The Laer castle in Meschede in Germany, which was the ancestral seat of the Duke of Westphalia Fuerstenberg, is to be converted to district heating. The oil heater will then be switched off, but not completely dismantled. The district heating will be supplied by a wood-fired heating station, providing heating power of 600 kW. When used to full capacity this heating station requires two tonnes of wood chips daily. Horizontal directional drilling (HDD) has been selected in order to protect the properties of the pipes delivered in PE-endless rolls.

The administration at the Duke’s stately home assigned the installation work to the company Bohrtechnik Spiekermann from Schmallenberg. They selected the new Grundodrill 15 XP HDD rig for the job. The bore path runs over a length of 90 m from a forecourt beneath a 12 m wide stable building across the castle’s inner courtyard, right up to the Duke’s residence wing, where all past and present heating systems are situated. Here, the fitters were already preparing two core bores, each with a diameter of 300 mm for the forward and reverse mode of the heating pipes through the 1.6 m thick castle wall.

Inside the stable building, an intermediate pit was excavated. A specific feature of this bore was that this intermediate pit was to be used in order to install two 140 mm district heating pipes with a PE core pipe of 75 mm diameter in one direction over a length of 70 m, and in the opposite direction over a length of 20 m, 160 mm district heating pipes with a PE core pipe 90 mm in diameter. An empty pipe ND 63 for the control cable was also installed.

The soil at a bore depth of 5.5 m was mainly clay-stone. The soil in the target pit area was extremely rocky, partially grown but partially filled with massive quarry stones. The MDH bore head applied was the right choice and the pilot bore was completed in only one day.

The bore head had to work its way up over an extremely short distance of 5 m to a depth of approximately 3 m at a gradient of 30 per cent, directly behind the water pit and just ahead of the castle wall. After this stage of the boring was completed, the bore head could be exposed and the upsizing bores of 200 mm and 370 mm could begin.

The 370 mm backreamer was also used for the installation of the pipe bundle. Due to the very limited space in front of the castle wall and the cold temperatures, the connection of the three plastic pipes to the backreamer proved to be very difficult. Despite these challenges the pipe installation ran very smoothly and only took three hours to reach the intermediate pit. The pipe cross-section was exchanged in the pit and the 160 mm district heating pipe and the empty pipe were connected. The Grundodrill 15 XP required only half an hour for the remaining 20 metres.

The bore team had completed all the work within one week and was able to clear the jobsite. The Duchess and Duke were very happy with the results as they barely noticed any bore work taking place.