Search Results (30)

Freeze–thaw cycles cause mechanical deterioration and instability of slope rock masses in open-pit coal mines located in the cold regions of Northwest China. In this study, the research object is fine-grained sandstone from the Yan’an Formation in the Tarangole mining area of the Ordos Basin. Here, indoor freeze–thaw cycling, uniaxial compression, and triaxial compression tests were conducted to systematically analyze the deformation behavior, strength evolution, and failure modes of the sandstone under varying numbers of freeze–thaw cycles, freezing temperatures, and confining pressures, thereby revealing its freeze–thaw damage mechanism. The results show that the number of freeze–thaw cycles is the dominant factor affecting the elastic modulus. Freezing temperatures (especially between −5 °C and −15 °C) and the number of freeze–thaw cycles (particularly the first 10 cycles) significantly reduce peak strength. In addition, confining pressure can significantly enhance the resistance to deformation (under 15 freeze–thaw cycles, the elastic modulus increases by 181.8% as confining pressure rises from 0 to 2 MPa). Within the low confining pressure range (0–1.5 MPa), peak strain decreases monotonically with increasing confining pressure and is independent of the number of freeze–thaw cycles. Finally, the increase in the number of freeze–thaw cycles and the decrease in temperature jointly promote crack development, and the failure mode shifts from pure shear to a shear-tension composite mode. The underlying cause lies in the evolution of interparticle cementation within the soil skeleton and in the associated pore–crack structure. In addition, based on fracture damage mechanics and the modified Weibull distribution, a damage evolution equation and a constitutive model for sandstone considering freeze–thaw cycles and temperature effects were established and validated. Therefore, the research findings can provide a theoretical basis for slope support, freeze–thaw disaster prevention and mitigation, and stability assessment in the Tarangole mining area and other cold regions. Full article

In the design of shaking table tests concerning saturated sand–pile interactions, quantitatively achieving similarity in liquefaction responses between the model and the prototype has long been a challenging task. In addition, the dynamic shear modulus of the prepared model soil often fails to satisfy the ideal similarity conditions, which further exacerbates the difficulty of realizing liquefaction response similarity. To address the above issues, the authors have proposed a liquefaction similarity law for saturated sand–pile shaking table tests under horizontal excitation, considering the dynamic shear modulus error of the model soil. To further verify the accuracy of the proposed liquefaction similarity law, investigate its simulation capability, and evaluate its applicability under different conditions, this paper establishes and validates numerical models of saturated sand–pile dynamic interaction systems based on shaking table test results and conducts a series of parametric analyses via numerical simulation. The results indicate that when the proposed similarity law is applied, the acceleration similarity ratio should be set to 1, which can satisfy both gravity similarity and elastic force similarity simultaneously. A comparison with the artificial mass similarity law demonstrates the distinct advantages of the proposed similarity law. Finally, the applicability of the proposed similarity law under different parametric conditions is verified, and the influence of various parameters on the accuracy of the back-calculated results using the similarity law is investigated. Full article

With the rapid development of infrastructure and the need to protect natural ecosystems, manufactured sand is used to replace river sand in concretes. To compare the deterioration patterns of concretes made with different sands, C50 specimens using basalt (C50X), tuff (C50N), and granite (C50H) manufactured sands and river sand (C50T) were prepared, then tested outdoors by full burial in a sulfate saline soil and indoors by accelerated freeze–thaw in a sulfate solution. The outdoor experiments indicate that C50X deteriorated the slowest, whereas the resistance to mass loss ranking was: C50X > C50H > C50N > C50T. In the indoor freeze–thaw experiments, C50X also performed best, retaining 51% relative dynamic modulus of elasticity (RDME) after 450 cycles. X-ray diffraction and scanning electron microscopy showed that C50T was weakened by abundant MgSO₄·7H₂O crystals, while C50X formed a denser matrix that limits salt-crystallization expansion. Moreover, a GM(1,1)-Markov model was developed to forecast long-term durability. For C50X, the model predicted an estimated service life of 68 months in the outdoor environment, at which point it is projected to reach the 5% mass loss failure threshold. Separately, it forecasted that the RDME would remain above 41% after 450 indoor freeze–thaw cycles. Full article

