Resumen de Advanced image analysis techniques for laboratory experiments on soils
The understanding of soil behavior is the foundation where the geotechnical engineering is built on. Experimentation is essential to improve this comprehension, and then to be able to translate it into models, theories, or laws. In a proper scientific method, experimentation is present in all phases of model development from conception to validation.
This Thesis focuses on laboratory experimentation. The experiments are interesting because they are an abstraction of reality, focusing on the objective of the investigation. The main advantage of laboratory experiments is the high reproducibility, which, together with the control of the initial and contour conditions, enables to analyze the effects of different variables on the soil behavior.
This Thesis focuses on the development and improvement of methodologies and techniques to provide more and better information from the laboratory experiments in a massive and non-invasive way. The developed methodologies are based on the analysis of sequential images of experiments which are able to provide the spatial distribution through the domain of the analyzed variables.
The first technique presented and validated is the Particle Image Velocimetry - Numerical Particle (PIV-NP). This is a post-process to enhance the image correlation methods (PIV). The method is able to transform the instantaneous displacements measured by PIV between two consecutive images on fixed points in the space into accumulated displacements and strains on points (Numerical Particles) which represent portions of the moving soil analyzed. The method is especially suitable for the analysis of large displacements and strains experiments and combines the advantages of Eulerian and Lagrangian scheme. The validation of the method is done by means of synthetic examples and laboratory tests.
For application on unsaturated soils, the Thesis presents a methodology to measure the degree of saturation (Sr) using Short-Wave InfraRed images (SWIR). The methodology is based on the relatively high absorbance of light by water in specific wavelengths of the SWIR spectrum (1400 -1550 nm and 1900 – 2000 nm) respect to the solid particles of soils. The methodology is created to be applied in a sequence of images to analyze the spatial distribution of degree of saturation and its evolution in time. The average Pixel Intensity is measured in a grid of points in each image. The Pixel Intensity is normalized and translated into its correspondent degree of saturation using the calibration curve previously calibrated.
Both techniques, PIV-NP and Sr measurements from SWIR image, are combined into an integrated methodology. The result provides the position, velocity, acceleration, strains, and degree of saturation in time of the analyzed moving soil discretized into numerical particles. This allows to compare and correlate directly all the variables. The methodology offers different options to display the results: surface (2D), line (1D), and particle (0D). The information that provides each display dimension is complementary and useful for a complete understanding of the soil behavior.
Finally, the integrated methodology is also applied combining the PIV-NP with a more mature technique to measure the degree of saturation in transparent soils developed in Canada. The study of the dry footprints on the seashore is the chosen case to show the capability of the combined techniques on the analysis of soil behavior. The three different options of results display are crucial to understanding the correlation between the degree of saturation and the velocity of failure.
The methodology and techniques developed can be used in any geotechnical laboratory and conform a base to extend the volume of data that can be obtained from the experiments, but especially enhancing the utility of the information deduced from the data.
