Development characteristics and engineering properties of sedimentary expansive soil in the Zhuyuan area, eastern Yunnan

This study employs multiple methodologies including field investigation, geophysical exploration, shallow well engineering operations, and laboratory analysis to examine the development characteristics and engineering geological properties of expansive soil in the Zhuyuan area of eastern Yunnan. The findings reveal that the sedimentary expansive soil in the Zhuyuan area primarily occurs in the upper Neogene Ciying Formation (N₂c), with its distribution significantly controlled by faults systems. From the perspective of material composition, expansive soil predominantly consists of quartz and clay minerals, with notable proportions of feldspar and gypsum. In terms of engineering characteristics, the expansive soil in this area has challenging properties including high dispersibility, high plasticity, and high porosity. The soil presents clay content ranging from 22.0% to 69.1%, liquid limit from 38.1 to 63.0, plastic limit from 20.4 to 36.9, plasticity index from 14.8 to 26.1, and natural porosity ratios predominantly approaching 1, with maximum values reaching 1.51. The free expansion rate ranges from 33-65, classifying it as weak expansive soil. Microstructural analysis indicates that the primary clay minerals comprise curved sheet-like illite/montmorillonite mixed layers. The microstructure exhibits a “face edge”configuration with well-developed interlayer micropores, facilitating water migration and wet swelling and drying shrinkage process. These adverse engineering geological characteristics of sedimentary expansive soil in the Zhuyuan area constitute the primary factors contributing to frequent geological disasters in the region. Consequently, geological disaster prevention and control efforts must thoroughly consider the engineering geological characteristics of expansive soil, particularly the influence of hydrodynamic forces. The implementation of comprehensive prevention measures including drainage systems, support structures, and slope protection, is essential for management of these geological challenges.