Calibration and Validation of S3F Sensor for Measuring Normal and Shear Stresses in Soil

Abstract

Abstract Innovative sensors can provide new capabilities to monitor and understand the behavior of soil, rock, and geo-structures and help geotechnical engineers make informed decisions about the construction and maintenance of geo-structures. This study introduced, calibrated, and validated one such sensor, the Surface Stress Sensitive Film (S3F) point sensor, for both normal and shear stress measurements in soil and along the soil–structure interface. The measurements of the S3F sensor rely on the deformation of an elastic film that is monitored by a magnetic floating element embedded in the elastic film and a Hall effect sensor. This sensor provides measurements of the 3-D deformation of the film, which are converted to normal and shear stresses using an a priori calibration. The calibrations of the S3F sensor were performed considering the effect of the loading areas, loading and unloading conditions, and soil particle sizes. Then, the performance of the S3F sensor to measure the normal stresses in soil and shear stresses at the soil–wooden block interface under static tension and pull-out conditions was evaluated. It was found that the normal stress calibration curves depended on the sizes of the loading areas because of the stiff housing boundary effect. However, the shear stress calibration curves were independent of the loading areas. The S3F sensor showed an ability to measure normal stresses in three different types of soils, including two silica sands from Ottawa, Illinois, with particle sizes ranging between sieve No. 20 and 30 (Ottawa 20/30 sand) and sieve No. 50 and 70 (Ottawa 50/70 sand) and finely ground silica silt (Sil-Co-Sil). The S3F sensor also showed an ability to measure the shear stresses at the soil–structure interface, which match well with the theoretical shear stresses. The S3F sensor has potential for stress measurements at the soil–structure interfaces in foundations, tunnels, pipes, and retaining systems.