Model tests on the bearing capacity of precast open-ended micro pipe piles in soft soil

Laboratory 1g model tests were carried out to study the bearing capacity and load transfer mechanisms of precast open-ended micro pipe piles in soft soil. The single pile, 2 × 2 and 3 × 3 pile groups were designed and tested under vertical compression, uplift and horizontal loads, respectively. A steep fall pattern occurred in the load–displacement curves of piles under vertical compression and uplift loads. The measured soil plug length and axial force indicated that the piles could be considered as fully plugged friction piles under vertical compression load. The pile groups behaved in a non-integral failure mode under vertical uplift load and a conical wedge failure mode under horizontal load. At the early loading stages under vertical compression and uplift loads, the pile shaft resistance of the upper part tended to be fully mobilised earlier than that of the lower part. At the later loading stages, the pile shaft resistance of the upper part decreased, whereas the shaft resistance of the lower part still showed a little increase. The maximum bending moment of the pile occurred at a depth of about 10D_p under horizontal load.