Bulletin of Engineering Geology and the Environment最新文献

Debris flows pose significant threats due to their high velocity and fluid-like consistency. This research evaluates the intricate failure mechanisms of the rainfall-induced debris-flow event in Nenmara, Palakkad district, Kerala, India, on August 16, 2018, through detailed investigations. A geophysical (Multi-channel Analysis of Surface Waves (MASW)) test was carried out to obtain the shear wave velocity (V_s) of substrata. The dewpoint potentiometer and ring shear test were used to assess unsaturated soil strength and residual shear parameters to analyse the progressive failure mechanism of the landslide using the numerical model LS-RAPID. The mineralogical studies in the Nenmara region reveal that the soil originated from charnockite rocks containing quartz and clay minerals. The low V_s of 197 m/s at 2 m depth indicates the loose and unconsolidated soil layer at the site. The debris flow initiates when the pore water pressure ratio (r_u) rises to 0.40 with a peak velocity of 11.9 m/s and 13.9 m/s in the X and Y directions, which led to the demolition of 3 buildings and the loss of 8 lives. The deterministic analysis reveals that r_u above 0.30 can trigger a landslide near the Nenmara location. The rainfall threshold analysis suggests that 148 mm of daily or 210 mm of continuous rainfall over five days can trigger landslides around the Nenmara region. This research combines geophysical, geotechnical, and numerical simulations to make a substantial contribution to disaster management in comprehending the mechanism of debris flow by identifying triggering factors, and it will help to find the appropriate mitigation measures for future hill area development.

In this study, we investigated the deformation features of steep overhanging anti-dip slopes based on their scale, the rock layer thickness, and the unsupported length. Centrifuge tests were performed for various configurations of simplified overhanging anti-dip slopes. The steep overhanging anti-dip slopes expressed flexural and block toppling behavior in all of the centrifuge tests in this study. The toppling is a progressive behavior: firstly, the shallow rock layers deform slightly as the deformation starts. Afterward, the deformed rock layers toppled, and the rock layers behind them deformed insignificantly. In terms of the scale effect, increasing the slope scale could raise the toppled and deformed zone of the overhanging anti-dip slope. As the unsupported length of the slope is long, the deformation behavior tends to be flexural toppling. When the rock layer thickness increases, the deformation behavior is similar to block or block-flexure toppling. A normalized bending stiffness (K’) is then proposed in this study to discuss the deformation behaviors from material mechanics viewpoints. We found that the K’ is related to the toppling behavior of the overhanging anti-dip slopes. With a small K’ value, the rock layers in an overhanging anti-dip slope deformed close to a flexural toppling. A much smaller K’ value was also obtained for an actual flexural toppling case. Therefore, the findings indicated that the deformability of an overhanging anti-dip slope could be analyzed from a material mechanics viewpoint, and the deformation characteristics depend highly on its normalized bending stiffness.

This study presents a coupled hydromechanical element-free Galerkin (EFG) model to simulate land subsidence induced by groundwater withdrawal. The EFG algorithm was validated with unsaturated hydraulic and hydromechanical benchmark problems, showing satisfactory agreement with the finite element method (FEM) and theoretical results. We qualitatively investigate the effects of groundwater pumping on land subsidence and hydraulic head variation in both isotropic and anisotropic aquifers, taking into account unsaturated effects. Our results indicate a nonlinear correlation between groundwater extraction and both decrease in hydraulic head and increase in land subsidence. In anisotropic aquifers, initial discrepancies are observed between the EFG and FEM models, although final land subsidence and hydraulic head values are closely aligned. Comparative results between the two methods show that, for the anisotropic aquifer, land subsidence and hydraulic head variation trends from the EFG method exhibit better agreement with those of the isotropic aquifer. A parametric study reveals that the elastic modulus and Poisson’s ratio significantly affect land subsidence levels. While hydraulic conductivity influences the rate of hydraulic head decline and onset of subsidence, it has a minor effect on steady-state values. These findings emphasize the importance of accurate in-situ measurements of elastic modulus and Poisson’s ratio for the precision and reliability of feasibility studies in groundwater extraction projects.

