Experimental study of mechanical properties of joints in a new-type prefabricated double cabin utility tunnel

Modernization of urban infrastructure is the premise for improving urban operation efficiency. The traditional direct burying method of the municipal public pipeline requires repeated excavation for maintenance, which seriously affects the traffic and appearance of the city and interferes with the everyday life and work order of residents. With the rapid development of urbanization recently, the city’s underground utility tunnel appears at a historical juncture. To cope with the industry’s urgent need for efficient and green construction technology, China is strongly promoting urban utility tunnels and its development toward prefabrication. The prefabricated utility tunnel efficiently uses the urban underground space, intensively manages various municipal pipelines, and solves the “zipper road” problem; it also has the advantages of increased production efficiency in a short construction period and green environmental protection. The joint is the weakest link of the structure in a prefabricated utility tunnel, and its mechanical properties directly affect the deformation and bearing capacity of the entire structure. A new type of prefabricated double cabin utility tunnel with a “U-shaped ferrule joint bars connection” was proposed. The validity of the method was confirmed through testing the mechanical properties of four full-scale joints, including one bottom L-shaped cast-in-place side joint, one bottom L-shaped assembly side joint, one top L-shaped assembly joint, and one bottom T-shaped assembly joint specimen. The result obtained the mechanical properties of the joint full-scale specimen, such as cracking load, crack development law, bearing capacity, failure mode, and member ductility. Furthermore, the specimens of new prefabricated utility tunnel joints had flexure-shear failures near the corner points despite their high bearing capacity and ductility. Using U-shaped ferrule joint bars provides consistent performance and can obtain mechanical properties comparable with those of cast-in-place joint specimens.