Bulletin of Engineering Geology and the Environment最新文献

This study uses discrete element method models to simulate the fragmentation and deposition of landslides with varying volumes on terrains with different slopes and heights. The slope motion process during the numerical simulations of the landslide movement can be divided into three stages based on changes in the kinetic energy. The variations in the kinetic and frictional energies throughout the mass motion are used to establish pertinent parameters to analyze the dynamics of the slider fragmentation characteristics. Building on prior research, the impact of the slope on the mobility and deposit morphology, including the apparent and equivalent friction coefficients and the ratio of the width to length as a deposit morphology model, is examined using motion models. Concurrently, the three experimental variables (the slope gradient, slope height, and sliding block volume) are analyzed and discussed in conjunction with the motion and deposit morphology models. Previous studies indicate that the quantification of landslide fragmentation is only applicable to rock landslides and has limitations. In the numerical simulations, distinct contact models for pre- and post-fragment particles are defined to enumerate the total number of intact particles. Subsequently, a dimensionless parameter is formulated to quantify the degree of slope fragmentation. The relationship of this parameter with the motion and deposition models is subsequently explored. The results show that increased fragmentation reduces the landslide mobility, indicating that fragmentation is an energy-consumptive process that hinders landslide motion. These findings provide insights into the mechanisms of long-runout landslides and contribute to the reproduction of landslide dynamics.

This study explores the mechanical behavior and properties of sand-rubber-gravel (SRG) mixtures under various testing conditions. Through an extensive series of experimental tests—including direct shear, oedometer, saturated and unsaturated triaxial, and cyclic triaxial tests—the effects of rubber and gravel additions on sandy soil are systematically evaluated. The findings reveal that the appropriate content of rubber and gravel is crucial for ensuring the improvement of soil properties. An insufficient addition may not significantly enhance the soil’s properties, while an excessive amount can lead to a deterioration of its mechanical characteristics. With the optimal mixture ratio, test results show significant improvements in shear strength and deformation resistance of the SRG mixtures compared to pure sand. Under saturated and unsaturated conditions, the SRG mixtures demonstrate enhanced bearing capacity. In addition, dynamic response of SRG mixtures to varying cyclic loads are revealed through cyclic triaxial tests. The study confirms the feasibility and effectiveness of using SRG mixtures to improve the mechanical properties of sandy soils, suggesting their potential for diverse geotechnical applications.

This study focuses on the Xuanzhenguan Tunnel, a representative engineering associated with the Lanzhou-Chongqing Railway in China. The tunnel has a total length of 7,447 m, with a maximum burial depth of approximately 265 m. The surrounding rock consists of medium-thick, horizontally bedded argillaceous siltstone with high integrity, and no groundwater was encountered during excavation. However, the construction process revealed severe deformation and structural failure. To analyze the damage characteristics of the tunnel and the influencing factors, field investigations, three-dimensional in-situ stress measurements, and laboratory rock mechanics tests were conducted. A geomechanical model, referred to as the horizontal compression-buckling failure, has been proposed to describe the behavior of horizontally bedded rock formations under high in-situ stress. Utilizing the principles from plate mechanics theory, a rectangular thin-plate mechanical model was developed, and the buckling equation under biaxial loading was derived to ascertain the critical load. For the deformed section between DK626 + 840 and DK626 + 850, the critical load was 12.3 MPa. Parametric analyses demonstrated the effects of load ratio, aspect ratio, plate thickness, span, and rock mechanical properties on the critical load. These findings offer practical recommendations for the design and construction of similar tunnel projects and hold considerable significance for engineering applications.

