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Engineering Geology
Elsevier Science B.V.
Engineering Geology

Elsevier Science B.V.

0013-7952

Engineering Geology/Journal Engineering GeologySCIISTPEIAHCI
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    Effects of particle shape on dynamic mechanical behaviours of coral sand under one-dimensional compression

    Wang T.Wang M.Ma L.Li Z....
    18页
    查看更多>>摘要：? 2022 Elsevier B.V.Coral sand is characterized by high porosity, high compressibility and high crushability mainly due to its irregular particle shape and internal pore structure. Single coral particles in a size fraction tend to have a variety of shapes from bulky to flaky, which emerges as one of the most pivotal factors affecting the macro-scale performances of coral sand. A series of confined one-dimensional dynamic compression tests were conducted on coral sand with four classified shapes (e.g., blocky, dendritic and rodlike, flaky particles, and coral debris) via a modified 37-mm-diameter split Hopkinson pressure bar (SHPB) apparatus. The effects of particle shape on the dynamic mechanical behaviours of coral sand at high strain rates were assessed in terms of the stress-strain response, compressibility, particle breakage and the change in particle shape measures. It is revealed that coral sand exhibits high small-strain stiffness, a low crushing strength, a notable strain hardening and a high compressibility behaviour as subjected to dynamic compression at high strain rates. In the low-stress level, it is the high interparticle friction and interlocking induced by the irregular shape form and rough surface texture that lead to a gentle descending tendency in the void ratio. While in the high-stress level, it is the particle crushing along with its rearrangement that results in the high compressibility of the coral sand assemblage. In general, the particle crushing strength tends to decrease as the particle shape shifts from bulky to elongated and to flaky. The large-strain stiffness decreases and the compressibility increases with an increase in the overall particle irregularity. Coral particles are prone to be more spherical and smoother as the average degrees of sphericity, convexity and aspect ratio approach to unity, due mainly to the intense asperity damage and primary fracture under dynamic tests. Furthermore, the percentage in the degrees of sphericity, convexity, aspect ratio and flatness increases with respect to the initial degrees of themselves. It can be further postulated that the extent of breakage could be quantified by the statistical change in the particle measures such as sphericity and convexity aside from particle dimensions for granular materials with irregular shapes.
      原文链接:
    • NSTL
    • Elsevier

    Mechanical and micro-structural damage mechanisms of coal samples treated with dry–wet cycles

    Yu L.Yao Q.Chong Z.Li Y....
    14页
    查看更多>>摘要：? 2022 Elsevier B.V.The construction of mine goafs as an underground reservoir to store and utilise mine water can effectively alleviate the contradiction between coal and water in the arid mining areas in western China. Understanding the effects of water on the mechanical properties and micro-structure of coal is essential for the stability design of coal pillar dams subjected to repeated water erosion. In this study, ultrasonic, X-ray diffraction, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and uniaxial compression tests were conducted on coal samples with zero to five dry–wet cycles to investigate the changes in water absorption characteristics, pore structure, microscopic morphology, and mechanical properties as the number of dry–wet cycles, n, increased. Moreover, the connection of the pore structure and microscopic morphology with the mechanical damage was established. The results showed that the peak stress and elastic modulus were negative exponential functions of n. As n increased, the moisture content saturation and homogeneity of the coal sample increased, the number of pores increased, and tiny pores within the coal converted to medium-to-large pores. Further, the peak stress had a good negative linear fit to the porosity and internal damage defined by the integrated area of the T2 curve. According to the SEM test results, the coal underwent five stages during a dry–wet cycle: uniform and dense original structure, particle aggregation, pore development, fracture sprouting, and overall structural fragmentation, with a gradual decrease in structural integrity. The damage variable, D, was defined by the fractal dimension, F, of the SEM images, enabling the quantitative characterisation of the coal microscopic damage during the dry–wet cycle; moreover, D/F was an exponential function of n. Finally, the damage mechanism of coal samples was interpreted from both macroscopic (i.e. NMR) and microscopic (i.e. SEM) perspectives, and they showed good agreement. Our results could provide a reference for the long-term stability assessment and design of coal pillar dams.
      原文链接:
    • NSTL
    • Elsevier

