Investigation of a non-explosive directional roof cutting technology for self-formed roadway

Traditional explosives have characteristics of high risk,large vibration,and poor directional fracturing.Consequently,an instantaneous expander with a single crack surface(IESCS),which is a novel nonexplosive directional rock-breaking technique,has been developed.The directional roof-cutting mechanism of the IESCS method,driven by high-pressure gas,was theoretically analyzed.Laboratory experiments and numerical simulations proved the directional slitting effect of the IESCS method to be excellent.Compared with shaped-charge blasting,the charge of IESCS was reduced by 8.9%,but the crack rate increased by 9%in field tests.After IESCS pre-splitting,the roof directionally collapsed along the cutting line,and the gangue filled the goaf.Moreover,the directional roof cutting by the IESCS could decrease roadway stress.The average pressure of hydraulic supports on the cutting side of the roof was 31%lower than that on the non-cutting side of the roof after pre-splitting.After the self-formed roadway constructed by the IESCS was stabilized,the final relative displacement of the roof and floor was 157.3 mm,meeting the required standard of the next working face.Thus,the IESCS was effectively applied to directional roof pre-splitting.The results demonstrate the promising potential of IESCS in the mining and geotechnical fields.

CUTTING-DIRECTION BURR FORMATION IN ORTHOGONAL PRECISION CUTTING

The cutting burr is one of the common phenomena occurring in metal cutting.In this paper,the forming processes,main effect factors and change law of the cutting direction burr in orthogonal cutting have been studied and related theories are analyzed based on the cutting experiments.The result shows that:(1)the forming processes of cutting direction burr consist of normal cutting,flexure deformation of end surface of workpiece,plastic effect,continuous cutting and shear break separating in orthogonal cutting;(2)a new phenomenon is found that cutting direction burr is formed with the shear break separation of the chip and workpiece machined surfaces;(3)the size of cutting direction burr varies with workpiece materials,cutting parameters and geometric parameters of the cutting tool.

Failure mechanism of directional roof cutting and design method optimization

Directional roof cutting(DRC)is one of the key techniques in non-pillar coal mining with self-formed entries(NCMSE)mining method.Due to the inability to accurately measure the expansion coefficient of the goaf rock mass,the implementation of this technology often encounters design challenges,leading to suboptimal results and increased costs.This paper establishes a structural analysis model of the goaf working face roof,revealing the failure mechanism of DRC,and clarifies the positive role of DRC in improving the stress of the roadway surrounding rock and reducing the subsidence of the roof through numerical simulation experiments.On this basis,the paper further analyses the roadway pressure and roof settlement under different DRC design heights,and ultimately proposes an optimized design method for the DRC height.The results indicate that the implementation of DRC can significantly optimize the stress environment of the working face roadway surrounding rock.At the same time,during the application of DRC,three scenarios may arise:insufficient,reasonable,and excessive DRC height.Insufficient height will significantly reduce the effectiveness of the technology,while excessive height has little impact on the implementation effect but will greatly increase construction costs and difficulty.Engineering verification shows that the optimized DRC design method proposed in this paper reduces the peak stress of the protective coal pillar in the roadway by 27.2%and the central subsidence of the roof by 41.8%,demonstrating excellent application results.This method provides technical support for the further promotion of NCMSE mining method.

Cultural Practices for Propagation of Spatholobus suberectus via Cutting into Polybags

In this paper,the propagation of Spatholobus suberectus Dunn.was optimized based on the research results conducted in propagation for many years and the actual need for the planting materials.According to the requirements of Good Agricultural Practices for Chinese Medicinal Drugs,cultural practices for propagation of S.suberectus were summed up and standardized,including the environmental requirements,land preparation,bed preparation,cutting of scions,cuttings treatment,cutting,management of cuttings at the nursery,bagged cuttings ready for transplanting,packing and handling,transportation,and preparation of records for archives.

Comprehensive Review of Studies on Metamorphic Rocks

Marble is a metamorphic rock, which is one of the 3 basic rock types (magmatic, sedimentary, metamorphic) forming the earth’s crust. The major characteristic sought after in a rock mass in the field for it to be exportable and usable as marble is its suitability to be cut in blocks. In the process of producing marble slabs from marble blocks, the blocks are expected not to contain potentially problematic hard or weak zones and their geomechanical and chemical properties should conform to the relevant standards. Ignoring of the geological properties of the rock in the process of deciding for marble production at a marble site and determination of production location, direction and method is the most important parameter that would increase production loss. In order to reduce losses by determination of geological properties of marble, many academic studies have been conducted on the effects of water saturation, temperature, freezing and thawing on its mechanical and fracture properties. There are further studies on crack propagation in marble under stress. However, even those marble blocks that are obtained based on geological parameters may suffer serious cracks or fractures due to stresses caused by their weight and geometry. Therefore, cutting direction is of critical importance in order to minimize marble waste in the process of cutting a marble block which is brought to the inventory or processing site with cracks, cavities or fractures. Certain studies exist within such context, where the geometry of the discontinuity within a block is determined using non-destructive methods, such as ultrasonic testing, in order to determine the appropriate cutting direction. Such studies made use of ultrasonic waves to determine the physical and chemical structures of magmatic and sedimentary rocks by measuring the progress velocity of sonic waves in the rock. Said studies, however, mostly worked on sedimentary and magmatic rock specimens, focusing less on metamorphic rocks such as marble due to their anisotropic properties. Understanding the academic literature studies on marble would provide significant contribution to the reduction of production losses during the processing marble blocks in processing plants and the achievement of production efficiency levels that are within economic limits. Within such scope, this study has reviewed the past academic studies on marble, classified them under 6 categories, and comprehensively analyzed each category based on materials, testing setups, test specimens, test parameters and research techniques.