Research progress of rock mechanics in deep mining

With the gradual development of coal mining into deep strata, the large deformation failure and strong dynamic impact disasters of surrounding rock caused by deep mining are becoming more and more serious. Under the complex geomechanical conditions including high ground stress, high ground temperature, high permeability, strong mining disturbance, strong rheology, and multi-field coupling, the stress field characteristics, rock fragmentation properties, strata movement and energy accumulation and release laws of deep mining areas are significantly different compared with those in shallow mining areas. In response to the rock mechanics issues in deep mining, this paper discusses the research progress made by the authors and team in three aspects: deep coal mining methods, failure mechanism and control of surrounding rock in deep roadway, and deep thermal disaster and geothermal utilization. The main results are as follows: ① the theory of balanced mining and the 110/N00 methodology for achieving balanced mining were proposed and applied in kilometer deep mines. ② The deep shaft construction mode with non-uniform pressure was proposed, and a SAP system to realize the stable lifting was developed. A mine construction method which can greatly reduce the roadway quantities and improve the coal recovery rate was invented. ③ Multiple experimental systems suitable for studying the macroscopic failure of deep soft rock under the effects of water, high temperature, high pressure, structural effects, multi-field coupling were developed. A supercomputing system capable of performing microscopic-level calculations was established. Based on the experimental results, the mechanism of large-scale deformation and failure of deep soft rock and its multi-scale mechanical properties were revealed. ④ An experimental system for simulating deep shock-type and strain-type rock bursts was built, and it was revealed that the rock burst is a nonlinear dynamic behavior in which energy is instantaneously released along the excavation-free surface. ⑤ The theory of excavation compensation support for deep roadway was proposed, and a NPR materials with extraordinary mechanical properties such as high constant resistance, high elongation, strong energy absorption, and impact resistance were invented. ⑥ A thermodynamic experimental system which can simulate deep high temperature, high humidity, and high-pressure environments was constructed, and a high temperature exchange machinery system (HEMS) for heat disaster treatment and heat source resource utilization was established. The above research achievements have been applied in the field of deep mining and can provide guidance for the complex rock mechanics problems faced by deep mining

Prediction of rockburst based on experimental systems and artificial intelligence techniques

Rockburst is characterized by a violent explosion of a certain block causing a sudden rupture in the rock and is quite common in deep tunnels. It is critical to understand the phenomenon of rockburst, focusing on the patterns of occurrence so these events can be avoided andor managed saving costs and possibly lives. The failure mechanism of rockburst needs to be better understood. Laboratory experiments are one of the ways. A description of a system developed at the State Key Laboratory for Geomechanics and Deep Underground Engineering (SKLGDUE) of Beijing is described. Also, several cases of rockburst that occurred around the world were collected, stored in a database and analyzed. The analysis of the collected cases allowed one to build influence diagrams, listing the factors that interact and influence the occurrence of rockburst, as well as the relations between them. Data Mining (DM) techniques were also applied to the database cases in order to determine and conclude on relations between parameters that influence the occurrence of rockburst during underground construction. A risk analysis methodology was developed based on the use of Bayesian Networks and applied to the existing information of the database and some numerical applications were performed. Conclusions were established.Fundação para a Ciência e a Tecnologia (FCT

Advances in multifield and multiscale coupling of rock engineering

No abstract available

Increased Expression and Altered Methylation of HERVWE1 in the Human Placentas of Smaller Fetuses from Monozygotic, Dichorionic, Discordant Twins

<div><h3>Background</h3><p>The human endogenous retroviral family W, Env(C7), member 1 gene (<em>HERVWE1</em>) is thought to participate in trophoblast cell fusion, and its expression is diminished in the placentas of singleton intrauterine growth-retarded pregnancies. However, there is limited information about the role of <em>HERVWE1</em> in discordant fetal growth in twins. This study was to compare <em>HERVWE1</em> gene expression between the placentas of discordant monozygotic twins and to identify its regulation by methylation.</p> <h3>Methodology/Principal Findings</h3><p>Fetuses from twenty-one pairs of monozygotic, dichorionic, discordant twins were marked as “smaller” or “larger” according to birth weight. Placental <em>HERVWE1</em> mRNA and protein expression profiles were analyzed using quantitative RT-PCR and immunohistochemistry (IHC) staining. Methylation profiles of the <em>HERVWE1</em> promoter region were analyzed using a pyrosequencing assay. DNA methyltransferase (<em>DNMT</em>) transcript levels were analyzed by RT-PCR. 5-methyl cytosine (5-MC) was stained using an immunohistochemical assay. There was a significant negative correlation between <em>HERVWE1</em> mRNA levels and birth weight in twins (<em>P</em><0.01). Whereas the mean methylation level of the <em>HERVWE1</em> promoter region was diminished in the smaller group in discordant twins(<em>P</em><0.01), increased mRNA and protein levels of <em>HERVWE1</em> were found in smaller fetuses compared with larger fetuses in discordant twins(<em>P</em><0.01). There was no significant difference in 5-MC staining intensity between discordant twins (<em>P</em>>0.05). The <em>DNMT3b3</em> mRNA levels in the smaller group were significantly downregulated compared with the larger group in discordant twins(<em>P</em><0.05), whereas the <em>DNMT3b7</em> mRNA levels in the smaller group were significantly upregulated compared with the larger group in discordant twins(<em>P</em><0.05).</p> <h3>Conclusions/Significance</h3><p>In discordant, monozygotic, dichorionic twins, <em>HERVWE1</em> expression was higher in smaller fetuses and lower in larger fetuses. Methylation of the <em>HERVWE1</em> gene promoter region may participate in the regulation of <em>HERVWE1</em> gene expression in discordant twin pregnancies.</p> </div

