It will never be entirely flat because of the shape of the crotch seam, so I designed a bag with an elastic opening at the top so it wouldn't be a problem.
它永远不会完全因为裆缝形状扁平的，所以我设计了一个在顶部弹性打开袋子，以便它不会成为一个问题。
2
Base on the site observation and experimental research, the paper studied the top coal structure for the top coal caving mining in steep inclined seam sections.
在现场观测及实验研究基础上，对急倾斜水平分段放顶煤开采过程中顶煤体结构进行了研究。
3
First, based on similar material model test, top coal cave-in characters in steep and thick seam were studied as well as failure law of main roof and features of surface subsiding.