Seepage causes the soil structure changing that would influence the safety and stability of geotechnical infrastructures significantly. However, the effect of grain size distribution on seepage behaviors subject to suffusion of sand remains unclear to date. A series of suffusion tests on different grading considering the fines content and grading parameter was carried out to explore the seepage behaviors of gap-graded sand. The results showed that the suffusion evolution process of the gap-graded sand can be divided into three stages: stabilization, development, and failure stage. Fines content and grading parameter have a significant influence on the hydraulic conductivity of gap-graded sand. The critical hydraulic gradient, including initiation and failure hydraulic gradient, of different grading gap-graded sand can be obtained. The final fines loss rate decreases with an increase in fines content, and increases with an increase in grading parameter. The variation of global and local hydraulic conductivity of gap-graded sand can be described as a “tree structure”, which can be distinguished into two stages: “tree trunk” and “dendrites”. The local hydraulic conductivity of the upper parts is smaller than that of the lower parts of the sample. A three-dimensional surface describing the correlation among the fines eroded ratio, the suffusion time, and the initiation hydraulic gradient is proposed and verified by the tested data of sand and sandy gravel samples.

To examine the deformation, failure modes, and deterioration properties of sandstone containing water when exposed to acidic conditions, we initially performed uniaxial compression tests on sandstone specimens with varying pH levels and moisture contents. Microscopic fracture images were then captured using an scanning electron microscope. A quantitative assessment was conducted to analyze the reduction in strength, macroscopic and microscopic deformation, and failure characteristics, energy transformation, and the progression of damage in sandstone containing water. Finally, the damage degradation mechanism under acidic conditions was explored from a water-rock interaction perspective. The results showed that peak strength was lower in wet sandstone, with gradual reductions in elastic modulus (E) and compressive strength (σ) as water content increased. At 2.58% water content, maximum reductions in E and σ reached 42.3% and 43.07%, respectively. Failure initiated with microcracks, which expanded into through-going fractures and large spalling areas. Higher water content intensified the damage. Acid corrosion roughened fracture surfaces and increased porosity, with the most severe internal corrosion occurring at pH 4. Energy evolution during loading reflected microcrack compaction, initiation, propagation, and macroscopic failure. Increased water content correlated positively with damage, though high H⁺ concentration initially had a limited impact. This study can provide strong support for geotechnical engineering and environmental remediation.

Rectangular tunnels under inclined fault dislocation are prone to experience bending, shearing and torsional displacement, which further leads to cross-sectional warping and distortion due to the coordination of the deformation. However, the existing beam models underlying ground-tunnel interactions fail to consider these cross-sectional deformations (CSDs), which inevitably underestimates the structural responses of tunnels. Thus, the paper presents a new Vlasov-beam-based ground-tunnel interaction model for rectangular tunnels in fissured ground. In the new model, the rectangular tunnel is regarded as a Vlasov beam with five CSDs incorporated on Winkler foundation, including bending, shearing, torsion, warping and distortion. Besides, new three-dimensional ground reactions are introduced considering the discontinuous ground-tunnel contact and the active and passive ground-tunnel interactions. A finite element equation for the new model is derived based on the principle of minimum potential energy. Moreover, the proposed method is verified by two case studies, and the superiority of the proposed method over the existing methods is illustrated. Finally, parametric analyses are conducted to explore the effect of critical variables on the deformation behaviors of rectangular tunnels, including cover depths, intersection angles and ground coefficients. Besides, the impacts of cross-section distortion, warping and torsion on tunnels are discussed. The proposed method contributes to a better understanding of structural responses of tunnels under ground fissure, facilitating the new design and countermeasure methods of the disturbed tunnel.