According to existing ecological problems, one of the promising developments is the creation of polyfunctional materials, which can be biodegradable, along with possessing antibacterial activity. The present research proposes biocomposites based on PLA with silver nanoparticles (AgNPs) and natural polysaccharides obtained in a twin-screw extruder. Introduction of polysaccharides to PLA-based biocomposites with/without AgNPs led to significant decrease in the elastic modulus and tensile strength, while the elongation at break remained almost unchanged. Thanks to the presence of natural polysaccharides, there was intensified biodegradation in soil despite the AgNP availability. The maximal mass loss was 29% for the PLA–PEG₁₀₀₀–starch + AgNPs (80:10:10 + 0.5 wt%) biocomposite. Analyses of the systems before and after soil exposure were carried out using DSC and FTIR spectroscopy methods. According to a thermal analysis, it was found that PLA crystalline regions degrade during exposure to soil. The same feature was detected during the spectral analysis. The intensity of the characteristic absorption bands of PLA decreased. Furthermore, it was found that the dark areas on the surface of the materials are of a polysaccharide nature and may be signs of biofouling of the materials by microbial flora. The tests on fungus resistance showed that biocidal additives such as AgNPs in PLA-based biocomposites with polysaccharides did not inhibit the development of mycelial fungi–biodestructors. And the increased amount of chitosan in the films contributed to their more active destruction by the end of the observation period. It was demonstrated that such biocomposites can inhibit bacterial growth. Full article

Given the limitation of existing slope collapse monitoring technology, which relies on surface sensors, and the difficulty in capturing the precursors of deep rock and soil instability, this study used rock anchor embedded sensing technology to conduct collapse tests on artificial simulated slopes. Two groups of control conditions were designed: (1) shotcrete reinforced slope and natural slope; and (2) GFRP anchor and spiral steel anchor support system. The deformation characteristics of the slope at the initial stage of collapse were analyzed. The results show that the monitoring method based on the stress–strain response of deep rock mass significantly improved the early warning effect. GFRP anchor had a lower elastic modulus and responded more sensitively to small displacements than spiral steel anchor. Shotcrete reinforcement transformed slope deformation from ‘local dispersed deformation’ to ‘overall coordinated deformation’ and delayed slope instability via the ‘deformation hysteresis effect’. This study provides key technical parameters for the intelligent monitoring system of high-risk slopes as well as support for pre-disaster emergency evacuation decision-making and the establishment of intelligent early warning systems. Full article

With global sustainable construction growth, fully recycled coarse aggregate concrete (RCAC)—eco-friendly for cutting construction waste and reducing natural aggregate over-exploitation—has poor durability in seasonally freezing saline-soil regions (e.g., Tumushuke, Xinjiang): freeze-thaw and salt ions (NaCl, Na₂SO₄) cause microcracking, faster performance decline, and shorter service life, limiting its use and requiring better salt freeze resistance. To address this, a field survey of Tumushuke’s saline soil was first conducted to determine local salt type and concentration, based on which a matching 12% NaCl + 4% Na₂SO₄ mixed salt solution was prepared. RCAC specimens modified with fly ash (FA), silica fume (SF), and polypropylene fiber (PPF) were then fabricated, cured under standard conditions (20 ± 2 °C, ≥95% relative humidity), and subjected to rapid freeze-thaw cycling in the salt solution. Multiple macro-performance and microstructural indicators (appearance, mass loss, relative dynamic elastic modulus (RDEM), porosity, microcracks, and corrosion products) were measured post-cycling. Results showed the mixed salt solution significantly exacerbated RCAC’s freeze-thaw damage, with degradation severity linked to cycle count and admixture dosage. The RCAC modified with 20% FA and 0.9% PPF exhibited optimal salt freeze resistance: after 125 cycles, its RDEM retention reached 75.98% (6.60% higher than the control), mass loss was only 0.28% (67.80% lower than the control), and its durability threshold (RDEM > 60%) extended to 200 cycles. Mechanistic analysis revealed two synergistic effects for improved performance: (1) FA optimized pore structure by filling capillaries, reducing space for pore water freezing and salt penetration; (2) PPF enhanced crack resistance by bridging microcracks, suppressing crack initiation/propagation from freeze-thaw expansion and salt crystallization. A “pore optimization–ion blocking–fiber crack resistance” triple synergistic protection model was proposed, which clarifies admixture-modified RCAC’s salt freeze damage mechanism and provides theoretical/technical guidance for its application in extreme seasonally freezing saline-soil environments. Full article

