Physical modelling of transient processes at the slurry supported tunnel face during shield excavation

Zizka, Zdenek; Schößer, Britta; Thewes, Markus

doi:10.1201/9780429321559-63

Cited by 3 publications

(3 citation statements)

References 2 publications

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“…As a result, the slurry-infiltrated layer that is formed in front of the tunnel face is extremely thin, only approximately 20 mm. This is dangerous for the tunnel face because a filter cake with such a thin slurry-infiltrated layer is vulnerable to damage when considering the cutting depth of the cutting tools (Zizka, 2019). For infiltration of water-bentonite slurry into medium and coarse sands, the hydraulic conductivity of sand for slurry is also significantly reduced, but the infiltration distance is much greater, reaching about 300 mm in 1 h.…”

Section: Discussionmentioning

confidence: 99%

Effects of sand and slurry characteristics on pressure infiltration of bentonite slurry into sand

Zhou

Bezuijen

et al. 2024

Géotechnique

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Two series of experiments were carried out to examine pressurised bentonite slurry infiltration into saturated sand columns. Three types of sand were examined, and water–bentonite and water–bentonite–sand slurries were used in Series 1 and 2, respectively. Series 1 investigated the effect of sand particle size and Series 2 examined the effect of the fine-sand particle content in the slurry. Scanning electron microscopy (SEM) imaging was used to observe the morphological features of the dry slurry-infiltrated sand samples. A solution for the infiltration distance during mud spurt for water–bentonite–sand slurry infiltration was verified using the data from Series 2. The infiltration test results showed that the hydraulic conductivity of the slurry-infiltrated coarse sand for slurry in Series 2 was lower than that in Series 1. Visual observations and the SEM images showed that sand particles were bound to a bentonite film, indicating that, during infiltration, the channels for fluid flow among the sand particles are blocked by the bentonite particles adhered to the sand particles. The solution for the infiltration distance during mud spurt for water–bentonite–sand slurry infiltration showed good agreement with the experimental results.

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Section: Discussionmentioning

confidence: 99%

Effects of sand and slurry characteristics on pressure infiltration of bentonite slurry into sand

Zhou

Bezuijen

et al. 2024

Géotechnique

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“…The lining element is configured to be impermeable, thus limiting seepage to the tunnel face alone. With reference to the experimental investigations conducted in Zizka [41], other parameters are set as follows: γ slu = 12 kN/m 3 and k, the permeability coefficient, is 5 × 10 −8 m/s. The groundwater level H w and excess slurry pressure p differ from the working conditions.…”

Section: Numerical Simulation Of Seepage Flow Due To Excess Slurry Pr...mentioning

confidence: 99%

“…The lining element is configured to be impermeable, thus limiting seepage to the tunnel face alone. With reference to the experimental investigations conducted in Zizka [41], other parameters are set as follows: The numerical pore pressure distribution of a typical case is presented in Figure 5, where H w /d = 1.0, p = 50 kPa. As a result of the influence of excess slurry pressure, the hydraulic conditions have undergone a significant alteration, and the pore pressures ahead of the tunnel are noticeably greater than the hydrostatic pressures, particularly in the vicinity of the tunnel face.…”

Section: Numerical Simulation Of Seepage Flow Due To Excess Slurry Pr...mentioning

confidence: 99%

Tunnel Face Stability Considering the Influence of Excess Slurry Pressure

et al. 2023

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With excess slurry pressures exerted on the tunnel face, slurry particles tend to infiltrate into the soil in front of the tunnel. There will be excess pore pressure ahead of the tunnel in the case of infiltration, leading to an impairment in the supporting effect contributed by the excess slurry pressure. Corresponding to three slurry infiltration scenarios distinguished by the forms of the filter cake, different pressure transfer models are employed to describe the pore pressure distribution. Using the kinematic approach of limit analysis and the numerically simulated seepage field, the study of tunnel face stability under different slurry infiltration cases is extended by employing a 3D discretization-based failure mechanism. In addition, two simple empirical formulas describing the pore pressure distributions above the tunnel and in advance of the tunnel are established and verified. Combined with the dichotomy method and strength reduction method, the safety factors yielding rigorous upper-bound solutions are obtained by optimization. The proposed method is validated by a comparative analysis. The developed framework allows considering the influence of excess pore pressure on the whole failure mechanism and the three-dimensional characteristics of seepage. A parameter analysis is performed to study the effect of the excess slurry pressure, hydraulic conditions, soil strength properties, and pressure drop coefficient. The results show that the steady-state flow model leads to much more conservative results than the full-membrane model. The safety factor increases with the increasing excess slurry pressure and the decreasing pressure drop coefficient. The present work provides an effective framework to quickly assess the face stability of tunnels under excess slurry pressure considering different filter cake scenarios.

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Laboratory model test of slurry shield tunnelling in saturated sandy soil

Fang

Walton

et al. 2023

Géotechnique

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Experimental tests were carried out using a laboratory-scale model of slurry shield machine to investigate the mechanical behaviors of soil in response to excavation in saturated sandy ground. The experimental model includes a miniature slurry shield machine that can approximate real tunnel construction, replicating the in-situ methods of cutterhead excavation, temporary support with pressurized slurry at the face, advancement of the shield machine, and a slurry circulation system. The effect of slurry characteristics, soil permeability, and advance rate of the shield machine on the ground displacement, slurry infiltration, and excess pore water pressure were analyzed, and these data were compared with predictions in previous studies. The results confirm that the model tests can effectively simulate the principal operations of a real slurry shield machine. Compared to the test results presented, previously proposed models tend to overestimate the increase rate of pore water pressure in front of tunnel face, especially in the cases of lower-permeability soil, higher concentrations of bentonite mixed slurry and lower advance rates. The slurry-infiltrated zone in front of the shield machine is non-uniform across the tunnel face and extends radially to a larger area than the tunnel diameter. The shape of the slurry-infiltrated zone can be categorized as one of two typical types: (a) cone; (b) bulb.

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Physical modelling of transient processes at the slurry supported tunnel face during shield excavation

Cited by 3 publications

References 2 publications

Effects of sand and slurry characteristics on pressure infiltration of bentonite slurry into sand

Effects of sand and slurry characteristics on pressure infiltration of bentonite slurry into sand

Tunnel Face Stability Considering the Influence of Excess Slurry Pressure

Laboratory model test of slurry shield tunnelling in saturated sandy soil

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