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

这项研究的重点是一个区域的亚临界裂纹增长的速度非常慢，这可能会发挥重要的作用，在时间依赖性断裂周围的地下开口。当我们考虑放射性活性物质的长期稳定性和有效屏蔽时，非常慢的速率可能很重要。用双扭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，初步的实验表明，在加载/卸载循环与非常小的温度变化相关的滞后可以累积增加试样的挠度。在本研究中，加载系统和样品的温度保持恒定在0.1 K，通过使用双室系统。亚临界裂纹目前仍在扩展。1996年3月的增长率相当于每年1毫米。当裂纹处于均匀拉应力场中时，裂纹扩展速率随裂纹长度的增加而加快。在此条件下，本研究所获得的试验结果将为探讨地下洞室的长期稳定性和有效支护提供重要的依据。

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.