Selection of the Most Appropriate Soil Conditioning Set in Mechanized Boring of Tehran Subway Line 7 Tunnel

In recent years، tunneling with the Earth Pressure Balance (EPB) shield has been applied in urban areas in different soils types. The most common technology in the mechanized tunneling is using the EPB machine. Soil conditioning operation can be carried out through the screw conveyor. Knowing different soil conditioning agents and their affects in different soils types is quite important in selection of the most appropriate foam-polymer to be used. Selecting the most appropriate soil conditioning set needs different precise studies so that the properties of the conditioned soil can be determined and the measurable data can be specified. Selection an appropriate strategy (for soil conditioning during boring) highlights the importance of the ground risks involved so that conclusive decisions can be made regarding the type of the physical behavior of the foam and other additives. Methodology and Approaches: The soil layers in this project were divided into 6 units (ET-1 to ET-6). In this study، It was revealed that every unit needed specific additives depending on its geological and geotechnical specifications and the soil conditioning parameters for every unit would be different. The optimum amount of conditioning agents and types of additives to be used in the tunnel route (considering the geological risks that needed conditioning، and the presence and expanse of different soil units) were studied in 3 separate stages based on the guiding tables، standards، and laboratory and field tests. Results and For soil conditioning، used material was made of 3 different foam types (A، B and C: A & B for ordinary soils with medium stability and C for adhesion and impermeable soils with high stability) for respectively 60% and 30% of the tunnel route. The FIR change amplitude in the project has been estimated to be 20% to 80%; maximum consumption has been in the interval of 20% to 40% and FER has been equal to 4 to 7.