The Middle Route Project of South-to-North Water Diversion passes through Nanyang Basin, Henan Province, where the expansive soil is extensively distributed and the slope stability of expansive soil canal is the main engineering geological problem. On the basis of large number of experimental results, the mineralization composition, grain composition, physical-me-chanical features and expansibility of weak, medium and strong expansive soil in Nanyang Basin were analyzed, and their micro-structure, crack development and engineering features were described. The relevance and differences of the weak, medium and strong expansive soil were introduced. The suggestions for judging and treating the weak, medium and strong expansive soil in the large-scale canal were put forward.%南水北调中线工程通过的南阳盆地广泛分布有膨胀土，而膨胀土是影响渠道边坡稳定的主要工程地质问题之一。以大量试验成果为基础，对弱、中、强膨胀土的矿化成分、颗粒组成、物理力学特性、膨胀性等进行了统计和分析；系统阐述了膨胀土的微观结构、裂隙发育状况和工程特性。针对弱、中、强膨胀土(岩)的关联性及差异性，提出了大型渠道工程弱、中、强膨胀土处理的工程措施建议。对类似输水工程的膨胀土判断及施工控制有参考作用。
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