Abstract: Large size municipal stormwater discharge sewer pipes are frequently installed in urban area of coastal cities and cities near the river. These large size sewer pipe installations will un-inevitably affect the adjacent environment. This paper presents a case history of a storm water discharge sewer pipe project at Guanggu 1st Road and Gaoxin 4th Road interchange. In this project, an underground tunneling excavation of a large diameter sewer pipe was utilized to pass underneath an active high-pressure natural gas pipeline with a diameter of 720 mm. The numerical simulation was performed on the tunnel excavation with double-side pilot tunnel method by using commercial software Plaxis. The results indicate that, the ground subsidence value and area of ground subsidence increase with the progressive of the tunneling; the settlement along the cross section of the tunneling could be predicted by the Peck curve. The location of the maximum ground settlement is above the center of the sewer pipe and the observed ground settlement value is 24.76 mm, which was less than the settlement control value setup for the project.

Key words: municipal tunnel excavation with doubleside pilot tunnel method, gas pipelines, settlement control value, numerical simulations