MXene materials have got great attention from researchers of environmental treatment for the great electrochemical performance. Monolayer-Ti3C2Tx (Tx is the surface terminal groups such as —O, —OH and/or —F species), as a typical structural MXene, always shows better chemical-physical characteristics than multilayer-Ti3C2Tx. Thus, we prepared monolayer-Ti3C2Tx electrode by HF etching method and absolute ethyl alcohol intercalation-delamination treatment for capacitive deionization (CDI). The prepared monolay-Ti3C2Tx shows a higher specific surface area (235.6 m2/g) and a thinner thickness (0.8 nm). Moreover, a series of systematic investigation demonstrated that monolayer-Ti3C2Tx has obvious promotional phenomenon on electrochemical properties (e.g., mass specific capacitance increased from 52.1 F/g to 144.7 F/g). The NaCl adsorption capacity of monolayer-Ti3C2Tx, is 30.7 mg/g in 1000 mg/L NaCl solution at 1.2 V. We concluded that the electro-sorption mechanism could be expressed as double electric layer and monolayer coverage by a good fitting of Langmuir isotherms and the pseudo-second-order kinetics equation. This work would provide a new strategy for the application of monolayer-Ti3C2Tx material in wastewater treatment in the future.
Lithium (Li) metal is considered as the candidate for the next generation of Li metal battery (LMB) anodes due to its high capacity and the lowest potential, which is expected to meet the requirements of energy storage devices. Unfortunately, the uncontrollable growth of Li dendrites during the charge/discharge process, as well as the resulting problems of poor cycling stability, low coulomb efficiency and safety risk, has restricted the commercialization of Li anode. Herein, an in-situ interfacial film containing three-dimensional (3D) rod-like micron-structure silver (Ag) is constructed on the surface of the Li metal. Due to the 3D rod-like micron-structure used to homogenize the distribution of current density, achieving uniform nucleation and growth of electrodeposited Li, the produced Li-Ag alloy was employed to restrain the formation of “dead” Li and the in-situ formed LiNO3 was utilized to facilitate the stability of solid-electrolyte interface (SEI) film, so the growth of dendritic Li is suppressed via the synergistic effect of structure and surface chemistry regulation. The obtained Li anode can achieve cycling stability at a high current density of 10 mA/cm2. This work considers multiaspect factors inducing uniform Li electrodeposition, and provides new insights for the commercialization of LMB.
Desulfurization and denitrification by using ozone has been widely used in recent years, but the technology for generating ozone at this stage has some shortcomings, which needs to be improved urgently. This paper advocates using mud-phosphorous slurry to produce ozone, which is environmentally friendly and economical. At the same time, SO2 and NOx can be removed from mud-phosphorous slurry simultaneously. The amount of ozone generated during desulfurization and denitrification is particularly important, thus, this paper studies the effects of the temperature of reaction, oxygen content and solid-liquid ratio of mud-phosphorus slurry on the amount of ozone generated. The results showed that under the optimum conditions (the reaction temperature was 60 °C, the solid-liquid ratio of mud-phosphorus slurry was 5.0 g/40 mL, the oxygen content was 30%), the amount of ozone was the largest, and the maximum generation amount was 573.8 mg/m3. Under these conditions, the removal rates of SO2 and NOx can reach 99.5% and 99% respectively. This paper also analyzes the products of desulfurization and denitrification, and proposes the corresponding reaction mechanism.
A light and temperature dual responsive copolymer, poly(7-(4-vinylbenzy-loxyl) -4-methylcoumarin-co-N-vinyl caprolactam-co-tri(ethylene glycol)methyl ether methacrylate) (PVNM), was grafted on the surface of dopamine-based mesoporous silica nanoparticles (MSNs). The resulting polymer brush, MSNs-g-PVNM, was characterized by FT-IR, TEM, TGA and XPS. The dual responsive behaviors of MSNs-g-PVNM were systematically studied. With imidacloprid as the model guest pesticide, the loading percentage and loading efficiency of the polymer brush were determined as 9.2% and 40.6%, respectively. The release efficiency of imidacloprid in MSNs-g-PVNM was the lowest value of 5.4% at 20 °C and 365 nm, and it reached the highest value of 52.4% at 50 °C and 254 nm. The loss percentage of imidacloprid on the leaves contained imidacloprid-loaded MSNs-g-PVNM (8.4%) was much less than that contained only imidacloprid (25.2%) after three rinses. It was confirmed that the release process of imidacloprid was well regulated through changing external conditions such as light and temperature.
