In designing port and airport facilities, it is important to investigate the deformation and failure modes of the target structure and its ground in order to make a rational design under severe external conditions. In the study of deformation - failure behavior of geo-materials, laboratory tests, model experiments and numerical simulation have been carried out to reveal the mechanism. In particular, model experiments are important from the viewpoint of validation of numerical simulation results. The model test results have been investigated through the measurements by various sensors and image analysis. Recently, three-dimensional data of strain field have obtained by X-ray CT scan, the displacement of each particle and its strain distribution using image analysis have been actively investigated. On the other hand, stress fields have often been measured by earth pressure gauges or pore water pressure gauges as a point measurement. The photo-elasticity material and X-ray diffraction methods enables to investigate for two or three dimensional measurements, but these method needs an expensive equipment such as polarizers and synchrotrons, and limitation in particle shapes or measurement interval due to tomographic scan. Currently, there is a difference in measurement level.
The authors focused on the mechanoluminescence material for visualizing the inter-particle contact force and its transition of soil particles as a solution of the problems mentioned above. The mechanoluminescence material is force induced luminance material. In this study, we reported the introduction of the mechanoluminescence phenomenon, application for granular material through the coating, calibration and its validation in 2D assemblies. Moreover, an application of pile penetration process as a typical geotechnical problem was also reported.

Key Words: Granular material, Mechanoluminescence, Visualization, Force chains, Pile penetration,