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To explore the effect of rapid excavation unloading under high pressure on delayed rockburst, a true triaxial double-sided rapid unloading rockburst experiment and a biaxial compression failure experiment without unloading were carried out. The results show that the rapid unloading of excavation before the occurrence of rockburst will cause unloading damage, and the axial strain, acoustic emission (AE) count, and AE energy will suddenly increase at the unloading point. The AE source shows that the rapid unloading produces many tensile cracks, mainly distributed near the free surface. The axial peak stress of the rockburst and the stored strain energy before failure are higher than those of biaxial compression, so the ejection velocity of free surface fragments is also higher at failure. Key words: rockburst experiment, delayed rockburst, fast unloading, energy storage, acoustic emission (AE), AE source, Introduction Hydropower engineering construction, mining of mineral resources, and geological disposal of nuclear waste involve deep rock mass excavation. A rockburst is a sudden failure mechanical phenomenon during the excavation [...]

Background: This study investigated the characteristics of Monson's sphere in Chinese young adult females with individual normal occlusion to provide a reference for oral rehabilitation in prosthodontic and orthodontic treatments. Methods: Points at the dental cusps and incisal edges were selected from 51 digital mandibular dental models of Chinese young adult females (aged 18–22 years) with individual normal occlusion. Monson's spheres were fitted to the selected points based on the least-squares principle and the radii were calculated. The deviation of each selected point from its relative spherical surface was also calculated. The radii and deviations of these points were examined using conventional descriptive statistics and distributions of the most deviated points inside and outside the spheres were analyzed. Results: The mean radius of Monson's sphere in Chinese young adult females was 79.60 ± 14.13 mm. The deviation of each selected point from its relative sphere surface was 0.38 ± 0.30 mm. The maximum deviations inside and outside the sphere were 0.93 ± 0.25 mm and 0.95 ± 0.30 mm, respectively. The most deviated points outside the spheres were mainly distributed at the distolingual cusps of the mandibular second permanent molars (31.37%), while those inside the spheres were mainly distributed at the mesiolingual cusps of the mandibular first permanent molars (45.10%). Conclusions: The radius of Monson's sphere in Chinese young adult females was smaller than the classic four-inch value suggested by Monson. Deviation was observed from all selected points to their Monson's sphere surface, with the most deviated points distributed primarily in the molar region. [ABSTRACT FROM AUTHOR]

Impact rockburst is induced by the combined static and dynamic loads after excavation.There are two types of impact rockburst experiments，one is induced by changing the static load and another is induced by changing the amplitude of dynamic load.The sandstone fragments after these two experiments were collected.Meanwhile，the sandstone fragments generated from the similar compression experiment under static load were collected too.And the mass， length，width and thickness of each fragment has been measured respectively.The quantities and mass distribution of fragments with coarse，medium，fine and micro grains in different size ranges，and size distribution were further analyzed.The crushing level and shape characteristic of fragments were obtained.Then the fractal dimensions were calculated.The results show that the degree of crushing level of fragments from impact rockburst is higher and with obvious slice shape；the ways of combined static and dynamic loads have a little effect on the crushing level and scale characteristic of fragments from impact rockburst experiments；energy dissipation from impact rockburst experiments is higher than that of similar compression experiment.