Bulletin of Engineering Geology and the Environment最新文献

Karst collapse as a unique environmental geological hazard in karst areas, easily causes changes in surrounding water and soil environments. Train-induced vibration is a significant inducement for shallow karst ground collapse. Previous studies on the dynamic properties of surrounding soil under train vibration loads often neglected the impact of time intermittent effects. Taking the red soil covering a typical potential karst collapse area along a high-speed railway in China as the research object, field monitoring of the vibration characteristics of the surrounding environment was conducted. A series of continuous loading and continuous-stop-continuous dynamic triaxial tests and scanning electron microscopy (SEM) tests were designed considering factors such as loading frequency, intermittent duration, and dynamic stress amplitude. The effects of loading intermittence on the dynamic response and microstructure of red soil were compared and analyzed. The experimental results show that the drainage and unloading of red soil samples during the intermittent phase dissipate the accumulated excess pore water pressure and adjust the internal particle and structure of the soil, reducing the accumulation of plastic deformation during subsequent loading stages. The residual strain under vibration loading conditions considering the time intermittent effect is significantly reduced, and the residual strain decreases significantly with the increase of time intervals. The weakening effects of both macro and micro characteristics of red soil in karst-prone areas are significantly enhanced with the increase of intermittent time. The research results are of great significance for the prevention and control of karst ground collapse in karst areas.

In deep geothermal resource development, the brittleness index plays a key role in assessing the feasibility of hydraulic fracturing. However, understanding how rock brittleness evolves after high-temperature exposure remains a critical challenge. This study examines the mechanical response of granite subjected to biaxial stress following high-temperature treatment in the laboratory. We analyzed the mechanical properties, energy storage characteristics, and failure behavior using high-speed cameras. Integrating mineralogical properties, thermal damage mechanisms, and strain energy density theory, we evaluated granite’s brittleness under thermal stress. The results reveal that wave velocity and porosity change significantly with increasing temperature, especially beyond 400 °C. Both peak and residual stresses increase with temperature and confining pressure, while peak strain decreases. The pre-peak energy storage coefficient first rises, then declines with temperature, with confining pressure enhancing storage, particularly between 400 and 600 °C. Calculations of elastic strain energy predict rockburst tendencies, with the palm face showing higher susceptibility, consistent with high-speed camera observations. Brittleness peaks at 400 °C under confining pressure above 10 MPa, with lower temperatures enhancing brittleness and higher pressures promoting plasticity. Failure modes shift from tensile and splitting cracks at 25–200 °C to shear cracks at 400–800 °C. At 800 °C, increased confining pressure promotes energy dissipation, leading to more cracks and altered failure modes.

Flexural strength is one of the important mechanical parameters of dimension stones used as flooring and surface covering. European Standards (EN) define two methods for determining flexural strength which are under concentrated load (FS₃) and under constant moment (FS₄). However, these test methods require precise sample preparation and specialized testing equipment. This study aims to establish correlations to practical estimation of FS₃ and FS₄ values from each other and also from common rock mechanics tests. For this purpose, 32 groups of building stones were tested in a comprehensive experimental study and a data set was generated. The following main findings were revealed; FS₄ values are approximately 10% higher than FS₃ values, Schmidt (HS_L) and Leeb (HL_D) hardness methods provide moderate prediction accuracy with R² value of ~ 0.7, uniaxial compressive strength (UCS), point load strength index (PLI), and Brazilian indirect tensile strength (BTS) tests provide higher prediction accuracy with R² value of ~ 0.8, especially when combined with P-wave velocity (V_P) values. In addition, anisotropy coefficients (C_A) were calculated between 3.7% and 23.1% for sample groups and it was revealed that the test parameters decreased as the C_A values increased. Based on these findings, a flexural strength classification with five categories was proposed to serve as a guideline for practical applications and projects.

