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Principles for Pipe Avoidance on Fully Automatic Wet-Spraying Trolleys
Release time:
2026-09-17
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Summary:
In tunneling and underground engineering, the concrete delivery pipelines of fully automated wet‑spraying rigs often need to be routed alongside or intersect with power cables, water supply lines, high‑pressure air hoses, ventilation ducts, and temporary drainage systems. Pipeline clearance is not a single operational task; rather, it constitutes a comprehensive technical system that encompasses pipeline installation standards, coordination with various utility lines, optimization of bends and joints, and ongoing pipeline condition maintenance. A well‑designed clearance strategy not only mitigates the risks of pipe blockages and bursts but also effectively reduces pumping pressure losses and extends the service life of the pipelines.
I. Active Avoidance of Horizontal and Vertical Pipe Routing
When laying pipelines in both horizontal and vertical sections, proactive measures should be taken to avoid intersections and overlaps with other utility lines. Horizontal pumping pipelines should be routed in straight runs to minimize concrete flow resistance and reduce the risks of segregation and pipe blockage caused by elevation changes. Vertical pumping pipelines must not be connected directly to the pump outlet; instead, a horizontal section at least 20 meters long must be installed at the lower end of the vertical run, with a check valve positioned near the pump. This arrangement allows the self-weight–induced backpressure of the vertical line to be absorbed by the horizontal buffer section, thereby preventing the pump outlet from experiencing excessive static pressure surges. When installing downward‑sloping pipelines, a horizontal section should be added at the outlet, with a length no less than five times the elevation difference of the sloped run. For steeper slopes, an air‑vent valve should also be installed at the upper end of the gradient to prevent accelerated concrete flow under gravity, which could lead to vacuum formation or segregation within the pipe.
II. Proper Control of Bent Pipes and Hoses
Pipeline routing should minimize the number of bends and flexible hoses. Along any given pipeline, concrete delivery pipes of uniform diameter should be used to prevent abrupt changes in flow velocity and localized turbulence caused by sudden diameter transitions. Where flexible hoses are unavoidable, their bending radius should be kept as close to 180° as possible, and kinking must be strictly avoided. At the pump outlet, directional changes on a horizontal plane should be minimized to prevent significant pressure losses. When using elbows, excessive bend angles should also be avoided; the greater the number of bends and the smaller the radius of curvature, the larger the pressure loss and the more severe the dynamic loads on fixed supports.
III. Clearance Rules Between Pumping Pipelines and Adjacent Utilities
The clearance requirements around pumping pipelines must adhere to the fundamental principles of coordinated multi‑pipeline installation. Supply air ducts, water supply pipes, and electrical cables should, wherever possible, avoid the main flow paths of concrete delivery pipelines to prevent crossings and entanglements. Where crossings are unavoidable, concrete delivery pipelines should be given priority and routed in a straight line; power cables and other vulnerable utilities should be routed overhead or enclosed within protective conduits. During pipeline installation, the clear distance between the outer surface of a pipe and the edges of adjacent pipe fittings shall not be less than 10 mm. Flanges or union joints on pipes in the same row must be staggered by at least 100 mm. Pipes passing through walls shall be fitted with sleeves, with the joint positioned at least 800 mm from the wall surface. Pumping pipelines must not come into direct contact with reinforcing steel or formwork, nor should they be laid directly across high‑traffic areas or material‑handling routes. Pipe joints and clamps must be securely fastened and sealed to prevent grout leakage.
IV. Pipe Clearance at the Mid‑Platform Accessway and Material Stacking Area on the Working Face
On the shotcrete working face, the concrete delivery pipeline must be laid in such a way as to provide safe access for the trolley and facilitate material transfer. During construction, the wet‑spraying machine must be positioned securely and kept level, with all wheels firmly on the ground. Pipelines should be routed as close as possible to the tunnel wall or the edge of the invert platform, and firmly anchored with brackets and pipe clamps to prevent them from being crushed when equipment reverses or turns. In areas beneath the working platform, at cross‑passage intersections, and in zones where arch support is densely installed, pipelines should be routed along the structure’s side and elevated using steel‑section supports, thereby avoiding the travel paths of heavy transport vehicles and excavation equipment. Prior to laying the pipelines, the working face must be locally cleared to remove loose rock fragments and rebar ends that could come into contact with the pipes, thus preventing damage to the pipe exterior from hard, sharp objects.
