Abstract:

When shield cuts the pile foundation directly, the cutterhead is jammed and the cutters are damaged often. As a result, it is urgent to explore the feasibility of directly cutting of reinforced concrete pile foundation with ϕ25 mm main reinforced bar by shield to improve the construction efficiency. The test on pile foundation cut by disc cutter and tearing cutter is carried out on TBM modal tunneling test platform, and the fracture morphology of reinforced bar, force characteristics, cutting parameters, cutter damage and cutterhead vibration characteristics are comprehensively analyzed. The analytical results show that: (1) The main failure mode of reinforced bar cut by disc cutter is rolling failure, and the effective reinforced bar breaking ratio is 90.6%; and that by tearing cutter is shear failure, and the effective reinforced bar breaking ratio is 85.4%. (2) Compared with full disc cutter, cutting parameters of the full tearing cutter fluctuate greatly, the cutting process is unstable, and the vibration impact is large; moreover, due to the large lateral impact force, the collapse form of tearing cutter alloy varies. (3) The impact resistance effect of the disc cutter is better than that of tearing cutter, and the forward cutting effect of the tearing cutter is better than that of the disc cutter, which indicates that the combination of disc cutter and tearing cutter can be adopted. (4) The advancing speed of reinforced bar cutting should not be too fast (less than 3 mm/min for tearing cutter and less than 5 mm/min for disc cutter), and the torque fluctuation should be paid more attention to during the cutting process. The test results have been successfully applied to Shenzhen Metro pile cutting project, and the test and practice results show that it is feasible to directly cut the large diameter reinforced concrete pile foundation with ϕ25 mm main reinforced bar.

Key words: shield, pile foundation cutting, disc cutter, tearing cutter, mechanical characteristics, cutting parameters, fracture morphology