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Method for Arranging Pipelines Inside Tunnels Using a Fully Automatic Wet-Spraying Carriage
Release time:
2026-09-14
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Summary:
When an automated wet‑spraying carriage is used for shotcrete operations inside a tunnel, the delivery pipeline serves to convey the concrete under high pressure from the pump to the nozzle. The rationality of the pipeline layout directly affects both spraying efficiency and construction safety. The following outlines the specific methods for pipeline arrangement within tunnels.
I. Route Selection Principles: Level, Straight, and Gentle
Pipeline installation within tunnels should adhere to the fundamental layout principles of “level, straight, and gentle,” in order to minimize concrete flow resistance and reduce the risk of pipe blockage. Pipeline routing should follow the tunnel wall as closely as possible, extending in a straight line to minimize the number of bends and flexible hoses used. When a change in direction is unavoidable, preference should be given to large-radius bends (with a bending radius of at least 1 m), and 90° elbows should be avoided. Each elbow introduces significant localized pressure loss; the greater the number of bends, the larger the pumping pressure loss and the more severe the impact on fixed supports. Within the same pipeline run, conveyance pipes of identical diameter should be selected to prevent abrupt velocity changes and localized turbulence caused by diameter transitions.
II. Treatment of Critical Connection Joints
The connection between the pump outlet and the pipeline is a stress‑concentration zone in the piping system. At the outlet of a wheeled wet‑spraying boom pump, a horizontal pipe should be installed, with an elbow fitted at its upper end to change the concrete’s transport direction from vertical to horizontal. The pump outlet should not undergo any further directional changes within the horizontal plane, as this would result in significant pressure losses.
When pumping and spraying upward at a height exceeding 15 m, or when pumping and spraying downward, a U‑shaped connection should be used; if a direct connection is employed, valve box blockage may occur, potentially rendering pumping impossible. For horizontal spraying, either a U‑shaped or a direct connection may be used, with the specific choice determined by site conditions.
III. Pipeline Slope Direction and Corner Control
Pipeline installation shall ensure straightness and smoothness, with no local depressions or protrusions. Joints must be tightly sealed, pipe supports must be stable and reliable, and joint gaps must be free of grout leakage. At bends, the slope should be gentle; dedicated bent fittings must be used, and it is strictly prohibited to form corners by forcibly bending straight pipes or by cutting and splicing sections. When installing horizontal pipelines along tunnel arches or sidewalls, a slight slope of 0.5% to 1% should be provided to allow concrete to flow naturally under its own weight. For downward‑sloping pipelines, a short horizontal section should be installed at the lower end to prevent accelerated flow under gravity, which could lead to vacuum formation or segregation within the pipe.
IV. Pipe Fixing and Support Spacing
Conveyor pump pipes must be secured with supports, which shall be firmly attached to the tunnel wall or supporting structure. At pipe bends, support spacing shall be increased. Support configurations shall be determined by structural calculations, and wooden pads must be installed between the supports and the pipeline as shock absorbers; direct connections to reinforcing steel, scaffolding, or formwork are prohibited. For horizontal pipelines, support points should be provided at intervals of 2 to 3 meters; for vertical pipelines, each pipe must have no fewer than two fixed supports, and additional supports shall be installed within 0.5 to 1.0 meter of either end of bent sections.
Pipes shall be securely connected, with clamps tightly fastened and properly sealed to prevent grout leakage. It is strictly prohibited to install worn‑out pipes in the high‑pressure downstream section, as insufficient wall strength could lead to pipe bursts. For long‑distance pipeline installations, vibration‑damping supports should be provided at appropriate locations, or rubber pads should be installed between the pipes and their mounting fixtures to absorb the impact of pumping surges and prevent fastening bolts from loosening due to prolonged cyclic loading.
V. Pipeline Protection and Safety Measures
At locations along the pipeline within the tunnel where personnel or equipment pass, the pump pipe shall be protected. Protective measures may include constructing wooden shields or wrapping the pipe with multiple layers of discarded close‑mesh netting. The protective layer must cover pipe joints and areas with frequent pedestrian traffic to prevent high‑pressure concrete spray from causing injury due to pipe abrasion or loose joints. Pipeline installation shall ensure construction safety and facilitate pipe cleaning, fault troubleshooting, and maintenance.
VI. Prevention of Cement Slurry Deposition and Blockage
Inside the tunnel, pipelines remain in place for an extended period after each grouting operation, which can lead to cement slurry deposition and blockage. Therefore, following each spraying cycle, the pipelines should be thoroughly cleaned with high-pressure water or compressed air without delay. During long-distance or prolonged pumping operations, a dedicated inspector should patrol the pipeline route, paying particular attention to joint leaks, loose supports, and any abnormal vibrations. Any abnormalities detected must prompt immediate shutdown and corrective action.
VII. Pipeline Adjustments in Special Tunnel Sections
At tunnel–cross passage intersections, sections with abrupt cross‑section changes, and areas where steel arch support is densely installed, pipeline routing should prioritize alignment along the tunnel wall and passage through the support gaps, thereby avoiding interference with ventilation ducts, power supply lines, drainage pipes, and other utilities. When installing pipelines in steel arch‑supported segments, the conduits shall be routed through the sides of the arches; supports should be anchored to the steel arches or rock bolts, and direct welding to load‑bearing parts of the arch is prohibited. For pipe sections requiring frequent disassembly and cleaning—such as the flexible hose connections at the nozzle outlets—sufficient working space must be provided, and quick‑connect fittings that facilitate easy removal and reinstallation should be installed at the joints.
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