LABORATORY CALIBRATION OF EARTH PRESSURE CELLS

Abstract

Strain-gauge type soil pressure transducers are widely used in laboratory and field investigation on the performance, and health monitoring of geo-structures to accurately measure the soil pressure. Even though these pressure plates are sold with the factory-measured calibration factors, these sensors should be re-calibrated in the laboratory before using them because the calibration can be affected by the data-logging system and the length of the cable used. Therefore, in this study, a laboratory calibration procedure for strain-gauge type soil pressure plates was proposed. The soil pressure transducer was embedded in a uniform-fine- sand medium in a specially designed pressure cylinder, and the pneumatic pressure was applied into the system as gradual increments. After that, the calibration chart of the pressure gauge was developed based on the sensor outputs for different pressures applied. Then the calibrated soil pressure transducer was used in the laboratory pavement model test to measure soil pressure at the base-subgrade interface under a surface loading area. The measured soil pressure values were compared with the estimated vertical stresses from elastic theories to validate the pressure measurements and the calibration process of the soil pressure transducer. Test results revealed that there is a satisfactory agreement between the pressure measured by the soil pressure transducer and theoretical estimations. Thus, the calibration process of the soil pressure transducer and its outputs are proven to be accurate.