Study on acoustic emission characteristics of sandy mudstone under uniaxial loading and unloading of Buertai Coal Mine
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摘要: 采掘反复扰动诱导的加卸载效应是造成井巷工程岩体破坏的重要诱因,但目前缺乏对西部广泛分布的弱胶结砂质泥岩在加卸载状态下力学响应的研究。针对该问题,以国家能源集团神东布尔台煤矿钻孔BK209中砂质泥岩为研究对象,采用单轴分级加卸载试验方案(设置I,II,III 3种加卸载路径,其中加卸载路径I采用位移控制,加卸载路径II,III采用荷载控制),研究不同加卸载路径下砂质泥岩的力学及声发射(AE)特征。研究结果表明:① 加卸载路径I下试样应力达到峰值后跌落较快,表现出脆性特征;加卸载路径II下试样应力达到峰值后跌落有限,有一定残余强度;加卸载路径III下试样应力达到峰值后分级跌落,表现出一定延性特征。② 加卸载路径越短,卸载阶段弹性模量增加越大,主要是因为在加载过程中新生裂隙接触面因剪切滑移产生碎屑,卸载路径短,受到拉应力脱落的碎屑充分充填到附近空隙,裂隙面之间的摩擦能力变强。③ 第1次加载阶段,路径I下AE振铃计数呈先增后减的对称变化,路径II下AE振铃计数呈左偏峰变化,路径III下AE振铃计数呈增减波动变化,中间波动较大;第2次加载阶段,在加载路径I,III下,当应力增至临近峰值,达到砂质泥岩屈服极限时,AE振铃计数陡增,出现Kaiser点;最后1次加载至峰值过程中,路径I下AE振铃计数先均匀持续发生,接着渐进式增加,路径II,III下AE振铃计数均先均匀持续发生,临近峰值应力呈跳跃式增长。④ 第1次加载阶段,由于应力较低,AE振铃计数较少,AE处于相对平静期;在卸载阶段,基本无振铃计数,AE处于间歇期;随着应力提高和加卸载次数增多,AE振铃计数相对增加,AE处于波动期;最后1次加载至峰值的过程中,砂质泥岩处于破坏阶段,AE振铃计数激增,AE进入活跃期。Abstract: The loading-unloading effect induced by repeated mining disturbance is an important inducement to cause the rock mass failure in roadway engineering. However, there is a lack of research on the mechanical response of the widely distributed weakly cemented sandy mudstone in west China under loading and unloading conditions. In order to solve this problem, the sandy mudstone in borehole BK209 of Shendong Buertai Coal Mine of National Energy Group is taken as the research object, and the uniaxial graded loading and unloading test scheme is adopted (I, II and III loading and unloading paths are set, wherein the loading and unloading path I adopts displacement control, and the loading and unloading paths II and III adopt load control). This paper studies the mechanical and acoustic emission (AE) characteristics of sandy mudstone under different loading and unloading paths. The result shows the following four points. ① Under the loading and unloading path I, the stress of the sample drops rapidly after the stress peak, showing the characteristics of brittleness. Under the loading and unloading path II, the stress drop after the peak stress of the sample is limited and the stress has a certain residual strength. Under loading and unloading path III, the stress of the sample falls after the peak stress, showing certain ductility characteristics. ② The shorter the loading and unloading path, the greater the increase of elastic modulus in the unloading section. The main reason is that the detritus is produced by shear slip in the interface of the new fracture during loading process. When the unloading path is shorts, the detritus falling off under tensile stress fully fills the nearby gap. Therefore, the friction capacity between the fracture surfaces becomes stronger. ③ In the first loading stage, the AE ringing count under the path I is in a symmetrical change of first increasing and then decreasing. The AE ringing count under the path II is in a left-biased peak change. And the AE ringing count under the path III is in a fluctuation change of increasing and decreasing, and the fluctuation in the middle is large. In the second loading stage, under the load paths I and III, when the stress increases to near the peak value and reaches the yield limit of sandy mudstone, the AE ringing count increases sharply and Kaiser point appears. During the last loading to the peak value, the AE ringing count under path I first occurs uniformly and continuously, and then increases gradually. The AE ringing counts under paths II and III occur uniformly and continuously, and the stress near the peak increases in a leaping manner. ④ In the first loading stage, the AE ringing count is less because of the low stress, and the AE is in relatively quiet period. In the unloading stage, there is basically no ring count, and the AE is in intermittent period. With the increase of stress and loading and unloading times, the AE ringing count increases relatively. The AE is in a fluctuating period. During the last loading to the peak value, the sandy mudstone is in the destruction stage, and the AE ringing count increases sharply. The AE enters the active period.
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表 1 试样基本参数及岩层特征
Table 1. Sample parameters and strata characteristics
编号 直径/mm 高度/mm 波速/(km·s−1) 密度/(g·cm−3) 加卸载路径 抗压强度/MPa 循环级数 岩性描述 11 24.94 50.28 1.344 2.24 I 13.72 1 灰褐色,局部破碎,夹薄层棕色泥岩,含灰绿色砂质包裹体;断口平坦,含砂量少许,夹薄层粉砂岩 12 24.82 50.62 1.330 2.22 I 13.19 1 21 24.65 50.28 1.302 2.26 II 12.68 1 22 24.57 51.24 1.136 2.24 II 18.74 2 23 24.18 50.92 1.087 2.33 II 22.64 2 31 24.80 50.98 1.116 2.17 III 8.06 1 32 24.63 51.17 1.179 2.28 III 11.23 1 33 24.89 53.41 0.912 2.12 III 13.16 1 表 2 砂质泥岩单轴加卸载弹性模量
Table 2. Elastic modulus of sandy mudstone during uniaxial loading and unloading
加卸载
路径试样
编号加载阶段弹
性模量/GPa加载阶段平均
弹性模量/GPa卸载阶段弹
性模量/GPa卸载阶段平均
弹性模量/GPaI 11 2.11 1.66 3.24 2.65 12 1.21 2.06 II 21 0.94 0.92 1.55 1.52 22 0.93 1.26 23 0.91 1.74
III31 0.63 0.99 1.16
1.5632 1.12 1.74 33 1.22 1.79 -
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