Inner Mongolian serpentine ore was subjected to sulfuric acid leaching tests, and the effects of the leaching process parameters on the leaching efficiency of different metals were investigated. The leaching efficiency of Mg, Fe, Al, Ni, and Co reaches 93.98%, 60.09%, 82.08%, 90.58%, and 94.06%, respectively, under the leaching conditions of 5 mol/L H2SO4, liquid/solid ratio of 4 mL/g, and leaching temperature 100 °C. Hence, the valuable metals in serpentine were effectively recovered by sulfuric acid leaching. The leaching behaviors of Mg, Fe, and a small amount of Al were analyzed using X-ray diffraction. The results show that the unreacted Mg and Fe remained as MgFe2O4, and Al formed Al2Si2O5(OH)4 in the leaching residue. The kinetics of Mg and Ni in the leaching process was studied respectively. The leaching kinetics of Mg conformed to the shrinking core model with an activation energy of 16.95 kJ/mol, which was controlled by the combination of the diffusion and chemical reaction. The leaching kinetics of Ni accorded with the Avrami equation with an activation energy of 11.57 kJ/mol, which was controlled by diffusion. In the study, the valuable metal elements were extracted from serpentine minerals with high efficiency and low cost, which possessed important practical values.
Oolitic hematite is an iron ore resource with rich reserves, complex composition, low grade, fine disseminated particle sizes, and a unique oolitic structure. In this study, a microwave-assisted suspension magnetization roasting technology was proposed to recover and utilize the ore. The results showed that under the conditions of microwave pretreatment temperature of 1050 °C for 2 min, a magnetic concentrate with an iron grade of 58.72% at a recovery of 89.32% was obtained by microwave suspension magnetization roasting and magnetic separation. Moreover, compared with the no microwave pretreatment case, the iron grade and recovery increased by 3.17% and 1.58%, respectively. Microwave pretreatment increased the saturation magnetization of the roasted products from 24.974 to 39.236 (A·m2)/kg and the saturation susceptibility from 0.179×10−3 m3/kg to 0.283×10−3 m3/kg. Microcracks were formed between the iron and gangue minerals, and they gradually extended to the core of oolite with the increase in the pretreatment time. The reducing gas diffused from outside to inside along the microcracks, which promoted the selective transformation of the weak magnetic hematite into the strong magnetic magnetite.
To reveal the potential effect of surfactant on improving surface wettability of copper ore, the droplet spreading behavior of sulfuric acid solution contained surfactant was visualized using high-speed camera and an image processing method, and the solid-liquid interaction was discussed in this study. The results show that liquid surface tension and ore surface roughness are the main factors affecting surface wettability. The effect of sulfuric acid solution concentration and surfactants on the surface wettability of ore is revealed via quantitative spreading area, spreading coefficient, and contact angle. The results of droplet spreading experiment show that the higher concentration of surfactant and sulfuric acid solution result in improving the wettability of ore, spreading coefficient, and decreasing contact angle. The “leaching reaction coefficient” and “surface activity coefficient” are introduced to modify the mathematical expression of the equilibrium contact angle.
