Abstract:

To prevent excessive deformation of the ground and adjacent structures caused by shield tunneling through large-diameter piles and to ensure the safety of under passing stations, this study proposed a combined cutter system consisting of “six-tooth cutters” and “tearing cutters”. The cutting performance and wear resistance of the six-tooth cutter were improved by optimizing the cutter parameters. The cutter width was increased from 100 mm to 150 mm and the rake angle was increased from 10° to 15°. A pile-cutting model for the combined tearing-cutter and six-tooth-cutter system was established using the explicit dynamic solver. The pile failure mechanism, mechanical response, and deformation effect on the surrounding environment were systematically investigated through theoretical analysis and field measurements. Firstly, the pile cutting process was shown to proceed through four failure stages: concrete cutting, steel bar scratching, bending, and necking fracture. The tensile-shear composite fracture mechanism of the steel bar under the “tear-first, shear-later” synergistic action was clarified. Secondly, the mechanical characteristics of the cutters were quantified. The reliability of the numerical model was verified through macroscopic cutting force comparison, mesoscopic fracture morphology analysis, and consistency analysis with classical theories. Finally, field settlement monitoring results were used as engineering validation for this optimized mechanism. The results show that the six-tooth cutter is dominated by cutting force, which surged from 8kN to 300-400 kN upon engaging the steel bar, while the tearing cutter is dominated by penetration force with a peak value of 647 kN. The construction induced a maximum ground and station settlement of only 5.10 mm and a heave of 2.26 mm. These deformations are far below the control thresholds.

Key words: shield pile cutting, combined cutter, six-tooth cutter, ripper cutter, cutter cutting, ground subsidence