3.2 Experimental setup and procedure
Figure. 2 (a) shows the schematic diagram of in-house fabricated
experimental setup for conducting HETs. As suggested by Wan and Fell
(2004a) and Xie et al. (2018), the setup included a water tank, a soil
specimen, and two chambers for inflow and outflow. The eroding fluid was
supplied by the water tank with a high gravity potential. The fixed
height of the water tank determined the constant head between two ends
of the soil specimen. Flow rate in experiments can be adjusted by
changing the height of the water tank. The soil specimen was compacted
in an acrylic (transparent) cylindrical mold to form a small soil column
with a diameter of 30 mm and a length of 50 mm. A 7 mm-diameter hole
path was drilled at the center of the soil specimen along the axis (Říha
and Jandora 2015). The eroding fluid passed through the hole path to
connect two chambers. The inflow chamber was filled with some gravels to
stabilize the flow. The outflow chamber was connected to the atmosphere
and the PVC collectors were used to receive the erosion.
The soil specimen was prepared at the maximum dry density with optimum
moisture content. Before the tests, the prepared specimen was kept in a
desiccator for 24 hours for moisture equalization. Initially, the inflow
chamber and the hole path in the specimen were filled with the fluid
slowly without causing any erosion. The head difference between the
inlet and outlet of the specimen was adjusted for a flow rate and kept
constant in each test. The erosion was continuously collected every 10
seconds to track the temporal variation of erosion. The test was
performed until erosion became insignificant. This was judged based on
visual inspection. The HETs were conducted under different hydraulic
conditions (i.e. the variance of flow rates: 2920, 4200, 5450, 7000,
8400, and 10000 ml/min) to verify the stability of proposed model and
also repeatability of tests.