Strength Of Loess Research Articles

An investigation on the thixotropic parameters and mechanical properties of loess

The analysis of thixotropic mechanical properties of loess has a significant influence on the calculation of the strength of compacted loess foundation. In order to distinguish the consolidation growth strength of loess from the thixotropic strength, a resting thixotropic instrument is developed. The proposed device is capable of maintaining a constant volume pressure. To attain the goals, after selecting the representative Xi’an loess, the samples were pressed by the resting thixotropic instrument under constant volume pressure. Eight resting ages were also set. Moreover, the thixotropic mechanical properties of loess soil were studied at 6 months resting ages through uniaxial compression without lateral limit and triaxial CU test. The thixotropic triaxial shear strength ratio Jt, thixotropic triaxial shear strength recovery ratio Kt and thixotropic cohesion recovery ratio Lt were defined, the mechanical properties of which were investigated under different stress states. The obtained results demonstrated the obvious thixotropy of Xi’an loess, the strength of which was found to increase with an increase in the resting age. This is while, an increase in the resting age was observed to decrease the its growth rate. Moreover, the unconfined thixotropic strength was found to increase by 1.75 times after resting for 160d, which corroborates the influence of thixotropic strength in designing the foundation bearing capacity of loess. Furthermore, the recovery ratio of unconfined thixotropic strength and the growth ratio of eccentric stress strength were found to be 0.187 and 0.115, respectively. In addition, the thixotropic triaxial shear strength ratio Jt, the recovery ratio of thixotropic triaxial shear strength ratio Kt, and the recovery ratio of thixotropic cohesion ratio Lt were observed to be 0.15, 0.527, and 0.5, respectively. The obtained results suggest the resting age of 40 days to be used as the inflection point for the recovery of thixotropic strength such as uniaxial compressive strength, peak deviator stress, shear strength and cohesion of loess. Despite the insignificant variation range of the friction Angle in the resting process, the contribution ratio of friction force in increasing the shear strength was also found to be much greater than that of the cohesion.

Analysis and Optimization of Tensile Strength for Loess Stabilized by Calcium Carbide Residue

Calcium carbide residue (CCR) can be reutilized to solidify the loess for road construction as a base or subbase due to its rich Ca(OH)2 facilitating pozzolanic reaction with water and soil particles. This study examines the effect of curing time, CCR contents, and dry unit weights on the tensile strength (Rt) of CCR-stabilized loess through the splitting tensile test. Aiming to predict the Rt values, the ratio of porosity (n) controlled by compacted effort and initial volumetric CCR content (Liv), namely n/Liv, was chosen as a prediction parameter and then modified to n/Liv0.064 for compatible variation rate with Rt values. A prediction model for the splitting tensile strength of CCR-treated soil was proposed considering the modified ratio n/Liv0.064 and curing days. The results indicate that Rt values showed a nearly linear positive correlation with CCR contents and dry unit weights, logarithmic increase with the extension of curing time, but no apparent relationship with the ratio n/Liv. The modified ratio n/Liv0.064 can reflect the trend of Rt values at different curing days since the coefficients of determination were almost greater than 0.90 except for the specimens cured for seven days. The proposed prediction model had a good fit for laboratory data with 97% acceptability and close to 3% error. It can be applied for estimating the Rt values of CCR-stabilized loess using curing time and an optimized ratio of porosity and initial volumetric CCR content. From the aspect of practical engineering, the reutilization of CCR can reduce construction costs, waste disposal costs, and environmental pollution.

Mechanical Properties and Microscopic Study of Steel Slag–Fly Ash-Solidified Loess under Alkaline Conditions

