Calibration of Smart Irrigation Sensor (SIS-UMS) for the blanket layer soil from old railway lines

The sensor SIS (Smart Irrigation Sensor-UMS) was selected to be used in monitoring the soil matric suction changes in an old railway line. The sensor was calibrated using a soil taken from the blanket layer. This layer was created mainly by the interpenetration of the subgrade soil into the ballast layer under the trains' actions. The sensitivity of its mechanical behaviour to water moisture changes is a key point when evaluating the maintenance of the railway line involved. Obviously, monitoring the suction helps for this evaluation. In the present work, a SIS sensor was installed beside a T8 tensiometer-UMS and a high-capacity tensiometer in a plastic box of 240-mm in diameter and 240-mm in height. The readings of the high capacity tensiometer were recorded automatically in voltage and were converted in kPa using the calibration curve carried out in laboratory. The values of the SIS sensor and the T8 tensiometer were measured by a box INFIELD 7 with manual reading based on the calibration of the supplier. The comparison of the matric suction between three sensors shows that the measurements of two tensiometers are similar. Values of approximate of 2.4 times lower were measured by the SIS sensor.