A horizontal directional drilling (HDD) project in Zurich, Switzerland, has enabled the city to launch an ingenious energy-saving project. With the help of a Vermeer directional drill, the local electric utility has created a system to provide an environmentally friendly alternative to conventional air conditioning and heating by using water from Lake Zurich.

The company behind this innovative idea is the energy company of Zurich (ewz), which supplies water from Lake Zurich for direct and indirect air conditioning and heat pumps to cool and heat buildings along the eastern lakeside. This successful solution significantly reduces the customers’ energy costs and is environmentally friendly at the same time. The drilling part of the project was contracted to the engineering company suisseplan Ingenieure AG, with HDD specialists Schenk AG submitting a successful tender.

The project involved installing two pipelines: a suction line and a return line. The suction line will draw water from the lake and pump it at high pressure (10 bar or 145 psi) into the pumping station. Here, the water will be filtered before being pumped to nearby buildings. After being used in the air conditioning and heating systems of those buildings, the water will be returned to the pumping station, re-filtered and restored to the lake via the return line. While it may sound pretty straightforward, there were some challenges along the way.

Good Preparation Was Vital

A detailed bore path plan is critical to any successful project, so suisseplan and Schenk kicked off preparations by developing one. They also obtained the necessary permits to drill into the lake (a protected area) and to perform fusion welding on the lakeshore promenade.

Schenk decided to use a Vermeer NAVIGATOR® D100x120 directional drill with FIRESTICK drill rods.

“We love Vermeer equipment, and especially the Firestick drill rods. They are one-piece and therefore much stronger, more durable and more reliable than other products available,” said Beni Schenk, one of the company’s directors. A Vermeer MX850 mixing system was set up to mix the bentonite drilling fluid.

Since the operation took place in the depths of a cold Swiss winter, a heated tent was erected over the machine. “This was not only for the benefit of the operator, but to ensure that the bentonite/water mix did not freeze. If it had, it would have forced us to stop drilling,” explained Beni Schenk.

Drilling Gets Under Way

Work began with a pilot bore for the suction line. The bore started in the pumping station, a structure located near buildings, roads and a paved area, making it essential to avoid surface disruption.

With 200 m to drill to the water, Schenk chose a Vermeer Trihawk 3 150-mm (6-in.) drillhead, and a DCI  Eclipse locator plus cable sonde to monitor its progress. Almost immediately, the Eclipse encountered the first of various obstacles that generated unwanted signal interference — in this case, the steel walls of an old building nearby. These not only degraded the signal, but also forced the bore to descend to 22 m. Steel wires anchoring numerous floating buoys to the bottom of the lake put the Eclipse to the test.

“We chose the Eclipse because it’s the most sophisticated locator on the market,” said Beni Schenk. “Although the steel walls and wires produced interference, we didn’t really have any problems following the drillhead. The only real challenge was encountered by the operator who followed its progress from a fibreglass boat off the shoreline, and experienced some seasickness on the windy lake!”

Breakthrough

When the bore reached the water, it took some careful manoeuvring between the concrete piles supporting the promenade before the drillhead arrived at a point where it could safely break through the lake floor.

Divers working from a pontoon then attached the drillhead to a winch and pulled up the drillhead and rods. They replaced the drillhead with a 750-mm fluted reamer with long shark teeth for the backream. This fairly unusual combination of reamer and teeth was chosen to ensure good penetration and mixing of the bentonite with the surrounding loam and clay. All the bore holes on the project were stabilized with a mixture of 25 kg of tunnel gel, 1 liter of EZ-MUD liquid polymer and 1 liter of penetrol per cubic metre of water.

During the pilot bore, resistance from large stones — probably part of an ancient settlement — had already been identified. With the larger reaming drillhead, this resistance increased.

“Encountering ancient settlements underground is one of the risks of an HDD application,” said This Hunziker from Vermeer Switzerland. “For this reason, archaeologists are frequently called in to jobsites to evaluate if there’s a need for archaeological excavations.” A single backream was sufficient to create the required bore size. The 560-mm diameter HDPE pipe was quickly and easily pulled through.

For the return line, a similar process was followed. However, the return line used a 500-mm diameter HDPE pipe. This in turn meant a smaller 650-mm fluted reamer with long shark teeth could be used to enlarge the borehole.

Pulling in both pipes proceeded without any problems, which was remarkable considering their lengths and the circuitous route through soil and water. The suction line was an impressive 270 m long, or three times the length of a standard football pitch, and the return line measured 212 m.

Quick Implementation

In total, the entire project was completed in just two months, with five people from Schenk involved full-time on the project and two divers sub-contracted. Creation of the boreholes and pulling in the HDPE pipes took only six days for each bore. The fusion welding and pressure testing of the 12-m HDPE pipe sections, on the other hand, took 14 days. As this work was carried out on the promenade, it attracted numerous passers by and local residents curious to observe as the two pipelines grew to their final impressive lengths.

The Future Is Water

The staff of ewz was particularly impressed with Schenk’s professionalism. The entire project was completed well within deadline and budget and with minimal disruption to local residents and traffic.
As to the future, ewz and Schenk hope to realise more projects like this in the Zurich area. This innovative application is also attracting significant interest from other electric utilities that may follow ewz’s lead in moving from conventional air conditioning equipment and heating systems to environmentally friendly alternatives.

Hester Regoort
is a technical writer for Two Rivers Marketing, Des Moines, Iowa.

The Drilling Specialists

Schenk AG, based in Heldswil, Switzerland, is a privately owned company with 33 employees that undertakes HDD projects throughout Switzerland. The company was founded in 1969 by Ernst Schenk and is now run by three brothers and a brother-in-law.

Schenk AG owns 12 drill rigs, 13 excavators, two crawler tractors, various cable plows, a new super-long front excavator and various complementary items such as recycling units and rock-drilling equipment. The majority of its HDD units are from Vermeer, ranging from the compact D6x6 to the large D100x120. The relationship between Schenk and Swiss dealer Vermeer AG goes back a number of years.

In a highly competitive market, Schenk stands out from the crowd by developing their own systems to handle any drilling job around. What’s more, if they want a project but have no drill rig the right size to do it, they are happy to invest in the necessary equipment. This means that their collection of drill rigs is extremely comprehensive, whereas many competitors focus on a more limited range. Consequently Schenk can undertake challenging projects that others are wary of accepting — a commitment that has given Schenk an excellent reputation.

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