Tunnel Lining Formwork

Working process of  tunnel lining steel formwork trolley

First, Before commencing tunnel construction, it is imperative to verify that the conditions align with the template trolley's design specifications. As the template trolley is a non-standard piece of equipment, its operational parameters must be checked against the design requirements to ensure safe and effective lining operations.

Roadway Surface Inspection: Confirm that both the elevation and condition of the roadway surface adhere to the design criteria. The roadway surface elevation should be as specified, and the condition should be a smooth concrete surface.

Ground Screw Support Positioning: Ensure that the positioning of the ground screw supports is in accordance with the design requirements. Refer to the provided illustration for the correct layout.

Railway and Sleeper Compliance: Inspect the sleepers and rails to ascertain that they meet the design specifications, ensuring stability and proper alignment for the trolley's operation.

Short Side Wall Height Verification: Check the height of the short side wall to confirm it matches the design requirements, which is crucial for the trolley's maneuverability and the integrity of the lining.

Release Agent Application: Verify that the outer surface of the steel formwork is properly coated with a release agent to facilitate easy demolding and maintain the quality of the concrete lining.

By conducting these thorough checks, you can ensure that the template trolley operates optimally and meets the project's design and safety standards.

Second, Erecting the Formwork

Once the tunnel lining formwork trolley has been maneuvered into the lining position, the formwork can be erected. The vertical formwork should be released before proceeding with the setup.

The process of erecting the vertical formwork is as follows

Positioning the Trolley: After the trolley arrives at the designated lining position, the gantry supports are lowered to engage the jacks. These jacks are then positioned on the rails and secured tightly.

Raising the Vertical Cylinders: Activate the hydraulic motor and manipulate the manual reversing valve handle to elevate the vertical cylinders. Adjust the steel formwork trolley template to the required height as specified.

Aligning the Centerline: Operate the manual reversing valve handle to move the horizontal cylinders. Position the steel template trolley template so that its centerline coincides with the centerline of the lining. Then, use the manual reversing valve to raise the vertical cylinders to the desired height and secure the vertical jacks at the top of the gantry.

Adjusting the Side Templates: Operate the manual reversing valve handle to extend the lateral cylinders. Roughly position the steel formwork side templates to their predetermined locations. Note that the side mold cylinders should be adjusted individually on each side.

Installing Side Screws: Attach the side screws to secure the formwork in place.

Final Adjustments: Turn off the motor and gently move the manual reversing valve handle back and forth to release pressure from the lateral cylinders. Fine-tune the lateral jacks to ensure the steel formwork side templates are in the correct pouring state.

Securing the Ground Screw Jacks and Plugging Boards: Install the ground screw jacks and plugging boards to complete the setup.

By following these detailed steps, the formwork can be erected efficiently and accurately, ensuring a smooth lining process.

Third, Grouting 

Grouting can be started once the vertical formwork is fully set. Prior to grouting, it is essential to apply a release agent to the outer surface of the tunnel lining formwork. This step reduces surface adhesion during demolding, facilitating easier removal of the formwork.

The grouting port comprises a working window and a grouting port itself. The grouting sequence should start from the bottom row of working windows. Grout until the concrete is just about to close the working window, then close the window. Proceed to grout from the second row of working windows, continuing in this manner until the final row is reached. Conclude the grouting process by capping the grouting port.

During the grouting work, pay attention to the following points:

Pre-Grouting Inspection: Before each grouting session, thoroughly check the screws and jacks for any looseness. This precaution prevents deformation of the trolley during the grouting process.

Concrete Pouring Guidelines: Ensure that the maximum drop height of the concrete does not exceed 3000mm. The height difference between the front and back of the steel formwork trolley should be kept within 600mm, and the height difference between the left and right sides should not exceed 500mm.

Final Grouting Details: When grouting to the end through the grouting port, always use the low-speed gear. Monitor the pressure at the grouting port closely to avoid excessive pressure that could result from forced concrete injection, potentially causing the formwork to deform.

By adhering to these meticulous procedures, the grouting process can be executed smoothly, ensuring the integrity and quality of the tunnel lining.
Fourth, Demolding 

Once the grouting is complete, the concrete must be given sufficient time to solidify before demolding can commence. The demolding process should be carried out as follows:

Remove Support Components: Begin by removing the side jacks, ground screw jacks, and plug boards.

Activate Hydraulic System: Start the hydraulic system and use the manual reversing valve handle to control the lateral cylinders. Carefully withdraw the side forms from the lining. The cylinders are designed to retract over a stroke of 190 mm to 300 mm.

Retract Foundation Jacks: After the side forms are removed, retract the foundation jacks to prepare for further demolding.

Control Vertical Cylinders: Operate the manual reversing valve handle to control the vertical cylinders, ensuring that the tunnel lining formwork is fully detached from the lining surface. When retracting the cylinders, it is crucial to do so in several stages to avoid forcing the demolding in one go. The vertical cylinders have a retraction stroke ranging from 150 mm to 250 mm.

By following these steps meticulously, the demolding process can be executed smoothly and safely, preserving the integrity of both the formwork and the newly solidified concrete lining.

Fifth, Moving the Formwork

After the tunnel lining formwork has been successfully demolded, the process of moving it to the next position can begin. Start by closing the gantry support jacks, then use the gantry to support the jacks. Once this is done, you can start the walking motor to move the formwork.

When moving the tunnel lining formwork, pay attention to the following points:

Ensure Complete Stop: The formwork must come to a complete stop before it can be reversed to ensure safety and prevent damage.

Addressing Slip Issues: If the rail slope is too steep and the trolley begins to slip, sprinkle some dry sand on the rail surface to increase traction and eliminate the slipping.

Repeat the Cycle: Continue to repeat the four processes of erecting the vertical formwork, grouting, demolding, and moving to complete the entire operation process efficiently.

By adhering to these guidelines, the movement of the tunnel lining formwork can be carried out smoothly and safely, ensuring the continuity and efficiency of the construction process.