In order to improve the durability of loess-based composite coal gangue porous planting concrete (LCPC), the effects of fly ash and slag powder content on the durability and microstructure of LCPC were studied. In this paper, fly ash and slag powder were mixed into LCPC, and freeze-thaw cycle and dry-wet cycle tests were carried out. The compressive strength, dynamic elastic modulus, and mass change were used as evaluation indices to determine the optimal mix ratio for LCPC durability. Scanning electron microscopy (SEM) was performed, and the experimental design was carried out with the water–cement ratio, fly ash, and slag powder content as variables. The microstructure characteristics of LCPC were analyzed. The results show that the maximum number of freeze-thaw cycles can reach 35 times and the maximum number of dry-wet cycles can reach 50 when 5% fly ash and 20% slag powder are used. With an increase in the water-cement ratio, the skeleton of the loess gradually became complete, and its structure became more compact. In the micro-morphology diagram, the mixed fly ash and slag powder particles are not obvious, but with an increase in dosage, the size of the cracks and pores gradually decreases. The incorporation of fly ash and slag powder can play a positive role in the durability of LCPC and improvement of its microstructure. The results of this study are crucial for improving the application performance of ecological restoration, soil improvement, and long-term stability of structures, and can provide a scientific basis for the sustainable development of environmentally friendly building materials. Full article

Straw reinforcement improves the mechanical properties of soil matrices by uniformly incorporating dispersed straw materials, demonstrating advantages in strength enhancement, toughness improvement, and deformation control. This study aims to compare the reinforcement effects of different types of straw on soil and clarify the optimal method for straw-based soil stabilization. For wheat straw-reinforced soil using different processing methods (straw segment, straw powder, and straw ash) and mass contents, the basic geotechnical properties of each mixture were first determined. Triaxial tests were then performed under varying confining pressures and compaction conditions to assess the strength and modulus characteristics of the different reinforced soil specimens, and the microstructural characteristics of fiber-reinforced soil were investigated using scanning electron microscopy (SEM) analysis. The experimental results indicated that the strength and ductility of soils increased significantly with the addition of straw. The optimal performance of straw-reinforced soils occurred at 0.3% content. The elastic modulus increased by 85%, 64%, and 57% under confining pressures of 50 kPa, 100 kPa, and 200 kPa, respectively. At 200 kPa, straw segments provided the highest modulus increase of 57%, while straw ash achieved the greatest strength improvement of 97%. Furthermore, considering both compaction effects and cost efficiency, a compaction degree of 95% is recommended for straw-reinforced soil in engineering applications. Based on scanning electron microscopy, it was observed that the distribution characteristics of different straw types within the soil exhibit distinct patterns. This study aims to provide data to support the efficient utilization of straw materials in engineering applications. Full article

Coffea canephora genotypes adopt distinct strategies to cope with drought and rehydration. We hypothesized that the greater drought tolerance of genotype ‘3V’ compared to ‘A1’, previously reflected in physiological and anatomical leaf traits after two water-stress (WS) cycles, could also be observed in P–V curve responses, root and branch anatomy, leaf midrib elongation (CVL), and root distribution. The ‘3V’ and ‘A1’ plants were grown under well-watered (WW) conditions and two cycles of water stress (WS). The ‘3V’ was more sensitive to WS, with reduced branch xylem vessel density (BXVD), while ‘A1’ demonstrated increased BXVD. Root xylem vessel area (RXVA) decreased to a greater extent in ‘3V’ than in ‘A1’, and both genotypes showed increased bulk elastic modulus. Regardless of water conditions, ‘A1’ maintained a higher relative leaf water content at the turgor loss point (RWC_TLP). Morphological acclimation did not occur in the second WS cycle. The ‘3V’ plants developed greater root mass in deeper soil layers than ‘A1’ under the WS condition. These findings suggest that ‘A1’ follows a conservative drought-avoidance strategy with lower physio-morphological plasticity, while ‘3V’ exhibits greater drought tolerance. Such responses highlighted coordinated physiological, morphological, and anatomical adaptations of the above- and below-ground organs for resource acquisition and conservation under WS. Full article

