Abstract: The study develops and discusses a novel stress-controlled permeameter, which is designed to account for chamber pressure environments. Additionally, a permeability testing method suitable for foam-conditioned sandy soil is proposed to evaluate its permeability characteristics under the chamber pressure encountered in earth pressure balance shield tunneling. The developed permeameter is used to conduct permeability tests on foam-conditioned sandy soil under water and soil pressure, examining their effect on the soil′s permeability and the mechanisms involved. The results reveal the following: (1) The novel permeameter effectively simulates the chamber pressure environment, successfully decoupling water pressure from the hydraulic gradient, thus demonstrating its rationality and reliability; (2) Foam-conditioned sandy soil behaves as a quasi-saturated material, with gas encapsulated by liquid membranes, confirming the applicability of the constant-head permeability test method; however, the sample saturation process must be omitted; (3) The initial permeability coefficient of foam-conditioned sandy soil increases while the duration of the initial stability phase decreases sharply with increasing water pressure. Higher water pressure leads to foam contraction, reducing its water-blocking capacity, thus increasing the likelihood of water loss. In contrast, the increasing soil pressure causes an opposing trend in permeability relative to water pressure. Sample compression reduces the cross-sectional area of pore channels, while simultaneously allowing the foam to remain within the pores for a longer duration.

Key words: earth pressure balance shield, foam-conditioned sandy soil, permeability test, soil chamber pressure, permeameter