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本文介绍了作者在联邦德国卡尔斯鲁厄大学土岩力学研究所利用该所研制的大型三轴试验机进行周期荷载下大型三轴试验的情况和结果。岩石为薄层灰岩,试件直径为60cm,高为120cm。整个研究工作是基于分析不可逆变形的观点来探讨变形和强度特性的。在周期荷载作用下,不可逆变形的总量随着循环次数的增加而增长;但在不同的应力水平下,不可逆变形的发展趋势具有显著的,甚至是质的差异。应力水平很低时,最初几次的循环荷载将导致产生较大的不可逆变形;随着循环次数之增加,其不可逆变形的增长率逐步衰减,最终趋向于一个比较稳定的常值。但是当应力水平达到某一“门槛”值后,情景则迥然不同;循环次数之增加将促使不可逆变形的加速增长,最终导致整个试件的破坏。试验结果表明,这一特征应力值略低于常规三轴试验中的所谓“屈服值”。研究结果表明,每一个加荷-卸荷循环过程中的不可逆变形主要发生在超过这一“门槛”值后的区段内。研究这样的特征值对于探讨周期荷载作用下岩体的力学性质是十分重要的。由试验获得的不可逆变形与循环次数的关系曲线在形态上与流变曲线十分相似。也许,这并不是偶然现象。文章建议研究常规试验的强度值、流变试验的长期强度与周期荷载下的强度之间的关系。显然,这对于解决岩体工程问题中的强度取值和安全储备系数等问题具有重要意义。
This article describes the situation and results of the large-scale triaxial test under cyclic loading using the large-scale triaxial tester developed by the author at the Institute of Geotechnical Mechanics at the University of Karlsruhe in the Federal Republic of Germany. The rock is a thin layer of limestone with a test specimen diameter of 60cm and a height of 120cm. The entire research work is based on the analysis of the irreversible deformation point of view to explore the deformation and strength characteristics. Under cyclic loading, the total amount of irreversible deformation increases with the number of cycles; however, under different stress levels, the development trend of irreversible deformation has significant or even qualitative differences. When the stress level is very low, the first few cyclic loads will lead to a greater irreversible deformation; with the increase of the number of cycles, the growth rate of its irreversible deformation gradually attenuates and eventually tends to a relatively stable constant value. However, when the stress level reaches a certain threshold, the situation is very different; an increase in the number of cycles will accelerate the acceleration of irreversible deformation, eventually leading to the destruction of the entire specimen. Test results show that this characteristic stress value is slightly lower than the so-called “yield value” in conventional triaxial tests. The results of the study indicate that the irreversible deformations during each loading-unloading cycle mainly occur within the zone after the threshold value is exceeded. It is very important to study such eigenvalues to explore the mechanical properties of rock mass under cyclic loading. The relationship between the irreversible deformation and the number of cycles obtained by the experiment is very similar to the rheological curve in morphology. Perhaps this is not a coincidence. The article proposes to study the relationship between the strength values of conventional tests, the long-term strength of rheological tests and the strength under cyclic loading. Obviously, this is of great significance in solving problems such as strength values and safety reserve factors in rock engineering problems.