The increasing demand for iron ore in the world causes the continuous exhaustion of magnetite resources. The utilization of high-phosphorus iron ore becomes the focus. With calcium carbonate (CaCO3), calcium chloride (CaCl2), or calcium sulfate (CaSO4) as additive, the process of direct reduction and phosphorus removal of high-phosphorus iron ore (phosphorus mainly occurred in the form of Fe3PO7 and apatite) was studied by using the technique of direct reduction-grinding-magnetic separation. The mechanism of calcium compounds to reduce phosphorus was investigated from thermodynamics, iron metallization degree, mineral composition and microstructure. Results showed that Fe3PO7 was reduced to elemental phosphorus without calcium compounds. The iron-phosphorus alloy was generated by react of metallic iron and phosphorus, resulting in high phosphorus in reduced iron products. CaCO3 promoted the reduction of hematite and magnetite, and improved iron metallization degree, but inhibited the growth of metallic iron particles. CaCl2 strengthened the growth of iron particles. However, the recovery of iron was reduced due to the formation of volatile FeCl2. CaSO4 promoted the growth of iron particles, but the recovery of iron was drastically reduced due to the formation of non-magnetic FeS. CaCO3, CaCl2 or CaSO4 could react with Fe3PO7 to form calcium phosphate (Ca3(PO4)2). With the addition of CaCO3, Ca3(PO4)2 was closely combined with fine iron particles. It is difficult to separate iron and phosphorus by grinding and magnetic separation, resulting in the reduced iron product phosphorus content of 0.18%. In the presence of CaCl2 or CaSO4, the boundary between the generated Ca3(PO4)2 and the metallic iron particles was obvious. Phosphorus was removed by grinding and magnetic separation, and the phosphorus content in the reduced iron product was less than 0.10%.
Columnar jointed rock mass with unique geometric and geological properties is one spectacular example of geometrical order in nature. Columnar joints are generally accepted to be formed by spatially uniform volume contraction during cooling. In this paper, substantial field work was performed to study the geological characteristics of irregular columnar jointed basalt on the left bank dam foundation in the Baihetan Hydropower Station, where the columnar jointed rock mass is extensively exposed due to excavation. The quantitative measurements of the sizing of polygonal crack pattern of columnar joints and assessment of their degree of irregularity were summarized. Considering the irregularity of polygonal crack pattern, a modified Voronoi polygon (MVP) method was developed to model the special polygonal crack pattern of columnar joints. The new polygonal pattern obtained by the MVP method consists of a large number of irregular polygons, of which the degree of irregularity is consistent with the field measurement results. This method can reproduce the rapid evolution from an initial ideal regular hexagonal pattern to a final actual irregular polygonal pattern as the degree of irregularity increases. The compression tests of columnar jointed rock mass with different irregularity show that the geometric irregularity has a great influence on its mechanical properties. This numerical construction method provides a reliable way to reconstruct columnar joint structure with specific polygonal crack pattern, which is consistent with onsite columnar jointed basalt.
Based on the field destructive test of six rock-socketed piles with shallow overburden, three prediction models are used to quantitatively analyze and predict the intact load-displacement curve. The predicted values of ultimate uplift capacity were further determined by four methods (displacement controlling method (DCM), reduction coefficient method (RCM), maximum curvature method (MCM), and critical stiffness method (CSM)) and compared with the measured value. Through the analysis of the relationship between the change rate of pullout stiffness and displacement, a method used to determine the ultimate uplift capacity via non-intact load-displacement curve was proposed. The results show that the predicted value determined by DCM is more conservative, while the predicted value determined by MCM is larger than the measured value. This suggests that RCM and CSM in engineering applications can be preferentially applied. Moreover, the development law of the change rate of pullout stiffness with displacement agrees well with the attenuation form of power function. The theoretical predicted results of ultimate uplift capacity based on the change rate of pullout stiffness will not be affected by the integrity of the curve. The method is simple and applicable for the piles that are not loaded to failure state, and thus provides new insights into ultimate uplift capacity determination of test piles.
To describe the deformation and strength characteristics of the corroded rock-like specimens containing a single crack under uniaxial compression, a damage constitutive model combining hydro-chemical damage with coupling damage of micro-flaws and macro-cracks is proposed. Firstly, based on phenomenological theory, the damage variable of the rock-like specimens subjected to water environment erosion and chemical corrosion is obtained. Secondly, a coupled damage variable for cracked rock-like specimens is derived based on the Lemaitre strain equivalence hypothesis, which combines the Weibull statistical damage model for micro-flaws and the fracture mechanics model for a macro single crack. Then, considering the residual strength characteristics of the rock-like materials, the damage variable is modified by introducing the correction coefficient, and the damage constitutive model of the corroded rock-like specimens with a single crack under uniaxial compression is established. The model is verified by comparing the experimental stress — strain curves, and the results are in good agreement with those provided in the literature. Finally, the correction coefficient of the damage variable proposed in this paper is discussed. The damage constitutive model developed in this paper provides an effective method to describe the stress — strain relationship and residual strength characteristics of the corroded rock-like specimens with a single crack under uniaxial compression.
