Vacuum preloading with vertical drains

Abstract

A centrifuge model test program has been conducted to investigate the effective depth of vacuum pressure in clay and to compare the effectiveness of soil improvement by vacuum preloading against conventional surcharge method. In this study, an experimental setup for applying vacuum pressure in-flight was developed and pre-fabricated vertical drains were modeled. Two different series of model tests were carried out in the centrifuge. In the first test series, no drains were installed in which vacuum pressure was applied solely or combined with a reduced amount of surcharge. In the second test series, vacuum pressure was applied in conjunction with vertical drains. From this study, it is found that vacuum preloading can be adopted as a suitable improvement technique for improving very soft clay. It is also observed that the effectiveness of the vacuum pressure is reasonably good along the entire clay depth if it is applied in conjunction with drains. However, the effectiveness seems to be lower in greater depths if there are no drains installed. In vacuum preloading with drains, the rate of settlement is faster than that of equivalent surcharge preloading. The test results show that the combination of reduced surcharge with vacuum pressure produces similar soil improvement results with the equivalent surcharge pressure tests results. To solve the problem of surcharge shortage, vacuum pressure could be combined with reduced amount of surcharge to achieve the same desired results.