Mechanical Properties of Rock With Intersection Structures and its Progressive Failure Mechanism

To investigate the influence of intersection structures on the mechanical properties and failure mechanisms of rock materials, a series of uniaxial compression tests on complete red sandstone specimens and specimens with various hole shapes (T-shape, cross-shape, and shaft-roadway-shape) were conducted by the Instron 1346 servo-controlled rock mechanics testing machine. Flac3D software and digital image correlation (DIC) were used to simulate the internal stress distribution of rock specimens and reproduce the process of fracture, i.e., cracks initiate, propagate, and coalesce with each other into macroscopic failure under progressive loading. The results show that the intersection structure has a signiflcant weakening effect on the mechanical properties of the rock. The rock strength, elastic modulus, and peak strain of specimens can be ranked as complete specimens > cross-shaped intersection structure specimens > T-shaped intersection structure specimens>shaft-roadway-shaped intersection structure specimens. The energy consumption ratio of the intersection structure specimens before the peak reaches more than 30%, which is approximately twice that of the intact specimens. The brittleness coefflcients of the four types of specimens are 0.18, 0.26, 0.21, and 0.20, respectively. The intersection structure specimens induced different degrees of tensile and compressive stress concentration zones on the top and bottom sides of the intersection center point. As a result, initial tensile cracks parallel to the loading direction and shear cracks leading to spalling failure on both sides of the holes were formed. With the increase of the axial stress, secondary tensile cracks extending on the opposite direction appeared at the upper and lower corners of the hole. When the far-fleld cracks that propagated along the diagonal line coalesced with secondary tensile cracks, macro shear-failure of the specimens appeared. With the increase in axial stress, the principal strain monitored during the fracture process of the specimens gradually increased, then it slowly decreased after the peak. The arched boundary of the T-shaped intersection structure specimen had good stability because of its advantage of suppressing the occurrence of the spalling failure. The shaft-roadway-shaped intersection structure could provide compensation space for the secondary tensile cracks due to the existence of the vertical well. The degree of inhibition of initial tensile cracks was so small that the type of specimens was highly prone to instability or failure.National Key Research and Development Program of China during the Thirteenth Five Year Plan Period: The Continuous Mining Theory and Technology on Spatiotemporal Synergism of Multi-mining Areas within a Large Ore Block for Deep Metal Deposit [2017YFC0602901]; Fundamental Research Funds for the Central Universities of Central South University [2018zzts215]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Rock mechanics parameters

Rock mechanics parameters for simulation in the paper

Multistage fuzzy comprehensive evaluation of landslide hazards based on a cloud model.

To accurately study the risk assessment of landslide disasters, firstly, the environmental conditions of induced landslide disasters are regarded as a fuzzy system, and the landslide risk factors in the multi-level analysis system are constructed to build a multi-level fuzzy evaluation index system. Then, the cloud model theory is introduced to improve the importance scale and membership degree involved in the evaluation process, and the multi-level fuzzy comprehensive evaluation method of landslide risk improved by a cloud model is proposed. Thus, a multi-level fuzzy evaluation cloud model for evaluating landslide risk is established. Finally, using the improved cloud model method, a multistage fuzzy comprehensive evaluation of landslide risk is conducted for the K112+210~K112 +630 section of the Long Chuan to Huaiji Highway Project in Guangdong Province. The results show that the improved cloud model can solve the problem of uncertainty in the process of landslide preparation and occurrence, greatly improve the effectiveness of landslide evaluation results, and provide an effective reference for landslide disaster prevention

Data from: Plastic limit bearing calculation of blasting-roof in deep hole mining and its applications

In order to solve the problem that blasting-roof thickness was hard to determine in deep hole mining, the plastic bearing calculation method of blasting-roof was proposed. Aim at typical boundary conditions of blasting-roof, mechanical analysis model of plastic bearing was built. The external work and internal work of blasting-roof under plastic limit state were calculated. Based on virtual work principle, the limit bearing formulas of blasting-roof under various boundary conditions were derived. Taking a VCR stope as the object, the safe blasting-roof thickness was determined as 6m by derived formula (considering safety coefficient). Numerical model of stope was constructed by Surpac-Flac3D technique, while blasting-roof stability was simulated under different thickness. The variation of simulated indexes (stress, plastic zone volume) prove that theoretical calculation is reliable. The plastic bearing calculation method can provide a new way for determining blasting-roof thickness in deep hole mining

Data from: Plastic limit bearing calculation of blasting-roof in deep hole mining and its applications

