Abstract: The proposed deep excavation for a highway underpass site in Zhujiajian of Zhoushan was 450m in length and its excavated depth varied from 0 to 8 meters. A combined sheet pile system with steel pipe piles and Usection sheet piles (OUCSP), in which the Usection piles are 12m long and the steel pipe piles are 15m or 18m long, respectively, has been used as the supporting structure with two layers of steel pipe struts for the excavation of the underpass structure in areas with the excavation depths less than 5 meters. The deep excavation site is located in peaty soft soils and was improved with deep mixing cement-soil columns. This application shows that OU-CSP has the advantages of cost effective, short construction schedule and much higher stiffness over other types of supporting structures such as SMW retaining wall. Due to above advantages, OU-CSP is feasible to the construction of long, narrow, and deep excavation such as that of highway underpass.

Key words: deep excavation, OU combined sheet pile, highway underpass, retaining wall