Abstract: To study the expansibility and mechanical property of expansive soil in natural state, a series of expansion and mechanical property experiments, were carried out on Nanyang weak expansive soil with different humidifying degrees under the same initial condition. Through the experiments, the following conclusions are drawn: with the increase of humidifying moisture content, both natural expansibility and loaded natural expansion rate gradually increased at first, then slightly reduced, and finally became stable step by step. Load-free expansion rate almost increased in linear manner in earlier stage, then gradually became stable. By shearing strength experiments of expansive soil with different humidifying degrees, linear relation curve and relational expression between cohesion, internal friction angle and humidifying moisture content were developed. For completed projects, actual expansion property and shearing strength of expansive soil can be obtained by moisture content monitoring, which can be used to assess safety conditions of projects.

Key words: weak expansive soil, natural expansibility, natural expansion rate, shearing strength