Strength Of Loess Research Articles

Retraction Note: Structural strength of loess in mountainous areas and optimization of rural public management services based on 5G Internet of Things

Retraction Note: Structural strength of loess in mountainous areas and optimization of rural public management services based on 5G Internet of Things

RETRACTED ARTICLE: Structural strength of loess in mountainous areas and optimization of rural public management services based on 5G Internet of Things

This article introduces the current status of cellular IoT technology and demonstrates the evolution from C-IoT to the fifth-generation mobile communication system, including key technologies such as network function virtualization, software-defined networking, and mobile edge computing and big data. A detailed analysis of key technologies and solutions shows that 5G C-IoT can effectively expand the business functions of C-IoT. As we all know, loess is widely distributed in Northwest China. Due to the large-scale development of the western region and the development of the “One Belt, One Road” project, the special structure and degradability of loess has more and more significant impacts on the project, which is essential for maintaining structural strength in all directions. The opposite sex is essential. Research shows that with the development of rural revitalization strategies, the demand for public products and services in rural areas will also increase. Therefore, there is an urgent need to improve the level of rural public administration. On this basis, this article analyzes the current situation of public products and services of rural public organizations in China. The rural government is currently city-oriented, but the grassroots government lacks long-term planning, the management scope of rural autonomous organizations is narrow, and the governance capabilities in rural areas and terrain insufficient. This article provides appropriate optimization suggestions and finds effective methods to improve the level of rural public management. When building a new situation, problems such as low public administration efficiency, lack of management talents, and imperfect management systems have become obstacles to the construction of a new rural economy. Therefore, this article puts forward suggestions on the current dilemma of public management in China’s new agricultural construction to ensure the development of new rural economic construction.

Triaxial Shear Behavior of Basalt Fiber-Reinforced Loess Based on Digital Image Technology

Engineering construction in loess areas often requires improvement of loess. Basalt fiber-reinforced soil due to complexity of material composition often exhibits poorly predictable mechanical behavior. In this study, digital image technology-based unconsolidated-undrained (UU) triaxial shear tests were carried out on loess samples at three fiber lengths (L) and four fiber contents (η). Results prove the improvement of the shear strength of loess by basalt fiber inclusion, which varies in inverted u-shaped pattern with fiber length or fiber content, with the maximum at η = 0.6%, L = 12 mm. Digital Image Technology was employed to analyze the damage characteristics and strain field of the surface of the sample at different loading time. The volumetric strain of the reinforced sample decreases at higher fiber content or fiber length, from shear contraction to dilatancy. The unreinforced sample exhibits a typical brittle failure mode with visible shear band, while plastic failure for reinforced samples with an overall bulging failure mode. A statistical damage constitutive model of fiber-reinforced loess was established with limited parameters calibrated. The rationality of the model was verified by comparisons of measured and calculated stress-strain data.

Deterioration characteristics of cement-improved loess under dry-wet and freeze-thaw cycles.

The effects of cement dosage, compaction coefficient, molding method (vertical vibration method and static pressure method), and dry-wet and freeze-thaw cycles on the mechanical strength of cement-improved loess (CIL) were studied to reveal its strength degradation law under dry-wet and freeze-thaw cycles. Results show that when using the vertical vibration molding method, the strength degradation effect of CIL can be improved by increasing the cement dosage and compaction coefficient; however, it is not obvious. Under the action of dry-wet cycle, damages, such as voids and cracks of CIL, develop continuously. Further, the strength deteriorates continuously and does not decrease after more than 15 dry-wet cycles. Therefore, the dry-wet cycle degradation system is selected by considering the most unfavorable conditions. In the process of freeze-thaw alternation, the pores and fissures of CIL develop and evolve continuously and the strength deteriorates continuously under the joint influence of water and low temperature. The strength tends to become stable after more than 12 freeze-thaw cycles. According to the safety principle, the deterioration coefficient of the freeze-thaw cycles is 0.3.

