Mechanical Properties Of Loess Research Articles

Mechanical behavior and strengthening mechanism of loess stabilized with xanthan gum and guar gum biopolymers

Abstract The structural properties of loess are susceptible to change when subjected to external loads and complex environments, leading to various geological disasters. To investigate the mechanical behavior and strengthening mechanism of loess stabilized with biopolymers such as xanthan gum and guar gum, especially for soils with low bearing capacity and stability in engineering applications, we conducted research on the improvement of soil with xanthan gum and guar gum, tests including unconfined compressive strength, disintegration, direct shear, and microstructure tests were conducted. Among the four different dosages of biopolymers (0%, 0.5%, 1%, 2%) and four different curing ages (1 day, 3 days, 7 days, 14 days), the 2% content of biopolymer and 14 days had the greatest impact on the mechanical properties of loess, Both the compressive and shear strength, as well as the water stability of solidified loess, improve with higher content of xanthan gum and guar gum or prolonged curing time; however, the disintegration rate decreases. Microscopic analysis indicates that the biopolymers effectively fill the gaps between soil particles and attach to the particle surfaces, forming fibrous and reticular structures that improve the interparticle bonding and ultimately increase the strength and water stability of the loess. Xanthan gum and guar gum biopolymers can improve the mechanical properties and water stability of loess, enhance the erosion resistance and improve the water-holding capacity. These outcomes suggest that guar gum and xanthan gum biopolymers have the potential to serve as environmentally sustainable alternatives to conventional soil stabilizers.

Effects of clay grains on the shear properties of unsaturated loess and microscopic mechanism

Different clay grains affect the structural strength of loess through the cementation of skeletal particles. This study investigates both clay-clay grains and quartz-clay grains. Clay-clay grains mixed loess (CM-L) and quartz-clay grains loess (Q-L) samples were prepared, and their unsaturated shear properties analyzed. X-ray diffractometry (XRD) analysis was conducted to determine the types and proportions of clay grains. Ball mill grinding and laser particle size analysis were employed to ensure comparable sizes of clay grains, while mercury intrusion porosimetry (MIP) tests confirmed similar pore characteristics. Scanning electron microscope (SEM) and unsaturated triaxial consolidation and drainage tests explored the impact of different clay grains on loess shear characteristics, assessing both microscopic and macroscopic performance. The results indicate that CM-L loess exhibits higher cohesion and a lower internal friction angle at the same matric suction level. The cohesion and internal friction angle of both CM-L and Q-L loess exhibit a linear relationship within the range of 50–200 kPa matrix suction. The cohesive force ranges for CM-L and Q-L loess are 60.31–80.07 kPa and 43.01–69.60 kPa, respectively, while the ranges for internal friction angles are 19.95°-19.59° and 25.91°-25.06°, respectively. Compared to Q-L loess, CM-L loess exhibits an average difference in cohesion of 23.18 kPa and in internal friction angle of -5.72°. The microscopic variation in shear strength can be attributed to the “fish scale-like” interlocking state between clay-clay grains and the “tower-like” scattering arrangement of quartz-clay grains. In conclusion, the effect of different clay-grain types on the shear strength of loess varies significantly. The present study elucidates the relationship between the influence of different clay grains on the mechanical properties of loess and their microscopic structural characteristics, thereby providing crucial data for investigating the microscopic effects on the structural strength of loess.

Advanced multi-scale characterization of loess microstructure: Integrating μXCT and FIB-SEM for detailed fabric analysis and geotechnical implications

Loess, a Quaternary wind-blown deposit, is a problem soil that gives rise to frequent geohazards such as landslides and water-induced subsidence. The behaviour of loess is controlled by its microstructure, consisting of silt-sized skeleton particles and complex bonding structures formed by clay-sized particles. Achieving a deep understanding and precise modelling of loess behaviour necessitates comprehensive knowledge of the realistic 3D microstructure. In this paper, a correlative investigation of the 3D loess microstructure is performed using X-ray micro-computed tomography (μXCT) and focused ion beam scanning electron microscope (FIB-SEM). Details of clay structures in loess, such as clay coatings, clay bridges and clay buttresses, are visualized and characterized in 3D based on FIB-SEM images with a voxel size of 10 × 10 × 10 nm3. The clay structures exhibit a diverse degree of complexity and their impact on the mechanical properties of loess is highlighted. Statistical analysis of the skeleton particles, including size, shape and orientation, are derived from μXCT images with a voxel size of 0.7 × 0.7 × 0.7 μm3. The findings provide insights into the collapse mechanism and particle-scale modelling of loess. The combination of μXCT and FIB-SEM proves to be a powerful approach for characterizing the intricate micro-structures of loess, as well as other geomaterials.

