عنوان مقاله [English]
In recent years, tunneling with the Earth Pressure Balance (EPB) shield has been used 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.
Selection of 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 have been divided into 6 units (ET-1 to ET-6). In this study, it has been revealed that every unit needs specific additives depending on its geological and geotechnical specifications, and also, the soil conditioning parameters for every unit would be different. The optimum amounts of conditioning agents and types of additives to be used in the tunnel route (considering the geological risks that need conditioning, and the presence and expansion of different soil units) have been studied in 3 separate stages based on the guiding tables, standards, and laboratory and field tests.
Results and Conclusions
The materials, used for soil conditioning, have been made of 3 different foam types A, B and C in which foam types A & B are used for ordinary soils with medium stability and foam type C is used for adhesion and impermeable soils with high stability. These foam types have been used for soil conditioning in the tunnel route. The Foam Injection Ratio (FIR) change amplitude in the project has been estimated to be 20% to 80%; maximum consumption of the foams has been in the interval of 20% to 40% of the tunnel route, and Foam Expansion Ratio (FER) has been equal to 4 to 7.