The densification of granular soils using vibro methods

The method of densifying in-situ sandy soils using deep vibration (vibro) was first developed in Germany over 60 years ago. Since then the technique has been extended to improve a wide range of soil types for structures of up to 30 storeys in height. A major development in the vibro market worldwide over the last 25 years has been the treatment of soils to resist the effects of liquefaction during seismic events. It is well known that the presence of silt and clay fines inhibits the physical in-situ densification of sandy soils. Experience has shown that a maximum fines content of about 15% would normally permit the performance of vibro compaction methods without the addition of stone aggregate. However, the development of new vibrators and modified construction techniques has enabled sands with significantly higher fines content to be treated. The paper describes how densification of granular soils has progressed with the development of new equipment, the greater appreciation in the manner in which soils respond to both vibration and displacement, and the importance of workmanship during treatment. A number of case histories including in-situ test results, long-term monitoring of ageing effects and references to treated sites already subjected to earthquakes are presented.