In order to keep track of the operational state of power grids, the world's largest sensor system, smart grid, was built by deploying hundreds of millions of smart meters. Such a system makes it ...possible to discover and make quick response to any hidden threat to the entire power grid. Non-technical losses (NTLs) have always been a major concern for their consequent security risks as well as immeasurable revenue loss. However, various causes of NTL may have different characteristics reflected in the data. Accurately capturing these anomalies faced with such a large scale of collected data records is rather tricky as a result. In this paper, we proposed a new methodology of detecting abnormal electricity consumptions. We did a transformation of the collected time-series data which turns it into an image representation that could well reflect users' relatively long term consumption behaviors. Inspired by the excellent neural network architecture used for objective detection in computer vision, we designed our deep learning model that takes the transformed images as input and yields joint features inferred from the multiple aspects the input provides. Considering the limited amount of labeled samples, especially the abnormal ones, we used our model in a semi-supervised fashion that was brought about in recent years. The model is tested on samples which are verified by on-field inspections and our method showed significant improvement for NTL detection compared with the state-of-the-art methods.
Shallow slope may be stable during rainfall but slide a period of time after rainfall stopped. This delay failure mechanism of rainfall-caused landslide is still unclear. This paper aims to reveal ...the mechanism of the delay failure of rainfall-caused landslides, and propose a monitoring and early warning scheme for such disasters. The characteristic of the seepage field after rainfall and its relations with the stability of slope are investigated numerically. The results show that, after the rainfall stopped, the pore water pressure and volume water content (VWC) of the deep slope will continue to change with the same trend as before the end of the rainfall for a period of time. For an observation point in slope, the VWC continues to increase, and matric suction continues to decrease, which continue to decrease the factor of safety after rainfall stopped. This is the direct cause of the delay failure. The detailed flow chart of the warning system is given as a solution.
Transversely isotropic rocks, which are special anisotropic materials, are widely encountered in civil, mining, petroleum, geothermal, and radioactive waste-disposal engineering. Rock is frequently ...subject to cyclic loads resulting from natural and human-caused events. However, to date, the fracture mechanism of transversely isotropic rocks under cyclic loading remains poorly understood. To address this gap, uniaxial monotonic-loading and cyclic-loading tests were performed on slate specimens by the MTS815 system, during which acoustic emission (AE) signals inside the rock were monitored, and finally the fracture surfaces of the tested rock were scanned by scanning electron microscopy (SEM). Through these tests, the anisotropic mechanical properties, damage evolution, AE characteristics and fracture pattern of slate as a transversely isotropic rock were studied. The results show that the peak strength of specimens varies with the loading–foliation angle under monotonic and cyclic loading, following a U-shaped trend. The deformation modulus during unloading is more capable of characterizing the damage inside the specimen than that during loading. By defining the damage degree based on dissipation energy, it is found that the damage variable is influenced by the loading–foliation angle and the cyclic stress step. The AE characteristics of specimens exhibit significant anisotropy, closely correlated to the loading condition and loading–foliation angle. Regardless of cyclic stress step, the AE counts of specimens with a loading–foliation angle of 0° are mainly distributed near the peak region, whereas those of specimens with other loading–foliation angles occur primarily in the early stage of each cyclic loading. Finally, it is revealed that the fracture mechanism of slate specimens is determined by the loading–foliation angle, loading condition, and cyclic stress step.
To study the damage evolution of rocks under the action of wet and dry cycles, nuclear magnetic resonance (NMR) technology was used to test red sandstone under different times of wet and dry cycles. ...The T2 spectral distribution curve, porosity, spectral peak area, and damage distribution curve of the rock were obtained, and the quantitative relationship between porosity, damage degree, and number of cycles was established. The results show that with the increase of the number of wet and dry cycles, the T2 spectral curve of rock gradually moves to the right, but the moving amplitude gradually decreases. The porosity and spectral area increase with the increase of the number of wet and dry cycles, coupled with a declining growth rate, and the maximum increase in porosity is 18.789%. The damage degree of rock increase with the increase of the number of cycles, but with the continuous increase of the number of cycles, the damage rate decreases, and finally the damage degree of rock tends to be a constant value.
Elastic parameters and the subcritical crack growth of different bedding angle slate specimens were studied using uniaxial compression testing and the double torsion constant displacement load ...relaxation method using SANS and MTS Insight machines. To study the relations of the mode-I stress intensity factor KI versus the subcritical crack growth velocity V, the fracture toughness KIC, the stagnation speed, and the threshold values, the double torsion constant displacement load relaxation method was carried out. The related rules between the bedding angles (β) and the uniaxial compressive strength, fracture toughness, and threshold values were investigated. Experimental results show that the uniaxial compression, the fracture toughness, and the threshold value curves move to the bottom then increase with the increase of the β angle. In addition, its fracture toughness is minimal when the β angle of the slates is 45°, and crack initiation and crack propagation are generated under load, which can lead to the failure of the slate. lgKI-lgV relations of transversely isotropic slates measured by this method are in accordance with linear rules, which is in good agreement with the Charles theory. The range of K0/KIC for these different bedding angle slates is from 0.511 to 0.789. The test results would provide the basis for studying seepage and time-dependency of rock engineering stability.
