Liquefaction induced by deep vertical vibratory compaction

Three case histories were analysed where three different methods of deep vertical vibratory compaction were used to treat loose, water-saturated sand. Vertically oscillating probes not only generate cylindrical waves with strong ground vibrations that cause compaction of the soil but may also result in liquefaction. Cone penetration tests (CPTs) were performed before and after treatment to evaluate the compaction effect. Soil liquefaction could be observed on all sites during the start of deep vibratory compaction. On two sites, the onset of liquefaction could be documented by vibration measurements. A conventional CPT-based liquefaction analysis was performed, which suggested that liquefaction could be expected at all sites. The case histories analysed in this study suggest that vertically oscillating probes have the potential of being used as full-scale liquefaction testing machines. A new concept is outlined that could be used to establish the liquefaction hazard at a particular site.