Loess Samples Research Articles

Effects of Freeze-Thaw Cycles on Strength and Wave Velocity of Lime-Stabilized Basalt Fiber-Reinforced Loess.

Basalt fiber is a new environmentally-friendly material with excellent potential for soil reinforcement in geotechnical engineering construction. This study explores the effects of freeze–thaw cycles on the unconfined compressive strength (UCS) and P-wave velocity (Vp) of lime-stabilized basalt fiber-reinforced loess. Reinforced loess samples with different proportions of basalt fiber and lime were subjected to 0, 1, 5, and 10 freeze–thaw cycles, and their UCS and Vp were subsequently measured. The test results showed that the addition of basalt fiber and lime to loess could enhance strength and improve resistance against freeze–thaw damage, and the freeze–thaw damage of reinforced loess decreases with the increase of basalt fiber content and length. A relationship between UCS and Vp of the reinforced samples was obtained for the same number of freeze–thaw cycles, and this relationship exhibited linear characteristics. The fitting results indicate that the Vp can be used to estimate the UCS after freeze–thaw damage. The research results not only have important practical significance in the application of basalt fiber in geotechnical engineering but also provide a reference for the non-destructive testing of the strength of loess after freeze–thaw cycles.

Characterizing undrained shear behavior of loess subjected to K0 loading condition

Undrained shear behavior of loess after the K0 consolidation was investigated through laboratory experiments. Both the monotonic and cyclic triaxial tests were performed on the intact loess samples retrieved from a construction site in Yan'an city, China. It was found that the coefficient of lateral earth pressure at rest (K0) of the intact loess is stress-dependent, and it varies between 0.46 and 0.85. Under the monotonic loading condition, the peak q in the undrained shear test is higher for the samples under the K0 consolidation than those under the isotropic consolidation. Besides, the cyclic loading tests were conducted on the loess samples subjected to different magnitudes of the initial deviatoric stress, including the K0 stress state. The test results revealed that different initial stress conditions cause distinctly different failure patterns. It includes the cyclic mobility with progressive development of the axial strain, and limited deformation followed by an abrupt gain of the axial strain with no precursor. In accordance to the build-up of the excess pore water pressure during the tests, each failure pattern of loess was interpreted in the q-p' diagram alongside the undrained instability state (UIS) line. The outcomes of this paper suggest a pressing need to thoroughly consider the K0 values of the intact loess with variations of the initial stress state.

Analysis of the influence of iron source and its occurrence state on the color of celadon glaze

Using different iron sources of industrial iron oxide, loess, slag, and golden soil, iron elements were introduced into the formula respectively, and celadon samples were prepared in a reducing atmosphere. To reveal the influence of iron source on glaze color, the celadon samples were analyzed by Spectrophotometer, X-ray fluorescence spectroscopy, X-ray diffractometer, scanning electron microscope, and X-ray photoelectron spectrometer. The results show that the glaze color of the samples is quite different, samples using iron oxide and golden soil as iron source raw materials are sky-green, the loess sample is olive green, and the slag sample is similar to the bean green. There are many quartz crystals in the glaze of iron oxide samples, and the turbidity is high. The liquid-liquid phase separation size close to the quartz crystal is large, and far away from the crystal is small. Industrial iron oxide is the easiest to reduce, followed by goethite in golden soil, and reduction of hematite in slag and the iron in loess in the form of isomorphic is successively more difficult. The difference in the form of occurrence of iron is the most essential factor that causes the difference in glaze color.

Effect of high temperatures on the magnetic susceptibility of loess.

Coal fires refer to fires generated by the self-combustion of coal seams, which have a maximum temperature of 1000 °C. Such fires can significantly alter the properties of surrounding rock and soil. However, in Northern Shaanxi, China, coal resources are abundant, and the buried depth of coal seams is shallow; therefore, coal fires often occur. Because Northern Shaanxi is located in China's Loess Plateau, there is a large amount of loess accumulation on the surface. For this reason, it is imperative to study the effects of high temperatures on loess. In this paper, the loess samples are heat treated at different temperatures (200-1000 °C), and their surface redness (a*) and mass magnetic susceptibility (χ) are measured to simulate the high-temperature effects of coal fires on the loess in northern Shaanxi, and also study its chromaticity changes and abnormal magnetic properties. The results show that (1) the loess χ value is affected by the heat-treatment temperature; at 600 °C, the χ value decreases, increasing rapidly above after 850 °C. Further, the magnetic susceptibility changes significantly. (2) The thermal-induced transformation of ferromagnetic minerals and the buried depth of loess are the main reasons for these changes in magnetic susceptibility and red chroma of loess.

