The separation of a project into straight sections with bends only inside of the jacking pits often requires more and deeper jacking pits. With the help of curvature drives the quantity and the depth of these jacking pits can be optimised. On the other hand, curved drives require special jacking equipment and a special design of the allowable jacking forces.

The curvature always results in an angular deflection of the joints and an eccentric longitudinal loading of the pipes. The eccentric longitudinal loading has to be considered in particular by the calculation of the maximum allowable angular deflection of the joint between the pipes and the maximum allowable jacking force of the pipes.

The pipe system

Centrifugally cast GRP jacking pipes have a long record in Europe, Japan and the United States, with more than 500 km of pipes installed by the jacking method. The pipe has been supplied to jacking projects for more than 20 years, displaying properties such as corrosion resistance, ruggedness, solid walls and a maintenance free life. HOBAS GRP pressure pipes are so far the only GRP pressure pipes on the market that can be jacked.

Because of the high compressive strength, the pipe has a smaller wall thickness and therefore a smaller external outside diameter than most of the other conventional pipes for jacking. Excavation, lubrication and equipment costs are also reduced because of the smaller external diameter.

The jacking pipe is available in diameters from DN250 up to DN3,000 in unit length of 1, 1.5, 2, 3 and 6 metres. The jacking pipe is designed either for gravity or for pressure applications up to PN10. The coupling of the pipe is available in GRP and stainless steel. The allowable jacking force of centrifugally cast GRP jacking pipes is dependant on the wall thickness, with other wall thicknesses available on demand.

Testing times

Over the past 25 years, dozens of independent verifications of the properties of centrifugally cast GRP pipes have been performed. Tests have been carried out by testing samples of strips and full pipes under centric and eccentric loads.

At the University of Illinois, the University of Bochum, the University of Dortmund and at the test laboratory of IKT Gelsenkirchen, full length pipes in diameters between DN500 and DN700 were tested.

In 2005, at the University of Aachen, a test of centrifugally cast GRP pipes under a cyclic angular deflected joint was carried out. The findings were that this pipe react linear elastic under eccentric longitudinal loading. While the pipe was loaded by a longitudinal force, the pipe ends were moved ±20 cm square to the pipe axis and the longitudinal stress and strain were measured at the spigots and over the pipe length.

The material properties of:

σa= 90 N/mm²

Σa= 0.7 per cent

The ultimate compressive stress in axial direction and elongation at break in axial direction was verified under these test circumstances. The Warsaw Project E1

Warsaw Waterworks designed a 3.5 km gravity sewer pipeline with a diameter of 2,000 mm for the connection of a downtown living quarter with the new sewer treatment plant Czajka. The pipe was installed at a depth between 4.7 m and 10.6 m to achieve a slope of 0.063 per cent. The maximum expected groundwater level was 2 m below the surface.

Particular challenges of the pipeline route included the crossing of the Warsaw Underground railway with a distance of only 0.6 m, the crossing of a main railway to Warsaw Main Station and the crossing of several sewers. Warsaw Waterworks selected a jacking installation with curved drives in a minimum radius of 200 m to overcome these obstacles, and because the installation was partially under very narrow roads.

Warsaw Waterworks choose centrifugally cast GRP pipes for several reasons. The company had a decade of a good experience of installing more than 10 km of GRP pipes in diameters between DN1,000 and DN2,400. The high corrosion resistance would ensure a long lifetime and the hydraulics would provide a high flow capacity.

The project was contracted in mid-2006 and started in October 2006. The pipeline was partitioned in 15 sections for the installation. The longest drive had a length of 543 m with a curve with a radius of 40 m. In order to satisfy the various requirements of all sections, the contractor finally decided on three different pipes. For the straight sections a pipe with a nominal stiffness of 32,000 N/m² and an allowable jacking force was selected. For the curved parts pipes with a nominal stiffness of 50,000 N/m² was selected in a unit length of 1.5 m giving an allowable jacking force of 3,600 kN for the 300 m radius and in a unit length of 1 m and an allowable jacking force of 3,000 kN for the 200 m radius.

The Zielona Gora Project in Poland

A pipeline with a diameter of 1,000 mm and a length of 63 m had to be built in Zielona Gora, Poland in 2003. The City of Zielona Gora opted for a curved jacking installation in consideration of the difficult traffic situation. The location of the pipeline was downtown, under a road, between an egg shaped sewer DN700/1,000 and the foundation of a multi-storey building.

The route with the least disturbance to traffic was a curved drive with a radius of 90 m. The client was fully aware of the risk of a drive with a radius of 90 m. However, because of previous good experience with several curved drives with GRP pipes with 1,200 and 1,400 mm diameter, the City of Zielona Gora approved the installation of centrifugally cast GRP DN1,000 pipes with an external diameter of 1,099 mm and a nominal stiffness of 160,000 N/m².

These pipes were designed for an allowable jacking force of 4,000 KN for the straight sections and for 1,400 KN for the curved drive. All the pipes that had to pass the curve had a unit length of 1 m, while the rear straight section used 3 m long pipes. Despite the technical challenges up to 24 m per day was successfully installed.

The Hexbach Project in Essen Germany

In the city of Essen, Germany, Essen Waterworks decided to construct a new pipeline with a diameter of 2 m over a length of .1 km to replace an old corroded and leaking sewer. The only available route for the installation of the new pipeline was a green zone and a park area in the southwest of the city.

Because of these environmental considerations, Essen Waterworks decided to construct the pipeline using centrifugally cast GRP pipes installed with microtunnelling. In order to minimise the disturbances, a route of three curved drives with two jacking and two reception pits was planned.

The first drive had a length of 450 m including a curve in a length of 375 m with a radius of 600 m. The second drive had a length of 840 m including an S-curve 490 m long, with a minimum radius of 600 m. The last drive had a length of 820 m including a curve of 640 m with a radius of 1,000 m. The selected pipe has an outside diameter of 2,047 mm and a wall thickness of 81 mm. The centrifugally cast GRP pipes are designed for an allowable jacking force of 9,000 KN for the straight parts of the drives and for 6,000 KN for the curves with a radius of 600 m. The installation was carried out by a jacking machine with an open front. The soil was transported by trolleys. For the prevention of pipe damage, the angular deflection of the joints was permanently measured and controlled by the system CO-Jack.