Fulfilling the role of a soil conditioner, foam plays a pivotal role in Earth Pressure Balance (EPB) shield tunnelling by enhancing soil properties such as lowering permeability and increasing flowability. This study introduces a macro-model designed to quantify foam penetration behaviour in saturated sand, utilising rheological properties. To validate this model, experiments were conducted to replicate the foam penetration behaviour. Six sand beds characterised by varying particle sizes, along with foam having an expansion ratio of fifteen, were employed for penetration tests under different hydraulic conditions utilising a sand column device. The rheological profile of the foam is described by the power-law model, as also found by rheometer tests, although with different parameters. The flow behaviour of foam within the sand column conforms to the flow equation that governs powerlaw fluids in porous media. The developed model effectively predicts the foam penetration process under varying hydraulic conditions compared with the experimental results. Furthermore, the fitting results of the experimental data indicate that the flow behaviour index of the foam remains approximately 0.09 across all tests, regardless of the type of sand used. In contrast, the model-derived generalised permeability coefficient strongly correlates with the effective particle size (d10) of the sand bed. Overall, the model effectively quantifies the foam penetration behaviour, accounting for changes in infiltration velocity and pore water pressure, which is essential for understanding the transfer of support pressure in EPB shield tunnelling.

A major full-scale experiment called the Tunnelling and Limitation of Impacts on Piles (TULIP) project was conducted in 2020 on Line 16 of the Grand Paris Express project to analyze the tunnel boring machine-soil-pile interactions during tunnel excavation near deep structures. This paper presents the greenfield ground response observed when the tunnel boring machine (TBM) crossed the TULIP site: surface displacements, subsurface displacements, and pore water pressures are presented. The originality of the paper lies in the fact that details are provided not only on the site geological and geotechnical characteristics, but also on the TBM operation: a detailed analysis of the variations in pressure inside the cutting chamber of the earth-pressure balanced machine (EPBM) is proposed. This paper reports factual data without bias induced by a preconceived numerical model, but highlights open questions that challenge the advanced numerical models, that will be required to analyze completely the tunnel-soil-pile interactions.

Soil conditioning technology is usually required to modify the excavated soil to a fluid plastic state during the construction with earth pressure balance (EPB) shield. 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 10 %, the rheological curve of three agents conditioned sand conforms to the Herschel Bulkley model. The higher content polymer reacts with bentonite to increase 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.