ABSTRACT
A series of model tests was carried out in the PARI Mark II Geotechnical Centrifuge (Kitazume & Miyajima 1995). A specimen strong box with inside dimensions of 70 cm in length, 20 cm in width and 60 cm in depth was used for all model tests. Figure 1 shows a typical example of the model ground setup, in which a normally consolidated clay ground of 20 cm thick, five rows of DM columns and a surface improvement layer are modeled. The model clay ground was subjected to
1 INTRODUCTION
The Deep Mixing Method (DMM), an in-situ soil stabilization technique using cement and/or lime as a binder, is often applied to improve soft soils (CDIT 2002). A group column type improvement has been extensively applied to foundations of embankment or lightweight structure. An improved ground design procedure in Japan mainly for reinforcing embankments (PWRC 2004) assumes two failure patterns related to external and internal stabilities. The external stability is evaluated for possibility of sliding failure, in which the DM columns and the clay between are assumed to show horizontal displacement on a stiff layer without any rearrangement of columns. For the internal stability, the possibility of rupture breaking failure is evaluated by a slip circle analysis, assuming the shear failure mode of DM columns.
