In underground excavations, different failure features can be induced by complex geological stresses. Therefore, many researchers have investigated rock behaviour and failure mechanisms under ...high-stress conditions. This study investigated the different failure characteristics to determine the stress-induced cracking mechanisms. Accordingly, a series of tests were performed on a volcanic rock (rhyodacite) under one- to three-dimensional stress states. The results indicated that the samples exhibited different failure characteristics/modes under different stress states. Under 1-D and 2-D compression, the rock exhibited unstable brittle failure induced by tensile cracking (Mode I fracture). Under axisymmetric triaxial stress (σ1 > σ2 = σ3 > 0), the rock exhibited stable failure, and as σ3 increased, the failure mode transitioned from Mode I fracture to Mode II fracture to distributed cataclastic failure. In contrast, under a three-dimensional differential stress state (σ1 > σ2 > σ3 > 0), the risk of unstable failure increased with increasing σ2, and the rock exhibited localized shear failure (Mode II fracture). Based on the acoustic emission (AE)-based cracking classification method, further studies were also conducted on the failure mechanism. Finally, based on the energy release and cracking propagation, the mechanism of the σ2 effect on unstable failure was assessed.
•Three stress-induced cracking mechanisms were revealed.•Tensile cracks were preferentially induced during the failure evolution.•The unstable failure can be induced by a higher (σ2-σ3).
The timely and accurate assessment of casualties is the key for and basis of emergency rescue work after an earthquake. In this paper, through exponential fitting of historical seismic data, an ...evaluation model of death based on the building destruction ratio is proposed. Through the analysis of historical seismic data, we propose the concept of an anti-lethal level and construct the corresponding coefficient. We use factors such as earthquake magnitude, intensity, and occurrence time, the population density, and the anti-lethal level in the region as correction factors for the predicted number of casualties and build a model for evaluating the number of casualties based on coefficient correction. The evaluation results are relatively accurate; the
R
2
index of the proposed model is 0.8768, whereas the
R
2
of the two comparison models selected in this paper is 0.619 and 0.4603, respectively. The accuracy of the proposed model results is much higher than that of the other models, which illustrates the effectiveness of the model presented in this paper. It also indicates that the model proposed in this paper can provide a scientific basis and data support for earthquake emergency rescue work.
•Field investigated seismic vulnerability of building environment at mid-resolution.•Satellite nighttime light, vegetation index and reflectance to estimate vulnerability.•The performance of random ...forest model is better than spatial interpolation method.
Building damage after seismic disasters is one of the most vital factors threatening people's lives. The seismic vulnerability of buildings over large scales at the regional or country level is a key parameter for the mitigation of seismic disaster risk and rapid assessment of casualties after seismic events. To acquire the seismic vulnerability of buildings over large areas, a machine learning method based on mid-resolution satellite optical images is proposed. Taking field-investigated building vulnerability at the satellite pixel scale as a reference, the 15 most correlated features are calculated based on VIIRS nighttime light, MODIS vegetation index and surface reflectance, and texture data from Landsat-8 OLI surface reflectance products. Taking Yancheng, Jiangsu Province, China, as the study area, where 401 pixel-level seismic vulnerabilities (PLSVs) of the building environment are acquired based on field investigations, support vector regression (SVR) and random forest (RF) models are proposed using the 15 features calculated from satellite optical images. The results show that the proposed method can be used to estimate the PLSV with a root mean square error of approximately 0.1, with the PLSV normalized between 0 and 1. The machine learning model proposed in this study has a better accuracy for PLSV estimation than spatial interpolation.
Microwave energy can be used to assist mechanical rock breakage for civil and mining engineering operations. To assess the industrial applicability of this technology, microwave heating of basalt ...specimens in a multi-mode cavity (a microwave chamber) at different power levels was followed by conventional mechanical strength and fragmentation effect tests in the laboratory. X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray spectroscopy were used to determine the mineral composition and distribution of the basalt, to aid interpretation of crack propagation patterns and the associated strength reduction mechanism. These analyses demonstrated that cracks mainly occurred around olivine grains, primarily as intergranular cracks between olivine and plagioclase grains and intragranular cracks within olivine grains. Strength reduction during microwave fracturing of basalt is driven by heat from enstatite (a microwave-sensitive mineral) and volumetric expansion of olivine (a thermally expansive mineral). Uniaxial compressive, Brazilian tensile, and point load strengths all decreased with increasing microwave irradiation time at rates that were positively related to the power level. For a given power level, mechanical strength reduction can be estimated from linear relationships with irradiation time. On the other hand, a power function best described burst time (the irradiation time at which the specimen burst into fragments)
vs
. power level (for a given specimen size) and burst time
vs
. specimen size (for a given power level) relationships. Microwave-induced hard rock fracturing can be an integral part of new methods for rock breakage and tunnel excavation.
