Research and Practice on Filling Technology of Fully Mechanized Coal Mining Face through Trend Abandoned Roadway

Taking the fully mechanized mining face (FMMF) through the abandoned roadway (AR) in a coal mine in Shanxi Province, China as the engineering background, the field investigation, theoretical analysis, numerical simulation and field test were comprehensively used to study the instability mechanism of the trend AR. The deformation and failure evolution of the trend AR roof were deduced into four stages: initial deformation, bending and separation deformation, fracture failure, and collapse destruction. The high span ratio proved to be the key factor affecting the stability of the trend AR, and the control principle of timely support and reduction of roof span should be followed for controlling the roof of trend AR. Comparing the traditional method through the trend AR with the perspectives of technological and economic benefits, the technology of filling and controlling the trend AR with the high water material over in the FMMF was proposed, and the effect of the filling body on the roof of the trend AR was revealed. The key parameters of the filling body were identified: the strength of the filling body is 1.0 MPa, and the water-cement ratio corresponding to the high-water material is 8:1. Based on this information, the process of the trend AR filling was designed systematically. Industrial tests show that during the FMMF through the trend AR, the roof was effectively supported by the filling body and the normal coal mining was not significantly affected, so the safe mining of coal resources was guaranteed

Stabilization Mechanism and Safety Control Strategy of the Deep Roadway with Complex Stress

With the increase of mining intensity of coal resources, some coal mines in China have gradually entered the deep mining stage. The complexity of the stress environment of the deep rock stratum leads to the difficulty of coal mining. Among them, the control of the deep roadway is one of the bottlenecks restricting the safety mining of the deep coal resources in China. By means of statistical analysis, the factors affecting the stability of the deep roadway were summed up: roadway occurrence environment, driving disturbance, and support means. The mechanical model of the deep roadway was established with the theory of elastic-plastic mechanics, the distribution characteristics of the plastic zone of the roadway were revealed, and the influence laws of lateral pressure coefficient, vertical stress, and support strength on the stability of the roadway were analyzed. Through numerical simulation, the law of stress, displacement and the plastic zone distribution evolution of the deep roadway, the mechanism of horizontal stress, and the mechanism of bolt support on the roadway were studied. On this basis, the safety control strategies to ensure the stability of the deep roadway were put forward: improving the strength of the roof and floor, especially the bearing part of the top angle and the side angle, enhancing the stability of the two sides of the roadway and controlling the floor heave, and making the surrounding rock of the deep roadway release pressure moderately, so as to make the roadway easy to be maintained under the low stress environment. These meaningful references were provided for the exploitation of deep coal resources in China

Study on the Stability Principle of Mechanical Structure of Roadway with Composite Roof

With the typical composite roof roadway and roof fall accidents in the Guizhou Province of China as the research background, the expression of damage parameters of composite roof was deduced according to Weibull statistical distribution, generalized Hooke’s law and Mises yield criterion, and the influence of shape and scale parameters of Weibull on damage characteristic was discussed. Based on the infinite slab theory, the expressions of deflection and layer separation of each layer of the composite roof were obtained, the critical load expression of each delamination was determined, and the influence of roadway width, overlying strata load, elastic modulus, shape parameters and scale parameters on the stability of composite roof was explored. The research shows that the bolt support can effectively reduce the layer separation between the composite roofs and enhance the stability of the composite roof. On this basis, it is proposed that for the surrounding rock control problem of roadways with composite roof, the active support technology with bolts as the core should be adopted

Research on the Evolution Characteristics of Floor Stress and Reasonable Layout of Roadways in Deep Coal Mining

The safe and efficient mining of deep coal resources is severely restricted by the dynamic disasters caused by high gas and high ground stress. Taking a deep mine in China as the research background, a mechanical model of the front supporting stress with the working face was constructed through theoretical calculations. Based on the limit equilibrium theory, the stress distribution in the plastic zone and the elastic zone of the lateral working face was derived; based on semi-infinite plane mechanics model, the floor vertical and horizontal stress distribution was deduced. Then, the roadway surrounding rock stress and displacement field distribution evolution characteristics were revealed through numerical simulation. On this basis, the reasonable floor gas drainage roadway (FGDR) layout was determined: internal staggered layout was used with FGDR, the vertical distance to the working face is 20 m, and the horizontal distance to the working face end is 15 m; the open-off cut of FGDR was arranged in an external staggered layout, the vertical distance to the working face is 20 m, and the horizontal distance to the open-off cut of the working face is 15 m. It is an important practical significance for the layout of FGDR, the control of surrounding rocks, and the improvement of gas drainage effects under similar conditions through the research results

Development of Modified Grouting Material and Its Application in Roadway Repair Engineering

It is very extraordinary for the success of coal mine roadway grouting with the following factors of high early strength, good fluidity, and convenient pumping, but the existing grouting materials make it difficult to achieve the above characteristics at the same time. Therefore, a modified grouting material is developed, which is composed of two kinds of dry materials A and B, which are mixed with water and in equal amounts. The physical and mechanical properties of modified grouting materials under different ratios were tested by laboratory orthogonal test, and the optimal ratio of grouting materials and additives was obtained: (1) the water-cement ratio is 0.8 : 1; (2) base material: the mass ratio of cement, fly ash, bentonite, and water is 1 : 0.3 : 0.1 : 1.44; (3) admixture: the mass ratio of water reducer C, accelerator D, and retarder E is 1.5% : 0.05% : 0.3%. The basic properties of the modified grouting materials were studied from the aspects of slurry flow state, diffusion range, and grouting parameters by using the numerical simulation method, and the reinforcement mechanism of slurry to the broken surrounding rock properties of the roadway was revealed: (1) the grouting pressure is the main factor affecting the slurry diffusion radius; (2) the mechanical properties of the roadway surrounding rock are improved, the plastic zone and deformation of surrounding rock are reduced, and the active support function of the anchor and cable is enhanced through grouting reinforcement; (3) the control effect of the roadway is improved, and the balanced bearing with anchorage structure of the roadway surrounding rock is realized through grouting reinforcement. On this basis, the modified grouting material is applied to roadway repair and reinforcement engineering practice. The field monitoring data show that the production practices were guided by roadway repair and reinforcement technology with the modified grouting material, as the core of the roadway surrounding rock control effect is good, and the modified grouting material has a wide range of application prospects