Study on Physical and Mechanical Properties of Q4 Loess in Lanzhou Rail Transit Area

Background: It has been observed that part of the tunnel of rail transit of line 1# in Lanzhou city passes through loess. Loess has obvious water sensitivity and anisotropy, these obvious characteristics have different degrees of influence on different projects. Objective: This study aims to compare the differences of shear strength with the vertical and horizontal direction through the triaxial and direct shear test, and permeability of samples in different directions. Method: The Q4 loess undisturbed sample from vertical and horizontal directions near tunnel face were selected in order to study the physical mechanical properties of Lanzhou rail transit section, and many related experiments were also carried out. Results: The results show that the anisotropy of the shear strength of the surrounding rock (Q4 loess) is significant near the tunnel face with a depth of 15m. The failure stress in the vertical direction is 1.33 times to that in the horizontal direction, and the permeability coefficient in the vertical direction is 1.37 times to that in the horizontal direction. In different directions, the internal friction angle of loess is basically the same. The cohesion force is different in different directions and different test methods. In general, the vertical strength of Q4 loess is greater than the horizontal strength. Conclusion: This characteristic is due to the structural characteristics of loess. Therefore, in the design and construction of loess tunnel, the mechanical parameters in different directions of loess should be considered, and the influence of different test methods on the measured parameters should also be considered.

The Tensile Strength of Loess in Northwest China by Unconfined Penetration Test and the Distinct Element Simulation

The unconfined penetration test (UP test) is one of the indirect methods to measure the tensile strength of soils. Through a series of UP tests of undisturbed and remolded loess, the split angle (α) of the wedge body which was shaped in the process of the experiment was discussed. And then, the particle movement, the force transfer, and the fracture development law of the sample were studied by the distinct element method (PFC2D). The experiment and numerical simulation results show the following: (1) the split angle (α) presents an exponential decrease with tensile strength (σt) and a linear decrease with internal friction angle (φ); (2) K that can be written as tan (2α + φ) is a coefficient to calculate tensile strength, which is equal to 2.00 for remolded loess and 1.50 for undisturbed loess; (3) the distinct element simulation shows that the resisting force by the UP test comes from both tensile stress and shear stress; (4) the tensile fractures and shear fractures appear at almost the same time when the tensile stress is approximately 70% of tensile strength.

Durability-Aimed Design Criteria of Cement-Stabilized Loess Subgrade for Railway

The subgrade is the foundation of railway construction, so its strength and stability are very important to ensure the safety and stability of a train. Loess is widely distributed in northwestern China, and it must be stabilized before being used in railway subgrade construction because loess is sensitive to water. Railway subgrade withstands not only the train load but also repeated attacks from the environment and climate because it has to be exposed to natural environment after construction. Therefore, the strength of cement-stabilized loess deteriorates continuously because of the above factors. Taking account of long-term stability, the influences of load on the cement-stabilized loess as well as the strength reduction laws of cement-stabilized loess under wet–dry cycling and freeze–thaw cycling were analyzed in this study. Additionally, the respective reduction coefficients were obtained. Finally, the strength design criteria of cement-stabilized loess subgrade were put forward based on railway subgrade durability by analyzing the obtained reduction coefficients and the critical dynamic strength of railway subgrade.

Research on stability analysis of structural loess slopes based on combined tensile-compression-shear strength theory

The long-term stable existence of western high and steep loess slopes is closely related to the special structural properties of loess, and there are often tensile stress areas at the top of the slope. It is important to evaluate the stability of upright slopes by reasonably considering the tensile strength of loess. Based on the combined tensile-compressive-shear strength theory of structural loess, the structural parameter field, displacement increment contour distribution field and small principal stress distribution field law characteristics of an upright slope are analyzed and studied by using the finite method of strength discounting. The results show that when there is no load or constant load on the top of the slope, the structural parameter distribution field and displacement increment contour field of the slope show an obvious “slip zone”, and the “slip zone” becomes more and more shallow with the increase of water content; when there is a uniform load on the top of the slope, the slip zone becomes more and more shallow with the increase of water content. When there is a uniform load at the top of the slope, the “shear zone” becomes more and more shallow with the increase of load intensity, and the surface uniform load intensity is bigger with the same water content, and there is a risk of local sliding; when there is no load at the top of the slope or the load remains unchanged, the small main stress field of the slope has different degrees of tension zone penetration, and the smaller the water content is, the bigger the tension zone is, and the amplitude is also bigger; when the slope has no load at the top of the slope or the load remains unchanged, the small main stress field of the slope has different degrees of tension zone penetration. The smaller the water content is, the larger the tensile zone is, and the amplitude is also large; when there is a uniform load on the top of the slope, the location of the tensile zone on the slope changes, shifting from the original back edge of the slope surface to a certain range on the top of the slope, and with the increase of the load strength, the tensile zone becomes smaller and smaller, and with the increase of the water content, the tensile zone also becomes smaller and smaller.

