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This study investigated the dynamic recrystallization (DRX) mechanism and hot-deformation behavior of the solution-treated Mg-0.5Bi-0.5Sn-0.5Mn (BTM000) alloy during hot compression at temperatures ranging from 175 to 225 °C with a strain rate of 0.001–1 s−1. Processing maps and constitutive equation were used for a detailed analysis. The results showed a strong correlation with a coefficient of 0.987669, indicating the accuracy of proposed method in predicting the hot deformation behavior. The average activation energy (Q) was found to be 139.10 kJ/mol, and the stress component (n)was calculated to be 7.96, suggesting that cross-slip is the primary deformation mechanism. Based on the processing maps, the most suitable processing conditions were found to be within the range of 210–290 °C with a strain rate of 0.37–1 s−1. At a low strain rate of 0.001 s−1, the dominant deformation mechanism observed was pyramidal slip. However, at higher temperatures (175–325 °C) and a strain rate of 1 s−1, a transformation from basal slip to a combination of basal slip and pyramidal slip was observed. Under low-temperature and low-strain-rate conditions (175 °C/0.001 s−1), continuous dynamic recrystallization (CDRX) was the dominant mechanism. In contrast, under other deformation conditions (175 °C/1 s−1, 325 °C/0.001 s−1, 325 °C/1 s−1), a synergistic effect between discontinuous dynamic recrystallization (DDRX) and CDRX was evident. Through quasi-situ kernel average misorientation (KAM) characterization, it was observed that the local storage energy associated with CDRX was significantly lower compared to the combination of CDRX and DDRX, indicating a higher likelihood of CDRX occurrence.

The addition of Sn improves the properties of Mg–Bi-based alloys, and can potentially overcome the high-temperature limitations of magnesium (Mg) alloys. However, high-Sn alloying leads to stress concentration during hot extrusion. Hence, in this study, the dynamic recrystallization (DRX) mechanism and hot-deformation behavior of a novel precipitate-free Mg–0.25Bi–0.25Sn alloy during hot compression conducted at 250–400 °C with strain rate of 0.001–1 s−1were examined in detail by constructing processing maps and deriving constitutive equation. The obtained correlation coefficient was 0.99113, indicating that the proposed method can adequately predict the hot deformation behavior of the studied alloy. The calculated average activation energy was 143.0336 kJ/mol. According to the processing maps, the ideal processing areas corresponded to the conditions of 300–400 °C/0.001 s−1/1 s−1and 400 °C/0.1 s−1. In addition, a transformation of prismatic slip to pyramidal II slip was observed at 350 °C, and the continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) processes occurred during hot compression. The classification of the dominant DRX mechanisms was based on the Zener–Hollomon parameter (Z). Under high-Zdeformation conditions, CDRX and DDRX occurred simultaneously; however, CDRX was the predominant process. Under medium-Zdeformation conditions, DDRX was the only DRX process. Under low-Zdeformation conditions, DDRX dominated over the DRX mechanism and was partially accompanied by CDRX.

Compared with I-shaped and U-shaped supports in soft rock roadway, concrete-filled steel tubular (CFST) support, as a new supporting form, has stronger bearing capacity with reasonable price. So it is becoming more and more popular in roadway supporting of coal mine in China. In this article, the surrounding rock in soft rock roadway was classified into three different types: hard rock in deep coal mine, soft surrounding rock, extremely soft surrounding rock. And, according to the characteristics of deformation failure of the CFST support and the surrounding rock in the industrial tests, three different strength assessments, including assessment of axial compressive strength, assessment of lateral flexural performance, assessment of hardening rate of core concrete, were proposed through mechanical analysis and laboratory tests for the three different types of the surrounding rock, respectively. Moreover, aimed to insufficient flexural strength of the support or low hardening rate of the core concrete in some of the roadway supporting, strengthening lateral flexural performance or making early strength concrete was necessary for the above unfavorable situations. The laboratory test results showed that the ultimate bearing capacity for the CFST support with φ194*8mm of steel tube reinforced by φ38mm round steel was 31% greater than that of the unreinforced one, 177% greater than that of the U-shaped one with equivalent weight per unit length.

The soft rock roadway is classified by uniaxial compressive strength of rock and water-physical properties, which includes hard surrounding rock in deep mine, soft surrounding rock, and extremely soft surrounding rock. Aimed to the situation of being hard to support the extremely soft rock roadway, with combination of the specific project of return airway crossheading roadway of sea area NO.2 mining district in Beizao coal mine, a compound roadway supporting technology based on the concrete-filled steel tube support, reinforced concrete lining, with combination of yield supporting technology was used for this specific project, for which the mechanical model of the pressure-bearing ring structure was analyzed and calculated by using fixed-end arch theory in structural mechanics and Lame formula in Elastic theory. The field test results showed that this new compound roadway supporting technology was an ideal method to support the extremely soft rock roadway, which could control the deformation of roadway and realize the stability of roadway, effectively.

Part of the east wing belt roadway in -450 level east, NO.1 mining area, Dashu village coal mine, Jizhong Energy Fengfeng Group was under the 172102 working face’s stop mining coal pillar. The phenomenon of the stress concentration was obvious, the pressure of the roadway was large and the surrounding rock damaged severely. Concrete filled steel tube supports were used in stress concentration region. The supports type was φ194×8mm, and distance between supports was 800mm. They were of rapid construction speed, better supporting effect. The numerical simulation results also showed that the concrete filled steel tube supports can reduce deformation of the roadway surrounding rock in stress concentration region effectively.

East auxiliary roadway of Pingshuo Mine No.3 passed through coal bed washout with the roof rock crushing, which leaded to roadway support difficulty. by experimental tests on axially loaded F168mm STCC (steel tube confined concrete ) short columns with different steel tube wall thickness, UBC(ultimate bearing capacity) of selected F168 × 7 mm steel tube confined concrete short columns was 2650 kN, support pressure was 1.16 MPa., then support scheme of F168 × 7 mm steel tube confined concrete supports was proposed. The result of FLAC3D simulation was that the maximum displacement of surrounding rock was 55.6mm. On-site support practice also showed that the support scheme guaranteed the stability of the roadway sounding rock

Through testing the mountainous shallow-buried coal seam mining working face strata behaviors in Faer mine field, it got the strata behaviors: it was of large roof pressure, high rate of safety valve opening in hydraulic support, and even some supports crushed or took separation between top beams and tail beams. Traditional method of calculating supports’ resistance can not be applied to mountainous shallow-buried coal seam mining working face. With the discrete element simulation software UDEC it analyzed the strata movement feature, and got that the overlying strata took collapse and horizontal displacement after mountainous shallow-buried coal seam mined, and the strata movement feature was different between reverse slope mining and positive slope mining.