Bulletin of Engineering Geology and the Environment最新文献

Understanding the leakage routes plays an important role in a successful remediation of water loss by consequently reducing its cost and time. Among the common methods for reducing uncertainty in leakage analysis, the geology, hydrochemistry, environmental isotopes, grouting analysis, water-balance calculations, and water level monitoring are applied at this study to find the dominant leakage routes at the Roudbal Dam site. Results show that two leakage routes are probable, through the karstic limestone at the right bank of reservoir. Leakage along the first route is based on the following evidence: (a) the occurrence of bedding plane conduits; (b) the appearance of leakage in the access gallery down gradient of grout curtain; (c) the similarity of water chemistry and isotopic content; (d) the close correlation of water-level response in open boreholes to fluctuation in reservoir water levels; and (e) inadequate sealeing of grout curtain in depth and length. For the second route, leakage evidence is based on: (a) the interpreted hydraulic connectivity of karst aquifers especially by the presence of springs at transverse faults; (b) the elevation of discharge zones approximately 300 m lower than reservoir water level; (c) the similar water chemistry and isotopic content; (d) the results of water-balance calculations; and (e) no grout curtain was constructed on this route. To reduce uncertainty along any proposed leakage route, a thorough hydrogeological investigations (including spring monitoring, tracer test, borehole drilling and karst assessment) and geophysical evaluation (particularly in sites with complex structure) are needed. It is concluded that to reduce uncertainty in the addressing leakage routes, the applied approach at each dam site must be based specifically on the local geological and hydrogeological conditions.

Rock mass deformability is evaluated by Young’s modulus (E), which provides the bases of stability assessment for designing and developing large engineering structures. Modulus of elasticity (E) is the most commonly used input parameter for rock mass characteristics and classification systems, stability analysis of surface/underground engineering structures, and rock failure criteria. However, E is conventionally obtained from the borehole tests, which have significant limitations and do not provide a thorough evaluation of rock mass deformability for lateral and vertical coverage of large areas. Conventional determination of in-situ geomechanical parameters is a complex system problem, which has always been a challenge under uncertainty and data lack. Alternatively, throughout the last decades, several attempts were made to assess the subsurface geology via geophysical-based approaches. Geophysical approaches are more cost-effective, quicker, and user-friendly and offer volumetric data of the subsurface. In this contribution, for the first time, we advance a non-invasive geophysical approach of controlled-source audio-frequency magnetotellurics (CSAMT) for quick estimation of 2D/3D E to evaluate the complex geological subsurface over one km depth. These results are important to better understand the complex engineering geological conditions, to assess the failure probability in the early stage, and to provide safety, stability, and cost evaluation support for successful development of the deep underground engineering infrastructures. Our approach fills the gap between accurate geotechnical models and insufficient geological information, gives more objective indices, and provides a reference for more accurate design of engineering structures in areas lacking sufficient mechanical drilling data.

The use of the Equotip hardness tester in engineering geology has increased significantly in recent years, especially in estimating the strength of weak and weathered rock materials. Weathering and fracturing, besides lithology, influence the overall behaviour of the rock mass and the response of the non-destructive tester. In this study, more than 9,000 Equotip rebound measurements were collected from twelve rock outcrops of several geological formations in central Italy, using a regular measurement grid approach. In addition, linear scan lines were combined with the analysis of photogrammetric sampling windows to determine geomechanical indexes such as Rock Quality Designation (RQD), Joint Volumetric Count (Jv) and Fracture intensity (P21) to be coupled with the Equotip measurements. A strong correlation was found between RQD, Jv, P21 and the Equotip rebound. The study presents an innovative approach by integrating extensive Equotip rebound measurements with geomechanical indices (RQD, Jv, P21) and advanced photogrammetric techniques. This combination provides new quantitative constraints on the relationship between fracture intensity, lithological variation, and mechanical properties of rock masses. Our findings highlight the potential of Equotip testing as a fast and reliable tool for in-situ rock mass quality assessment, also in heterogeneous geological settings, improving hazard management and engineering design.