Experimental study on ring shear properties of fiber-reinforced loess

With poor mechanical properties and engineering characteristics, loess soils alone cannot meet the requirements of high-speed railway subgrade and large-sized building foundations based on shear strength and bearing capacity. Therefore, it is necessary to improve the mechanical properties of loess. In soil reinforcement, encouraging outcomes have been achieved by using fibers as reinforcement material for its relatively low costs and the low environment impact results from this material. To investigate the mechanical properties and the reinforcement mechanism of fiber-reinforced loess, ring shear tests were performed on loess samples with varying polypropylene fiber contents (0%, 0.25%, 0.50%, 0.75%, and 1%) and moisture contents (12%, 14%, 16%, 18%, and 20%). Furthermore, the macroscopic structure and microscopic images of the shear plane of reinforced specimens were analyzed as well. The test results showed that firstly polypropylene fibers significantly improved the peak strength and the residual strength of loess, and the optimal fiber content and the optimal moisture content were found to be 0.5% and 16%, respectively. The theoretical relationships between the fiber content Fc, the moisture content Mc, the peak strength τ, and the residual strength τr of reinforced loess were quantitatively determined. In addition, the fiber reinforcement mechanism was revealed based on the macroscopic shear plane of fiber-reinforced loess and SEM microscopic images of the shear plane.

Evaluation of Structural Strength and Parameters of Collapsible Loess

Abstract Loess is one of the problematic soils with a worldwide distribution for its collapsibility. To study structural strength and parameters of collapsible loess, a number of double-oedometer t...

Numerical investigation of the tensile strength of loess using discrete element method

The tensile strength of loess is important for the tension-related crack and failure in the Loess regions. While the previous work on the tensile strength of loess mainly focuses on the test method and its variation with different internal and external factors, the micro-mechanical characteristics of the tensile experiments are seldom studied. Taking the unconfined penetrated test (UP test) as example, the tensile strengths and internal stress distributions of undisturbed loess samples under the loading plate-sample ratios (d/D) ranging from 0.05 to 0.95 are numerically investigated using discrete element method. The internal stress distribution, failure pattern of sample and variation of internal crack are clearly reflected by the discrete element modelling. The DEM simulation results also show that: 1) the d/D in the range of 0.15 to 0.35 is recommended for measuring the tensile strength of undisturbed loess; 2) the tensile strength of undisturbed loess increases with d/D recommended above ;3) the failure of sample is mainly controlled by the tensile stress when the d/D is equal or lower than a critical d/D 0.50, while that is mainly controlled by the compressive stress when the d/D is larger than a critical d/D 0.50. This study shows the capability of discrete element method to simulate the UP test, thereby providing us a relatively reliable way to investigate the tensile strength of loess numerically and to explore the internal stress and crack distribution of soil sample.

An experimental investigation on engineering properties of undisturbed loess under acid contamination.

Even though soil acidification can cause significant destabilizing effects on various geotechnical issues, studies have rarely been conducted to determine the influence of soil structure on the impact of acid-contaminated soil. The current work aims to understand the effect of acid fluids on engineering behavior of undisturbed loess through laboratory tests. The sampling site is in a typical region of Loess Plateau, China. The variations in particle size distribution, Atterberg limits, uniaxial compression strength, and permeability were investigated with the help of microstructure for a better understanding of the governing mechanism of undisturbed loess subjected to acid fluids. It was found that exposure to acid fluids can improve the particle size distribution of loess. In contrast, the experimental results indicated that acid fluids can decrease Atterberg limits and strength and permeability of loess, although Atterberg limits and strength of loess are considerably increased in a highly sulfuric acid environment. Then, analyzing the engineering response in the light of microstructure revealed that the face-to-face contacts primarily exist in loess prepared with hydrochloric acid and nitric acid, respectively, whereas the mosaic structure is indeed active in sulfur-contaminated loess. Furthermore, a micro-conceptual structure was proposed based on the experiment led to the conclusion that the cementitious salt and structural characteristics play a dominant role in governing the engineering behavior of loess under acidic conditions.

