Existing pile foundations underpinning is needed when the bearing capacity is not enough to resist the superstructures. In this study, a series of experiments were carried out on the 2×2 model piled raft foundation considering underpinning by a micropile in sand soil. The experiments aimed at investigating the effect of the raft on load sharing characteristics and settlement reduction behavior subjected to additional loads after underpinning with the micropile. The experimental results showed the raft had higher capacity on reducing the settlement and transferring loads from piles to the raft under vertically loading than the free-standing pile group which is not in contact with soil. The results also showed that consideration of the raft effect is an efficient way to save construction cost and reduce the number of underpinning piles in the practical underpinning design.
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