Water rich tunnels are often subject to lining seepage and water leakage. The water pressure behind lining is the main factor that causes the tunnel diseases. To calculate the water pressure of tunnel lining, axisymmetric analysis, mirror image method, and conformal transformation method are commonly used. However, axisymmetric analysis and mirror image method are only applicable to the tunnels in high water level. The conformal transformation method can be applied to both high and low water level tunnels, but cannot consider the effects of grouting rings and lining. This paper simplified the seepage of groundwater into a fan-shaped vertical shaft seepage problem, and derived the analytical formula of lining water pressure considering the shape of tunnel. A semi-analytical method of lining water pressure considering the influence of waterproof and drainage systems was proposed. The results show that the water pressure is related to the height of the initial water head, permeability coefficient of materials and geometric sizes of lining. According to the reduction degree of water pressure, it can be divided into three areas, namely, uniform reduction area of arch, discharge area of longitudinal drainage pipe and uniform reduction area of invert. With the increase of water head of the tunnel vault, the water pressure difference between vault and invert increases gradually, and the invert is easy to be damaged. The research results can provide guidance for the structural design and optimization of water rich tunnel.

Earthquake has crucial effect in stability of the rock mass in Grotto Temple. However, only a few studies begin with the mountain of Grotto Temple and explore the interactions between rock mass stability of the mountain and that of temple. Firstly, the mechanical and displacement characteristics of North Grotto Temple (NGT) were analyzed, with a particular focus on effects of seismic waves, utilizing the finite difference modelling software FLAC 3D. Subsequently, mechanical properties, displacement nephogram, displacement response characteristics, and acceleration response characteristics of the mountain under seismic conditions were analysed. The simulation results indicate that there was no abrupt displacement at the location of NGT, but the stress changes were complex. Significant stress concentration effects were observed on slope and cliff faces, especially at the site of NGT, leading to relatively large displacements in that area. The phenomena of amplified peak displacement and peak acceleration were particularly pronounced. Additionally, strong shear stresses were observed near contact surfaces, suggesting potential shear sliding failure along these interfaces. This study not only provides theoretical basis for conservation, reinforcement, and monitoring of NGT, but also offers new research perspectives on the stability of rock masses in cave temples.

Granite undergoes varying degrees of weathering when subjected to weathering processes, resulting in weathered granite soil (WGS) with different degrees of weathering. This study focuses on granite residual soil (GRS) and completely weathered granite (CWG) within WGS of varying weathering degrees. Initially, a one-dimensional compression test and a consolidated undrained triaxial test are employed to investigate and compare the mechanical characteristics. Subsequently, the microscopic evolution mechanisms from the fresh granite (FG) to WGS are analyzed through X-ray diffraction, fluorescence spectroscopy, and scanning electron microscopy tests. Finally, various relationships between the physical and mechanical parameters of WGS and their weathering characteristics are developed. The findings reveal that GRS exhibits a smaller compression index than CWG but possesses a larger compression modulus. CWG demonstrates a higher critical stress ratio and effective internal friction angle at the critical state, and the CWG's dynamic elastic modulus exceeds that of GRS. Upon normalization to yield E/E_dmax, GRS confidence region resides below that of CWG. As weathering increases, the primary minerals in granite undergo weathering to produce secondary minerals, and the overall structural integrity declines. Furthermore, a strong correlation exists between the physical and mechanical parameters of WGS and its weathering indices. This study offers invaluable insights into the mechanical characteristics and microstructural mechanisms of WGS. Moreover, offering theoretical underpinning for future pertinent engineering construction endeavors.

The aggregate breakup of structured soft clay has an important influence on the properties of the soil. In this paper, the aggregate breakup of structured soft clay under one-dimensional compression is investigated based on FESEM images, and the relative breakage Br is used to assess the degree of aggregate breakup, and the results show that: The structured soft clay consists of dispersed clay particles, clay aggregates and pores. When the soil is loaded, not only pores change but also clay aggregates breakup occurs. The compression process is divided into three stages: initial structured breakup stage, aggregate breakup stage, and compression stabilization stage. The degree of aggregate breakup is increasing with the increase in vertical load, the greater the degree of breakup, the greater the fractal dimension, and the maximum Br is 0.33. The void ratio decreases nearly linearly with the increase of Br, and the compressive modulus changes exponentially when the Br exceeds 0.20. The empirical formulae established can be utilized to predict the void ratio and compression modulus, and provide a reference for studying the aggregate breakup of structured soft clay.

