The rock fracturing in the jointed tunnel face ground with TBM: Experimental and numerical study
- Publisher:
- Elsevier
- Publication Type:
- Journal Article
- Citation:
- Theoretical and Applied Fracture Mechanics, 2023, 125, pp. 103933
- Issue Date:
- 2023-06-01
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| Filename | Description | Size | |||
|---|---|---|---|---|---|
| 1-s2.0-S0167844223001969-main.pdf | Published version | 26.35 MB |
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To investigate the fracture patterns in the jointed samples during the tunnel boring machine (TBM) excavation, rock-like material samples were tested in the lab experiments and were numerically simulated with PFC2D. For this purpose, 33 samples, 150 mm × 150 mm × 50 mm, with 4, 6, and 10 joints and 0°, 30°, 60° and 90° angles between joints and the joints axis were prepared and tested by two cutters applying load to the sample after being cured for 28 days. Compressive strength and tensile strength of material were 7.4 MPa and 1 MPa, respectivly. Distance between two cutters was considered as 10 mm, 20 mm, and 50 mm. Loading rate was 0.016 mm/s. Fracture growth and chipping formation, displacement field evolution, failure stress, external work at peak load, fracture energy and optimum disc spacing were measured. The results show that in the jointed samples with more joints, the crack starts with lower initial crack stress due to the smallness of the rock bridge. Chipping formation from the samples may propagate appropriately in the samples with an optimum spacing (20 mm) between disc cutters. When the spacing is too large, the cracks cannot reach each other, which creates the rock chips to release into the free face area between disc cutters. The too-small gap between the disc cutter's spacing causes crushing phenomena and increases excavation energy. When cutter spacing was 10 mm and joint angle was 60°, the external work at pick load was decreased by 18% related to maximum external work. When cutter spacing was 20 mm and joint angle was 60°, the external work at pick load was decreased by 32% related to maximum external work. When cutter spacing was 50 mm and joint angle was 60°, the external work at pick load was decreased by 22% related to maximum external work. Similar phenomena were occurred for fracture energy. The results of the PFC2D simulations match the observations from the actual lab tests.
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