Targeting the concern that nearby inflexible buildings may be at risk for safety issues due to the surface deformation caused by foundation pit excavation disruptions, this paper took the large-scale foundation pit in the Hongshaquan second mine stope in Xinjiang as the research backdrop. To examine the deformation mechanism, generic numerical simulation models were built with varying excavation depths. The unloading effect of foundation pit excavation was addressed using the Fourier integral approach, which is based on elastic theory. An elastic theoretical analytical approach for the surrounding deformation during disturbances due to the excavation of foundation pits was derived by superimposing the unloading impact of the surrounding soil and including pertinent boundary conditions. By contrasting the outcomes of the numerical simulation with the theoretical analysis and the real on-site monitoring data, the accuracy of this approach was confirmed. The findings indicated that the deformation of the surrounding ground surface rises as the excavation depth grows during the foundation pit excavation process in open-pit mines. The deformation decreases with increasing distance from the slope crest to the monitoring location. The deformation of the surrounding ground surface reduces as the rock and soil mass’s elastic modulus and Poisson’s ratio rise. However, the deformation of the surrounding ground surface increases as the excavation depth and slope angle rise. This study offers fresh ideas and approaches for examining how the surrounding ground surface deforms while a foundation hole is excavated. Full article

Sandy soils are a type of geomaterial that may require improvements due to lack of cohesion. In this study, first, the lack of cohesion of sand was resolved using clay, and the soil was stabilized with cement and lime (4% and 3% of the dry weight of materials, respectively) and finally reinforced with recycled tire fibers of 20 to 30 mm in length for improved strength and ductility. Next, 747 samples with different fiber contents at different curing temperatures and ages were prepared and a unconfined compressive strength (UCS) test was carried out. Next, a novel approach employing multivariate nonlinear regression techniques and obtained empirical data was applied to formulate a mathematical model for predicting the UCS and the modulus of elasticity (E_s) of the reinforced and stabilized soil. This model can serve as a valuable tool for building engineers in designing building foundations. The comparison of the obtained UCS and E_s results and those predicted using the proposed model showed a correlation of >95% (R² ≥ 0.95). The fibers effectively increased the failure strain, thus resulting in the greater ductility of the samples. As an example, in 14-day samples cured at 60 °C with 0%, 0.4%, 1%, 1.7%, and 2.5% fibers, the failure strain showed an incremental trend of 1.47%, 1.87%, 2.08%, 2.20%, and 2.92%, respectively. Scanning electron microscopy (SEM) was used to study the microstructure of the samples and to explain the strength experimental outcomes. SEM images showed a desirable interaction between the fiber surfaces with the soil mass and the reduction in porosity and the occurrence of pozzolanic reactions through stabilization. The results also showed that the reinforcement effectively improved the ductility, as desired for building foundations; however, it resulted in reduced strength, although a greater strength compared to the untreated soil was achieved. Although soil stabilization has been widely studied, limited research focuses on stabilizing soil with clay, lime, cement, and recycled tire fibers. This study offers design engineers an estimation scheme of the strength properties of stabilized and reinforced foundations. Full article

The investigation of wave propagation in the geological environment is warranted, and will ultimately help to provide a better understanding of the response of subsoil to excitation. Frequently utilized physical modeling represents a simplification of the global natural system for the needs of the investigation of static and dynamic phenomena with regard to the time domain. The determination of appropriate model materials is probably the most important task for physical model creation. Considering that subsoil represents a crucial medium for wave propagation, an evaluation of suitable model materials was carried out. A plate load test with a circular plate is a non-destructive method for determining the static bearing capacities of soils and aggregates, which are usually expressed by the deformation modulus E_def,2 (MPa) and the static modulus of elasticity E (MPa). A lightweight deflectometer test was used to characterize the impact modulus of deformation E_vd (MPa), which is determined based on the pressure under the load plate due to the impact load. A representative propagation of the load–settlement curve for the PLT and the acceleration–time curve for the hammer drop test were investigated. The calculated E values were found to be in the interval between 2.6 and 5.7 kPa, and depending on the load cycle, the values of E ranged from 2.6 to 3.1 kPa. The modulus E from the hammer drop test was significantly larger than the interval between 10.6 and 40.4 kPa. The values of the dynamic multiplier, as a ratio of the hammer drop value to the PLT value, of the modulus E ranged from 4.1 to 13.0. The output of the plate load testing was utilized for the calibration of the finite element method (FEM) numerical model. Both the physical and numerical models showed practically ideal linear behavior of the mass. However, the testing of gelatin-like materials is a complex process because of their viscoelastic nonlinear behavior. Full article

