As the problems of serious bottom drum and roadway broken surrounding rock are influenced by repeated mining in multiple coal seams, the factors affecting the surrounding rock deformation of a +980 m ...roadway in Faer coal mine by analyzing the rock composition and obtaining borehole video data are investigated. The mechanism of the overburden caving affected by repeated mining of multiple coal seams is analyzed theoretically, and the numerical simulation is conducted to evaluate the deformation mechanism of roadway bottom drum. A combined support technology is proposed consisting of bolts, anchor cables, grouting, and pressure relief grooves. The measurements obtained during a 50 d monitoring period indicate that the deformations of the roof, floor, and both sides of roadway in the repaired and reinforced section are only 26, 56, and 26 mm, respectively. The fissures filled with slurry in the rock surrounding roadway can prevent further deformation of the rock mass.
The stable bearing capacity of roadside backfill body (RBB) is the key to control the surrounding rock deformation of gob-side entry retaining (GER) in deep mining. In this paper, slump and uniaxial ...compressive strength tests were conducted to study the changes of the slump and RBB mechanical properties of RBB fresh mixture under the influence of different percentages of fly ash (FA), river sand, and amounts of steel fiber (SF) admixture. The results show that (1) the slump first increases and then decreases with the increase of the FA proportion, while 20% of FA proportion is the critical point. In addition, SF has little influence on slump. However, when the proportion of FA is 60% and the content of SF is 0.4%, the slump reaches the minimum value of 130 mm. (2) The peak strength and residual strength increase with the increase of the FA proportion, and the strength gain starts to decrease when the FA proportion exceeds 40%. Moreover, SF only has a small effect on the peak strength when the dosage is 0.8%. (3) The post-peak strain difference decreases with the increase of the FA proportion and increases with the increase of the SF content. The addition of SF can make up for the reduced capacity of RBB to post-peak deformation caused by the addition of FA to a certain extent. (4) The addition of fly ash does not change the brittle failure mode of RBB. Furthermore, after the addition of SF, RBB changes from brittle to ductile failure mode. This study can provide experimental and theoretical basis for improving the bearing capacity of RBB and maintaining the stability of GER.
Replacing protective inter-block coal pillars (PICPs) with cemented artificial pillars is proposed here to address low coal recovery rates. The use of cemented artificial pillars also reduces ...resource waste when PICPs are used in the short-wall block mining (SBM) process. A coal mine test area in northern Shaanxi, China, was employed as the study site. Artificial pillar replacement techniques were developed based on the layout characteristics of a typical SBM workface. High-strength cemented backfill materials for artificial pillars were manufactured using innovative material ratio testing, and the optimum ratios for backfill materials are discussed. A cusp catastrophe model of an artificial pillar was then developed and used to deduce the conditions and critical widths necessary to generate catastrophic instability of an artificial pillar. This theoretical analysis was validated using FLAC3D simulations. Using the test site conditions, the simulations revealed that when an artificial pillar had a width of 14 m, the destruction of the pillar and associated stope was gradual and would not cause catastrophic instability. Field monitoring performed at the test site verified the theoretical analysis and numerical simulation results, confirming that it was feasible to replace PICPs with cemented artificial pillars.
The mechanical properties of cemented paste backfill (CPB) are crucial for stope safety. Some mining areas in the Yellow River basin face a shortage of coal gangue, and these areas have abundant ...river sand (RS) resources. The use of RS as a fine aggregate can optimize the particle gradation of the material and improve the strength of the material. The effects of different fly ash (FA) and RS ratios on uniaxial compressive strength (UCS), elastic modulus, and microstructure of CPB were studied using uniaxial compression test and scanning electron microscopy. The results showed that with increasing FA content, UCS gradually increased at 7 and 14 days of CPB. However, at 28 days, the UCS of CPB first increased and then decreased. When the FA content was 40%, UCS at 28 days of backfill material reached its highest value of 14.76 MPa. The elastic modulus decreased as FA content increased and reached its maximum value of 1.54 GPa when FA content was 40%. FA optimized particle composition, promoted hydration reaction, and improved CPB strength; however, when FA content was more than 40%, it hindered cement hydration, thus deteriorating UCS. Based on Weibull distribution and prepeak correction factor, a damage constitutive model was established to describe the stress–strain process of CPB under load. The results of this research will provide a theoretical and experimental basis for CPB engineering design.
