Trenchless techniques have been used in Poland since the early 1990s when investment in transportation business required tunnelling under roads, railways and congested urban areas to avoid disruption and damage caused by excavation.

The popularity of No-Dig technologies has increased due to the development of remote-controlled drilling equipment and the introduction of hydraulic excavation. Today, a great range of trenchless options are employed for installing or rehabilitating underground infrastructure such as sewers, water mains, gas, energy and communications lines, tunnels and underpasses, road and railway drainage, hydro-technical culvert and eco-culverts; including animal underpasses.

Pipe jacking and microtunnelling

The various methods and drilling equipment led to categorising Trenchless Technology depending on the type and scope of work and application.

In the pipe jacking process, pipes are exposed to great horizontal and vertical loads. This is why mechanical strength, pipe joints and the roughness co-efficient of the exterior pipe surface determine if pipes are suitable for this type of installation. Once the line has been installed, the material is once again put to the test as it needs to resist hydrodynamic loads from rinsing.

Trenchless education

Poland also invests in trenchless research and relies on its numerous technical institutions, colleges and laboratories whose results are promptly put into practice. Recent analyses conducted by the Civil Engineering Institute of the Wroclaw University of Technology were presented at the 2010 World Tunnelling Congress held in Vancouver, Canada.

Pipe in Poland

In Poland, centrifugally castglass fibre reinforced plastics (CC-GRP) pipes, reinforced concrete, as well as polymer-concrete and stoneware pipes are commonly used for microtunnelling. CC-GRP is favoured for a variety of reasons. The composite thermoset pipes are available within a range of diameters (up to DN 3,000 mm), high rigidity and high corrosion resistance. They are comparably light walled, are available for non-pressure as well as gravity applications and are optimally suited for the forces they are exposed to during jacking. Due to the production process, the pipes’ exterior and interior walls are very smooth, which creates little friction during the installation and provides excellent hydraulic conditions for optimal service.

In Poland, the static-strength calculations for pipes installed by microtunnelling are tested according to the guidelines of ATV-A 161. The tests are carried out by microtunnelling engineers, sometimes in consultation with the pipe suppliers. In extremely challenging cases, when computer modelling becomes necessary, the calculations may be conducted by specialised research institutions.

The ATV-A 161 guidelines can determine the minimum pipe wall thickness for the length of drive designed. These calculations include defined safety co-efficients, and regard material parameters and the designated installation technology. It is a commonly applied method that forms the basis for calculating microtunnelling ducts irrespective of the utilised material.

In the case of CC-GRP pipes, the compressive strength characteristically amounts to 90 MPa. Due to a wide range of wall thicknesses, up to twelve types for each diameter, the calculations allow contractors to choose the optimal thickness constituting the most economically justified solution. The material’s high compressive strength results in a small wall thicknesses and therefore smaller exterior diameters at required interior diameter. Lower jacking forces are thus necessary and costs regarding the installation process, as well as hoisting equipment and thrust pits, are reduced. Less excavation material leads to less transportation costs and less emissions.

Thanks to the material’s high resilience (a relatively low Young module at high compressive strength) it is not necessary to use wooden separators, rectilinear microtunnelling, in bends of angle joints connected with the pipe control. Apart from the previously mentioned characteristic compressive strength, the material is characterised by a relatively high longitudinal strain of 0.7 per cent. Tests conducted over a span of 25 years at the Universities in Bochum, Dortmund and Illinois confirm these properties. In practice, numerous contractors look back on an array of successful CC-GRP installations by microtunnelling on straight as well as curved routes.

Groundbreaking in Poland

The first major microtunnelling project using GRP pipes was from 1997–1998 in Toruń, Poland. After the successful installation of the 973 m long collector, with a diameter of DN 1,600 mm, glass fiber composites became more widely applied for microtunnelling across the entire country.

Impressive jobs such as the Ślęża collector in Wrocław, or the collector under Prymasa Tysiąclecia Street in Warsaw followed soon after. The latter implemented in 2001–2003 was, at the time, the largest jacking project in Europe and represented a technical milestone. The works were conducted in water in a depth of 9–11 m carrying sand and clay, which was difficult to separate from the drilling fluid. The 6 km long pipeline route was divided into five sections of which the longest, 470.5 m, was executed with three intermediate jacking stations.

Bentonite was injected in all sections to reduce friction between pipe and soil, keeping the necessary jacking forces beneath 6,500 kN. Despite challenging conditions, the DN 2,400 mm diameter CC-GRP pipeline, with a nominal stiffness of 32,000 N/m2 and a 76 mm thick wall, could be jacked with extraordinary precision, deviating less than 1 cm.

An even greater challenge on the technical level was met and completed with a further project in Warsaw. A 3,000 mm OD CC-GRP collector was jacked to connect the west of Warsaw to the wastewater treatment plant ‘Czajka’ in 2010. The 7.1 km of pipe was jacked in two sections. There was an 840 m section of pipe that was meant to be jacked from both ends, meeting in the middle. However, due to the accuracy, the installation was able to be jacked in one single drive.

The contractor followed the project plan and erected an intermediate station every 100 m. Only the last was put into service to make sure that the last drive, at 1,200 tonnes, would run smoothly. In the second stage of the project, pipes were jacked beneath the main road of the district Bialoleka. An open trench would not have been possible since the construction works would have impaired the traffic on the three-lane road. A single drive over 910 m was then the longest single drive in the project.

Rehabilitation

Trenchless rehabilitation methods have developed parallel to jacking and boring installations in Poland. They are commonly applied for underground networks in cities – particularly those which are difficult to access. In general, these technologies can be roughly divided into several groups:

• FFP – fold and form pipe – or close-fit renewal
• CIPP – cured-in-place pipe renewal
• Insitu applied coatings – these do not lend structural strength to the renovated line but serve to increase durability and lend tightness
• Sectional sliplining with adapted profiles.

In Poland, GRP is also used for these installations, especially for renewing large diameter conduits. The first large diameter project was a 3 km long collector with a diameter of 1,600 mm with GRP profiles and was reconstructed in Wrocław in 1999.

The success of this undertaking and the experience gained in the course of its execution triggered further rehabilitation projects across Polish cities. For the renewal of non-circular structures GRP profiles are often the only technical solution that not only re-establish or improve the line’s original efficiency in terms of tightness and hydraulic properties, but also increase its structural strength as exemplified in the renovation of an old sewage collector in Cracow 2009. The GRP profiles were fully adapted to the given structure to maintain the hydraulic capacity of the channel. This included the fabrication of a shelf.

Infrastructural plans

Like many other countries in the European Union, Poland has seen the importance in using Trenchless Technology within its urban infrastructure. This can be shown through the program that was instated by the Decree of the Council of Minister in 2004, which says the majority of newly installed or rehabilitated infrastructure should use Trenchless Technology.

The benefits of pipe jacking and microtunnelling in Poland highlight the importance of using trenchless techniques when it comes to urban infrastructure. Having the right equipment and guidelines can reduce costs and environmental concerns.