Modification and Application of a Small Pipe Jacking Machine for Cutting Large-Diameter Reinforced Concrete Piles

With the continuous densification of transportation networks,underground construction often encounters obstacles such as reinforced concrete piles.Shield machines can readily break through such obstacles owing to their high cutting capability,whereas small pipe jacking machines have limited cutting capacity,making direct cutting of large-diameter reinforced concrete piles extremely challenging.To address this issue,this study was conducted based on a reinforced concrete pile-cutting project using a small pipe jacking machine at Zhanongkou Station of Hangzhou Metro Line 18.A small pipe jacking machine suitable for pile cutting was developed through cutterhead tool optimization,power-system upgrading,muck-discharge system modification,and monitoring-system implementation.Full-scale field tests were conducted to verify its engineering applicability in terms of cutterhead cutting performance,power-system compatibility,muck-discharge efficiency,and machine attitude control.The results show that the stepped cutterhead configuration integrating disc cutters,shell cutters,and scrapers enables effective compressive-abrasive cutting of rebars;compressive-abrasive rebar fractures account for 94.5%,and disc-cutter wear remains below 1 mm,indicating that cutterhead performance meets operational requirements.Two parallel-driven 30kW variable-frequency motors produce maximum operating torque and thrust values of only 40.2% and 13% of the rated capacities,respectively,showing that the power system is well matched to pile-cutting loads.The shaftless screw conveyor with an inner diameter of 300mm effectively discharges the cuttings,as 70% of the severed rebars are shorter than 30cm.The machine attitude remains generally stable during cutting,indicating that direct cutting of reinforced concrete piles by a small pipe jacking machine is feasible and provides a reference for similar underground obstacle-removal projects.