小湾电站深切河谷边坡演化动力学过程及机制研究

小湾水电站坝址位于高山峡谷区,深切峡谷形成演化的动力学过程决定了坝区边坡目前的形态特征、岩体结构特征及稳定性状况,由此深刻影响边坡设计方案和建基面的选择。基于现场工作和分析测试成果,得出主要结论有:(1)由于河谷形成过程中的卸荷作用及风化作用,边坡浅表层改造强烈,产生了大量的中缓倾角裂隙,坡面附近近SN向陡裂张开、扩展; 浅表层发育了大量近EW向挤压带(面); (2)岸坡浅表层中缓倾角结构面的产生机制,包括沿原构造节理扩展和新生裂隙; 坡体下部的中缓倾角裂隙会因差异卸荷回弹而继续扩展,坡体中上部岩体质量劣化,在地应力场调整过程中,因剪切滑移继续扩展,坡体逐渐进入时效变形阶段。(3)对河谷边坡进行了地质—工程分类,指出各类边坡可能变形失稳模式包括倾倒变形、平面滑动、阶梯状滑动、楔形滑动和堆积体滑动等5种。

STUDY ON GEODYNAMICAL PROCESS AND EVOLUTION MECHANISM OF DEEP-INCISED RIVER VALLEY SLOPE OF XIAOWAN HYDROPOWER STATION

Xiaowan hydropower station locates in the mountain-gorge region,the geodynamical process of the deep-incised river valley decides its present morphological characteristics,rock mass structure and stability,and deeply effects slope design plan and selection of dam base surface.Based on field investigation and experimental analysis,these main conclusions are formed as follows: (1)The exogenetic reconstruction of deep-incised valley slope is very strong because of unloading and weathering effect,and a great number of middle-gentle fissures are generated,the SN high dip angle fissures near slope surface are propagated and gapping; and a great number of EW compressed zone(surface)generated near the slope surface.(2)the generation mechanism of middle-gentle fissures includes propagation of old joint and new generation,the middle-gentle fissures in river valley bottom are further propagated because of differential unloading rebound,and when rock mass quality in the upper slope is stepwise lowering and so earth stresses are stepwise adjusted,the middle-gentle fissures are propagated because of shear slide,the river valley slope stepwise enter time-effect deformation period; (3)The geo-engineering classification of river valley slope is proposed,the potential deformation failure modes of each classification are topping failure,plane slide,steplike slide,wedge failure and accumulation body faiure etc.