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Pipes

The most common materials used for pipe jacking are concrete pipes or vitrified clay. Steel and glassfiber reinforced plastic (GRP) are other materials used in certain circumstances.  The choice of material can be influenced by the pipe diameter, length of drive, ground conditions or the intended end use of the pipeline.

Concrete jacking pipes

Concrete jacking pipes should be obtained from a certified manufacturer and be manufactured to the recognised standards, or the local equivalent. This will ensure they can achieve the loading strength to resist jacking forces. Pipes are available in lengths between 1 and 4 metres and are designed such that the jacking forces may be transmitted along the pipeline without damage to the joint. Flexible joints must be watertight at given draw and deflection limits.

Vitrified clay pipes

Vitrified clay pipes for microtunnelling and pipe jacking are manufactured to achieve a high axial strength. They are made to withstand jacking forces and any future ground loads during their lifetime. Pipe ends have an accurate joint profile with collars (typically stainless steel) and rubber seals. Pipe length varies according to the microtunnelling system used, the pipe diameter and constraints of space. Typical pipe segment lengths usually range from 1 to 2.5 metres, although lengths of 0.75 metres are available for small diameters and longer pipes are sometimes available.

Joint deflection and the joint face geometry

Probably the most important aspects of design in respect of pipes for a pipe jack project are the allowable degree of joint deflection and the joint face geometry. In general, the deflection at the pipe joint face should not exceed 0.5°. To ensure squareness, the joint face should be manufactured to the recognised standards, or the local equivalent. Pipes for both microtunnelling and pipe jacking contain the entire joint within the normal pipe wall thickness.

Packer material

Concrete and clay pipes must also be fitted with a suitable packer material to ensure the even distribution of the jacking force across the joint. This prevents damage to the ends of the pipes during the jacking process. Medium density fibreboard (MDF) has been found to be the best material from which to fabricate joint packers. If GRP pipes are being used, no packer rings are needed.

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