Trenchless construction methods are playing an increasingly important role due to their sustainability. There are also many cases where there is no alternative to using trenchless technology, such as when crossing under roads, railway lines or rivers. This was the case in Pont-à-Mousson, France, where a district heating pipeline had to be installed under the Moselle River. Here, it was the combination of two NODIG methods that achieved the goal despite the complicated geological conditions. A GRUNDORAM horizontal ramming machine had to provide initial support in the form of a so-called casing pipe in order to realise this culvert in the form of an almost 300 m long controlled HDD bore under the river.
A pioneer in district heating
In 2016, the town of Pont-à-Mousson on the Moselle became the first town in France to have a district heating network supplied by biogas plants. Initially, public administration buildings were heated, and over the following years more and more homes were connected to the network. Now, in the summer of 2023, as part of the further expansion of the district heating network, the Moselle River had to be crossed with a Ø 560 mm pipeline, for which an 80-ton HDD drilling rig was used.
According to the available soil survey, a water-impermeable clay layer with only small stones was to be expected under the Moselle - ideal conditions for the undercrossing - ideal conditions for the undercrossing using the HDD method. In the riverbank area, however, the soil was very soft and therefore not drillable. Nevertheless, the large area drilling was made possible using the pipe ramming technique by driving a casing on each side of the riverbank through which the controlled pilot drilling could enter and exit. This created ideal conditions for a safe crossing under the Moselle.
The entire Moselle project was entrusted to Groupe Gendry (GSL), which has extensive trenchless experience working with large HDD rigs but does not have rammers in its fleet and has only worked with them to a limited extent. A subcontractor, Forages du Nord-Ouest (FNO) from Normandy, which not only has 28 years of experience with all types of NODIG, but also owns a GRUNDORAM Goliath pipe rammer, was called in to carry out these vital preparatory works.
HDD Assist enables river crossing
Dynamic pipe ramming has long been a proven method for installing media or protective pipes up to ND 4,000 mm in all displaceable soils. The GRUNDORAM is connected to the pipe to be installed by means of an attachment cone and aligned axially behind the pipe. The piston strikes the head of the rammer housing. The resulting impact energy is transmitted directly to the ramming pipe via the attachment cone, which is driven through the ground hit by hit. Obstacles in the ground do not have to be moved, but are crushed, so that the drive is not only powerful, but also precise. As a result of these features, pipe rammers are also ideally suited to the successful completion of complex HDD drilling operations: These so-called HDD Assist & Rescue methods can, for example, support the pipe pull-in with dynamic impact force, loosen stuck drill pipes or, as in Pont-à-Mousson, ram steel casing pipes through non-drillable soils in order to start and end the horizontal bore.
FNO's Goliath is already 12 years old but has lost none of its 18,600 Nm impact force. To enable the pipeline to be installed under the Moselle in the soft riverbank soil, a 30-metre-long, spirally welded steel pipe with a diameter of 1,220 mm and a thickness of 12.5 mm was driven into the ground at an angle of 30 degrees on both sides of the Moselle. To do this, Forages du Nord-Ouest's experienced staff lifted six-metre-long pipes into the construction pit, welded them together and then drove them into place at a quick ramming speed of up to 20 metres per hour. Finally, an auger boring machine was used to remove the soil inside the newly installed casing pipes. This took only three days per casing pipe, even though they had to be reworked in places.
Gentle network expansion thanks to trenchless technology
Once the casing pipes were ready on both banks of the river, the actual installation of the district heating pipeline under the Moselle could take place in October 2023. The first step was to use the HDD drilling rig to create a pilot bore along the route, starting through the casing pipe on the right bank and exiting through the pipe on the left bank. In a second step, the bore channel was widened to accommodate the district heating pipe with a diameter of 600 mm. Finally, the pre-insulated pipe, which is almost 300 m long and weighs 10 tonnes, was pulled into the widened trench in one piece. It runs 40 metres below the water level.
