考虑垮落岩体应变硬化特性的采场覆岩破坏特征研究

Study on failure characteristics of stope overlying rock considering strain hardening characteristics of caved rock mass

煤炭开采引起的覆岩运动、变形和破坏直接影响地下水库的储水库存与水源补给能力,为了科学精确化计算地下水库库容,有必要考虑采空区垮落岩体在渐进压实过程中体现出的应变硬化力学特性对采场覆岩“两带”高度分布特征的影响作用。以李家壕煤矿为工程背景,基于垮落岩体在压实过程中体现出的应变硬化力学特性,采用双屈服模型和提出的反演计算方法对采场覆岩破坏特征进行研究,推导得出垮落岩体应力表达式,分析其影响因素,提出了数值仿真计算方法,并采用理论分析与现场实测等研究手段揭示了垮落岩体应变硬化特性对采场覆岩“两带”发育规律的影响作用。研究结果表明:(1)随着应变的增加,垮落岩体的应力先缓慢增大,当达到某一临界应变后,应力呈近似指数型快速增长;且随着碎胀系数的增加,应力呈现指数型增长所对应的临界应变亦随之增大。(2)基于FLAC^(3D)内置的双屈服模型,并提出了盖帽压力与材料特性的反演计算方法,实现了采空区垮落岩体应变硬化特性的仿真计算。(3)模拟结果表明,当考虑垮落岩体的压实和支撑作用时,顶板岩层运动范围和程度降低,引起的塑性区破坏范围亦随之降低,垮落带高度为15 m,减少16%,断裂带高度为65 m,减少13.3%,并基于现场实测结果,验证了上述仿真计算方法的可行性。

The overburden movement,deformation and damage of the overlying rock caused by coal mining directly affect the water storage and water supply capacity of the underground reservoir.In order to scientifically and accurately calculate the storage capacity of the underground reservoir,It is necessary to consider the influence of the mechanical properties of strain hardening in the progressive compaction process of the caving rock mass in the goaf on the height distribution characteristics of the two zones of the overlying rock in the stope.Taking Lijiahao Coal Mine as the engineering background,based on the mechanical properties of strain hardening in the compaction process of the caving rock mass,the double-yield model and the proposed inversion calculation method were used to study the failure characteristics of overlying rock in stope.The stress expression of the caving rock mass was deduced,and its influencing factors were analyzed.The numerical simulation calculation method was proposed,and the theoretical analysis and field measurement were adopted to reveal the influence of strain hardening characteristics of the caving rock mass on the development law of the two zones of overlying strata in stope.The research results show that:(1) The stress of the caved rock mass increases slowly with the strain increase;the stress exhibited an exponential growth when the strain reached a critical strain,and with the increase of the fragmentation coefficient,the critical strain also increases.(2)Based on the built-in double-yield model of FLAC^(3D),the inversion calculation method of cap pressure and material properties was proposed,and the simulation calculation of the strain hardening characteristics of the caving rock mass in the gob was realized.(3)The numerical modelling results indicate that when the compaction and support of the caving rock mass were considered,the movement range and degree of the roof strata were reduced;the height of caving zone was 15 m,a decrease of 16%.The height of fractured zone was 65 m,which was reduced by 13.3%.Based on the field measurement results,the feasibility of the above simulation calculation method is verified.