IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684, p-ISSN: 2320-334X PP 20-29 www.iosrjournals.org International Conference on Innovations in Civil Engineering 20 | Page SCMS School of Engineering and Technology Finite element study on vibration isolation using dual open trench barriers Ankurjyoti Saikia 1 , Atanu Kumar Dutta 2 , Utpal Kumar Das 3 1 (Civil Engineering, Tezpur University, India) 2 (Civil Engineering, Jorhat Engineering College, India) 3 (Civil Engineering, Tezpur University, India) ABSTRACT: The vibration screening effectiveness of an isolation scheme comprised of a pair of open rectangular trenches of identical cross-sections is numerically investigated in this work. The finite element study is carried out in PLAXIS 2D under plane-strain conditions on a linear elastic, isotropic, and homogeneous half- space subjected to a vertical harmonic excitation. The response of the dual trench barrier in intercepting vertical and horizontal components of vibrations is studied with respect to the variations in its geometric features. The geometric features; i.e. the distances of the trenches from the source, their depths, and widths are made dimensionless by normalizing with respect to the Rayleigh wavelength of vibration. The effects of barrier depths and widths are investigated for active and passive cases separately and results are depicted in non- dimensional forms. The effects of these features and their significance in reducing ground-borne vibrations are discussed and few guidelines are made regarding their optimal selections. Comparison of results obtained with present finite element scheme shows close agreement with published results which justifies its accuracy. A dual trench barrier may be adopted as an effective alternative to a single trench as it requires lesser depth than the latter. Keywords – Vibration isolation, dual trench, open trench, finite element, half-space 1. INTRODUCTION Ground vibration induced by traffic, vibrating equipments, construction activities etc. sometimes needs to be screened as it may cause malfunctioning of high-precision instruments, annoyance, and damage of structure and sub-structure in extreme circumstances. Ground-borne vibration propagates in the form of body waves and surface waves (Rayleigh waves). The problem is often handled by constructing barriers across the line of propagation of surface waves as nearly two-thirds of the total vibration energy is transmitted in the form of Rayleigh waves that too within a narrow zone close to the ground surface [1]. Open or in-filled trenches, solid or tubular piles, sheet piles etc. are examples of such barriers. In active isolation scheme the barrier is placed close to the source; whereas in passive case barrier is placed either apart from the source or in proximity of the structure/site to be protected. Several numerical and experimental studies have been carried out after the experimental study of Woods [1] on screening of surface waves by open trenches. Beskos et al. [2] and Dasgupta et al. [3] conducted two-dimensional (2-D) and three-dimensional (3-D) boundary element studies on vibration isolation using open and in-filled trenches. Simplified models for designing open and in-filled trenches developed by Ahmad and Al- Hussaini [4] and active isolation using open trenches by Ahmad et al. [5] in a 3-D scenario are subsequent contributions. Yang and Hung [6] developed a finite/infinite element scheme to study isolation effectiveness of open/in-filled trenches and elastic foundations in reducing ground vibrations caused by the passage of trains. Few more literatures on isolation of train-induced vibrations are Hung et al. [7] using open/in-filled trenches and wave impeding blocks; Ju [8] using open/in-filled trenches and ground improvement methods; Di Mino et al. [9] using open trenches respectively. Klein et al. [10] adopted a 3-D boundary element code to study the screening effect of open trenches. Adam and Estorff [11] employed coupled boundary element and finite element algorithm to study the attenuation of train-induced building vibrations using open trenches. Alzawi and El Naggar [12] performed full-scale experimental study on open and geofoam filled trenches supported by 2-D finite element approach. The scopes of all these previous works are limited to the study of vibration isolation by single trenches (open or in-filled) except the investigation of Hwang and Tu [13] on the screening performance