Dynamic response of rubber-sand bags: application for machine foundations

Rubber Soil Bags (RSBs), containing mixtures of sand and rubber, were assessed as low-cost systems to improve the dynamic response of a machine foundation or similar vibrating system. In this paper, both steady-state vibration tests using a semi-large scale vibrating system and post-impulse free vibration tests are reported. Geotextile bags were filled with 5 different proportions of rubber particles (0%–10% by mass) mixed with sand. A geophone measured the velocity response of the system. Accelerometers were placed above and below the bags. To diagnose the influence of the bags on the dynamic response of the system, Resonant Amplitude, Resonant Frequency, Equivalent Dynamic Stiffness, Equivalent Damping Ratio, Equivalent Dynamic Shear Modulus and Equivalent Dynamic Shear Strain were measured and computed above the bags. The results show that increasing the rubber content leads to a decline of both stiffness and frequency. Damping decreased so that the vibration amplitude increased at low rubber contents (from 0% to 7.5%), but the trend reversed at 10% rubber content such that the damping was greater, and the amplitude less, even than the no-rubber case. Additionally, results showed that vertical displacement beneath the bag was increasingly reduced relative to the above-bag value as rubber content increased.