In order to solve the problem that blasting-roof thickness was hard to determine in deep hole mining, the plastic bearing calculation method of blasting-roof was proposed. Aim at typical boundary conditions of blasting-roof, mechanical analysis model of plastic bearing was built. The external work and internal work of blasting-roof under plastic limit state were calculated. Based on virtual work principle, the limit bearing formulas of blasting-roof under various boundary conditions were derived. Taking a VCR stope as the object, the safe blasting-roof thickness was determined as 6m by derived formula (considering safety coefficient). Numerical model of stope was constructed by Surpac-Flac3D technique, while blasting-roof stability was simulated under different thickness. The variation of simulated indexes (stress, plastic zone volume) prove that theoretical calculation is reliable. The plastic bearing calculation method can provide a new way for determining blasting-roof thickness in deep hole mining

Reconstruction of 3D Shapes of Granite Minerals and Generation of Random Numerical Specimens

AbstractThe existing methods of generating random mineral grains in numerical rock specimens mostly adopt random polygons (in 2D) or random polyhedrons (in 3D) to represent mineral grains. Although this simplification is effective and reasonable, the complex three-dimensional (3D) shape of mineral grains can be reconstructed by computed tomography (CT) scan and image processing techniques, and then, random grains with real shape can be generated in a numerical specimen. In this paper, we proposed an improved grain-based model to construct random mineral grains with real 3D shape in numerical specimens. The granite specimens with granular minerals are scanned by CT. After the CT slices are denoised and corrected, the minerals, including biotite, quartz, and feldspar, are segmented from the CT slices to reconstruct the 3D mineral shapes; these shapes are stored in grain library. By importing the grain library in PFC (Particle Follow Code, a simulation software), heterogeneous specimens with random mineral grains are constructed, and uniaxial compression tests are carried out on them. Results show that the ranges of Young’s modulus, Poisson’s ratio, and uniaxial compressive strength of these numerical specimens are similar to those of real specimens measured in the laboratory. Therefore, the proposed method is feasible and reasonable. This work can provide a reference for the study of constructing heterogeneous numerical rock specimens in rock mechanics

TβRII Regulates the Proliferation of Metanephric Mesenchyme Cells through Six2 In Vitro

The transforming growth factor-β (TGFβ) family signaling pathways play an important role in regulatory cellular networks and exert specific effects on developmental programs during embryo development. However, the function of TGFβ signaling pathways on the early kidney development remains unclear. In this work, we aim to detect the underlying role of TGFβ type II receptor (TβRII) in vitro, which has a similar expression pattern as the crucial regulator Six2 during early kidney development. Firstly, the 5-ethynyl-2′-deoxyuridine (EdU) assay showed knock down of TβRII significantly decreased the proliferation ratio of metanephric mesenchyme (MM) cells. Additionally, real-time Polymerase Chain Reaction (PCR) and Western blot together with immunofluorescence determined that the mRNA and protein levels of Six2 declined after TβRII knock down. Also, Six2 was observed to be able to partially rescue the proliferation phenotype caused by the depletion of TβRII. Moreover, bioinformatics analysis and luciferase assay indicated Smad3 could transcriptionally target Six2. Further, the EdU assay showed that Smad3 could also rescue the inhibition of proliferation caused by the knock down of TβRII. Taken together, these findings delineate the important function of the TGFβ signaling pathway in the early development of kidney and TβRII was shown to be able to promote the expression of Six2 through Smad3 mediating transcriptional regulation and in turn activate the proliferation of MM cells

Method for Identifying and Forecasting Mining-Induced Earthquakes Based on Spatiotemporal Characteristics of Microseismic Activities in Fankou Lead/Zinc Mine

The risks associated with underground mining at Fankou Lead/Zinc Mine in South China are growing due to the large-scale mining activities there. To recognize mining-induced earthquakes and assess the risk per mining level, a microseismic monitoring system, which is used to record microseismic events, is installed at multiple mining levels in Fankou Lead/Zinc Mine. The purpose of this study is to identify mining-induced earthquakes and to evaluate the risk per mining level by analyzing the spatiotemporal characteristics of microseismic activities in the Fankou Lead/Zinc Mine. In this study, the Gutenberg-Richter (G-R) relationship is applied to compute the b-value, which is used to obtain the maximum magnitude (M (max)) of microseismic event that probably occurs at each mining level. Then, the evaluation of the recurrence period for M (max) and the probability of the microseismic event with the magnitude M (max) is carried out and the M (max) at each mining level is determined based on the recording period of microseismic events. The results show that factors such as the maximum rock vibration velocity, source parameters, displacement, microseismic waveform and energy ratio (ES/EP) can be used to distinguish whether a recorded microseismic event is mining-induced earthquake. Additionally, we propose a method to assess the possibility of mining-induced earthquake at each mining level based on M (max) and predict the recurrence time of microseismic event with the magnitude M (max). The of two years results of microseismic events monitoring demonstrate that the current study is promising for identifying mining-induced earthquakes, assessing the risk of mining-induced earthquakes, predicting the potential maximum microseismic event in a region and estimating its recurrence period and its probability in the Fankou Lead/Zinc Mine