Experimental Observations of Settlement of Footings Supported on Soft Clay Reinforced with Granular Columns: Laboratory Model Study

The inclusion of granular columns in soft clay deposits leads to improvements in bearing capacity and overall stiffness, along with a reduction in consolidation settlement. Many laboratory investigations have focused on aspects of bearing capacity, but published data on settlement performance are limited. This paper reports on some interesting findings obtained from a laboratory model study with respect to these issues. In this investigation, 300 mm diameter by 400 mm long samples of soft kaolin clay were reinforced with single or multiple granular columns of various lengths using the displacement and replacement installation methods. The experimental findings revealed that, for the same area replacement ratio, limited settlement reduction was achieved for single long floating columns and end-bearing column groups. Marginal improvements in settlement performance were also achieved for columns installed by the displacement method. No settlement reduction was achieved for short single floating columns, whereas short floating granular column groups produced increased settlements. These observations were verified using contact pressure measurements between the footing and column/surrounding clay.