Mechanical behavior and constitutive model for loess samples under simulated acid rain conditions

Acid rain is mainly composed of sulfuric acid and nitric acid aqueous solutions, which can deteriorate the mechanical properties of soil and thus threaten the safety of soil engineerings. In this paper, the influence of sulfuric acid rain on mechanical properties of loess soil samples was studied. The diluted sulfuric acid solution has respectively pH 5.0, 4.0 and 3.0 to simulate the acid rain condition, and the triaxial compressional tests and scanning electron microscope were carried out to investigate the deteriorated properties and evolution of the microstructure of the saturated loess samples. The results demonstrated that acid rain made the porosity of loess samples larger, and changed the pore distribution and contacts of soil grains, so that the mechanical properties of loess samples varied in some degree. With the decrease of pH value, both the peak value of the deviatoric stress and volumetric contraction of loess samples decreased, which reduced the parameters of shear strength of loess samples. Furthermore, a framework of the chemical–mechanical model for loess under the action of acid rain was established, in which loess was considered as a porous medium material, and the influences of acid rain with different pH values were taken into account in the double-hardening constitutive model, and the model was also verified by the triaxial test results finally.

Microstructure and compressibility evolution of sulfate saline compacted loess under drying-wetting cycles

Soil salinization not only can induce environmental problems but also cause notable changes in the engineering performance of soil, especially the compacted loess that is often exposed to drying-wetting (D-W) cycles in Northwest China. To explore the changes in compression behavior of the saline compacted loess under D-W cycles, a series of the oedometer tests were conducted on compacted loess samples with different D-W cycles and sodium sulfate content. In addition, the changes in microstructural properties of the loess samples were also investigated by scanning electron microscope (SEM) tests. The results demonstrate that the compressibility coefficient of the loess samples increases with D-W cycles and tend to stabilize after three cycles, while varies linearly with salt content. The compressibility deterioration equation for the based on the compressibility coefficient was then established considering both D-W cycles and salt content, which can well predict the compressibility deterioration of saline compacted loess under D-W cycles. Due to the repeated gasification and liquefaction of pore water and the repeated dissolution and crystallization of sodium sulfate, the skeleton of saline compacted loess with higher salt contents or more D-W cycles tends to loosen, which greatly enhances the effective connectivity of the pores and leads to the deterioration of compressibility. Finally, the compressibility deterioration ratios due to D-W and salt erosion were discussed by decoupling analysis. These findings can provide references for the engineering practice in loess areas.

Influence of Wet-Dry Cycles on Uniaxial Compression Behavior of Fissured Loess Disturbed by Vibratory Loads

In this study, the influence of wet-dry cycles on the uniaxial compression behavior of fissured loess after vibration was investigated by small shaking table tests, wet-dry tests, and uniaxial compression tests. Results show that the initial elastic modulus and peak strength both decline after wet-dry cycles while the morphology of stress-strain curves shows insignificant changes. Except for samples with a fissure angle α = 45°, where the bimodal stress-strain curves were observed, all show softening trend. The failure mode can be classified into four main types: fracture failure (α = 0° and 15°), slip-fracture coupled failure (α = 45°), slip failure (α = 60°), and compression shear failure (α = 30° and 90°). The failure modes of samples at α = 0°, 15°, 45°, and 60° are independent of wet-dry cycles but strongly depend on fissure angle, while those at the other fissure angles are more susceptible to wet-dry cycles. The uniaxial compressive strength (UCS) of fissured loess samples before vibration are greater than those after vibration. The relationship between UCS and fissure angle before and after vibration show double-valley pattern. A binary medium model for fissured loess considering vibration and wet-dry cycles was constructed, which was verified by test data.

