Deep Mixing Induced Property Changes in Surrounding Sensitive Marine Clays

This paper presents a field study of installation effects of deep mixed columns on properties of the sensitive Ariake marine clay. Cone penetration tests were performed in the field to evaluate the change in the strength of the surrounding clay with time. Soil samples were taken before and after column installation to evaluate variations of physical, mechanical, and chemical properties of the surrounding clay. Test results indicated that the water content of the surrounding clay decreased while the concentration of cations increased as sampling locations approached the columns. Shear strength of the surrounding clay decreased during the installation but recovered after a short period of curing. Shear strength continued to increase with time over a period of 70days. Based on the regression results, the surrounding soil after the installation of the columns took approximately 10days to recover to the strength value before installation. On average, the shear strength of the surrounding clay increased over the original strength by approximately 23% after 40days and 50% after 70days, respectively. Discussion is presented on strength changes and key influence factors including soil disturbance and fracturing, thixotropy, consolidation, and diffusion of cations from deep mixed columns to the surrounding clay.