Fuzhou subway Line 1 was planned to cross an island in middle of the river and the shield tool changing area was to set up on the island. Stability reinforcement should be made for excavation face of tool changing area; the upper part was medium-fine sand with strong permeability and poor stability. MJS method was adopted in the design for strengthening and water sealing with pile diameter≥2200mm and overlapping 700mm. On the island, there was 5.6m thickness of miscellaneous fill layer, followed by silt, medium sand and fine sand layers, drilling was difficult for MJS method because of the risks of drill pipe holding and burying. High-power top drive drilling rig can easily pass through backfill and sand layers with double-pipe. A certain length outer casing was retained in the sand as protecting casing to prevent hole collapse, guide-hole difficulties for MJS construction method in complex strata were successfully resolved.