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Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering albedo (SSA) and the complex refractive index (m=n-ik) of Icelandic dust from five major emission hotspots were retrieved between 370–950 nm using online measurements of size distribution and spectral absorption (βabs) and scattering (βsca) coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured βabs and βsca increased from 0.90–0.94 at 370 nm to 0.94–0.96 at 950 nm in Icelandic dust from the different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asia. The spectral complex refractive index was retrieved by minimizing the differences between the measured βabs and βsca and those computed using the Mie theory for spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive index (n(λ)) was found to be 1.60–1.61 in the different samples and be independent of wavelength. The imaginary part (k(λ)) was almost constant with wavelength and was found to be around 0.004 at 370 nm and 0.002–0.003 at 950 nm. The estimated complex refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed in Icelandic dust may contribute to its high absorption capacity in the shortwave part of the spectrum. The k(λ) values retrieved for Icelandic dust are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing towards the near-infrared. In Icelandic dust, k(λ) between 660–950 nm was 2–8 times higher than most of the dust samples sourced in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate that has not been accounted for in climate predictions.

The stability of the surrounding rocks of large underground powerhouses is always emphasized during the construction process, especially in large-scale underground projects under construction, such as the Baihetan hydropower station in China. According to field investigations, numerical simulations and monitoring data analysis, we present a comparative analysis of the deformation and failure characteristics of the surrounding rocks of underground powerhouses on the left and right banks of the Baihetan hydropower station. The failure characteristics and deformation magnitude of the underground powerhouses on the left and right banks are quite different. Under the disadvantageous condition where the maximum principal stress intersects the axis of the powerhouse at a large angle, the left bank underground powerhouse shows prominent stress-controlled failure characteristics such as spalling, slack collapse and concrete cracking. Although the maximum principal stress is in the favorable condition which intersects the right bank powerhouse at a small angle, the relatively high intermediate principal stress with an angle subvertical to the right bank powerhouse plays an essential role in its deformation and failure, indicating that the influence of high intermediate principal stress cannot be ignored. In addition, structural plane-controlled failure and large deformation are also more evident on the right bank due to the extensive distribution of weak structural planes and complex surrounding rock properties.

Debris avalanches have complex structures due to the internal discreteness of fragmentation events. From a meso perspective, a debris avalanche is essentially a collection of debris particles of various sizes. Friction and collision events are directly influenced by the gradation of debris particles, restricting the movement process of debris avalanches. Accordingly, a series of numerical simulations have been conducted to research the influence of motion behavior based on experimental tests. The results indicate that the inhomogeneous character of a debris avalanche creates a conducive particle structure for the movement of the debris avalanche, in which the fine particles can play a role in the conversion of sliding to rolling at the bottom, causing the reduction of friction dissipation and the differentiation of particle friction resistance along the vertical direction, which continues until deposition. Sudden decreases in friction resistance occurring on high-speed, fluid-like debris avalanches are primarily correlated to the particular particle structure due to the significant inhomogeneity of particle gradation.

Landslide dams formed by successive rock slides in the same location may cause severe and long-term destruction to affected areas. However, studies on the formation of landslide dams that result from successive rock slides are still at early stages. In this paper, a flume test that could model rock fragmentation and the flow of fragmentary material is used to study the formation of landslide dams triggered by successive long-runout rock slides. The tests assess the effects of number of blocks, the number of times the blocks are released, and the initial arrangement of blocks before release on the dam geometry. The maximum and minimum landslide dam heights rise with the increasing number of blocks in each series of tests, while there is minimal or even no growth in the dam length for some series. Additionally, more block releases produce larger minimum dam height but smaller maximum dam height. Together, these results indicate that more releases are prone to fully block the flow channel by forming a steep dam. Furthermore, the initial block arrangement is also found to influence the landslide dam formation. In this study, landslide dams caused by successive rock slides are divided into two types: the stable type, namely, the landslide dam(s) already formed by the previous slide event(s) maintains general stability before the next slide lands on the dam surface; the unstable type, namely, the landslide dam(s) by the previous slide episode(s) has failed before the next damming slide occurs. Field investigations showed that slide episodes in both types of successive landslide dams are influential for the dam formation and river morphology.

