Bulletin of Engineering Geology and the Environment最新文献

As a common foundation material for railway subgrades, red mudstone is prone to fatigue damage and deformation under the impact of high-cycle train loads. To comprehensively understand the dynamic damage and deformation behaviour of soft red mudstone, high-cycle cyclic loading tests were carried out to investigate the deformation and crack evolution of soft red mudstone based on acoustic emission (AE) parameter analysis. Then, monotonic compression was performed, and the impact of self-healing on AE characteristics was studied. Tests results showed that cyclic loadings are more likely to cause the matrix loosening and produce small size micro-cracks compared with monotonic loadings. And AE signals exceeding 300 kHz of high frequency increases with the increase of loading frequency, indicating the size of micro-cracks decreases with the increase of loading frequency. The proportion of shear cracks increases exponentially with the increase of upper limit stress but decreases linearly with the increase of loading frequency. Kaiser effect of soft red mudstone decreases or even disappears under the effect of self-healing with the increase of the interval time Δt between cyclic and monotonic loads. In addition, it is found radial strain is more sensitive to the rock’s damage progression compared to axial strain. There is a stronger correlation between axial strain and the damage under cyclic loading conditions than under monotonic loading conditions. The volume strains of rock samples under cyclic loading are relatively smaller compared to monotonic loading under the same damage variable.

Accurate estimation of rock block size is crucial in geotechnical engineering, yet it often encounters challenges due to the complexity of modeling methods or the limitations of oversimplified approaches. This study introduces a novel equation that enhances the accuracy of rock block size estimation by incorporating joint persistence; an important factor frequently overlooked in existing models which describes the extent to which discontinuities split the rock mass. To this end, a three-dimensional discrete fracture network (DFN) was developed using 3DEC v.7.0 to model rock masses containing three non-persistent joint sets. The DFN model was carefully calibrated by removing boundary blocks and optimizing model sizes. The analysis of 125 distinct models led to the development of a practical correlation for estimating the size of rock blocks with non-persistent joints from an existing method for rock masses containing fully persistent discontinuities. The new equation, validated through cross-validation, offers a more reliable tool for practitioners, improving accuracy in rock block size estimation and supporting better decision-making in the field. The application of the newly developed equation to the Burgo Dam spillway in Australia was also shown to result in more accurate volume estimates than the existing methods.

The tensile strength and soil water characteristics of unsaturated soils plays a critical role as a fundamental property in various road engineering projects. The purpose of this study is mainly to investigate the tensile strength and soil water characteristics of compacted and desiccated specimens with varying water contents with under the dry density of 1.5, 1.6, and 1.7 g/cm³ using the filter paper method and Brazilian splitting test. The research findings reveal that during the drying process, as the water content decreases, the overall morphology of the pore size distributions remains largely consistent with a tri-modal distribution, in contrast to the bimodal distribution observed in compacted specimens. Furthermore, desiccated specimens exhibit better water retention behavior compared to compacted specimens. Additionally, compacted specimens reach their peak tensile strength at a critical water content, whereas desiccated specimens progressively increase their tensile strength until stabilizing. In the desiccated specimens, a significant amount of bonding material fills the soil pores, resulting in the formation of a stable bonding force between particles and aggregates. This phenomenon leads to a continuous increase in the tensile strength of the desiccated specimens. The study further establishes a tensile strength model that incorporates the influence of physicochemical forces. The accuracy and reliability of this model were confirmed by comparing its results with experimental data from the test soil in this study, as well as other available resources.

