A review on state-of-the-art research on long-term deformation of tunnels

Ruiwang YU[1]

Executive Summary

Literature search was carried out on research articles on long-term deformation of tunnels (tunnel settlement, track rotation, tunnel distortion in transverse and longitudinal directions) recently published in major geotechnical publications. Papers on this topic, however, are scarce as shown in Table 1, which tabulates details of the available literature. Different types of tunnel construction methods are covered, such as cut-and-cover, open face TBM, earth pressure balance TBM and immersed tube (cases using NATM were not found). Long-term deformation of tunnels in rock is not covered in this literature review.

Research on this topic is concentrated in three countries, namely China, Japan and UK. Shanghai and London are the two cities that mostly affected by the problems, possibly because of the long-term history of metro tunnel being used, complex geological conditions as well as the large scale of underground transportation tunnels.

The major factors identified are: (1) groundwater/oil/gas extraction underneath the tunnel location caused ground subsidence (2) consolidation of soft soil underneath the tunnel location (3) nearby construction activities, and (4) creep of soft soil. It is worth noticing that creep was believed to contribute to the long-term settlement but almost all research that studied this effect concluded that this is minor compared with other factors.

Facts from tunnel deformation monitoring

Limitations of current research

Though these researchers concluded that groundwater/gas/oil extraction and soil consolidation largely contributed to the long-term deformation of tunnels. Effects of soil creep cannot be overlooked. The method adopted by these researchers in assessing the creep (or they called secondary consolidation) is very simple, for example, only one soil parameter, i.e., secondary compression index was used in References (1) and (4) to quantify the settlement due to creep. The parameter obtained is extremely sensitive to the representativeness of the sample, its quality and laboratory test details. Reference (2) even directly ignored any possible contribution of creep and only considered consolidation due to excess pore water pressure dissipation in back analysis. It is a pity that the case reported in Reference (2) actually has the longest monitoring period while the data may be not properly interpreted.

Reference (3) is a high-quality paper on modelling the long-term settlement of tunnels. Anisotropy of soil permeability and modulus due to layering, and appropriate boundary conditions applied to the tunnel are investigated in detail.  Field measurement of tunnel deformation, however, was not available to support the numerical results. Effect from creep was also not discussed. Recently, researchers from Norway (e.g. Degago & Grimstad, 2016) have been working closely with the industry on models for settlement analysis considering creep, which is worth attention.

References

Di, H., Zhou, S., Xiao, J., Gong, Q., and Luo, Z. (2016). “Investigation of the long-term settlement of a cut-and-cover metro tunnel in a soft deposit.” Engineering Geology, 204, 33–40.

Komiya, K., Takiyama, K. and Akagi, H. (2006). “Settlement behaviour of a shield tunnel constructed in subsiding reclaimed area.” The 5^th International Conference on Geotechnical Aspects of Underground Construction in Soft Ground, Taylor & Francis.

Wongsaroj, J., Soga, K., and Mair, R. J. (2007). “Modelling of long-term ground response to tunnelling under St James’s Park, London.” Géotechnique, 57(1), 75–90.

Ng, C. W. W., Liu, G. B., and Li, Q. (2013). “Investigation of the long-term tunnel settlement mechanisms of the first metro line in Shanghai.” Canadian Geotechnical Journal, 50(6), 674–684.

Shen, S. L., Wu, H. N., Cui, Y. J., and Yin, Z. Y. (2014). “Long-term settlement behaviour of metro tunnels in the soft deposits of Shanghai.” Tunnelling and Underground Space Technology, 40, 309–323.

ADDIN Mendeley Bibliography CSL_BIBLIOGRAPHY Cooper, M. L., Chapman, D. N., Rogers, C. D. F. and Chan,  a. H. C. (2002). “Movements in the Piccadilly Line tunnels due to the Heathrow Express construction.” Géotechnique, 52(4), 243–257.

Grantz, W. C. (2001). “Immersed tunnel settlements Part 2: Case histories.” Tunnelling and Underground Space Technology, 16(3), 203–210.

Degago, S. A., and Grimstad, G. (2016). “Evaluation of soil parameters for creep calculations of field cases.” Proceedings of the 17th Mordic Geotechnical Meeting - Challenges in Nordic Geotechnic, 25th - 28th of May 2016, 651–660.