With the engineering case of bored grouting pile construction in the work area at north band of Lingkun bridge for Wenzhou regional railway, the analysis and discussion are made on the technical measures adopted to overcome difficulties of rotary drilling rig construction in over-water holing at the estuary and the engineering effects. The difficulties are involved as strong tidy sea area encountered, large depth of bored pile, very unstable flow plastic formation at the upper part, the pile bottom extending deep into the pebble layer with sudden mud leakage possibility and hole collapse easily caused by tidal effect, and so on.