Settlement prediction for soft ground improved by columns

Abstract

A simple method of calculating the consolidation settlement of soft subsoil improved by a floating cement-stabilised column–slab system subjected to embankment loading has been proposed, and the method has been applied to three case histories in Fukuoka, Japan. The proposed method adopts the methodology of treating a part of the soil–cement column improved layer with a thickness of Hc as an unimproved layer and calculating its compression using the properties of the soft soil only. Based on coupled finite-element analysis results using a unit cell model, two bilinear functions with variables of the improvement area ratio (α) and the improvement depth ratio (β) by the columns have been proposed to determine the value of Hc. Both the proposed method and the method currently used in Japan (proposed by the Japanese Institute of Construction Engineering (JICE)) were used to calculate the settlement (compression) of the soft layers for three case histories in Fukuoka, Japan. Comparing the calculated results with the field values shows that the proposed method yielded much better predictions than that of the JICE method. It is suggested that the proposed method can be used to design the improvement of soft clayey ground using the floating cement-stabilised column–slab system.