Abstract
Abstract Earth pressure balance tunnel boring machines are commonly used to excavate tunnels in soft soils. These types of machines use conditioning agents that permit changing the mechanical and hydraulic behavior of the soil and help to form a plastic paste. Conditioning is therefore the key point to explain the increasing number of applications of this technology in many different types of soils. The aim of this study is to investigate soil parameters (foam injection ratio (FIR), foam expansion ratio (FER), soil moisture content, and the percentage of fine-grained soil) to reach an optimum slump test in the range between 15 and 20 cm. In general, it was found that by increasing the soil moisture content, the FIR decreased to achieve the optimum slump, and also by increasing the percentage of fine-grained at a constant moisture content, the FIR increased to reach the optimal slump. This study has also permitted a comparison with field data from the Tabriz urban railway line 2 project.
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