ADVANCING UNDERSTANDING OF THE RELATIONSHIP BETWEEN SOIL CONDITIONING AND EARTH PRESSURE BALANCE TUNNEL BORING MACHINE CHAMBER AND SHIELD ANNULUS BEHAVIOR

Earth pressure balance tunnel boring machines (EPB TBMs) are used for the excavation of tunnels in soft ground beneath the water table to minimize surface settlements by counteracting earth and water pressures. To guarantee effective EPB TBM face support and performance, it is necessary to understand the mechanical behavior of foam-conditioned soil under realistic pressure conditions. This dissertation investigates the behavior of foam-conditioned soil under applied total pressures. The effect of total stress, effective stress, and key soil parameter void ratio on the shear strength and compressibility of foam-conditioned soil is examined. The test results show that the vane shear strength and compressibility are mainly influenced by the void ratio and effective stress, which starts to develop below a certain e/emax ratio. Further tests were performed to determine if muck collected from the belt conveyor of an EPB TBM can be used to assess the behavior of conditioned soil in the excavation chamber. The study found little to no relationship between the measured muck shear strength and TBM torque. It was concluded that the collected muck is not a representative sample of the conditioned soil in the chamber. This was attributed to the deterioration of foam over time, and the extended time the soil is transported and mixed in the screw conveyor. In addition, this thesis investigates if apparent density can be used to assess the soil conditioning performance and the soil behavior in the excavation chamber of an EPB TBM. It was found that apparent density evaluation methods can be used to identify air pockets and plugging issues in the excavation chamber of an EPB. Furthermore, the study investigates if conditioned soil from the face fills and pressurizes the gap between the EPB shield exterior and the surrounding ground. The study showed that the pressures in the shield gap mainly follow the bulkhead pressure, which indicates that conditioned soil from the face fills and pressurizes the shield gap. It was found that the shield pressures are mainly influenced by the soil type, soil conditioning, bulkhead pressure, and the grouting pressure.