裂隙发育过程对采动裂隙椭抛带压实区的影响研究

Study on influence of fracture development process on compaction area of overlying strata in working face

采空区瓦斯抽采的关键是了解工作面上覆岩层裂隙的演化过程。为了研究综采工作面覆岩采动压实区演化规律,高效进行煤矿采空区瓦斯抽采工作,以神东某矿区2207工作面为原型,通过物理相似模拟实验,利用自主研发的覆岩裂隙监测系统将图像进行直方图均衡化增强和中值滤波去噪处理,获得二值化裂隙图像后利用分形理论定量描述裂隙率,对典型周期来压覆岩垮落裂隙率进行统计分析,建立了裂隙发育程度受工作面推进时间的时空函数和采动裂隙椭抛带压实区演变修正模型。结果表明:覆岩平均裂隙率变化符合DoseResp函数关系,裂隙的发育过程包括产生、扩展蔓延、压实闭合3个阶段,裂隙在产生、闭合这2个阶段发育速率较平缓,而在扩展阶段发育速率陡增。采空区上覆岩层裂隙场形成旧裂隙区、压实区和新裂隙区3个区域,裂隙发育周期的不同导致旧裂隙区与新裂隙区在发育状态、压实程度和空间形态上有着明显差异,这些差异导致了采空区覆岩非对称性下沉现象的发生。通过分析覆岩应力恢复与覆岩内部裂隙演变关系,进一步验证了采用DoseResp时间函数曲线可以很好的表现采空区上覆岩层裂隙异速演变特征。最后建立了考虑覆岩裂隙异速演变效应的采动裂隙椭抛带压实区修正模型,并结合现场工程实践,有效提高瓦斯抽取高位钻孔布置的准确性,为工作面的安全开采提供理论指导。

The key to gas drainage in goaf is to understand the evolution process of overlying strata fissures on working face.In order to study the evolution law of mining-induced compaction area of overburden rock in fully mechanized mining face and efficiently carry out gas extraction in goaf of coal mine,taking No.2207 working face of a mining area in Shendong as the prototype,through physical similarity simulation experiment,the self-developed overburden rock fracture monitoring system is used to perform histogram equalization enhancement and median filtering denoising on the image.After obtaining the binary fracture image,the fractal theory is used to quantitatively describe the fracture rate,and the fracture rate of overburden rock caving under typical periodic weighting is statistically analyzed.The space-time function of fracture development degree affected by the advancing time of working face and the evolution correction model of mining-induced fracture elliptical zone compaction area are established.The results show that the change of the average fracture rate of the overlying rock conforms to the DoseResp function relationship.The development process of the fracture includes three stages:gen-eration,expansion and spread,and compaction and closure.The development rate of the fracture is gentle in the two stages of generation and closure,while the development rate increases sharply in the expansion stage.The fracture field of overlying strata in the goaf forms three areas:old fracture area,compaction area and new fracture area.The difference of fracture development cycle leads to obvious differ-ences in development state,compaction degree and spatial form between the old fracture area and the new fracture area.These differences lead to the occurrence of asymmetric subsidence of overlying strata in goaf.By analyzing the relationship between the stress recovery of the overburden rock and the evolution of the internal cracks in the overburden rock,it is further verified that the DoseResp time function curve can well show the allometric evolution characteristics of the overburden rock cracks in the goaf.Finally,a modified model of the compaction zone of the mining-induced fracture elliptical parabolic zone considering the allometric evolution effect of the overburden fracture is established.Combined with the field engineering practice,the accuracy of the high-level borehole layout of gas extraction is ef-fectively improved,which provides theoretical guidance for the safe mining of the working face.