Weak interlayers are difficult to be measured using the traditional macroscale Rock Mechanics Experiment, which requires intact and standard rock samples. Because the zones of weak interlayers are usually narrow and variable, and the geomaterials in weak interlayers are fragmented and muddy. This work combines the microscale Rock Mechanics Experiment (micro-RME) and Accurate Grain-Based Models (AGBM), in order to investigate the mechanical property of the weak interlayer found during the construction of Sichuan-Tibet Railway. The composition and mechanical property of rock-forming minerals in weak interlayers were tested using micro-RME, TESCAN Integrated Mineral Analyzer and nanoindentation testing. Based on the results of micro-RME, the AGBM was established to achieve the macroscale property of weak interlayers. The influence of weak interlayers on the deformation of surrounding rocks was discussed numerically.

The complex geological conditions and operational performance of reconditioning modified earth pressure balance shield (M-EPBS) machines can critically influence tunnel excavation and construction safety. To address this, the study proposes a comprehensive framework for assessing the overall construction performance of reconditioned shield machines in compound strata. This framework employs fuzzy mathematics theory and analytic hierarchy process (F-AHP) to construct a three-level multi-factor evaluation matrix and establish comprehensive membership function relationships. We then quantify the weight of each factor and the interval membership function, followed by a relative superiority analysis of the interval matrix. A shield tunneling case study is utilized to evaluate the model, focusing on layer conditions, shield design parameters, and shield construction parameters. The study also addresses the challenges encountered during the tunneling process and the corresponding countermeasures. The results reveal that the proposed framework is effective, user-friendly, and adaptable for selecting and evaluating M-EPBS machines in compound strata. This framework provides a novel approach for feasibility assessments, safe operation management, pre-shield design evaluations, and post-shield construction verifications.

Landfill is the main method for disposing of municipal solid waste (MSW). However, landfill instability destruction accidents occur frequently, and the instability is influenced by multiple factors. Due to the complex composition of MSW and its obvious heterogeneous properties, landfill stability is the most significant engineering challenge in landfill operations. This paper has provided a review about status quo of MSW disposal and researched the impact factors of MSW landfill stability through extensive literature research. In view of the landfill process and specific heterogeneity of MSW, a finite element model about spatial changes in engineering properties on MSW body has been proposed. Then the sensibility analysis of the engineering properties on heterogeneity municipal solid waste body stability has been conducted, and the influence curves for the safety factors of the MSW body have been proposed. Finally, suggestions have been proposed that can provide technical support and can serve as a reference for the design, operation, and maintenance of MSW landfills.

Toppling failure commonly occurs in anti-dip slate slopes due to foliation splitting and gravitational deformation. The study uses centrifuge tests and the discrete element method (DEM) to investigate the influence of foliation and existing fractures on the toppling failure evolution of anti-dip slopes. Six centrifuge tests with slate blocks obtained from an actual slope were carried out. Then, a proposed foliation model was implemented in the DEM software 3DEC to simulate the failure evolution of anti-dip slopes. The 3DEC analysis was validated by the actual failure pattern of slopes in centrifuge tests. The results indicate that the toppling failure of the anti-dip slope was initiated by existing fractures rather than the original cohesive foliation. Though the slate foliation is regarded as a weak plane in the rock mass, it retains a higher strength than the existing fracture, so the toppling failure is difficult to initiate from the cohesive foliation. The closer the fracture is to the free surface, the more pronounced the damage. In addition, the simulation indicates that the existing fracture's position also affects the anti-dip slope's failure degree. The fractures on the top propagate more easily than those on the bottom.

