In early 2016, Marti Geotechnik approached us with a very special project. Construction of a federal road involves slipping two tunnel jacking pipes beneath a town. In order to avoid possible subsidence in the local geology, compensation injections must be performed beneath the buildings.
To permit drilling of fan-like injection bores, five shafts with a diameter of 5.8 m were sunk into the ground. Overlapping bored pile walls were also created that will be excavated to ground level upon completion. The injection bores to be created were created at a slight downward slope and a length of up to 47 m. An injection screen was created in which the bores are distanced 2 m apart at their target cross-sectional area. The deviation between bores must not exceed 1% of the drilling length. Because of the geological conditions involved, the bores had to be created with casing. The outer diameter of the casing is around NW114.
The strict requirements made it impossible to use the existing shaft drilling machine. Because the existing machine was not in a position to deliver the torque and feed forces needed, the entire shaft drilling machine had to be redesigned.
Only the proven substructure could be retained. The kinematics of the substructure permit the machine to rotate 360° (slewing ring) about its own axis, an inclination of the drilling axis of up to 15° (tilt cylinder) and height adjustment capability of approx. 1,700 mm (shear kinematics). The lower minimum achievable reference mark of the bores is around 1050 mm. Through modification of the mast and installation of a double-head drilling machine, extension and retraction forces could be increased to 100 kN and the torque to a maximum of 28,000 Nm.
All drilling and set-up functions can be precisely controlled via the FFS600 radio remote control. This way, the operator can select his or her location and need not be in the danger zone.
This project tapped all the of the expertise at Morath. Starting with knowledge of the right drilling methods and continuing through to mechanical engineering. All in all, working with Marti Geotechnik, we successfully organised a solid solution.