Three-dimensional pore structure characteristics of granite residual soil and their relationship with hydraulic properties under different particle gradation by X-ray computed tomography

• The micropores and complex pore structure help to increase water retention capacity. • Soil properties and soil structure comprehensively affect hydraulic properties. • The quantitative relationship between pore structure and hydraulic properties is analyzed. The pore structure characteristics and hydraulic properties, including saturated hydraulic conductivity and soil water retention curve (SWRC), for granite residual soil under different particle gradation were carried out by high-resolution X-ray computed tomography (CT) and pressure plate. The relationship between three-dimensional pore structure characteristics and hydraulic properties were quantitatively analyzed. The results show that the decrease of the average pore/throat radius and the CT-connected porosity with the particle diameter decreases, but the fractal dimension value increases, indicating that the soil pore structure became complex. The effect on hydraulic properties is the comprehensive effect of soil properties and soil structure . Adding big particles improved the saturated hydraulic conductivity by increasing the soil pore connectivity and decreasing the fractal dimension. In addition, the micropore spatial variation and complex pore structure help to increase the water retention capacity.