# Design Study of Steel Fibre Reinforced Concrete Shaft Lining for Swelling Ground in Toronto, Canada
## 6 Conclusions  
SFRC has been studied and used as an alternative material to take advantages of their workability and economic benefits over traditional RC. In this paper, a design study was conducted to replace originally designed RC shaft lining using SFRC in terms of geotechnical engineering. Several geological and structural design reports used in original lining designs were utilised, and theoretical and experimental approaches were used to determine SFRC designs corresponding to the original RC. The axial load and bending moment of the shaft lining were derived using Canadian concrete design codes CSA A23.3 combined with RILEM TC-162 TDF, and several analytical solutions with uniform and non-uniform loading cases were adopted for the evaluation of SFRC shaft lining performance. In addition, a numerical analysis model developed for Georgian Bay shale with swelling behaviour was used to determine if the proposed installation timing of the shaft lining is appropriate, and to evaluate the long-term stability of the shaft lining.  
According to the structural analysis, RC with 20 M@300-radial and 15 M@300-vertical steel bars are characterised by an extremely high axial load and bending moment capacity of approximately 6100 kN/m and 880 kNm/m, respectively. The SFRC showed a relatively low bending moment with 370 kNm/m, while showing a high axial force corresponding to the RC with 5800 kN/m. The calculated hoop thrust and bending moment under both uniform and non-uniform loading cases were within the capacity of the SFRC lining, and thus it is estimated that an alternative design of a circular shaft, using SFRC, possesses sufficient load-bearing resistance. Therefore, it has been demonstrated that the SFRC lining poses an excellent alternative to steel bars in conventional RC for use as circular shaft structures, with both improved construction efficiency and structural capacity. Numerical analysis using the \"swello\" constitutive model, coded in FLAC 2D finite difference program, was performed to evaluate whether the proposed timing of the shaft lining is appropriate, and estimate the long-term stability. According to the results of the numerical analysis, the shaft lining installed at the proposed timing is expected to be structurally stable in the long-term, and furthermore, it could be considered that the installation time can be reduced by up to 20 days. Therefore, it can be concluded that the SFRC lining, installed 70 days after excavation, can sufficiently withstand the long-term ground swelling behaviour and can reduce the construction schedule by reducing the delays due to TDD. The construction cost could also decrease by reducing the waiting time for the shaft lining installation.  
Figure 10: Maximum lining forces on shaft walls.  
**Author Contributions:** Conceptualisation, S.S.L.; methodology, S.S.L.; validation, M.S.K.; formal analysis, M.S.K.; data collection, M.S.K.; writing--original draft preparation, M.S.K.; writing--review, S.S.L.; supervision, S.S.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.