ISOLATION OF FAST COMPRESSIVE WAVES BY BARRIERS COMPOSED OF SEVERAL ROWS OF PILES IN SATURATATED SOILS

The lengths of elastic piles are considered as much larger than the diameters, so the isolation of incident fast longitudinal waves (simplified as P₁ waves) by discontinuous barriers composed of several rows of piles can be simplified as a two-dimensional plane problem. The conformal mapping method of complex functions and the expansion method of wave functions are adopted, the stresses and displacements are considered as continuous at the boundaries between the piles and adjacent saturated soils, and then the theoretical solutions for the complex coefficients in the scattering wave potential functions are obtained. By studying the normalized displacement amplitudes behind the barriers, which are the ratios of displacement amplitudes of soils caused by both the incident and scattered waves to those only by the incident P₁ waves, the isolation effects of the barriers composed of one, two and three rows of piles are compared, and the results show that 1) the isolation effects of barriers composed of several rows of piles for incident P₁ waves with higher frequencies are much better than those with lower frequencies;2) the vibration isolation effects improve obviously and effective isolation areas increase obviously with the row number of piles increase;3) when the row number of cylindrical cavities reach three, the vibration isolation effects of some locations behind the barriers exceed 70%, which is much ideal for the vibration isolation.