Study on the Use of a New Pre-Supporting Technique for the Construction of an Underground Transit System

This paper elaborates on the use of an underground construction technique called concrete arch pre-supporting system (CAPS) in construction of the Tehran subway mass-transit system. CAPS technique is a time and cost effective method consisting of consecutive construction of arch shaped frames throughout the length of underground structures. This method facilitates underground excavation without any surface activity disruption. As part of this research, an underground station in line 3 of Tehran transit system was studied using a numerical technique. A model was developed in the finite element code to represent the pre-supporting structure and final underground structure. Based on the results of the analyses it was concluded by properly modeling CAPS technique in the finite element software, the axial and bending moments developed along final linings of the underground station are significantly lower than forces and bending moments along frame built using conventional cut and cover tunnels. The results of analyses were used to design the final lining of underground station.