Time-Dependence of the Mechanical Behavior of Loess after Dry-Wet Cycles

The structure, time-dependent mechanical deformation, and strength characteristics of loess, which is loose and porous with well-developed vertical joints, are greatly affected by the dry-wet cycles, which are attributed to periodic artificial irrigation, rainfall, and water evaporation. To better understand the creep characteristics of loess under the effect of dry-wet cycles, Q2 loess samples obtained from the South Jingyang County, China, were subjected to different dry-wet cycles (0, 5, 10, 15, 20) and sheared in triaxial creep tests. The experimental results revealed that: firstly, the maximum value of the deviatoric stress corresponding to creep failure gradually decreases with an increase in the dry-wet cycles. Secondly, the long-term strength of the loess after dry-wet cycles were obtained through the Isochronous Curve Method. It is found that the long-term strength and the number of dry-wet cycles showed an exponential decreasing relationship. In addition, the creep damage mechanism of loess due to dry-wet cycles is proposed. This study may provide the basis for understanding the mechanical behavior of the loess under the effect of dry-wet cycles, as well as guidelines for the prevention and prediction of loess landslide stability.

Mesoscopic Characteristics and Performance Evaluation of Loess Treated by Different Anti-Seismic Subsidence Technologies

The meso-structure of the soil has an important restriction on its engineering properties. Based on dynamic triaxial tests and SEM meso-structure test experiments, this study investigated the meso-scale structural deformation characteristics of Q3 loess samples treated by physical, chemical, and compound improvement methods, before and after strong earthquakes of typical seismic subsidence loess. On this basis, the seismic subsidence performance of the improved method is given under the conditions of frequent earthquakes, fortifying earthquakes, and rare earthquakes. The results show that 1) the physical improvement method has the most obvious effect on the elimination of macropores and overhead pore structures; 2) the chemical method can generate unique glass beads or flocculated fine structures, which can greatly enhance the strength of the soil and play the role of filling, cementing, or buffering, respectively, in the event of a strong earthquake; 3) for several improved treatment methods, the amount of seismic subsidence increases non-linearly with the increase in peak acceleration; and 4) in the event of frequent earthquakes, the earthquake subsidence can be eliminated by the method of adding fly ash, and when the fortification earthquake comes, the dynamic composite method can completely eliminate the seismic subsidence of the site. The related results can give reasonable suggestions for the treatment of seismic subsidence of different foundations in the “resilient urban and rural” and key engineering construction and seismic design of China’s loess area.

Exploration on mechanical test method of improved loess under dry-wet cycles

The stability of loess subgrade is affected by many factors. Dry-wet cycle is a common factor that causes damage to the strength of loess subgrade. In order to study the influence of dry-wet cycle on the stability of loess subgrade, reveal the mechanism of dry-wet cycle damage to the strength of loess subgrade It is necessary to sample the loess soil samples in this area, and perform compaction test, dry-wet cycle test, unconfined compression test and scanning electron microscope test on the soil sample to analyze the influence of dry-wet cycle on the strength and microstructure of loess soil. . In this way, the potential relationship between the microstructure and the strength of the soil can be obtained. The results show that the loess drywet cycle causes the loess's tensile strength and compressive strength to decrease with the increase of the number of dry-wet cycles. The dry-wet cycle effect gradually reduces the shear structural strength of the undisturbed loess and eventually disappears. Scanning electron microscope tests found that the humidification process caused slight movement of the particles, while the drying process resulted in permanent deformation of small pores.

Methods and exploration for mechanical testing and microscopic testing of loess under freeze-thaw cycles

The stability of loess subgrade is affected by many factors. Freeze-thaw cycles are a common factor that causes the strength of loess subgrades to be damaged. In order to study the influence of freezethaw cycles on the stability of loess subgrades, reveal the mechanism of freeze-thaw cycles on the strength of loess subgrades. It is necessary to sample the loess soil samples in this area, and perform compaction test, freeze-thaw cycle test, unconfined compression test and electron microscope scanning test on the soil sample to analyze the influence of freeze-thaw cycle on the strength and microstructure of loess soil. . In this way, the potential relationship between the microstructure and the strength of the soil can be obtained. The results found that the freeze-thaw cycle of loess led to a trend of first increase and then decrease in soil strength. The microstructure showed a trend of smaller soil particles and increased soil voids. The potential relationship between the microstructure and the strength of the soil was analyzed. It explains the conclusion that the strength of the soil first increases and then decreases.