In total, Pont-à-Mousson's district heating network is currently being extended by 10 km, including new pipelines in the town centre. The first phase, which was commissioned in 2015, already covered 10 km on the right bank. Trenchless technology has now made it possible to extend the network on the left bank of the Moselle in a gentle and sustainable way.
A pioneer in district heating
In 2016, the town of Pont-à-Mousson on the Moselle became the first town in France to have a district heating network supplied by biogas plants. Initially, public administration buildings were heated, and over the following years more and more homes were connected to the network. Now, in the summer of 2023, as part of the further expansion of the district heating network, the Moselle River had to be crossed with a Ø 560 mm pipeline, for which an 80-ton HDD drilling rig was used.
According to the available soil survey, a water-impermeable clay layer with only small stones was to be expected under the Moselle - ideal conditions for the undercrossing - ideal conditions for the undercrossing using the HDD method. In the riverbank area, however, the soil was very soft and therefore not drillable. Nevertheless, the large area drilling was made possible using the pipe ramming technique by driving a casing on each side of the riverbank through which the controlled pilot drilling could enter and exit. This created ideal conditions for a safe crossing under the Moselle.
The entire Moselle project was entrusted to Groupe Gendry (GSL), which has extensive trenchless experience working with large HDD rigs but does not have rammers in its fleet and has only worked with them to a limited extent. A subcontractor, Forages du Nord-Ouest (FNO) from Normandy, which not only has 28 years of experience with all types of NODIG, but also owns a GRUNDORAM Goliath pipe rammer, was called in to carry out these vital preparatory works.
HDD Assist enables river crossing
Dynamic pipe ramming has long been a proven method for installing media or protective pipes up to ND 4,000 mm in all displaceable soils. The GRUNDORAM is connected to the pipe to be installed by means of an attachment cone and aligned axially behind the pipe. The piston strikes the head of the rammer housing. The resulting impact energy is transmitted directly to the ramming pipe via the attachment cone, which is driven through the ground hit by hit. Obstacles in the ground do not have to be moved, but are crushed, so that the drive is not only powerful, but also precise. As a result of these features, pipe rammers are also ideally suited to the successful completion of complex HDD drilling operations: These so-called HDD Assist & Rescue methods can, for example, support the pipe pull-in with dynamic impact force, loosen stuck drill pipes or, as in Pont-à-Mousson, ram steel casing pipes through non-drillable soils in order to start and end the horizontal bore.
FNO's Goliath is already 12 years old but has lost none of its 18,600 Nm impact force. To enable the pipeline to be installed under the Moselle in the soft riverbank soil, a 30-metre-long, spirally welded steel pipe with a diameter of 1,220 mm and a thickness of 12.5 mm was driven into the ground at an angle of 30 degrees on both sides of the Moselle. To do this, Forages du Nord-Ouest's experienced staff lifted six-metre-long pipes into the construction pit, welded them together and then drove them into place at a quick ramming speed of up to 20 metres per hour. Finally, an auger boring machine was used to remove the soil inside the newly installed casing pipes. This took only three days per casing pipe, even though they had to be reworked in places.
Gentle network expansion thanks to trenchless technology
Once the casing pipes were ready on both banks of the river, the actual installation of the district heating pipeline under the Moselle could take place in October 2023. The first step was to use the HDD drilling rig to create a pilot bore along the route, starting through the casing pipe on the right bank and exiting through the pipe on the left bank. In a second step, the bore channel was widened to accommodate the district heating pipe with a diameter of 600 mm. Finally, the pre-insulated pipe, which is almost 300 m long and weighs 10 tonnes, was pulled into the widened trench in one piece. It runs 40 metres below the water level.
In total, Pont-à-Mousson's district heating network is currently being extended by 10 km, including new pipelines in the town centre. The first phase, which was commissioned in 2015, already covered 10 km on the right bank. Trenchless technology has now made it possible to extend the network on the left bank of the Moselle in a gentle and sustainable way.
