Volume loss and face pressure evaluation in Tehran metro line 6, south extension

Abstract

Tehran metro line 6-south extension (ML6-SE) project passes beneath a congested residential area. To limit the ground surface settlement and to avoid structural damages to the buildings, ground surface settlements are carefully measured in consecutive sections perpendicular to the tunnel alignment with 10–15 m spacing. In this study, the relationships between maximum surface settlement and its influential factors are inspected. Then the volume loss is calculated using the information of settlement graphs. Finally, the face pressure is estimated at a given maximum surface settlement and/or volume loss defined by the serviceability limit state. In this regard, a database of operational, geotechnical, and geometrical parameters is set up first. Then, statistical analysis is used to find the influential parameters of the ground surface settlement, volume loss, and face pressure. Results of the analyses show; face pressure and water head are among the primary influential factors of the ground surface settlement. With the use of monitoring data, ground characteristics, and TBM operational parameters, the volume loss is back-calculated and an empirical formula is introduced for the prediction of face pressure considering serviceability limit state to limit the ground surface settlement below a specific value.