Variable-diameter shield tunneling machine and in-hole variable-diameter construction method thereof

The invention provides a variable-diameter shield tunneling machine. The variable-diameter shield tunneling machine comprises a shield body, a main drive, a variable-diameter cutterhead, a propelling device, a pipe piece assembling system and a mechanical excavation device. The shield body comprises a variable-diameter front shield, a shield body sleeve shell and a tail shield; the mechanical excavation device comprises a telescopic mechanism and an expanding excavation mechanism; the telescopic mechanism is arranged on the duct piece assembling system and can translate and rotate along with the duct piece assembling system; the expanding excavation mechanism is arranged on the telescopic mechanism and can be driven by the telescopic mechanism to stretch out and draw back in the radial direction, so that after the tail shield and the variable-diameter front shield are disconnected, a soil layer is excavated between the tail shield and the variable-diameter front shield, and an expanding excavation space is fo