The soil’s creep characteristics significantly impact both the effectiveness of the support system and the enduring stability of the engineering structure. During construction, dewatering is often carried out, which results in seepage within highly permeable soils. To scrutinize the creep behavior of silty fine sand under seepage conditions, triaxial compression tests and triaxial creep tests were conducted on the silty fine sand, subject to three distinct seepage flow rates: 0.5 ml/min, 1.0 ml/min, and 1.5 ml/min. The test results indicate that seepage reduces the maximum stress capacity of the soil and increases its creep deformation. Particularly under relatively high deviatoric stress and seepage flow rates, the specimens exhibit three stages: transient creep, stationary creep, and acceleration creep. Notably, the axial creep deformation rate shows a positive correlation with both seepage flow rates and deviatoric stress. Concurrently influenced by seepage and creep, fine particles within the specimen accumulate in the central and upper regions, whereas the lower section is characterized by larger particles. The progressive increase in pore water pressure, intricately linked to the impeding effect of fine particles on permeation pathways, catalyzes the creep-induced deformation of the specimen. Based on the experimental results, a modified Burgers model has been established. This model takes into account seepage, sliding damage, and particle fragmentation. A comparative analysis, contrasting the modified Burgers model against calculated values derived from the traditional Burgers and Kelvin-Voigt models, underscores the effectiveness of the proposed model. Specifically, the modified Burgers model adeptly captures the transient creep, stationary creep, and acceleration creep stages of silty fine sand, especially under varying seepage flow rates.

Severe rheological failure of extremely soft rocks poses a significant threat to the safety and long-term stability of roadways. Herein, four long-term triaxial creep tests were conducted under low confinements and deviatoric stresses. The results show that greater deviatoric stress leads to more obvious creep deformation, while the confining pressure can delay the occurrence of accelerated creep and restrain the creep rate and lateral deformation. The total axial strain reached 4.03% under 0.6-MPa confinement, and the creep strain of the extremely soft coal rock was much larger than that of hard rocks. Additionally, two important features distinguish extremely soft coal rocks from common rocks, namely, the creep rate did not converge in the steady-state creep stage under each applied stress level and a “gradual” squeezing deformation instability occurred in the accelerated creep stage. Furthermore, the steady-state creep rate increased exponentially with an increase in deviatoric stress and decreased following a power function with confining pressure. Then, a modified Burgers model with a nonstationary viscous coefficient was proposed to reflect the dual and nonlinear influence of confining pressure on steady-state creep rate. Moreover, several principles and suggestions for the long-term stability control of extremely soft rock roadway are discussed. Finally, a novel nonlinear creep constitutive model was established by connecting a nonlinear viscoplastic element considering both creep time and applied stress with the modified Burgers model in series. The findings are essential for creep behavior prediction and stability control in extremely soft rock engineering.

Dispersive clay is widely distributed in the Songnen Plain of northeast China, causing serious embankment damage to hydraulic engineering, and the research on the relevant failure mechanism is still incomplete. In this study, based on the real stress path of dispersive clay failure, a mechanical experimental method under plane strain conditions was adopted to investigate the strength properties of dispersive clay. The results showed that under plane strain conditions, the stress-strain curve of dispersive clay exhibited the strain hardening type, distincted from the conventional strain softening type under triaxial vertical conditions, and the strength difference was approximately twice at a consolidation stress of 50 kPa. The stress-strain relationship of the principal stress also showed the strain hardening type, and the relationship between the stress-strain was approximately linear. Under low consolidation stress, the coefficient of the intermediate principal stress reached 0.44, indicated a significant influence of the intermediate principal stress on the strength of the clay. Under low consolidation stress, the failure mode of dispersive clay was characterized by swelling with no obvious spatial shear band, while under high consolidation stress, the failure mode exhibited a shear band located diagonally. Additionally, the strength properties of dispersive clay were weakened by the leaching of chemical ions in the clay, showed different compaction and strength under different consolidation stresses.

The shear behavior of soft-hard joints is important in the stability analysis of rock structures. However, available experimental studies on the shear behavior of soft-hard joints are relatively limited. In this study, a series of direct shear tests were conducted to evaluate the shear stress-displacement curves and the dilatancy of soft-hard joints with different joint roughness coefficient JRC, wall strength ratios, and normal stresses. Acoustic emission technique was applied to investigate the mesoscopic damage evolution of soft-hard joints with shear displacement. Results showed that the shear stress-displacement curves of soft-hard joints were divided into elastic, damage, softening, and residual stages. Peak and residual shear strengths increased with JRC, wall strength ratio, and normal stress. The peak shear displacement increased with wall strength ratio and normal stress, while it decreased with JRC. The damage coefficient increased with JRC, wall strength ratio, and normal stress, and the soft wall surface exhibited a higher damage coefficient compared to the hard wall. The damage spots on the soft wall surface progressively enlarged with wall strength ratio and normal stress. The percentage of tensile cracks was typically higher than 50%. The proposed empirical model based on Barton model and Asadollahi model could accurately predicted the entire shear stress-displacement curves of soft-hard joints obtained from direct shear tests. The findings in this study should be beneficial for estimating the shear response of soft-hard joints under constant normal stress.