Despite numerous studies of single piles and practical experience with their application, methods for calculating settlements of pile foundations remain limited. The existing objective need for specialized methods of pile foundation settlement calculation that take into account the rheological properties of the base soils is becoming more and more important, especially in the construction of unique objects in complex ground conditions. When predicting the stress–strain state of the pile–raft-surrounding soil mass system, it is allowed to consider not the entire pile foundation as a whole, but only a part of it—the computational cell. In the present work, we have solved the problems of determining the strains of the computational cell consisting of the pile, the raft and the surrounding soil according to the column pile scheme and hanging pile scheme, on the basis of the Kelvin–Voigt rheological model, which is a model of a viscoelastic body consisting of parallel connected elements: Hooke’s elastic spring and Newtonian fluid. According to our results, we obtained graphs of the dependence of strains of the computational cell on time at different pile spacing and different values of coefficients of viscosity of the surrounding soil, and a formula for calculating the reduced modulus of deformation of the pile. The results of the present study can significantly improve the accuracy of calculations during construction on clayey soils with pronounced rheological properties and, as a result, increase the reliability of pile structures in general. Full article

The growing number of end-of-life (EoL) photovoltaic (PV) panels as waste materials is forcing many countries to face the challenge of addressing this issue. The presented research explores the utilization of a by-product of this waste material, namely glass powder, with gypsum in geotechnical engineering to improve clay-soil properties. The approach is to integrate these materials to address the sustainable management of EoL PV panels, an underutilized resource in geotechnical applications. Furthermore, the study extensively examines the physical properties of clay soil, gypsum, and glass powder. Composite samples are created by adjusting the proportions of gypsum (0%, 5%, 10%, and 15%) and glass powder (0%, 4%, 8%, and 12%) relative to the soil’s dry mass. Compaction processes are performed at dry densities of 1500 and 1700 kg/m³, with 7, 28, and 56 days of curing duration. Various tests, including ultrasonic pulse velocity (UPV), unconfined compressive strength (UCS), assessments of wet and dry cycle durability, scanning electron microscope (SEM) analyses, and X-ray diffraction (XRD) analyses, are conducted. The results reveal that gypsum consistently improves the soil’s strength and stiffness features, while initially adding glass powder reduces these properties before showing improvement at a 12% content. Correlations have been proposed to determine the unconfined compressive strength (q_u), initial shear modulus (G₀), and modulus of elasticity (E) to be acquired utilizing just a single test. Moreover, a correlation has been developed to predict the unconfined compressive strength and elastic modulus of any specimen through non-destructive testing. Additionally, microstructural analyses unveil intricate interactions, showcasing the progress of pozzolanic reactions, identifying silicon-rich compounds from glass powder, and elucidating how additives transform soil structure. Full article

Unpaved roads are essential as transportation infrastructure. These roads are traditionally built utilizing local soils and aggregates. The application of different materials to improve the strength and the overall performance of these road solutions has been investigated. This study focuses on the assessment of the suitability of reinforcing a fine soil using natural fibres from the forest value chain—specifically, pine needles—for unpaved forest roads. The resilient response of both unreinforced and reinforced soils was assessed with RL-CBR tests (California Bearing tests with repeated load) for different percentages of natural fibres incorporated into the soil. The force–penetration response, CBR value, recoverable and permanent displacements, and equivalent modulus were estimated. The effect of different load stages on the elastic response of both unreinforced and reinforced soils was also evaluated. The CBR values improved with the addition of pine needles; the best response was observed for specimens reinforced with 1% (mass) of these natural fibres (the CBR value increased by 45%). The equivalent modulus also was improved, showing that the stiffness of the soil increased with the inclusion of reinforcement. The findings imply that RL-CBR studies offer a promising method for obtaining important design parameters, especially for unpaved forest roads where investments in soil characterization are frequently limited. Full article