EP0095134A2 - Method and apparatus for drilling - Google Patents

Abstract

In order to produce even large boreholes with a good verticality, without the need for special measuring measures and special adjustment processes, a drill head which can be rotated by means of drill rods is brought into a position after drilling a drilling section while reducing its radial working dimension, in which it is free, without a supporting system hangs on the borehole wall, on the drill pipe, then a guide device is fixed to the borehole wall and then the radial working dimension of the drill head is increased again before or at the start of the next drill section. An advantageous device, which is particularly suitable for carrying out this method, contains a bracing device with a guide part and a drilling head (1) which has at least one tool which can be moved from an external working position to a further internal position and vice versa.

Description

The invention relates to a method for drilling substantially vertical bores, in particular large-hole bores, shafts or the like., For a drill head rotatable by means of a drill rod or the like. after drilling a drilling section, the drilling direction is specified using a device that can be fixed relative to the borehole wall.

The object of the invention is to provide an advantageous method for producing substantially vertically directed bores of the type specified at the outset, with which relatively large boreholes, in particular also over about 1.5 to 2 m, can be drilled with good verticality when working with rotating drill rods to let.

Furthermore, the invention is intended to provide an advantageous device for drilling a hole with good verticality.

To achieve the object, the invention provides in a method of the type mentioned that the fixable on the borehole wall device is solved, the drill head is brought in a stationary state in a hanging position on the drill string and then the direction for the next drill section is determined, whereby the diameter of the drill head is changed from a relatively larger to a relatively smaller value to determine the direction for the next drilling section.

With such a method, it is possible in a particularly simple manner to produce even large boreholes with good verticality, without the need for special metrological measures and special adjustment processes. Rather, it is sufficient to simply fix the direction with the drill head hanging. If there had been a deviation from the vertical in the previous drilling section, a correction will then be made in the next drilling section, the drilling head possibly processing a crescent-shaped area of the rock. The verticality will then be reached again very soon, be it in the immediately following drilling section or in the case of a very large deviation in the following drilling section or sections.

There are also various possible implementations for the method. Thus, it is once provided that, in the case of two successive and possibly also further drilling sections, each of these is drilled with the relatively larger diameter of the drill head. The diameter of the drill head that is reduced to determine the direction for the second drill section is then increased again before or at the start of this second drill section.

In another embodiment, it is provided that in two successive and possibly also further drilling sections, each of them is drilled with the relatively smaller diameter of the drill head and the diameter of the drill head is only increased between the two drill sections and with this diameter at least one approximately corresponding to the drill head height Length is drilled, that afterwards the diameter of the drill head is reduced again, then in the hanging state of the drill head the direction is determined for further drilling and then the next drilling section is drilled.

The drilling of the limited length section with the larger diameter advantageously takes place within the drilling section preceding the new direction specification, i.e. within the corresponding stroke of the drill head movement relative to the tensioning device. Drilling with the larger diameter can be done in the downward direction. However, it may also be advantageous, after completion of a drilling section in the downward direction with a small diameter, to drill a certain length with the larger diameter again upwards, that is to say also within a stroke which is possible without loosening the device which can be fixed to the borehole wall. The loosening of the same occurs only when the drill head is brought into the bore area with the larger diameter and is to assume its state hanging on the drill pipe.

Finally, the possibility is also included of drilling a length with a larger diameter after completion of a drilling section in a separate intermediate step, for which the device which can be fixed to the borehole wall is brought into a position which provides the required stroke.

When speaking in this description and in the claims of an enlarged or reduced or of a relatively larger and relatively smaller diameter of the drill head, this should not only mean a maximum and a minimum working diameter of the drill head in the sense of two possible states, although this will be the case in most cases, but diameters in a range between a maximum and a minimum diameter can also be considered, which then become differentiate relatively larger and relatively smaller.

The term “drilling section” is not only to be understood as meaning that the full stroke of the drill head is used relative to the device that can be fixed to the borehole wall, but also a section that can only make up part of this stroke.

An advantageous device for drilling substantially vertical bores, which is particularly suitable for carrying out the described method, is characterized according to the invention in that the boring head has at least one tool which can be moved from an external working position to a further internal position and vice versa, by the tool Adjustment of the working diameter of the drill copies can be reduced and enlarged.

The range of such movement of one or more tools or groups of tools can e.g. taking into account a certain drilling stroke, also in the sense that the movable tools can only assume two positions, namely an outer and an inner one. The design can also be made so that the tools are adjustable in intermediate positions between the end positions.