To study the acoustic emission (AE) time-varying and frequency spectrum characteristics of coal and rock deformation and failure in deep mines under high temperature and high stress, and then reveal the acoustic precursor characteristics of coal and rock deformation and fracture. In this paper, the time series of AE signals under different thermal-mechanical conditions are tested and analyzed by four experimental unconstrained heating, uniaxial compression, graded loading, and temperature-pressure coupling. It is found that the AE signals increase gradually with the increase of temperature and load. Based on this, the AE frequency domain characteristics of coal rock fracture process under staged loading and thermal-pressure coupling conditions were analyzed. The results showed that the AE signals coexisted in the high and low frequency bands, the amplitude of the high-frequency signals changed slightly, and the low-frequency high-amplitude phenomenon appeared. Finally, the time-frequency acoustic signal characteristics are tested before and after the rock burst in the coal mine site. The laws of space-time evolution of microearthquake energy and frequency before and after rock burst are studied. It is found that the phenomenon of “lack of earthquake” begins to appear three days before the rock burst. The amplitude of the signal increased at the pre-seismic time, and the low-frequency signal developed. Based on this, the precursor characteristics of unstable fracture of impact ground pressure were discussed. The research of this paper will provide theoretical support and practical basis for the monitoring and early warning of coal and rock dynamic disasters.

Cyclic loading and seepage pressure (P_w) have a significant impact on the mechanical properties, crack evolution, and permeability of rocks, making these factors crucial considerations in rock engineering applications. This study presents the results of triaxial monotonic and cyclic loading tests conducted on subsea granite under varying seepage pressures. The findings indicate that both cyclic loading and P_w weaken the mechanical properties of granite. As the number of cycles increases, granite undergoes greater deformation, damage, and energy dissipation. Initially, the elastic modulus (E) increases before decreasing, while Poisson’s ratio (υ) rises. Under triaxial cyclic loading, granite’s stress-strain behavior, crack development, and permeability evolve through distinct stages, including crack closure, initiation, extension, and connection. Higher P_w accelerates crack evolution and enhances permeability, leading to an earlier transition from compaction to dilation, accompanied by increased deformation, accelerated damage, greater energy dissipation, and reduced strength. At higher P_w, macro-failure characteristics include greater fragmentation and surface cracking. Scanning electron microscopy (SEM) and backscattered electron (BSE) analyses show an increase in micro-scale fracture surfaces and deeper fractures after failure, indicating intensified damage and a looser rock structure.

Landslides pose significant threats to human lives and infrastructure, and precise understanding and prediction are necessary for effective disaster mitigation. Traditional monitoring methods primarily focus on surface displacement monitoring, which has limitations in understanding the complex evolution of sliding surfaces. This also restricts the improvement in the accuracy and timeliness of deformation prediction models. This study takes the Xinpu landslide in the Three Gorges Reservoir area as an example, utilizing fiber Bragg grating (FBG) technology to monitor the shear strain and shallow soil moisture content during the landslide deformation process. Combining geotechnical and hydrological parameters, a shear strain prediction method considering deformation lag effect is proposed based on machine learning methods. Our findings demonstrate the effectiveness of FBG technology for accurate shear strain monitoring. The integration of hydrological and geotechnical parameters enhances strain prediction accuracy, reflecting the complex interplay of factors influencing landslide deformations. This study presents a shear strain prediction model for shallow sliding surface, contributing to early warning systems and landslide disaster management.

The crucial aspect of sustainable construction relies heavily on the durability of the building stones. In this study, the durability of two low-porous Iranian building stones, trachyte and gabbro, was evaluated using various durability tests, including salt crystallization, freeze-thaw, wetting-drying, acid resistance, thermal shock, and combinations of these processes. To monitor the effects of these alteration tests, non-destructive methods such as colorimetry, saturation-buoyancy technique, and P-wave velocity measurement were employed, along with polarized microscopy, chemical analysis, and physical and mechanical testing to understand the behavior of the stones. The samples were tested for durability through 48 cycles to evaluate their resistance. For each durability test, the color variation, dry weight variation, and P-wave velocity variation were calculated at 8, 16, 24, 32, 40, and 48 cycles. Results show that the gabbro sample, mainly composed of plagioclase (> 90%), has better physical and mechanical behaviour than trachyte. The color change for trachyte samples exposed to thermal shock and combination cycles of weathering processes tests and all gabbro samples is higher than 2 (perceptible at a glance). The important parameters in this variation are related to the efflorescence of salt crystals on the surface, type of surface finishing, soluble agents, and degradation of stone minerals. The significant dry weight variation (DWV) observed in trachyte during the salt crystallization test can be attributed to the salt crystallization within the stone’s pores, which exert pressure on the internal structure, leading to material loss and increased degradation. However, in gabbro, a very low reduction is observable in all durability tests. Also, trachyte samples have higher DWV (lower durability) than gabbro samples. The P-wave velocity variation (PWVV) reduction shows a marked decrease (⁓25%) in P-wave velocity for gabbro, whereas trachyte showed no tangible loss (< 5%) in wave’s velocity.

