Engineering geological investigations along the Tabriz subway extension focusing on ground surface settlement, northwestern Iran

The purpose of this paper is to assess the engineering geological characteristics of soil and rock، and to predict ground surface settlement due to tunneling in main part of Tabriz subway line 2 which has a length of 12 km. The total length of the excavation line is 20 km between International fair and Kara malek. Tunnels will be excavated by employing EPB Shields 9. 2 m in diameter. Geology in this section is mainly composed of sand (SM)، silt (ML) and Sedimentary rocks (marl، siltstone، claystone and sandstone). Laboratory experiments and field studies were conducted for the study area. Field studies consisted of geological mapping، in situ testing، core drilling and sampling for laboratory studies. Uniaxial compressive tests، triaxial compressive strength test and deformability tests were conducted in the laboratory. For more Precise investigations، Subway path was divided into three geotechnical zones. These zones mainly consist of fine grained soils، coarse grained soils and Sedimentary rocks، respectively. Settlement predictions were performed using PLAXIS 3D Tunnel، a 3D finite element computer software. Excavation، ground support and face support steps in FEM analyses were simulated. Predictions were performed for typical geological parts in each zone، which is considered as critical in terms of ground surface settlement. Based on the results acquired from this method، ground surface settlement in some parts of Tabriz urban railway line 2 can be a problem during tunneling. Further، the ground condition improvement such as grouting and dewatering must be performed before tunneling.