Investigation on active isolation of machine foundations by open trenches

Ground disturbance due to waves generated by a machine foundation can be detrimental to adjacent structures or sensitive equipment operating nearby. Most of the vibratory energy that affects structures nearby is carried by surface (Rayleigh) waves that propagate in a zone close to the ground surface. Therefore, for machine foundations vibrating from moderate to high frequencies, the amplitude of ground motion can be reduced significantly by installing a wave barrier around the source. A three-dimensional boundary element algorithm incorporating quadratic elements has been used to perform an extensive parametric study on the effectiveness of open trenches as wave barriers. The key geometrical and material parameters that govern the performance of an open trench wave barrier have been identified, and a design formula in the form of an algebraic expression has been developed for estimating the vibration screening effectiveness of such barriers. Furthermore, through comparisons with published field test data and rigorous boundary element solutions, the validity of the design formula has been established.