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Coal seams were buried extremely shallowly in the trench slope area, which is prone to inducing surface cracks, seriously threatening the surface environment and mine safety production. The development of surface mining cracks varies at different locations in the trench slope area. In this research, we aimed to study the dynamic characteristics and laws of surface crack widths at different mining locations in the trench slope area and reveal the evolution mechanism of surface crack widths. Taking the 125,203 working face in Anshan Coal Mine in Shaanxi Province, China, as the geological prototype, we analyzed the full-cycle dynamic change law and planar distribution law of the surface crack widths in the trench slope area by combining the unmanned aerial vehicle remote sensing technology and field actual measurements and revealed the dynamic evolution mechanism of surface mining cracks in the trench area. The research results showed that the dynamic changes of surface crack widths varied at different locations of the slope. The surface crack width in the downslope area increased first and then stabilized with the advance of the working surface; the crack width at the bottom of the trench shows the dynamic change characteristic of increasing–decreasing–slightly increasing–stabilizing with the continuous advance of the working surface. The surface crack width in the upslope area showed the dynamic change of increasing–decreasing–stabilizing with the continuous advance of the working surface. Influenced by the surface morphology, the development mechanisms of surface mining cracks were different. The research results can provide practical guidance for selecting the best treatment time for surface cracks in different areas. [ABSTRACT FROM AUTHOR]

With the application of a large-mining-height working face of a mine in Shanxi as the test surface, segmented water injection, borehole television and microseismic monitoring were employed to detect the damage height of overlying rock and digitally analyse the inclination of cracks before and after mining and the relationship between the number of cracks and depth, including the number of cracks and width. A similar simulation test was conducted of the fracture evolution process. The results of this study indicated that the height of the caving zone in fully mechanized cave mining reached 40.2 m, and the height of the water-conducting fracture zone reached 126.5 m. Premining fractures were dominated by high angles and small widths. Upon gradual advancement of the coal mining face, the number of cracks linearly increased, and newly formed cracks mainly exhibited low angles and moderate widths. At the early stage of mining, the number and width of cracks gradually increased with increasing advancement of the working face location. Due to the presence of overlying strata, the mined-out area could be compacted, and the number of cracks could be reduced, thus forming the characteristics of repeated cracks. During working face advancement, upon overburden collapse, cracks could appear, thereby gradually increasing the number and width of cracks. In the area near the coal wall ahead of the working face, the number of cracks remained large due to supporting pressure occurrence, and the crack density in the overburden was distributed in a snake-like pattern. [ABSTRACT FROM AUTHOR]

The study investigated the development of lexical diversity and syntactic complexity, two key indicators of writing quality, in Chinese second language (L2) writing. The Guiraud Index and T-unit length were used to measure lexical and syntactic growth through a cross-sectional design. Seven hundred and sixty-five narrative essays were collected from grade 3-6 students in Singapore's primary schools. Statistical analyses showed a general upward trend in lexical and syntactic development over the 4 years. In line with a dynamic account, the lexical and syntactic components grew in a non-linear and non-parallel manner with both progress and regress during the process. Furthermore, a trade-off was found between more varied word use and longer sentences in the data, though it faded with grade level. While L2 subsystems tended to compete with each other at earlier stages of language learning, their interactions changed over time. Moreover, variations were observed not only across grade levels but also between learner groups at the same stage of learning. By extending a dynamic approach to writing development at early stages of Chinese learning, the study informs theory regarding the dynamics of L2 growth and has significant implications for the teaching of Chinese writing in the Singapore context. [ABSTRACT FROM AUTHOR]