Particle size composition characteristics of weathered debris from grey–green slate under the action of freeze–thaw and dry–wet cycles

The material basis for soil formation is rock weathering debris. Understanding the particle size composition characteristics of rock weathering debris and its impacts is important for improving the soil structure of dry farmland in the central dry zone of Ningxia,China. In this study, the particle sizes of weathered debris collected from grey–green slate after indoor simulations of freeze–thaw and dry–wet cycles tests were examined. The results were as follows: (1) Under 16 treatments, the weathering debris of grey–green slate contained about 10% or less very fine sand and coarse silt, while clay, fine silt, and fine sand were the most abundant sizes (at least 60% of the total). (2) Under each treatment, the average particle size of the grey–green slate weathered debris was 5.52Ф (silt grade). The overall skewness was high, but the symmetry was poor. The particle size frequency distribution curve had many broad peaks or multiple peaks. (3) The fractal dimension was associated with very fine silt but had a strong negative correlation with fine sand and medium-coarse sand. The results indicate that fractal dimension can reflect the grain size characteristics of weathered debris. The mineral element content of the grey–green slate somewhat affected the fractal dimension, and it positively correlated with environmental electrical conductivity (EC) and element-leaching amount; it negatively correlated with particle size, temperature, and pH. According to the findings, the fractal dimension can accurately represent the particle size distribution of weathered debris. The generation of grey–green slate weathering debris should be considered in the formation and development of local soil.