Cemented tailings backfill (CTB), an evolutive man-made soil or porous medium, is extensively utilized in underground mines as a sustainable solution for the disposal of tailings (mine waste) and/or ground control. At the early stages of curing, CTB is commonly saturated and weakly cemented, and thus subjected to the risk of seismically-induced liquefaction caused by mine blasts, rock bursts and earthquakes. The resulting intrusion of liquefied backfill mass into the mine tunnels may give rise to significant casualties and loss of production. In the present study, an evolutive bounding surface plasticity model is developed to capture the hydro-mechanical response of hydrating CTB under cyclic loading. Specifically, the changes of model components (yield and plastic potential functions, etc.) due to evolution of material properties are incorporated into the prototype bounding surface model. Then, the material property changes induced by binder hydration are determined and coupled to a binder hydration model that quantifies the curing process of CTB. Therefore, the developed model can be employed to assess the cyclic response of hydrating CTB at any given time of interest during its early age of curing when seismically induced liquefaction is of primary concern. The simulated results show good agreement with the experimental data for both monotonic and cyclic loadings. The proposed model can therefore provide more insight into the behavior of early-age CTB under seismic loading, and contribute to designing cost-effective CTB structures and assessing the risk of liquefaction.

In the process of underground cavern excavation, the existence of the interlayer shear zones or large faults often makes the surrounding rock tend to be unstable or even deformed. Under the influence of interlayer shear zone C2, different degrees of deformation and failure occurred in many parts during the excavation of the Baihetan left bank underground powerhouse. Based on field monitoring and numerical calculation, this paper studies the deformation and failure characteristics of the rock mass with C2 in the whole excavation process and the failure mechanisms are analyzed. The results show that C2 has poor mechanical properties. In the process of excavation, it mainly induces two failure modes: rock collapse and shear deformation, which specifically leads to rock collapses, large deformation and shotcrete cracking in the main powerhouse, and shear deformation in the omnibus bar caves. In addition, the similarities and differences between this study and other studies on the deformation and failure of surrounding rock of underground powerhouse in recent years are discussed, and the relevant treatment measures for C2 are given. The above research results can be a reference for other related studies.

Seismicity sequence following a main earthquake usually contains much meaningful information for unveiling the focal mechanism and predicting the reoccurrence interval of large earthquakes. The spatiotemporal evolution of earthquakes before and after the 2008 Wenchuan earthquake (Ms 8.0) is analysed comprehensively in this study. The frequency-magnitude relation of the 3493 earthquake events retrieved from the database of the International Seismological Centre indicates that the adopted catalogue is complete for magnitudes ≥Ms 3.4. The seismicity during the 10 years before the Wenchuan earthquake remained stable, including the magnitudes and focal depths. However, seismicity attenuated sharply in the year following the Wenchuan earthquake, and the magnitude of earthquakes before the Wenchuan earthquake decreased gradually. The area of the seismogenic zone of the 2008 Wenchuan earthquake was smaller than the earthquake stricken area. The earthquakes that occurred in the Longmenshan fault area and adjacent area in the study period were mainly shallow earthquakes. The focal depths of earthquakes in the study area became stable gradually after the Wenchuan earthquake, mainly within the range from 10 to 16 km. The earthquakes in the study area were mainly distributed with an along-dip distance of 0–20 km, and the seismicity was distributed uniformly along the fault strike.

