Vibration response of closely spaced footings protected by use of rubber sheet: An in-situ investigation

It is essential to protect sensitive equipment located in the vicinity of vibration sources (VS). As the well-known method of using wave barriers is ineffective to protect facilities that are located very close to a VS, in this study the effect of a thin rubber sheet to protect a nearby foundation (NF) was assessed. This was achieved experimentally at a site using a semi-large scale machine foundation model as the VS and a similar concrete foundation as the NF. The effects of the rubber sheet position (beneath the VS and NF) and of the rubber sheet thickness (6, 12, 18 and 24 mm) were assessed within the vibration frequency range 10–70 Hz and at various NF to VS distances (Distance/Foundation Width = 1 to 10). The testing illustrates that, by increasing the rubber sheet thickness beneath the VS/NF, there is a consequential resonant response frequency reduction at the NF. Moreover, it was found that placing the rubber sheet beneath the VS is more efficient at reducing the NF's resonant amplitude while placing the rubber sheet beneath the NF is more effective in protecting the NF from the resonant frequency variation. This is due to the dominance of the VS's resonant frequency.