Field permeability at shallow depth in a compacted fill

This paper presents a series of field double-ring infiltration tests (DRTs) for investigating the hydraulic conductivity of a compacted silty clay fill that contains some desiccation cracks. These field tests were conducted at three different depths in the fill, to characterise the variations of conductivity with depth. The hydraulic conductivity of the fill was also measured in the laboratory on block samples using a three-directional permeability cell (sample size: 200 mm × 200 mm × 200 mm) and a one-dimensional permeameter (sample size: 70 mm in diameter and 45 mm high). A perched water table was detected in the fill using tensiometers shortly after the start of each DRT, showing the presence of preferential flow paths in the fill. The hydraulic conductivity decreases with increasing depth. The larger hydraulic conductivity of the surface soil indicates the possible presence of macropores and cracks at shallow depths of the fill. The coefficients of variation of the hydraulic conductivity measured from the DRTs (influence volume: 300 mm in diameter and 450 mm high) and the three-directional permeability cell tests are smaller than those measured from the small-size, one-dimensional permeameter tests. The variability of the measured hydraulic conductivity increases as the sample size decreases.