Embankment Construction on Marshland using Vacuum Consolidation Technology

Vacuum consolidation is a soil improvement technique that accelerates construction on soft ground by using the action of the atmospheric pressure in combination with a ground pore-pressure relief system. As an alternative to the conventional preloading (physical surcharge), vacuum assisted consolidation can be used to consolidate soft alluvial soils, to improve bearing capacities prior to construction, and to reduce post-construction settlements. This paper presents case history of roadway embankments of 3.3 to 7.9 m high on three marshland sites using vacuum consolidation technology. Lack of shear strength of the soil at the project site did not allow construction of embankments without soil improvement. Although the use of conventional wick drains and subsequent application of surcharge was sufficient to solve the consolidation problem in most areas, in some specific areas a different approach was needed because of acute slope instability combined with strict construction schedule requirements. Vacuum consolidation was applied in three sites with recent alluvial clayey soil deposits. In addition, the sub-soil was fully instrumented with a number of pore pressure, multi-point settlement gauges and inclinometers for real-time monitoring of the embankment during construction at the marshland zones. The details of design and site monitoring program along with post-construction performance for three sites are presented here.