Auger Boring Small Diameter GRP Pipe Under Dutch Railway

In 2010, due to the establishment of new industrial plants in Rotterdam’s harbor, a new 10,000-volt power line became necessary for sufficient power supply. Since the railway network’s safety measures prerequisite a protective pipe for all pressure lines and cables running beneath the railway, ProRail, the company in charge of the Dutch railway network, set about seeking for an adequate small diameter solution.

Quick installation was a crucial factor, so that the usually employed GRE pipe, which has to be glued at the joints was ruled out. ProRail turned to HOBAS Benelux. The easy to handle, light weight HOBAS GRP Pipes are quickly assembled due to their push to fit couplings. HOBAS Benelux had been authorized supplier for pipelines undercrossing the Dutch railway for a decade. Until then, the smallest diameter for HOBAS GRP listed by ProRail had been De 427 mm. Thanks to the flexibility in the design of HOBAS Pipes, the required diameter De 220 Jacking Pipes were produced with a wall thickness of 20 mm to suit the required maximal auger boring force of 148 kN and to comply with all of the network’s other safety measures.
The 36-meter host pipe was installed in 4 m depth within only one day only. The contractor was pleased with the result and further small diameter auger boring and jacking projects beneath the railway were implemented with GRP so that ProRail extended the listed range of GRP diameters by DN 200.

SIDEBAR: Q/A with Duco van Rijsbergen (DVR), Head of Customer Service, HOBAS Benelux

Who can supply pipes for railway projects?

DVR: Not just any pipe can be installed beneath railways. Here in the Netherlands, for instance, the pipe supplier needs to be authorized by ProRail, the company in charge of the Dutch railway network. And in order to enter this list in the first place, the products have to fulfill the requirements and standards of the railway network. These are important safety measures.

Apart from this, the contractors also need a permit from ProRail for installation works beneath the railway. Once this has been achieved they will be given a date and time slot in which the works have to be completed. This can be quite challenging regarding timing and logistics for both the contractor as well as the pipe supplier. Careful planning, flexibility and close cooperation between both parties are crucial.
Are there particular requirements the pipes need to fulfill?

DVR: First of all, they have to withstand the loads from the trains. A pipe installed in 2 m depth, for instance, has to bear a load of approximately 60 kN/m² – this equals 6 tons on 1 square meter. In 4 m depth, there are still 28 kN/m² working on the pipe1. The pipe needs to be rigid enough that ring deformation is below the security margin set by the railway company. If the pipe gives in too much the soil would sink as well as the rails above and this would put train traffic in danger. Our production process allows designing the pipes to suit these requirements perfectly. Continued testing at in-house but also independent laboratories as well as decades of experience and a long track record prove how safe our pipe systems are for this type of project.
Then there is also stray current induced corrosion that needs to be considered. The ground surrounding the rails is a parallel conductor to the rails. Any metal structure in the ground including pipes and cables will attract stray current and corrode. GRP is non-conductive and therefore not affected by this. This is why HOBAS Pipes are often also used as protective pipes for e.g. gas lines or cables.

What advantages do HOBAS GRP Pipes in railway applications have compared to other materials?
DVR: Another remarkable advantage regarding rail applications, apart from being non-conductive, is the GRP material’s weight. HOBAS Pipes are sturdy but at the same time very light compared to other materials. This facilitates their handling. Small diameter pipes of 1 to 2 meter lengths — usually used for jacking — can even be carried to the construction site by one or two workers. Generally speaking, there is less heavy equipment involved which reduces costs and efforts. Low weight also speeds up the installation rate. When you are already pressed for time this is a welcome advantage.
Which installation methods are preferred?

DVR: There are very few open-cut projects. In most cases, the pipes are laid by trenchless methods such as jacking, auger boring or sliplining. These are least disruptive – train traffic does not have to be stopped. Here, in the Netherlands we have about 40 railway crossing projects per year of which around 80 percent are auger bored or jacked and approximately 20 percent sliplined with HOBAS Centrifugally Cast but also NC (Non Circular) GRP Pipes. Thanks to their accurate outer diameters, smooth pipe walls and flexibly designed high stiffness classes HOBAS GRP Pipes are highly suitable for practically all methods.
What applications do you see most often?

DVR: Ninety percent of orders from HOBAS Benelux are for protective pipes hosting pressure pipelines. The carrier pipes usually transport stormwater or sewage, but there are also gas pipes or cables. Reason for this is a safety regulation stipulated by ProRail to which pressure pipes and cables are to be placed in a protective pipe. The rest are gravity pipes. To us it does not really make a difference: Apart from gravity or pressure pipe systems, HOBAS also provides double pipes, meaning that the protective pipe by HOBAS may also host a HOBAS Pressure Sewage or Water Pipe.