After the reaming operation of the Raise borer Machine is completed, the cutterhead needs to be recovered and relocated. Based on the on-site construction conditions, operation safety management, and equipment transportation requirements, two special construction plans are formulated: one for recovery from the wellhead upward and the other for recovery from the well bottom downward.

Both schemes must strictly adhere to the principles of “preparation before operation” and “protection before construction,” with comprehensive safety supervision throughout the entire process, standardized operating procedures, and strict prohibition of non-compliant or skipped-step operations, thereby ensuring the intact retrieval of the cutterhead, the personal safety of personnel, and orderly on-site construction.

I. Construction Steps for Wellhead Recovery of the Cutterhead

1. Preparation of Construction Materials and Tools

2. Initial Fixing of the Cutterhead and Installation of Lifting Gear

After the 3m shaft is completely connected and expanded, the Raise borer Machine head slowly lowers the cutterhead, fixes the cutterhead on the base plate with a plug board, and tightens the male and female lifting caps on the head and cutterhead pull rod, respectively.

Then, use a ∅22 steel wire rope (or other U-shaped buckle) to connect the male and female lifting caps. Lift the machine head, remove the insertion plate, lower the cutterhead, and secure the cutterhead to the steel beam of the construction platform with four steel wire ropes. Remove the steel wire rope between the male and female lifting caps, retract the Raise borer Machine, and then move the Raise borer Machine out of the construction tunnel.

① Schematic diagram of tunneling chamber excavating the cutterhead

② Schematic diagram of the cutterhead being retrieved from the ground

3. Fabrication and Installation of the Wellhead Gantry

After the drilling rig is moved out, lay 40×200×2300 mm wooden planks as padding (secure the planks with 200 mm long galvanized nails) to cover the wellhead, and then install a gantry frame on the roof directly above the wellhead.

4. Installation and Trial Hoisting of the Lifting Hoist

Install two 10-ton hoists above the large cutterhead at the lifting points, suspend and properly install two Φ20 steel wire ropes, and then conduct a trial lift.

5. Formal lifting and hoisting of the cutterhead

After the two suspension steel cables have been tensioned, with no deformation observed in the upright columns or cross beams, personnel, protected by safety ropes, slowly lift the cutterhead to ensure its smooth extraction.

6. Landing of the Cutterhead and Platform Erection

When the bottom of the cutterhead reaches the level of the existing steel girder, remove the four wire ropes from the original suspended cutterhead and move the steel girder to the bottom of the cutterhead.

7. Cutterhead Transfer and On-Site Cleanup

At the steel girder locations, place square timbers as shims to create a continuous working platform for personnel access; install the tires under the protection of safety ropes. Alternatively, use a scraper loader to lift the cutterhead onto the machine and transport it to the trackless maintenance adit for inspection, then employ the scraper loader to tow the I-beam from the shaft mouth back to the designated storage area.

8. Wellhead Protection and Removal of Tools and Equipment

Upon completion of the transfer of the cutterhead and steel beams, the shaft opening shall be immediately fully enclosed and isolated with dedicated guardrails, and conspicuous safety warning signs shall be installed to prohibit personnel from approaching. Subsequently, all tools and equipment used, as well as any remaining materials, shall be individually inventoried and removed; the work site shall then be thoroughly cleared of debris and waste to maintain cleanliness, thereby completing the entire shaft-opening recovery operation.

II. Construction Steps for Bottom-of-Well Cutterhead Recovery

1. Underground Wellhead Protection and Enclosure

Board up the enlarged wellhead with 5-cm-thick wooden planks to ensure safety during the operation of the lifting and lowering rod.

2. Lowering the cutterhead and installing the pad ring

Before lowering the cutterhead, a spacer ring must be installed. Subsequently, drill pipes are connected one by one and lowered together with the cutterhead until the cutterhead reaches the bottom of the well. The clearance between the bottom of the cutterhead and the ground should be maintained at approximately 20 cm.

Pay particular attention to the details: at the threaded connection between the cutterhead tie rod and the first drill pipe, a standard metal washer (6–8 mm thick) must be installed. The outer diameter of the washer should match the outer diameter of the drill pipe. After the cutterhead is lowered to the ground, this washer will be cut off and removed to facilitate the disassembly of the threaded rod.

3. Safety Monitoring of Upper and Lower Roadways

Once the cutterhead has been lowered to a clearance of 20 cm above the ground, a dedicated supervisor shall be stationed at the upper mid-section of the shaft opening to provide timely warnings of loose rock and debris falling from above, thereby ensuring that the area above the work zone remains safe and under control.

A protective scaffold has been installed in the cutterhead working area of the lower tunnel section—constructed using a steel frame and thickened protective panels to cover the cutterhead and the operators’ work zone, thereby creating a physical barrier that effectively intercepts falling debris and rock fragments from above, preventing them from directly impacting the working face below and reducing the risk of injury.

4. Cut and remove the cutterhead using the shim ring.

The crew uses a cutting machine to connect to the external power supply and then cuts and removes the spacer ring between the cutterhead tie rod and the first drill pipe. Subsequently, the cutterhead is manually rotated and dismantled using auxiliary tools.

5. Ensure proper safety warnings are in place during cutterhead transportation.

Safely transport the cutterhead to the designated location. Dismantle the protective safety canopy. Evacuate all personnel from the bottom cavern, and install a safety isolation net and warning signs at the cavern entrance.

6. Drill Pipe Recovery and On-Site Protection

Retrieve the drill pipe from the wellhead in accordance with standard operating procedures. Upon completion of the drill-pipe retrieval, remove the wooden planks from the wellhead. Disconnect the drilling rig from the steel beam of the wellhead base frame, then perform a normal back-rotation and relocate the rig. Ensure adequate safety protection at the wellhead by installing a safety isolation net and posting appropriate safety warning signs.

Both recovery schemes for the Raise borer Machine must strictly adhere to the principles of “safety first, standardized procedures, and closed-loop management.” From the preliminary preparation and mid-term operation to the final wrap-up, responsibilities must be assigned to specific individuals and control measures must be fully implemented throughout the entire process, ensuring the intact recovery of the cutterhead, zero casualties among personnel, and zero hidden dangers on site, thereby successfully completing all construction tasks for the recovery of the Raise borer Machine cutterhead.