The stability of crown pillar is critical during the transition from open pit to underground mining. Mining-induced fractures in the pillar form water seepage channels, which can cause potential ...water inrush hazards. A microseismicity-based method to establish seepage channel network and assess damage state of rock mass in the pillar is proposed. The formation processes of seepage channels and associated rock failure mechanism were analyzed. First, the spatiotemporal evolution of the microseismic (MS) events was presented, based on which the development process of the fractured zone was determined. Second, moment tensor inversion (MTI) was utilized to interpret the focal mechanism of the MS events. A 3D rose diagram was utilized to measure the fracture orientations and determine the main fracture surfaces, and a fracture network was subsequently established. Meanwhile, the distribution characteristics of the fracture radii and volumes were discussed. The results show that shear fractures were dominant in pillar and accounted for more than 90% of all MS events. The overall damage tensor of the pillar was subsequently assessed based on the MS-derived fractures, and the maximum damage direction was determined. Third, a fast chronological expansion method was proposed to iteratively build a connected network with a combination of MS event locations and the corresponding fracture orientations. The MS-derived connected network was used to estimate the distances of event-to-event seepage, from which the shortest seepage channel from each individual event to the network was determined in chronological order. Seepage channels between hydraulic recharge and discharge points were inferred. These results could be helpful for better characterization of seepage channel development and the implementation of pillar reinforcement.
► The higher the concentration of sulfate, the greater the expansion in specimens. ► The higher the water-to-cement ratio used, the more severe the damage found. ► The chloride ions can substantially ...reduce the sulfate attack. ► The higher the concentration of chloride, the less the expansion in specimens. ► Expansion and damage can be described by a new model based on micromechanics.
This paper describes an experimental study on the expansion and subsequent damage of concrete specimens immersed in pure water, sulfate solutions of different sulfate concentrations, and mixed solutions of different sulfate and chloride concentrations. Based on experimentally obtained results, a theoretical expansion model is proposed for predicting the stresses, strains and volume expansion developed during the process of sulfate attack. The model proposed is based on the assumption that concrete may be treated as a porous visco-elastic material, and was developed by using a micromechanics approach method. The internal expansion force produced by delayed ettringite and gypsum is considered as the main cause of the expansion. The expansion model was validated using the experimental results obtained.
Avoiding and controlling dam crest cracking is one of the most difficult problems facing high core rockfill dams of more than 100 m. However, few studies have been conducted on the characteristics ...and causes of dam crest cracking based on long-term measurement data. In this study, a real case of a dam suffering cracking at the crest was studied. The dam has a maximum height of 186 m and has been in service for 10 years. The spatiotemporal characteristics of the dam crest cracking were determined based on monitoring data obtained using crack monitoring instruments, radar detection, seismic refraction tomography, and pit exploration. The causes of dam cracking were analyzed based on the deformation inclination and strain index. The factors controlling the cracking (such as the dam structure, geological structure, and materials' properties) were investigated. The results show the following. 1) The cracks mainly occurred at the interface between the core wall and the downstream dam shell. 2) The cracks mainly developed during the impoundment and operation periods with high water levels, and there was no convergence trend within the 10 years of operation. 3) Uneven settlement and uneven horizontal displacement were the main reasons for the crack formation. 4) The factors influencing the cracking include dam zoning, the geological structure, wetting, and the rheological properties of the rockfill materials, and the reservoir level. The results of this study provide an important engineering reference for the prevention and control of dam crest cracking in high rockfill dams.
•Spatiotemporal characteristics of the dam crest cracking were revealed.•The causes of dam cracking were analyzed through inclination and strain index.•It is shown that uneven deformation is the main reason for cracks.•The influences of structure, material and geology on cracks were discussed.
Cavitation damage is a micro, high-speed, multi-phase complex phenomenon caused by the near-wall bubble group collapse. The current numerical simulation method of cavitation mainly focuses on the ...collapse impact of a single cavitation bubble. The large-scale simulation of the cavitation bubble group collapse is difficult to perform and has not been studied, to the best of our knowledge. In this study, the equivalent model of impact loading of acoustic bubble collapse micro-jets is proposed to study the cavitation erosion damage of materials. Based on the theory of the micro-jet and the water hammer effect of the liquid–solid impact, an equivalent model of impact loading of a single acoustic bubble collapse micro-jet is established under the principle of deformation equivalence. Since the acoustic bubbles can be considered uniformly distributed in a small enough area, an equivalent model of impact loading of multiple acoustic bubble collapse micro-jets in a micro-segment can be derived based on the equivalent results of impact loading of a single acoustic bubble collapse micro-jet. In fact, the equivalent methods of cavitation damage loading for single and multiple near-wall acoustic bubble collapse micro-jets are formed. The verification results show the law of cavitation deformation of concrete using equivalent loading is consistent with that of a micro-jet simulation, and the average relative errors and the mean square errors are insignificant. The equivalent method of impact loading proposed in this paper has high accuracy and can greatly improve the calculation efficiency, which provides technical support for numerical simulation of concrete cavitation.
