A Numerical Test of Soil Layering Effects on Theoretical and Practical
Beerkan Infiltration Runs
Abstract
With reference to a more compacted and less conductive upper soil layer
overlying a less compacted and more conductive subsoil, a simple
three-dimensional (3D) infiltration run is expected to yield more
representative results of the upper layer than the subsoil. However,
there is the need to quantitatively establish what is meant by more
representativeness. At this aim, numerically simulated infiltration was
investigated for a theoretically unconfined process under a null ponded
head of water (d0H0 setup, with d = depth of ring insertion and
H = ponded depth of water) and a practical beerkan run (d1H1
setup, d = H = 1 cm). The considered layered soils
differed by both the layering degree (from weak to strong) and the
thickness of the upper soil layer (0.5-3 cm). It was confirmed that
water infiltration should be expected to be more representative of the
upper soil layer when this layer is the less permeable since, for a 2-h
experiment, the instantaneous infiltration rates for the layered soil
were 1.0-2.1 times greater than those of the homogeneous low permeable
soil and 1.3-20.7 smaller than those of the homogeneous coarser soil
that constituted the subsoil. Similarity with the homogeneous fine soil
increased as expected as the upper layer became thicker. For a weak
layering condition, the layered soil yielded an intermediate
infiltration as compared with that of the two homogeneous soils forming
the layered system. For a strong layering degree, the layered soil was
more similar to the homogeneous fine soil than to the homogeneous coarse
soil. Using the practical setup instead of the theoretical one should
have a small to moderate effect on the instantaneous infiltration rates
since all the calculated percentage differences between the d1H1 and
d0H0 setups fell into the relatively narrow range of -18.8% to +17.4%.
A sequential analysis procedure appeared usable to detect layering
conditions but with some modifications as compared with the originally
proposed procedure. The practical setup enhanced the possibility to
recognize the time at which the characteristics of the subsoil start to
influence the infiltration process. In conclusion, this investigation
contributed to better interpret both the theoretical and the practically
established 3D infiltration process in a soil composed of a less
conductive upper soil layer overlying a more conductive subsoil and it
also demonstrated that modifying a recently proposed procedure only
using infiltration data could be advisable to determine the time when
layering starts to influence the process.