Abstract: The circulation water discharge  culvert in Sanmen Nuclear Power Plant is within the thick soft soils. It is characterized as having a complicated geotechnical conditions, long total linear length and the variation of the box width. Three deep excavation alternates are used: anchored soldier pile and lagging wall, soldier pile plus rake and gravity wall. A slurry wall is formed by using the jet grout between the soldier piles. The transporting of the excavated soils is through the artificial island. The construction and the safety of the excavated area is warranted through an integral system consisting of supporting piles, slurry wall as well as foundation structure piles at the bottom. The paper also presents the results of the construction optimization of the installation sequence.

Key words: Deep Excavation in Soft Soils, Supporting System, Soil Improvement.