Digital image-based analysis of a small-scale dam failure during wetting

Abstract

The use of digital images and the correlation of them in time is commonly used in geotechnical laboratory experiments to measure surface variables in a non-invasive and massive way. Digital image correlation-based methods provide a measure of the motion of soil. More recently, measurements of the degree of saturation on soil surface using digital images have also been developed, although its application and validation are still limited. This methodology is based on the fact that almost all soils become darker (less light reflective) due to wetting. This article uses image-based analysis techniques to evaluate the behaviour during wetting of a small-scale dam made of compacted fine sand. With the aim of validating the measurements from images, soil moisture sensors were installed in the dam. The tested soil was previously calibrated to determine the correlation of light reflectance and the degree of saturation covering from dry to fully saturated range. Measurements of velocity, displacements, deformations and the degree of saturation in time are evaluated during the experiment based on images recorded in the visual and shortwave infrared (SWIR) light range. The methodology is described step-by-step including camera and lighting system, sample preparation, image acquisition and image analysis. The techniques used allow the changes in the degree of saturation in soil in motion and the failure mechanisms associated with the wetting process to be observed. The results obtained through image analyses show good agreement with the parameters obtained in point measurements with conventional sensors. The results also show some limitations of the method, mainly associated with the accumulation of errors in the tracking of soil particles during large displacements.