Experimental Study of Soil-water Characteristic Curves of Granite Residual Soil

Given the construction needs for roads and slopes in the Youxi Development Zone in Fujian, this paper takes Youxi granite residual soil as the research object. A pressure plate apparatus was employed to measure its moisture-increasing and moisture-reducing soil-water characteristic curves (SWCCs) . By combining particle size distribution curves, mineral composition, micro-pore structure, liquid-plastic limit, and dry density of different soil types, the paper systematically explores the influencing mechanisms of SWCCs in different granite residual soils. The results showed that: 1) three granite residual soils with grading curve coefficient Cc<1 or Cc>3 exhibited poor grading with some range particle size gaps. and usually the granite residual soil possessing the mass fraction below 50% with d < 0.075 mm showed sand particle matrix being dominant. Due to above the poor particle gradation and dominant sand particle matrix, the pore diameter variation between aggregates in soil was obvious, and these would lead to pronounced bottleneck effects during drying and wetting processes and eventually a relatively large hysteresis loop area for the SWCCs existed. 2) the weathering degree, mineral composition, plasticity index, and concentrations of high-valence cations (such as iron) in granite residual soils would obviously influence the SWCCs characteristics. Weathering affected mineral composition, thereby altered clay mineral content and plasticity index. A higher plasticity index indicated stronger water-combining capacity of soil particles, and leaded to a wider variation ranges in both volumetric water content and matric suction, which eventually expanded the range of the SWCCs. Additionally, the liquid limit was positively correlated to residual volumetric water content, granite residual soil with higher liquid limit would exhibit a greater residual volumetric water content.