The 2019 Shuicheng landslide was a typical landslide in that failure occurred in the slope deposits and there was a close correlation with the antecedent rainfall. The initiation mechanism was analysed using field investigations, laboratory tests and numerical simulations and the characteristics of mass movement were quantitatively assessed. The numerical results indicated that the infiltration of rainfall decreased the shear resistance of the slope and increased the pore water pressure and soil weight, resulting in a large deformation of the slope and a gradual deterioration in its stability. After saturation, as the pore water pressure coefficient (ru) approached 0.3, the overall safety factor decreased to 1 and failure eventually occurred. Quantitative mass assessment showed that the unique terrain aggravated the erosion and entrainment effects and that the inclusion of loose material and water promoted the movement of the debris avalanche by changing it into a fluidized state, resulting in a much larger landslide volume with a long runout distance. As a result, the volume of the failed mass, which was calculated by an unmanned aerial vehicle and terrestrial laser scanning modelling techniques to be c. 4.7 × 105 m3 in the source area, almost quadrupled to >2.0 × 106 m3.

Rock damage induced by underground excavation would cause irreversible degradation in the hydro-mechanical performance of the engineering rock mass depending on the excavation method , in-situ stress, and change of ambient conditions. As exploitation of resources continues being operated at hostile depths of the Earth's lithosphere, adaptive excavation design thus becomes imperative for ensuring sustainable mining development in the increasingly challenging environment. In this study, a new thermal-mechanical framework is developed to characterize the successive blast loading, transient unloading, and air-cooling sequence for dynamic excavation in prestressed geothermal deposits. To capture the complex rock behavior across vastly different timescales, a new diagnostic tool is proposed for identifying the exact source, nature, and range of excavation damage based on the stress projection technique. By scrutinizing the rock response throughout the excavation process via loading path evolution, novel insights are obtained in this study into the underlying mechanism and relative contribution of each sub-loading process in damage generation under different geopressure , geothermal, and excavation conditions. Our calculations demonstrate quantitatively that the release of in-situ stress and air-cooling of the working environment constitute the predominant causal mechanisms of rock damage for major deep excavation projects. Furthermore, our analysis has shown explicitly that the perturbation to the redistributed stress field by tunnel ventilation could stimulate rock creeping and thus give rise to stability concern for excavations buried in highly stressed deposits of intense geothermal anomalies . The findings of our study could refine the understanding of the complex excavation response and thus contribute to improved adaptive design for excavation work in hostile geological environments.

Tailings backfill, which is a subsurface fill mass, has been extensively utilized worldwide in underground mines to fill mined-out cavities for the purposes of ground control and tailings disposal. Just after placement, very early-age backfill which commonly contains a large volume of water exhibits little or no interparticle bonding, and is subjected to the risk of liquefaction induced by routine mine blasting. In this study, a modified total-stress viscoplastic cap model is developed to investigate the blast-induced liquefaction susceptibility of very early-age fill mass under various practical backfilling and field conditions. The developed model well represents the strain-rate and fluid-compressibility dependence of nonlinear material behavior under such dynamic conditions, and also captures the development of excess pore pressure due to irrecoverable volume changes. The model is validated against a series of blast and impact tests on saturated natural soils (sand and silt) and tailings fill masses, and a good agreement is found between the experimental and simulated results. Subsequently, the model is applied to investigate the effects of drainage conditions, distance from detonation, stope size, location of retaining structure, and blast sequence on the liquefaction susceptibility of early-age fill mass after mine blasting. The results obtained from the study will provide practical insight into the blast liquefaction potential of backfill mass in field conditions.

The consolidation of a cemented mine fill is controlled by the rate of backfilling in regard to its permeability as well as the companion chemical shrinkage due to hydration reaction. A unified equation is derived in the study to delineate the one-dimensional (1D) deposition and consolidation of shrinking mine fills based on a generic description of the entangled chemo–hygro–mechanical processes. The proposed equation has taken into account the compressibility of each phase and the refinement of pore space due to phase exchange of water during hydration, which are lacking in other 1D formulations. The resulting equation would thus allow for more rational and convenient analyses of mine-fill consolidation during accretion and after deposition with a unified model. The improvement is practically at the mere expense of introducing only one additional parameter (the stiffness of solid grains) compared with existing benchmark equations. Parametric analyses performed with the proposed equation have revealed the limitations of the original Gibson and other 1D solutions in realistic assessment of mine-fill consolidation due to the lack of considerations for internal couplings. The proposed equation could also provide more reliable benchmark solutions for verification of complex numerical tools that incorporate coupled modelling of mine-fill behaviours.

