大尺度岩样单轴循环加载的力学特性试验研究

EXPERIMENTAL STUDY ON MECHANICAL CHARACTERISTIC OF LARGE-SCALE ROCK UNDER UNIAXIAL CYCLING LOADING

通过大尺度岩样的单轴压缩试验，探讨其受压过程中裂缝的扩展规律等特性，结果表明：（1）大尺度岩样的应力-应变曲线、裂缝扩展和小尺度岩样的声发射特性类似，具有良好的“记忆”功能，且都与其先前所受的最大荷载有密切的关系，只有当其所受的荷载达到先前所受的最大荷载时，先前形成的裂缝才扩展，表明其内部应力梯度陡峭：（2）相同表观应力下，表观应变比局部点应变大2个数量级，表明岩石是具有细观特征（细观非均匀性）的材料，其宏观力学行为是细观特征相互作用、放大的综合结果：（3）大尺度岩样局部点平均轴向应变与表观应力近似呈线性关系，每个循环的斜率大致平行，而平均横向应变随循环次数的增加明显增大；（4）超声波速随循环次数的增加以波动和急剧减小间隔方式进行衰减。

Mechanical experiments on large-scale rock samples（length xheight xwidth： 1 000 mm × 1 000 mm × 600 mm） under uniaxial cycling loading are conducted and studied. The experimental results are as follows： （1） like the acoustic emission characteristic, the rules of both stress-strain curves and crack development are closely related to the largest loading that rock experiences previously, and only when the loading reaches to the peak value can the previously formed cracks develop. The fact shows the stress gradients are steep in the rock sample： （2） the stress-strain curves of the large-scale rock specimens under cycling loading are basically the same as those of the standard rock specimen： （3） the observed strain is 100 times larger than the point strain under the same observed stress. It shows rock is a kind of material with microcosmic characteristics （microcosmic heterogeneousness）. The macroscopical mechanical behaviors of rock are the comprehensive results of interaction and magnification among microcosmic characteristics; and （4） it has a nearly linear relationship between the average axial point strain and the observed stress. The slope of the relationship curve in each cycle is nearly parallel. The average transverse point strain and its dispersion coefficient increase as the cycling number increases. It shows rock cracks mainly develop paralleling loading orientation under uniaxial compression. This process is irreversible accompanied by energy dissipation.