In this paper, the aim is to achieve safe, rapid excavation of an extra-long, large-cross-section highway tunnel in Eastern Tianshan, as well as to reduce production costs, simplify production processes, reduce cycle time, and improve production efficiency. In this study, we explored a new technology for smooth blasting without a detonating cord. A series of sympathetic detonation experiments were conducted in the tunnel face to determine critical distances. The critical distance for No. 2 rock emulsion explosive under blasthole constraints was successfully measured to be approximately 1.0–1.1 m. Based on the critical distance, a new charging structure was designed for tunnel excavation. To assess the influence of the new charging structure on blasting performance, its economic benefits, and its feasibility, full-section tests were performed in the East Tianshan Tunnel. The application of the new charging structure produced good smooth blasting results. It not only simplified the charging process and produced smooth blasting without detonating cord in peripheral holes, but also guaranteed normal excavation, an appropriate tunnel profile, and reasonable overbreak and underbreak volumes. This had remarkable economic benefits and possesses better promotional value.
Lightweight composites consisting of 6063 aluminum alloy matrix reinforced with AlCoCrFeNi high-entropy alloy (HEA) particles were fabricated by the powder metallurgy through hot pressing and hot extrusion under vacuum. A detailed microstructural characterization was carried out along with the analysis of mechanical properties. The results revealed that the observed uniform distribution of HEA powders and a good bonding strength resulted in an effective strengthening and increased plastic strain of the reinforced composite. The tensile properties of composites were effectively improved by the addition of 10 and 30 vol % of reinforcing HEA particles.
In recent decades, researchers have paid more attention to the indirect tensile test than to the direct tensile test (DTT) of rocks, mainly due to difficulties in the alignment and the stress concentration at the end of an intact cylindrical specimen. In this paper, a new flattened cylinder specimen and a clamp device were designed to obtain the true tensile strength of the rock in DTT. Stress distributions of the specimen with different lengths (l) and cutting thicknesses (t) were analyzed, and damage processes of the specimen were monitored by the Digital Image Correlation (DIC), the fractured sections were also scanned. Different mechanical parameters were also obtained by the DTT of the flattened cylinder specimens and the intact cylinder specimens, as well as the Brazilian disc. Research results show that the tensile strength obtained by DTT is smaller than the Brazilian disc and is slightly greater than the intact cylindrical specimen. The flattened cylinder specimen with 0.20 ≤ 2t/D < 0.68 and 0.10 ≤ l/D ≤ 0.20 is recommended to measure the true tensile strength of rock material in DTT. This new shape of the specimen is promising to be extended in the uniaxial or triaxial direct tension test.
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