Bialoleka, the northernmost district of Warsaw, marks the starting point of the Zeran canal, a man-made waterway that connects Warsaw's Vistula river with the Zegrze reservoir and, in turn, the Narew and Bug rivers. Averaging 25m in width (reaching 41m at its widest point) and measuring between 2.5m and 3m in depth, the canal flows from Warsaw's industrial port of Zeran along a course of 17.6km, in places running parallel to the 633 main road, to reach the reservoir, situated close to the village of Nieporet. The canal passes through a lock in Zeran and a weir in Nieporet. Along its entire length, the canal is crossed by one footbridge, eight road bridges and four railway bridges.

While Warsaw is known for its subterranean spring water with more than 100 springs providing the city's inhabitants with drinking water every day it on its own is nowhere near enough to supply the city's entire population of two million. The solution to this issue is the municipal waterworks in central Warsaw which treats water from the Vistula to produce drinking water.

However, the networks of pipes, which were built in the late 19th century, have aged and deteriorated and are in any case not nearly extensive enough. Very few of those old supply lines can be restored, with the majority having to be replaced time and time again with new piping, or in a bid to expand the existing network to incorporate more residential areas, completely new pipes have to be added to the system.

One such new pipeline to supply water from the municipal waterworks was for the Bialoleka district. It involved passing pipeline under both the Zeran canal at its widest point and the 633 that runs parallel to it. This was no mean feat for various reasons, with certain unknown quantities, namely the ground conditions and the course of utilities; a gas line and an electricity cable, giving cause for concern.

With this stretch measuring around 200m in length, laying a pressure line of ductile cast iron pipes (DN 500, 630mm external socket diameter, construction length 6m) under the canal and the main road called for trenchless horizontal directional drilling.

The company contracted to undertake the drilling work was the Pabianice-based firm of Rutex run by Lukasz and Grzegorz Ruta, who made use of a Tracto-Technik supplied GRUNDODRILL 25N. Providing a power output of 190kW and running on biodiesel, it makes light work of drilling tasks with 245kN tensile and thrust force and a torque of 10,000Nm. With a total weight of 18t and a working width of just 2.5m, the GRUNDODRILL25N was the perfect machine for the 200m stretch in Bialoleka.

Assisted by Andrzej Wieszolek of Tracto-Technik, the Rutex team decided which drilling tools to use and determined the composition of the drilling fluid. With no reliable information regarding the ground structure available, the general expectation was for loose sand and gravel, and the drilling equipment had to be chosen accordingly.

The team selected a 150mm diameter soft drill head plus a bentonite suspension with a mixing ratio of approximately 40kg/m3 for the drilling fluid - to act as cutting and pumping medium, a lubricant and coolant as well as a stabiliser for the 200m long borehole.

The DCI F5 detection system was deployed for precision location work - a depth of almost 14m was required at all times. Graduated backreamers were also on hand to expand three planned borehole clearings.

The GRUNDODRILL 25N executed the pilot bore (150mm diameter) as the machinery was guided through the sandy, gravelly subsoil with relative ease. Nevertheless, the pilot bore could only be drilled in individual stages, through no fault of the mechanical power or technology, but owing instead to the various other utilities that were located in unknown underground locations.

Right at the very start of the drilling work, the machine had to be repositioned upon discovery of an intersecting DN 500 gas pipe - a discovery that caused much delay. Further disruption to the pilot bore was caused by a power cable found under the road, the course of which could not be predetermined - this challenge called for extreme caution and finesse.

The pilot bore was completed as an interim step after an initial expansion to 440mm using a medium soil reamer. Two subsequent stages of expansion, to 660mm and 860mm, also used a graduated reamer before the ductile cast iron pipes were finally drawn into the borehole.

Since the water table was extremely high and there was a danger of the pipes rising up once drawn through the borehole, they were weighted down with water. With no hydrants available to fill the pipes, the water had to be transported especially to the site in addition. Last, but not least, the exit point to the bore path, right next to the canal, was very steep, causing further complications that had to be factored into the schedule and the physical plans.

In spite of those complications and challenges, the entire build was completed in just four days, seven hours of which was the pipe installation itself.