Novel soil nail diameter expanding device and diameter expanding method

The invention provides a novel soil nail diameter expanding device which comprises a core shaft knob, a core shaft, a core shaft knob advance and retreat control device, a drill rod and a cylindrical gear, wherein the core shaft knob and the cylindrical gear are connected through the core shaft; the cylindrical gear is positioned inside the drill rod; the novel soil nail diameter expanding device further comprises a first diameter expanding wing and a second diameter expanding wing; the first diameter expanding wing and the second diameter expanding wing are respectively connected onto the drill rod through connecting parts; a gear rack is respectively arranged on each of the first diameter expanding wing and the second diameter expanding wing; the gear racks are meshed with the cylindrical gear. The invention further provides a soil nail diameter expanding method. According to the novel soil nail diameter expanding device and diameter expanding method, the diameter of a soil nail hole at a soil nail anchorage section can be very conveniently enlarged to the size meeting the design requirement, so that the design purposes of economy, safety and reasonableness of a supporting structure can be achieved, and the construction cost is reduced.