    Experimental and analytical studies on the influence of weathering degree and ground-environment analog conditions on the tribological behavior of granite

    Sandeep C.S.He H.Senetakis K.
    16页
    查看更多>>摘要：? 2022 Elsevier B.V.Weathering is a geological/geo-environmental process that degrades and transforms rocks, contributing to landslides and instability of geo-systems and infrastructures. The effects of weathering on rock characteristics at the grain scale is crucial for understanding the impact of geological environment-processes on the physical and mechanical behavior of rocks, as well as how these processes are linked to the large-scale behavior of geological systems. In the present study, an investigation on the tribological behavior of highly and completely decomposed granitic rock (termed HDG and CDG, respectively) is presented using micromechanical-based experimental and analytical methods on miniature specimens. Emphasis is placed on examining the influence of the weathering degree and by taking into account analog ground-environment interaction effects on the constitutive (contact) behavior and interface friction of the weathered rocks. The high roughness and coating exposed on the surfaces of the tested samples because of the decomposition of feldspars and micas had important influences on the tribological behavior of the rock. Significant differences were also observed based on the state of the specimens, i.e., nominally dry, immersed in water, or by removing the surface coating from a washing process. An attempt was made to understand the differences between variously weathered materials and provide some basic modeling that can be useful in discrete-based analyses of geomechanics and engineering geology problems. Comparing a broad range of geological materials, including granite of grade I-II revealed that the transportation-sedimentation process and in-situ chemical weathering or rock crushing resulted in significant variabilities in the surface morphological characteristics of the grains. In some aspects of their tribological behavior, HDG grains (grade IV) were rather similar to grade I-II compared with the observed response of grade V. Analog wetting-drying cycles, simulated based on cyclic normal contact tests revealed significant accumulation of plastic displacements for the weathered rocks compared with sedimentary type materials, which implies higher sensitivity of weathered rocks to stress state changes caused by various geo-environmental influences. This is crucial to be considered in the constitutive modeling of ground-environment interaction.
      原文链接:
    • NSTL
    • Elsevier

    Effect of ocean environmental particles on compressibility, electrical resistivity, and stiffness characteristics of mixtures

    Kim S.Y.Lee J.-S.Hoang Q.N.Park J....
    12页
    查看更多>>摘要：? 2022 Elsevier B.V.The influence of diatoms, which have distinct physico-chemical characteristics, is a key factor in the investigation of deep-sea sediments. The objective of this study was to investigate the compressibility, electrical resistivity, and stiffness of sand–silt–diatom mixtures performing oedometer tests. The specimens were prepared by mixing fines containing silts and diatoms into sand, and the fines contents were 0%, 10%, 20%, and 30% in weight (FC00, FC10, FC20, and FC30). The oedometer test was carried out from 5 to 640 kPa, and the electrical resistivity, shear wave velocity, and compressional wave velocity were obtained during loading and unloading. The test results show that the electrical resistivity and compressional wave velocity have transitional behavior at FC10 owing to the dominant effect of fines. The shear wave velocity decreases with an increase in fines contents despite a lower void ratio due to the fines. Moreover, the equivalent bulk modulus of the mineral from back-calculation also exhibits a transition at FC10. However, both compression indices from the measured data and the asymptotically-sound compaction model equation exhibit the transition at FC20. In addition, FC20 is located on the boundary between the sand-dominant and transitional mixtures in the triangular chart of ternary mixtures. The results suggest that the transitional fines content of mechanical behavior changes at the points of large and small strains.
      原文链接:
    • NSTL
    • Elsevier

    Quantitative risk assessment of two successive landslide dams in 2018 in the Jinsha River, China