In detail, the drill head can be designed in various ways, in particular also in the manner of an extension drill, undercutter or the like. The tool, which can be moved from the outside inwards and vice versa, can be arranged pivotably and / or displaceably on a drill head or base body. Accordingly, several tools can be moved together in groups in the specified manner.

Although drive devices of various types can be considered for the execution of the movements of such tools, the invention provides in particular hydraulic actuation devices, namely piston-cylinder units.

In an embodiment in which the clamping pieces of the tensioning device are displaceable by means of hydraulic piston-cylinder units, the design is advantageously made such that the piston-cylinder units for the clamping pieces and the hydraulic actuating devices for the movable tools on the drill head, on the one hand, in the sense an outward movement of the clamping pieces and the tools can be acted upon separately with pressure medium and on the other hand can be acted upon together with pressure medium in the sense of an inward movement of the clamping pieces and the tools. In addition to hydraulic oil, water can also be used as the pressure medium.

If the device is designed in the manner specified above, in particular a pressure medium supply line for the actuating devices of the movable tools can be guided through the drill string or formed by it.

The piston-cylinder units for the clamping pieces are advantageously unlockable check valves or other suitable hydraulic locking blocks or the like. assigned, which results in a simple system.

In a further advantageous embodiment of the device, on the clamping pieces or on parts movable with them, e.g. Piston rods, brackets or the like. Acting elements are provided, through which control elements can be indirectly or directly actuated to influence the outward movement of the clamping pieces. As a result, the adjustment process of the clamping pieces against the borehole wall can be made particularly inexpensive, in particular also with regard to the uniformity of the last part of the adjustment or the pressing against the borehole wall.

The action elements can be parts of different types, including limit switches or the like. According to a special feature, movable sensing elements are provided on the clamping pieces or on parts connected to them for simultaneous movement, which protrude outwards over the clamping pieces in the idle state so that they come into contact with the borehole wall in front of the latter and then pushed back by a certain amount can be. The drive system for moving the clamping pieces, namely a hydraulic system, is advantageously designed with appropriate control elements in such a way that all clamping pieces first come into a position in which the sensing elements have come into contact with the borehole wall and only then a last relatively small one of all clamping pieces Distance is traveled through which the clamping pieces are pressed against the borehole wall at the same time. The previous routes may vary depending on the local situation. In the case of a hydraulic system, the desired sequence can be achieved with the aid of valves, in particular different pressure stages being switched in succession.

• Fig. 1 eine Ausführung der erfindungsgemäßen Vorrichtung, teils im vertikalen Längsschnitt, teils schematisch, in einer Arbeitsposition,
• Fig. 2 die Vorrichtung nach Fig. 1 in frei hängender Lage,
• Fig. 3 einen Schnitt nach der Linie III - III in Fig. 2,
• Fig. 4 die Stelle F in Fig. 3 in größerem Maßstab im Schnitt,
• Fig. 5 die Vorrichtung zu Beginn eines weiteren Bohrabschnitts,
• Fig. 6 eine Ausführung eines Druckmittelsystems für eine Vorrichtung der in Fig. 1 bis 5 dargestellten Art,
• Fig. 7 und 8 die Vorrichtung bei einer anderen Ausführung des Verfahrens,
• Fig. 9 eine weitere Ausführung eines Druckmittelsystems und
• Fig. 10 eine Einzelheit an einem Spannstück.

Further details, features and advantages of the invention result from the following explanation of exemplary embodiments, from the associated drawing and from the claims. Show it:

• 1 shows an embodiment of the device according to the invention, partly in vertical longitudinal section, partly schematically, in a working position,
• 2 shows the device according to FIG. 1 in a freely hanging position,
• 3 shows a section along the line III-III in FIG. 2,
• 4 shows the location F in FIG. 3 on a larger scale in section,
• 5 shows the device at the beginning of a further drilling section,
• 6 shows an embodiment of a pressure medium system for a device of the type shown in FIGS. 1 to 5,
• 7 and 8, the device in another embodiment of the method,
• Fig. 9 shows another embodiment of a pressure medium system and
• Fig. 10 shows a detail on a clamping piece.

