Bentonite grouting is utilized widely in geotechnical engineering to stabilize the excavation and prevent seepage in sandy soils. However, the infiltration behavior of bentonite slurry in sandy soil is not well understood, primarily due to rheological blocking and the formation of a filter cake. This study performed infiltration column tests to investigate the infiltration behavior under various conditions, including slurry concentration, sand properties, grouting pressure, and infiltration duration. Monitoring included infiltrated distances (calculated from drainage volume), pore pressure at different depths, and bentonite distribution using methylene blue titration. Results indicate that rheological blocking occurs during the infiltration process as bentonite slurry, which is a shear-thinning fluid, increases in viscosity with a decreased shear rate. This phenomenon is more pronounced with higher slurry concentrations, leading to reduced infiltration distances. Additionally, in soils with pore throats smaller than bentonite particles, a filter cake forms above the surface of the grouted soil, decreasing the pore pressure and further reducing infiltration distance. The distribution of bentonite content remains consistent across the infiltrated zone, resulting in a linear pressure drop. Based on these findings, the study proposes a novel model that combines the generalized Darcy's law, the Herschel-Bulkley rheological model, and mass conservation of slurry to predict the spatiotemporal progression of the infiltration front. This model, which was validated using experimental data, accurately predicts the effects of rheological properties and filter cake formation on infiltration. The results of this study provide valuable insights into infiltration processes and enhance the application of bentonite slurry in grouting.

Existing analytical solutions available for simulating slurry infiltration do not account for the effect of particle dispersion and blockage at the same time. In view of this, a mathematical model of slurry particle migration in a saturated porous media with the convection-dispersion-deposition effect is established, and a semi-analytical solution of the particle transport problem with time discretization is obtained using an integral transformation. The correctness and rationality of the method are verified by comparing the experimental and theoretical results of the one-dimensional particle transport problem in constant pressure injection and constant velocity injection modes. The results of the method are in good agreement with those obtained from commercial finite element analyses. The spatiotemporal distribution of particle concentration, slurry deposition, soil porosity, pore water pressure, flow velocity in soil column can be easily obtained by the method. The pore water pressure calculated using this method is compared with the measured result during slurry shield drilling stops, demonstrating the potential application of this method in slurry engineering. The parametric analysis indicated that increasing the excavation chamber pressure and slurry concentration can accelerate the pore water pressure dissipation and the mud cake formation.

In the construction of slurry shield tunneling, the infiltration of slurry will cause excess pore water pressure in the surrounding soil. The distribution of excess pore water pressure and slurry infiltration zone are closely related to the stability of the tunnel face. Considering the influence of cutter head rotation and slurry specific gravity on pressure boundary conditions, this study proposed a multi-field coupling model to describe the dynamic transmission of excess pore water pressure and distribution of slurry infiltration range in three-dimensional. The temporal and spatial variation of soil pores characteristics parameters and slurry rheological properties owing to the deposition and diffusion of slurry particles is considered. The proposed model is verified by the in-situ testing measurements from in Beijing East Sixth Ring Road reconstruction project. In the prediction results, the spatial distribution of excess pore water pressure around the tunnel face appears bubble-shaped, and the shape of the slurry infiltration zone is close to flattened cake. The range of pressure dissipation and the thickness of particles infiltration zone are positively correlated with soil permeability coefficient, slurry pressure, while negatively correlated with the mass concentration of slurry. In the cases of low-permeability soil, appropriately increasing the content of slurry particles can improve the compactness of the filter cake.

In slurry shield tunneling, the stability of tunnel face is closely related to the filter cake. The cutting of the cutterhead has negative impact on the formation of filter cake. This study focuses on the formation time of dynamic filter cake considering the filtration effect and rotation of cutterhead. Filtration effect is the key factor for slurry infiltration. A multilayer slurry infiltration experiment system is designed to investigate the variation of filtrate rheological property in infiltration process. Slurry mass concentration CL, soil permeability coefficient k, the particle diameter ratio between soil equivalent grain size and representative diameter of slurry particles d(10)/D-85 are selected as independent design variables to fit the computational formula of filtration coefficient. Based on the relative relation between the mass of deposited particles in soil pores and infiltration time, a mathematical model for calculating the formation time of dynamic filter cake is proposed by combining the formation criteria and formation rate of external filter cake. The accuracy of the proposed model is verified through existing experiment data. Analysis results show that filtration coefficient is positively correlated with slurry mass concentration, while negatively correlated with the soil permeability coefficient and the particle diameter ratio between soil and slurry. As infiltration distance increases, the adsorption capacity of soil skeleton to slurry particles gradually decreases. The formation time of external filter cake is significantly lower than internal filter cake and the ratio is approximately 3.9. Under the dynamic cutting of the cutterhead, the formation time is positively associated with the rotation speed of cutter head, while negatively with the phase angle difference between adjacent cutter arm. The formation rate of external filter cake is greater than 98% when d(10)/D-85 <= 6.1. Properly increasing the content or decreasing the diameter size of solid-phase particles in slurry can promote the formation of filter cake.

Bentonite slurry is frequently used to temporarily stabilize the excavation for slurry tunnel boring machines (TBMs) driving in permeable soils, such as sand and gravel. In this study, two types of bentonite slurries (BS1 and BS2) were subjected to a series of infiltration column tests and modified fluid-loss tests under various pressure levels. Monitoring of water discharge and pore pressures at different depths of the sand bed enabled the identification of two effective sealing patterns during infiltration: the formation of a filter cake and rheological blocking. BS1 exhibited a tendency to form a filter cake, which played a vital role in effectively transferring the applied pressure to the underlying soil skeleton. The application of higher pressure facilitated the rapid formation of a filter cake, resulting in a shorter time span for slurry invasion and minimizing fluid loss. On the other hand, rheological blocking was dominant when using BS2, and the maximum infiltration distance was found to linearly increase with the applied pressure. A comparison between the measurement and a simple prediction model derived from Darcy's law revealed an overestimation of the infiltration distance during slurry invasion. Furthermore, based on the modified fluid-loss test, higher pressure was found to densify the filter cake and result in lower hydraulic conductivity.