A multidisciplinary engineering-based approach for tunnelling strengthening with a new fibre reinforced shotcrete technology

This paper describes the relevant research activities that are being carried out on the development of a novel shotcrete technology capable of applying, autonomously and in real time, fibre reinforced shotcrete (FRS) with tailored properties regarding the optimum structural strengthening of railway tunnels (RT). This technique allows to apply fibre reinforced concrete (FRC) of strain softening (SSFRC) and strain hardening (SHFRC) according to a multi-level advanced numerical simulation that considers the relevant nonlinear features of these FRC, as well as their interaction with the surrounding soil, for an intended strengthening performance of the RT. Building information modelling (BIM) is used for assisting on the development of data files of the involved design software, integrating geometric assessment of a RT, damages from inspection and diagnosis, and the characteristics of the FRS strengthening solution. A dedicated computational tool was developed to design FRC with target properties. The preliminary experimental results on the evaluation of the relevant mechanical properties of the FRS are presented and discussed, as well as the experimental tests on the bond between FRS and current substrates found in RT. Representative numerical simulations were performed to demonstrate the structural performance of the proposed FRS-based strengthening technique. Computational tools capable of assuring, in real time, the aimed thickness of the layers forming the FRS strengthening shell were also developed. The first generation of a mechanical device for controlling the amount of fibres to be added, in real time, to the FRS mixture was conceived, built and tested. A mechanism is also being developed to improve the fibre distribution during its introduction through the mechanical device to avoid fibre balling. This work describes the relevant achievements already attained, as introduces the planned future initiatives in the scope of this project.

Description

Acknowledgments: This study is a part of the I&DT project in co-promotion with companies ‘‘RoboShot@FRC - Robotized system for the shotcrete of optimized fibre reinforced concrete in railway tunnels’’, Co-promotion project number 47075, call 17/SI/2019. This work was partly financed by FCT / MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020, under the Associate Laboratory Advanced Production and Intelligent Systems ARISE under reference LA/P/0112/2020, under the R&D Unit INESC Coimbra, Advanced Robotics and Smart Factories (ROBiTECH) group, under reference UIDB/00308/2020, as well as under the Scientific Employment Stimulus - Institutional Call CEECINST/00051/2018. The authors would like to acknowledge the collaboration of Dr. Jos´e Granja and the PhD Candidate Mohamad El Sibaii on the development of the example depicted in Fig. 2.2.

Keywords

Tunnel strengthening Fibre reinforced shotcrete (FRS) mix design Experimental characterization of FRS properties BIM Multiscale analysis and design Shotcrete automation and robotization