大渡河谷底卸荷松弛现象及其形成机制

The unloaded and relaxed phenomena in the valley bottom of the Daduhe River and its genetic mechanism

近年来越来越多的大渡河钻孔资料揭示,谷底浅表层岩体破碎、弱风化、强度低、透水性较强,具有明显的卸荷松弛现象。通过钻孔覆盖层及谷底岩体钻孔岩心研究并结合已有的研究成果的深入分析后表明,在谷底刚形成时,谷底出现应力包,应力集中足以在较短时间内使谷底岩体沿结构面发生剪切破坏形成谷底松弛带,然后应力集中向深部转移。覆盖层年龄测定结果表明,大渡河谷底形成距今已有25 ka,正是在这一漫长的岁月里由谷底应力集中导致谷底岩体变形松弛,逐渐形成现今的弱风化、弱卸荷带。

More and more borehole data from Daduhe River in the recent years show that the rockmass on the valley bottom is fragmented, moderately weathered, low strength and high permeable to water, having an obvious phenomena of unloaded and relaxed. Based on the study of the river bed overlay and borehole and the associated researched results, it is concluded that as soon as the bottom formed, the high stress concentration existed, the stress was big enough to form shear failures in the river bed rockmass and relaxed zones, then the stress Concentration zone moved toward the lower position. The dating of the overlay shows that the valley bottom of the Daduhe River formed 25 000 years ago, the unloaded and relaxed zone formed just during this long period, forming a continuous zone with the slope moderately unloaded.