膨胀土是一种特殊的黏性土，具有遇水膨胀、崩解、软化，失水收缩、干裂、硬化等工程特性，膨胀土掺入水泥后其工程特性会发生改良。选取南水北调中线工程南阳段中膨胀土，进行水泥改性研究。通过改性后的自由膨胀率试验，确定水泥的最佳掺量；通过胀缩特性试验，研究水泥改性对降低膨胀潜势的改良效果；并通过无侧限抗压强度、压缩等力学性质试验，研究水泥改性对抑制膨胀土强度软化、模量减小的效果。为膨胀土现场水泥改性的设计施工提供科学的、有价值的依据。

Expensive soil is a kind of special clay, with engineering features of hydro-expansiveness, disintegration, softening, shrinkage after losing water, drying crack and hardening. When the expensive soil is blended with cement, its engineering features will be improved. The expansive soil of Nanyang section of the Mid-route of South-to-North Water Transfer Project is selected to perform the test of cement-modification in this paper. The optimum blending quantity of cement is determined by free  expansion rate test after the improvement. And the improving effect of reducing swelling potential by cement-modification is studied by tests of expansion and shrinkage. Meanwhile, the reinforcing effect of cement-modification on the suppression of module and strength softening of expansive soil is researched by unconfined compression test and compression test. A scientific and valuable basis is provided for the design and construction of site cement-modification of expansive soil.