浅埋薄表土层特厚煤层强制放顶条件下主要地裂缝演化规律实测

Field survey on the evolution of main ground cracks under condition of forced hard roof caving in mining ultra-thick coal seams under shallow overburden

黄河流域是我国重要的生态屏障,也是我国重要煤炭基地集中区,生态保护与煤炭开采矛盾在此处异常突出。晋北煤炭基地具有典型浅埋薄表土层特厚煤层坚硬顶板的埋藏条件普遍采用强制放顶技术进行煤炭资源生产,但鲜见相关地理及技术条件下的地表主要裂缝演化规律研究,地表主要裂缝的产生制约着此类矿井生态保护与煤炭开采协同发展。为此,针对该条件下地裂缝的演化规律进行了实测研究,得到:①主要裂缝产生于开采边界,表现为先张拉、后上下错动且裂缝上部与下部脱离、上台阶下方会出现空洞。②工作面“见方”时,开采各边界主要裂缝发育情况类似,“见方”后,关键层按循环爆破步距(20 m)的3倍周期垮落,两侧巷道上方地表主要裂缝也按60 m“跳跃式”发育。③工作面正上方主要裂缝宽度及高差始终小于其他3处开采边界的主要裂缝,且闭合速度每隔一个放顶步距发生一次改变。④深(采深)厚(采厚)比较小、表土层薄时易造成对地表破坏最严重的边界不可自修复大裂缝,且裂隙带直达地表,绝大多数主要裂缝处于采场边界内,裂缝闭合周期更短,约9 d。⑤110和N00工法及错层位等无煤柱开采技术可扩大均匀沉陷区范围,缓解边界台阶裂缝损害,有利于源头治理和节省成本。

The Yellow River Basin is an important ecological barrier and also an important coal base concentration area in China.The contradiction between ecological protection and coal mining is prominent.Under the conditions of typical shallow overburden,extra-thick coal seam and hard roof in the Northern Jinbei coal base,the forced roof caving method is generally adopted,but the research on the evolution of surface cracks is rare,which restricts the coordination of ecological protection and coal mining in such mines.This paper presents a field meas-urement research on the evolution of main ground fractures under such conditions.The main conclusions are:①The cracks formed were mainly at the mining boundaries,which first stretched,then staggered up and down,and the upper and lower parts of the cracks were separated,and cavity appeared below the upper step.②When the working face became“square”,the development of cracks at the all boundaries was similar.After“square”,the key strata was caved in a three-times distance of the cyclic blasting step(20 m),i.e.,every three times of forced caving,60 m,was the period of cyclic failure and collapse.The main ground fractures above the gate roads on both sides also developed in a“step”manner of 60 m.③The cracks right above the working face were smaller than other three sides in terms of crack width and altitude difference,and the closure speed changed once per cycle forced caving distance.④The ratio of mining depth to mining height was small and the topsoil was thin leading to the non-self-repairing large cracks at the mining boundary which has the most serious impact on surface.The fracture zone directly reached the surface.Most of the main cracks were inside the edge of the stope and the closure cycle were shorter,approximately 9 days.⑤The 110 and N00 method and split-level longwall mining without gate pillars can expand the uniform subsidence area and mitigate the boundary crack damage,which are good for healing from the root and saving investment.