Finite element study of vibration isolation using an underground trench

The purpose of this dissertation is to evaluate the performance of the underground trench as a barrier to isolate structures from surface vibrations. The tool used to perform this evaluation is the Finite Element Method (FEM). A two-dimensional (2D) FEM computer program was developed and verified by comparing its results to those of well known theoretical and experimental vibration results: for a one-dimensional (ID) beam; for a 2D plate in plane stress; and, for the open trench. The FEM code was found to agree reasonably well for all three well-characterized theoretical and experimental results obtained by other researchers. It was then used to investigate the usefulness of the underground trench, a new concept for surface vibration isolation of structures.

In performing the evaluation of surface vibration effectivenes of the underground trench a general criterion based on surface vibration amplitude was developed. This general criterion allowed judging the effectiveness of a particular underground trench configuration on a quantitative basis, permitting comparisons to be made which are consistent for different underground trench configurations. The effectiveness of the underground trench structure was then studied in detail. Use was also made of the Taguchi Method for Experiment Design to minimize the number of computer runs that needed to be made, while at the same time optimizing the design parameters that define an underground trench. The results obtained show that the underground trench structure is as effective as the open trench in isolating structures from surface vibrations.