In situ experimental study of vibration reduction using thick concrete slabs with natural and cement-improved subgrade

Abstract

Thickening the foundation slab and improving the subgrade soil using geo-techniques are effective measures for controlling unwanted vibrations at high-tech facilities. In this study, the vibration-reduction performance of 1-m-thick concrete slabs with natural and cement-improved subgrades was investigated based on in situ frequency sweep tests. One 1-m-thick concrete slab rested on 1-m-thick compacted sandy gravel backfill atop an undisturbed subgrade was constructed on the north side of the experimental site, and another identical concrete slab rested on 1-m-thick compacted sandy gravel backfill atop a cement-improved subgrade was constructed on the south side. The vibration-reduction effect was evaluated by comparing the free-field ground vibrations and surface vibrations of the two slabs at three pairs of evaluation locations. In terms of peak velocity, the 1-m-thick concrete slab with the natural subgrade exhibited a slight vibration amplification effect at low frequencies and a significant reduction effect at middle and high frequencies; the 1-m-thick concrete slab with the cement-improved subgrade exhibited a continuous vibration reduction action at all frequencies. In terms of RMS velocity, the vibration-reduction performance of the 1-m-thick concrete slab with the cement-improved subgrade was better than that with the natural subgrade. The results demonstrated that the vibration-reduction effect of the thick concrete slab was significant and could be increased by improving the subgrade using the cement grouting method.