Photoelastic Sensors for Measurement of K_o

The objective of the study presented herein is to show the usefulness of photoelasticity, in conjunction with digital image processing, for determining stresses in geotechnical laboratory tests. To illustrate this, photoelastic sensors were manufactured and calibrated to determine the lateral stress during loading and unloading in a 2-dimensional granular assembly under K_o conditions. The sensors are square glass plates with a circular opening in the center, which results in stress concentrations around the perimeter of the opening and thereby increases the sensors sensitivity. Using digital image processing to quantify the intensities of light colors in the photoelastic sensors according to red, green, and blue (RGB) components, it is shown that R-intensity is the most sensitive to applied stress and was thus used to determine induced stresses. The procedure used to calibrate, as well as the resulting calibration charts, are discussed in detail.