To address the geological hazard posed by unstable loess slopes prone to collapse and landslides, a high-strength geopolymer cementing material was developed utilizing green steel slag–fly ash as its primary constituent and activated through the application of sodium silicate alkalinity. The mechanical properties and microstructure changes of loess under varying dosages of steel slag–fly ash geopolymers and curing age were investigated through a series of tests, including unconfined compressive strength, direct shear, disintegration, electron microscope scanning, and X-ray diffraction. The findings indicate that the incorporation of geopolymers can significantly enhance the internal friction angle, cohesion, and unconfined compressive strength of loess, while mitigating the disintegration quantity and rate of stabilized soil. When 20% geopolymer is mixed into the solidified soil and cured for 28 days, the resulting solidified soil exhibits an internal friction angle of 31.12°, a cohesion of 81.09 kPa, and an unconfined compressive strength of 570.86 kPa. These values are 1.62 times, 1.76 times, and 3.36 times higher than those of loess, respectively. Moreover, the solidified soil shows minimal disintegration within 1800 s, with only 1.97% disintegration. The curing age of solidified soil has a significant impact on its curing effect. Enhancing the curing time can considerably enhance the mechanical properties of solidified soil. When the geopolymer content is 20% and the curing time is extended to 28 days, the internal friction angle, cohesion, and unconfined compressive strength increase by approximately 0.23 times, 0.48 times, and 1.61 times, respectively, compared to a curing time of 7 days. By analyzing SEM and XRD, it was found that the hydration of steel slag–fly ash geopolymer produces C-S-H and C-A-S-H cementing materials, which effectively fill the gaps between soil particles and enhance the mechanical properties of solidified soil. The research findings can serve as a theoretical foundation for the consolidation of loess subgrade utilizing steel slag–fly ash geopolymer.

Study on Shear Behavior and Mechanism Based on Shear Functional Unit of Loess Microstructure

The structural specificity and hydrological sensitivity of loess have a strong impact on its long-term stability and safety. This topic is being actively researched and focuses on the macromechanical behavior of the shear strength of loess disturbed and its micromechanisms from the perspective of the dry–wet cycle (especially involving soluble salt erosion). In this paper, the correlation between micro-structural shear functional units and macroscopic degradation behavior was established by combining the changes in physicochemical properties of mass loss, surface cracking, strength deterioration, and structural disturbance of the loess with scanning electron microscopy (SEM) microscopic images in different dry–wet cycles and different salt contents. Results revealed that with the increase in dry–wet cycles and salt content, the mass loss of soil deteriorated and the surface crack rate increased. The cohesion of soil showed an overall decreasing trend, which decreased more obviously in the early stage of the dry–wet cycle, followed by a slow decrease, and tended to be constant after nine dry–wet cycles. However, the internal friction angle increased and then decreased during the whole cycle, and its value generally changed little. According to the deterioration and decay of shear strength, it can be concluded that the structural disturbance of loess increased with the increase in dry–wet cycles and salt content. At the same time, further linear quantization fitting of the structural disturbance parameters showed that the structural parameters had a positive correlation with salt content and a power function with dry–wet cycles, where dry–wet cycles seemed to play a dominant role in the loess structural deterioration rather than salt content. The microscopic study demonstrates that the dry–wet cycles and salt content do not directly affect the cohesion and internal friction angle of soil but change the basic shear structural unit of aggregate and then cause an essential impact on c and φ, which in turn have an essential impact on soil strength attenuation. This paper not only helps to elucidate the essence of water–soil–salt structural interactions but also provides theoretical references for sustainable development research in environmental engineering, geological engineering, and other related fields.

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.

Influence of Dry-Wet Cycles on the Structure and Shear Strength of Loess

The dry-wet cycle is an important factor that causes slope instability and foundation settlement in loess regions. In order to study the effects of the dry-wet cycle on the structure and shear strength of loess, isotropic compression tests and triaxial shear tests were carried out on loess with different numbers of dry-wet cycles. The results show that the dry-wet cycles mainly reduce the cohesion of loess, and the most obvious decline is after the first cycle; however, they have no effect on the angle of internal friction of loess. The structural yield strength and structural parameters of loess can represent the structure of loess well, which gradually decrease with the increase in the number dry-wet cycles and water content. The initial yield surface is approximately an ellipse, which gradually shrinks with the increase in water content and dry-wet cycles. The structure and cohesion of loess have similar changes, and there is an obvious exponential function relationship between them.

Multi-scale analysis of the mechanism of microbially induced calcium carbonate precipitation consolidation loess.

