高地应力环境下坚硬岩体河床坝基开挖的变形破坏机理研究

DEFORMATION AND DAMAGE OF HARD ROCK MASS RIVER BED DUE TO DAM FOUNDATION EXCAVATION UNDER HIGH IN-SITU STRESS

小湾水电站坝基岩体在开挖过程中,暴露出一系列的变形破坏现象,主要表现为"板裂"、表面岩爆、沿已有裂隙张开、扩展和错动等。在对上述变形现象分析的基础上,研究了高应力环境下坝基岩体开挖的地质力学响应,发现:河床坝基岩体在开挖过程中所表现出的变形主要集中在坝基浅表,且具有时效性。根据变形破坏现象分析和变形响应研究,对高地应力环境下坚硬岩体河床坝基开挖的变形破坏机理有了新的认识,是河谷下切和开挖卸荷过程中的应力重分布造成的浅表生改造的结果。最终,将河床坝基岩体的变形破坏归纳为"压致拉裂—卸荷回弹"模式,且以压致拉裂为主。

The rock mass forming the dam foundation of Xiao Wan hydroelectric station during excavation revealed a series of deformation and fracture phenomena.It mainly behaved as a ＂split plate＂ and surface rock bursts,and cracks along the existing structure,expansion and dislocation,and so on.On the basis of the analyses of the abovementioned phenomena,this paper studies the geological mechanic response of the rock mass due to the dam foundation excavation in the high in-situ stress environment.It is found that the rock mass deformation during excavation is mainly concentrated on the shallow surface of the dam foundation,which has time effect characteristics.According to analyses of deformation-destruction phenomenon and the study of deformation responses,the mechanism of deformation-destruction is understood.The mechanism applies to the excavation of the hard rock river bed of the dam foundation in the high in-situ stress environment.Shallow and superficial transformation result from the stress redistributed during down-cutting of river and unloading of excavation.Ultimately,it can be summarized that the deformation and fracture of river bed are a ＂pressure rupture-unloading rebound＂ model,and the pressure-rupture is the main type.