In the drawing, the numeral 1 denotes a drilling tool in the form of a drilling head, the base body 2 of which, with roller chisels, cutting rollers 3 or the like which are only indicated schematically at individual points. is provided. In addition, the boring head 1 has at least one cutting roller 4 to be addressed as a caliber tool in this embodiment, and its carrier designed as a two-armed lever 5 is pivotally mounted on a pin 6 such that it is actuated by an actuating device 7 from a working position (FIGS. 1 and 5) projecting radially outward beyond the contour K of the base body 2 of the drill head 1 into a retracted inner position (FIG. 2 and 6) and vice versa. 1 to 5, the cutting roller 4 is in its retracted position even within the outer contour K of the drilling head 1. In another embodiment, however, such cutting rollers 4 can also have their inner position over the contour K of the base body 2 of the Project head 1 without thereby leaving the basic principle of the invention. The desired result can be achieved with various designs of such drill heads and movable tools. 6 shows two tools 4 that can be adjusted in the aforementioned sense. With a drill head with a maximum working diameter of 4.0 m, the diameter reduction is advantageously at least 0.2 m.

The actuating device 7 for pivoting the respective cutting roller 4 is in particular a hydraulic piston-cylinder unit (cf. FIG. 6), which is connected in a suitable manner in an articulated manner to the carrier 5 of the cutting roller 4 via a push or piston rod 8. In the working position, the carrier 5 of the cutting roller 4 bears against a stop 9 on the base body 2 of the drill head 1, so that a secure absorption of all stresses is ensured.

The drill head 1 is connected to a drive shaft 10 to a befind in a known manner by einer.über days _-. Union usual means of rotationally drivable, in Figure 1 only, indicated by dash-dotted drill string G connected. It can be a screw rod or a flange rod. Both the drill pipe G and the drive shaft 10 are particularly advantageously hollow, so that a drilling process with flushing can be used, in particular according to the principle of the air lifting process.

In the area of the device which adjoins the drill head backwards, a bracing device, designated overall by the number 11, is arranged. As a guide part, this has a frame-like support body 20, to which four radially directed pressure medium cylinders 12, which are regularly distributed over the circumference, are fastened at two levels E1 and E2 which are at a vertical distance from one another. The retractable and retractable pistons 13 (FIG. 6) with the piston rods 14 carry at their ends clamping pieces 15 in the form of plates, shields or the like, which are held on the piston rods in an angularly movable manner and which are against the wall W of the drill head 1 Drilled hole B can be pressed and then hold the support body 20 firmly in the clamped position.

In the embodiment shown, the support body 20 forming the guide part of the tensioning device 11 surrounds a one-part or multi-part load weight, designated overall by the number 30. In the example shown, this consists of a housing 31 which is filled with lead, concrete or another material 32 suitable for weighting. It rests on a foot part 33, on which the bearing 34 of the drill head 1, which is indicated only largely schematically, is located in the axial and radial directions. Corresponding recesses 35 are provided in the load weight 30, which between the the drill head 1 and the clamping device 11 offer the required space for the cylinders.

The loading weight 30 is designed and mounted in such a way that it interacts with the guide part 20 of the tensioning device 11 in such a way that, in the tensioned operating state, the direction of the drill head 1 is correct. In this case, guide strips 36 made of suitable material are attached to the housing 31 or a part connected to them, which slide on corresponding guide pieces 37 on the support body 20, as can be seen in particular in FIGS. 3 and 4.

All cylinders can be pressurized at the same time, so water or hydraulic fluid, so that the clamping pieces can all be extended together, and also with different ways to the clamping pieces against the borehole wall.

In the design of the hydraulic system, as shown in the diagram in FIG. 6, a line 21 is provided for supplying pressure medium to the full spaces of the cylinders 12 or for removing medium therefrom, which line is guided, for example, on the outside of the drill pipe and over one another Ring transmitter or rotary distributor 22 with ring channel 23 in lines 24, 25 continues on the non-rotating part (tensioning device 11 and loading weight 30) of the device (only indicated in FIG. 1). An unlockable check valve 26 is assigned to these lines in front of each cylinder 12. In Fig. 1, the number 48 indicates a torque arm for the rotary distributor 22.

Another extending along the drill string or formed by this and continuing on the drive shaft 10 Line 41 leads, with branches, to the full spaces of cylinders 7 used for adjusting movable tools 4.

A third line 42 arranged on or formed by the drill string opens out on the one hand into a further annular channel 43 of the rotary distributor 22, which is connected via lines 44, 45 to the annular spaces of the cylinders 12 of the tensioning device 11, and on the other hand sits in one on the drive shaft 10 along line 47 continues, which branches and is connected to the annular spaces of the cylinders 7. A control line 46 branches off from each of the lines 44 and 45 to the check valves 26 for unlocking the same. By supplying pressure medium to the line 42, the clamping pieces 15 and the tools 4 can thus be moved inwards at the same time.

