The problem of structural isolation from ground transmitted vibrations by open or infilled trenches under conditions of plane strain is numerically studied. The soil medium is assumed to be linear elastic or viscoelastic, homogeneous and isotropic. Horizontally propagating Rayleigh waves or waves generated by the motion of a rigid foundation or by surface blasting are considered in this work. The formulation and solution of the problem is accomplished by the boundary element method in the frequency domain for harmonic disturbances or in conjunction with Laplace transform for transient disturbances. The proposed method, which requires a discretisation of only the trench perimeter, the soil-foundation interface and some portion of the free soil surface on either side of the trench appears to be better than either finite element or finite difference techniques. Some parametric studies are also conducted to assess the importance of the various geometrical, material and dynamic input parameters and provide useful guidelines to the design engineer.
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"To decrease or eliminate the effects of vibration on infrastructures and facilities, two types of vibration isolation methods have been proposed, which are active vibration isolation and passive vibration isolation. Regarding the passive vibration isolation, open or filled trenches and piles are employed as wave barriers [Beskos et al., 1986; Liao and Sangrey, 1978]. Trenches are often used to isolate vibrations for shallow structures, while piles are much more widely utilized due to their capabilities to be exempted from the influence of high groundwater level and to enhance the capacity of ground simultaneously. "
[Show abstract][Hide abstract] ABSTRACT: The isolation of surface wave-induced vibration using periodically modulated piles in soil is investigated. We demonstrate through simulations the dependence of complete bandgaps on the lattice symmetries, geometric parameters of the piles and material properties of the soil. The simulated results suggest that the piles modulated with square and hexagonal lattices are much more favorable for the formation of complete bandgaps than those modulated with honeycomb lattice. The height of the piles also plays a significant role in governing the evolution of complete bandgaps. Besides, complete bandgaps can be tuned by tailoring the volume fraction of the piles and the geometries of the pile cross section. Our results indicate that the contrast in the Young's modulus and the density is vital for the evolution of complete bandgaps and the viscosity of the soil should be considered as well. The analysis of surface wave propagation in a finite number of piles confirms the simulated complete bandgaps and also reveals that the complete bandgaps stem from Bragg interferences. This paper not only demonstrates the promising application of periodically modulated piles as wave barriers but also provides design guidelines for civil engineers.
International Journal of Applied Mechanics 08/2014; 06(04):1450042. DOI:10.1142/S1758825114500422 · 1.62 Impact Factor
"Woods  performed a series of field experiments to investigate effectiveness of trench and sheet-wall barriers for vibration isolation, and presented guidelines for the dimensions of an open trench to achieve a ground amplitude reduction of 75% or more. Comprehensive literature reviews of this topic have been reported by previous researchers   . Generally, a trench is regarded as effective for vibration insulation; however, sometimes, practical use of a trench is limited to small or medium trench depth because of soil instability, and high underground water level. "
[Show abstract][Hide abstract] ABSTRACT: Near-field scattering of surface waves by a single surface-breaking crack in solid medium has been well investigated by prior researchers. However, there have been few studies for more realistic problems involving near scattering of surface waves by distributed surface-breaking cracks. One possible reason is complexity caused by the interaction of surface waves between multiple cracks. In this study, interaction of surface waves between two surface-breaking cracks with various crack spacing was investigated. The experimental study was performed on Plexiglas specimens with non-contact sensors (air-coupled sensors, and a laser vibrometer), and compared with numerical simulation results. The effects of crack depth h, spacing a, and the number of cracks N on surface wave transmission were studied. Analyses show that for the very small crack spacing (a/h<0.2), the distributed cracks can be regarded as a single surface-breaking crack. However, for a/h ranging between approximately 1 and 6, transmission coefficient of surface waves is significantly affected by interaction between cracks. The transmission coefficients have the lowest value when a/h is between 2 and 3. When a/h is large (a/h>6), transmission coefficients obtained from experiments, and numerical simulations agree with the theoretical results based on non-interaction crack assumption.
"Common vibration countermeasures that have been adopted include the construction of open trenches, in-filled trenches, and wave impeding blocks (WIBs). Previous works related to trenches that may be cited include Woods (1968), Beskos et al. (1986), Ahmad et al. (1996), and Yang and Hung (1997), among others. As for the works on WIB, the following may be cited: Schmid et al. (1991), Antes and von Estorff (1994), and Takemiya and Fujiwara (1994). "
[Show abstract][Hide abstract] ABSTRACT: This paper is aimed at studying the effectiveness of different vibration countermeasures in isolating the ground vibrations induced by trains moving at sub- and supercritical speeds, with respect to the Rayleigh wave speed of the supporting soils. The vibration countermeasures considered herein include the installation of open trenches, in-filled trenches, and wave impeding blocks. The 2.5D finite/infinite element approach developed previously by the authors is employed in this study. This approach allows us to consider the load-moving effect of the train in the direction normal to the two-dimensional profile considered, and therefore to obtain three-dimensional results using only two-dimensional elements. The moving train is simulated as a sequence of moving wheel loads that may vibrate at some specific frequencies. The performance of the three types of wave barriers in isolating soil vibrations for trains moving at sub- and supercritical speeds with various excitation frequencies is evaluated with respect to some key parameters, along with suggestions made for enhancing the isolation efficiency.
Journal of Geotechnical and Geoenvironmental Engineering 12/2004; 130(12). DOI:10.1061/(ASCE)1090-0241(2004)130:12(1283) · 1.60 Impact Factor