To reduce geological disasters caused by expansive soil, it is crucial to use a new type of modified material to rapidly improve soil strength instead of traditional soil improvement materials such as lime and cement. Nanographite powder (NGP) has excellent properties, such as high adsorption, conductivity, and lubrication, since it has the characteristics of small size, large specific surface area, and high surface energy. However, previous studies on the improvement of expansive soil with NGP are not processed enough. To study the improvement effect of NGP on expansive soil, non-load swelling ratio tests, consolidation tests, unconfined compressive strength tests, mercury injection tests, and micro-CT tests on expansive soil mixed with different NGP contents were performed. The results show that the non-load swelling ratio, mechanical properties, and porosity of expansive soil show some increasement after adding NGP. The strength of expansive soil reaches the maximum when the NGP content is 1.450%. The cumulative mercury volume and compressive strain of expansive soil reach the maximum with the 2.0% NGP content. Finally, the modification mechanism of swelling, compressibility, microstructure, and compressive strength of expansive soil by NGP is revealed.
Adding polypropylene (PP) fibers and coarse aggregates has become a popular way to enhance the strength and stability of the cemented tailings backfilling (CTB) body. It is essential to explore the influence of tailings-aggregate ratio and fiber content on the mechanical properties of CTB samples. The comprehensive tests of the unconfined compressive strength (UCS), slump and microstructure were designed, and the regression models were established to characterize the effect of the strength, ductility and fluidity. The results indicate that the tailings-aggregate ratio of 5:5 and PP fiber content of 0.5 kg/m3 are the optimum point considering the UCS, cracking strain, peak strain and post-peak ductility. The tailings-aggregate ratio is consistent with the unary quadratic to the UCS and a linear model with a negative slope to the slump. Microstructural analysis indicates that PP fiber tends to bridge the cracks and rod-mill sand to serve as the skeleton of the paste matrix, which can enhance the compactness and improve the ductility of the CTB. The results presented here are of great significance to the understanding and application of coarse aggregates and fibers to improve the mechanical properties of CTB.
Traditional soil additives like Portland cement and lime are prone to cause the brittle fracture behavior of soil, and possibly, environmental impacts. This study explores the potential use of polyurethane organic polymer and sisal fiber in improving the mechanical performance of sand. The effects of polymer content, fiber content, and dry density on the unconfined compressive strength (UCS) and direct tensile strength (DTS) of the polymer-fiber-sand composite were evaluated. The results showed significant increase in UCS and DTS of the reinforced sand with the increase of polymer content, fiber content, and dry density. At high dry density condition, a single peaked stress — strain curve is often observed. Higher polymer content is beneficial to increasing the peak stress, while higher fiber content contributes more to the post-peak stress. The combined use of polymers and fibers in soil reinforcement effectively prevents the propagation and development of cracks under the stress. Scanning electron microscopy (SEM) test was also performed to investigate the micro-structural changes and inter-particle relations. It was found through SEM images that the surface coating, bonding, and filling effects conferred by polymer matrix greatly enhance the interfacial interactions, and hence provide a cohesive environment where the strength of fibers could be readily mobilized.
The aim of this paper is to investigate the effect of nitrite intercalated Mg−Al layered double hydroxides (Mg−Al LDH−NO2) on mortar durability under the coexisting environment of Cl− and SO42−. Cl− and SO42− binding properties of Mg−Al LDH−NO2 in simulated concrete pore solutions, Cl− and SO42− diffusion properties of mortars with Mg−Al LDH−NO2 were examined. The steel corrosion and resistance of mortar against SO42− attack were also evaluated. The results indicate that Mg−Al LDH−NO2 can effectively adsorb the Cl− and SO42− in simulated concrete pore solution, and inhibit the diffusion of Cl− and SO42− into cement mortars. The presence of SO42− can greatly affect the uptake amount of Cl−, and there is a coupled effect of Cl− and SO42− on their penetration into mortar specimens. In addition, Mg−Al LDH−NO2 can greatly upgrade the resistance of mortars against SO42− attack and well prevent the steel from corrosion. However, Cl− will aggravate the SO42− attack and SO42− can initially decrease and then increase the steel corrosion.
