Abstract: The expansive performance of in-situ expansive soil is significantly influenced by its natural characteristics such as water content and structural properties. Effectively and accurately determining the in-situ expansion potential of expansive soil is a key challenge in engineering. To evaluate the expansiveness of in-situ expansive soil, artificial and natural expansive soils were selected as research subjects. Low-frequency electrical tests and expansion ratio experiments were conducted to establish an evaluation model for the non-loaded expansion ratio of expansive soil based on low-frequency electrical indicators. The research results indicate that the expansion ratio without load decreases as water content increases at a constant dry density. The soil’s expansiveness is significantly influenced by the initial water content and pore structure characteristics. The final expansion ratio is correlated with the water absorption characteristics of soil mineral particles. Additionally, changes in water content and dry density can significantly impact the resistivity index. The strong sensitivity between resistivity index and soil water content, along with the characterization of water absorption capacity in expanded soil minerals, suggests that the resistivity index is a valuable tool for assessing the expansion behavior of in situ expanded soil. Based on this foundation, resistivity, dry density and water content were normalized. A comprehensive indicator Q, which combines normalized water and electricity data, was introduced. Furthermore, an evaluation model for the non-loaded expansion ratio of in-situ expansive soil was developed. Through validation with existing experimental data, the proposed electrical evaluation model for the expansion ratio of in-situ expansive soil exhibits direct and efficient attributes, offering a dependable assessment of the expansive potential of in-situ expansive soil.

Key words: electrical resistivity, expansive soil, expansive characteristics, low frequency electrical method, evaluation model