煤炭开采与岩层运动

采矿是从地层内获取煤炭资源的过程,是一次对矿区地层的扰动,必然引起岩层运动和地层内应力场与裂隙场的改变,从而影响矿压显现、地下水流失和地表沉陷等安全与环境问题。因此,采动岩层运动及其对安全与环境的影响规律是煤炭开采的基础科学问题,对这些规律的认识将提高煤炭开采的科学性。由于采动岩层运动的复杂性,至今仍然有很多问题没有解决。介绍了采动覆岩运动的块体结构形式、岩层运动对工作面空间维护的影响、岩层运动对覆岩裂隙演化与地下水和地表沉陷等环境问题的影响、岩层运动对采动应力场影响等方面的研究进展与存在的主要问题,明确了岩层运动研究的重点和方向。结果表明:采动岩层运动是一种坚硬岩层破断前的应力集中和破断后形成块体的力学行为,坚硬岩层的破断和块体运动具有突变和不连续性,破断块体互相咬合可能形成"大变形"结构,块体咬合结构的S-R稳定性将对矿压显现、采动裂隙和地表沉陷等产生重要影响。岩层运动是一个"黑箱",目前仅仅在控制原理上得到解释,达到"灰箱"程度。因此,岩层控制在很多场合只能是"宏观"控制。"砌体梁"结构力学模型的建立明确了支护原理和支架工作阻力估算原则。一般情况下,按照4～8倍采高岩柱自重估算支架工作阻力可以满足工程需要,在大采高或薄直接顶、浅部开采、特殊压架条件等情况下支架工作阻力估算应采用上限,个别条件下单纯提高支架阻力仍无法彻底解决压架问题,还需配套实施相关工程措施加以防范。根据覆岩关键层破断块体结构的稳定性,将我国不同表土层条件下的地表沉陷划分为3种类型,提出应根据地表沉陷的不同类型进行预测、控制与选择复垦方法。关键层的赋存与破断特性对采动应力分布影响显著。目前,由于应力集中引起的事故比瓦斯事故更难以预防,为此,深部和构造应力集中区域只能开设试验矿井。

Behaviors of strata movement in coal mining

Coal mining involves extracting the resources from the earth.It will disturb the strata in the mining area,which inevitably causes strata movement and the change of stress and fracture fields,thus affect safety and environmental such as the occurrence of ground pressure,groundwater loss and surface subsidence.Therefore,mining induced strata movement and its influence on safety and environment are the basic scientific problems of coal mining.The understanding of these laws will improve the scientific nature of coal mining.Because of the complexity of strata movement,however,there are still several issues to be addressed.This paper introduces the mining induced strata movement of the block structure,which is followed by the review of advances and outstanding issues in the influence of strata movement on longwall face support,mining induced fractures evolution,groundwater,surface subsidence,and mining induced stress field.It is found that mining induced strata movement is a combination of stress concentration caused by the span of thick and hard strata and the mechanical behaviors of the rock blocks associated with the breakage of the strata.During the collapse of thick strata and the corresponding rock block movement,the characteristics of mutations and discontinuities typically occur.In such a process,a structure that can sustain large deformation may be formed after the rock blocks are hinged.The “R-S” stability of the structure causes significant influence to such phenomena as the occurrence of ground pressure,mining induced fractures and surface subsidence.Mining induced strata movement is like a “black box” system.Currently it is just explained in the aspect of control principle,and reaches the level of a “gray box” system.Therefore,strata control refers to “macroscopic” control in many engineering cases.The Voussoir Beam model has established longwall support theory and the estimation principle of support working resistance.In a general case,the support resistance that is determined as the weight of the overburden with a thickness of 4-8 times the mining height could meet the safety requirements of most mining projects.Specially,8 times should be chosen for the longwalls with a large mining height or a thin immediate roof,a shallow cover depth,or the support crush risks.As for some particular conditions,however,support crush cannot be avoided by the single measure of increasing support resistance,but should be combined with other engineering precautionary measures.According to the stability of rock blocks of overburden key strata,three types were proposed to characterize surface subsidence for varied alluvium conditions in different areas of China.It is suggested that subsidence type should be considered during the selection of subsidence prediction,control and reclamation methods.The presence of key strata and the corresponding breakage characteristics play a vital role in the distribution of mining induced stress.At present,the prevention of accidents caused by stress concentration is harder than that of methane accidents.With this in mind,it is suggested that only test style mines could be established in the areas with tectonic stress concentration or a large depth.This paper points out the direction for the study of strata movement and the corresponding influence on safety and environment in the coal mining industry.