Direct Measurement of intermediate-range Casimir-Polder potentials

We present the first direct measurements of Casimir-Polder forces between solid surfaces and atomic gases in the transition regime between the electrostatic short-distance and the retarded long-distance limit. The experimental method is based on ultracold ground-state Rb atoms that are reflected from evanescent wave barriers at the surface of a dielectric glass prism. Our novel approach does not require assumptions about the potential shape. The experimental data confirm the theoretical prediction in the transition regime.Comment: 4 pages, 3 figure

Vibration Isolation Using In-filled Geofoam Trench Barriers

A significant amount of numerical and experimental research has been conducted to study the vibration isolation by wave barriers considering open trenches, in-filled concrete or bentonite trenches, sheet-pile walls, and rows of piles. A few studies have investigated the use of expanded polystyrene (EPS) geofoam material as wave barriers, which indicated that in-filled geofoam trenches can be used as effective wave barriers. However, no engineering design method is available to date for the design of such type of wave barriers. This dissertation presents comprehensive experimental and numerical investigations on the use of in-filled geofoam trench barriers to scatter machine foundations vibration, in order to provide some recommendations and design guidelines for their implementation in design. Two- and three-dimensional time-domain finite element models have been developed utilizing the finite element package ABAQUS. The numerical models have been verified and then used to study the effectiveness of different configurations of in-filled geofoam wave barriers. All the proposed configurations performed well in scattering surface waves. However, the single-continuous wall system was considered to be more economic and practical alternative for wave scattering. Based on the findings of the preliminary numerical investigations, a full scale field experimental study has been conducted to investigate the performance of in-filled geofoam trenches. An innovative approach to construct geofoam trenches involving hydro-dig technology was utilized. A series of experimental tests have been conducted to evaluate the performance of both open and in-filled geofoam trench barriers considering their geometry and distance from the source of disturbance. The results of the field experimental investigations were analyzed and interpreted to provide recommendations for implementation in design. Experimental results confirmed that in-filled geofoam trench barriers can effectively reduce the transmitted vibrations and its protective effectiveness is comparable to the open trench barrier. An extensive numerical parametric study was conducted to investigate the behaviour of in-filled geofoam wave barrier under different soil conditions and to point out the key parameters that dominate the performance of in-filled geofoam trench barriers. The influence of various key parameters on the screening performance were carefully analyzed and discussed. A model using Multiple Linear Regression (MLR) analysis was developed for design purpose. Finally, an artificial neural network (ANN) model has been developed, which aims at extrapolating the parametric study results to predict the in-filled geofoam wave barrier protective effectiveness in different soil profiles with different geometric dimensions

Simple Design Methods for Vibration Isolation by Wave Barriers

Rectangular wave barriers (open or infilled trenches) are frequently used in engineering practice to reduce the ground vibrations caused by propagating surface (Rayleigh) waves of relatively small wave lengths. This paper presents models involving simple algebraic formulas for the design of rectangular wave barriers in homogeneous soil deposits. Both vertical and horizontal ground vibrations are considered. An extensive parametric investigation was conducted using a direct boundary element method algorithm. Simple models based on the key dimensionless parameters that control the vibration screening effectiveness were then developed. The utility of such models is established through comparisons with rigorous numerical solutions and available experimental data. Vibration screening by open trenches in layered soils was also studied to identify the effects of layering on vibration screening

Simple Model for Active Isolation of Machine Foundations by Open Trenches

Ground disturbance due to waves generated by a machine foundation can be detrimental to adjacent structures or operation of sensitive equipment nearby. For machine foundations vibrating at moderate to high frequencies, the amplitude of ground motion can be reduced significantly by installing a wave barrier around the source. A three-dimensional boundary element algorithm incorporating quadratic elements has been used to perform an extensive parametric study on the effectiveness of open trenches as wave barriers. Based on the results of the study, a simple model in the form of an algebraic expression is developed for estimating the vibration screening effectiveness of open trench wave barriers. Furthermore, through comparisons with published field test data and rigorous boundary element solutions, the validity of the simple model is established

Field Experiments on Wave Propagation and Vibration Isolation by Using Wave Barriers

In this paper, the obtained results from the experimental Studies describe the basic characteristics of wave propagation and ability of possible measures to reduce the impact of soil vibrations on structural response for both active and passive isolation cases. A series of field tests on the foundation vibrations generated by electrodynamic shaker are performed to examine the screening efficiency of open and in-filled trench barriers which are constructed for full-scale measurement. From field measurements of amplitude with and without the barrier, the amplitude reduction ratio is estimated at different points of interest. Wave propagating characteristics and frequency-dependent screening effects of the wave barriers are investigated according to various isolation material stiffnesses. The remarkable outcomes from these experimental Studies can be briefly generalized as follows: backfilled trench with softer material than soil is more effective for the passive isolation than the active one. The reduction effects of wave barriers depend on the frequency of vibration source for both passive and active isolation cases. In-situ measurements confirm that vibration screening systems using open or in-filled trench barriers can be applied as a reduction measure for soil vibrations due to a moving load which is considered as stationary wave Source in this problem. (C) 2008 Elsevier Ltd. All rights reserved

Experimental and Numerical Investigation on Vibration Screening by In-Filled Trenches

In-filled concrete and soil-bentonite trenches have been used in practice for many years as wave barriers to reduce transmission of moderate to high frequency ground vibrations generated by machine foundations or traffic. An experimental investigation on the influence of various geometrical and material parameters on vibration screening effectiveness of in-filled barriers has been conducted. The experimental data are compared with numerical (BEM) Solutions as well as with design formulas of Ahmad and Al-Hussaini (1991)

Use of Tyre-Derived Aggregate as Backfill Material for Wave Barriers to Mitigate Railway-Induced Ground Vibrations

[Abstract] The use of piles as barriers to mitigate vibrations from rail traffic has been increasing in theoretical and practical engineering during the last years. Tyre-derived aggregate (TDA) is a recycled material with some interesting applications in civil engineering, including those related to railway engineering. As a novelty, this paper combines the concept of pile wave barriers and TDA material and investigates the mitigation effect of pile barriers made of TDA on the vibrations transmitted by rail traffic. This solution has a dual purpose: the reduction of railway vibrations and the recycling of a highly polluting material. The mitigation potential of this material when used as backfill for piles is analysed using a numerical scheme based on a 3D finite-difference numerical model formulated in the space/time domain, which is also experimentally validated in this paper in a real case without pile barriers. The numerical results show insertion loss (IL) values of up to 11 dB for a depth closed to the wavelength of Rayleigh wave. Finally, this solution is compared with more common backfills, such as concrete and steel tubular piles, showing that the TDA pile is a less effective measure although from an environmental and engineering point of view it is a very competitive solution