The execution of underground pipelines using trenchless technologies and microtunnelling subjects concrete pipes to extreme conditions. For a pipeline to withstand the enormous pressure of hydraulic jacking without cracking, its geometry must be millimetrically exact. This is where the manufacturing quality of pipe jacking moulds becomes the critical success factor for any heavy precast concrete plant.
Unlike conventional pipelines, where minor clearances are acceptable in open-trench applications, jacking pipes require perfect parallelism between their faces, a high-precision spigot and socket joint, and absolute watertightness. This technical guide delves into the steel fabrication criteria, design, and tolerances that plant managers and procurement officers must consider before commissioning the manufacture of this industrial equipment.
Jacking Pipes: Structural Demands and the Critical Role of the Mould
The pipe jacking method involves pushing reinforced concrete pipes from a launch shaft to a reception shaft, using thrust stations equipped with hydraulic jacks. During this process, the pipe acts as a structural column transmitting massive axial forces, often exceeding several thousand tonnes.
Any geometric imperfection in the pipe will cause concentrated stress points. If the pipe faces are not perfectly perpendicular to its axis, or if there are variations in wall thickness, the force of the hydraulic jacks will spall or crush the concrete. The steel mould is solely responsible for ensuring that the final precast element possesses the squareness, concentricity, and surface finish required to minimise friction with the natural ground.
Differences Between Pipe Jacking Moulds and Standard Concrete Pipe Moulds
At first glance, a cylindrical mould might appear identical for any application. However, at the level of steel fabrication design, the engineering behind jacking pipes differs drastically from that required for standard drainage pipes.
The Steel Collar and Joint Precision
In jacking pipes, the joint is not a simple bell and spigot. Generally, an embedded steel collar (or band) is used at the end of the pipe, accompanied by an elastomeric compression seal and a pressure distribution ring (usually made of wood or composite materials). The mould must feature highly precise recesses in its bases (top and bottom forming rings) to house these metal components during concrete pouring, ensuring they do not shift by a single millimetre.
Resistance to High-Frequency Vibration
To achieve the high compressive strengths required for microtunnelling (frequently exceeding 50 MPa), very dry concrete mixes with extremely low water-to-cement ratios are used. This requires compaction using high-frequency vibrators attached to the mould (external vibration) or through radial compression systems. The mould must have exceptional structural rigidity, equipped with reinforcing ribs and thick steel plates, to avoid mechanical fatigue or elastic deformation during intensive vibration.
The Risk of Adapting Modular Moulds for Jacking Pipes
One of the most common technical errors in the precast sector is attempting to use modular formwork systems, designed for other purposes, by adding extensions to manufacture jacking pipes. Multiple bolted connections and joints between modular panels create micro-flexing during vibration.
These flexions result in concrete burrs, grout loss, and slight ovalisation of the pipe. In a standard pipeline, this is merely an aesthetic issue; in pipe jacking, an ovalisation of just a couple of millimetres can prevent the pipe from fitting correctly with the tunnelling shield or cause the thrust line to jam mid-drive underground. Opting for custom manufacturing completely avoids these uncertainties.
Geometric Precision: Tolerances, Collars, and Watertightness
As a manufacturer of pipe jacking moulds, it is imperative to establish the framework of permissible tolerances with the client from the preliminary design phase. In heavy steel fabrication applied to this sector, the following parameters are closely monitored:
- Cylindricity and Concentricity: The internal and external diameters must maintain strict consistency along the entire effective length to ensure uniform wall thickness that can withstand concentric loads.
- Squareness (Perpendicularity): The end faces must be rigorously at 90 degrees to the central longitudinal axis. Any deviation generates a dreaded “wedge” effect during jacking, bursting the joint.
- Base Ring Machining: The forming rings that shape the joint are often manufactured from high-precision machined or laser-cut parts, guaranteeing the perfect seating of the steel collar and the rubber seal.
Data Required to Request a Quote for Pipe Jacking Moulds
To expedite the engineering process and obtain an accurate quote, the technical procurement manager must provide detailed information. Avoiding generalities ensures the manufacturer correctly gauges the steel weight and equipment complexity. Gather the following data to request a quote for pipe jacking moulds:
- Diameters and Geometric Milestones: Internal diameter (ID), external diameter (OD), and effective length of the pipe.
- Pipe Drawings and Joint Details: Exact design of the steel collar, type of elastomeric seal, and wooden or compensator ring.
- Plant Kinematics and Handling: Load capacity of available overhead cranes and height under hook. This determines if the mould requires a quick-release design, special hinges, or specific lifting systems.