Through extensive laboratory experiments on unsaturated soils, it has been discovered that particle shape and matric suction significantly influence their mechanical properties. Prior studies have typically examined these factors individually and from a macroscopic perspective. In this study, the aspect ratio is utilized as a representative parameter for particle shape. Employing the Hill constitutive model, a series of triaxial shear numerical experiments of simulations on unsaturated soil were conducted. The results indicate a non-linear relationship between peak deviator stress and aspect ratio, with peak deviator stress initially increasing, then decreasing, and reaching its maximum at an aspect ratio of 1.2. The patterns observed in friction angle, cohesion, and critical stress ratio in relation to aspect ratio mirror those seen in peak deviator stress, with the friction angle exhibiting fluctuations as the particle aspect ratio increases. At a matric suction of 0 kPa, changes in particle shape have a negligible impact on mechanical properties. However, as matric suction increases, the volumetric strain’s dilatancy turning point is advanced, and the effect of particle shape becomes progressively more pronounced. Under varying conditions of particle shape and matric suction, the alteration in bedding angle affects the peak deviator stress and stress ratio, albeit the extent of this influence is limited.

During the construction of engineering projects, it is inevitable to cross fault and fractured zones, which are key geological factors that affect the stability of surrounding rock in tunnels. To study the distribution pattern of instability in surrounding rock and the optimization of synergetic support systems in fault-crossing tunnels, a comprehensive identification method integrating multi-source geological information was proposed, fully considering the geometric shape and distribution characteristics of rock fractures. The location of faults in actual projects was determined using this method, and a detailed three-dimensional numerical model was established accordingly. By simulating tunnel excavation, the spatial distribution pattern and grading characteristics of unstable blocks in surrounding rock were analyzed. Meanwhile, based on the original support methods, the effectiveness of synergetic support in stabilizing surrounding rock in tunnels was revealed, and initial support measures tailored to the characteristics of fault-crossing tunnels were proposed. The research results can provide reliable references for disaster prediction, prevention, and control in fault-crossing tunnels and underground engineering.

This study investigates the complex interplay between wetting–drying (W-D) cycles and initial compaction states on desiccation cracking and the mechanical behavior of different clayey soils. Natural CH, CL, and ML soils, distinguished by their chemical composition and plasticity, are subjected to a meticulously designed experimental program. The specimens are remolded at various initial compaction states, including the optimum moisture content (w_opt) having maximum dry density (γ_dmax), and wet and dry sides of the compaction curve having identical initial dry density (γ_d0). Subsequently, they undergo multiple W-D cycles, systematically documented through cinematography. Mechanical response is assessed after different W-D cycles. It is observed that desiccation cracking within both CL and CH initiates after the first W-D cycle, intensifying rapidly after the second cycle and reaching an optimal cracking state after the third cycle. The crack analyses indicate a transition from surface cracking to deeper-seated cracks with an increase in W-D cycles. CH soil, characterized by a 2:1-layered clay mineral with a high propensity for swelling and shrinkage, exhibits elevated desiccation cracking at high w₀ for identical γ_d0. Notably, CH soil exhibits maximum cracking at the w_opt and γ_dmax. In contrast, CL soil, characterized by a 1:1-layered clay mineral, displays an inverse response across all compaction states, and ML soil, characterized by a scarcity of clay mineral, shows insignificant cracks. This disparity in behavior is closely attributed to clay mineralogy and microstructure, which define the underlying mechanism responsible for the generation of internal stresses in the soil structure induced by moisture fluctuations causing desiccation cracking. Stiffness and unconfined compressive strength (q_u) of CH and CL increase and compressibility decreases as w₀ increases after undergoing W-D cycles due to the volume shrinkage response of specimens. Meanwhile, for a particular compaction state, strength decreases while compressibility increases with increasing W-D cycles.