Abstract Cyclic load affects the mechanic behavior and stability of rock mass. Although cyclic load effect has been extensively studied for yielding stage, it is somewhat unclear in early stage of rock stress-strain curves. This paper describes an experimental study, carried out cyclic load test in elastic deformation phase, on sandstone, limestone, and concrete specimens, to research the mechanical behavior. The result showed strengthening effect of cyclic loads in elastic deformation stage within the first 100 cycles of the cyclic loads. The irreversible deformation under cyclic loads displayed similarity to creep curves, and it increased along with cyclic unloading stress level. Further analysis on cyclic times and unloading stress level demonstrated that there's threshold of strengthening effects under cyclic loads in elastic deformation stage, which could be developed in two aspects: (1) Strength increased with cyclic times until it reached an optimal cycling time then it decreased, and (2) the strength initially increased with unloading stress level then it decreased when the optimal unloading stress level was attained. The optimal cyclic times and optimal unloading stress were calculated according to quadratic function. The result showed that the optimal cyclic times increased with the decrease of unloading stress level. The optimal cyclic unloading stress level is about 30% of elastic limitation stress under same cycling times. Different specimens showed different strengthening potential under uniaxial cycling load since the initial porosity of specimens are different. The conclusion offered by this work would be beneficial to decisions of geoengineering and constructions.

中文翻译：

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基于试验研究的循环荷载对岩石和混凝土的加固作用

摘要 循环荷载影响岩体的力学行为和稳定性。尽管在屈服阶段已经广泛研究了循环载荷效应，但在岩石应力-应变曲线的早期阶段尚不清楚。本文描述了一项实验研究，在弹性变形阶段对砂岩、石灰岩和混凝土试件进行循环载荷试验，以研究其力学行为。结果表明，在循环载荷的前 100 个循环内，循环载荷在弹性变形阶段具有强化作用。循环荷载作用下的不可逆变形与蠕变曲线相似，并且随着循环卸载应力水平的增加而增加。对循环次数和卸载应力水平的进一步分析表明，弹性变形阶段循环载荷下强化效果的阈值，可以从两个方面发展：（1）强度随着循环次数的增加而增加，直到达到最佳循环时间然后下降，（2）强度最初随着卸载而增加当达到最佳卸载应力水平时，应力水平下降。根据二次函数计算最佳循环次数和最佳卸载应力。结果表明，最佳循环次数随着卸载应力水平的降低而增加。最佳循环卸载应力水平为相同循环次数下弹性极限应力的30%左右。由于试件的初始孔隙率不同，不同试件在单轴循环载荷下表现出不同的强化潜力。