Improving Soft soil Using Combined Cement Deep Mixing Column and Preloading with Prefabricated Vertical Drains

摘要

Either deep mixing method (DMM) or preloading method has been used independently to improve the soft soil foundation. Each method has its own benefits. A combined approach was applied for the improvement of thick soft clayey foundation in an experimental section of an expressway embankment. Short DMM column was used to improve the shallow soft soils, and long prefabricated vertical drains (PVDs) was inserted between DMM columns to promote the consolidation of deep soft soils under the embankment load. The static load tests and the field monitoring of settlements and earth pressures were carried out before and during and construction process and the preloading period. The results revealed that this combined method succeeded in consolidation of deep soft soils underneath the DMM column. Contrasting to the long DMM column, shorter column is cost effectively and can also satisfy the requirement of the bearing capacity. In the section treated by the combined method, the stress under the embankment distributes more evenly.