Mechanical properties of deep sandstones under loading rate effect

Abstract

The advance speed of the working face in coal mines can significantly affect the fluctuation frequency of abutment pressure in front of the coal body. Moreover, it has a certain correlation with the change of axial loading rate in coal and rock mechanics test. Therefore, uniaxial compression tests under various loading rates of 0.05, 0.1, 0.15, 0.25, 0.5 MPa/s were conducted using 2000 kN triaxial testing machine and PCI-2 acoustic emission test system to study the loading rate effect on the mechanical properties of deep sandstones. The results show that 1) the peak strength and elastic modulus of the deep sandstone increase with the loading rate increasing; 2) with the loading rate increasing, the deep sandstone transforms from plastic-elastic-plastic to plastic-elastic and moreover, the failure mode gradually transfers from type I to type III; 3) With the loading rate increasing, the total input strain energy, elastic strain energy, and dissipated strain energy generally increase; 4) the damage variable presents the evolution characteristics of inverted “S” shape with time, and with the loading rate increasing, the damage degree of the deep sandstone is aggravated. The conclusion obtained can provide the theoretical basis for the stability control of the surrounding rock in deep engineering.

摘要

煤矿工作面推进速度对煤体前方支承压力波动频率有显著影响，且与煤岩力学试验中轴向加载速率的变化有一定的相关性。为此，采用2000 kN三轴试验机和PCI-2 声发射测试系统，对深部砂岩进行了0.05，0.1，0.15，0.25 和0.5 MPa/s 五种不同加载速率下的单轴压缩试验，进而研究加载速率对深层砂岩力学特性的影响。结果表明：1)深部砂岩的峰值**度和弹性模量均随加载速率的增大而增大; 2)随着加载速率的增大，深部砂岩由塑-弹-塑性体向塑-弹性体转变，破坏模式逐渐由I 类型向III 类型转变;3)总输入应变能、弹性应变能、耗散应变能均随着加载速率的增大而增大;4)损伤变量随时间的延长呈现出倒“S”型演化特征，且随着加载速率的增大，深部砂岩的损伤程度加剧。上述所得结论可为深部工程围岩稳定性控制提供理论依据。