Microbial-induced calcium carbonate precipitation (MICP) treatment of consolidated loess has the advantages of high efficiency and environmental protection. In this study, changes in the microscopic pore structure of loess before and after MICP treatment were compared and quantified, combined with test results at different scales, to better understand the mechanisms of MICP-consolidated loess. The unconfined compressive strength (UCS) of MICP-consolidated loess is significantly increased, and the stress-strain curve indicates improved strength and stability of the loess. X-ray diffraction (XRD) test results show that the signal strength of calcium carbonate crystals is significantly enhanced after loess consolidation. The microstructure of the loess was determined by scanning electron microscopy (SEM). The loess SEM microstructure images are quantitatively analyzed using comprehensive image processing methods (including gamma adjustment, grayscale threshold selection, median processing). The changes in microscopic pore area and average pore sizes (Feret diameter) of the loess before and after consolidation are described. More than 95% of the pores consist of pores with a pore area of less than 100 μm2 and an average pore size of less than 20μm. The total percentage of pore numbers with pore areas of 100-200 and 200-1000 μm2 decreased by 1.15% after MICP consolidation, while those with 0-1 and 1-100 μm2 increased. The percentage of pore numbers with an average pore size greater than 20μm decreased by 0.93%, while the 0-1, 1-10, and 10-20μm increased. Particle size distributions revealed a significant increase in particle size after MICP consolidation, with an increase of 89μm in D50.

Improving hydro-mechanical behavior of loess by a bio-strategy

Loess is widely distributed all over the world, covering about 10% of the land surface on earth. China is one of the countries with the most serious loess soil erosion in the world, especially the loess plateau. This is mainly related to the poor water stability and mechanical properties of the loess. A new coupling method of bio-cementation (Microbially Induced Calcite Precipitation: MICP) and sand additive to improve the hydro-mechanical behavior of loess was proposed. The feasibility, coupling improvement mechanism and the effects of sand content, bio-cement treatment cycle and cementation solution (CS) concentration were investigated through a series of tests. The results indicated that the proposed method was effective to improve the water stability and structure strength of loess. The coupling improvement performance were positively related to the sand content. When the sand content was 40%, compared to bio-cement treatment, the coupling treatment was 9 times deeper in treatment depth, 3.5 times stronger in peak structure strength, and the sum slaking rate was less than half. The coupling improvement mechanism can be attributed to the form of the double layers including hard crust and cemented layer. With the addition of sand, the thickness, structure strength and water stability of the double layers increased. The main reason is that there were more interfacial voids between sand particles and loess particles, increasing the permeability of loess and treatment depth, forming more amount of calcium carbonates. Based on the experimental condition in this study, 1.0 M of CS concentration was the optimal spaying strategy to improve the hydro-mechanical properties of loess.

Impact of Evaluation of Freeze–Thaw Cycles on Collapse Zone at Entrance and Exit of Loess Tunnel

The entrance and exit of loess tunnel are easily affected by freezing and thawing, which leads to collapse in cold regions. Based on the slip line network method, this paper proposed a graphical method and analyzed the impact of evaluation of freeze–thaw cycles on the collapse zone at the entrance and exit of a loess tunnel. Firstly, the slip line network method was improved for a graphical calculation program, and the program was validated by monitoring the data of collapse evolution in an unlined loess tunnel in situ. Then, some triaxial tests of freeze–thaw cycles were carried out on loess, and the attenuation law of loess strength was summarized after freeze–thaw cycles in cold regions. Finally, the graphical calculation program was applied to evaluate the impact of freeze–thaw cycles on collapse range in the unlined loess tunnel. The results show that introducing the classic slip line field into the analysis process of a tunnel collapse zone can provide a feasible and efficient analysis method for a tunnel surrounding rock collapse arch for tunnel engineering, and the collapse zone increases with the growing number of freeze–thaw cycles. Moreover, the attenuation of loess strength which suffered from the freeze–thaw cycles would cause the collapse zone area to increase by a maximum of 16.13%.

Macroscopic mechanical behavior and microstructural evolution of compacted loess in the Chinese Loess Plateau

Understanding the mechanical behavior of compacted loess is of great significance to engineering construction on the Loess Plateau. To gain an in-depth knowledge of the variations in compressibility, shear strength and microstructure of compacted loess at different dry densities and water contents, a series of macro and microscopic tests were carried out on the loess samples, including oedometer compression tests, direct shear tests and scanning electron microscope imaging. The pore properties of loess in microscopic images were investigated using the particle (pores) and cracks analysis system. The relationship between pore microscopic indicators and mechanical parameters was explored by multivariate statistical analysis. The results show that the compression coefficient of compacted loess decreases with increasing dry density, of which trend is more significant at high water content. Both cohesion and internal friction angle decrease with increasing water content, but the former is more sensitive to changes in soil moisture. Besides, the evolution sequence of compacted loess structure is basically overhead-mosaic-flocculation with the increase of compactness and saturation. The difference is that with the compaction, the pores in the loess sample change from macropores into mesopores and then to small pores, and the directional distribution and morphological complexity of the pores weakens; while with the humidification of the loess sample, small pores and macropores transform into mesopores, and the pores are more oriented and more complex in shape. During this process, the micropore content changes are weak. Moreover, mesopores content and pore fractal dimension have a positive effect on compressibility, while micropores content and orientation probability entropy have a positive effect on shear strength.

