Vacuum preloading may endanger the surrounding buildings and buried pipes. From the variation of water table

lateral displacement and settlement out of the reinforcing area

the influence range of vacuum-surcharge preloading is 12.5 m outside the edge of treated area. To reduce the deformation of surrounding soil

three different control methods such as cement mixed piles wall

stress release trench and underpinned root piles are studied experimentally. Inward lateral displacements chiefly occur at 6 m below the ground. The maximum lateral displacements outside the cement mixed piles wall are 1/3 of the inside one and after loading the outside deformation is far less than the inside one. The maximum lateral displacements inside the stress release trench are 3/10 of those inside the piles; and the maximum lateral displacements outside the trench are 3/8 of those outside the piles. As far as reducing the lateral displacements at vacuum preloading stage in this experiment

the stress release trench is much better than the cement mixed piles wall; but at the vacuum-surcharge preloading stage

outward displacement of the deep subsoil near the trench is much more obvious. The settlement of underpinned foundation of iron tower by root piles is very small.