Vibration isolation using open or filled trenches Part 2: 3-D homogeneous soil
ABSTRACT The isolation of structures from ground transmitted waves by open and infilled trenches in a three-dimensional context is numerically studied. The soil medium is assumed to be elastic or viscoelastic, homogeneous and isotropic. Waves generated by the harmonic motion of a surface rigid machine foundation are considered in this work. The formulation and solution of the problem is accomplished by the boundary element method in the frequency domain. The infinite space fundamental solution is used requiring discretization of the trench surface, the soil-foundation interface and some portion of the free soil surface. The proposed methodology is first tested for accuracy by solving three characteristic wave propagation problems with known solutions and then applied to several vibration isolation problems involving open and concrete infilled trenches. Three-dimensional graphic displays of the surface displacement pattern around the trenches are also presented.
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ABSTRACT: Ground vibrations generated by construction activities can adversely affect the structural health of adjacent buildings and foundations supporting them. Therefore propagation and rate of attenuation of construction induced ground vibrations is important during construction activities, particularly in urban areas where constructions are carried out in the vicinity of existing structures. In practice wave barriers are installed in the ground to mitigate the ground vibration propagation and hence to minimise the effect of ground vibrations on surrounding structures. Different types of fill materials such as bentonite, EPS geofoam and concrete are used in constructing wave barriers. In this study, a three-dimensional finite element model is developed to study the efficiency of different fill materials in attenuating ground vibrations. The model is first verified using data from full scale field experiments, where EPS geofoam has been used as a fill material in wave barriers. Then the same model has been used to evaluate the efficiency of open trenches, water filled wave barriers and EPS geofoam filled wave barriers on attenuation of ground vibrations. EPS geofoam is found to be the most efficient fill material, providing attenuation efficiency closer to open trenches. The efficiency of EPS geofoam and water filled wave barriers can be significantly increased by increasing the depth of the wave barrier.Soil Dynamics and Earthquake Engineering 11/2014; · 1.30 Impact Factor
Conference Paper: Pier vibration isolation for lightweight interferometry telescopes[Show abstract] [Hide abstract]
ABSTRACT: The Navy Prototype Optical Interferometer (NPOI) in Flagstaff, Arizona, makes use of separate smaller telescopes spaced along a Y-array and used simultaneously to simulate an equivalent single large telescope. Each telescope is mounted on a massive reinforced concrete pier tied to bedrock. The mass of the pier dampens most, but not all, of the unwanted vibration in the required spectrum. The quality and resolution of a stellar image depends on minimizing movement of the mirrors due to vibration. The main source of pier vibration is due to the soil-pier interaction. Surrounding environmental and man-made vibration propagates through the soil as body and surface waves, and forces the pier to move. In this paper, a novel concept based on a sleeve/air gap system to isolate the soil from the pier is used to minimize the vibration input to the telescope. An example of the concept is presented with respect to the future implementation of a 1.4-m diameter composite telescope at the Navy Prototype Optical Interferometer.Optical Engineering + Applications; 09/2007
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ABSTRACT: In this review paper, we concentrate on the use of boundary integral equation (BIE) based methods for the numerical modeling of elastic wave motion in naturally occurring media. The main reason for using BIE is the presence of the free surface of the earth, whereby large categories of problems involve continua with a small surface to volume ratio. Given that under most circumstances, BIE require surface discretization only, substantial savings can be realized in terms of the size of the mesh resulting from the discretization procedure as compared to domain-type numerical methods. We note that this is not necessarily the case with man-made materials that have finite boundaries. Thus, although the emphasis here is on wave motion in geological media, this review is potentially of interest to researchers working in other scientific fields such as material science. Most of the material referenced in this reviews drawn from research work conducted in the last fifteen years, i.e., since the year 2000, but for reasons of completeness reference is made to seminal papers and books dating since the early 1970s. Furthermore, we include here methods other than the BIE-based ones, in order to better explain all the constituent parts of hybrid methods. These have become quite popular in recent years because they seem to combine the best features of surface-only discretization techniques with those of domain type approaches such as finite elements and finite differences. The result is a more rounded approach to the subject of elastic wave motion, which is the underlying foundation of all problems that have to do with time-dependent phenomena in solids.Soil Dynamics and Earthquake Engineering 03/2015; 70. · 1.30 Impact Factor