A new method for determining loess particle size distribution based on ‘core + clothes’ structure

AbstractThe particle size distribution (PSD) of loess particles and agglomerates is the key factor determining the microstructure of loess. The PSD largely determines many physical and mechanical properties such as mechanical strength, deformation characteristics and permeability of loess. In this paper, we combined image processing, geometric measurements and statistical methods to quantitatively characterize the scanning electron microscopy (SEM) images of loess. A new method based on the ‘core + clothes’ structure is proposed to determine the PSD. The developed Gaussian mixture model is applicable to describe the overall distribution of the image pixel density. Determining pixel density distribution and particle boundary allows for the measurement of various geometric parameters. The comparison analyses suggest that the sieve‐hydrometer method has a well‐developed test procedure; however, the measured particle size is limited to 0.075 mm. The laser diffraction method is simple and fast, yet only weak agglomerates can be dispersed, and very fine particles are influenced by size data conversion theory and light source parameters. X‐ray microtomography has the advantage of a non‐destructive sample preparation and intuitive process. However, the results are greatly affected by the parameter settings and segmentation algorithm, and the segmentation effect is poor for particles with a size smaller than 12 μm. The new image processing technique developed in this study improves the limitation of the measurement results via changes in the loess state (water content, stress level). Moreover, different PSDs can be determined according to the variation of functional units. This work is of great significance for the study of numerous properties related to the loess state.

Improvement of strength and impermeability of fiber-reinforced loess by bentonite and polypropylene fibers: a response surface analysis

Improvement of strength and impermeability of fiber-reinforced loess by bentonite and polypropylene fibers: a response surface analysis

Preparation and water erosion resistance properties of tara gum-g-poly (acrylic acid-co-methyl methacrylate) emulsion

The main purpose of this paper is to synthesize a new kind of green and environmental protection emulsion, which can be used as water erosion resistant materials. Here, a non-toxic polymer was prepared by grafting acrylic acid (AA) and methyl methacrylate (MMA) onto the long chains of tara gum (TG) to synthesize a copolymer emulsion (TG-g-P (AA-co-MMA)). The structure, thermal stability, morphology and wettability of the polymer were characterized by conventional methods, and the effects of key synthesis conditions on the performance of the emulsion (viscosity) were optimized. The erosion resistance and compressive strength of polymer-treated loess and laterite soils were evaluated under laboratory conditions. The results showed that the successful grafting of AA and MMA monomers onto TG improved its thermal stability and viscosity. In soil performance tests with low amounts of polymer additive, a 0.3 wt% application of TG-g-P (AA-co-MMA) to loess could resist continuous precipitation for >30 h with an erosion rate of 2.0 %. The compressive strength of the laterite treated with 0.4 % TG-g-P (AA-co-MMA) was 3.7 MPa, which was about three times that of the untreated soil. The results from this study suggest that TG-g-P (AA-co-MMA) emulsions have good potential for soil remediation applications.

Effect of fracture distribution on the triaxial shear behavior of loess

Fractures are widespread phenomena on loess slopes in northwestern China. Fractures are of various types and have different distribution patterns, and they are important factors affecting the mechanical properties of loess. In this paper, the effect of different fracture distribution modes (fracture angle, fracture position and fracture combination) on the shear strength of loess is investigated by carrying out consolidated undrained triaxial shear tests. The results show that the existence of fractures in loess can significantly weaken the strength of the soil under consolidated undrained conditions. Compared with unfractured loess, fractures weaken the shear strength of loess mainly by weakening the cohesion. The internal friction angles of fractured loess, however, are hardly affected by the existence of fractures and the fracture distribution mode. Furthermore, a comparison of three fracture distribution modes, namely, the fracture angle, position and combination, reveals that the fracture angle is the most significant factor weakening the loess strength, followed by fracture combination, and the least is fracture position. In addition, confining pressure increments can greatly improve the shear strength of both unfractured and fractured loess, and confining pressure increments can inhibit the weakening effect of fractures on loess strength.