After an earthquake, the important task of emergency rescue work is to minimize casualties, but due to the suddenness of earthquake disasters, it is difficult to obtain enough disaster information ...immediately, especially personnel distribution and movement information. The traditional methods of obtaining disaster data are through reports from the disaster area or field investigations by the emergency rescue team; this work lags, and its efficiency is low. This paper analyzes the feasibility of using mobile phone location signal data in earthquake emergency rescue work in several respects, such as quantity, location, change rate, and epicentral distance. The results show that mobile phone location signal data can quickly obtain the situation of personnel distribution and quantity after an earthquake, and we find the change rate, distance, etc., can determine the approximate range of the earthquake impact field. Through the data distribution in different time periods, the movement of personnel after the earthquake can be obtained. Based on several situations, we can determine the basic situation of the disaster-stricken areas in times after the earthquake, especially the personnel relevant to the situation, and these data can provide a scientific basis for emergency rescue decision making.
The time-dependent deformation, creep rate, and long-term strength of Jinping marble under different 3-D stress states were studied by using true triaxial creep experiment. A 3-D ...visco-elastic-plastic creep model, which can describe the accelerated creep， was developed according to the true triaxial time-dependent deformation curve. The results show that the time-dependent behaviour of Jinping marble is affected by the stress level. When the stress is less than the long-term strength, not obvious time-dependent behaviour of the rock sample is found, and the strain remains unchanged after primary creep. When the stress exceeds the long-term strength, the time-dependent behaviour of the rock sample gradually increases with increasing σ1 and a clear steady state creep stage is seen in the strain-time curve. With constant σ1 and σ3, the time-dependent deformation and creep rate in the three main stress directions gradually decrease with increasing σ2. Compared with conventional triaxial test data, a large intermediate principal stress increases the time-dependent dilatation in the σ3 direction. In addition, a 3-D visco-elastic-plastic creep model considering damage is proposed to describe the creep behaviour of hard rock under different 3-D stress states. The model results fit the experimental results, and the selection of model parameters is closely related to the intermediate principal stress. The model results also verify the applicability of the 3-D element model.
Since Von Kármán first published conventional triaxial test data on rocks in 1911, the primary installation method has consisted of using a cylindrical specimen sandwiched by two metal platens. The ...mismatch in the elastic parameters (Young's modulus and Poisson's ratio) between the metal platens and rock specimen in the elastic and yielding ranges produces an interface friction when axially loaded, which results in a non-uniform stress distribution at the end of the specimen; this situation is defined as the end friction effect. Lubrication is an effective method to decrease the friction between opposing solid faces by applying a solid or fluid anti-friction agent. To reduce the end friction effect in rock mechanics uniaxial or conventional triaxial compression tests, anti-friction agents, such as "stearin" or stearic acid, a Teflon sheet, Teflon and copper sheets, and low-modulus insert materials, have been widely used. The theoretical solution method has been employed to analyse the stress distribution within a circular cylinder, in which the friction coefficient and boundary condition were considered.
The study introduced a true triaxial testing apparatus for conducting time-dependent experiments on hard rocks under high stress. The apparatus consists of two-rigid loading platens to apply the ...maximum and intermediate principal stresses, and a flexible loading system with which to apply the minimum principal stress, under constant-temperature control. It includes a simple sample-installation system, an acoustic emission acquisition system, data acquisition system, and a software interface. The novel apparatus overcomes the long-term eccentric loading problem faced when testing rock samples using a biaxial double-closed-loop servo-control mode. In addition, using an integrated structural design, the stiffness of the apparatus was increased, which was conducive to improving the data precision obtained in small-scale deformation experiments involving hard, stiff, or strong, rock samples. It also provides the possibility of studying the post-peak time-dependent behaviours of hard rocks under high stress. To verify the advantages of this apparatus and investigate the influence of intermediate principal stress on the time-dependent behaviour of hard rock, this study demonstrated the experimental methods and results for pre- and post-peak time-dependent of hard rock under true triaxial compression. The experimental results showed that intermediate principal stress exerted a significant influence on the time-dependent behaviour, and long-term deformation and strength, of hard rocks: post-peak fractured rocks still exhibited a certain time-dependent strength. The results also validated the reliability of this true triaxial time-dependent apparatus.
With recent developments in communication technologies, vehicular networks have become a reality with various applications. However, the cybersecurity aspect of vehicular networks is still an open ...issue that needs to be addressed with novel defence mechanisms against attacks. This paper first presents the state-of-the-art communication technologies in vehicular networks (either inter-vehicle networking or in-vehicle networking) along with their applications. Then we explore novel technologies including machine learning and blockchain as cybersecurity defence mechanisms in vehicular networks. Based on the extensive survey, we highlight some insights for future research to secure vehicular networks.
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