Evaporation and permeameter data hydraulic properties stony soil

We used the evaporation method to determine the hydraulic conductivity and the retention curve of a soil sample. The principle of this method is to simultaneously measure the matric head at different depths and the water content of an initially saturated soil sample submitted to evaporation.

The experiments were performed over cylindrical Plexiglas samples of 1 L (height: 65 mm), perforated at the bottom to allow saturation from below and open to atmosphere on the upper side to allow evaporation of the soil moisture. Four 6 mm-long ceramic tensiometers (SDEC230) were introduced at 10, 25, 40 and 55 mm in height, respectively denoted T1 to T4 (the reference level is located at the bottom of the sample). In order to avoid preferential flow due to the introduction of the tensiometers on a same vertical line, each hole of the sample was horizontally shifted of 12 degrees vis-à-vis the center of the tube. The tensiometers are connected through a tube to a pressure transducer (DPT-100, DELTRAN). The setup was filled with degased water. The variation in pressure of the drying soil was recorded every 15 min by a CR800 (CAMPBELL SCIENTIFIC). Tensions beyond the consolidation point were not taken into account. The consolidation point refers to the state from which the measured pressure head starts to decrease as bubbles appear and water vapour accumulates (typically 68 kPa cm in this case).

The total water loss as a function of time was monitored by a balance (OHAUS) with a sensitivity of 0.2 g with an accuracy of  1 g with a time resolution of 15 min. A 50 W infrared lamp was positioned 1 m above the sample surface to slightly speed up the evaporation process. The light was turned off for the first 24 hours of every experiment, as the evaporation rate is already high in a saturated sample. A measuring campaign lasted until 3 of the 4 tensiometers ran dry (the tension sharply drops down to approximately a null value). At the end of the experiment, the sample was oven dried for 24 hours at 105°C to estimate the .