Effect of Polypropylene Fiber on the Unconfined Compressive Strength of Loess with Different Water Content

Fiber-reinforced soils have been of great interest to experimenters for building foundations’strength performance, time, and economy. This paper investigates the effects of water content and polypropylene fiber dosage and length on loess’s unconfined compressive strength (UCS) according to the central composite response surface design test procedure. The water content is 11%–25%, the mass ratio of fiber to soil is 0.1%–0.9%, and the fiber length ranges from 6–18 mm. The response surface method (RSM) developed full quadratic models of different variables with response values. After analysis of variance (ANOVA), the mathematical model developed in this study was statistically significant (p ≤ 0.05) and applicable to the optimization process. The optimization results showed that the optimal water content values, fiber amount, and fiber length were 16.41%, 0.579%, and 14.90 mm, respectively. The unconfined compressive strength of the optimized specimens was increased by 288.017 kPa. The research results can reference the design and construction of fiber-reinforced soil in practical projects such as road base engineering and foundation engineering.

Experimental study of the effect of bound water on the shear strength and structural units of Malan loess

The structural specificity and hydrological sensitivity of loess have a big impact on its strength, deformation and long-term stability and safety. This topic is being actively researched, and focuses on the macromechanical behaviour of the shear strength of loess and its micromechanisms from the perspective of bound water. In this study, based on the combined determination of isothermal adsorption and the liquid–plastic limit, bound water is analysed qualitatively and quantitatively, and the entire humidity sequence is divided in a new method. The shear strength of Malan loess measured by the direct shear test is also analysed to investigate the relationship between bound water, shear strength and basic structural units. The results show that the adsorption patterns for the Malan loess in the three regions studied are approximately the same but, at the same humidity, their maximum moisture content ( W мг ) was, from highest to lowest, 7.13% in Chan he, 6.54% in Yan'an and 5.54% in Hei fang tai, which is related to clay minerals and their contents in the soil. In addition, the change in strength of the loess is divided into three stages using the maximum moisture content ( W мг ) and plastic limit ( W P ) as the characteristic moisture content. The patterns of strength change for the loess in the three regions is similar throughout the moisture content sequence: all stages show a negative correlation between moisture content and shear strength but the internal mechanism of each stage is not the same due to the different connection forces between the basic structural units of the loess. The change in bound water content caused by the cementation of glue and clay particles also yields certain changes in cohesion, which is linearly fitted to the shear strength and its parameters. Finally, the bound water in the soil changes the microstructure of the soil, and determines the combination characteristics and contact mode of the ‘core clothes’ in the microagglomerate structure of the loess. This study describes the essence of soil–water structural interactions and provides theoretical references for applications in geotechnical engineering fields such as slope protection and road construction.

Mechanical properties of loess subgrade treated by superabsorbent polymer

Moisture variation is one of the crucial factors affecting the strength and deformation of loess. In this study, superabsorbent polymer (SAP) was introduced as moisture regulator to enhance the ability of accommodating moisture variations of loess and then to improve the stability of loess subgrade. Water migration test was first performed to evaluate the variation law of the effect of SAP on the moisture content of loess in a closed system. Then mechanical tests were carried out to investigate the influence of SAP on the mechanical properties of loess. Besides, microscopic tests were conducted to find out chemical and physical behavior of SAP on the loess. Test results demonstrated that SAP can significantly reduce the water content of loess by 8.26–26.42 %. The unconfined compressive strength (UCS) of loess increased by 37 % after 14 days curing with an optimum SAP content of 1 %, reaching 100 kPa. The dynamic resilient modulus (MR) gradually decreased as a result of SAP addition. The dissipated energy and damping ratio of loess reached the maximum values (100 mJ and 5 %, respectively) at 1.0 % SAP content, which were 10 times and 5 times higher than that of pure loess, respectively. The treatment of loess by SAP was mainly caused by the coupling of physical and chemical water absorption of SAP in the water environment. The incorporation of SAP had no effect on chemical functional groups and mineral composition of loess, but caused water redistribution, thereby changing the mechanical properties.

