MECHANIZED TUNNELING-INDUCED SETTLEMENTS IN URBAN ENVIRONMENT: THE CASE STUDY OF TABRIZ UNDERGROUND RAILWAY

In this paper, measured settlements of Tabriz Urban Railway line 2 (TUR2) are presented. TUR2 with a length of about 22 km will connect the eastern part of the city to its western part. The process of excavating TUR2 has begun since 2015 using earth pressure balanced (EPB) TBM with a cutting-wheel diameter of 9.49 m and a steel shield with an external diameter of 9.46 m in front and 9.44 m at the tail. For the lining of the tunnel, 350 mm-thick precast concrete segments with a length of 1.5 m are installed just behind the shield. The data have been recorded during the construction of the tunnel from west-shaft to station-02 (S02). The distance between west-shaft and S02, which has been investigated here, is about 2000 m. In this route, based on conducted studies,the ground mainly consists of sand and gravel (SM) containing minor portion of fine-grained soil (ML). Thus, in general, the ground condition could be assumed to be non-cohesive at this site. The TUR2 tunnel is entirely under water table varying from 14 to 22 m. The data analyzed and discussed throughout this paper have been recorded at 180 green-field surface locations (pins) between west-shaft and S02. Settlement measurements are back-analyzed using Gaussian empirical predictions both in longitudinal and transversal directions. In addition, volume loss has been calculated using final maximum surface settlements. Subsequently, observed and calculated settlement curves have been compared. In addition to settlements, face pressure and tail void grout injection pressure have been recorded during the excavation process of TUR2, as presented in this paper. Jancsecz and Stainer presented an empirical formula for determination of face pressure to investigate the efficiency of the analytical methods in comparison with field data. Then, the development of settlements during shield passage and probable correlation between volume loss and face pressure was investigated. Observations show that a vast majority of the settlements measured at the ground surface falls in the range of allowable values.