Experimental study on improvement design of loess curing in engineering environment

This paper investigated the characteristics of improved loess curing in engineering environment. Loess was divided into silt and silty clay, and lime and lime-fly ash were selected as admixture materials. Direct shear tests and permeability tests were performed to research the rules in strength and permeability. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests were performed to analyze the improved mechanism. The conclusions are as follows: (1) compared with results curing in laboratory conditions, the fast change periods of strength and permeability starts later and continues longer time for each improved type when curing in engineering environment. For fast change periods of strength, the remolded compacted loess and 2:8 lime-treated loess are between 14~28 days, 3:7 in 14~90 days, and lime-fly ash-treated loess in 28~180 days. As far as permeability is concerned, the permeability coefficient of lime-treated loess and lime-fly ash-treated loess reaches 10−7cm/s in 90 days and 180 days, respectively. (2) Over the long term, the improvement effect still occurs at a slow rate. From 180 to 1090 days, the strength of lime-treated loess and lime-fly ash-treated loess increased by 13.2~16.5%, and their permeability coefficients decreased by 4~7.7%. (3) The properties of untreated loess have a significant role in strength and permeability, and silt and silty clay own different effect ways. (4) Curing conditions and untreated loess properties results to differences of improved loess in age standard and improvement effect, these effects should be considered in engineering projects.

An Experimental Study on the Deformation and Strength Characteristics of Q3 Loess under a Plain Strain Anisotropic Consolidation Condition

To study the strength, deformation characteristics, and intermediate principal stress of intact loess, vertical loading stress tests with different initial stress state k value were conducted under different confining pressures. Plane strain tests were carried out by the transformed true triaxial apparatus of Xi’an University of Technology. The study shows that loess tends to be in a plastic failure state in different confining pressures and k values, and the stress-strain relationship curve is of a hardening type. Results reveal that loess lateral and volume deformations have nonlinear relationships with its vertical deformation, and volume deformation shrinks in the process of shearing. The effect of confining pressure on soil deformation is greater than k value. The intermediate principal stress coefficient decreases with the increase of the confining pressure and transforms from increasing to decreasing with the increase of k value (ranging from 0.2 to 0.4). In brief, the loess failure strength is closely related to k value, confining stress, and spherical stress state. When k value increases, cohesion effect reduces, whereas internal friction angle increases linearly. The influence of k value on soil strength and deformation is closely related to confining pressure.

Freeze-thaw resistance of eco-material stabilized loess

In the Loess Plateau in Northern China, repeated freeze-thaw (FT) cycles deteriorate the strength and structure of loess as a foundation soil, resulting in the instability or failure of supporting structure. Lignosulfonate is an eco-material, utilized as an effective and nontraditional stabilizer to improve the engineering properties of metastable soils. A series of laboratory tests, including unconfined compression tests, cyclic loading-unloading tests and scanning electron microscopy, on calcium lignosulfonate (CL)- and sodium lignosulfonate (SL)-stabilized loess were performed to investigate the stabilization effect, deterioration mechanisms of the FT cycles, and the resistance to FT cycles. Two traditional stabilizers, quicklime (QL) and sodium silicate (SS), were selected, and the engineering properties of QL- and SS-stabilized loess were compared with those of CL- and SL-stabilized loess. The results showed that the strength values of CL- and SL-stabilized loess specimens decreased by 34.2% and 50% respectively, after 20 FT cycles, whereas those of the traditionally SS- and QL- stabilized specimens decreased by 85.3% and 82.87%, respectively. The elastic moduli of SL- and QL-stabilized loess specimens decreased by 22.1% and 92.0%, respectively. The mean energy dissipations of nontraditionally treated specimens also decreased significantly less than those of traditionally treated specimens. Overall, the results showed CL and SL had better stabilization effects on engineering properties of loess than QL and SS, and their stabilized loess specimens exhibited stronger resistance to FT cycles. The study findings demonstrated the significant potential of lignosulfonate for extensive application in cold loess areas.

Experimental Study on Main Physical Parameters Controlling Shear Strength of Unsaturated Loess

It is particularly important to study the strength of unsaturated loess, and its accurate determination is crucial to the stability analysis of soil slope and foundation and calculation of earth pressure. In order to reveal the control mechanism of physical parameters on the shear strength of unsaturated loess, the intact and remolded loess were used as the research object; sandy silt, quartz flour, and quartz sand were used as contrast; the systematic direct shear tests of unsaturated loess, sandy silt, and quartz sand under different conditions of water content, dry density, and clay content were carried out. The results show that the cohesion, internal friction angle, and shear strength of unsaturated loess piecewise functionally decrease with the increase of water content, its shear strength increases linearly with the increase of dry density, and its internal friction angle shows an upward quadratic function relation with the increase of clay content. The law results of comparing sandy silt, quartz flour, and quartz sand with loess considering water content and dry density are the same; therefore, the equation of shear strength of unsaturated loess is proposed for practical engineering reference, and by the first derivative analysis of the equation, it is feasible to determine the control proportion of the three parameters on the shear strength of unsaturated loess. A stage-like difference between the three control proportions is observed, depending on the combination variations of water content and clay content.

