小湾水电站坝基岩体弹模与地应力测试研究

为了评价小湾水电站坝基岩体开挖后的卸荷松弛效应、确定卸荷深度和研究卸荷岩体的应力分布特征，同时采用钻孔弹模法和水压致裂法在坝基开挖面进行了5个深度20—30m钻孔的岩体变形与地应力测试。测试结果表明开挖卸荷影响较明显，钻孔浅部（深度小于11m）弹模明显降低；坝基岩体表层20m以内的最大水平应力一般小于10MPa，显示了一定程度的应力集中现象。其次，根据卸荷带划分结果和工程地质条件进行了二维弹塑性有限元应力场模拟分析。分析结果和实测结果一致，表层开挖卸荷岩体中应力有所释放，河床以下20～50m范围存在明显应力集中。

Experimental Study of Borehole Elasticity and Geostress in Xiaowan Hydropower Plant's Dam Foundation Rock Mass

In order to evaluate the effect of unloading relaxation,the unloading depth and the stress redistribution due to dam foundation's excavation of Xiaowan Hydropower Plant,situated on Lancang River,both borehole elasticity and hydrofracturing stress measurements were conducted in five holes of 20~30m deep,drilled from the excavated rock surface.Results reveal that the unloading effect is notable with significant decrease of elasticity modulus in the shallow depth of about 11m.Also the maximum horizontal stress is less than 10 MPa in the shallow layer in 20m and some stress concentration appears.Then,a two dimensional plasto-elastical FEM stress analysis is completed based on the geological condition and the unloading characteristics.FEM modelling shows basically the same tendency: the stress relaxation due to excavation unloading is evident in the shallow zone and there is important stress concentration 20~50m under the riverbed.