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In this research, the Strength and deformation behaviors, cracking process, and local stress evolution of sandstone specimens containing a circular opening and two joints (called H-J sandstone specimens in this study) were researched by experiment and numerical simulation (two-dimension particle flow code). The effect of different joint positions around the opening has been specifically studied by changing the ligament angle (${\beta }$). The test results show that peak strength and peak strain firstly decrease then increase with the increasing ${\beta }$, while the peak strain presents an overall upward trend. Three types of coalescence failure patterns between the opening and joints formed, and the corresponding cracking process and acoustic emission (AE) characteristics are highly related to the ligament angle. Based on the micro-parameters calibration, a good agreement was achieved between experimental and numerical simulation. The numerical results show that the local stress evolution around the opening is highly corresponding to the cracking process. The microcracks initiation and propagation cause obvious stress fluctuations, drops or increasements of minimum principal stress, while the cracks coalescence results in obvious reduction of maximum principal stress and drops of stress-strain curve. It also be found that the stress distribution and magnitude around the opening tend to be closely related to both coalescence failure and strength characteristics of H-J specimens. Finally, the cracking mechanism between the opening and joints was revealed based on particle displacement fields. The results show that different cracking mechanism may cause different local stress changes, which finally determines the overall mechanical behavior of specimens.

With the continuous westward shift of China’s coal production center, the western mining areas will play an increasingly important role in ensuring national energy security. It is urgent to extract coal economically and efficiently and realize scientific mining under the premise of ensuring the safe and environmental capacity. This paper systematically summarizes the research progress of coal seam separation water disaster at home and abroad, and elaborates the problem of coal seam separation water disaster from four aspects: formation mechanism of coal seam separation water, disaster-causing mechanism, prediction and early warning of water disaster and key prevention and control technologies. This paper summarizes the research on mining overlying strata separation and the formation mechanism of overlying strata separation water, and summarizes the formation of coal seam overlying strata separation water into three basic conditions: water separation, the existence of recharge water around the separation bed, and the separation space lasting long enough. However, the prevention and control of coal mine water disaster under complex geological conditions is an important problem restricting coal mine safety at present. The water damage prediction of overlying strata separation is summarized from three aspects: prediction of the location of available water separation, prediction of the periodicity of water inrush and prediction of the amount of water inrush, according to the development characteristics of bed separation. In this paper, the water damage prediction of overlying strata separation is summarized from three aspects: prediction of the location of available water separation, prediction of the periodicity of water inrush and prediction of the amount of water inrush. According to the development characteristics of bed-separation and the location of bed-separation water, the main prevention and control methods of bed-separation water damage, such as diversion hole, advance drain hole and ground direct pump hole, are proposed.

A novel self-centering prestressed concrete (SCPC) pier with external energy dissipators (EDs) has been recently proposed to minimize the structural damage and residual deformations, and enhance the corrosion-resistant capability. In the SCPC pier with external EDs, internal post-tensioned basalt fiber-reinforced polymer (BFRP) tendons are used to provide the self-centering ability, and the energy dissipation is realized through the external aluminum bars. Previous cyclic load tests of 1/3-scaled specimens showed that the SCPC pier with external EDs had desirable self-centering and energy dissipation capacities. In this study, a three-dimensional finite element (FE) model is developed using the ANSYS software. The FE model can capture the complex behavior of the proposed pier, such as gap opening/closing at the pier-foundation interface, energy dissipation of EDs, and self-centering capacity. Good agreement is observed between the numerical and experimental results, demonstrating the accuracy of the developed FE model. This will enable the parametric studies on the seismic performance of the SCPC pier with external EDs in the future.

A novel self-centering prestressed concrete (SCPC) beam-column connection with web friction devices has been recently proposed for moment-resisting concrete frames. This paper presents the fragility analysis results of a SC concrete frame and a conventional reinforce concrete (RC) frame at various performance levels. Three performance limit states (i.e., Immediate Occupancy, Life Safety and Collapse Prevention limit states) are defined based on the peak story drift ratio and two other performance limit states (i.e., Re-centering and Repairable limit states) are defined based on the residual story drift ratio. Statistical analyses of the seismic demands reveal that the SC frame reduces the softening and dispersion of the residual story drift behavior. Fragility curves indicate that the SC frame experiences much smaller residual deformations and shows considerable reduction in the median fragility and probability of exceedance for the residual drift-related performance levels, as compared with the conventional RC frame.

The polyethylene lined tubing is the key to enabling the industry to meet some of the energy security challenges that nations face today. It is well known that manganese is an important element in polyethylene lined tubing. In this paper, a simple spectrophotometric method was described for the determination of manganese in polyethylene lined tubing. The method was based on the oxidation-reduction reaction between ammonium persulfate and manganese(II) producing manganese(VII) in the presence of silver nitrate as a catalyst. The characteristic wavelength of maximum absorption of manganese(VII) was obtained locating at 530 nm. Under the optimum reaction conditions the absorption value was proportional to the concentration of manganese in the range of 0.2%~1.9% (R2 = 0.9997), and the relative standard deviation was less than 3.0% (n=5). The proposed method was applied successfully to determine manganese in polyethylene lined tubing real samples.

The polyethylene lined tubing is the key to enabling the industry to meet some of the energy security challenges that nations face today. It is well known that manganese is an important element in polyethylene lined tubing. In this paper, a simple spectrophotometric method was described for the determination of manganese in polyethylene lined tubing. The method was based on the oxidation-reduction reaction between ammonium persulfate and manganese(II) producing manganese(VII) in the presence of silver nitrate as a catalyst. The characteristic wavelength of maximum absorption of manganese(VII) was obtained locating at 530 nm. Under the optimum reaction conditions the absorption value was proportional to the concentration of manganese in the range of 0.2%~1.9% (R2 = 0.9997), and the relative standard deviation was less than 3.0% (n=5). The proposed method was applied successfully to determine manganese in polyethylene lined tubing real samples.