Mechanical Characteristics and Stress Evolution of Cemented Paste Backfill: Effect of Curing Time, Solid Content, and Binder Content

The clarification of the variation on the strength of the cemented paste backfill (CPB) under the coupling of multi-factor is the foundation of the CPB design of the mine. In this article, the physical and mechanical properties of the CPB under the coupling effect of curing time, solid content, and binder content were experimentally and theoretically investigated. The results show that 1) the increase in binder content can effectively increase the later strength of CPB. 2) A sensitivity parameter considering the span of multi-factor was constructed, indicating that the curing time has the greatest impact on the uniaxial compressive strength (UCS), and the variation in solid content has the least impact on it, which can be verified by the stress–strain curves. 3) Curing time and binder content can effectively change the stress evolution, which is reflected in reducing the strain corresponding to the peak stress, enhancing the characteristics of the peak stress and increasing stress drop. The results of this study aim to explain the essence of the influence of each factor on the mechanical behavior of CPB in the view of stress–strain evolution, which will help to better understand the mechanical characteristics of CPB and quantify the sensitivity of the mechanical properties to various factors.

Dynamic Evolution Law of Overburden Rock in Shallow-Buried Super-High Fully Mechanized Working Face and Determination of Support Strength

The objective of this study was to reveal the law of overburden movement and stress evolution during the mining of super-high fully mechanized mining faces. Based on the 12401 fully mechanized mining face of Shangwan Coal Mine in Shendong, this study conducted research and analysis using the methods of similarity simulation experiment, numerical simulation, and field measurement. The results showed that the maximum and minimum principal stresses in the coal seam in front of the working face are concentrated with the advance of the working face. The degree of stress concentration increases with the increase in the advancing range, and the concentration degree of the maximum principal stress and the change gradient is greater than that of the minimum principal stress. But the range of the peak lead coal wall is lower than that of the minimum principal stress of the peak lead coal wall. The phenomenon of stress recovery exists in the goaf. With the increase in the advancing range of the working face, the degree of stress recovery gradually increases, and the degree of maximum principal stress recovery is higher than that of the minimum principal stress recovery. The large fractures observed near the working face are closely related to the underground pressure, relatively large fractures appear on the surface, and the fractures become narrower near the two pathways. Only caving and fissure zones exist in the thin bedrock overburden, and the bending subsidence zone changes with the bedrock thickness. The support strength of the hydraulic support should not be less than 1.47 MPa. This research on the overburden movement and stress evolution law of a super-high fully mechanized mining face can provide theoretical guidance for the exploitation and utilization of extrathick coal seam resources. It has broad engineering prospects.

The Effect of Grain Boundary Carbides on Dynamic Recrystallization During Hot Compression of Ni-Based Superalloy Haynes $$282^{\mathrm{TM}}$$

In alloys where carbides are the main grain boundary phase, the role of carbides during hot working is not known. Here, we address the effect of grain boundary carbides on the dynamic recrystallization during hot compression of Ni-base superalloy Haynes 282. When excluding variations from experimental factors neither stress evolution nor final microstructure indicated that carbides exerted a significant influence on the dynamic recrystallization. The carbide solvus temperature is not a critical limit during thermomechanical processes.