The lines 21, 41 and 42 are connected for days to a control device by means of which pressure medium can optionally be supplied or removed from a source from each line.

In Fig. 1 the borehole B is shown as vertical. If there is a deviation from the vertical V after drilling a section, as shown in Fig. 2 is indicated by the direction of the borehole walls W and a dash-dotted line A, the procedure according to the invention is as follows when using a device of the type explained.

The clamping pieces 15 of the tensioning device 11 are retracted by pressure medium supplied via the lines 42, 44, 45, the check valves via the lines 46 be unlocked, and the drill head 1 is lifted off the bottom S of the borehole B by a small amount by means of the drill pipe. In addition, the most radially projecting tool 4 or several such tools 4 are pivoted back inward from the external position, so that the overall state according to FIG. 2 results. The drill head 1 then hangs completely freely and unhindered on the drill pipe and can adjust itself exactly vertically under the influence of gravity, because it has no support system on the borehole wall W. Then, the clamping pieces are cylinder-piston units 15 by means of the extended by supplying pressure medium through the line 21 again, so that they rest against the _B ear hole wall W, as shown in FIG. 5 illustrates. The pistons 13 in the cylinders 12 and thus the clamping pieces 15 can travel different distances, as required by the different distances after the vertical position of the device has been taken relative to the inclined borehole wall W. In addition, the clamping pieces 15 can adjust themselves accordingly on the piston rods 14 thanks to the articulated attachment. As a result of the relieved lines 42, 44, 45, 46, the check valves 26 are in the blocking position.

Then the lowering of the drilling head 1 and the beginning of a further drilling section can be started, the drilling head 1 being rotated again by means of the linkage and the drive shaft 10 as a continuation thereof and the movable tool 4 or the movable tools 4 using the associated actuating device 7 is pivoted outward again by supplying pressure medium via line 41. As a result of the perfect guidance during the previous vertical adjustment, this new drilling section is now drilled in the vertical direction.

If there is a very large deviation from the vertical, the case where the drill head 1 does not hang completely freely even when the tools 4 are swiveled in, but still lies against the wall of the borehole on one side, then the next drilling section still largely corrects the drilling direction towards the vertical. The verticality is then e.g. reached again in the following drilling section.

In the embodiment of the method explained above in connection with FIGS. 1 to 5, the drilling of the individual drilling sections takes place with the enlarged diameter of the drilling head 1. Its diameter is reduced in each case only to determine the further drilling direction with the position hanging on the drill pipe (FIG. 2).

However, it is also possible to drill successive drill sections with a relatively smaller diameter and to produce an extension only for the definition of a new drilling direction, in which the drill head can assume its position hanging on the drill pipe. This is illustrated in FIG. 7, which shows the state achieved in such a procedure before the start of drilling the next drilling section with a newly defined drilling direction, that is to say a state as shown in FIG. 5 for the method of operation explained further above.

The previous drilling section with the wall W1 has been drilled with the drilling head 1 with its smaller diameter, ie with tools 4 swung in, as is also the condition for further drilling according to FIG. 7. The letter D denotes the diameter of the borehole B drilled or to be drilled with such a state of the drill head 1. It is assumed that there is a deviation A from the vertical V which is corrected. By swiveling the tool or tools 4, the Knife of the drill head 1 enlarged and thus drilled a length L, which results in an enlarged borehole part BE. The drilling of this extension BE can already take place within the preceding drilling section using the stroke of the drilling head 1 relative to the clamping device 11 by the tools 4 being pivoted out during this drilling section. However, it is also possible, after the completion of a normal drilling section with the smaller diameter, to produce the extension BE by drilling upwards by the required amount with the tools 4 extended. This is illustrated in FIG. 8.

When the tools 4 are retracted, that is to say of reduced diameter, the drill head 1 is brought to a height after loosening the clamping pieces 15 by means of the drill pipe, in which it is located in the region of the extension BE and hangs freely on the drill pipe. He then usually has enough space to assume a vertical position. The new guiding direction thus given is then fixed by pushing out the clamping pieces 15 and pressing them against the borehole wall. The next drill section can then be drilled. This is indicated in FIG. 7 by the dash-dotted line N.

9 shows a modified embodiment of a hydraulic system for supplying the cylinders 12 of the tensioning device 11, only four cylinders lying in one plane being shown. The diagram with the associated explanation applies accordingly to the cylinders in the second level. The cylinders and their parts are identified by the same numbers as in FIGS. 1 to 6.