Shear strength and meso-pore characteristic of saturated compacted loess

Abstract With the increasing demand for filling engineering construction in the Loess Plateau, the engineering problems related to saturated loess caused by rainfall and irrigation are also increasingly prominent. This work studied the shear characteristics of saturated compacted loess by experiments, and qualitatively and quantitatively explained the meso-mechanism of the effect of compaction degree on the shear characteristics combined with the meso-pore characteristic parameters. The study shows that the stress–strain curve of saturated loess under 80 and 85% compaction degree is strain softening, it is strain weak softening under 90% compaction degree, and strain hardening under 95% compaction degree. The failure strength and pore water pressure have a good fitting linear relationship with compaction degree, and the fitting correlation coefficients are more than 0.97. Under 95% compaction degree, the pore water pressure increases with the development of axial strain, then decreases after the peak, and may appear negative. With the increase in compaction degree, the micro and small pore content of the saturated loess soil increases, the medium, large and super large pore content decreases, the proportion of pore area decreases, the pore shape becomes uniform and smooth, the complexity of pore shape decreases, the pore arrangement tends to be regular and neat, and the directionality increases. The research results can provide references for engineering design, construction, and numerical calculation of filling engineering in loess area.

Experimental study on strength characteristics and internal mineral changes of Lime-stabilized loess under High-Temperature

• Effect of lime treatment on compression and shear strength of loess were studied. • Tests were carried out at a wide temperature range (30 ∼ 300 °C) and 5 lime contents. • Treatment with lime improved the strength of loess at high-temperatures. • Multiple methods XRD, TGA, DSC reveal the mechanisms of the lime-loess reactions. In this study, lime-stabilized loess with five lime contents (0 %, 3.5 %, 7 %, 10.5 %, and 14 %) treated at four temperature levels (30 °C, 100 °C, 200 °C, and 300 °C) were tested for 48 h in a series of laboratory experiments to investigate the mechanical strength characteristics and internal mineral changes of lime-stabilized loess under high temperature. The unconfined compressive strength (UCS) tests and shear box test results show that the compressive and shear strengths of lime-stabilized loess are larger than those of plain loess, not only at room temperature but also at high temperatures. Under the same lime content, the mechanical strength of each sample was greatly improved after high-temperature treatment. As the heat-treatment temperature increased within the test temperature range, the compressive and shear strengths gradually improved. These mechanical strength test results prove that adopting lime-stabilized loess as the building material for structures vulnerable to high temperatures is feasible. When compressive and shear strengths were selected as the evaluation criteria for determining the lime content, the optimal lime content in this study was 7 %. X-ray diffraction and thermal analysis test results revealed that the strength enhancement of lime-stabilized loess is mainly derived from the lime slaking reaction, pozzolanic reaction, and crystallization reaction. High-temperature treatments can promote the reaction rates of these processes.

Pull-out characteristics of herbaceous roots of alfalfa on the loess in different growth stages and their impacts on slope stability

Plant roots can provide additional cohesion to enhance soil strength, effectively prevent soil erosion, and improve slope stability. In this study, loess samples with herbaceous roots of alfalfa were obtained through artificial planting in order to measure and compare the shear strength and root pull-out force of loess with alfalfa roots in different growth periods, to analyze the enhancement effect of alfalfa roots in different growth periods on the strength of loess, to improve Wu and Waldron's model (WWM) based on the pull-out characteristics of alfalfa roots in different growth periods, to determine that the correction coefficient of WWM model is a time-related function, and to analyze the influences of alfalfa in different growth periods on loess slope stability under rainfall conditions using the infinite slope model. The results show that the cohesion of loess containing alfalfa roots is larger than that of plain loess, and the cohesion of loess containing alfalfa roots initially increases and then decreases as the alfalfa growth period progresses. The growth period of alfalfa has a significant effect on its root pull-out strength. As the alfalfa growth period progresses, the cohesion of the root-soil complex increases based on the improved WWM model, and it is significantly higher than the value obtained from direct shear tests. In the initial stage of alfalfa growth, the correction coefficient increases continuously, reaches its peak in one year, and then decreases. In addition, the stability coefficient of a loess slope within the alfalfa root distribution depth is always greater than that outside of the alfalfa root distribution depth, and the stability coefficient of a loess slope within alfalfa root distribution depth increases as the growth period progresses. The results of this study provide a reference for slope stability and soil and water conservation in loess areas.