Construction News - International Construction Industry
Construction News
UmweltBau GalaBau Bau Magazin

Evidence from Sweden: Pipe Express Handles Ground Water Well

STOCKHOLM/SWEDEN, April 15, 2015 – Just a few miles south of Stockholm, the semi-trenchless pipeline installation method Pipe Express saw its only third application worldwide. The special ground conditions made this still young method a economical alternative to an open-cut method of laying the pipe.

By Artur Graf zu Eulenburg and Lasse Lommel (translation)

The new technique developed by machine manufacturer Herrenknecht premiered in 2012 in the Netherlands with the laying of a 48-inch gas pipeline in sandy grounds (Read our report here). In 2014, the second application of Pipe Express was in Thailand for another gas pipeline construction in cohesive soil. Now, Pipe Express was employed for a third time in Sweden. The high ground water level at the site was the crucial factor for the decision towards employing Pipe Express.
In Sweden, Züblin Scandinavia constructed a new fresh water pipe on behalf of Stockholm Water. The pipeline has a diameter of 48 inches which corresponds to 1,220 millimeters and is supposed to have a pressure of 10 bar after completion. On a section of 1,036 meters, the contracting authority decided to use Herrenknecht’s Pipe Express. In this section, the ground was characterized by saturated, loamy soil and soft sediments with a few rock inclusions. The groundwater level reached the ground surface.

Under these circumstances, laying the pipe with a conventional open-cut trench would have required a sheet pile cut off wall over the whole length of 1,036 meters together with measures to cope with the ground water. A very expensive solution, which Stockholm Water and its planning partners Johan Lundberg AB and Sweco Environment AB did not favor much. Thus, they looked for an alternative. The engineering office Johan Lundberg suggested using Pipe Express. The final decision towards the use of Pipe Express was made at the bauma in Munich in 2013, where representatives from Stockholm Water consulted the Herrenknecht booth for detailed information and further advice.
In June 2014, the execution of the project was awarded to Züblin Scandinavia, which was previously not much involved in pipeline construction and entered uncharted waters with the Stockholm water pipeline.

Watch our bi-ConstructionNews reporter’s video from the site to see how fast Pipe Express moves forward. | Video: bi-ConstructionNews

Expectations met

Prior to the actual laying of the pipe, the anchoring of the Pipe Thruster’s counter bearing on the soft and saturated soil held some challenges for the team. After this task was mastered and the Pipe Thruster with a force of 500t was installed properly, the machine setup of Pipe Express took only four days.

The raw pipes are made of steel. They have a diameter of 1,220 millimeters and a wall thickness of 16mm. The anticorrosive coating on the inside of the pipes was made up of a 10 millimeters thick cement mortar lining, while the outside of the pipes is protected by a 6 millimeters thick PE-coating. With a length of 16 meters, one pipe weighs approximately 10 tons.
At the construction site, the single pipes were welded together to strings of 200 meters each and prepared for installation. For this reason, the drive of Pipe Express and the propulsion of the pipe had to be paused after every 200 meters in order to weld the next string onto the already installed pipe run.

The aligning of the pipeline included several bends, the overlaying ground ranged between 0.5 and 2.5 meters. Crossing cables were temporarily disconnected or re-routed. Just like it was the case at the successfully completed projects in the Netherlands and Thailand, the propulsion of Pipe Express in the grounds of the Sweden site proved to be smooth. The drive speed reached 70 centimeters per minute; the highest day performance achieved counted 221 meters in a 12 hours shift.

Pipe Express trenching unit at work

All you can see aboveground: The trenching unit conveys the excavated soil from the tunnel boring machine to the top and backfills it into the narrow trench. | photo: bi-ConstructionNews

International Interest

Pipe Express commenced operations on February 22nd and the tunnel boring machine successfully reached its target after 11 days. Karl Öhman from Züblin Scnadinavia, construction supervisor at the site, was contended and spoke of a smooth construction sequence. Öhman praised Pipe Express as an excellent technique, which met the expectations in Stockholm. Based on the experiences gathered on the site, Züblin Scandinavia would now be ready to offer Pipe Express as an interesting alternative to the conventional pipeline laying, said Öhman, given projects fulfill the necessary conditions.

The project in Sweden was met with great interest among experts. On site, brisk visitor traffic prevailed. Authorities and contractors, not only from Sweden but the whole world, from Russia to South Africa, visited Stockholm in order to inform themselves about Pipe Express’s performance live and in practice. Lutz zur Linde and Michael Lubberger, Herrenknecht’s sales and product managers for Pipe Express, were delighted. “We are absolutely convinced of the technical assets of this installation method. Now, it remains an important task to increase the international awareness of Pipe Express. And in this aspect, the project in Sweden was a big step ahead”, commented Lubberger.

Herrenknecht Pipe thruster in Sweden

Many international visitors take a look at the Pipe Thruster at work. With a thrust force of 500t, it pushes the pipeline into the ground. Its installation was difficult due to the soft, saturated soil. | photo: bi-ConstructionNews

Pipe Express

Pipe Express is a semi-trenchless installation method which was developed by the German underground specialist Herrenknecht. It is composed of two elements. The first is the so-called Pipe Thruster, which pushes the pipe forward horizontally. In Sweden, a model with a thrust force of 500t was employed. The second element is a trenching unit which is combined with a tunnel boring machine. The tunnel boring machine is mounted at the front of the pipeline. It digs the actual tunnel with diameters of up to 1.50 meters and lays the pipeline at the same time. The trenching unit directly conveys the excavated soil aboveground. No further jetting liquid is required to remove the loosened soil, which is directly backfilled in the trench behind the machine. Pipe Express is suited to lay steel pipes with a diameter between 36 and 60 inches. Currently, Herrenknecht commits to the laying of up to 2,000 meters long pipelines at a maximum driving speed of 1.5 meters per minute. The overlaying ground may range between 0.5 and 2.5 meters.