Although a large number of previous researches have significantly contributed to the understanding of the quasi-static mechanical behavior of cemented tailings backfill, an evolutive porous medium used in underground mine cavities, very few efforts have been made to improve the knowledge on its response under sudden dynamic loading during the curing process. In fact, there is a great need for such information given that cemented backfill structures are often subjected to blast loadings due to mine exploitations. In this study, a coupled thermo-hydro-mechanical-chemical (THMC)-viscoplastic cap model is developed to describe the behavior of cementing mine backfill material under blast loading. A THMC model for cemented backfill is adopted to evaluate its behavior and evolution of its properties in curing processes with coupled thermal, hydraulic, mechanical and chemical factors. Then, the model is coupled to a Perzyna type of viscoplastic model with a modified smooth surface cap envelope and a variable bulk modulus, in order to reasonably capture the nonlinear and rate-dependent behaviors of the cemented tailings backfill under blast loading. All of the parameters required for the variable-modulus viscoplastic cap model were obtained by applying the THMC model to reproducing evolution of cemented paste backfill (CPB) properties in the curing process. Thus, the behavior of hydrating cemented backfill under high-rate impacts can be evaluated under any curing time of concern. The validation results of the proposed model indicate a good agreement between the experimental and the simulated results. The authors believe that the proposed model will contribute to a better understanding of the performance of hydrating cemented backfill under blasting, and also to practical risk management of backfill structures associated with such a dynamic condition.

A new derivation of the three-dimensional (3D) limit equilibrium method for slope stability analyses is presented, which applies linear algebra operations to matrices to achieve a highly efficient algorithm while maintaining the rigorousness of the formulation. It satisfies six equilibrium conditions and includes all of the components of the intercolumnar forces. The generalized 3D Morgenstern-Price's (MP) assumption for the intercolumn forces is recast into incremental forms. The advantage is that the unknowns of the different physical meanings (i.e., factor of safety (FS) and the coefficients in the MP assumption) are determined by balancing the forces and moments independently. Along with the recasting correction coefficients, they are solved with the triple nested algorithm. The numerical instability that is related to the different orders of magnitude for the residuals is avoided. The varication examples show: (i) the insensitivity of the FS to the prescribed functions in the MP assumption, (ii) the reliability of the method to cope with a complicated slope geometry (simplified methods may provide a larger FS for certain cases), and (iii) the superior efficiency of the algorithm (requires several seconds to converge). This study proposes a practical way to track the irregular 3D tension cracking by repeating the analysis and excluding the columns with the negative normal forces at the bottom. This formulation is applied to a valley landfill slope in China. In comparison to the two-dimensional analysis, there are more reasonable/cost-effective measures to increase the system stability through 3D analyses for several conditions (e.g., seismic loading).

Optimum fragmentation of rocks during blasting is pivotal for the productivity of mining and civil engineering systems. Extensive studies on the ubiquitous fragmentation phenomena in nature and artificial processes have attested to the dominant control of the effective dimensionality and material brittleness on the size distribution of fragments. In this study, by further demonstrating that the impact of brittleness on fragmentation is physically inherent in the material dimension, we present new mechanistic insights into the blast-induced rock fragmentation via integrated analytical modelling, finite element simulation and image processing. A continuous-surface viscoplastic cap model was first calibrated step-by-step against rock behavior in different pressure and strain-rate regimes on various scales. Then, rock blasting was simulated under various bench dimensions and the fracture patterns were image-processed to provide quantitative insights into blast fragmentation. Our findings suggest that the fragments become smaller and rounder while their size distribution becomes more uniform as the rock dimensions decrease. We demonstrated that at smaller rock dimensions, the equivalent increase in energy density and suppression of pressure-induced ductility can conspire to assist crack bifurcation and thus create successively finer fragments towards the unbreakable limit. We also identified significant correlations between the fragment aspect ratio and its size and uniformity of distribution, highlighting the potential use of fragment shape as an indicator for evaluating blasting performance alongside conventional grading analysis.