As one of main directions of green mining, short-wall block backfill mining (SBBM) could provide active control of water-conducting fractures development and strata movement. Furthermore, it could ...solve the problem of gangue accumulation on surface. According to the physical similarity criterion and the characteristics of SBBM technology, the protection effect for surface water resources of SBBM was studied by physical similarity simulation tests. The results of tests had shown that SBBM decreased the water-conducting fractures development caused by strata movement after coal mining, and it has a significant effect in protecting surface water resources above the working face. Therefore, based on movement characteristics of overlying strata using SBBM, a mechanical analysis model was established under SBBM for a superimposed beams in elastic foundation with extended water-conducting fractures in overlying strata, furthermore, a method to calculate the height of water-conducting fractured zone (HWFZ) in SBBM was given, and the mechanical mechanism of water-conducting fractures development in overlying strata was revealed. The calculated HWFZ after SBM was only 2.0 m according to the mechanical model, whereas the measured HWFZ of the washing fluid loss and drilling TV imaging was 6.3 m in experimental SBBM working face. The field-measured data was closely consistent with the results of the tests (7.9 m) and the mechanical calculation (2.0 m), which verified the accuracy of physical similarity simulation tests and the mechanical model. The results of the study will enhance the recovery rate of coal resources, and they have a significant for protection of the ecological environment.
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•SBBM was proposed to recover coal seam under surface water.•Surface water resources protection effect using SBBM was analyzed by physical tests.•Mechanical mechanism of water-conducting fractures development was explained.•A method was proposed to calculate HWFZ in SBBM.
AbstractCemented gangue backfill bodies (CGBBs) are characterized by high brittleness and poor toughness in backfill mining technology. According to different types of waste tires corresponding to ...different processing and crushing means, waste tire steel fiber (WTSF) was divided into S-WTSF, P-WTSF, and H-WTSF. The influence of CGBBs with different types and amounts of WTSF on the early mechanical properties of the modified samples was studied. Uniaxial compressive strength (UCS) and scanning electron microscopy (SEM) tests on the modified CGBB samples were carried out. The results show that as the WTSF content increased from 0% to 1.5%, the UCS of CGBB samples modified with S-WTSF, P-WTSF, and H-WTSF at a curing time of 3 d first increased and then decreased; the turning point for S-WTSF and P-WTSF was 1%, and the turning point for H-WTSF was 0.5%, whereas the UCS of these modified CGBB samples at a curing time of 7 d decreased continuously with the increasing addition of WTSF content. The addition of WTSF made CGBB samples change from brittleness to ductility. With the increasing content of S-WTSF and P-WTSF, the toughness of the modified CGBB samples at a curing time of 3 d first increased and then decreased (the turning point was 1%), and that at the curing time of 7 d continued to increase. The toughness of CGBB modified with H-WTSF first increased and then decreased (the turning point was 0.5%) with the increase of the H-WTSF content. The toughness enhancement mechanism of CGBB modified by WTSF can be illustrated from a microscopic perspective as follows: WTSF is wrapped by hydration products, and the inlaying and bridging effects of WTSF are formed in the CGBB matrix. This research provides a basis for the improvement of mechanical properties of CGBB modified by WTSF and a new method for the reuse of discarded tires.
