Bulletin of Engineering Geology and the Environment最新文献

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.

The accurate identification of the characteristics of joints, fractures, extensions, and slips within the slope under earthquake action is essential for understanding the potential failure modes of bedding rock slopes (BRS). In this paper, an innovative method for separating low-frequency seismic response signals (LFSRS) and high-frequency rock damage signals (HFRDS) using VMD-HT was developed, and an index for identifying BRS internal damage using HFRDS was proposed. Three typical BRS cases types-blocky, soft-hard interbedded, and weak intercalation-included in the high seismic intensity area of southwest China were selected to prove the proposed method for separating damage signals. The seismic discrete element numerical modeling was utilized to analyze the crack development and damage evolution characteristics, and illustrate the patterns of seismic instability evolution in BRS. Through a comprehensive analysis of the time-domain, frequency-domain, and time–frequency domain signal characteristics, it was confirmed BRS exhibit a combination of LFSRS and HFRDS resulting from rock structural plane cracking and rock block collisions. The damage identification capability of the peak of marginal spectrum amplitude was assessed for LFSRS, proving its capability in locating damage and evaluating the distribution of seismic energy but failed to detect minor damage and determine the timing of damage occurrence accurately. The instantaneous high-frequency energy level index (IEL_h) was introduced using HFRDS, enabling the identification of crack initiation and propagation locations within the slope and pinpointing the moment of crack appearance. A quantitative relationship between the IEL_h index and the damage degree was finally established. The findings of this study are highly significant for the in-depth exploration of the seismic failure mechanism of the BRS landslide from the perspective of energy-based transmission characteristics.

The determination of ground pressure is an important prerequisite for the design load of tunnel. Currently, in the emerging field of shallow rock large diameter shield tunnels, the study of ground pressure is limited by the lack of comprehensive engineering case studies and experimental data. This study provides a comparison of elaborate numerical analysis method and Fibre Bragg Grating (FBG) monitoring method for the ground pressure in a shallow rock large-diameter shield tunnel based on a case study. Firstly, the elaborate 3D numerical model is developed by finite difference software to simulate the process of shield tunnelling. Construction details such as the force distribution, liner application, over-excavation gap and shield tail gap are considered in the simulation process. The elaborate numerical analysis method for the ground pressure in shallow rock large-diameter shield tunnels is presented. Then, using the elaborate numerical analysis method, the impact of key parameters such as support force at the tunnel face, grouting pressure, tunnel diameter, and tunnel depth on ground pressure are assessed. The new FBG monitoring method is developed to measure ground pressure in shallow rock large-diameter tunnel. Finally, the ground pressure obtained by the elaborate numerical analysis method is compared with that obtained by the new FBG monitoring method. The result shows that the elaborate numerical analysis method is generally larger than the new FBG monitoring method, with a reasonable 15% difference. The ground pressure that obtained by FBG monitoring shows the initial rapid increase, followed by gradual increase, eventually stabilising.

Currently, the mechanical properties of calcareous sand are mainly studied through triaxial tests, as traditional uniaxial compression tests fail to capture real loading conditions and soil strength anisotropy. To address this, true triaxial tests were conducted to examine the effect of the intermediate principal stress parameter (b) on the three-dimensional strength and deformation behavior of calcareous sand. In the constant b and σ₃ tests, as the b value increased, both the strength and peak friction angle (φ_ps) of calcareous sand were increased, while the tangent slope of the dilatancy curve showed a gradual rise.. The φ_ps of calcareous sand was found to be higher compared to silica sand and coarse-grained soils. In the constant mean effective stress (p) and b test, the strength was increased with higher values of both b and p. The Matsuoka-Nakai 3D strength criterion proved more effective in fitting the 3D strength of calcareous sand in π plane. As the b value increased, the critical stress ratio (M_c) was decreased. A quadratic function can better represent the M_c of calcareous sand in the π plane under varying confining pressures. Furthermore, the M_c of calcareous sand was higher than that of silica sand and completely decomposed granite soil. This study provides a valuable experimental basis for understanding the 3D strength and deformation characteristics of calcareous sand in oceanic engineering infrastructure.

Tunnels excavated in squeezing ground conditions often experience time-dependent convergence, significantly challenging their stability and demanding robust support systems. Therefore, timely installation of supports is crucial for ensuring safe operations. The Convergence Confinement Method (CCM), which utilizes Longitudinal Deformation Profiles (LDPs), offers a practical tool to determine optimum support system installation points. However, many studies overlook the creep effect when analyzing LDPs and designing a preliminary support. To address this, present study investigates time-dependent LDPs for four tunnel chainages of the Seri Nala region, Atal tunnel, India. A visco-elastic perfectly plastic (VEPP) model was utilized to effectively capture the creep behaviour of the surrounding rock mass. A 2D plane-strain finite element back-analysis was conducted to evaluate the VEPP parameters using a field-instrumented data. Subsequently, these parameters including shear modulus, viscosities, and retardation time; facilitated the construction of LDPs through axisymmetric analyses, revealing the intricate deformation characteristics along the tunnel sections. Moreover, study was further extended to examine the effects of constitutive models, excavation rate and anisotropic stress ratios on LDPs. The findings reveal that different constitutive models produce distinct LDPs, with the Kelvin-Voigt and VEPP models producing significantly higher time-dependent displacements than traditional elastic and elasto-plastic models. This discrepancy underscores the importance of considering viscous and plastic behaviour into deformation analyses. Additionally, the study emphasizes the critical role of excavation rates in managing tunnel stability, as lower rates resulted in increased deformation due to creep effects. The transition from elastic to visco-elastic and visco-elastic perfectly plastic behaviour, influenced by anisotropic stress ratios, further highlights the complexities involved in tunnel design. Overall, this research provides valuable insights for researchers and practitioners, aiding in the safe and cost-effective construction of tunnels.