- Vibration and Pouring System: Specify whether external vibrators (pneumatic or electric) will be used so the correct anti-fatigue mounting plates can be designed, or if another compaction method will be employed.
- Estimated Production: Planned demoulding cycle, which will influence the number of bases (bottom rings) required for each inner and outer shell.
Common Mistakes When Ordering Custom Steel Moulds
In the industrial purchasing process, basing a decision solely on price or the estimated weight of the steel often leads to medium-term cost overruns. A common mistake is underestimating manoeuvrability. A robust mould that is poorly designed at its opening and closing points will drastically increase demoulding times, reducing the precast plant’s daily productivity.
Another frequent flaw is failing to define the watertightness system of the mould itself. Self-Compacting Concrete (SCC), which is increasingly used, is highly fluid. If the steel design of the perimeter closures is not hermetic, grout loss will occur, leading to honeycomb areas on the surface of the jacking pipe and weakening its structure.
Custom Manufacturing: The Competitive Edge of Industrias Relente
Unlike suppliers who simply sell standardised catalogue models, at Industrias Relente we work under a clear principle: we manufacture completely custom-made equipment based on the client’s drawings, measurements, handling capabilities, and real-world conditions. This makes a substantial difference in the day-to-day operations of a precast plant.
The advantage of avoiding modular or standard moulds is that you do not have to adapt the precast element to the mould or settle for approximations; the equipment is manufactured directly for the exact geometry demanded by the jacking project. In numerous projects, this precise alignment between the client’s actual workshop capabilities and our specialised steel fabrication accelerates the start of production and avoids costly post-adjustments, machining, or on-site welding. We apply this same philosophy when designing custom moulds for precast elements as complex as pits, manholes, and heavy box culverts.
Synergies with Microtunnelling Drilling Tools
Supplying infrastructure for trenchless works requires a high-performance tool ecosystem. Civil engineering companies operating pipe jacking equipment often also integrate foundation and piling systems. In this regard, the same demand for robust steel fabrication and precision machining that we apply to our moulds is transferred to our deep drilling tools, such as buckets, augers, and core barrels, ensuring comprehensive and reliable solutions for mechanised excavation.
Practical Checklist Before Contacting the Manufacturer
If you are setting up a new production line or need to renew your equipment for an outfall sewer project or another jacking work, review this technical list before requesting your quotation:
- Do you have the final pipe jacking drawings approved by the project engineering team?
- Are the details of the steel collar clear (thickness, steel grade, width)?
- Has the type of watertight seal (profile, housing) been defined?
- Have you checked the estimated weight of the empty mould + concrete against your crane’s capacity?
- Has the number of necessary auxiliary equipment (extra base rings, lifting spreaders) been decided?
- Have you consulted technical steel fabrication guides to understand the impact of plate thickness on equipment durability?
Frequently Asked Questions (FAQ) About Pipe Jacking Moulds
What are the differences between a standard pipe mould and one for jacking pipes?
The main difference lies in the extreme geometric precision, the thickness of the steel plates to withstand higher vibration energy without deformation, and the complexity of the top and bottom forming rings, which must be prepared to house the metal joint collars required by microtunnelling systems.
Why is it a risk to use modular systems to manufacture jacking pipes?
Modular systems feature multiple bolted connections that yield micrometrically under high-frequency vibration. This causes concrete burrs, loss of watertightness, slight ovalisations, and faces that are not perfectly parallel. On-site, these incorrect tolerances cause the concrete to shatter under the immense pressure of the thrust station’s hydraulic jacks.
What tolerances are handled in the manufacture of the steel mould?
It depends on the project requirements, but in jacking pipes, millimetric tolerances in diameters and squareness are standard (usually less than ±1-2 mm depending on the design code and pipe diameter), requiring steel fabrication and welding processes with strict thermal deformation controls and, sometimes, final machining of key components.
What technical information is needed to quote the manufacturing?
Dimensioned drawings of the final pipe (ID, OD, length), technical details of the steel joint to be used, concrete type, compaction method (external vibrators, etc.), and the client’s plant logistical limitations, such as the maximum lifting capacity of overhead cranes.
The reliability of your production line begins with the proper design of your formwork equipment. At Industrias Relente, we analyse your project to deliver an efficient, durable steel tool perfectly aligned with your technical requirements. If you need to ensure the geometry of your precast elements and avoid on-site failures, we invite you to request a quote for pipe jacking moulds with our industrial engineering team.