Introduction
Double ring infiltrometers are among the common test methods for
in-situ measurement of the soil infiltration rate. DRI test described by
ASTM D3385 consists of open inner and outer cylinders that should be
manually inserted into the ground and be partially filledwith a constant
head of water. The infiltration rate is calculated by measuring the
volume of liquid added to the inner ring to keep the liquid level constant
(ASTM, 2009). The size dependency of saturated hydraulic conductivity
measurements in porous media has been studied by several researchers
and there have been several proposed dimensions as the minimum
required diameter of test cylinders. Swartzendruber and Olsen (1961)
reported that the setup with 60 and 50 cm for the outer and inner
ring radius respectively was the most satisfactory throughout all the
various conditions studied in a sandy soil. Ahuja (1976) reported that
when an outer ring of 90 cm diameter was employed for an inner ring
of 30 cm diameter, the lateral flow was practically eliminated. Bouwer
(1986) suggested that a diameter of at least 100 cm should be used
for accurate saturated hydraulic conductivity measurements. Youngs
(1987) concluded that the results were consistent from site to site