The temperature distribution in laminated beams underging thermal boundary conditions has been investigated. The thermal boundary conditions are general and include various combinations of prescribed heat fluxes and temperatures at the edges. An analytical solution of temperature for the laminated beam is present on the basis of the heat conduction theory in this paper. The proposed method is applicable to the beams with arbitrary thickness and layer numbers. Due to the complexity of the boundary conditions, the temperature field to be determined was considered from two sources. The first part was the temperature field from the complex temperature conditions at two edges of the laminated beam. The solution for the temperature of the first part was constructed to satisfy temperature boundary conditions at two edges. The second part was the temperature field from the upper and lower surface temperatures without taking account of the thermal conditions at two edges. In this part, the exact solution for the temperature was obtained based on the heat conduction theory. The convergence of the solution was examined by analyzing terms of Fourier series. The validity and feasibility of the proposed method was verified by comparing theoretical results with numerical results due to the equivalent single layer approach and the finite element method (FEM). The influences of surface temperatures, beam thicknesses, layer numbers and material properties with respects to the solution of the temperature field of the beam were investigated via a series of parametric studies.
The hydraulic reclamation coral clay is a new type of clay, formed during the sorting process of coral island reef reclamation. The foundation of the hydraulic reclamation coral reef consists of coral sand, silt, and clay. The part of the particles with particle size less than 0.075 mm contain more than 50% forms clay. As a new type of clay, the geotechnical properties were rarely reported in previous studies. In this paper, the physical and mechanical properties, microstructure and mineral composition were comprehensively researched by a series of laboratory tests. The results show that coral clay is a low liquid limit clay with high pore ratio and high saturation. From the aspect of mineral compositions, the coral clay studied consists of calcite and aragonite, while the chemical composition of it is calcium carbonate. The void ratio has a significant effect on the compressive properties of coral clay. With the increase of the void ratio, the compression coefficient a1–2 and compression index Cc gradually increase, and the compression modulus Es gradually decreases. The undrained stress — strain curve of coral clay shows a strain-softening behavior, and the peak strength and residual strength are positively linear correlated with confining pressure.
Considering the variation of cohesion along the depth, the upper bound solution of active earth pressure for a rough inclined wall with sloped backfill is formulated based on a log-spiral failure mechanism. For a more accurate prediction, the influence of intermediate principal stress is taken into consideration using the unified strength theory. Converting the search for the active pressure to an optimization problem, the most critical failure surface can be located by a natural selection-based gravitational search algorithm (GSA). The proposed method is validated compared with existing methods for noncohesive and cohesive cases and proved to be more accordance with the limit equilibrium solution. The influences of the variation of soil cohesion and intermediate principal stress on active earth pressure coefficient are then fully studied. It can be concluded that both the variations of soil cohesion and intermediate principal stress have a significant influence on the active earth pressure coefficient.
In the process of deep projects excavation, deep rock often experiences a full stress process from high stress to unloading and then to impact disturbance failure. To study the dynamic characteristics of three-dimensional high stressed red sandstone subjected to unloading and impact loads, impact compression tests were conducted on red sandstone under confining pressure unloading conditions using a modified split Hopkinson pressure bar. Impact disturbance tests of uniaxial pre-stressed rock were also conducted (without considering confining pressure unloading effect). The results demonstrate that the impact compression strength of red sandstone shows an obvious strain rate effect. With an approximately equal strain rate, the dynamic strength of red sandstone under confining unloading conditions is less than that in the uniaxial pre-stressed impact compression test. Confining pressure unloading produces a strength-weakening effect, and the dynamic strength weakening factor (DSWF) is also defined. The results also indicate that the strain rate of the rock and the incident energy change in a logarithmic relation. With similar incident energies, unloading results in a higher strain rate in pre-stressed rock. According to the experimental analysis, unloading does not affect the failure mode, but reduces the dynamic strength of pre-stressed rock. The influence of confining pressure unloading on the shear strength parameters (cohesion and friction angle) is discussed. Under the same external energy impact compression, pre-stressed rock subjected to unloading is more likely to be destroyed. Thus, the effect of unloading on the rock mechanical characteristics should be considered in deep rock project excavation design.