Collisions are the most complex part of rockfall movement processes and significantly affect the scope and movement distance of rockfall hazards. An accurate analysis of collisions is helpful for obtaining reliable rockfall trajectories. In this study, the energy loss during collision is characterized by normal and tangential coefficients of restitution (COR), and the rockfall collision and motion processes are simulated via numerical methods. Contact theory and a method for calculating COR are considered for three-dimensional sphere discontinuous deformation analysis (SDDA) to simulate collisions during rockfall movement. A detailed calibration method is proposed to obtain the critical parameter “contact yield stress” of the normal COR (NCOR). Through parameter sensitivity analysis, the inherent velocity loss in SDDA is investigated, and correction strategies are proposed. Additionally, the effects of the material, incident angle, and impact velocity on COR are studied, and the fundamental reasons for the change in COR caused by various factors are discussed. Finally, based on the topography of a high and steep dangerous rock slope in the Wulong area of Chongqing, China, rockfall motion in complex terrain was simulated, and the simulation results were compared with the traces of rockfall left behind and stopping area in the field. The results show that the SDDA considering COR can simulate the collision process of rockfall movement, which has important practical value for rockfall risk assessment.

Landslide susceptibility assessment has made significant strides in meeting the urgent requirements for disaster prevention and mitigation. However, the inherent imbalance in landslide distributions poses challenges and thus various sampling strategies emerge. Yet, these strategies alter the original dataset distribution, necessitating a deeper understanding of their impact on susceptibility mapping. This study integrates multi-source information, including morphological, geological, hydrological, and land-use data in the northwest of Oregon State, to train four models—Decision Trees, Random Forest, Adaboost, and Gradient Tree Boosting —using both balanced and imbalanced training sets. Results reveal that models trained on imbalanced datasets generally exhibit superior classification performance. Models using balanced datasets predict more positives (landslides) at higher susceptibility levels, while those applied imbalanced datasets classified more negatives at lower levels. By employing the Shapley Additive Explanations method, the consistency in model decision-making was established and identified the top five most influential factors: distance to roads, slope roughness, geological age, roughness, and elevation. Furthermore, the consequences of FN (False Negatives) and FP (False Positives) were discussed, concluding that FN may lead to loss of life, and FP may result from prediction inaccuracies, dataset incompleteness, and forthcoming landslides, hence allowing for a certain amount. It suggests that models with balanced datasets are preferable for minimizing the quantity of FN and effectively capturing landslides at high and very high susceptibility areas. The findings provide valuable insights into the impact of positives and negatives ratios on landslide susceptibility and offer support for optimizing dataset sampling.

The present study provides multidisciplinary research on the alteration of petrographic, mineralogical, geochemical characteristics, and physical properties of Himachal gneiss due to weathering. Three different weathering grades fresh, slightly, and moderately weathered gneiss are collected from Kullu, Himachal Pradesh, India. The petrographic and mineralogical analyses are done by thin section and XRD analyses. The microstructural and geochemical studies of gneiss samples were performed using scanning electron microscopy (SEM) and X-ray fluorescence (XRF) respectively. The petrographic images revealed a large amount of alteration in the plagioclase due to weathering. The pervasive sericitization of plagioclase is observed in moderately weathered gneiss samples. The quartz grains are intact and only minor fracturing in some quartz grains is observed in moderately weathered gneiss samples. The SEM images indicate that the inter-granular and intra-granular micro-cracks increase with the weathering grades. The XRF results are used to obtain the different chemical weathering indices and their suitability for Himachal gneiss. Among twenty-five chemical weathering indices, the CIA, CIW, alkaline ratio, PIA, LOI, and WI show a suitable trend and can be used for assessing the weathering of Himachal gneiss. In addition, alterations in the physical properties of gneiss are observed due to weathering. The bulk, dry, saturated densities and slake durability index decrease while the porosity increases with the progressive weathering of gneiss. The progressive weathering significantly reduces the gneiss's uniaxial compressive strength (UCS). For all three weathering grades of gneiss, the maximum and minimum values of UCS were observed at 90˚ and 30˚ foliations, respectively.