Photoelastic and photographic study of a granular material

Glass ballotini can be used as a special granular material that reveals information about stress conditions when viewed using polarised light. Simultaneously, techniques for observing displacement fields can be used to produce information about internal strains. The combination of photoelastic and photographic observation has potential for extending knowledge of internal conditions in two-dimensional samples of granular material. The procedures described in this note indicate some interesting possibilities for experimental soil mechanics. The use of digital photography with polarised light permits incremental results to be obtained from the photoelastic images. The use of digital photography in non-polarised light with particle image velocimetry analysis gives the opportunity to obtain experimental displacement and strain fields with great accuracy and local detail. The use of standard image processing and graphics software permits precise comparison of features of the incremental strain and stress fields by superimposing corresponding images.