The bavarian administration of castles decided to extend the north wing of the castle into an event- and showroom, since that part was untouched since the construction of the building.
For heating, it was considered to use a water/water system operated with the water of the lake. Due to the distance between the castle and the lake, a geothermal system with borehole heat exchangers was chosen. The north wing of the new castle on the island Herrenchiemsee stayed untouched since the construction and since King Ludwig II had died. With the development planning to extend the north wing into a cultural centre it was considered to use geothermal probes already.
Geology, stratigraphy, characteristics
Miocene marine siltstone (“Schlier”), arenaceous marl, calcareous sandstone
Since the island results as a monadnock of the glacier during the last ice age, it was expected to find resistant ground. Due to the considerable energy exchange, it was planned in advance with a drilling depth of 250m. According to the geological map GK 25 Prien, there are Miocene marine siltstone, arenaceous marl of the upper freshwater molasses (Helveticum) and calcareous sandstone. With the local mining authority it was an operating plan concerning mining law prepared and set.
With the pilot hole in July 2009 the expectations were confirmed.
Drilling method, piping, drilling equipment
The cable tool percussion drilling was chosen. The drill cuttings are brought to the top by air pressure. Due to the compact foulded molasses (“Faltenmolasse”), the drill bit moved away slightly and the borehole distance was set to 20m.
Details of the grouting process
The boreholes were grouted with the contractor procedure with a colloidal mixer with its drill stem to the final depth. The calculated amount of grouting material was almost sufficient due to the homogenuous geological conditions, what lead to great satisfaction of the customer and the contractor.