The Sand Compaction Pile Method (SCP) is a major method to improve soft clay ground. Natural sand is
generally used as a filling material of SCP. However, iron and steel slag has been recently applied as a
new material because natural sand is difficult to be obtained in Japan. When the slag piles are installed
into the soft clay ground, the expected ground deformations are lesser than the case of natural sand piles.
In this study, loading tests using hollow cylindrical torsional test apparatus were conducted to
investigate the deformation behavior of composite ground consisting of slag and clay. The deformation
behavior of these materials is examined by numerical analyses. The shear strength parameters and the resistance of the treated ground under earthquake excitation were examined through the current series of tests.