    Yang J.Shi Z.Peng M.Zheng H....
    15页
    查看更多>>摘要：? 2022 Elsevier B.V.Two large successive co-site landslide dams blocked the Jinsha River in the Sichuan Province of China in 2018. A quantitative risk analysis was carried out to quantify potential human and economic losses resulting from the failure of these dams, especially the interaction between the co-site landslide dams, and to further investigate the influence of digging a diversion channel on risk mitigation. Flood routing for three scenarios (i.e. after the first dam formation, when the second landslide mass was added, and with a diversion channel after failures) were simulated using HEC-RAS. The human and economic losses were evaluated using a human risk assessment model together with empirical formulations. The results show that the risk of breaching floods had increased significantly after the second co-site landslide dam formation on the pre-existing loose deposits of the first dam. This amplification effect of outburst floods was so great that the peak outflow resulting from the breaching of the second landslide dams was more important, leading to greater economic losses than those resulting from the breaching of the first dam. However, the expected loss of life caused by the breach of the two landslide dams appeared small because of the sufficient time lag provided by the long distance between the residential area and the dam site. The simulations also outline the importance of the diversion channel in decreasing the peak outflow rate and hence downstream risks. A parametric analysis shows that a deep channel with a moderate longitudinal gradient can significantly decrease the peak outflow discharge at the dam site. Flood intensity and risks to downstream towns did not change because of the relatively small attenuation rate of the peak outflow rate. However, a shorter height of the residual dam can be obtained by optimizing the diversion channel, and the amplification effects of such co-site dam can be significantly reduced in the future.
      原文链接:
    • NSTL
    • Elsevier

    Random finite element analysis on uplift bearing capacity and failure mechanisms of square plate anchors in spatially variable clay

    Chen X.-J.Liu Y.Fu Y.
    14页
    查看更多>>摘要：? 2022 Elsevier B.V.Square plate anchors are increasingly used to provide uplift bearing capacity for both onshore and offshore infrastructures. Past research on the behavior of plate anchors mostly assumed that the soil strength is uniform or linearly increasing with depth without considering the geological uncertainty due to soil spatial variability. This study therefore conducted a series of three-dimensional random finite element analyses on the uplift bearing capacity and failure mechanisms of square plate anchors considering the combined effects of anchor buried depth and soil spatial variability. It was found that two typical types of failure mechanisms, namely, a localized rotational scoop failure mechanism and a global shear failure mechanism would form in random soils with relatively weak and strong soil strengths, respectively. A larger buried depth of at least 3B (B = width of plate anchor) is required to ensure a localized failure mode in random soils. Moreover, the mean uplift bearing capacity in random soils is generally lower than the corresponding deterministic value. For this reason, the deterministic uplift bearing capacity is generally overestimated. Finally, this study provided a quantitative approach to predict the probability of failure for plate anchors considering the combined effects of anchor buried depth and soil spatial variability, which may benefit the estimation of the probability of failure for square plate anchors as part of the conventional factor of safety design approach.
      原文链接:
    • NSTL
    • Elsevier

    Probabilistic hazard assessment of landslide-induced river damming

    Zeng P.Wang S.Sun X.Fan X....
    21页
    查看更多>>摘要：? 2022Landslide-induced river damming poses a considerable threat to the safety of humans and infrastructure. Prediction of landslide-induced river damming is of great significance for quantitative risk assessment and emergency response planning. However, owing to the large uncertainties embedded in the input parameters and dynamic numerical models, a reliable physically based prediction of landslide dam formation is still challenging. In this study, we proposed a probabilistic framework to predict rockslide-induced river damming and its associated barrier lake. Both parameter and model uncertainties were considered to reproduce the run-out process and the deposition behavior of the Baige landslide based on dynamic numerical simulation, while calibrating the input parameters through a sequential Bayesian back analysis. The first slide of the Baige landslide was considered to calibrate the input parameters with observations at several deposition depths. The proposed method was validated by predicting the second slide-induced river damming using the calibrated results from the first slide. Furthermore, the second slide with deposition depth observations was employed to update the input parameters again. Through the sequential Bayesian back analysis, the probability of the river damming induced by the potentially unstable rock masses was predicted, which yielded a hazard zonation map of the barrier lake exceeding various water levels. This hazard zonation map may be employed to guide quantitative risk assessment and corresponding emergency response plans for future landslide-induced upstream backwater-inundation.
      原文链接:
    • NSTL
    • Elsevier

    Assessing the potential for reservoir induced seismicity from the Bisri dam project in Lebanon

