浅埋深长壁采场顶板切落破坏的时序特征试验

Experimental study on time series character of roof cutting in shallow working face

针对浅埋深长壁采场切顶压架灾害发生过程中的时间序列问题,采用实验室基础参数测试对典型浅埋深煤岩体破坏的时间效应进行三向围压加载实验,利用相似材料模拟手段对浅埋采场顶板切落破坏过程中多个参量的时间序列特征进行研究。研究得出:三向围压状态下,浅埋煤层顶板岩石易由“X”型破裂、强度屈服破坏转化为单一剪切破坏,且具有明显的时间效应;浅埋深工作面推进速度慢导致垂直采动应力与水平应力之差增大是顶板发生剪切破坏的主因;浅埋煤层基岩发生整体切落下沉前,覆岩采动裂隙存在“形成—发育—扩展到地表(岩层整体切落下沉)”的时间过程;切落位置与工作面推进速度相关,加快推进速度后,来压步距加大,支架受力下降,基岩整体切落位置基本发生在支架后方;切顶时煤层超前支承压力达到极值,随后应力降低;顶板应变在时间序列上依次经历“三区”:“初始应变稳定区—应变剧烈演化区—采空区应变稳定区”,工作面推进速度慢时,顶板岩层应变启动点超前,顶板切顶线前移,顶板应变幅值增大,超前支承压力启动点和峰值均比覆岩应变滞后,而支架压力与采动应力时间序列变化曲线规律类似,可相互表征。研究结果表明,通过对支架压力、采动应力、覆岩应变等指标的联合监测与预警值设计,可实现对浅埋采场切顶压架灾害的预测和防治。

In order to study the time series character of roof cutting process in shallow working face,the load test with three-dimensional confining pressure of typical shallow seam in the laboratory were used to study the time effect of based parameters,and similar simulation experiments were used to analyze the multi-parameter time series character of roof cutting process.The paper concludes that surrounding rock stress increases,the roof rock of shallow seam is easy to change from“X”type fracture and strength yield failure to single shear failure,and has obvious time effect characteristics.The face advance speed of shallow seam affects the difference between vertical mining stress and horizontal stress,the main reason of shear failure of roof is the increase of stress difference due to the slow face advance speed.Mining-induced fractures in overburden rock first form,develop,and extend to the surface(that is,the overall cutting and subsidence of the strata)before the overall cutting and subsidence of bedrock layer in shallow seam.The cutting position is related to the working face’s advance speed.When face advance speed is accelerated,weighting interval increases,support stress decreases,and the overall cutting position of the bedrock layer basically occurs behind the support.Abutment pressure reflects the formation process of roof caving accident,and it reaches stress extremum when cutting,then the stress decreases.In terms of time series,roof strain can be successively divided into“three zones”:“initial strain stability zone-strain violent evolution zone-goaf strain stability zone”.When working face advances slowly,strain starting point leads,the cutting line of roof moves forward,and basic roof strain amplitude increases.Both the starting point and peak value of advanced support pressure lag behind the overburden strain,and the time series curve of support pressure and mining stress is similar,which can be mutually characterized.The results show that the design of joint monitoring and early warning values of support pressure,mining stress,surrounding rock strain and other indicators can be used to predict and prevent roof cutting accident in shallow working face.