Experimental and Field Investigations on the Impact-Resistance Mechanical Properties of Negative Poisson’s Ratio Bolt/Cable

AbstractDynamic impact tests of negative Poisson’s ratio (NPR) and rebar bolts under different impact wavelengths were carried out using a self-developed NPR bolt tensile impact test system. Additionally, a field anti-impact test using blasting was performed to simulate rockburst, and the field anti-impact characteristics of the NPR and conventional cable were compared and analysed. The experimental test results revealed that the peak impact force of the NPR and rebar bolts was inversely proportional to the wavelength. The NPR bolt underwent only constant resistance structural deformation, and the rod body did not break. The rebar bolt body fractured and necked. Under the same impact wavelength, the impact force and elongation of the two bolt types were proportional to the impact velocity. Compared with the greater peak impact force of the rebar bolt, the NPR bolt output structure deformation reduced the peak impact force. At the same impact velocity, as the wavelength increased, the impact force of the NPR bolt decreased rapidly, and the number of peaks also decreased. The impact force peak value of the rebar bolt was high, the impact force-time curve had multipeak characteristics, and no apparent rapid attenuation occurred. The field test results indicated that the NPR cable could produce slip deformation under the action of an explosion impact force to absorb the impact energy and that it had special mechanical properties to maintain a constant resistance. Under the same equivalent blasting impact energy, the conventional cable test section collapsed completely. The NPR cable test section was stable overall, verifying that the NPR cable had better impact-resistance mechanical properties than conventional cable. The research results provide a reliable basis for the effectiveness of NPR bolts/cables in preventing rockbursts

Latest progress of soft rock mechanics and engineering in China

The progress of soft rock mechanics and associated technology in China is basically accompanied by the development of mining engineering and the increasing disasters of large rock deformation during construction of underground engineering. In this regard, Chinese scholars proposed various concepts and classification methods for soft rocks in terms of engineering practices. The large deformation mechanism of engineering soft rocks is to be understood through numerous experiments; and thus a coupled support theory for soft rock roadways is established, followed by the development of a new support material, i.e. the constant resistance and large deformation bolt/anchor with negative Poisson's ratio effect, and associated control technology. Field results show that large deformation problems related to numbers of engineering cases can be well addressed with this new technology, an effective way for similar soft rock deformation control

Mechanism of Strain Burst by Laboratory and Numerical Analysis

Strain burst is often considered to be a type of failure related to brittle rock material; therefore, many studies on strain burst focus on the brittleness of rock. However, the laboratory experiments show that strain burst can not only occur in hard brittle rock-like granite but also in the relatively ductile rock-like argillaceous sandstone. This result proves that behavior of rock material is not the only factor influencing the occurrence of strain burst. What must also be considered is the relative stiffness between the excavation wall/ore body and the surrounding rock mass. In order to further studying the mechanism of strain burst considering the whole system, the engineering geomechanial model and numerical model of strain burst due to excavation are built, respectively. In a series of numerical tests, the rock mass involving the excavation wall as well as roof and floor is biaxially loaded to the in situ stress state before one side of the excavation wall is unloaded abruptly to simulate the excavation in the field. With various system stiffness determined by the microproperties including the contact moduli of particles and parallel bond moduli in the models of roof and floor, the different failure characteristics are obtained. Based on the failure phenomenon, deformation, and released energy from the roof and floor, this study proves that the system stiffness is a key factor determining the violence of the failure, and strain burst is prone to happen when the system is soft. Two critical Young’s moduli ratios and stiffness ratios are identified to assess the violence of failure

Experimental Study on Mechanical Properties and Acoustic Emission Characteristics of Water Bearing Sandstone under Stable Cyclic Loading and Unloading

Due to the adjustment of energy structure, a large number of coal mines are abandoned. Considering the environmental and economic effects, many experts proposed to use the abandoned mine cavern as the reservoir of the pumped storage power station. Furthermore, considering the long-term effects of repeated pumping and drainage and hydrodynamic pressure on the surrounding rock in coal mines, a large amount of sandstone was collected from the Ruineng coal mine in Yan’an city to carry out a series of laboratory tests. Through uniaxial compression testing of rock samples with different water content rates, combined with acoustic emission (AE) analysis, the strength softening and macrodeformation characteristics are obtained, and the influence of water content on acoustic emission characteristics is clarified. The mechanical properties of water bearing rock under cyclic loading and unloading experiments with varying upper limits are obtained using a triaxial test system, and the precursory information of rock failure is captured, providing significant guidance for stability analysis and instability warning for surrounding rock in pumped storage power stations