Soil improvement by the vacuum preloading method for an oil storage station

Abstract

This paper presents a case study on the application of the vacuum preloading method for a soil improvement project in Tianjin, China. The site area was 50 000 m2, and the soft clay treated was about 20 m thick, including a very soft muddy clay layer 4–5 m thick, formed from dredged slurry. The water contents of the clays were higher than or as high as the liquid limits. A vacuum load of 80 kPa was applied for 4 months. The ground settled nearly 1 m, and the average degree of consolidation was greater than 80%. The undrained shear strength of the soil increased two- to threefold after treatment. The procedures used for soil improvement, the field instrumentation programme, and the field monitoring data are described and discussed.

Application of the Vacuum Preloading Method in Soil Improvement Projects

“…This method has been successfully used in a number of countries for land reclamation and soil improvement work (Holtz, 1975;Chen and Bao, 1983;Choa, 1990;Jacob et al, 1994;Bergado et al, 1998;Chu et al, 2000). Sand drains and, more recently, prefabricated vertical drains (PVDs) have often been used to distribute vacuum load and discharge pore water.…”

“…Compared with the fill surcharge method for an equivalent load, the vacuum preloading method is cheaper and faster (Chu et al, 2000). The vacuum preloading method has also been incorporated in the land reclamation process when clay slurry dredged from the seabed is used as fill material for land reclamation.…”

“…Thousands of hectares of land have been reclaimed in Tianjin, China, using this method. When the reclaimed land is subsequently used for industrial and infrastructure developments, the vacuum preloading method is used again to improve the foundation soil, which consists of a layer of consolidated slurry fill and the underlying seabed marine clay (Chu et al, 2000;Yan and Chu, 2003).…”

Lateral displacement of soft ground under vacuum pressure and surcharge load

“…embankment fill), vacuum pressure or combination of the both with prefabricated vertical drain (PVD) is a commonly utilized soft ground improvement method. Vacuum pressure results in settlement and inward (toward the center of the loading area) lateral displacement of a ground and causes cracks adjacent to the treated area, while surcharge load results in settlement and outward (away from the loading area) lateral displacement of a ground [1][2][3][4]. In an urban environment, controlling or minimizing the geotechnical engineering activity induced lateral displacement of a ground is important, sometimes may be a crucial design consideration.…”

Recent Advances in Soft Soil Consolidation

“…The use of vacuum can solve this problem, because it can increase effective stress by directly decreasing the excess pore pressure with no further increase of embankment surcharge. With PVDs, the vacuum can propagate into deep layers to consolidate the thick soft deposits in reclaimed land (Chu et al, 2000;Indraratna et al, 2005a). Vacuum preloading has been used extensively worldwide to accelerate soft soil consolidation, for example, the Philadelphia International Airport in the United States, Tianjin Port in China, the North-South Expressway in Malaysia, reclamation sites in Singapore and Hong Kong, and the Ballina Bypass and Port of Brisbane in Australia, among many other projects (Holtan, 1965;Choa, 1990;Jacob et al, 1994;Chu et al, 2000;Bergado et al, 2002;Yan and Chu, 2003).…”