The seepage cut -off wall for the river-crossing dam is usually installed in the sand and the sandy gravel. The dam site treatment depends on the geological conditions and the construction methods include trench-cutting without pilot hole, trench-cutting with pilot hole, percussive trenching, rotsry trenching and trenching by trench saw. The trench saw provides a new construction method for the new seepage cut-off walling material, but has its limitation.