A study of long-term strength of rock by using DT-method

本文研究的重点是亚临界裂纹扩展速度非常慢的区域，该区域可能在地下开孔周围的时间依赖性破裂中起重要作用。当我们考虑到放射性活性物质的长期稳定性和有效屏蔽时，非常慢的速率可能是重要的。用双扭转技术的松弛法对裂纹扩展进行了近两年的测量。在这种方法中，加载点必须是固定的。然而，初步实验表明，加载/卸载循环中的滞后与非常小的温度变化相关，可能是试件挠度的累积增加。在本研究中，加载系统和试样的温度保持在0.1 K以内恒定，采用双室系统。亚临界裂纹现在还在扩大。1996年3月的增长率相当于每年1毫米的增长率。当裂纹处于均匀拉应力场时，裂纹扩展速率随着裂纹长度的增加而加快。在这种情况下，本研究的实验结果将成为探讨地下洞室长期稳定性和有效屏蔽的重要措施。

This study focussed on a region of very slow rate of the subcritical crack growth which may play an important role in time-dependent fracture around underground openings. The very slow rate can be important when we consider very long term stability and effective shielding of radio active species. The crack growth was measured for almost two years with relaxation method of the double-torsion technique. In such a method, the loading point must be fixed. However, preliminary experiments showed that a hysteresis in a loading/unloading cycle associated with very small temperature variation could be cumulative increase in deflection of the specimen. In this study, the temperature of the loading system and the specimen was kept constant within 0.1 K,by using double chambers system. The subcritical crack is still growing now. The growth rate in March 1996 corresponds to the rate, 1mm/year. When the crack is in a uniform tensile stress filed, the growth rates should accelerate with increasing crack length. In such a condition, the experimental result obtained in this study will be an important measure for discussing long term stability and the effective shield of the underground openings.