Master of Science in Civil Engineering (MSCE)
Civil and Environmental Engineering
The use of high-speed data acquisition systems, inexpensive and reliable transducers, and better models of interpretation have combined to make elastic wave tomographic imaging of geotechnical engineering systems easier to accomplish both in the laboratory and in the field. An important application of these developments is that the evaluation of states of effective stress in soils using images of elastic wave velocity distribution. As a consequence, it is possible to experimentally estimate the state of induced and in-situ effective stresses and to compare these results with established models of stress distribution based on the theory of elasticity (e.g., Boussinesq’s solution). The effective stress versus shear wave velocity relationship follows a Hertz’ model. The parameters for this relationship are calibrated by testing the dry sand in both a modified triaxial cell and an oedometer cell hosting bender elements. The long term objective of this research is to obtain a tomographic image of the states of in-situ and induced stresses in clean, dry sand underneath a model footing. The post calibration test program consists of a test cell that is capable of yielding a Ko-state of stress condition while allowing independent control of simulated overburden pressure and bearing pressure. The elastic waves will be generated and received using bender elements (i.e., bimorph piezoceramic crystals). Justification of the travel time data from the test cell is made possible by a numerical integration of the Boussinesq solution for our stress conditions. Furthermore, velocity field images are presented as well as recommendations for improvements.
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Tanner, William M., "Travel time tomographic imaging of the distribution of the effective stress in clean sand under a model footing" (2004). LSU Master's Theses. 3710.