V. Location Selection and Avoidance During the Replacement and Maintenance of Worn Pipelines
Under prolonged high-pressure pumping and abrasive particle erosion, the wear rate along the inner surface of conveying pipelines is uneven, with bends wearing more rapidly than straight sections. When wall‑thickness loss exceeds a specified fraction of the original thickness, pipeline replacement should be considered; for frequently used lines or those handling concrete containing hard particles, the wear rate may be even faster. Regular inspections of concrete pipeline wear are essential; if wall thickness falls below the safety threshold, immediate replacement should be scheduled. Wall thickness can be roughly assessed by tapping—when wear reduces the wall thickness to a certain proportion of the original (e.g., less than 70% of the original), replacement should be contemplated.
Pumping pipelines shall be supported and securely fixed; wooden pads must be installed between the pipeline and any fixed structures to provide cushioning, and the pipeline must not be directly connected to reinforcing steel or formwork. Worn‑out pipes must not be installed in the high‑pressure section at the downstream end. Pipe joints shall use fittings that are free of cracks, surface damage, and kinks; clamps must be tightened securely, and sealing rings must be intact. When combining new and old piping, the new sections should be positioned in areas subjected to higher pumping pressures. The pipeline system must be reliably anchored, with tight joints that prevent grout leakage. After installation, the pumping pipeline must undergo a pressure‑testing procedure; it may only be put into service once the pipe wall strength and joint sealing have been verified to meet the required standards.
VI. Pipeline Avoidance and Protection in Special Environments
In water-rich tunnels or at high-altitude construction sites, the installation of concrete delivery pipelines must also address cooling and freeze‑protection requirements. The wall thickness of the pumping pipeline should be matched to the pumping pressure; high‑quality pipes should be used near the pump, and all pipe joints, sealing rings, bends, and other components must be intact and undamaged. Under intense sunlight, the pipeline should be covered with wet burlap or wet straw bags, and water should be applied promptly to cool it, preventing rapid evaporation of moisture in the concrete and consequent loss of slump. During cold seasons, thermal insulation measures must be implemented to protect the concrete inside the pipeline from freezing, which could compromise its workability and spraying quality. When the pipeline length within the tunnel is considerable, segmented buffer supports should be installed, with straight‑line transitions between sections; areas around vertical and horizontal bends experience greater stress, so support spacing in these zones should be denser.
VII. Frost Protection and Relocation of Pipelines During Winter Construction
During winter construction, freeze protection of pipelines is a critical step. Concrete delivery pipes should be wrapped with insulating materials to prevent the concrete inside from freezing and to maintain an adequate placement temperature. Prior to spraying, it is essential to verify that the system’s air pressure, electrical voltage, tie‑rod clamping force, rotor rotation direction, and the accelerator‑agent lines are all unobstructed. When stopping spraying, use high‑pressure air to thoroughly purge the spray hose and the accelerator‑agent lines; if the interval between two consecutive sprays exceeds 30 minutes, flush the wet‑spraying machine, the spray hose, and the accelerator‑agent lines with water. After completing the work, completely drain any residual concrete and accelerator agent from the pipelines to prevent freezing and blockage at low temperatures. In extremely cold winter conditions, only leave the site after confirming that the pipelines have been thoroughly cleaned, to avoid residual water freezing and causing the pipelines to burst.
VIII. Summary
The avoidance strategy for pipeline installation on fully automated wet‑spraying trolleys should be advanced holistically across three dimensions: the physical‑space dimension (clearance from tunnel structures, reinforcing steel formwork, and equipment), the pipeline‑coordination dimension (cross‑avoidance with ventilation ducts, water supply pipes, and cables), and the pipeline‑maintenance dimension (selection of new pipe locations, replacement of worn sections, wall‑thickness inspection, and corrosion‑protection and thermal‑insulation measures). The effective implementation of these avoidance plans hinges on meticulous pre‑operation planning of pipeline routes and the rational configuration of securing devices. Optimizing these avoidance measures can minimize the frequency of delivery‑pipeline failures, thereby enhancing the continuous operational capability of the wet‑spraying trolley and improving spray quality.
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