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Vibratory waves generated by dynamic loads exerted on a foundation can be propagated to a noticeable distance through the soil, having detrimental effects on sensitive structures in the path of the wave train. The present work examines, for different cases, the efficiency of annular open trenches in screening vibration energy induced by a shallow foundation. The results obtained are verified by reference to published field test data and numerical research, and suggest that the depth of the trench is the most crucial factor in its effectiveness. The trench performance improves as its depth increases, but this effect is coupled in a complex manner with the effects of other parameters, such as trench width and location. A trench excavated in loose materials is observed to have more efficiency, and as the soil density decreases, an increase in trench efficiency is apparent. Placing a trench adjacent to the source causes larger displacement; at greater distances from the source, the vibration reduction level (trench efficiency) increases. To provide a quantitative evaluation of active isolation performance in two zones concurrently, in front of and behind the trench, a new criterion, the trench efficiency index, is introduced, and the optimum geometric trench parameters are discussed in the paper.

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