采空区冒落矸石承压变形特征及侧向压力分布规律研究

Study on bearing deformation characteristics and lateral pressure distribution law of caved gangue in gob

在覆岩载荷作用下,采空区冒落矸石会产生施加于巷旁支护体或煤柱上的侧向压力,在时间效应影响下,侧向压力可能引发巷旁支护体或煤柱失稳,进而诱发地表塌陷。为研究采空区冒落矸石承压变形特征及侧向压力分布规律,研制了可测量侧向压力的组合式冒落矸石承压变形试验装置。以满足均匀粒径分布的5−30 mm的冒落矸石为例,通过设置相同加载总时长(16 h)、相同目标载荷(10 MPa)、不同数量加载水平(水平1、2、4),研究冒落矸石承压变形特征、侧向压力分布规律及试验前后粒径变化情况。结果表明:随载荷增加,冒落矸石变形逐渐增大,残余碎胀系数和空隙率逐渐减小,加载较恒载阶段尤为明显;恒载初期,轴向应变增长较快,而后逐渐变缓并趋于平稳,若不发生应变突增,时间-应变呈现对数关系;目标载荷相同,加载总时长一致,随加载水平数量增加,恒载阶段产生的总应变显著增加,分别为3.02%、9.07%和17.72%,表明随加载水平数量增加,虽然载荷对冒落矸石输入的总能量减少,但却对冒落矸石的滑移填充和结构调整起到了明显的促进作用;冒落矸石侧压力系数随着载荷增加明显变大;冒落矸石体展现出较强的载荷传递折减效应,自冒落矸石体顶界面垂直向下呈现递减变化;承压变形过程中,粒径为5~10 mm的冒落矸石含量处于动态平衡状态,为稳定粒径。

Under the load of overlying strata,lateral pressure from the caved gangue in gob will be exerted on the support body of gob-side entry retaining or coal pillar.As time goes on,lateral pressure may lead to instability of support body of gob-side entry retaining or coal pillar,and then induce surface collapse.In order to study the bearing deformation characteristics and lateral pressure distribution law of caved gangue in gob,a combined test device for bearing deformation of caving gangue that can measure lateral pressure is developed.The caved gangue with uniform particle size distribution of 5−30 mm is taken as an example.By setting the same total loading time(16 h),the same target load(10 MPa)and the different number of loading levels(1,2,4),the bearing deformation characteristics,lateral pressure distribution law and particle size change of caving gangue before and after test are studied.The test results indicated that:Along with the increase of axial load,the axial deformation of caved gangue increases gradually,the residual bulking coefficient and porosity decrease gradually,which are more obvious in loading stage than in constant loading stage.In the early constant loading stage,the axial deforma-tion of caved gangue grows rapidly,and then tends to be slow and steady gradually,if no strain surge occurs,the relationship between strain and time meets the logarithmic relationship.With the same target load and total loading time,as the number of loading levels in-creases,the total strain generated in constant loading stage increases significantly,and is 3.02%,9.07%,17.72%respectively,which indic-ates that the total energy input of caved gangue decreases with the increase of loading level number,but it plays a significant role in pro-moting the sliding filling and structural adjustment of caved gangue.The lateral pressure coefficient of caved gangue increases obviously with the increase of load.Caved gangue body shows strong reduction effect of load transfer and the value of load acting on caved gangue body decreases progressively from top to bottom.In the process of bearing deformation of caved gangue,the total amount of caved gangue with 5~10 mm particle size is in dynamic equilibrium.The research results have certain guiding significance for mining subsidence con-trol.