Study on coupling effect of soil structure and overconsolidation on mechanical properties of loess.

Soil structure and overconsolidation are two important factors that affect soil strength. Current research studies have primarily focused on the influence of single factors, and relatively few studies have studied the coupling effect of the two. In this paper, the effects of structure and overconsolidation on the mechanical properties of loess under certain conditions have been studied by compression tests and direct shear tests. Undisturbed loess, remolded loess, overconsolidated undisturbed loess, and overconsolidated remolded loess were investigated in this work. The results indicate that structure and overconsolidation can enhance the overall strength of the soil, but the effects of these two factors also interfere and weaken each other. The combined effect of structure and overconsolidation can lead to higher soil shear strength. Compared with remolded normally consolidated soil, when the vertical pressure is 50kPa, 100kPa, and 200kPa, the structure increases the strength of the original normally consolidated soil by 35%, 21%, and 7%, respectively. Overconsolidation increases the strength of the remolded overconsolidated soil by 51.3%, 40.9%, and 17.7%, respectively. The combined effect of structure and overconsolidation increases the strength of the original overconsolidated soil by 89%, 72.5%, and 32.7%, respectively. The increase in soil strength caused by the coupling effect is smaller than the sum of the strength increase caused by the two factors. The main reason is that the soil structure can reduces the compaction effect of overconsolidation, and the compaction load applied during the process of overconsolidation can also damage the soil structure, and the scanning electron microscopy observation is consistent with the experimental results and analysis. Finally, an empirical relation was developed for the effect of overconsolidation, structural properties, and their coupling on soil strength. The calculated results of the formula are highly consistent with the experimental data, and have good rationality and accuracy.

Effect of Freeze–Thaw Cycles and Initial Water Content on the Pore Structure and Mechanical Properties of Loess in Northern Shaanxi

Spalling disease caused by freeze–thaw cycles often occurs on the loess cut-slopes in northern Shaanxi. The deterioration of the pore structure and mechanical strength of loess under a freeze–thaw environment is one of the critical reasons underlying the occurrence of spalling disease in the slopes. In order to explore the effects of freeze–thaw cycles on the pore structure and the mechanical strength of loess, four initial water contents (7%, 9%, 12%, and 14%) and six freeze–thaw cycles (zero, one, three, five, 10, and 20) were considered in this study. Nuclear magnetic resonance (NMR) and triaxial compression tests were carried out to analyze and reveal the mechanisms of effect causing the deterioration of the soil strength that affects the stability of loess cut-slopes. The results showed that the porosity growth increased with the initial water content and continued to increase during the freeze–thaw process until a later stage of the freeze–thaw cycle, when it gradually stabilized. The stress–strain curves were primarily influenced by the number of freeze–thaw cycles, the initial water content of the samples, and the confining pressure. Both the cohesion and the internal friction angle exhibited a decay law that showed a significant decrease, then a slow decrease, and finally stabilization during the freeze–thaw process. Small and micropores were predominant among the pore structures of the loess, while medium pores were the second most common, and large pores were the least common. With the increase in the initial water content, the pores transformed from micropore structures to medium and large pore structures. The soil strength deterioration was primarily driven by the phase changes of the pore water, as well as the water migration during the freeze–thaw process. This study will be beneficial for identifying the characteristics and types of freeze–thaw disease in cut-slope engineering in seasonally frozen loess areas and providing a theoretical reference and design basis for achieving green and sustainable development in slope engineering, management, and maintenance.

Quantification of the spatial-temporal evolution of loess microstructure from the Dongzhi tableland during shearing

