Abstract: In this study, the technical schemes of rectangular pipe jacking machine in different composite strata are discussed. Based on the underpass expressline tunnel project at Tiangong Palace in Chongqing, China, the design and application of key systems such as excavation and mucking of rectangular pipe jacking machines in soft soil and rock composite strata are introduced. A layered excavation method for composite strata is proposed for the first time, and a blind area excavation device (rockbreaking roller) is developed. Based on finite element and industrial test analysis, the feasibility of the layered excavation method of composite multicutterhead + roller is verified, realizing the highefficiency cutting of 30MPa rock strata in the blind area and successfully implementing rectangular pipe jacking in fullface composite strata of soft soil and rock. Meanwhile, the combined mucking technology of the roller and the screw conveyor is developed for mixing and mucking in the lower part of the excavation chamber in composite formation. The mucking characteristics of the roller are analyzed based on computational fluid dynamics. The results show that the maximum mucking efficiency is achieved when the twinscrew 〖JP2〗mucking structure is adopted with a distance of ~900 mm〖JP〗 between the two screws. Finally, the feasibility of layered excavation and combined mucking technology in composite formation is validated through an industrial test, presenting a new solution for the application of rectangular pipe jacking machines in composite formation.

Key words: rectangular pipe jacking machine, composite strata, blind area excavation device, rockbreaking roller, excavation technology, mucking technology