    Basbous J.Nemer T.S.Yehya A.Maalouf E....
    13页
    查看更多>>摘要：? 2022 Elsevier B.V.Reservoir induced seismicity has been observed in multiple cases around the world. The Bisri dam project, planned to be constructed in the Bisri Valley in Lebanon, has overlooked the concerns for safety raised by experts, which puts thousands of people and various structures at risk. In this paper, we study the potential for reservoir induced seismicity from this project. We use a two-dimensional poroelastic model where fluid flow and solid deformation are coupled to estimate the change in Coulomb Failure Stress (CFS) and the rate of seismicity (R). The high permeability damage zone of the Bisri fault lies directly beneath the proposed reservoir, which allows the pore pressure to diffuse into deeper levels, decreasing the effective normal stress, destabilizing the fault, and increasing the seismicity rate. Our results show that the increase in the rate of seismicity remains decades after the initial impoundment indicating a high risk for protracted seismicity. Moreover, the activation of the Bisri fault can cause the reactivation of the Roum fault, which is a major and active branch of the Dead Sea Transform Fault that hosted the epicenters of recent and major seismic events in the region. Hence, the risk for induced seismicity from the Bisri project should be taken into consideration very seriously by the authorities.
      原文链接:
    • NSTL
    • Elsevier

    Large-scale landslide dam breach experiments: Overtopping and “overtopping and seepage” failures

    Zhou G.G.D.Li S.Lu X.Tang H....
    19页
    查看更多>>摘要：? 2022 Elsevier B.V.Landslide dams form when landslide materials reach rivers causing complete or partial blockage. It is known that overtopping water flows and seepage flows are two crucial processes that induce dam failure. In several instances, the landslide dams collapse is caused by the coupled influence of seepage flows and overtopping water. This study aims to evaluate the contribution of seepage flows to the overtopping failure of landslide dams in terms of dam stability, breach duration, and flow discharge. We conducted two field experiment tests to simulate landslide dam failure modes: overtopping failure and overtopping-seepage coupling. Results show that the internal erosion due to seepage induces the loss of fine particles, resulting in a fourfold increase in dam deformation relative to when seepage is minimal. In the case overtopping and seepage failure, the outburst duration is shortened by two-thirds, but the peak outburst discharge is increased by nearly two times compared with the pure overtopping failure. Sediments accumulate at the downstream channel for overtopping failure, but erosion is observed before accumulation when the “overtopping and seepage” failure occurs. Fine grain sizes are limited to the downstream bed for both failure modes, which indicates the equal mobility of sediments involved in the outburst flood from a landslide dam breach.
      原文链接:
    • NSTL
    • Elsevier

    The design of infrastructures in stiff jointed clay formations: A step towards a geological-geotechnical integrated approach

    Scarpelli G.Fruzzetti V.M.E.Ruggeri P.
    13页
    查看更多>>摘要：? 2022Due to its geological evolution the Mediterranean area is largely characterized by complex and weak formations. These formations make vulnerable and landslide prone many regions of the Mediterranean countries, with the consequence to expose vital infrastructures, as transportation system and lifelines, to unavoidable hazards. Recent developments in the geological field have given a comprehensive description of the processes that have originated these formations as well as the main features of this wide class of materials such as mélanges, hard soils and structurally complex formations. Differently, the translation into engineering terms of many geological aspects is still very limited and the designer is often left alone when he has to conceive a geotechnical design model (GDM) capable of capturing the design situation and the geotechnical properties of complex formations as relevant for design. Considering the operative framework outlined by the draft version of the new European code for geotechnical design (EC7), this paper presents a conceptual approach that can be followed when designing an embedded retaining structures in Stiff Jointed Clay (SJC), a specific sub-group of the complex formations, frequently affected by landslides, where, likewise in rocks, the scale effect strongly influences the selection of the representative ground properties. In particular, based on a prototype numerical model of a SJC formation implemented for one system of discontinuities, the paper will show the close relationship between the geometrical arrangement of the discontinuities, the geometry of the potential collapse mechanisms and the operational strengths to be used in the calculation models. The data from monitoring of a real case study are promising in the appropriateness of the proposed approach, despite the simplicity of the conceptual and calculation models adopted.
      原文链接:
    • NSTL
    • Elsevier