Effects of Jet Grouting on Adjacent Ground and Structures

The basement excavation of the Singapore Post Center involved extensive jet grouting to improve the soft marine clay present within the excavation. The treated soil mass, with much improved strength and deformation characteristics, was intended to act as an internal strut below the bottom of the excavation level, reducing movements caused by the basement excavation. This paper presents the performance of production grouting carried out during the construction of the building's basement. Results of monitoring suggest that the jet grouting caused the retaining diaphragm walls to move between 9.7 and 36.4 mm. The soils behind the walls also moved away from the excavation. Movements ranged from 35.3 to 53.6 mm within 1–2 m from the wall to 13.5 to 32.8 mm at 4.5–20.5 m away from the wall. The recorded soil heave ranged from 2 to 24 mm, with the majority of the measurements being less than 10 mm. The backward movements induced by the production grouting are similar to those induced by preloading a strut of braced excavation system. Provided the backward movements do not exceed the allowable limits, they would help in minimizing the ultimate positive movements induced by the subsequent basement excavation. The jet grouting also induced some bending moments on the diaphragm walls and caused the adjacent structures to tilt and move away from the jet grout area.