Pile and Concrete Arch Pre-supporting System (PCAPS) for Construction of Underground Subway Stations in Soft Grounds

One of the key parameters in the success of an underground project is the selection of the construction method based on the best scenario, which has strong effects on the host ground stability of the underground structures. This research introduces a construction method for double-deck underground subway stations in the soft ground, which is named Pile and Concrete Arch Pre-supporting System (PCAPS). This technique was originated from Concrete Arch Pre-supporting System (CAPS) for single-deck ones. This pre-supporting system for large span underground spaces is constructed by manpower-excavation method prior excavating the underground space in order to support the ground during the excavation of proposed underground cavity. PCAPS consists of concrete piles on the both sides of the underground cavity, arch beams (ribs) on its roof and final concrete lining inside the underground cavity, sequentially. State of the art of PCAPS is classified into four individual construction methods with various construction scenarios. The Molavi subway station (I7 station) belongs to line 7 of Tehran metro in Iran, was selected as a case study area to assessment the PCAPS construction method. The numerical simulation was employed to study the induced ground settlement of different PCAPS techniques, and then to select the optimal construction procedure under the same geotechnical conditions. The findings yield that the structural rigidity of the concrete piles and rib frames in PCAPS und upward/downward lining methods using different excavation sequences and staged constructions can control the ground deformations.