SPATIAL VARIABILITY IN DEEP SOIL MIXING - CENTRIFUGE MODEL AND FIELD DATA STUDY

Abstract

Deep soil mixing is often used for improvement of soft clay in underground constructions. The strength of cement-admixed ground often exhibits significant spatial variation. In this study, firstly, centrifuge model tests were conducted to investigate the binder distribution for different mixing blade configurations. The position of injection nozzles significantly affects the radial variation of the binder in the columns. A detailed parametric study was carried out, influencing factors, such as rotational speed, over consolidation ratio and binder density were discussed. Centrifuge modelling results show that the coefficient of variation of binder concentration decreases with increasing rotational speed and higher binder density. Secondly, field data from two sites were analysed to study the effect of in-situ water content on the strength of cement-treated marine clay. The calculated scale of fluctuation in binder concentration is much shorter in range than that of the in-situ water content. Finally, a statistical model was established, and the engineering implication was presented. The size of the sampled region has a significant effect on the scale of fluctuation which is captured. The results also highlight the co-existence of scale of fluctuation in the intra- or inter-column levels.