Rock pressure evaluation in coal face based on multi-factor decision-making theory.

The behavior of rock pressure is a natural and inevitable phenomenon during coal seam mining, resulting in numerous casualties and equipment damage annually. The ability to predict and assess the strength of rock pressure in the coal face beforehand has become crucial in preventing rock pressure accidents. This paper took the prediction of rock pressure strength in coal face as the research object, and based on the multi-factor decision-making theory, proposed a new method for the evaluation of rock pressure strength in coal face-"dual-dimension rock pressure strength evaluation method". Initially, the rock pressure strength index IA was obtained through the application of the law of sedimentary pressure control and microseismic monitoring data. The drilling data at the exploration scale served as references. Then, based on the rock pressure control mechanism, the rock pressure strength index IB was obtained by utilizing a type of Euclidean distance formula at the coal face scale. Finally, in order to mutually correct the two rock pressure strength indices, the rock pressure strength grade matrix was employed to acquire the rock pressure strength grade of the coal face. Applying this evaluation method to the coal face, the prediction outcomes aligned with the actual situation. Therefore, this method can provide a theoretical reference for the prediction of rock pressure strength and the prevention of rock pressure accidents in alternative areas.

Investigating the Deformation Characteristics of Buried High-Density Polyethylene Pipes: Considering the Effect of Sequentially Applying Pressure and Elevating Temperature.

High-density polyethylene (HDPE) materials have many applications in the municipal solid waste (MSW) landfills. HDPE gravity drainage pipes are commonly utilized in MSW landfills because of the polymer's resistance to harsh chemical conditions. When landfill wastes are freshly filled, the weight acting on the leachate collection pipe increases. The temperature of the leachate collection pipe increases as a result of the heat produced by the decomposition of organic components after waste filling. In this paper, the effects of sequentially applying pressure and elevating temperature on the deformation characteristics (such as deformations and strains) of HDPE pipes are investigated. Measurements of pipe deformations and circumferential strains from model experiments in which 110 mm HDPE pipes were backfilled with sand and subjected to 300 kPa of maximum vertical pressure at temperatures of 20, 60 and 80 °C showed the following results: (1) a classification of pipe behavior relative to the surrounding soil stiffness is advantageous for HDPE pipe design; (2) when temperature increases to 60 °C and 80 °C, the strain distribution around the pipe changes from V-shaped to U-shaped, and the pipe deformation profile changes from elliptical to rectangular; (3) when temperature increases from 20 °C to 60 °C, the vertical and horizontal pipe deflections increase by a factor of 1.08~1.19; (4) when temperature increases from 60 °C to 80 °C, the vertical and horizontal pipe deflections increase by a factor of 1.15~1.31; and (5) the existing analytical method that considers two extreme interfaces can capture the deformations measured in the model test well. In addition, preliminary recommendations for the design of leachate collection pipes are provided based on the analysis of differences in pipe profile versus temperature.

Effect of gas pressure on municipal solid waste landfill slope stability.

Slope failure in municipal solid waste (MSW) landfills is a common environmental disaster that poses serious ecological and health risks. Landfill slope stability (SS) is sensitive to leachate levels and gas pressure (GP) caused by the degradation of organic material, but the extent of these combined effects remains poorly understood. In this study, a simplified landfill GP calculation method is presented and a circular slide method that considers the combined effects of leachate and GP is established. The results show that the landfill GP is mainly affected by the gas production rate, gas conductivity of the solid waste (SW), and landfill depth. The safety factor of landfill SS is also significantly lower when GP is considered. The distribution of GP is affected by the depth of the failure circle and SW. Landfill slope instability can be explained by localized damage caused by GP breakthrough of the filled SW. This study probably provides important guidance for the design, operation, and management of MSW landfills.

Synergistic Strengthening of Mechanical Properties and Electromagnetic Interference Shielding Performance of Carbon Nanotubes (CNTs) Reinforced Magnesium Matrix Composites by CNTs Induced Laminated Structure.

In this study, we reported a laminated CNTs/Mg composite fabricated by spray-deposition and subsequent hot-press sintering, which realized simultaneous enhancement effects on strength and electromagnetic interference (EMI) shielding effectiveness (SE) by the introduced CNTs and CNT induced laminated 'Mg-CNT-Mg' structure. It was found that the CNTs/Mg composite with 0.5 wt.% CNTs not only exhibited excellent strength-toughness combination but also achieved a high EMI SE of 58 dB. The CNTs increased the strength of the composites mainly by the thermal expansion mismatch strengthening and blocking dislocation movements. As for toughness enhancement, CNTs induced laminated structure redistributes the local strain effectively and alleviates the strain localization during the deformation process. Moreover, it could also hinder the crack propagation and cause crack deflection, which resulted in an increment of the required energy for the failure of CNTs/Mg composites. Surprisingly, because of the laminated structure induced by introducing CNTs, the composite also exhibited an outperforming EMI SE in the X band (8.2-12.4 GHz). The strong interactions between the laminated 'Mg-CNT-Mg' structure and the incident electromagnetic waves are responsible for the increased absorption of the electromagnetic radiation. The lightweight CNTs/Mg composite with outstanding mechanical properties and simultaneously increased EMI performance could be employed as shell materials for electronic packaging components or electromagnetic absorbers.

A unit-cell model for thermal regulation of degradation of organics in solid waste.

It is a well appreciated fact that temperature is one of the key factors influencing the degradation of organics. Heat exchangers are a viable option that can be used to adjust the temperature in solid waste to an extent most suitable for waste degradation. This paper focuses on an experimental and theoretical investigation of the feasibility of using a water-circulating heat exchanger for thermal regulation of waste degradation. A cylindrical bioreactor with a central pipe connected to a water circulation system is devised and instrumented. The changes in temperature and gas production were monitored during the degradation of the organic component of the waste. Test results with and without thermal regulation are analyzed and compared. In addition, an analytical model is proposed to simulate the symmetrical heat transport behavior subjected to heat exchange. Heat generation due to the degradation of organics is taken into account. There was a good correlation between the analytical model prediction and the experimental data obtained from the laboratory test and field monitoring.