Isolation Of Elastic Waves By Discontinuous Barriers In Poroelastic Soil

Vibration isolation of structures from ground transmitted waves generated by machines, traffic, blasting or pile driving has received considerable attention in single phase soil, while little work has been done in poroelastic soil. With the rapid development of modern industry and urban expansion, the vibration in poroelastic soil has increasingly important influences on the surroundings. It is important to investigate how to impede or reduce the propagation of elastic waves in poroelastic soil, which not only provides a useful way for revealing the action mechanism of barrier and waves in poroelastic soil, but also has important application value in engineering.Firstly, based on Biot's poroelastic theory, the scattering of an elastic wave obliquely incident on a cylinder is studied and the scattering equation is given using cylindrical wave functions. The expressions for the backscattering spectrum and total scattering cross-section are subsequently calculated. The numerical results show that the influence of soil permeability on the backscattering spectrum is remarkable, and the total scattering cross-section decreases with an increase of obliquely incident angle.Secondly, the isolation of plane P and S waves by using a row of rigid or elastic piles as a barrier is investigated in a homogeneous unbounded space. Utilizing wave function expansion method, all of the potential functions of scattered waves are transformed into one coordinate system with the aid of Graff's addition theorem. Taking into account the orthogonality and linear independence of trigonometric functions, closed-form expressions for scattering coefficients are developed by imposing continuity conditions of pile-soil interfaces and equilibrium conditions of piles. The results indicate that the isolation effectiveness for plane S waves will become better with the decrease of the soil permeability. There is a significant difference in the isolation effectiveness of a row of piles between the poroelastic soil and the elastic soil.Thirdly, the effect of a row of elastic piles in reducing the vertical displacement (in the direction of pile axis) amplitudes of poroelastic soil is investigated. The wave field near certain pile is constructed as the sum of incident waves and scattering waves from all piles with the translational addition theorems for cylindrical wave functions. By imposing continuity conditions at the soil-pile interfaces, the unknown coefficients for potential functions of scattered waves are determined. Then, the soil displacements behind the pile barrier can be calculated. It is found that the modulus ratio between the pile and soil has significant influence on the reduction of vertical displacements, while the soil permeability has little influence on it.Finally, on the basis of Biot's theory without considering the inertial coupling effects between the solid-fluid phases of the medium, the piles are modeled as Euler-Bernoulli beams and the diffracted field by each pile is constructed only with Rayleigh waves. Six infinite linear systems of algebraic equations are obtained according to Graff's addition theorem and the application of suitable boundary conditions. The systems are subsequently solved in the complex least squares sense. Numerical calculation results show that the influence of soil permeability on the isolation of Rayleigh waves in poroelastic soil is different from that of plane S waves, and the pore water pressure behind the pile barrier can be reduced remarkably.