Landslides significantly impact human engineering practices. In the Wenshan section of the Tianbao-Houqiao Expressway in Yunnan, China, three closely spaced deformation zones emerged within the Xiangpingshan slope. Despite multiple rounds of reinforcement measures, including anti-slide piles and slope cutting excavations, one of these zones continued to experience deformation, posing a serious threat to both human life and property and causing frequent expressway closures. This study aims to analyze the surface features, deformation characteristics, and failure mechanisms of these deformation zones through detailed field investigations, InSAR analysis, numerical simulations, and monitoring data. The results show that the Xiangpingshan slope is an ancient landslide, characterized as an anti-dip layered rock slope. Engineering disturbance is the main triggering factor for these deformation zones. Zones I and II exhibit shallow deformation caused by sliding of the overburden. Zone III exhibits deep-seated deformation resulting from excavation disturbances. These disturbances initially triggered overburden sliding, followed by the sliding of the bedrock along fracture zones. A sliding-toppling failure mode is proposed for such slopes, which primarily occurs in anti-dip soft rock slopes. Reducing excavation and providing timely support after excavation, is crucial to prevent bedrock disturbance and the onset of deep-seated deformation. Additionally, this paper uses the Xiangpingshan landslide as a case study to summarize the multi-phase catastrophic process of large-scale toppling slopes, offering valuable insights for similar engineering projects.

To investigate fault activation and slip-induced hazards at different depths in coal mining, this study conducted unloading experiments on inclined sandstone interfaces under confining stresses of 10 MPa, 18 MPa and 30 MPa using a true triaxial loading machine. Seismic signals over fault surface sliding were collected using a multi-channel acoustic emission (AE) system. Statistics on the AE energy and dominant frequency with fault activation were calculated, and seismic localization and fracture type during faulting were derived for different initial confinement conditions. Scanning electron microscopy (SEM) and confocal laser scanning microscope (CLSM) techniques were used to characterize the micro features of fault sliding. Experimental results indicate that the unloading-induced slip instability process of the fault surface under different confining pressures is basically consistent, and the duration of fault surface slip is positively correlated to the initial confining pressure. The AE events are distributed near the fault surface and mainly represent tensile fracture, but shear events significantly increase after fault macroscopic slip. Both the fracture intensity and pore abrasion of the fault interface are higher for a larger confining pressure and the surface is apparently smooth when confining stress reaches 30 MPa. Based on the experimental results, the mechanical behavior of unloading-induced fault sliding correlated to AE signal characteristics and surface fracture separately was discussed. Finally, implications of the findings on the seismic monitoring and early warning of faulting-affected coal burst in deep mining were presented.

Drilling is a crucial operation in mining and construction, and optimizing it can significantly impact costs and operation time. Therefore, it is necessary to determine the parameters affecting the drilling and the correct understanding of these relationships can help to optimize the drilling operation. In the meantime, the relationships between the parameters of the drilling machine and the rock can be considered as a decisive operational condition. One of the effective parameters in drilling is the rock texture, which is measured based on the image analysis of thin sections. Additionally, the vibration caused by drilling can assist in determining the type of rock and its characteristics, guiding further operations. In this study, we utilized a laboratory-scale drilling machine to measure the vibration it caused during drilling and examined its relationship with the microfabric parameters of 10 different rocks. Statistical analysis indicated the highest and lowest correlation coefficient between vibration with aspect ratio and the equivalent diameter, respectively. These relationships can provide a good view of the impact of rock texture parameters on the vibration of the drilling rig on a laboratory scale. Also, by using the 3D surface plot and considering the combination of rock microfabric parameters, the drilling vibration can be predicted with much higher accuracy. This result shows that the drilling vibration is affected by a combination of rock microfabric parameters.