A device located above ground contains a pressure medium, for example water, from a tank 50 which draws a pump 53, the delivery line 54 of which leads to a directional control valve 55 which can be brought into the three switch positions shown by hand, for example. The desired maximum pressure can be at one a safety valve for the pump-forming valve 56 can also be set. Numbers 57 and 58 designate discharge lines leading to tank 50. From the directional control valve 55 two lines 51 and 52 start, which are provided by a rotor, rotary distributor 59 or the like provided at the upper end of the drill pipe. are connected to lines running on or in the drill pipe, which are located via a rotor, rotary distributor 22 or the like located on the device. continue. Until then, all parts of these lines have been given the same numbers.

Line 51 leads to e.g. preload valve 60 set to 10 bar, from which it extends as line 61 to another, e.g. to preload valve 62 set to 15 bar. Branching lines 63 lead from this to blocking blocks 66, which are each connected by lines 64 to the full spaces of the cylinders 12. Lock blocks 66 may e.g. how the unlockable check valves 26 are designed and switched in the embodiment according to FIG. 6 and have the same function as those. The number 65 denotes a hydraulic accumulator that can be charged to 70 bar, for example, and which is connected to the lines 63. This can compensate for leaks and ensures that the clamping pieces are always pressed firmly against the borehole wall while maintaining the high clamping pressure.

Control valves 68 are also connected to line 61 via lines 67, which on the other hand are connected to lines 64 via check valves 69. Lines 71 lead from line 51 to switching valves 70, from which lines 72 for the actuation of control valves 68 originate by means of pilot valves assigned to them. The switching valves 70 can be a function of the distances traveled by the piston rods 14 or the clamping pieces 15 or a function of certain reached positions of said parts can be actuated by suitable elements, including limit switches or the like. A particularly advantageous embodiment is that each clamping piece 15 '(FIG. 10) is provided with at least one sensing element 80 which protrudes somewhat above the clamping piece 15' and, for example, under the action of one or more springs in this front position determined by a stop is held and which is movably guided relative to the clamping piece 15 '. Each pushbutton element 80 is connected to an associated switching valve 70 by suitable transmission members 73 in such a way that the switching valve 70 is transferred from the position shown as effective in FIG. 9 to the second position when the pushbutton element 80 moves in when the clamping piece 15 'moves outward It comes into contact with borehole wall B and is thereby pushed back towards the clamping piece. 9 and 10 is a diagram of the numeral 76 one of a probe 80 or the like. Influenced organ indicated, which acts in the manner of a limit switch and causes the switching of the valve 70 via the transmission members 73.

The line 52 branches off and leads to the annular spaces of the cylinders 12. A back pressure valve 74, e.g. a spring-loaded check valve, and parallel to this a simple check valve 75 with reverse flow direction is provided. The back pressure valves 74 are set to a pressure which is favorable in view of the outward movement of the pistons 13, in which the pressure medium is displaced from the annular spaces of the cylinders 12.

If the directional control valve 55 is brought into a position in which the pressure medium delivered by the pump 53 flows into the line 51 and pressure medium can flow out of the line 52 via the line 57 to the tank 50, the pistons 13 are pushed out in the cylinders 12 and thus moving the held by the piston rods 14, not shown in Fig. 9 clamping pieces. The pressure medium flows via the preload valve 60, the line 61, the lines 67, the control valves 68 and the check valves 69 to the full spaces of the cylinders 12. This process continues until the sensing elements 80 come into contact with the borehole wall and thereby the switching valves 70 are operated so that they assume their second position. As a result, the lines 72 are depressurized, so that the control valves 68 are moved into their blocking position. As a result, the pressure in the line 61 rises, so that the pressure medium now reaches the full spaces of the cylinders 12 through the higher preload valve 62, the lines 63, the locking blocks 66 and the lines 64. As a result, the pistons 13, which in the previous process have already moved the clamping pieces to just before the borehole wall, are now simultaneously subjected to high pressure. As a result, the clamping pieces are pressed firmly against the borehole wall. The medium displaced from the annular spaces of the cylinders 12 has flowed out to the tank when the clamping pieces are extended via the back pressure valves 74, the lines 51, the directional control valve 55 and the line 57.