Efficient approaches for slope reliability computation with spatially variable soil properties are of great interest. In this paper, an advanced first-order second-moment method (AFOSM) combined with ...the limit equilibrium method (LEM) is adopted for efficient slope reliability analysis considering cross-correlated random fields of shear strength parameters. In the slope reliability analysis, random fields of the soil shear strengths are locally discretized along the slip surface. A systematic framework is presented for constructing a full correlation matrix incorporating both autocorrelation and cross correlation for the shear strength parameters in multiple soil layers, which could be useful for multi-layered slope reliability analysis involving cross-correlated spatially variable soil properties. A single-layered
c
–
φ
slope and a two-layered
c
–
φ
slope are investigated to illustrate and validate the proposed approach. As regards the examples, parametric studies show that slope reliability decreases with an increase in the autocorrelation distance and the cross-correlation coefficient between
c
and
φ
. Moreover, the effect of the vertical autocorrelation distance on the slope reliability is much more significant than that of the horizontal autocorrelation distance. The directly searched minimum reliability indices are all smaller than those computed with the deterministic critical slip surface. The slope reliability indices are affected by the number of slices, however, if a sufficient number of slices are used to represent the random field, increasing the number of slices does not significantly affect the reliability indices. The AFOSM is quite efficient for slope reliability analysis with spatially variable soil properties and its accuracy is satisfactory compared to the MCS. Although only a two-layered slope is considered in the illustrative example for convenient demonstration and easy understanding, the AFOSM is generally applicable to slopes with multiple soil layers.
•Glacier-related hazards occur worldwide, resulting in landslide dams with ice.•Overtopping process of a landslide dam with different ice amounts are studied.•Ice melt increases dam erodibility, ...reduces dam height, leading to an earlier overtopping.•Floods become larger and peak arrival time comes earlier with a larger ice amount.
With global warming, glacial collapse chain disasters have frequently occurred in high-mountain areas. In particular, the ice avalanche-glacial debris flow/landslide-barrier lake-flood burst chain disaster caused the most serious consequences. Different from the general landslide dam consisted of rocks and soils, the landslide dam initiated by ice avalanches contains a considerable amount of ice. The appearance of ice will influence the overall performance of the landslide dam by melting, which may cause differential settlements, local weak zones, a more porous structure, and a lower erosion resistance of the landslide dam. Such changes in the erodibility and geometry of the landslide dam will further affect the dam overtopping and flood routing process, which have not been investigated yet and urgently require further study. Therefore, in this study, a preliminary study of the effects of different ice fractions of the landslide dam is conducted, which mainly involves changes in the dam erodibility, the dam geometry, the overtopping development, the final breach size, the process of downstream flood routing, etc. Results show that with the increasing amount of ice melting, the coefficient of soil erodibility and the soil void ratio increase significantly, implying a more erodible dam material and a looser dam structure. The melting of ice can also induce obvious dam settlement, which further results in an earlier dam burst and a shorter rescue time. With the increasing initial ice amount in the landslide dam, the overtopping process develops more rapidly, the breach expands greater both horizontally and vertically, the subsequent flood becomes larger, and the peak arrival time comes earlier.
The transmission of sulfate ions in concrete results in formation of calcium sulfoaluminate crystals due to chemical reactions. The expansion of calcium sulfoaluminate crystals is the main cause of ...concrete corrosion damage. In this study, ultrasonic analysis was used to detect the modulus change of concrete due to sulfate corrosion to obtain the basic law of corrosion damage evolution. An exponential growth model was developed for the internal expansion force based on the chemical reaction rate of calcium sulfoaluminate crystallization. Then, the evolution equation of the number density of microcracks was derived based on their initiation and balance conditions. Finally, a statistical model was developed for the concrete damage evolution by integrating the volume of microcracks. It is shown that the statistical evolution model can well characterize the evolution of concrete corrosion damage.
A catalyst determines the mechanism of an organic chemical reaction, thus enabling the commercially viable formation of desired material products. Biopolymers offer new opportunities for the ...construction of catalysts by virtue of their biocompatibility, environmental benignity, and sustainability, as well as their low cost. Biopolymers are especially useful as carriers and precursors in catalysis application. The employment of biocompatible and biosustainable collagen and silk fibroin materials will revolutionize state-of-the-art electronic devices and systems that currently rely on conventional technologies. In this review, we first consider the ordered hierarchical structure, origin, and processing methods of collagen and silk fibroin. Then, the unique advantages and applicability of collagen and silk fibroin for constructing catalysts are summarized. Moreover, a summary of the state-of-the-art design, fabrication, and application of collagen- and silk fibroin-based catalysts, as well as the application of collagen- and silk-based catalysts, is presented by focusing on their roles as carriers and precursors, respectively. Finally, challenges and prospects are assessed for the construction and development of collagen and silk fibroin-based catalysts.
Sulfate attack tests were performed on concrete samples with three water-to-cement ratios, and micro-crack growth patterns on concrete surfaces were recorded. The expansive stress and crack ...nucleation caused by delayed ettringite formation (DEF) were studied using X-ray diffraction and scanning electron microscopy. By means of a digital image processing technology, fractal dimensions of surface cracking patterns were determined, which monotonously increase during corrosion. Moreover, it is shown that the change of fractal dimensions is directly proportional to accumulation of DEF, and therefore, a simple theoretical model could be proposed to describe the micro-crack evolution in concretes under sulfate attack.
Tungsten fiber-reinforced Zr41.25Ti13.75Cu12.5Ni10Be22.5 amorphous matrix composites (hereinafter referred to as Wf/Zr-based amorphous matrix composites) are considered as a potential new generation ...of projectile material, while the penetration behavior of Wf/Zr-based amorphous matrix composites is not fully clear yet. In order to better understand the penetration behavior of this composite material and study its armor-piercing performance, a ballistic experiment was performed and the hardness and microstructure around the crater of a target material were studied. A ballistic experiment was performed with a projectile of Wf/Zr-based amorphous matrix composite and a target of 4043 steel. After the ballistic experiment, the target was cut through the crater using a wire cutting machine into a sample with size 150 mm × 40 mm × 20 mm, which was later polished by different types of sandpaper. The micro-hardness was analyzed in a micro-hardness tester, and the microstructure was observed by SEM. According to this study, three layers were identified in the direction lateral to the crater, consisting of a martensite layer, a deformation strengthening layer, and the original structure layer. Moreover, the martensite layer initially thickened and then thinned in the direction longitudinal to the crater.
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