Centrifuge study on uniformity of wet deep mixing

The strength of the stabilised soil after wet deep mixing (DM) operation has often been found to be highly variable. Potential savings may be achieved by improving the uniformity of the DM process. However, the various factors that affect the non-uniformity of wet DM are not clearly understood. Conventionally, DM study is conducted in the field or using reduced-scaled models in 1g environment, which is either very limited (field results) or do not consider the effects of scale distortion (1g models). Using centrifuge modelling with appropriate scaling, this paper presents the details of three in-flight DM-installers, the use of these DM-installers in a number of centrifuge experiments to systematically study the effect of several factors that affect the uniformity of wet DM. Centrifuge results show that uniformity of mixing is affected by density differences between soil and the binder, the withdrawal rate and re-penetration of mixing blade, number of mixing blades and the blade angle. The effect of withdrawal rate, number of mixing blades and re-penetration can be approximately accounted for by the blade rotation number. Density difference between binder and soil was found to have a very significant influence on the uniformity of mixing and cannot be readily compensated for by increasing the blade rotation number. The blade angle also has an influence on the uniformity of mixing, mainly in the radial distribution of the binder within the improved soil.