Rheological Characterization of the Conditioned Sandy Soil Under Different Gas Pressure for Earth Pressure Balance Shield Tunnelling

Soil conditioning technology is usually required to modify the excavated soil to a fluid plastic state during earth pressure balance (EPB) shield construction. The steady pressure distribution in the excavation face is linked to soil fluidity. Compared with the slump test, the rheological behavior of the conditioned soil can better reflect the dynamic flow characteristics. A gas-loading rotational rheometer is developed to test the rheological properties of the conditioning agents and the conditioned sandy soil, which can overcome the disadvantage of uneven mechanical loading and create gas-loading conditions. The rheological properties of sandy soil conditioned by different agents under atmospheric and gas-loading pressure conditions were studied, and the influences of foam injection ratio (FIR), bentonite slurry injection ratio (SIR), and polymer injection ratio (PIR) on soil viscosity were analyzed. The test results show that the ambient air pressure only greatly influences the experimental group with foam. Under the same gas-loading pressure, the foam’s apparent viscosity decreases with the foam expansion ratio (FER) increasing. The rheological behavior of the conditioned sandy soil conforms to the Bingham model under atmospheric pressure and conforms to the Power Law model when PIR≤5% under gas-loading pressure of 3 bar. The Weissenberg effect accounts for the differences. When PIR>10, the rheological curve of three agents conditioned sand conforms to the Herschel Bulkley model. The higher content polymer reacts with bentonite to improve the soil viscosity, and blocks the foam seepage channel, making it difficult for the foam to re-enter the soil under gas-loading pressure. Investigating the rheological behavior of different conditioned sandy soil provides optimization strategies for EPB performance.