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Now showing items 1 - 6 of 6

  • Dynamic analysis of granite rockburst based on the PIV technique

    Hongjian Wang   Da’an Liu   Weili Gong   Liyun Li  

    Abstract This paper describes the deep rockburst simulation system to reproduce the granite instantaneous rockburst process. Based on the PIV (Particle Image Velocimetry) technique, quantitative analysis of a rockburst, the images of tracer particle, displacement and strain fields can be obtained, and the debris trajectory described. According to the observation of on-site tests, the dynamic rockburst is actually a gas–solid high speed flow process, which is caused by the interaction of rock fragments and surrounding air. With the help of analysis on high speed video and PIV images, the granite rockburst failure process is composed of six stages of platey fragment spalling and debris ejection. Meanwhile, the elastic energy for these six stages has been calculated to study the energy variation. The results indicate that the rockburst process can be summarized as: an initiating stage, intensive developing stage and gradual decay stage. This research will be helpful for our further understanding of the rockburst mechanism.
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  • Thermal image and spectral characterization of roadway failure process in geologically 45° inclined rocks

    Weili Gong   Yanyan Peng   Manchao He   Jiong Wang  

    Graphical abstract Highlights • Large-scale physical modeling of an overloaded tunnel in 45° inclined rock. • Characterization of rock response using loading rate, thermography and its spectra. • Oscillation of energy release, 〈 IRT 〉, revealing the stick–slip behavior. • Representing the static and dynamic interlayer slip by the processed thermograms. • Spectral precursors under different loading rate and overburden depth were captured. Abstract Large-scale geomechanical model test was conducted in order to investigate stability of an un-supported tunnel with rectangular cross section embedded in 45° inclined alternating strata of sandstone, mudstone and coal seam. The loading path consists of two groups: cases A–G with overburden depths from 296 to 948 m and small loading rate, and cases H–M with overburden depths from 1126 to 2047 m and fast loading rate. Infrared thermography, incorporated with image processing and Fourier transform, was employed to characterize the rock responses. Averaged temperature field, 〈 IRT 〉, represents energy release rate, oscillating at stick–slip pattern with different periods and amplitudes. Overburden depth and loading speed have a significant impact on 〈 IRT 〉 curve, i.e. small overburden depth and loading speed corresponds to long period and small amplitude; whereas, great overburden depth and fast loading speed to short period and high amplitude. The processed thermal image best represents rock behavior by two major IRT distribution modes. For loading cases A–G, the coal strata were over stressed indicated by high IRT while the mudstone strata were less stressed represented by low IRT, corresponding to the static interlayer friction. For loading cases H–M, the mudstone strata were over stressed indicated by high IRT while the coal strata were less stressed indicated by low IRT, corresponding to the dynamic friction. Fourier spectra and spatial frequency were employed to characterize the infrared sequence. Ultra-high spatial frequency component is a precursor for predicting the imminent dynamic event. Low spatial frequency component may be served as an indicator of the tunnel-wide sphere of influence that the stress redistribution extends.
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  • Enhancement of low-contrast thermograms for detecting the stressed tunnel in horizontally stratified rocks

    Weili Gong   Yanyan Peng   Xiaoming Sun   Manchao He   Shuaiyang Zhao   Huaqi Chen   Tian Xie  

    Highlights • Low-contrast thermogram is major limitations for rock failure experiment. • Image enhancement filter, MIF, is developed based on top-hat transformation. • Raw thermograms from rock failure detection are processed with new algorithm. • Rock mass response analysis was conducted using the new thermograms. • Obtained results are validated by comparison to the video photographs.
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  • Geomechanical Model Tests and Infrared Detection of Rock Responses for Tunnels Excavated in Sedimentary Rocks

