Sigmaringen in Germany is known for the castle of the sovereigns of Hohenzollern-Sigmaringen. The geology and hydrology of the region is moulded by glacial and pro-glacial broken rock troughs stemming from the rivers Danube and Lauchert and characterised by massive, bedded and also fissured rock formations, especially hard limestone from the Late Jurassic.
Within the vicinity, only 4 km away from this location fraught with history, the castle ruin Hornstein looms majestically on a ridge. High above, on the brow of a hill in the immediate neighbourhood of the castle ruin entrance, the steerable drill rig GRUNDODRILL 18ACS was brought into position.
Here, the community Bingen near Sigmaringen and the network operator EnBW wanted to install a line bundle consisting of three HDPE pipes 75 x 6.8 mm and 4 HDPE pipes 50 x 4.6 mm. The project was to be completed without trenches. The existing above ground level pipelines would have required pricy rehabilitation but after the new installation under ground they could be removed. The empty size Ø 75 pipes were intended for future use. One Ø 50 pipe was intended as a protection pipe for glass fibre cables. The other Ø 50 pipe were to serve as protection pipes for power cables. The new buried power cables were also to be used by the local operator of a biogas and photovoltaic plant which generates a total electricity of app. 550 kW that is fed into the electricity network.
The 100 m long bore has several complexity factors: besides the prevailing rocky ground consisting of hard Jurassic limestone (compacted lime), there is also a difficult terrain with up to 58 % inclination and a thick tree and shrub population. The company GAUPP Erd- und Tiefbau GmbH from Engen Welschingen was commissioned to carry out the installation works, supported by the company TT branch in Altbach near Stuttgart, who provided the GRUNDODRILL 18ACS rock drilling system.
Rock drilling - particularly in alternating rock structures - is the strong point of the GRUNDODRILL 18ACS. The pluggable inner tube of the twin tube rods is responsible for the drive of the roller bits during the pilot bore. The bits are arranged along the tip of the 1.55 m long rock breaker. The torque, with a maximum of 2500 Nm, is transmitted and utilised optimally.
The outer tube steers the rock breaker. The inclination angle is 1.75°. The transmitter for detection is positioned immediately behind the roller bits; this arrangement allows tracking and recording the bore shortly behind the bore head. The measuring system DCI F5 was applied for detection.
The extreme, unstable and slippery location on the slope demanded a safety cable as a special measure for the machine operator’s security.
The drilling depth was app. 5.70 m. The pilot bore with 160 mm in diameter was completed successfully after a single working day. Now the pilot bore hole had to be upsized to app. 300 mm. To do so, the hole opener was disassembled and a 12“ rock breaker which was connected to the drill rods and then pulled back. These working steps, interrupted only for mixing the drilling fluid, also required one working day. However, pulling in the pipe bundle was finished in only 1 ¼ hours.
All in all, this was a successful measure which was completed within only three days and was well received with lively interest by all, particularly the residents.