Understanding pore water distribution in soil is essential for elucidating water movement and mechanical properties, as it significantly influences soil strength and stability. Accurate assessment of this distribution provides a scientific foundation for civil engineering design, ensuring structural safety and durability. This study examines pore water distribution using plate load tests and Nuclear Magnetic Resonance (NMR). Results indicate that matric suction expels free water first, leaving bound water until a critical suction point is reached. As matric suction increases, the peak value of the T₂ relaxation time curve decreases, shifting leftward, reflecting water drainage from larger to smaller pores. Then, water expulsion occurs in three stages, with Stage III primarily indicating bound water content, quantified at 19.23%, including 3.3% as strongly bound water. An equation is derived to calculate the surface relaxation rate of 0.0176 μm/ms. Thus, the distribution of T₂ relaxation time can be transformed into pore size distribution, summarizing the characteristics of pore water distribution during the drying process. Finally, comparative analysis confirms the effectiveness of NMR in measuring bound water. These findings enhance our understanding of soil water distribution and highlight the need for advanced models that incorporate pore connectivity and water retention dynamics.

Rainfall and blasting are the main factors inducing landslide on open-pit slopes, however, the combined effect of both factors on the slope stability remains insufficiently understood. In this study, the secondary development of the seepage module is conducted using FISH language in the FLAC3D software to calculate unsaturated seepage. Focusing on the high slope of Dagushan open-pit mine, the responses of horizontal velocity and displacement at the slope monitoring points under different rainfall intensities is investigated. Additionally, the variation of the slope safety factor following blasting at different times during rainfall under the same daily rainfall is examined. The results indicate that the rainwater infiltration reduces the strength of rock mass and increases sensitivity to blasting, as evidenced by the gradual increase in peak velocity and displacement. Once the rainfall ceases, the peak velocity gradually returns to its initial state, while the peak displacement stabilizes at a steady value. Rainwater infiltration has a significant negative impact on the slope stability following blasting. As the daily rainfall increases, the required time between the cessation of rainfall and the resumption of blasting operations progressively lengthens.

Dispersive soil has poor engineering geological properties, which can lead to various geological hazards in practical engineering projects. This study utilizes guar gum, an eco-friendly biopolymer with great potential in soil improvement, to improve dispersive soils in western Jilin. Guar gum powder was added to the dispersive soil at dry mass ratios of 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, and 5%, and cured for 1, 3, 7, 14, and 28 days. The improvement effect was comprehensively evaluated by dispersion identification test, unconfined compressive strength test before and after immersion, disintegration test, matric suction test, and permeability test. The mechanism of guar gum in improving dispersive soil was further explained from the microscopic point of view by particle size analysis, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that more than 1.5% guar gum proportion was effective in eliminating soil dispersion. The cured soil had the best mechanical properties at 3.0% guar gum content. With the incorporation of guar gum, the hydrophysical properties of the soil were also improved. Guar gum wraps around soil particles, forming bridges through the hydrogel. Additionally, it fills the voids in the soil, leading to a denser aggregation of the soil particles. In conclusion, guar gum, as an environmentally friendly biopolymer, has a positive effect on the improvement of dispersive soils. The research results will provide theoretical guidance for engineering construction in dispersive soil areas.

To study the influence of water content (w) on the failure characteristics and energy properties of red sandstone, cylindrical specimens with varying w were prepared for uniaxial compression and single cyclic loading–unloading uniaxial compression tests. The effects of w on the mechanical properties, fractal dimension, failure intensity, energy properties, and acoustic emission (AE) of red sandstone were analyzed. The applicability of rockburst tendency indicators under different w conditions was examined, and the optimal w for preventing rockbursts was discussed. The findings indicate that water can weaken the strength and elasticity modulus of red sandstone. Water reduces the ultimate energy storage capacity while increasing energy storage efficiency. As the w increases, the fractal dimension of fragments, peak energy density, failure energy density, cumulative AE energy and count all decrease; the mean particle size increases, and these effects are significant at w ≤ 0.25w_s. The mean particle size decreases linearly with increasing peak elastic energy density. The rock fragmentation is primarily dependent on input energy; the more input energy, the more severe the rock fragmentation. The PES index can effectively characterize the rockburst proneness of red sandstone with different w. The optimal w to prevent rockburst is 0.25w_s achieved by injecting water for approximately 1.3 h. These results can provide theoretical guidance for the support design of caverns in water-bearing strata and disaster prevention in high-risk rockburst sections.