Visualization with X-ray microtomography of soil samples under a growing draining pressure

Visualization with X-ray microtomography of soil samples under a growing draining pressure

Sarah Smet1_{, Eléonore Beckers} 1_{, Erwan Plougonven}2_{, Angélique Léonard}2_{, and Aurore Degré}1

(1) BIOSE, Gembloux Agro-Bio Tech, ULiege, Gembloux, Belgium

(2) Chemical Engineering, PEP’s, ULiege, Liège, Belgium corresponding contact:

[email protected]

-4 kPa

Materials & Methods

- 20 soil samples (3cm x 5cm) from a silty-loam agricultural field in

Gembloux (Belgium)

- Soil water retention curve (SWRC) measured with pressure plates

- Samples scanned at various steps of the SWRC with an X-ray

microtomograh (microCT system Skyscan 1172) at a voxel size of 21,5³

µm³ (resampled to 43³ µm³)

- Saturated hydraulic conductivity (Ks) measured at the end of SWRC

- Air permeability (ka) measured at multiple steps of SWRC

-7 kPa

-10 kPa

-30 kPa

-70 kPa

-4 kPa

* Air-filled pores in black

-7 kPa

-10 kPa

-30 kPa

-70 kPa

Results

1) Are the global geometrical and topological microscopic parameters

different between water matric potential?

6 8 10 12 -4 kPa -7 kPa -10 kPa -30 kPa -70 kPa

µCT_PO [%] Proportion of isolated PO [%] 0,3 0,4 0,5 0,6 0,7 0,8

-4 kPa -7 kPa -10 kPa -30 kPa -70 kPa

AvgZ / 10 [-] Global connectivity [-]

a a

a

Yes, as well as: the Euler number, the tortuosity (τ), the average pore volume

(Avg_vol), the pore network length (L), the degree of anisotropy (DA), and the fractal dimension (FD)

…but, the characteristics

of one samples scanned at various water matric

potentials (h) remain similar between h a a b a, b c a a, b b a, b a a, b c b, c a, b b, c b, c c

2) And if we consider the geometrical and topological microscopic

parameters calculated on specific pore size ranges ?

0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16 0 300 600 900 1200 1500 f(r) [ -] Pore radius [µm]

-4 kPa -7 kPa -10 kPa -30 kPa -70 kPa

0 10 20 30 40 50 60 70 80 90 100 Ratio of isolate d p orosity [%] Pore radius [µm] -4 kPa -7 kPa -10 kPa -30 kPa -70 kPa Calculated parameters:

average pore volume, average coordination number, average surface connectivity, fraction of isolated porosity, and pore size distribution

-> No significant differences

between parameters calculated on specific pore size ranges

between water matric potentials. Through ANCOVA analyses: the significant differences were explained by the soil sample hydrodynamic

properties for: _{µCT_PO IPO AvgZ Global_con Euler τ Avg_Vol L DA FD}

Log(Ks) X X X X X X X

Ka X X X X X