Objective: The purpose of this article is to introduce a novel imaging device and technique for percutaneous dilatational tracheostomy (PDT) and evaluate its clinical application. Methods: We have ...modified the bronchoscope to generate a novel imaging device. The handle of the bronchoscope was removed and replaced with added fixation pieces to secure the new device to the endotracheal tube. Nine mechanically ventilated patients admitted to the intensive care department of Shandong Public Health Clinical Center who underwent PDT between July 2023 and January 2024 have been treated with this novel imaging device. The number of medical staff members needed for the operation, number of needle interventions, operation time, arterial blood gas analysis, and intraoperative complications were observed. Results: Three medical staff were involved in the procedure: an operator, an assistant, and a nurse. The first attempted needle intervention was successful in all patients, and no serious complications such as major bleeding, pneumothorax, mediastinal emphysema, accidental extubation, desaturation, hypercarbia, respiratory acidosis, hemodynamic abnormality, or posterior tracheal puncture occurred. The average time was 11.63 ± 1.56 minutes from skin incision to the needle insertion and 4.43 ± 1.99 minutes from needle insertion to tracheal placement. Conclusions: PDT guided by the novel device is safe, preserves human resources, saves operating space, keeps the view stable, and makes the procedure easy. It is worthy of further research and application.
During the process of constructional backfill mining, the cemented paste backfill (CPB) typically exhibits a high degree of brittleness and limited resistance to failure. In this study, the ...mechanical and damage evolution characteristics of waste tire steel fiber (WTSF)-modified CPB were studied through uniaxial compression tests, acoustic emission (AE) tests, and scanning electron microscopy (SEM). The results showed that the uniaxial compressive strength (UCS) decreased when the WTSF content was 0.5%, 1%, and 1.5%. When the WTSF content reached 1%, the UCS of the modified CPB exhibited a minimal decrease (0.37 MPa) compared to that without WTSF. When the WTSF content was 0.5%, 1%, and 1.5%, peak strain of the WTSF-modified CPB increased by 18%, 31.33%, and 81.33%, while the elastic modulus decreased by 21.31%, 26.21%, and 45.42%, respectively. The addition of WTSF enhances the activity of AE events in the modified CPB, resulting in a slower progression of the entire failure process. After the failure, the modified CPB retained a certain level of load-bearing capacity. Generally, the failure of the CPB was dominated by tensile cracks. After the addition of WTSF, a gradual increase in the proportion of tensile cracks was observed upon loading the modified CPB sample to the pore compaction stage. The three-dimensional localization of AE events showed that the WTSF-modified CPB underwent progressive damage during the loading, and the samples still showed good integrity after failure. Additionally, the response relationship between energy evolution and damage development of WTSF-modified CPB during uniaxial compression was analyzed, and the damage constitutive model of CPB samples with different WTSF contents was constructed. This study provides a theoretical basis for the enhancement of CPB modified by adding WTSF, serving as a valuable reference for the design of CPB constructional backfill.
In the collaborative filtering algorithm, the matrix factorization method based on rating data has been widely applied and developed, but the data sparsity problem affects the method recommendation ...quality. In view of this problem, a recommendation method (RHAOR) is proposed to integrate the review text hierarchical attention and outer product. Two parallel networks are used to process user review sets and item review sets, respectively. This paper applies aspect-level attention mechanism to the review text content, marks multiple words (or phrases) with aspect information, applies review-level attention mechanism to the review set, and marks valid reviews. The outer product is used to establish an outer product interaction matrix for user preferences and item features, and the multi-layer convolutional neural network is used to extract the outer product interaction feature. The outer product interaction feature is introduced into the improved latent factor model (LFM) for rating prediction. The experimental
β‐Ga2O3 nanowires and nanobelts with a length range of tens of micrometers to a few millimeters were successfully fabricated by a simple in situ chemical vapor deposition (CVD) method under normal ...pressure without any catalysts. The morphology and microstructure of the samples were studied by SEM, XRD, and EDS. The results indicated that the morphology of Ga2O3 depends on the effective heating time. Ga2O3 nanostructures were mainly collected at the gallium source position instead of in the downstream area. So, we propose that the growth process can be explained by a vapor–solid (VS) model. The ultraviolet (UV) sensing properties of a single nanowire were tested. From the nonlinear I–V curves, we find that a single nanowire behaves as a rectifier and has asymmetric characteristics. The photoresponse characterization presents that response time and recovery time were about 0.32 and 0.08 s, respectively. Our result indicated that a single β‐Ga2O3 nanowire possesses excellent UV sensing properties and it should be a good candidate for UV‐sensor development.