The construction of shallow, large-span tunnels has become a standard practice in urban development, presenting considerable engineering challenges and construction risks in conditions of hard rock. In order to address the limitations of existing support theories and construction designs, this paper introduces a support method based on the Excavation Compensation Method (ECM). The study develops a theoretical model of excavation compensation suitable for hard rock tunnels. This is achieved by analysing the effects of excavation and large span sizes, and by establishing trends in the variation of Mohr’s circle during the unloading compensation process. The study emphasises the pivotal role of 2G-NPR bolts, selected for their elevated tensile and shear strength and elongation, as a fundamental component of the compensation support system. Furthermore, the utilisation of a multi-source monitoring system throughout the construction phase permitted the implementation of high-frequency monitoring, thereby facilitating the prompt identification of any instability signals. The data obtained from the field monitoring demonstrate that the application of the 3D-ECM significantly reduces the deformation of the surrounding rock. In particular, there was a 27.6% reduction in crown settlement and a 69.7% reduction in surface subsidence, thereby confirming the effectiveness of this approach. The findings offer a theoretical basis for the construction of shallow, large-span hard rock tunnels and provide valuable insights into the optimisation of support systems.

The complex engineering geological environment and unique climatic conditions in the alpine mountains of Xinjiang breed a large number of landslide geological hazards, and the accurate landslide susceptibility assessment (LSA) is of great significance to disaster prevention and mitigation. In this paper, based on historical landslide data and field geological survey, 4262 landslides were collected and analyzed, and 12 conditioning factors such as elevation, slope angle, slope aspect, curvature, topographic relief, lithology, road network kernel density, fault kernel density, land use type, vegetation cover, and snow cover were selected and through the independence test. 70% of the landslides were randomly selected as training samples, and the susceptibility of landslides in the alpine mountainous region was evaluated and compared using single model (Normalized Frequency Ratio (NFR), Information (I), Certainty Factor (CF)) and coupled model (Normalized Frequency Ratio-Logistic Regression (NFR-LR), Information-Logistic Regression (I-LR), Certainty Factor-Logistic Regression (CF-LR)), respectively. The remaining landslides were used as test samples to evaluate the accuracy. The main results show that the frequency ratio of landslide susceptibility level increases significantly from low susceptibility zone to very high susceptibility zone. The accuracy of the coupling model is greater than that of the single model, and that of the I-LR coupling model is the highest. The mean value of the coupled model was smaller than that of the single model, while the opposite standard deviation indicated that the prediction ability of landslide susceptibility was more vital. The six models have successfully evaluated the landslide susceptibility in alpine mountainous regions.

The time-frequency joint analysis method was used to study the seismic response characteristics of high-steep rock slopes with weak structural planes. Two models of homogeneous slopes and anti-dip slopes were established using FLAC3D. The results of the time-frequency joint analysis reveal that the topography, geological conditions and seismic wave propagation directions strongly influence the seismic response characteristics of the slopes. The high slope dynamic response of a homogeneous slope shows that the peak ground acceleration (PGA) periodically changes in a certain pattern with elevation and is obviously amplified at the slope crest. Weak structural planes cause local amplification and attenuation of seismic waves, while the two effects of horizontal seismic waves are greater than those of vertical seismic waves when passing through weak structural planes. Frequency-domain analysis reveals that the direction of seismic wave propagation notably affects the value and variation rule of the peak Fourier spectrum amplitude (PFSA), while weak structural planes strongly affect only this value. The dynamic deformation characteristics of the slopes are clarified according to Fourier spectrum analysis and modal analysis. The low-frequency components and high-frequency components mainly cause overall and local deformations, respectively, of the surface slope. In addition, the dynamic response characteristics of the slopes are further analysed based on Hilbert energy, and the applicability of the seismic Hilbert energy spectrum to reflecting the dynamic deformation characteristics of the slopes is determined. Moreover, the connection between the local deformation of the anti-dip slope and the occurrence of a landslide was discussed.

This study presents an innovative application of force-energy equilibrium analysis to evaluate failure extension lengths (FEL) in excavation-induced translational landslides. Utilizing a combination of field data, mechanical balance analysis, and numerical simulations, we systematically investigate the effect of excavation on landslide dynamics. Our approach incorporates the existing energy balance framework and extends its application to excavation-induced translational landslides characterized by weak interlayer. The methodology focuses on capturing the intricate interplay between unloading forces, shear displacement, stress, and strain across various stages of landslide development. A case study of the Tongzilin landslide in Yanshan Township serves as a practical example, underpinning the validation of our theoretical model with real-world data. The proposed methodology provides a valuable reference for the prevention and management of excavation-induced translational landslides.