BC-function parameters describing the water retention characteristics of soils, soil-gravel mixtures, and gravels.

*<p><i>θ_s</i> for soil and soil-gravel samples were the measured value, and <i>θ_s</i> for gravel samples were calculated from density and bulk density. <i>RMSE</i>: square root of residual sum of squares values.</p

Packed bulk densities (g cm⁻³) of clay loam soil and gravel mixtures.

<p>Packed bulk densities (g cm⁻³) of clay loam soil and gravel mixtures.</p

The measured points and the regression surfaces of power function with variable of samples bulk density for soil-gravel mixtures (•: Measured point; mesh: Regression surface).

<p>The pressure head in the axe is the absolute value of the actual pressure head which is negative in the measurement.</p

The measured data and fitted water retention curves for soil-gravel mixtures with 3–5 mm gravels.

<p>Point: Measured data; Line: Fitted data. CL+S stands for the mixtures of clay loam soil and shale clasts with varied gravel content; CL+P stands for the mixtures of clay loam soil and pebble with varied gravel content. The pressure head in the axe is the absolute value of the actual pressure head which is negative in the measurement.</p

The measured and simulated saturated water contents for soil-gravel mixtures with varied gravel sizes.

<p>CL+S stands for the mixtures of clay loam soil and shale clasts; CL+P stands for the mixtures of clay loam soil and pebble.</p

Mineral composition of soil and rock fragments sampled in this study.

<p>Mineral composition of soil and rock fragments sampled in this study.</p

The measured and fitted data calculated by the trade-off parameters of power surface model with the variable of samples bulk density without considering gravel size change.

<p>The measured and fitted data calculated by the trade-off parameters of power surface model with the variable of samples bulk density without considering gravel size change.</p

Comparison between the regressed parameters by fitting two and all measured water retention curves of soil-gravel mixtures.

<p>Comparison between the regressed parameters by fitting two and all measured water retention curves of soil-gravel mixtures.</p

Regression empirical parameters for curved surface functions with <i>M_r</i> obtained by fitting all the measured water retention curves.

<p><i>R</i>2, <i>SEE</i>, and <i>REMS</i> stand for coefficient of determination, estimated standard error, and square root of the residual sum of squares, respectively.</p

Rotation speeds and equilibrium times corresponding to the tested pressure heads in the centrifuge method.

<p>Rotation speeds and equilibrium times corresponding to the tested pressure heads in the centrifuge method.</p