某高拱坝坝基开挖卸荷松弛时空效应

水利水电工程中坝基开挖造成的岩体卸荷松弛是影响工程质量和安全的重要问题,查明岩体卸荷松弛的时间规律和空间特征,为加固工程设计方案提供数据依据具有重要意义。在某高拱坝坝基开挖过程中利用声波测井技术对建基面岩体进行大面积长期观测,对声波数据进行统计分析,并结合现场卸荷松弛现象,总结出岩体开挖所引起的岩体在一定时间和空间上的卸荷效应及发育特征。结果表明:岩体的卸荷松弛主要发生在开挖后的前8个月,10~12个月后基本结束;卸荷松弛的速率先快后慢;原岩的岩体结构越完整,卸荷效应越低,反之则越高;松弛带厚度与坡比之间存在一个最优坡比值;岩体的卸荷松弛是由浅入深渐进发展的,浅层岩体卸荷松弛程度明显高于深部岩体,且持续时间更长;结构面和软弱夹层是卸荷松弛的重要部位,影响大型岩块的稳定

Spatio-temporal Effects of Excavation-induced Unloading and Relaxation of Rockmass of a High Arch Dam

The unloading and relaxation of rock mass caused by excavation of dam foundation in water conservancy and hydropower project is an essential problem affecting engineering quality and safety.Identifying the temporal and spatial characteristics of unloading and relaxation of rock mass, and providing data basis for reinforcement engineering design are of substantial significance.In this paper, the unloading effect and development of rock mass caused by excavation of a high arch dam foundation are summarized in temporal and spatial senses based on long-term observations via acoustic logging during excavation.Results unveil that(1) unloading and relaxation of rock mass mainly occurs in the first eight months after excavation and basically ends after 10-12 months. (2) Unloading and relaxation develops rapidly at first and then slows down.(3) The more complete the structure of the original rock mass, the lower the unloading effect, and vise versa. (4) An optimal slope ratio leads to a smallest thickness of relaxation zone. (5) Unloading relaxation of rock mass develops gradually from the shallow to the deep. The degree of unloading relaxation of shallow rock mass is evidently higher than that of deep rock mass, and so does the duration of unloading. (6) Structural plane and weak interlayer are important parts of unloading relaxation which affect the stability of large rock blocks.