EXPERIMENTAL STUDY ON DEFORMATION OF SOFT CLAY IMPROVED BY LOW REPLACEMENT RATIO SCP UNDER BACKFILLED CAISSON LOADING

ZAYEDUR RAHMAN, JIRO TAKEMURA, MASAYUKI KOUDA and KENJI YASUMOTO

ABSTRACT: In designing structures, especially harbor structures on soft clayey ground, deformation of the foundation ground may sometimes appear as a vital factor for rational design. Both the short and long term behavior of soft clay improved by sand compaction piles with low replacement ratios, which is subjected to backfilled caisson loading, were investigated through a series of centrifuge model tests. In model tests, the construction sequence from the installation of the caisson to backfilling was simulated in-flight. Effects of replacement ratio, improvement width, SCP location and loading rate on the behavior of the caisson were studied. It was found that settlement of the model ground can be effectively reduced by a higher replacement ratio, and long term settlement of caisson after backfilling is highly influenced by the settlement of the ground behind the SCP portion. A wider improvement area towards the fill is more effective in reducing the lateral displacement of the caisson both during and after backfilling, and the degree of consolidation of the clay part in Sep ground has a significant effect on short term lateral deformation.

Key words: backfill, centrifuge model tests, gravity caisson, long term deformation, low replacement ratio, sand compaction pile, stability, soft clay (IGC: K14/H7)