. This development of red clay is consistent with the proximal accumulation model, illustrating how the hydrosphere, atmosphere, and lithosphere interacted to shape the red clay deposits during the Late Miocene and Pliocene periods in the Ordos Plateau.

This research was undertaken to optimize the phenolic compound removal from Olive Mill Wastewater (OMW) by sawdust and red clay as natural adsorbents. Fractional factorial experimental design at 25−1 was used in order to optimize the experimental conditions for high removal efficiency. Statistics ANOVA analysis, Fisher's test, and Student's test suggested that the adsorbent dose has the most significant influence on polyphenol removal for both adsorbents. The maximum removal of polyphenols by sawdust reached 49.6% at 60 °C by using 60 g/L of adsorbent dose, pH 2, reaction time of 24 h, and agitation speed of 80 rpm. Whereas, for red clay, 48.08% of polyphenols removal was observed under the same conditions for sawdust except the temperature of 25 °C instead of 60 °C. In addition, the thermodynamic parameters suggested spontaneous process for both adsorbents, endothermic for the sawdust and exothermic for red clay. Furthermore, the phytotoxicity effect of OMW on durum wheat (Triticum turgidum L. var. durum) and white bean (Phaseolus vulgaris L.) seed germination was investigated. The obtained results showed that the untreated OMW inhibited the seed germination of T. turgidum and P. vulgaris seeds. OMW treatment with red clay followed by dilution (95% water) resulted in 87 and 30% germination of P. vulgaris and T. turgidum, respectively. While, the treatment of OMW with sawdust and dilution at 95% resulted in 51 and 26% germination of P. vulgaris and T. turgidum, respectively. [ABSTRACT FROM AUTHOR]

Phyllite soil and red clay belong to the soils that negatively impact the engineering performance of railway subgrade and may cause subgrade bulges, uneven subgrade settlement, and other subgrade distresses. In order to make full use of these two soils, a collaborative improvement plan was proposed. A series of tests were conducted to analyze the synergistic effects of lime and red clay on the improvement of phyllite soil. The tests included the no loading swelling ratio, swelling pressure, consolidation, and direct shear tests. Additionally, scanning electron microscopy was used to investigate the role of lime and red clay in soil improvement. The test results show that a red clay ratio of 60% + lime content of 3% is the optimal composite improvement scheme. The scheme led to a 93% reduction in the no loading swelling ratio and an 88% reduction in swelling pressure. Additionally, cohesion, the internal friction angle, and the compression modulus increased by 345%, 73%, and 373%. Red clay and lime had weak synergistic improvement effects on the no loading swelling ratio, the swelling pressure, and the internal friction angle of phyllite soil, that is, the synergistic improvement effect of red clay and lime was less than the sum of the single improvement effect but greater than the single improvement effect. Red clay and lime had a strong synergistic improvement effect on the cohesion and the compression modulus of phyllite, that is, the synergistic improvement effect of red clay and lime was greater than the sum of the single improvement effect. The microstructure analysis test results show that red clay can fill the pores of phyllite soil and improve its immediate strength. Through hardening and cementation, lime can enhance the strength of phyllite soil as well as address the issue of the reduced engineering properties of phyllite soil and red clay when exposed to water. Red clay and lime promote each other's reactions and have a synergistic improvement effect on phyllite soil. [ABSTRACT FROM AUTHOR]

Desiccation cracking is a common problem of red clay under wet and dry conditions. The presence of cracks could reduce soil strength properties, which is the major reason for shallow failure of red clay slopes. This study aims to propose some additives to improve the crack resistance as well as the strength of red clay. To this end, three natural fibers and three natural gels were primarily selected to modify red clay. Desiccation crack tests were conducted to identify the best fiber and gel in terms of crack resistance. Then, direct shear tests and uniaxial tensile tests were performed on the soil specimens modified by the best fiber and gel to determine the optimal dosages regarding strength improvements. The results demonstrated that natural gels reduced the crack resistance of red clay, while natural fibers could enhance the crack resistance. Lignocellulose was the best additive in improving the crack resistance of red clay, and the modified effect was positively correlated with the fiber dosage. Adding 1.5% lignocellulose into red clay could reduce the crack rate from 2.19% to 0.30%, with a reduction of 0.86 times. The tensile strength, shear strength and its parameters of lignocellulose-modified red clay showed a trend of increasing first and then decreasing with increasing lignocellulose dosage. At the optimal lignocellulose dosage of 0.75%, the shear strength and tensile strength were increased by 44.63% and 18.21%, respectively. The strength of red clay modified by both lignocellulose and guar gum was positively correlated with the dosage of guar gum, and the desirable dosage of guar gum was 1.0%. In engineering practice, the wet red clay mixed with 0.75% lignocellulose and grass seeds can be employed as planting soil and is sprayed uniformly onto the slope surface after excavation using a spraying planting machine. To further improve the strength of the planting soil, 1.0% guar gum solution can be sprayed on the soil surface. The findings could provide useful guidance for the protection of red clay slopes. [ABSTRACT FROM AUTHOR]