Abstract: Based on the concept of piperoof-support system,a 3D analysis model was developed for the insight to the function of piperoof applied in underground engineering of soft ground.The factors of construction procedure,interaction between the piperoof and support,in addition to the the stiffness and strength properties of shotcrete at early ages,could be taken into account in the 3D analysis model.Taking a subway of a metro station located in Shanghai as an example,the function of piperoof used to prevent the collapse of face and to control the ground settlement was analyzed.It was demonstrated that it was necessary to take the time effect of shotcrete at early ages into account,and the function of piperoof was implemented by redistribution of the released load by excavation in longitudinal and transversal direction,in addition to the grouting.