    Weili Gong   Manchao He   Hong Yan   Lifeng Li   Xiaodong Xu  

    Abstract Rock mass behavior is controlled mainly by weak planes in sedimentary rocks. Geomechanical model tests were conducted for simulating tunnel excavations in horizontal, the 45° and vertical inclined rock strata. Infrared thermography was employed for detecting rock responses during the excavations. Infrared temperature (IRT) curve obtained by averaging the matrices of the infrared sequence can be viewed as temporal observation of the overall energy release from the rock under excavation. The IRT curve characterizes the horizontal and vertical strata as linear behavior and the 45° inclined strata as piecewise linear behavior over the full-face excavation and the three strata as plastic-like behavior over the staged excavation, respectively. The constitutive heterogeneity can be represented by the Weibull modus obtained by curve-fitting to the Weibull model using the probability distribution of the IRT temporal observations. The vertical strata has the smallest Weibull modulus values corresponding to the higher heterogeneity compared with the else two strata models. The structural response of the rock under excavation was characterized by the IRT distribution of the infrared image. IRT distribution of the horizontal strata evolved from scattering distribution to localized high-temperature zone around the face. In contrast, IRT distribution for the 45° and vertical strata distributed as belt-like IRT parallel to the weak surface; indicating the frictional sliding damage mechanism. Most intense friction was observed in the excavation in the 45° inclined rock strata.
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  • Precursory waves and eigenfrequencies identified from acoustic emission data based on Singular Spectrum Analysis and laboratory rock-burst experiments

    Yuxin Gong   Zhanjie Song   Manchao He   Weili Gong   Fuqiang Ren  

    Abstract Important task for acoustic emission (AE) monitoring involves detecting frequency shift phenomenon and intense periodic components. In the present research, we investigate time dynamics embedded in AE signal acquired in the laboratory rock burst experiment on limestone sample. By applying the Singular Spectrum Analysis (SSA)-based algorithm developed in this research, we reconstruct the decomposed components and then select the main component with a decision-making process based on the criterion that it should be significant both in the eigenvector space and spectral domain, termed eigenfrequency. The frequency shift phenomenon is represented by the eigenfrequencies of the first main component consistently. Precursory waves of the first main component represents time dynamics of the rock burst process by elastic wave over the low-level loading phase, high-frequency wave with self-oscillating envelopes at unloading, low-frequency quasi-shock waves during the rheological delay phase and low-frequency shock wave at complete rock burst failure. Highlights • SSA-based algorithm was developed for analyzing AE data from rock burst test. • Main part of AE data were reconstructed with the decomposed components. • Selected main components are significant in eigenvector and spectral spaces. • Main eigenfrequecies well represent frequency shift in rock burst process. • Main component waves represent dynamic precursors in rock burst process.
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  • Dynamic tests for a Constant-Resistance-Large-Deformation bolt using a modified SHTB system

    Manchao He   Chen Li   Weili Gong   L.R. Sousa   Shenglin Li  

    Highlights • A Constant Resistance Large Deformation (CRLD) bolt was introduced. • Experiments on a Split-Hopkinson Tension Bar for CRLD bolts were performed. • Numerical simulations were carried out by using different codes. • Improved understanding of dynamic behavior of the CRLD bolt was achieved. Abstract Rockbursts frequently occur in deep underground excavations in a sudden or violent ejection of blocks of rocks from excavation walls. In addition to understanding rockburst mechanisms, rockburst control is an important issue for the safety of mining operations. Bolts and anchors are efficient measures to control rockbursts and permit the efficient exploration of underground excavations in mines. As mining depths increase, anchor and bolts with larger extension and higher loading capacity are needed. This paper introduces a Constant Resistant Large Deformation (CRLD) bolt which has been developed at the State Key Laboratory for Geomechanics and Deep Underground Engineering (GDUE), in Beijing, China. Static and dynamic tests were developed for this type of bolt. Advancements in Hopkinson tests were recently developed for CRLD bolts and Split-Hopkinson Tension Bar (SHTB) experiments for these bolts were performed. This paper presents the SHTB equipment and the results obtained with one and two CRLD bolts, as well a deep analysis of the obtained results. To better understand the complex nature of the problem, numerical simulations using several softwares were done for the case of one bolt, which had the dual goal of verifying the experimental and numerical results. In addition, the numerical predictions permit one conducting analysis the behavior of the bolt while targeting the development of large deformations. Finally some relevant conclusions are drawn.
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