Characterizing the influence of stress on foam conditioned sand for EPB tunneling

- The effect of stresses and void ratio on the conditioned soil behavior is examined.
- A field-portable pressurized testing chamber is introduced.
- Compression and vane shear tests were carried out on two granular soils.
- Void ratio and effective stress influence the conditioned soil behavior most.
- A certain void ratio is necessary to prevent the development of effective stress.

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 paper investigates the behavior of foam-conditioned soil under applied total pressures of up to 5 bar. The study examines the effect of total stress, effective stress, and key soil parameter void ratio on the behavior of foam-conditioned soil. Shear strength and compression tests were carried out in a field-portable pressurized test chamber on two granular soils with a variety of foam parameters. The results demonstrate that void ratio and effective stress are the main factors that influence the performance of foam-conditioned soil. It was determined that a certain ratio of void ratio to maximum void ratio was required to prevent the development of appreciable effective stress and, thus, high shear strength and low compressibility.