Study on Strength Recovery of Loosen Zone

地下洞口（如隧道或入口）周围的岩石可能会破裂。通常认为，随着时间的推移，松动区或损伤区逐渐扩大，稳定性随着时间的推移而逐渐降低。近年来，有人指出，在适当的条件下，松动区可以恢复强度。例如，如果用足够强度和刚度的材料来支撑隧道，那么支架和围岩之间的松动区就会被压实和固结。最后，稳定性会逐渐增强。迄今为止，对松动带或破坏岩石强度恢复的研究还很少。本研究对多滩（粉砂岩或泥岩）、太古凝灰岩、木町砂岩和三良安山岩的强度恢复进行了研究，实验步骤如下：1)将样品岩石（圆柱形试样）插入小管中，然后由伺服控制试验机破碎。2)将载荷增加到预定值，然后将破碎的岩石在管道内压实。3)将压实岩石从管道中拉出，进行单轴压缩或间接拉伸试验。试验结果表明：1)单轴压缩和间接拉伸试验均验证了强度恢复。2)不同岩石的强度恢复程度不同。在Dotan， 4种岩石中强度恢复最为显著。另一方面，桑美安山岩只表现出较差的强度恢复。3)风干条件下强度回复率远高于水饱和条件。

Rock around an underground opening such as tunnel or gateway may fail. It is usually considered that loosen or damaged zone is gradually extending with elapsed time and stability is gradually decreasing with time going.Recently, it was pointed out that loosen zone might be recovered in strength under a proper condition. For example, if a tunnel is supported with a material of enough strength and stiffness, the loosen zone between supports and surrounding rock is compacted and consolidated. Finally, the stability will be gradually increasing.Very few studies on strength recovery of loosen zone or failed rock have been done up to now. In this study, strength recovery of Dotan (siltstone or mudstone), Tage tuff, Kimachi sandstone and Sanjome andesite is investigated by the following experimental procedures :1) A sample rock (a cylindrical specimen) is inserted into a small pipe and then broken by a servo-controlled testing machine.2) Load is increased to the predetermined value and then the broken rock is compacted in the pipe.3) The compacted rock is pulled out from the pipe and uniaxial compression or indirect tension test is carried out. The experimental results indicate that :1) Strength recovery is verified in both uniaxial compression and indirect tension tests.2) A degree of strength recovery varies from rock to rock. In Dotan, strength recovery is most remarkable among the 4 rocks. On the other hand, Sanjome andesite shows only poor strength recovery.3) Strength recovery is much higher under air-dried condition than water-saturated condition.