Soil erosion induced by infiltration of a buried defective pipe is closely related to leaking locations, whereas it has received inadequate attention in literature. In this paper, the distinct effects of various leaking locations on internal erosion are investigated extensively using both experimental tests and numerical simulations. First, a series of experimental model tests are carried out to characterize the evolution of ground collapses due to pipe leaking at different defect locations and to quantify the related soil–water loss (SWL). The experimental results indicate that the defect location has a significant effect on the SWL rate and ground collapse. When the leaking location is changed from the pipe crown to its invert, both the soil- and water-loss rates accelerate dramatically, followed by a more severe ground collapse. Then, a validated two-dimensional (2D) finite-difference method and discrete-element method (FDM-DEM) coupling model is established to explore the distributions of earth pressure (EP), water pressure (WP) and water-earth pressure (WEP) against the pipe and to disclose the influence mechanism of different leaking locations. It is found that EP and WEP in the proximity of the defect reduce significantly after pipe leaking, while EP away from the defect increases due to seepage force and soil arching effect. In addition, the distribution of EP against the defective pipe during internal erosion can be divided into three typical zones: fluctuation, soil arching and stable zones. The findings of this study will be helpful for researchers and practitioners to understand the internal erosion of strata triggered by infiltration of defective buried pipeline.

Landslide-induced waves pose significant risks to human life, property, and infrastructure, especially in relatively narrow channels where wave propagation differs from that in reservoirs or coastal areas. This study introduces a drift-flux model, treating the two-phase mixture as a whole to simulate flow-like landslide-induced waves efficiently. The model combines the renormalization group k‑ε turbulence model and volume of fluid method to accurately describe wave formation and propagation. After verification through mesh size convergence tests and a benchmark experiment, the model is applied to the Baige landslide-induced waves in a narrow river channel on October 10, 2018. The results indicate that wave evolution occurs in four stages: run-up, inundation, run-down, and propagation along the valley. The run-up heights and wave decays vary between upstream and downstream locations at the same distance from the landslide center, depending on the extension direction of the river channel. The numerical predicted maximum run-up height of the Baige landslide-induced waves on the opposite hill slope is 112 m, consistent with the actual situation. However, the maximum run-up heights predicted by empirical equations are lower than both the actual and numerical simulated values due to the lack of consideration of multiple wave reflections in a narrow river channel. Utilizing the previous empirical equations to evaluate landslide-induced waves in a narrow river channel may result in underestimating their hazard. This study contributes to the risk assessment of landslide-induced waves in narrow water bodies, and its findings are essential for safety management and siting decisions regarding infrastructure and facilities.

Small strain properties of subgrade fill material are essentially required for the accurate estimation of deformation behavior of railway subgrade. Many attentions have received on small strain properties of soils under the isotropic stress state or low shear stress level. The high level of shear stress and stress ratio induce reduction in small strain stiffness and thus present the potential challenge to the deformation stability of the subgrade. However, there is not much attempt to investigate the small strain properties under high stress ratio. This paper explores the effects of stress path and stress state on small strain stiffness G_max and Poisson’s ratio v of heavily compacted fully weathered red mudstone (FWRM) under a broad range of stress ratio, via a series of stress-controlled triaxial and bender element tests. Three stress paths, named as constant stress ratio (SSP), constant confined pressure (VSP), constant axial stress (HSP) with stress ratio up to 33.0 were considered. Low level of shear stress slightly promotes G_max, while a significant reduction of G_max is triggered as the stress ratio exceeds a critical value. A unified correlation between the critical stress ratio and confined pressure is developed. The evolution of Poisson’s ratio is also described by a unified three-dimensional feature surface, which influence of stress path is identified by the location and shape of the surface.