Traditional mechanical rock breaking method is labor-intensive and low-efficient, which restrictes the development of deep resources and deep space. As a new rock-breakage technology, microwave irradiation is expected to overcome these problems. This study examines the failure characteristics, weakening law, and breakdown mechanism of deep sandstone (depth=1050 m) samples in a microwave field. The macroscopic and microscopic properties were determined via mechanical tests, mesoscopic tests, and numerical simulations. Microwave application at 1000 W for 60 s reduced the uniaxial compressive strength of the sandstone by 50%. Thermal stress of the sandstone was enhanced by uneven expansion of minerals at the microscale. Moreover, the melting of some minerals in the high-temperature environment changed the pore structure, sharply reducing the macroscopic strength. The temperature remained high in the lower midsection of the sample, and the stress was concentrated at the bottom of the sample and along its axis. These results are expected to improve the efficiency of deep rock breaking, provide theoretical and technical support for similar rock-breakage projects, and accelerate advances in deep-Earth science.
When underground cavities are subjected to explosive stress waves, a uniquely damaged zone may appear due to the combined effect of dynamic loading and static pre-load stress. In this study, a rate-dependent two-dimensional rock dynamic constitutive model was established to investigate the dynamic fractures of rocks under different static stress conditions. The effects of the loading rate and peak amplitude of the blasting wave under different confining pressures and the vertical compressive coefficient (K0) were considered. The numerical simulated results reproduced the initiation and further propagation of primary radial crack fractures, which were in agreement with the experimental results. The dynamic loading rate, peak amplitude, static vertical compressive coefficient (K0) and confining pressure affected the evolution of fractures around the borehole. The heterogeneity parameter (m) plays an important role in the evolution of fractures around the borehole. The crack propagation path became more discontinuous and rougher in a smaller-heterogeneity parameter case.
With regard to blasting in deep rock masses, it is commonly thought that an increase in the in-situ stress will change the blast-induced rock crack propagation and ultimately affect rock fragmentation. However, little attention has been given to the change in seismic wave radiation when the fractured zone changes with the in-situ stress. In this study, the influences of in-situ stress on blast-induced rock fracture and seismic wave radiation are numerically investigated by a coupled SPH-FEM simulation method. The results show that the change in blast-induced rock fracture with in-situ stress has a considerable effect on the seismic wave energy and composition. As the in-situ stress level increases, the size of the fractured zone is significantly reduced, and more explosion energy is transformed into seismic energy. A reduction in the size of the fractured zone (seismic wave source zone) results in a higher frequency content of the seismic waves. In a nonhydrostatic in-situ stress field, blast-induced cracks are most suppressed in the direction of the minimum in-situ stress, and thus the seismic waves generated in this direction have the highest energy density. In addition to P-waves, S-waves are also generated when a circular explosive is detonated in a nonhydrostatic in-situ stress field. The S-waves result from the asymmetrical release of rock strain energy due to the anisotropic blast-induced fracture pattern.
Eccentric decoupling blasting is commonly used in underground excavation. Determination of perimeter hole parameters (such as the blasthole diameter, spacing, and burden) based on an eccentric charge structure is vital for achieving an excellent smooth blasting effect. In this paper, the Riedel-Hiermaier-Thoma (RHT) model was employed to study rock mass damage under smooth blasting. Firstly, the parameters of the RHT model were calibrated by using the existing SHPB experiment, which were then verified by the existing blasting experiment results. Secondly, the influence of different charge structures on the blasting effect was investigated using the RHT model. The simulation results indicated that eccentric charge blasting has an obvious pressure eccentricity effect. Finally, to improve the blasting effect, the smooth blasting parameters were optimized based on an eccentric charge structure. The overbreak and underbreak phenomena were effectively controlled, and a good blasting effect was achieved with the optimized blasting parameters.
