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Research on the Rock Pressure Behavior at Close-Distance Island Working Faces under Deep Goaf

In order to realize the safe and efficient mining of the short-distance isolated island working face under the deep goaf area, the 120502 isolated island working face of Liuzhuang Mine was taken as the engineering background. The method of combining numerical simulation and field measurement were used comprehensively to systematically simulate and study the spatial evolution of the stress field, plastic strain field, and fracture field of coal rock during the mining process. The leading support pressure and the vertical displacement of the roof in the overlapping section and noncoinciding section of the isolated working face and the goaf above were measured on site. The results are that the peak value of the advanced support pressure of the overlap section and the nonoverlapping section is 10 m before the coal wall of the working face; the advanced support pressure of the nonoverlapping section is 33.3 MPa, and the vertical displacement of the roof is 300 mm. The advanced support pressure and the vertical displacement of the roof in the noncoincidence section were significantly higher than those in the coincidence section of 18.2 MPa and 210 mm. The results are consistent with those predicted by numerical simulation. This provides theoretical support for the safe mining of the 120502 isolated island working face in Liuzhuang Mine and, at the same time, provides a reference for the study of similar working faces in other domestic mining areas.

Research of the Surrounding Rock Deformation Control Technology in Roadway under Multiple Excavations and Mining

To effectively control the large surrounding rock deformation of the mining roadway under multiple excavations and mining in Wangcun coal mine, the field investigation, numerical simulation, field test, and monitoring were conducted, and the characteristics of stress and deformation evolution of the surrounding rock under the influence of multiple excavations and mining were analyzed; then the collaborative supporting technology of high prestressed bolt and short anchor cables was proposed in this study. The results show the following: (1) under the influence of multiple excavations and mining, the peak vertical stress of the typical air-return roadway reaches 23 MPa, and the deformation increases by about 2.8 times after the mining of adjacent panel. (2) The principle of the roadway support under the influence of multiple excavations and mining in Wangcun coal mine is determined; from the perspective of prestress, we can conclude that the active support of short anchor cables is better than that of long anchor cables. (3) Based on the results of the field monitoring, the bolt stress can be divided into four stages: the loss stage of prestress, the sudden-decrease stage of the roof periodic weighting, the decrease stage of advanced support, and the rapid-increase stage of strong disturbance. Due to the large anchorage range of anchor cables, there is no decrease stage of advanced support. After the application of prestress, the bolt stress of side bolts and top bolts decreases, and the reduction amplitude is up to 30 kN. (4) As the panel advances, the deformation of the surrounding roadway increases, and the growth rate is also increasing gradually. However, the final displacement of the roof, floor, and two sides is within 18 mm. The bolt and anchor cables are not broken, and the control effect is good. The research results have a certain reference value for similar roadway control.

Analysis of the Deformation Characteristics of the Surrounding Rock Mass a Deep Tunnel during Excavation through a Fracture Zone

Aiming at geological disasters triggered by fracture zones in surrounding rocks during the excavation of deep railway tunnels, the research investigated deformation and failure of surrounding rocks triggered by sudden changes of rock quality encountered in a tunnel excavation project. The research started from analysis of a field case: the Daliang Tunnel on the Gansu–Qinghai section of the Lanzhou-Urumuqi second double-track railway in China. The deformation profiles of surrounding rocks at different distances from the fracture zone was evaluated. The deformation of surrounding rocks in and around the fracture zone was studied by combining in-situ measurement, theoretical research, and numerical simulation. In addition, relationships of deformation of surrounding rocks in the section of the fracture zone with the materials and length of advanced support as well as the excavation footage behind the fracture zone were discussed. Analysis of the results showed that there is an inflection point on the deformation curves of surrounding rocks far ahead of the fracture zone; however, it is difficult to observe the inflection point on deformation curves of surrounding rocks in engineering practice as the rocks there have undergone substantial deformation before being exposed. A combination of material properties and length of advanced support is conducive to controlling the deformation of surrounding rocks in the fracture zone. Taking a rate of deformation of surrounding rocks in the fracture zone as less than 0.1 mm/d as the stability criterion, the excavated length of that rock mass behind the zone at a footage of 1 m/d is about two thirds of that at 2 m/d and half of that at 3 m/d when the deformation stabilizes.

History and global status of the new coronavirus covid-2019 and aspects of previous infections of sars-cov and mers-cov: A systematic review

Introduction: Coronaviruses (CoV) are a diverse group of viruses which has been described in the literature since 1960, SARS, MERS and the most recent SARS-CoV-2. This new virus is causing worldwide pandemic outbreak on the first half of 2020, thousands of deaths and a major economic crisis. Objective: Due to this new context, the present study aimed to conduct a systematic study review on the global status of the new coronavirus (COVID-2019) and its aspects in comparison to the previous SARS-CoV infections and MERS-CoV. Methods: The study was conducted from January to September 2020, 89 clinical cases were submitted to further analysis and 77 studies were selected to systematic review under the PRISMA guidelines. Major findings and Conclusion: In some countries the SARS-CoV-2 pandemic appears to be out of control. In case of suspicion, tests are essential to identify early stages of invection and, if necessary, patients need to be put in quarantine and other public health measures should be taken in accordance to the World Health Organization guidelines. Advanced support is needed to identify and isolate infected patients, especially vaccines and medicines that help to control the virus and the epidemiological situation in each country. These measures are expected to reduce the rate of new cases of SARS-CoV-2.

Application Study on Active Advanced Support Technology in Deep Roadway under Mine Goaf

To solve the problems of the rapid advance of the working face was delayed by complicated working procedure and high labor intensity, and the severe damage of roof bolt (anchor cable) induced by advanced hydraulic support, the deformation characteristics of surrounding rock, and the supporting principle of grouting truss anchor cable were analyzed theoretically by taking the roadway of 3_(down) coal seams 2326# working face in Sanhekou coal mine as the research object; then, the mechanical model of supporting structure of roadway under goaf was established. Based on this model, the optimal supporting scheme was determined, and the active advanced support technology scheme of “advanced grouting truss anchor cable” was proposed to take the place of the existing single pillar. The deformation and failure characteristics of surrounding rock of the working face leading roadway were observed and analyzed on-site. Within the allowable range of reading error, the results showed that the maximum displacement of medium-deep base point and shallow base point of two roadways was 15.2 cm and 10.9 cm, respectively; the pressure value had a more obvious jump increase when the distance between each measuring point and the working face was about 35 m, which means the range is strongly affected by the advance mining, and the area affected by advanced mining was 35 m ahead of the working face. It was observed that the lowest position of roof separation development ranged from 0.71 m to 2.73 m. The separation layer was generally distributed in the range of 0.73 m-2.49 m, and the fracture area was roughly distributed in the range of 0.01 m-0.62 m. Under the condition of overlying goaf, there was a complete stress structure, which can meet the requirements of suspension support.