An apparatus for sinking a substantially vertical slot in the ground in a single operation or step in making a sealing or supporting wall, e.g. for diverse mining applications, can comprise a machine frame with a rectangular cross section guided in the slot in the ground with a plurality of guide surfaces and at least one driven cutting wheel positioned at the lower end of the machine frame. An example of this apparatus is described in European Patent application No. 0 109 907 published 30 May 1984.
The machine frame comprises an upper guide frame and a lower guide frame. The cutting wheels are mounted on the lower guide frame. A controlling piston-cylinder unit is positioned on the upper guide frame. The unit provides steering control of the lower guide frame about two mutually crossing axes. These axes define respective degrees of freedom which coincide with the axes of the machine frame cross section.
The lower guide frame has a plate which is connected to the opposing plate of the upper guide frame. However, the mounting is accomplished by a resilient member.
The piston-and-cylinder devices are so mounted that the lower guide frame opposing the upper guide frame has two superimposed pivotal degrees of freedom, i.e. it is pivotable about two mutually perpendicular, normally horizontal, axes. However, rotation of the tool about a vertical axis is not possible. Inspite of the described allowed pivotal degrees of freedom, forces can occur in the known device which, especially for large depths, cause deviations from the proper wall alignment or the vertical orientation or plumbness of the slot in the ground. Also, pivoting is not easy in the direction of slot propagation in the ground.
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