Dynamic characteristics of marble damaged by cyclic loading
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摘要: 利用MTS 815电液伺服岩石实验系统进行上限应力为80%、85%、90%、95%单轴抗压强度的大理岩单轴压缩循环加卸载实验,每种上限应力条件分别设置20、40、60、80次循环。再利用分离式Hopkinson压杆对损伤岩样进行动力学实验。分析了循环加卸载上限应力及循环次数对大理岩塑性应变的影响,揭示了大理岩动态力学参数和破碎吸收能随损伤变量的演化规律。实验结果表明:塑性应变与循环次数呈正相关,且上限应力越大,塑性应变趋于稳定所需的循环次数也会增大;动态单轴抗压强度、动态弹性模量随损伤变量增加呈指数衰减;破碎吸能占比以损伤变量D=0.343为临界点分为两个阶段,D<0.343时,破碎吸能占比稳定在10%左右,数值约为13 J,当D>0.343时破碎吸能占比随损伤变量增加不断增大。研究结果可为岩体工程的设计、施工及支护参数的选取提供参考。Abstract: The rock mass will bear the cyclic loading during the construction of underground engineering. Mechanical properties of the damaged rock mass under disturbance of cyclic loading are important for supporting capacity of the surrounding rock. Moreover, the disturbed rock mass is also potentially threatened by impact loads such as blasting. Therefore, it is necessary to investigate the re-bearing mechanical behavior of disturbing rock mass under cyclic loading. The cyclic loading experiments with four various maximum cyclic stress levels were carried out by using MTS 815 test system. The maximum cycling stresses are 80%, 85%, 90%, and 95% of uniaxial compressive strength respectively and the numbers of cycle are set to be 20, 40, 60 and 80 for each maximum cyclic stresses. The dynamic tests of the disturbed rock sample were conducted by using split Hopkinson pressure bar (SHPB). We analyzed the effects of maximum cyclic stress and the numbers of cycle on plastic strain and revealed the evolution law of dynamic strength and dynamic elastic modulus of marble with damage variable. The test results show that the plastic strain positively correlated with cycles, and the larger the maximum cycling stress, the more the cycles required to reach the stable plastic strain. The dynamic uniaxial compressive strength and dynamic elastic modulus decrease exponentially with the increase of the damage variable. The ratio of breakage energy divided into two stages and the critical point of damage variable is D=0.343. When D<0.343, the breakage energy ratio is stable at about 10%, and the value is about 13 J. When D>0.343, the ratio of breakage energy increases with the increase of damage variable. The findings of this research can provide guidelines for the selection of the mechanical parameters of the surrounding rock and the optimization of the support scheme.
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Key words:
- rock mechanics /
- cyclic loading /
- SHPB /
- damage variable /
- dynamic properties /
- energy
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表 1 等荷载循环加卸载试样
Table 1. Cyclic loading and unloading specimens under equal load
σuls/σucs 循环次数 80 60 40 20 80% T37 T40 T43 T46 T38 T41 T44 T47 T39 T42 T45 T48 85% T25 T28 T31 T34 T26 T29 T32 T35 T27 T30 T33 T36 90% T4 T1 T7 T10 T5 T2 T8 T11 T6 T3 T9 T12 95% T13 T16 T19 T22 T14 T17 T20 T23 T15 T18 T21 T24 表 2 不同上限应力及循环次数下波速
Table 2. Wave speed for different upper limit stress and number of cycles
σuls/σucs 循环次数 平均波速/(km·s−1) 损伤变量 80% 20 4.951 0.124 40 4.774 0.186 60 4.605 0.242 80 4.288 0.343 85% 20 4.639 0.231 40 4.513 0.273 60 4.288 0.343 80 4.117 0.395 90% 20 4.513 0.273 40 4.401 0.308 60 4.178 0.377 80 3.989 0.432 95% 20 4.362 0.320 40 4.288 0.343 60 4.083 0.405 80 3.844 0.472 0 0 5.291 0 -
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