Seawater-induced degradation of shield tail grease: An experimental study on property evolution and micro-mechanisms

Abstract

Shield tail grease is crutial for the safety of shield tunneling in coastal urban areas, yet its performance degradation under seawater intrusion remains insufficiently studied. In this study, grease samples were subjected to immersion in freshwater and seawater at various concentrations. A series of laboratory tests were conducted, including rheological, adhesion, and cone penetration measurements. The effects of sea salt content and immersion time on grease properties were systematically studied, and microstructural changes under different conditions were compared using scanning electron microscopy (SEM). The results indicate that although seawater intrusion do not alter the rheological model of the grease (Herschel-Bulkley model) at 25 °C, it reduced the peak shear strength by 9.52%. With prolonged immersion time, the yield stress of the grease increases by 4.5% to 22.3%, while the viscosity coefficient and adhesion decreases by 4.5% to 14.4% and 85.2% to 87.2%, respectively. The cone penetration value exhibits a trend of initial increasing and then decreasing. At a sea salt content of 6.0%, the grease reaches its peak yield stress and adhesion, while cone penetration reaches minimum value. Microstructural analysis reveals that as immersion time increases, the grease porosity first decreases and then increases. This study provides a theoretical basis for understanding the performance degradation mechanisms of shield tail grease in marine environments, and offers practical guidance for ensuring tail seal safety.

Keywords

Shield tail grease / Seawater intrusion / Rheological properties / Microstructural analysis / Property degradation

References

[1] Q.H. Qian, Present state, problems and development trends of urban under- ground space in China, Tunn. Undergr. Space Technol. 55 (2016) 280-289, doi: 10.1016/j.tust.2015.11.007.

[2] W.Z. Chen, X.Y. Tan, J.P. Yang, Review of state-of-the-art in structural health monitoring of tunnel engineering, Smart Undergr. Eng 1 (2025) 40-50, doi: 10.1016/J.SUE.2025.05.004.

[3] Y.J. Wei, Y.Y. Yang, M.J. Tao, D.L. Wang, Y.X. Jie, Earth pressure balance shield tunneling in sandy gravel deposits: a case study of application of soil conditioning, Bull. Eng. Geol. Environ. 79 (2020) 5013-5020, doi: 10.1007/s10064-020-01856-1.

[4] Y. Zeng, Y.J. Wei, Y.Y. Yang, S.H. Xu, H.M. Zhang, Y.X. Jie, A novel real-time clas- sification method of mixed weathered mudstone-sand-pebble formation ahead of an EPBS using DBOKM-SMOTE and stacking ensemble learning, Tunn. Undergr. Space Technol. 165 (2025) 106870, doi: 10.1016/j.tust.2025.106870.

[5] G.H. Jin, C.L. Gao, Z.Q. Zhou, H.C. Tu, X.B. Jiang, D.J. Wang, Z.L. Zhang, X.H. Li, Spatiotemporal evolution characteristics of inundation in multi-level subway sta- tions and inter-station tunnels: A multi-stage quantitative model, Smart Undergr. Eng. (2025) (In Press), doi: 10.1016/j.sue.2025.08.001.

[6] D.L. Xu, X.H. Zhang, W. Chen, X. Jiang, Z. Liu, Y. Bai,Utilisation of the deep under- ground space in Shanghai, Proceed. Institut. Civil Eng. - Municipal Eng. 172 (2019) 218-223, doi: 10.1680/jmuen.18.00029.

[7] H.T. Yu, C. Cai, A. Bobet, X. Zhao, Y. Yuan, Analytical solution for longitudinal bending stiffness of shield tunnels, Tunn. Undergr. Space Technol. 83 (2019) 27-34, doi: 10.1016/j.tust.2018.09.011.

[8] J. Su, Y. Pan, X. Niu, C. Zhang, Effect of shield tunneling on adjacent pile foundations in water-rich strata, Transp. Geotech. 52 (2025) 10557, doi: 10.1016/j.trgeo.2025.101557.

[9] Y.S. Xu, S.L. Shen, L. Ma, W.J. Sun, Z.Y. Yin, Evaluation of the blocking effect of retaining walls on groundwater seepage in aquifers with different insertion depths, Eng. Geol. 183 (2014) 254-264, doi: 10.1016/j.enggeo.2014.08.023.

[10] P. Chaipanna, P. Jongpradist, 3D response analysis of a shield tunnel segmental lining during construction and a parametric study using the ground-spring model, Tunn. Undergr. Space Technol. 90 (2019) 369-382, doi: 10.1016/j.tust.2019.05.015.

[11] D.L. Jin, Y. Yang, D.J. Yuan, X.G. Li, J. Chen, Y.Y. Gan, S. Zheng, The role of wall slip and temperature in shield tail seal performance: A novel modeling approach, Tunn. Undergr. Space Technol. 157 (2025) 106333, doi: 10.1016/j.tust.2024.106333.