The physical and mechanical properties of loess are significantly influenced by its microstructural characteristics. The microstructure evolution is of great importance to better understand the loess deformation mechanism. To quantitatively and qualitatively characterize the microstructure evolution of intact loess during shearing, SEM and EDS were carried out at 5 typical strain states during triaxial tests. In addition, the microstructure at different positions inside the samples was also observed to study the spatial evolution. The results indicate that the intact Malan loess studied has a metastable structure with a high porosity of 0.45, widely distributed spaced pores, point contacts and weakly cemented chains. During deformation, the microstructure in the middle part of the sample is most sensitive to deformation and has the significant variations and local difference. The microstructure evolution can be described in four stages: weak compaction stage, initial stage of structural collapse, massive structural collapse stage and structural stability loss stage. These four stages correspond to the four special stages of deformation, and the deformation process is expounded from the perspective of microstructure. The peak stress point is the critical point at which the external stress exceeds the initial structural yield strength. The failure of weak cementation and unstable contact, which leads to the massive collapse of the spaced pores, is the intrinsic factor of structural system instability. The appearance of local microcracks indicates that the shear strength of loess sample begins to decrease, and the deformation velocity will increase. These results from the study of the spatial–temporal evolution of loess microstructure contribute to a better understanding of the catastrophic disaster–causing behavior and the physical mechanism of deformation in the study area.

Experimental study of the particle agglomeration on its mechanical properties of collapsible loess

Loess, distributed all over the world, exhibits the behavior that is related to their formation history, mineralogy, and microstructure, which can cause serious geotechnical engineering problems. This paper presents the Baozhong railway is a key transportation channel for Guyuan city in Ningxia province of northwestern China. Based on field investigations treasure middle section of the railway in the study area, it is found that the more serious diseases subgrade settlement, local roads embankment platform dislocation occurs and lots of cracks were founded. For several years, with the train speed increasing, and due to the influence of widespread flood irrigation on the farmland, the subgrade experienced a degree of settlement. This settlement was not alleviated after three treatments, which seriously affected train safety. In order to analyze the reason for the railway line settlement, soil samples were collected from the collapsible loess subgrade. Consolidation test, particle size analysis test, X-ray diffraction test (XRD), and scanning electron microscopy test (SEM) were performed to investigate the mechanism of the subgrade disease. The results reveal that loess collected from severe differential settlements at locations has a highly compressible, and its clay content and agglomeration level was generally low. These results illustrated that the particle size of 20–50 microns has a direct effect on its mechanical properties of loess. This part of the particles has a cementation effect. It can effectively connect the large particles of the skeleton to form particle agglomerates and is an effective composition of loess clay minerals. Therefore, the loess structure was not stable due to its relatively low internal molecular attraction. When such saturated collapsible loess subgrade subjected to train vibration load, the soil might be liquefied, and its structure might be instable. If the drainage of the subgrade was not well designed, severe differential settlements would occur. The research is of great significance to clarify the relationship between loess particle composition, microstructure and its macromechanics, providing a vital reference for the engineering construction in the loess-dominated areas.

Effect of Freeze-Thaw on Mechanical Properties of Loess with Different Moisture Content in Yili, Xinjiang

Various geological disasters such as collapses, landslides, and mudslides occur frequently in Yili, Xinjiang. The loess in this area provides a basis for the occurrence of landslides and other disasters. At the same time, Yili Valley is typically a seasonally frozen soil region. The freeze–thaw cycle is an essential disaster-inducing factor. However, scholars have lain a research emphasis on the material source of the Yili Loess, while lacking a systematic investigation of the degradation mechanism of the soil’s physical and mechanical properties under the freeze–thaw action. Therefore, it is prudent to investigate the changes in mechanical properties of loess in this region under the freeze–thaw cycle. In this study, focusing on a typical loess landslide in Yili, some in situ soil samples were collected to conduct related physical and mechanical tests. According to the maximum dry density and optimum moisture content of the loess in the region, four different groups of soil samples with varying moisture contents were prepared and subjected to different freeze–thaw cycles. The changes of apparent individual characteristics under freeze–thaw cycles were observed, and a consolidated undrained (CU) shear test was carried out to obtain the changes of shear strength indices of loess samples with varying moisture contents under freeze–thaw cycles. The results showed the obvious development of characteristics during freeze–thaw cycles, with the growth of many frost and ice crystals. At the freezing stage, the growth of ice crystals led to hexagonal peeling bodies on the surface layer. At the thawing stage, a rapidly melting network ice crystal pattern imposed a thermal thawing disturbance on the surface rock soil. After multiple freeze–thaw cycles, the soil’s peak strength dropped significantly and the internal friction angle changed slightly, but the cohesion was adversely affected, with frequent fluctuations. The present study enhances the research level of loess’s mechanical and strength properties under freeze–thaw cycles and provides a theoretical foundation for preventing loess landslides in this region.

