After the flood disaster - House owners convert to gas heating
The flood disaster on the Danube and other nearby rivers in June 2013 caused immense water damages which left numerous home owners in misery and despair. The most most serious damages are those due to soaked walls, ruined gardens or destroyed heating systems. With oil operated heatings, the damaged oil tanks are an additional danger for the environment. For this reason many house owners have decided to have their heating systems converted from oil to gas. This requires a house connection , i.e. the installation of a gas pipe from the transport pipeline in the road up to the resident’s house.
The house owner expects an immediate and cost-effective installation which is only possible on the condition that open trenches are avoided. A further cost optimisation is achieved if as many house owners as possible in one town or in a residential estate decide to change over to gas. In a demonstration project by the utility Bayernwerk in Erlau on the Danube the quick and cost saving installation trenchless method proved to be exemplary and very successful.
In total 5 house connections were to be installed in three different streets, all situated on the same estate close to the Danube. For three of these connections the proven non-steerable GRUNDOMAT soil displacement hammer was applied due to the short bore distances. For the other two connections with bore lengths over 20 m the steerable GRUNDOPIT Keyhole technology was applied.
With the GRUNDOMAT Soil displacement hammer from the cellar to the main service line
The GRUNDOMAT soil displacement hammer is the quickest and most favourable possibility to produce a trenchless house connection. The hammer is ready for application very quickly, simple to operate also due its light weight. The hammer is started after a levelling process through a previously produced core hole bore from the house and pulls a PVC protection pipe OD 63 directly into the bore hole up to the Keyhole during the installation process. After installation of the product pipe the connection to the main line can be made right away and the gas fitting in the cellar can be installed. The core bore hole is sealed off with a building entry set from the inside without the need of any excavation work on the outer wall. If the working steps are well planned, then up to 3 house connection per day can be achieved.
For applying the soil displacement technology the soil conditions and bore length are the decisove factors. Bore lengths of around 10 metres are the usual installation distance in penetrable soils. Extrememly water-bearing and rocky ground can not be penetrated. These conditions define the geo-technical application limits.
The further development of the GRUNDOMAT N generation does now cover „borderline“ soil structures, e.g. loose, pebbled gound which is usually found close to rivers. The most important thing is that the soil displacement hammer reaches the target precisely, avoiding any deviations from the planned pipeline. In critical cases the course of the hammer can be detected and surveyed. Slight deviations are no cause for concern, as long as there is a sufficient distance to adjacent service and disposal pipes. Otherwise the hammer must be retrieved in reverse mode and re-started.
Another aspect which must not be underestimated is the fact that only one head hole is required for the connection to the main pipe. There is no need for the usual head hole to be dug up by hand in front of the house wall, as the soil displacement hammer is started from the cellar. The size of the target pit should be as small as possible to keep costs down to a minimum and usually is the same length as the machine, so that it can be retrieved safely. For these applications short version soil displacement hammers are available.
The GRUNDOPIT Keyhole bore technology
A completely different variation, which was also applied in Erlau, is the steerable GRUNDOPIT Keyhole-Bore technology. Using this technology the bore does not not start from the cellar but the opposite way out of a keyhole from the main service pipe into the cellar. The bore head is detected at the surface and allows for steerable bores up to lengths of approximately 25 m.
The specual feature of this method is the form and size of the keyhole and almost completely automated and remote-controlled bore process. Open minded operators can learn how to operate this bore technology quickly and qualify themselves for new tasks or improve their professional perspectives that way. The keyhole is circular and has a diameter of only 65 cm. It is accessible and can be produced at depths of up to 1,45 m. The operator always stands outside the keyhole which guarantees a higher grade of safety while working.
Another aspect in favour of the keyhole is its circular shape as there are no tension peaks, which is normally the case with the corners of standard rectangular construction pits and often the cause for tears appearing later.
To produce the keyhole a core drill unit bores the road open above the connection point. The bore core is removed and inserted back in place later on. The keyhole is excavated using a suction excavator, i.e. there’s only little excavated material which can be stored practically in a big bag and later be re-instated. The GRUNDOPIT K bore rig is set up inside this keyhole above the pipe, fixed in place and stabilised with extended brackets against the pit wall and above the ground with adjustable support feet. The bore rig is then connected to a hydraulic power unit and ready for operation. The rig works fully automatically and is steered via a remote control. For the bore process special drill rods are transported vertically with a lift to the bottom of the bore and then screwed together horizontally for the bore application.
The drill rods with the bore head are now driven forward successively into the service room of the building, where the bore head is exchanged for a core hole borer and the bore hole in the cellar wall is cut cleanly. Afterwards another tool exchange takes place, namely the core boring borer is exchanged for an upsizing head. Now the PVC protection pipes up to OD 63 can be pulled in.
The drill rods are loosened inside the keyhole one after the other and returned to the surface via the lift. Also with this variation the brickwork is sealed off tightly against gas and water with a buiding enty device without the need of an additional assembly pit.
The connection of the house service connection to the main transport line is part of the sophisticated system solution. As the keyhole is not accessible the line is equipped with the fitting in the form of a plug connection from above, or in this case with a welding connection after the disassembly of the bore rig.
After the bore and pipe installation work is completed the keyhole is filled and seal off layer by layer. The previously excavated bore core is the key which seales off and closes the keyhole almost tension free. Additional asphalting work is not necessary.
The total of 5 bores were all completed to fullest satisfaction of all participants. The bore crew could leave after only 2 working days.
Although the soil displacement technology and the keyhole bore technology function in a very different way the can both be used for the same type of application. Thus it is important to consider fundamental parameters such as soil type, bore length, jobsite surroundings to choose the appropriate installation method.
The keyhole technology will play a major part in the future: This is what network operators are convinced of as well as longer house service lines with difficult bore paths can be completed synchronically without any large jobsite pits (preserving road surfaces).
Both, soil displacement ang keyhole technology, have shown that the installation of gas service lines can be carried out quicker and cheaper compared to the open trench method.