A case study of performance comparison between vacuum preloading and fill surcharge for soft ground improvement

Abstract

Vacuum preloading and fill surcharge are two common ground improvement methods, which have been successfully utilized in many soil improvement and land reclamation projects all over the world. Therefore, continuous study on them is of great necessity for deepening the research for both optimizing the solution of treating soft grounds and predicting the deformation performance. This paper presents a case study of a land reclamation project, in which both vacuum preloading and fill surcharge methods were compared based on the detailed field monitoring data, in situ and laboratory tests of two selected areas treated with well-controlled construction quality. The results indicate that the vacuum preloading method can accelerate the consolidation progress more effectively and exhibit better performance in reducing the water content of soft soils. In this method, a stable vacuum pressure was kept beneath the air-tight membrane, and the bentonite-slurry cut-off walls were installed surrounding the treated land to prevent the vacuum leakage throughout permeable interlayers. However, the vacuum pressure decreased significantly along the depth, which affected the efficiency of improving the deeper soil layer. On the other hand, the fill surcharge method can accelerate consolidation and improve the strength of soft soils in a relatively slow but predictable way. Furthermore, four different methods are adopted to predict the ultimate settlements of ground in this study, including Asaoka's method, hyperbolic curve method, exponential curve method, and new simplified B method. In general, good performance of the four methods can be observed by comparing measured and predicted settlements.