If the clamping pieces are loosened from the borehole wall and moved inwards, the directional control valve 55 is brought into a different position, in which pressure medium conveyed by the pump 53 now reaches the line 52, while the line 51 with the lines connected to it now via the Line 57 to the tank 50 is open. The pressure medium flows from the lines 52 via the opening check valves 75 to the annular spaces of the cylinders 12 and pushes back the pistons 13 thereof. The medium displaced from the full spaces of the cylinders 12 flows via the blocking blocks 66, which are now opened like the blocking blocks 26 according to FIG. 6. and further via lines 63, 61, 51 and 57 back to the tank. The preload valves 60 and 62 are connected or combined with switch valves, not shown, in particular automatic, in such a way that the backflow of the medium is made possible.

All of the features mentioned in the above description or shown in the drawing, if the known prior art permits, should be regarded as falling within the scope of the invention on their own or in combinations.

Claims (15)

1. A method for drilling substantially vertical bores, in particular large-bore bores, shafts or the like., Or the like for a drill head rotatable by means of a drill pipe. will give, characterized in that said means released, the drill head is brought into a standstill state to a hanging on the drill string position, and then set the direction for the next bore section _- the direction of drilling provided by the boring out of a drill portion using a with respect to the borehole wall fixable means with the diameter of the drill head being changed from a relatively larger to a relatively smaller value in order to determine the direction for the next drilling section. 2. The method according to claim 1, characterized in that in two successive drilling sections each of the same is drilled with the relatively larger diameter of the drill head, the 'to determine the direction for the second drill section reduced diameter of the drill head before or at the beginning of this second drill section again is enlarged. 3. The method according to claim 1, characterized in that in two successive drilling sections each of them is drilled with the relatively smaller diameter of the drill head and the diameter of the drill head is only increased between the two drill sections and is drilled with this diameter at least approximately a length corresponding to the drill head height that the diameter of the drill head is then reduced again, then the direction for further drilling is made in the suspended state of the drill head and the next drill section is then drilled. 4.Device for drilling substantially vertical bores, in particular large-diameter bores, shafts or the like, with a drill head which can be rotated by means of a drill pipe and which has an extendable and retractable clamping piece which can be pressed against the wall of the borehole produced and in which the drill head moves backwards adjoining area of the device arranged clamping device with a guide part for a part movable relative to it together with the drill head in the drilling direction, in particular for carrying out the method according to claim 1, characterized in that the drill head (1) at least one from an external working position into a more internal Position and vice versa movable tool (4), by adjusting the diameter of the drill head (1) can be reduced and enlarged. 5. The device according to claim 4, characterized in that the movable tool (4) is arranged pivotably. 6. The device according to claim 4, characterized in that the movable tool is arranged displaceably. 7. The device according to claim 4, characterized in that the drill head in the manner of an undercutter ( _R eamers) or the like. is trained. 8. Device according to one of claims 4 to 7, characterized in that hydraulic actuating devices (7) are provided for moving the tool or tools (4). 9. The device according to claim 8, wherein the clamping pieces of the clamping device are displaceable by means of hydraulic piston-cylinder units, characterized in that the piston-cylinder units (12, 13) for the clamping pieces (15) and the hydraulic actuating devices (7) for the movable tool or tools (4) on the drill head (1) in the sense of an outward movement of the clamping pieces (15) and the tools (4) can be acted upon separately by pressure medium and in the sense of an inward movement of the clamping pieces (15) and the tools (4) can be acted upon together with pressure medium. 10. The device according to claim 9, characterized in that the piston-cylinder units (12, 13) for the clamping pieces (15) unlockable check valves (26) are assigned. 11. The device according to one of claims 4 to 90, characterized in that on the clamping pieces (15, 15 ') or on parts movable with these acting elements (76, 80) are provided by the control elements (68) for influencing the outward movement of the Clamping pieces (15, 15 ') can be actuated directly or indirectly. 12. The apparatus according to claim 11, characterized in that on the clamping pieces (15 ') on this outwardly projecting movable probe elements (80) are provided as acting elements. 13. Device according to one of claims 11 and 12, wherein the clamping pieces of the tensioning device are displaceable by means of hydraulic piston-cylinder units, characterized in that the hydraulic system for supplying the piston-cylinder units (12, 13) in dependence on the action members (76, 80) has actuable valves (68), by means of which the conditions for the supply of the piston-cylinder units (12, 13) can be changed. 14. The apparatus according to claim 13, characterized by hydraulic components (60, 62), by means of which upon actuation of the valves (68) by the action members (76, 80) the piston-cylinder units (12, 13) pressure medium can be supplied with increased pressure is. 15. Device according to one of claims 13 and 14, characterized in that the hydraulic system in pressure medium supply paths (51, 61, 63) contains two preload valves (60, 62) adjustable to different pressures.

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