The Impacts of Overburden Pressure on Hydraulic Conductivity Functions of a Loamy Sand Soil

by Open Science Repository Agriculture
(October 2013)


The van Genuchten (vG) and Brooks-Corey (BC) hydraulic functions were used to describe the soil water retention curve (SWRC) of unsaturated loamy sand soil. The objective of this study was to investigate the impacts of overburden pressure, especially on the vG model α-parameter. The uni- and bimodal vG parameter α for both soil samples extruded at 15 cm depth with overburden pressure of 38.7 kPa and 120 cm depth with overburden pressure of 309.3 kPa were compared and aligned to the Kosugi´s approach for estimating the pore size distribution of the SWRC. The AIC statistical analysis showed that bimodal vG approach provided better estimates of the α-parameter. For uni-modal case, the pore sizes described by probability density functions f(1/µ) for both soil samples were characteristically Gaussian with f(1/µ) values for Ap samples at 0.0032 and α-parameter at 0.0831 while the f(1/µ) for BvSw was 0.002 and α-parameter 0.0341. For the bimodal case, the f(1/µ) suggesting primary pores for Ap samples was at 0.0017 and α₁-parameter (0.074) and for secondary pores 0.0052 and α₂-parameter (0.144). The f(1/µ) for primary pores for BvSw was at 0.0011 and (α₁ = 0.012 while this for secondary pores was 0.0028 and (α₂ = 0.0083). Although the peak values of the density functions for both uni-modal and bimodal cases for Ap samples were greater than those of BvSw, where larger primary pores were predominant at the soil upper surface than at below as conditioned by good soil structure and aggregation, this did not suggest the effects of overburden pressure on the pore size distribution as a function of depth.

Keywords: overburden pressure, soil water retention curve, parameter estimation and optimization, pore size distribution.

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The Impacts of Overburden Pressure on Hydraulic Conductivity Functions of a Loamy Sand Soil

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