Numerical Study on Backfilling the Tail Void Using a Two-Component Grout
Publication: Journal of Materials in Civil Engineering
Volume 30, Issue 3
Abstract
In shielded mechanized tunneling, the annular gap caused by the tunnel boring machine (TBM) driving must be backfilled instantaneously using a suitable grout. A two-component grout composed of a chemically retarded cement slurry and an accelerator is pumped into the annular gap behind the TBM shield, where it gels and attains sufficient mechanical stiffness in a very short time. This property of the grout helps restrict immediate ground movements adjacent to the TBM tail shield and reduce volume loss. In this study, the hardened two-component mix is tested using a confined oedometric condition, and a complete time-dependent hardening stiffness evolution is developed. Moreover, the freshly prepared grout is tested in terms of its performance suitability (storage and transportation) and serviceability owing to permeability and dewatering. The obtained parameters from the oedometer tests are incorporated into a numerical simulation of an earth pressure balance (EPB) excavation focusing on modeling of the backfilling procedure using finite-difference method (FDM) software. The study also focuses on distinguishing between two commonly used backfilling techniques implemented in numerical analyses. The numerical model consists of testing a regular tunnel section using a newly introduced hardening soil (HS) constitutive model with the soil parameters obtained from the Torino, Italy, metro case. Another set of synthetic softer soil parameters are chosen to highlight the soil properties in the model response. The two-component grout satisfies all the prerequisites for a good backfilling material in its fresh and hardened state. The grout attains sufficient mechanical strength in a very short time, remains impermeable, and achieves a stiffness of 43 MPa in 28 days. The results obtained from the oedometer tests enable development of a complete time-dependent stiffness evolution of the grout. The implementation of hardening behavior of the two-component grout is evident in terms of ground settlements when compared with the conventional backfilling simulation technique.
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Acknowledgments
This research has been supported by the German Research Foundation (DFG) through the Collaborative Research Center (SFB 837). The authors would like to express utmost gratitude to the organization for constant support and funding during this research. They would also like to express sincere appreciation toward Itasca consulting group for providing the license to use FLAC3D under the Itasca education partnership and their constant mentorship during the period of this research. The authors would also like to thank Infra.To for providing valuable data from the Torino metro case.
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Published In
Journal of Materials in Civil Engineering
Volume 30 • Issue 3 • March 2018
Copyright
©2018 American Society of Civil Engineers.
History
Received: Dec 19, 2016
Accepted: Aug 29, 2017
Published online: Jan 3, 2018
Published in print: Mar 1, 2018
Discussion open until: Jun 3, 2018
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