Abstract: To improve the necessity, feasibility, and safety of gravity-flow sewage pipelines in utility tunnels, a case study is conducted on a completed utility tunnel project of Jinding-Hengqin express line in Zhuhai National High-tech Industrial Zone, key design points about gravity-flow sewage pipeline in utility tunnel are summarized and analyzed, and the cross-section, vertical, auxiliary, and structural designs are highlighted. Some key design points are concluded as follows: (1) When requirements for pipeline operation and maintenance are high and there is enough budget, gravity-flow pipeline can be incorporated into utility tunnel. (2) It is suggested that gravity-flow sewage pipeline can be arranged in a separated cabin to improve implementation and operation safety of utility tunnel when construction conditions allow. (3) Auxiliary design of sewage pipeline can adopt the combination of straight-through inspection well and cleanout opening for better structural integrity and pipe cleaning. (4) Wavy vertical design can be used and the main structure of utility tunnel can be connected to intersecting structure with one wall plate, thus to make full use of vertical conditions and avoid a large increase of project cost caused by the increasing buried depth of utility tunnel.

Key words: utility tunnel, gravity-flow sewage pipeline, vertical design, structural connection, attachment setting