Effect of Sulfate on the Aggregation of Clay Particles in Loess

The type and structure of clay minerals are among the main factors affecting the physical and mechanical properties of loess, and the salt content plays a dominant role in many factors affecting aggregation. In this study, the grain size analysis, Atterberg limits tests, scanning electron microscopy (SEM), and energy spectrum analysis (EDS) were used to explore the microstructure and physicochemical mechanisms of the aggregation of clay particles. Finally, the unconfined compressive test, direct shear test, and elastic wave velocity test were conducted to explore the effect of sulfate agglomeration on loess properties. The results show that the salt-washing process leads to the loss of the original soluble salt, dispersion of the original aggregates, and increase of fine particles, such as fine silt and clay. With the increase of sulfate content, the content of fine silt and clay decreases, the liquid limit and plasticity index decrease, the plasticity limit remains unchanged, the aggregate content of fine silt and clay increases, the adsorption capacity weakens, and the diffusion layer compresses and thins. The mechanical test results show that when the sulfate content is less than 3%, the sulfate is almost completely dissolved and the aggregate is less, which increases compressive strength and the cohesion; when the sulfate content is more than 3%, too much sulfate cannot be dissolved and precipitated; hence, the aggregate increases. However, the existence of large volume mirabilite crystals reduces the cementation, which reduces the compressive strength, increases the internal friction angle, and weakens the cohesion.

Mechanical Properties of Loess and Filling Materials of High-Speed Railway Vibration Isolation Trench in Loess Area

The special properties of loess make its impact on the vibration propagation of high-speed railways different from other soils. In this study, the static and dynamic characteristics of loess were studied by static and dynamic triaxial tests. The experimental results show that when the frequency is the same, the dynamic stress-strain relationship curve moves up with the increase of the confining pressure. The frequency has little effect on the initial tangential dynamic modulus of the undisturbed loess. we studied the static and dynamic characteristics of loess and discussed the implementation methods of viscoelastic artificial boundary and infinite element boundary in high-speed rail dynamic response analysis. The vibration reduction and isolation effect of the trench with different filling materials (the concrete, gypsum, foamed plastic, and rubber) was studied. The results show that the comprehensive performance of the foamed plastics is better from the perspective of durability and stability of the vibration isolation trench wall. The research results can provide a reference for the selection of filling materials for high-speed railway vibration isolation trench in loess area.

Microstructure of unsaturated loess and its influence on strength characteristics

Previous studies have shown that structure has a significant influence on the mechanical deformation of unsaturated loess, but there is little published information focused on the influence mechanism of microstructure and mesostructure on the mechanical properties of loess. In this paper, the unsaturated undisturbed loess and its remolded loess under the same physical condition were taken as the research objects. The unsaturated triaxial shear tests with constant suction and net confining pressure were carried out, and the microstructure differences between the two are compared by using SEM and CT scanning to reveal the influence of structure on strength characteristics. The test results show that the cohesion and internal friction angle of undisturbed loess are greater than those of remolded loess. The angle of undisturbed soil particles is obvious, and the particles are bracket contact with good cementation. The remolded loess particles are close to round shape, and the particles are inlaid contact with destroyed cementation. The average radius of undisturbed soil is higher than that of remolded soil, indicating that there are bracket pores in undisturbed soil, but the bracket structure and macropores are deformed during shear deformation, and good structural and cementation ensure the strength of loess specimens.

Retraction Note: Mechanical properties of loess in mountainous area based on fuzzy clustering and construction of basketball venues

Retraction Note: Mechanical properties of loess in mountainous area based on fuzzy clustering and construction of basketball venues

Review of chemical stabilizing agents for improving the physical and mechanical properties of loess

Review of chemical stabilizing agents for improving the physical and mechanical properties of loess

Research on the Mechanical Properties of Loess in Northern Shaanxi Province and Deterioration Process of Its Mechanical Performance

The regional research is conducted on the mechanical properties and mechanical performance of loess in loess slop of the northern Shaanxi Province, China. On the precondition of conforming to the related technical regulations, the related equipment was purchased or selfdesigned and machined to conduct large-scale in-situ direct shear test and participatory shear test on a high loess slope in northern Shaanxi Province, China. Through the multiple field shear tests of loess and red soils on a four-level platform of side slope in engineering tunnel, the relation curves of shear stresses of two soil types with the shear displacement were comparatively analyzed, and the change laws of relation curves of shear strength index and shear rate of soil samples with the displacement were obtained. The deterioration development laws of soil mass were revealed through the in-situ test, thus laying the data foundation for analyzing the sliding mechanism of slopes and the interaction between anti-slide piles and soil around piles.