The TRW-3000 true triaxial rock testing machine was used to conduct loading and unloading tests of sandstone under different σ2, and the true triaxial lateral unloading mechanics and energy ...characteristics of sandstone under different σ2 were studied. The experimental results show the following: (1) compared with the results of the loading test, the peak strength of the sandstone under the unloading σ3 path is reduced, the unloading direction has obvious expansion and deformation, and the amount of expansion increases significantly with the increase of σ2; sudden brittle failure occurs at the end of unloading. E gradually decreases with the increase of H, and it performs well to use the cubic polynomial to fit the curve of E-H. (2) The Mogi–Coulomb strength criterion can accurately describe the true triaxial strength characteristics of sandstone under loading and unloading conditions. Compared with the results of the loading test, the values of c and φ obtained based on this criterion under the unloading σ3 path are reduced. (3) Under the condition of unloading σ3, U,Ue, and Ud, when the specimen is broken, are all linearly positively correlated with σ2. Ud increases nonlinearly with the increase of H, and as σ2 increases, the slope of the Ud-H curve becomes larger, and the specimen consumes more energy under the same unloading amount. Most of the energy absorbed by the specimen under the unloading σ3 path is converted into Ue, but as σ2 increases, Ud /U increases, and the energy consumed when the specimen is broken is greater.
The constitutive relation of rock joints in the percolation environment has always been a frontier research topic in the field of geotechnical engineering, involving nuclear waste disposal, dam ...foundation construction, tunnel tunneling, and other fields. In this study, a shear statistical damage constitutive model of rock joints considering seepage pressure was proposed, which takes into account the statistical damage, stage deformation characteristics and seepage action in the process of joint shear deformation. By introducing the seepage pressure reduction coefficient and establishing the relationship between the model parameters and the seepage pressure, the prediction of joint shear stress-displacement curves under different seepage pressures was achieved. The comprehensive comparisons between the theoretical results and the experimental results reveals that the model can accurately reflect the shear deformation law of joints and reasonably simulate the shear stress-displacement relationship of joints. And ultimately, the physical significance of the model parameters and their relationship with shear strength characteristics are discussed via the gray correlation method. The model and verification results presented in this study can deepen the understanding of the shear behavior of joints subject to high seepage pressure and contribute to the design and optimization of geotechnical engineering in the percolation environment.
In order to reveal the internal stress distribution and failure characteristics of a pre-existing cylindrical cavity in granite under triaxial cyclic loading, bonded particle models containing a ...cavity were established to investigate the variation in crack propagation, stress distribution, number of micro-cracks, elastic modulus, and Poisson’s ratio with an increase in cavity diameter. The results show that the cavity diameter has a significant effect on the tensile cracks, compression-shear failure zone, and compressive stress distribution. The peak strength decreases as the diameter of the cavity increases. However, the number of cracks increases and the plastic deformation increases more obviously. With the increase of the cyclic axial stress, the decrease rate of the elastic modulus shows the rule of “first slow, fast later,” and the Poisson’s ratio increases. The distribution of local stress of σ1,σ2, andσ3 explains the behavior of the cracks around the cylindrical cavity well.
In this paper, to investigate mixed-mode I-II fracture behaviors, three different asymmetric notched semi-circular bending specimens (ANSCB) were designed by adjusting the angle and the distance ...between supporting rollers to conduct asymmetric three-point bending tests. Several aid technologies, including acoustic emission (AE), digital image correlation (DIC), crack propagation gauge (CPG), and scanning electron microscopy (SEM), was utilized to monitor and assess the fracture characteristic. Meanwhile, the fractal dimension of the fracture surface was assessed based on the reconstructed digital fracture surface. The results show that mixed-mode I-II ANSCB three-point bending fracture is a brittle failure with the characteristics of the main crack being rapidly transfixed and the bearing capacity decreasing sharply. Based on the DIC method, the whole fracture process consists of a nonlinear elastic stage, fracture process zone, crack initiation stage and crack propagation stage. The crack initiation is mainly caused by the tension-shear strain concentration at the pre-existing crack tip. At the microscale, the crack propagation path is always along the grain boundary where the resultant stress is weakest. According to the monitoring of the AE, it can be found that micro-tensile cracks are mainly responsible for the asymmetric three-point bending fracture. The data obtained by CPG suggest that the subcritical crack growth rate is positively correlated to the ultimate load. In addition, asymmetric loading leads to a coarser fracture surface, and thus a higher fractal dimension of the fracture surface. The current study can provide a better understanding of the mixed-mode I-II fracture behaviors of rock.
•Red sandstone containing pre-existing crack was tested under fatigue-creep tests.•Combined AE, SEM and DIC techniques for combined measurement analysis.•A macro and meso multi-scale analysis of the ...rock fracture mode was carried out.•A damage evolution model was established based on the LURR theory.•The improved Harris distribution was used to establish the damage model.
To study the effect of creep loading on the fracture mode and damage evolution process of jointed rock masses during fatigue loading, a series of multilevel cyclic loading and unloading tests (MCT) and fatigue-creep tests (FCT) were carried out on jointed sandstone samples. First, a combined detection platform was built using acoustic emission (AE), scanning electron microscopy (SEM) and digital image-related (DIC) technologies. Then, the fracture mode of the sample is analyzed at the macro- and mesoscale. Finally, based on the loading and unloading response ratio (LURR) theory, assuming that the internal damage of the sample obeys the improved Harris distribution, a damage evolution model of the sandstone sample was established, and the applicability and validity of the model were verified. The test results show that applying creep load during the fatigue loading process can increase the axial strength, reduce the axial deformation, weaken the energy dissipation, and exhibit the phenomenon of early hardening. In terms of fracture mode, applying creep load can change the type of cracks that dominate the failure of the sample, improve the shear resistance, and increase the brittleness when the sample is broken. At the same time, the dislocation movement between the grains, pressure solution and splitting phenomenon will be enhanced, and the types of micro-defects will increase. In terms of the damage evolution process, a short-term low-stress level creep load can reduce the rate of damage growth, thereby increasing the fatigue life of the rock mass.
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