[12] L.Q. Cao, D.L. Zhang, Q. Fang, L. Yu, Movements of ground and exist- ing structures induced by slurry pressure-balance tunnel boring machine (SPB TBM) tunnelling in clay, Tunn. Undergr. Space Technol. 97 (2020) 103278, doi: 10.1016/j.tust.2019.103278.

[13] Y. Liang, X.Y. Chen, J.S. Yang, J. Zhang, L.C. Huang, Analysis of ground collapse caused by shield tunnelling and the evaluation of the reinforce- ment effect on a sand stratum, Eng. Fail Anal. 115 (2020) 104616, doi: 10.1016/j.engfailanal.2020.104616.

[14] Q.Y. Yao, H.G. Di, C. Ji, S.H. Zhou, Ground collapse caused by shield tunneling in sandy cobble stratum and its control measures, B Eng. Geol. Environ. 79 (2020) 5599-5614, doi: 10.1007/s10064-020-01878-9.

[15] C. Yu, A. Zhou, J. Chen, A. Arulrajah, S. Horpibulsuk, Analysis of a tunnel failure caused by leakage of the shield tail seal system, Undergr. Space 5 (2020) 105-114, doi: 10.1016/j.undsp.2018.11.003.

[16] F. Ye, H.L. Feng, X.B. Han, X.M. Liang, H.D. Sun, W.J. Zhang, X.Y. Cao, Mecha- nism and preventive measures of slurry leakage at shield tail brushes under ab- normal shutdown condition —A case study, Undergr. Space 8 (2023) 144-161, doi: 10.1016/j.undsp.2022.03.003.

[17] X.Q. Li, Y.Y. Yang, F. Li, Comparative Study on Mechanical Properties of Sealing Grease Composed of Different Base Oils for Shield Tunnel, Materials 13 (3) (2020), doi: 10.3390/ma13030692.

[18] X.Q Li, Y.Y Yang, Experimental Study of Sealing Performance Test Methods and Sealing Mechanism of Shield Tail Sealing Grease, J. Test Eval. 49 (2021) 3366-3377, doi: 10.1520/JTE20190833.

[19] Z.N. Wan, S.S. Jing, S.C. Li, C. Yuan, W.F. Yin, C. Guo, Q. He, Numerical Simu- lation and Critical Threshold Analysis of the Failure Process for Shield Tail Seal- ing System under High Water Pressure, KSCE J. Civ. Eng. 28 (2024) 5919-5933, doi: 10.1007/s12205-024-2734-4.

[20] X. Shen, D.J. Yuan, L.Q. Cao, Y.B. Fu, D. Jin, Z.F. Gao, Experimental investigation of the dynamic sealing of shield tail grease under high water pressure, Tunn. Undergr. Space Technol. 121 (2022) 104343, doi: 10.1016/j.tust.2021.104343.

[21] X. Shen, D.J. Yuan, L.Q. Cao, D.L. Jin, X.S. Chen, Z.F. Gao, Experimen- tal investigation of the failure of shield grease seals under the influence of environmental factors: A case study, Eng. Fail. Anal. 133 (2022) 105975, doi: 10.1016/j.engfailanal.2021.105975.

[22] X. Shen, Z.K. Xu, X.S. Chen, J.Q. Wu, X.X. Li, Y.F. Chen, Experimental inves- tigation into the failure of shield tail grease under the influence of environ- mental factors based on rheological testing, Results Eng. 27 (2025) 106334, doi: 10.1016/j.rineng.2025.106334.

[23] D.L. Jin, Z.Y. Li, D.J. Yuan, Y.Y. Gan, J. Chen, H.P. Guo, Analysis of hydraulic break- down and seepage of tail sealing system in shield tunnel machines, Undergr. Space 21 (2025) 117-130, doi: 10.1016/j.undsp.2024.08.003.

[24] Z.L. Cao, S.H. Zhou, J.G. Liu, H.J. Guo, H.G. Di, Research on the grease rear pen- etration escape behavior and the sealing performance of shield tail under static pressure of shield tail brush, Tunn. Undergr. Space Technol. 164 (2025) 106785, doi: 10.1016/j.tust.2025.106785.

[25] H.P. Guo, D.L. Jin, C. Wang, D.J. Yuan, Z.Y. Li, T.D. Gao, Y.J. Hao, Experimental investigation on the impact of shield tail brush degradation on shield tail seal, Tunn. Undergr. Space Technol. 165 (2025) 106915, doi: 10.1016/j.tust.2025.106915.

[26] W.B. Zhu, C. Liu, X.C. Zhong, Z. You, N.W. Zhu, Performance evaluation of shield tail brush based on compression and grease escape tests, Chinese J. Geotechn. Eng. 45 (2023) 1086-1093 (In Chinese).

[27] National Energy AdministrationTest method for oxidation stability of lubricating greases (SH/T 0424-1992), Sinopec Press, 1992.

[28] Standardization Administration of ChinaLubricating greases —Determination of cone penetration (GB/T 269-2023), China Standards Press, 2023.