Visualizing 3-D Internal Soil Deformation Using Laser Speckle and Transparent Soil Techniques

This paper addresses the needs for non-intrusively measuring 3-D internal soil deformation in geotechnical engineering. In this research transparent soil is used to measure internal soil deformation under a model footing. Transparent soil is made of either amorphous silica gel or powder with a pore fluid having the same refractive index to model either sand or clay. An optical system consisting of a laser light, a CCD camera, a frame grabber, and a computer was developed to optically slice a transparent soil model. A distinctive laser speckle pattern is generated by the interaction of the laser light and transparent soil. Digital image cross-correlation was used to calculate 2-D displacement fields between two speckle images captured consecutively during footing settlement. A 3-D displacement field was obtained in Matlab® by combining multiple slices of 2-D displacement fields. The results showed that the developed optical system and transparent soil are suitable for more advanced 3-D soil deformation measurements.