This case study presents the design, operation, and results of a soil improvement project using the vacuum preloading method on 480 000 m2 of reclaimed land in Xingang Port, Tianjing, China. The areas treated with vacuum ranged from 5000 to 30 000 m2. The effects of soil improvement are demonstrated through the average consolidation settlement of 2.0 m and increases in undrained shear strengths by a factor of two to four or more. The study shows that the vacuum method is an effective tool for the consolidation of very soft, highly compressive clayey soils over a large area. The technique is especially feasible in cases where there is a lack of surcharge loading fills, extremely low shear strength, soft ground adjacent to critical slopes, and access to a power supply.Key words: vacuum preloading consolidation, soil improvement, soft clays, land reclamation, prefabricated vertical drains.

This paper discusses the use of the vacuum preloading method (VPM) in China. During the use and application of the VPM in China, Tianjin Port Engineering Institute introduced suf®cient modi®cations and improvements to the equipment and technology to achieve an increase in the vacuum beneath the sealing membrane, thus improving the consolidation of the soft clay being treated. When the preloading loads imposed by the VPM are incapable of meeting the operational requirements, a method of vacuum preloading in combination with surcharge ®ll may be employed. In some cases the surcharge ®ll was placed up to a height of 5´5 m with an imposed load of 100 kPa. Slopes often develop excessive displacement, destabilising the foundation, owing to the cutting operations and loads along the sides of the slopes. The VPM can be used to effectively solve such problems. Case studies of engineering projects are also presented, where (a) the VPM was used to improve and consolidate the slopes in coastal marine works and (b) clay-mixed retaining walls were erected in soft soil overburdened with a thick layer of sand when the method was used to improve soft soils.