Effect of Wetting and Drying Cycles on the Dynamic Properties of Compacted Loess

This paper investigates the dynamic properties of compacted loess under wetting and drying (W‐D) cycles. A series of tests were conducted on compacted loess samples, namely, the soil dynamic triaxial test and the scanning electron microscopy (SEM) test. The test results showed that the dynamic stress‐strain relationship of the compacted loess under the action of W‐D cycles accords with the Hardin–Drnevich model. The initial dynamic shear modulus (G0) and the maximum dynamic shear stress (τy) of the compacted loess first decreased and then increased with the number of W‐D cycles (n) increasing. The damping ratio (λ) increased linearly with the dynamic strain (εd) increasing in the semilogarithmic coordinate. The defined change rate of the damping ratio (η) first increased and then decreased with the n increasing. The macrostructure and microstructure characteristics of samples in the process of W‐D cycles indicate that the increasing number of pores in the humidifying process and the cracks on the surface and inside of samples during dehumidification lead to the structural damage and dynamic properties reduction of compacted loess. The main reasons for structure strengthening and dynamic properties increasing are that soil particle structure develops to mosaic structure, pore structure develops to uniform small pore, and matrix suction makes soil sample tend to be dense.

Experiments and Application of Reclamation of High-Mineralized Mine Wastewater for Confecting Grouting Slurry.

Owing to the high mineralization and high treatment cost, Ordovician limestone water is often regarded as a mine wastewater. In order to make rational use of mine water with high mineralization and turn waste into treasure. In this work, the natural water quality of Ordovician mine water in the Weibei coalfield had been tested, and the suspended matter and trace elements of Ordovician mine water in the selected deep detained area had been further tested. As a contrast, the water quality of Ordovician mine water after heating and concentration had been tested. The mechanical and hydraulic parameters of concentrated mine water-loess and concentrated mine water-cement slurry had been tested and compared with conventional slurry. The results showed characteristics of deep detained Ordovician limestone mine water is high salinity, certain suspended matters, limited special material and high permanent hardness. However, compressive strength of loess samples increased, while the permeability reduced. The initial setting-time of the modified material was short, while it showed an increased compressive strength. In practical terms, the quantity of grouting produced in engineering applications can be reduced by 16%, whereas the discharge of high-mineralized mine water can be decreased by about 40,000 m3/a.

Investigation of Changes to Triaxial Shear Strength Parameters and Microstructure of Yili Loess with Drying-Wetting Cycles.

This research examined the drying–wetting cycles induced changes in undrained triaxial shear strength parameters and microstructural changes of Yili loess. The drying–wetting cycles were selected as 0, 1, 3, 5, 10, 20 and 30. Then, we collected Yili loess samples and performed unconsolidated-undrained (U-U) triaxial shearing tests to ascertain the variation in shear strength parameters with drying–wetting cycles. Additionally, we investigated the microstructural changes of Yili loess samples under drying–wetting cycles simultaneously via nuclear magnetic resonance (NMR) and scanning electron electroscopy (SEM). Finally, we established a grey correlation model between shear strength and microstructural parameters. Under U-U conditions, the prime finding was that the loess’s shear strength parameters changed overall after drying–wetting cycles; in particular, the internal friction angle φ dropped significantly while the cohesion c changed only slightly during cycles. For all the cycles, the first cycle gave the highest change. Soil morphology deterioration was evident at the initial stage of cycles. During the entire drying–wetting cyclic process, pore size distribution showed progressive variance from two-peak to a single-peak pattern, while both porosity and the fractal dimension of pores increased gradually towards stability. Soil particle morphology became slowly simple and reached the equilibrium state after 20 drying–wetting cycles. Under cyclic drying–wetting stress, the shear strength parameter changes were significantly correlated to microstructural modifications. This investigation was related to loess in the westerly region. The findings were expected to provide new insight into establishment of the connection between microstructure and macro stress–strain state of loess. To some extent, it provided a theoretical basis for the prevention and control of loess engineering geological disasters in Yili, Xinjiang and other areas with similar climate and soil types.

