Vacuum Consolidation and Its Combination with Embankment Loading: Fid-Bau Portal

Vacuum Consolidation and Its Combination with Embankment Loading

Chai, J. C. / Hayashi, S. / Carter, J. P.

The characteristics of vacuum consolidation and the advantages of preloading soft clayey deposits by combining vacuum pressure treatment with embankment loading are discussed. Laboratory oedometer test results show that vacuum pressure induces less or about the same settlement compared to an applied surcharge load of the same magnitude. If the applied vacuum pressure is larger than the lateral stress required to maintain a k_o condition (no horizontal strain), there will be inward lateral displacement and the vacuum pressure will induce less settlement. In cases where the bottom of the soft clayey deposit is drained (e.g., where the clay overlies a sand or gravel layer), application of a vacuum pressure will cause less consolidation than an equivalent surcharge load because that at the bottom drainage boundary effectively the vacuum pressure can not be applied. For this type of subsoil condition it is suggested that if vacuum consolidation is combined with the use of prefabricated vertical drains (PVDs) for ground improvement, the PVDs should not penetrate the entire clayey layer. An equation for calculating the optimum penetration depth has been derived for this case. The advantages of combining vacuum pressure with embankment loading are discussed in terms of increasing the effective surcharge loading, reducing construction time in the case of road construction, and reducing the preloading-induced lateral displacement of the subsoil.