Amplitude Reduction of Surface Waves by Trenches

The effect of trenches and barriers in reducing the disturbances created by a time-harmonic line load acting on the surface of a linearly elastic, layered slab is investigated. In this approach, boundary conditions are applied which take into account the stresses due to disturbances propagating in the adjacent, regular, semi-infinite regions. The dimensions and the location of the barrier are systematically varied for several frequencies of excitation, and the results are found to be in agreement with experimental observation. It is shown that the trench effectiveness is primarily a function of the ratio of its depth to the wavelength of the propagating disturbances, h/λ. For a value of h/λ greater than 0.6 the disturbances are significantly reduced. The results indicate that the location of the trench and the shape of its cross section, however, are not important parameters. The influence of backfilled trenches is also investigated and these are found to be less effective in reducing the vibration amplitudes than open trenches.