Evaluation of the relationship between freezing point and suction in chloride loess

In this study, the relationship between freezing point and suction of four types of chloride loess samples (CaCl2, MgCl2, NaCl and KCl) was investigated by freezing point tests and filter paper method-based suction tests. Break points were observed from the freezing point versus water content curves near the plastic limit, which decline at higher salt contents. The freezing point declines roughly linearly with salt content for samples with 2–1 type chloride salts (CaCl2 and MgCl2), while decreases attenuatedly for those with 1–1 type chloride salts (NaCl and KCl). The higher the cation content, the more significant the freezing point depression, and the ranking of Mg2+ > Ca2+ > Na+ > K+ was roughly noted, which is linked with the cation hydration capacity. In addition, the relationship between the osmotic suction of samples h0soil and that of chloride solution h00solution was suggested to be described by a linear relationship. The freezing point of samples depends on both matric suction and osmotic suction. The limitations of the Mizoguchi's model were noticed through data analysis and by retaining its basic construct, a suction-based model for freezing point of chloride loess was established and verified.

Comparison of the liquid limit of loess defined by the Vasiliev and Casagrande test methods

The paper compares liquid limit values obtained by the Vasiliev and Casagrande apparatus in line with BDS 648:1984 and BDS EN ISO/ TS 17892–12:2018, on the basis of testing 25 silty loess samples. The results indicated that compared with the Vasiliev apparatus, the Casagrande apparatus gives a higher liquid limit. An equation allowing conversion of the liquid limit obtained by the Vasiliev cone penetrometer to the liquid limit by the Casagrande apparatus has been developed.

Characterization of the Relationship between the Loess Moisture and Image Grayscale Value.

This paper presents a model for estimating the moisture of loess from an image grayscale value. A series of well-controlled air-dry tests were performed on saturated Malan loess, and the moisture content of the loess sample during the desiccation process was automatically recorded while the soil images were continually captured using a photogrammetric device equipped with a CMOS image sensor. By converting the red, green, and blue (RGB) image into a grayscale one, the relationship between the water content and grayscale value, referred to as the water content–gray value characteristic curve (WGCC), was obtained; the impacts of dry density, particle size distribution, and illuminance on WGCC were investigated. It is shown that the grayscale value increases as the water content decreases; based on the rate of increase of grayscale value, the WGCC can be segmented into three stages: slow-rise, rapid-rise, and asymptotically stable stages. The influences that dry density and particle size distribution have on WGCC are dependent on light reflection and transmission, and this dependence is closely related to soil water types and their relative proportion. Besides, the WGCC for a given soil sample is unique if normalized with illuminance. The mechanism behind the three stages of WGCC is discussed in terms of visible light reflection. A mathematical model was proposed to describe WGCC, and the physical meaning of the model parameters was interpreted. The proposed model is validated independently using another six different types of loess samples and is shown to match well the experimental data. The results of this study can provide a reference for the development of non-contact soil moisture monitoring methods as well as relevant sensors and instruments.

The Trend of Permeability of Loess in Yili, China, under Freeze–Thaw Cycles and Its Microscopic Mechanism

Loess landslides induced by the freeze–thaw effect frequently occur in Yili, China. Freeze–thaw cycles cause indelible changes in the soil microstructure, affecting its permeability. This study investigated the impacts of freeze–thaw cycles on the permeability of Yili loess using permeability tests on undisturbed (virgin, in situ) and remolded loess samples taken before and after freeze–thaw cycles. Scanning electron microscopy and nuclear magnetic resonance techniques were utilized to investigate the microscopic mechanism of the freeze–thaw process on the loess. Grey relation analysis (GRA) was employed to analyze the correlation between macroscopic permeability and microscopic parameters (maxi. radius, eccentricity, fractal dimension, directional probability entropy, and porosity). The results revealed that the permeability and all the microstructure parameters have roughly shown the same trend: “fluctuation–towards equilibrium–stability”. Firstly, the permeability coefficients of original and remolded loess experienced three and two peaked–trends, respectively, before 30 freeze–thaw cycles. The trends eventually stabilized within 30–60 freeze–thaw cycles. Increased number of freeze–thaw cycles disintegrated large particles in undisturbed loess into medium–sized particles, and particle shapes became more uncomplicated. Medium–sized particles in the remolded loess agglomerated to larger particles with more complex shapes. Furthermore, the overall porosity of the originally undisturbed loess decreased, and large and medium–sized pores transformed into small pores and micropores. In contrast, the overall porosity of remolded loess increased. Finally, the results revealed that permeability coefficients of the undisturbed and remolded loess became closely related with eccentricity and porosity, respectively. This study provides a reference for preventing and governing the loess landslides induced by the freeze–thaw cycles and permeability reduction in construction on loess in seasonally frozen areas in Yili.

