不同中间主应力下应变型岩爆声发射特征研究

发布时间：2018-09-01 15:19

【摘要】：岩爆是深部开挖过程中一种常见的地质灾害。随着水利水电、交通、矿山开采等工程向地下深部开拓,岩爆的强度及发生频率呈上升趋势,严重威胁工程安全。国内外学者围绕岩爆的机理及预测问题开展了大量研究,但岩爆的孕育发生较为复杂,岩爆的发生机制仍不十分清楚,岩爆预测与防控已成为地下岩体工程建设中亟待解决的技术难题。因此,深入开展岩爆的基础试验研究具有重要的学术意义及工程价值。本文借助改进的岩爆真三轴试验系统,开展不同中间主应力下的应变岩爆试验,利用声发射监测系统对岩爆试验过程进行监测,分析了不同中间主应力下花岗岩应变型岩爆的声发射特征。并获得以下结论:(1)中间主应力对岩爆声发射撞击数及其分形维数Dt的变化特征具有显著影响。低中间主应力条件下,各组试验弹塑性阶段分形维数Dt小于0.3,撞击数在300左右。随着中间主应力在较低水平增加,“平静期”持续时间存在先增大后减小的变化趋势。最终破坏阶段各组试验撞击数有所增加,分形维数Dt大于0.3。高中间主应力条件下,弹塑性阶段撞击数分形维数Dt大于0.3,撞击数在500以上。塑性变形阶段“平静期”持续时间显著增长。在最终破坏阶段撞击数分形维数Dt小于0.3,撞击时降低至300以下。(2)中间主应力对岩爆声发射信号能量累积具有显著影响。低中间主应力下,声发射信号绝对能量累积较少,随着中间主应力在较小范围内的增加,绝对能量累积呈现先增大后减小的变化趋势。高中间主应力下,声发射绝对能量累积明显增多,并随着中间主应力的增大呈现递增。需要特别指出的是,不同中间主应力下,声发射的绝对能量变化规律与岩爆发生烈度变化规律基本上是一致,这说明了声发射绝对能量可以间接反映岩爆发生烈度。(3)中间主应力对岩爆声发射信号波形参数具有重要影响。不同中间主应力下声发射信号波形具有不同的参数特征。低中间主应力下,声发射波形的上升时间较长、持续时间较短、幅度较小;高中间主应力下,声发射波形的上升时间较短、持续时间较长、幅度较大。(4)从声发射的角度对不同中间主应力下应变型岩爆的发生机制进行了分析,发现了不同中间主应力对应变型岩爆的破坏具有不同影响。低中间主应力(10-90MPa)作用下,随着中间主应力的增大,其对声发射活动的抑制作用逐渐增强,试件内部破坏活动减弱,试件强度逐渐增强(90MPa时,试件强度最大)。声发射总撞击数、绝对能量累积随着中间主应力在较低水平内的增加呈现出先增大后减小的变化趋势,相应的岩爆烈度呈现出先增大后减小的变化趋势。高中间主应力(100-llOMPa)作用下,随着中间主应力的增大,其对声发射活动的抑制作用转变为促进作用,试件内部破坏活动增强,试件强度逐渐降低,声发射总撞击数及绝对能量累积显著上升,相应的岩爆烈度显著增强。(5)分析了岩爆前夕的声发射撞击数及分形维数Dt,发现声发射“平静期”前的撞击数相对较低(通常在300左右),撞击数分形维数Dt小于0.3,岩体可能发生受低中间主应力作用的岩爆。此种岩爆,岩爆坑较浅,破坏程度及范围较小,岩爆弹射速度快,弹射块体具有较大的杀伤力。若声发射“平静期”前的撞击数相对较高(通常在500以上),撞击数分形维数Dt值大于0.3,岩体可能发生受高中间主应力作用的岩爆,此种岩爆弹射破坏速度极快,岩爆坑较深,破坏程度及范围较大,容易造成隧洞内大面积掩埋,在实际工程中具有较大危害。
[Abstract]:Rockburst is a common geological hazard during deep excavation. With the development of water conservancy and Hydropower projects, traffic, mining and other projects to the deep underground, the intensity and frequency of rock burst are increasing, which seriously threatens the safety of engineering. The mechanism of rock burst is still unclear, and the prediction and control of rock burst have become a technical problem to be solved urgently in the construction of underground rock mass projects. Therefore, it is of great academic significance and engineering value to carry out the basic test research of rock burst in depth. The acoustic emission (AE) characteristics of strain-type rock burst in granite under different intermediate principal stresses are analyzed. The following conclusions are obtained: (1) The intermediate principal stress has a significant effect on the AE impact number and its fractal dimension Dt of rock burst. Under the stress condition, the fractal dimension Dt of each group is less than 0.3, and the impact number is about 300. With the increase of intermediate principal stress at a lower level, the duration of "quiet period" increases first and then decreases. The impact fractal dimension Dt of elastic-plastic stage is greater than 0.3 and the impact number is more than 500. The duration of "quiet period" in plastic deformation stage increases significantly. Under stress, the absolute energy accumulation of AE signal is less, and with the increase of intermediate principal stress in a smaller range, the absolute energy accumulation increases first and then decreases. The change of absolute energy of AE under inter-principal stress is basically the same as that of the intensity of rock burst, which indicates that the absolute energy of AE can indirectly reflect the intensity of rock burst. (3) The intermediate principal stress has an important influence on the waveform parameters of AE signals. The rise time of AE waveform is longer, the duration time is shorter and the amplitude is smaller under the low intermediate principal stress. The rise time of AE waveform is shorter, the duration time is longer and the amplitude is larger under the high intermediate principal stress. (4) The occurrence mechanism of strain-type rock burst under different intermediate principal stress is divided from the angle of AE. It is found that different intermediate principal stresses have different effects on the failure of strained rock burst. Under the action of low intermediate principal stress (10-90 MPa), with the increase of intermediate principal stress, the inhibiting effect on AE activity is gradually strengthened, the internal failure activity is weakened, and the strength of specimen is gradually strengthened (the maximum strength is at 90 MPa). The absolute energy accumulation increases first and then decreases with the increase of intermediate principal stress at a lower level, and the corresponding rock burst intensity increases first and then decreases. The total impact number and absolute energy accumulation of acoustic emission (AE) increased significantly, and the corresponding rock burst intensity increased significantly. (5) The AE impact number and fractal dimension Dt before rockburst were analyzed. It was found that the impact number before AE "quiet period" was relatively low (usually around 300). Rockburst may occur in rock mass under the action of low intermediate principal stress when the fractal dimension Dt is less than 0.3. This kind of rock burst has shallow rock burst pit, small damage degree and scope, rapid rockburst ejection speed and large lethality of the projectile block. If the impact number before the quiet period of acoustic emission is relatively high (usually more than 500), the fractal dimension Dt of the impact number is relatively high. When the value is greater than 0.3, rock burst may occur under the action of high and middle principal stress. The rock burst is destroyed very fast, the rock burst pit is deep, the damage degree and scope are large, and it is easy to cause large area burial in the tunnel, which is harmful to the actual project.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU45

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