Aiming at the circular chamber under uniform stress field in deep energy storage and mining, analytical solutions of stress and plastic zone of the surrounding rock under different far-field stress and internal pressure were derived based on bi-modulus theory and the elastic-brittle-ideal plastic constitutive model. Evolution trend of the elastic-plastic stress and plastic region with different elastic constant ratios and residual strength coefficients were analyzed in details. Results revealed that when the internal pressure was small, the three-direction principal stress was compressive stress and the stress field distribution of the surrounding rock was not affected by the moduli difference. The obtained solution was consistent with the solution from the elastic-brittle plastic drop model under the equal modulus theory. On the other hand, when the internal pressure was large, the tangential stress was changed. The surrounding rock can be divided into three zones, i.e., tensile plastic zone (TPZ), tensile elastic zone (TEZ) and compressive elastic zone (CEZ). The tensile and compressive dual modulus had significant influence on the demarcation point between TEZ and CEZ. In addition, the strength drop and the dual modulus characteristic had a coupling effect on the stress distribution in the surrounding rock. The related achievements further enrich the theory of deep rock mechanics.
Rock mass large deformation in underground powerhouse caverns has been a severe hazard in hydropower engineering in Southwest China. During the development of rock mass large deformation, a sequence of fractures was generated that can be monitored using microseismic (MS) monitoring techniques. Two MS monitoring systems were established in two typical underground powerhouse caverns featuring distinct geostress levels. The MS b-values associated with rock mass large deformation and their temporal variation are analysed. The results showed that the MS b-value in course of rock mass deformation was less than 1.0 in the underground powerhouse caverns at a high stress level while larger than 1.5 at a low stress level. Prior to the rock mass deformation, the MS b-values derived from both the high-stress and low-stress underground powerhouse caverns show an incremental decrease over 10% within 10 d. The results contribute to understanding the fracturing characteristics of MS sources associated with rock mass large deformation and provide a reference for early warning of rock mass large deformation in underground powerhouse caverns.
Source location is the core foundation of microseismic monitoring. To date, commonly used location methods have usually been based on the ray-tracing travel-time technique, which generally adopts an L1 or L2 norm to establish the location objective function. However, the L1 norm usually achieves low location accuracy, whereas the L2 norm is easily affected by large P-wave arrival-time picking errors. In addition, traditional location methods may be affected by the initial iteration point used to find a local optimum location. Furthermore, the P-wave arrival-time data that have travelled long distances are usually poor in quality. To address these problems, this paper presents a microseismic source location method using the Log-Cosh function and distant sensor-removed P-wave arrival data. Its basic principles are as follows: First, the source location objective function is established using the Log-Cosh function. This function has the stability of the L1 norm and location accuracy of the L2 norm. Then, multiple initial points are generated randomly in the mining area, and the established Log-Cosh location objective function is used to obtain multiple corresponding location results. The average value of the 50 location points with the largest data field potential values is treated as the initial location result. Next, the P-wave travel times from the initial location result to triggered sensors are calculated, and then the P-wave arrival data with travel times exceeding 0.2 s are removed. Finally, the aforementioned location steps are repeated with the denoised P-wave arrival dataset to obtain a high-precision location result. Two synthetic events and eight blasting events from the Yongshaba mine, China, were used to test the proposed method. Regardless of whether the P-wave arrival data with long travel times were eliminated, the location error of the proposed method was smaller than that of the L1/L2 norm and trigger-time-based location method (TT1/TT2 method). Furthermore, after eliminating the P-wave arrival data with long travel distances, the location accuracy of these three location methods increased, indicating that the proposed location method has good application prospects.
As an essential part of the industrial Internet of Things (IoT) in power systems, the development of advanced metering infrastructure (AMI) facilitates services such as energy monitoring, load forecasting, and demand response. However, there is a growing risk of privacy disclosure with the wide installation of smart meters, for they transmit readings and sensitive data simultaneously. To guarantee the confidentiality of the sensitive information and authenticity of smart meter readings, we proposed a privacy-preserving scheme based on digital watermarking and elliptic-curve cryptography (ECC) asymmetric encryption. The sensitive data are encrypted using the public key and are hidden in the collected readings using digital watermark. Only the authorized user can extract watermark and can decrypt the confidential data using its private key. The proposed method realizes secure end-to-end confidentiality of the sensitive information. It has faster computing speed and can verify the data source and ensure the authenticity of readings. The example results show that the proposed method has little influence on the original data and unauthorized access cannot be completed within a reasonable time. On embedded hardware, the processing speed of the proposed method is better than the existing methods.