白鹤滩水电站左岸边坡深部破裂成因探讨

在对白鹤滩水电站坝址区河谷地质条件、地应力分布及左岸边坡深部破裂发育特征详细分析的基础上,采用离散元数值软件UDEC以剥蚀法模拟河谷演化发育过程,分析白鹤滩水电站左岸边坡深部破裂的形成原因。模拟结果反映河谷应力场分布呈现出了典型深切河谷所具有的应力松弛、升高及原始三区以及谷底存在高地应力包的规律。同时对河谷边坡不同部位、不同阶段的应力变化规律进行了深入分析并结合现今河谷地质特征,认为该深部破裂是在河谷地层顺倾、区域高地应力、不对称V型河谷、下蚀迅速等特定条件下,在河谷演化过程中局部应力集中使岩体发生剪切屈服,并发育剪切破坏,河谷剥蚀卸荷后顺倾向错动带的出露使剪切破坏进一步发育成张性破坏的结果。

MECHANISM OF DEEP FRACTURES FORMATION IN LEFT BANK OF BAIHETAN HYDROPOWER STATION

On the basis of the detailed analysis of the valley geological conditions as well as geostress distribution and deep fractures in the left bank of Baihetan hydropower station, the evolvement and development of the site valley are simulated by using distinct element codes UDEC with denudation method to analysis the formation mechanism of deep fractures in the left bank. Simulation results show that valley stress field distribution presents the law of a typical deep valley with three stress districts of relaxation, increase and unchanged, as well as valley bottom existing high geostress fold.Based on the deep analysis of different parts in the valley slope, different stages of the stress variation and present valley geological features, it is considered that the deep fractures are results of the tensile failure. The outcrops of the consequent dip fault zones after the eroded valley unloads make shear failure further grow. Those shear failures are formed because the local stress concentrations make rock shear failure during the valley development process at the special geological structures such as the dip direction of rocks along slope, the high regional tectonic stress, the asymmetric v-shaped valley and rapid incision of Baihetan hydropower station valley.