ABSTRACT
Ground improvement methods such as Deep Soil Mixing (DSM) and Jet Grouting Piles (JGP), are widely used to stabilize soft soils in underground construction. However, DSM and JGP construction processes themselves cause movements and pore water pressure changes in the adjacent ground, and can potentially impact adjacent structures. To mitigate these detrimental effects, the mechanisms of ground movements during DSM and JGP processes need to be well understood and controlled during construction. This paper summarizes data from a deep excavation within underconsolidated marine clays, where DSM and JGP were designed to stabilize the excavation. Field measurements show that significant ground movements and wall deflections occurred during DSM and JGP installation (prior to excavation). We have simulated the ground improvement processes using simplified 2D finite element analyses. The analyses assume a net volume change associated with deep soil mixing (reflecting pressure differences between the wet ‘soilcrete’ and surrounding clay), while much larger movements occur due to jet grouting in the space between the previously installed DSM columns and the perimeter diaphragm wall panels. This behavior is reasonably simulated by introducing a set of boundary pressures to represent JGP construction. Further research is now needed to establish how the jet grouting process can be controlled to limit potential ground movements in very soft clays.
