Bulletin of Engineering Geology and the Environment最新文献

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.

In recent decades, there has been a significant surge in infrastructural development, resulting in a scarcity of suitable locations for the construction of substantial structures such as high-rise buildings, bridges, transmission line towers, etc. Given the inherent strength and stability of rocks in comparison to soil, foundation engineers consistently favor rock mass as the preferred foundation material. However, the behavior of rock mass is profoundly complex due to its non-homogeneous and anisotropic nature. Consequently, an in-depth examination of the behavior of rock mass under various types of loadings becomes imperative to facilitate informed and reliable engineering decisions in the context of rock-based foundations. In this research, the response of isolated square footing on jointed rock mass under eccentric inclined loading is investigated. Finite element software (FEM) Plaxis 3D was used for analysis. From the study, it was observed that, with an increase in the eccentricity and inclination of loading, the bearing capacity factor (N_σ) values decrease. Which means that the bearing capacity of jointed rock mass decreases with an increase in the eccentricity and inclination of loading. It was also observed from the study that, with increases in the GSI value, the load bearing capacity of the rock mass also increases. However, N_σ (Bearing Capacity Factor) values increase up to the GSI value of 35, and then it decreases as the GSI values further increase. Non-dimensional correlations have also been developed to determine the bearing capacity of square footing on jointed rock mass under eccentric inclined loading for different values of GSI.

The overburden fractures evolve with the backfill mining process shows a stage characteristic which plays a key role in understanding the quantitative correlation between fracture fractal and overburden deformation. In this study, the evolution of fracture network and the fracture fractal induced by the multiple layers backfill mining are firstly investigated based on the results of scale model and fractal dimension analysis. Then the quantitative correlation between fracture fractal and overburden deformation is achieved accordingly. The results show that the fracture network develops in 3 stages with high asymmetry during the upper layer mining, and 4 stages with the reopening of the previous vertical fractures during the lower layer mining. The fractal dimension changes with the height of water-conducting fractured zone show an exponential relationship and can be divided in 4 stages during the upper layer mining, and 3 stages during the lower layer mining, which is consistent with the evolution characteristics of fractal dimension changes with the mining process. The fracture ratio expressed by the ratio of the area occupied by the fracture to the analysis area exponentially increase with the advancement of the multiple layers backfill mining, and linearly with the fracture area. The fracture ratio, fracture area and fractal dimension jointly reflect the development degree and evolution characteristics of fractures, which can effectively represent the deformation and failure type of the overlying strata of the coal seam during the mining process. The result is an important basis for taking measures to mitigate the overburden failure and prevent the water and sand inrush or water-sand mixture inrush disaster.