大坝环境水质特征与化学潜蚀

大坝建成蓄水，坝址自然环境发生剧变，有利于库水中有机质的富集，致使下层库水弱酸性化和含侵蚀CO2.在向坝基运移过程中，与坝基岩石、帷幕、混凝土间产生物理化学作用，导致化学潜蚀的产生。钾、钠、硅、铝等元素是组成岩石的基本成分，钙是水泥的主成分，它们在坝基水中的大量迁移是化学潜蚀强的标志。坝基水所处的地球化学环境制约着这一作用的强度，弱酸性的氧化环境更有利于化学潜蚀作用的进行。在化学潜蚀过程中，胶粒的凝聚迁移可能携带岩石中粘粉级颗粒在排水孔口沉淀，因而坝基化学潜蚀作用可伴随机械管涌的出现。

Characteristics and chemical suffosion of the environment water around the dam site

Generally,great change of the environment around the dam will take place after the impounding of the reservoir.It is in favor of the enrichment of organic materials in water which containing erosive CO2.In the process of erosive water transferring towards the dam foundation,physicochemical reaction takes place in rock,grout curtain and concrete forming chemical suffosion.The transferring of great amount of kalium,sodium, silicon and aluminum into water is the signal of strong chemical suffosion.This effect is limited by the geochemical environment of the dam foundation.In the process of suffosion the clay powder in rock may deposit at the outlet of drainage orifice due to coagulating migration of colloidal particles.Consequently,the chemical suffosion is always accompanied by seepage.