Detrital zircon U–Pb age analysis of last glacial loess sources and proglacial sediment dynamics in the Northern European Plain

Loess deposits along the northern fringe of the European loess belt potentially record past changes in dust emission from areas proximal to former ice sheets. Recent chronologies from loess deposits across this region generally agree on greatly enhanced dust deposition rates when the Fennoscandian Ice Sheet reached its maximum extent during the late last glacial. However, uncertainties over the material's source and origin limit understanding of the causes of this enhanced dust activity. In particular, loess in southwestern Poland has been attributed to multiple origins, mainly involving glaciofluvial outwash plains along the Fennoscandian Ice Sheet margin and/or local sources in the mountainous areas of the Sudetes and Western Carpathians. Here we apply detrital zircon U–Pb age analyses for a large number of grains recovered from four loess samples taken from different stratigraphic units exposed at Biały Kościół in southwestern Poland, previously luminescence dated to MIS 4–2, to assess loess provenance as well as its temporal evolution during last glacial Fennoscandian Ice Sheet fluctuations. Furthermore, we analysed the detrital zircon U–Pb age spectra of five samples from potential source sediments to constrain the history of sediment recycling and mixing within the Northern European Plain prior to deflation and loess deposition. The broad range of zircon age components detected in the four loess samples suggests both Fennoscandian and closer Peri-Gondwanan proto-sources while a narrow, dominant Carboniferous age peak is consistent with sourcing from the local Strzelin Hills in the Sudetic foreland. However, the presence of both Fennoscandian and Peri-Gondwanan derived grains in samples from potential source sediments reveals that this mixture of sediment sources is widespread across the Northern European Plain, as a result of long-term glacial and fluvial reworking of cover sediments in the proglacial area throughout the Quaternary. Local rivers draining the Sudetic foreland transported this Fennoscandian-Peri-Gondwanan sediment mixture along with particles denuded from the Strzelin Hills, resulting in a nearby, temporally stable dust source for the Biały Kościół loess during MIS 4–2, while dust emission rates were substantially increased during the last glacial maximum. Given that our model for loess formation at Biały Kościół essentially involves sediment distribution via rivers prior to short distance aeolian transport, we infer that the proportion of northern ice sheet derived particles in European loess deposits is mainly controlled by the drainage pattern of major rivers in relation to Pleistocene ice margins where glaciofluvial sediment is abundant. Based on the presence of Fennoscandian derived zircon grains in European loess deposits, we constrain a southern limit of the influence of northern ice sheet dust sources along the central European highlands that currently divide drainage between the Northern European Plain and the Danube Basins.

Exploring the saturated permeability of remolded loess under inorganic salt solution seepage

The seepage of remolded loess with inorganic salt solutions can deteriorate its engineering properties. To gain insight into the mechanism responsible for changes in the permeability of remolded loess due to the invasion of inorganic pollutants, the saturated permeability tests were performed on remolded loess samples using deionized water (DW) and NaCl, CaCl2, AlCl3, and NaHCO3 solutions. Leaching tests were designed to determine the chemical components of leachates. Zeta potentials were measured to evaluate the electrochemical properties, and mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) tests were used to estimate changes in microstructure before and after seepage. The results indicate that the saturated hydraulic conductivity (Ksat) was positively correlated with the cation valence. With the increase of cation valence, the compression degree of double diffusion layer on the surface of clay particles increases, and a larger space for free water movement is formed. The salt effect promoted the dissolution of carbonate minerals of loess and enhanced permeability, for example, NaCl; while the common-ion effect of HCO3− inhibited their dissolution and even led to the calcite precipitation. In addition, the hydrolysis of Al3+ also significantly affected Ksat. Therefore, under the seepage of inorganic salt solutions, the order of Ksat of remolded loess samples was NaHCO3 < DW < NaCl < CaCl2 < AlCl3.