RETRACTED ARTICLE: Mechanical properties of loess in mountainous area based on fuzzy clustering and construction of basketball venues

RETRACTED ARTICLE: Mechanical properties of loess in mountainous area based on fuzzy clustering and construction of basketball venues

Effect and Mechanism of Quicklime on Stabilized Loess

Lime is a cheap and easily available building material, which can greatly change the physical and mechanical properties of soil and is widely used in engineering construction. This article summarizes the effect and mechanism of quicklime in improving loess mechanical properties. The changes of physical and mechanical properties of loess after lime added and the internal mechanism of lime-improved soil are summarized, also, the factors affecting lime-soil improvement are analysed.

Mathematical modeling study of the landslide state of the slope of the mountain "SHYM BULAK"

The data on the main causes of the causing landslide on the mountain slopes, in particular, the pictures of the landslide-collapse that occurred along the road between the Medeu dam and the Shym Bulak ski sports complex in the gorge of the high slopes of the Trans-Ili Alatau in Northern Tien Shan, are given. It also offers some data on the physical and mechanical properties of loess and loamy soils, with which the cover soils of these slopes are mainly composed. A finite-element model for the study of the stress-strain state (VAT) of soil deposits of slopes of an obliquely layered structure is proposed with instructions on the features of using isoparametric elements of a quadrangular shape with four nodes of an arbitrary shape. The landslide slope of the mountain is modeled by finite elements together with the highway and the lower slope at the foot of which the Kishi Almaty River flows. The results of the VAT study are presented and the places of the slope that are vulnerable to a landslide are identified as dangerous.

Quantitative Research and Characterization of the Loess Microstructure in the Bai Lu Tableland, Shaanxi Province, China

Loess is a special geotechnical material with strong structural properties, and the microstructural characteristics of loess significantly influence its macroscopic physical features, mechanical properties, and catastrophic behavior. In this paper, serial samples were extracted from the continuous loess and paleosol strata of the Bai Lu tableland; with these samples, the optical microscopy‐based serial sectioning method was adopted to study the quantitative characterization and variation in the loess microstructure. Three‐dimensional characteristics and quantitative parameters of the particles, pores, and throats of the loess were obtained. The results indicate that the volume, Eq‐Radius, and major‐minor axis ratio of the loess particles satisfy third‐order, third‐order, and second‐order Gaussian distributions, respectively. The Eq‐Radius of the loess pores and throats satisfies a first‐order Gaussian distribution, and the throat channel length satisfies a gamma distribution. With increasing stratum depth, the particles become more flattened, the throat radii become larger and the pore channels become slenderer. The variation in fitting parameters and the correlations between the macrophysical and mechanical properties of loess were then explored. The study of the microstructure of loess contributes to a better understanding of the catastrophic behavior of loess and the physical mechanism of geologic hazards in this area.

Study on K0 Characteristics of Unsaturated Loess Under Isotropic Stress Path

Loess mainly distributes in arid and semi-arid regions of central and Western China. It is a typical structural soil with special structure and special sensitivity to water. Based on the analysis and summary of previous studies on the mechanical properties of loess, the quantitative and qualitative effects of various factors, especially consolidation conditions, on the mechanical properties of loess are compared and analyzed. The structural change characteristics of loess under isostatic stress ratio compression test were studied. The results show that the strength and deformation characteristics of the soil are not only related to the stress state, but also affected by factors such as the generation mode and the stress path.

Study on Mechanical Behaviors of Unsaturated Loess in terms of Moistening Level

Water sensitivity is the special feature of unsaturated loess, which is the main cause of engineering problems in loessial regions. Previous studies have generally focused on potential changes on mechanical properties of loess when it is moistened to saturation, while the moistening process is often ignored. In order to investigate the mechanical behaviors of unsaturated loess during the moistening process, this paper takes unsaturated loess obtained from Ili, Xinjiang Autonomous Regions, China, as study object. A self-developed oedometer was used which was available for adding water into the soil sample during loading, measuring the coefficient of earth pressure at rest and matrix suction during moistening. Loess samples obtained from 3 buried depths were tested under 4 different vertical loads. The moistening level was defined to refer to the relative level of water content with regard to the initial and saturated water contents of a soil sample. Change tendencies of moistening deformation, the coefficient of earth pressure at rest as well as suction versus the moistening level were investigated.