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Experimental study on the mechanisms of bentonite slurry penetration in front of a slurry TBM

Tao Xu (UGent) and Adam Bezuijen (UGent)
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Abstract
Penetration of bentonite slurry reduces the effective support pressure at the tunnel face and thus the face stability during slurry shield excavation in saturated sand. The reduction of effective support pressure depends on the penetration distance of the bentonite slurry but also the hydraulic characteristics of the slurry-penetrated soil. The penetration of bentonite slurry, pressurized against saturated sand, therefore, was investigated in a laboratory set-up to improve the understanding of the mechanisms of two stages of the penetration: mud spurt and filter cake formation. The permeability of sand for bentonite slurry (k(b)), the permeability of filter cake for water (k(c)) and the Peclet number (Pe) at initiation of filter cake formation were calculated from the experimental results. It appeared that the values of k(b) and k(c) depend on the bentonite concentration of the slurry. Adding bentonite to the slurry decreases both k(b) and k(c). Due to the thixotropic nature of the bentonite, the permeabilities estimated from the viscosity of fluid are approximately a factor 2 to 3 higher than the measured ones. The estimated Pe is a bit higher than the expected value. It was also found that filter cake is only formed on the surface of the sand in front of the shield tunnel, thus is very vulnerable to damage. The excess pore water pressure caused by slurry shield tunneling will only be negligible due to filter cake formation during standstill.
Keywords
FRESH CEMENT GROUT, PRESSURE FILTRATION, FILTER CAKE, SHIELD, Bentonite slurry, Penetration, Permeability, Mud spurt, Filter cake, Laboratory test

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MLA
Xu, Tao, and Adam Bezuijen. “Experimental Study on the Mechanisms of Bentonite Slurry Penetration in Front of a Slurry TBM.” TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY, vol. 93, 2019.
APA
Xu, T., & Bezuijen, A. (2019). Experimental study on the mechanisms of bentonite slurry penetration in front of a slurry TBM. TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY, 93.
Chicago author-date
Xu, Tao, and Adam Bezuijen. 2019. “Experimental Study on the Mechanisms of Bentonite Slurry Penetration in Front of a Slurry TBM.” TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 93.
Chicago author-date (all authors)
Xu, Tao, and Adam Bezuijen. 2019. “Experimental Study on the Mechanisms of Bentonite Slurry Penetration in Front of a Slurry TBM.” TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 93.
Vancouver
1.
Xu T, Bezuijen A. Experimental study on the mechanisms of bentonite slurry penetration in front of a slurry TBM. TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY. 2019;93.
IEEE
[1]
T. Xu and A. Bezuijen, “Experimental study on the mechanisms of bentonite slurry penetration in front of a slurry TBM,” TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY, vol. 93, 2019.
@article{8625579,
  abstract     = {Penetration of bentonite slurry reduces the effective support pressure at the tunnel face and thus the face stability during slurry shield excavation in saturated sand. The reduction of effective support pressure depends on the penetration distance of the bentonite slurry but also the hydraulic characteristics of the slurry-penetrated soil. The penetration of bentonite slurry, pressurized against saturated sand, therefore, was investigated in a laboratory set-up to improve the understanding of the mechanisms of two stages of the penetration: mud spurt and filter cake formation. The permeability of sand for bentonite slurry (k(b)), the permeability of filter cake for water (k(c)) and the Peclet number (Pe) at initiation of filter cake formation were calculated from the experimental results. It appeared that the values of k(b) and k(c) depend on the bentonite concentration of the slurry. Adding bentonite to the slurry decreases both k(b) and k(c). Due to the thixotropic nature of the bentonite, the permeabilities estimated from the viscosity of fluid are approximately a factor 2 to 3 higher than the measured ones. The estimated Pe is a bit higher than the expected value. It was also found that filter cake is only formed on the surface of the sand in front of the shield tunnel, thus is very vulnerable to damage. The excess pore water pressure caused by slurry shield tunneling will only be negligible due to filter cake formation during standstill.},
  articleno    = {103052},
  author       = {Xu, Tao and Bezuijen, Adam},
  issn         = {0886-7798},
  journal      = {TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY},
  keywords     = {FRESH CEMENT GROUT,PRESSURE FILTRATION,FILTER CAKE,SHIELD,Bentonite slurry,Penetration,Permeability,Mud spurt,Filter cake,Laboratory test},
  language     = {eng},
  pages        = {10},
  title        = {Experimental study on the mechanisms of bentonite slurry penetration in front of a slurry TBM},
  url          = {http://dx.doi.org/10.1016/j.tust.2019.103052},
  volume       = {93},
  year         = {2019},
}

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