Shear Strength and Microstructure of Intact Loess Subjected to Freeze‐Thaw Cycling

In the Loess Plateau, seasonal freeze and thaw cause great damage to the mechanical behavior and microstructure of soil, which leads to frequent geological disasters during winter and spring. To investigate the influence of freeze‐thaw (FT) cycling (FTC) on the shear strength and microstructure of intact loess, triaxial shear, nuclear magnetic resonance, and scanning electron microscope tests were carried out on soil samples after target FT cycles. The results indicate that the FTC has limited changes to the soil stress‐strain curve, but has a significant attenuation effect on the peak deviatoric stress. The peak deviatoric stress was attenuated by FTC but changed insignificantly after ten cycles. The cohesive force decays exponentially with the number of FT cycles, while the internal friction angle increases slightly. Moreover, under FTC, the T2 hydrogen spectra of soil samples showed a multimodal distribution, with the main peak appearing to have two obvious upward shifts that occurred at 6 and 10 FT cycles. Indeed, a depolarization phenomenon related to the directional frequency of soil particles was observed, and the mass fractal dimension of the pore network increased slightly. In an FT environment, the shear strength declines due to accumulated internal microstructural damage. These findings contribute to a better understanding of the response of loess to FTC and provide novel ideas for the prevention of frost damage in loess areas.

Study on the collapsibility sensitivity of loess in different acid environment by consolidometer

Cement connection of loess is an important internal factor of loess collapse, which has a direct impact on the sensitivity of the collapse. In this study, different concentrations of nitric acid were added into the immersion water solution of loess collapsibility test. The collapsibility deformation and stability time were measured under different pressure and acid environment. The test results show that: in acid solution, the collapsibility coefficient of collapsible loess increases more under low pressure, and the collapsibility stability time is prolonged under all levels of pressure; Loess has different collapsibility sensitive pressure range in aqueous solution and acidic solution. The structural strength of collapsible loess has an important influence on the depth of collapsible loesr. It is very important to the constructions on the loess area

Hydromechanical behavior and prediction of unsaturated loess over a wide suction range

Subgrade loess in arid and semi-arid regions subjected to high-suction conditions owing to low relative humidity and deep groundwater levels. Understanding the hydromechanical behavior of unsaturated compacted loess over a wide suction range is critical for resolving infrastructure problems in such areas. In this study, the water retention behavior of loess was investigated by imposing or measuring suction (s) using the axis translation technique, vapor equilibrium technique, and chilled mirror dew point technique. Triaxial tests were also performed to study the mechanical behavior of compacted loess under different net cell pressures (σ3n).The soil-water retention curves obtained using the different techniques are consistent. The degree of saturation and water content decreases significantly when s 0.5 MPa, indicating that undrained triaxial tests can be considered as those under constant suction. For the same σ3n, specimens show strain-hardening, shrinkage, and drum-shaped shear failure under low-s conditions and strain-softening, dilatancy, and oblique section splitting under high-s conditions. The failure deviator stress and cohesion of the compacted loess specimens increase with increasing s over the full s range (0–299.37 MPa). An equation to predict the shear strength of unsaturated loess over a wide s range is proposed. The intersection of the capillary water retention curve and adsorption water retention curve is set as a reference point (sR), where capillary degree of saturation is applicable for s ≤ sR and adsorption degree of saturation is added for s > sR. The predicted and measured shear strengths of the compacted loess specimens are in good agreement.

Influence of acid environment on Collapsibility of Loess

Cemented connection of loess is an important internal factor of loess collapsibility, which has a direct impact on its collapsibility. In this study, different concentrations of nitric acid were added to the immersion solution of loess collapsibility test, and the collapsibility sensitivity indexes of loess, such as collapsibility coefficient, stability time and collapsibility rate, were tested under acidic environment and different pressures. At the same time, scanning electron microscope was used to observe the changes of pore and structure of soil samples before and after the test. The test results show that in acid solution, the collapsibility coefficient of collapsible loess increases more under low pressure, and the collapsibility stability time of collapsible loess increases under different pressures. Loess has different collapsibility sensitive pressure range in aqueous solution and acidic solution. The structural strength of collapsible loess has an important influence on the depth of collapsible loess.