Crystal structure of the lead-containing organic–inorganic hybrid: (C18H26N2)3[Pb4I14(DMSO)2]·2DMSO

The title compound, tris(1,1′-dibutyl-4,4′-bipyridine-1,1′-diium) bis(dimethyl sulfoxide)di-μ3-iodido-tetra-μ2-iodido-octaiodidotetralead(II) dimethyl sulfoxide disolvate, (C18H26N2)3[Pb4I14(C2H6OS)2]·2C2H6OS, belongs to a class of organic–inorganic hybrid materials with novel functionalities. In this compound, C—H...O and C—H...I hydrogen-bonding interactions, π–π interactions, other short contacts and Pb octahedral chains are present, extending the crystal structure into a three-dimensional supramolecular network

Crystal structure of 5,15-dihexyl-5,15-dihydrobenzo[2,1-b:4,3-c′]dicarbazole hexane 0.375-solvate

The title compound, C38H40N2·0.375C6H14, crystallizes in the monoclinic space group P21/c and has a host–guest structure with the helicene molecules forming a porous structure and molecules of hexane inserted into the holes. The dihedral angles between the two carbazole sections of the right- and left-handed helicenes are 27.44 (3) and 25.63 (3)°, respectively. There are no classical π–π interactions or hydrogen-bonding interactions present between adjacent molecules in the crystal structure. The hexane solvent molecule shows positional disorder

A method for fault location using the phase difference of current in the protective layer at both ends of a cable section

This paper is based on the distribution characteristics of the protective layer current under the fault state of high-voltage cables, and discovers the monotonic variation law between the fault point position and the power frequency phase difference of the protective layer current at both ends of the cable fault section. A method for fault location using the phase difference of the protective layer current at both ends of the cable section is proposed. For a long cable line composed of multiple complete cross-connected sections, the cross-connected section can be located through the current power frequency phase difference P (section) at both ends of the metal sheath section, just like the section positioning within the complete cross-connected section. If P (section) ∈ (90°, 270°), then the section is a fault section; otherwise, it is a non-fault section. Finally, the relationship curve between the power frequency phase difference of the protective layer current at both ends of the fault section and the distance from the fault point is used to determine the fault location

Diversity Estimation and Antimicrobial Activity of Culturable Endophytic Fungi from Litsea cubeba (Lour.) Pers. in China

Endophytes are important components of forest ecosystems, and have potential use in the development of medical drugs and the conservation of wild medicinal plants. This study aimed to examine the diversity and antimicrobial activities of endophytic fungi from a medicinal plant, Litsea cubeba (Lour.) Pers. The results showed that a total of 970 isolates were obtained from root, stem, leaf, and fruit segments of L. cubeba. All the fungal endophytes belonged to the phylum Ascomycota and could be classified into three taxonomic classes, nine orders, twelve families, and seventeen genera. SF15 (Colletotrichum boninense) was the dominant species in L. cubeba. Leaves harbored a greater number of fungal endophytes but lower diversity, while roots harbored the maximum species diversity of endophytic fungi. For the antimicrobial activities, seventeen isolates could inhibit the growth of plant pathogenic fungi, while the extracts of six endophytes showed antimicrobial activity to all the tested pathogenic fungi. Among these endophytes, SF22 (Chaetomium globosum) and SF14 (Penicillium minioluteum) were particularly effective in inhibiting seven plant pathogenic fungi growths and could be further explored for their potential use in biotechnology, medicine, and agriculture

Research on Directional Controllability of Cracking in Hydraulic Fracturing of Hard Overburden Based on Local Stress Field Intervention

As a widely-used method of digging roadways in China, gob-side entry driving features specific advantages, such as a high recovery rate and good isolation effects. However, under the condition of hard overburden, the excessive bearing pressure of small coal pillars will easily cause serious internal damage in the coal and the run-through of the plastic zone, leading to harmful gas leakage in the goaf. Therefore, based on the engineering background of small coal pillars in the 18506 working face of Xiqu Coal Mine, this paper comprehensively adopts theoretical analysis, numerical simulation, industrial tests, and other methods, analyzes the evolution mechanism of isolated bearing and plastic fracture areas of small coal pillar under hard overburden, studies the influence law of hard overburden cutting parameters on the isolation and stability of small coal pillars, and puts forward the technology of actively cutting the top to weaken the stress concentration of coal pillars under hard overburden. With the reasonable cutting parameters determined, the controllable mechanism of hydraulic fracturing cutting under hard overburden further revealed, and the hydraulic fracturing cutting technology with “controllable cutting orientation of hydraulic fracturing with local stress field intervention” formed as the basic core, the stress situation on the roof is improved, realizing the stability control of the coal pillars for the roadway protection, and avoiding gas leakage and other disasters caused by small coal pillar destruction