EP3260650B1

EP3260650B1 - Device and method for drilling a shaft in a substrate

Info

Publication number: EP3260650B1
Application number: EP17177346.8A
Authority: EP
Inventors: Dieter Wim Jan Rabaut; Antonius Johannes Maria PROVOOST; Steven Francis Josephine ALEN
Original assignee: Geosea NV
Current assignee: Geosea NV
Priority date: 2016-06-22
Filing date: 2017-06-22
Publication date: 2019-01-30
Anticipated expiration: 2037-06-22
Also published as: PT3260650T; EP3260650A1; DK3260650T3; PL3260650T3; BE1023843B1; ES2722649T3

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and method for drilling a shaft in a substrate consisting of rock, clay and/or related materials. The phrase "rock, clay and/or related materials" is understood to mean diverse types of ground which can form the ground layers of a water basin or a land area up to a very variable depth. Such ground layers for instance form part of sea arms, streams and rivers, docks, storage reservoirs, access channels to locks or inlet docks, and coastal sea areas.

BACKGROUND OF THE INVENTION

A large part of the land surface on earth is covered with loose, non-consolidated material such as soil, clay, sludge, sand, gravel and stones. The depth of this so-called overburden (or top layer) varies from a few centimetres to hundreds of meters. Drilling through this overburden in order to reach a bearing layer is often problematic as a result of, among other factors, the tendency of the overburden material to drop behind the drill head and back into the drill shaft. This often makes it difficult to pull the drill string back up through the drilled shaft. Other problems may be caused by cavities and porosity in the overburden which interfere with the circulation of a flushing medium and thereby make it more difficult to carry the drilled out ground parts upward via the drill shaft with the flushing medium.
During drilling in an overburden use is for these and other reasons often made of a casing tube which is arranged on or in a bearing layer, such as for instance a rocky bottom, prior to or, at the same time as the drill string, during drilling in the overburden. The casing tube at least partially prevents the above stated adverse effects.
Because the thickness of the overburden (or the depth of a bearing layer) is often not known precisely and can moreover vary from position to position, in a known method a segmented casing tube is arranged in the substrate, wherein the casing tube is lengthened by adding more segments to the casing tube from above.
GB 2169333A discloses a device for drilling a shaft in a substrate by using reversed circulation drilling. The disclosed device comprises a casing tube, and a drilling means that can be lowered into the casing tube and is provided with a drill head with cutting tools. The drill head can be set into rotation for drilling. The casing tube is a one-piece element.
The known method has the drawback, among others, that much time is lost in lengthening and/or shortening the casing tube. This is detrimental to the drilling efficiency, this being understood to mean that the quantity of ground material drilled out per unit of time and power can be further increased.

SUMMARY OF THE INVENTION

The invention has for its object to provide a method and device for drilling a shaft in a substrate consisting of rock, clay and/or related materials, which at least partially obviate the above stated and other drawbacks.
The invention provides for this purpose a device according to claim 1. A device is particularly provided for drilling a shaft in a substrate consisting of rock, clay and/or related materials, wherein the device comprises a casing tube and means for arranging the casing tube in the substrate; and further a drilling means which can be lowered into the casing tube and is provided with a drill head with cutting tools, and means for setting the drilling means into rotation; wherein the casing tube comprises a first and a second part which are telescopically displaceable relative to each other along a common axis, extending in a longitudinal direction of both parts, between an extended position, in which the parts are coupled with coupling means, and a retracted position.
With the device according to the invention a method for drilling a shaft in a substrate consisting of rock, clay and/or related materials can be performed which comprises of arranging a casing tube in the substrate, wherein prior thereto a first part of the casing tube was displaced telescopically relative to a second part of the casing tube along a common axis, extending in a longitudinal direction of both parts, into an extended position, coupling the parts in the extended position, lowering a drilling means provided with cutting tools into the casing tube, uncoupling the parts and setting the drilling means into rotation in order to drill the shaft. A suitable drilling means comprises for instance an elongate drill string which rotates in the casing tube so that ground material is dislodged by the cutting action of the cutting tools. The dislodged ground material is generally discharged upward via an annular space between the drill string and the casing tube with a flushing agent (for instance, but not limited to, water, mud, air).
It has been found that with the method and device according to the invention the drilling efficiency is increased markedly relative to the known method, among other reasons because the drill head can be carried deeper into the substrate without a time-consuming lengthening of the casing tube by arranging additional casing tube segments being necessary for this purpose.
The invented method and device can be applied with any drilling means, such as the usual drill string constructed from segments, preferably a hollow drill string. It can be advantageous to apply a drilling means which can be anchored both in the longitudinal direction of the casing tube and perpendicularly thereof (the radial direction) against the inner wall of the casing tube using securing means, wherein the drilling forces can be absorbed in effective manner by transmitting these forces to the casing tube.
A further advantage of the invention is that manual operations for the purpose of casing tube lengthening are avoided, which increases the working safety; fewer people are after all present in the vicinity of rotating parts, as is the case in the known method.
The coupling means which in an extended position of the casing tube couple the first part to the second part are preferably embodied such that they rigidly connect the two parts in the extended position, both in the longitudinal direction of the parts and in a rotation direction around a longitudinal axis of the casing tube. In this way the telescopic casing tube acts as a structural whole in the extended position.
A suitable embodiment of the device according to the invention comprises coupling means comprising a female coupling part connected to the first part and a male coupling part connected to the second part. The two coupling parts co-act in order to realize a rigid coupling in the extended position.
The position of the female coupling part in the longitudinal direction of the first casing tube part can in principle be chosen freely. In order to obtain the longest possible extended casing tube it is advantageous to characterize the device according to an embodiment in that the female coupling part is situated on an upper side of the first part. This advantage is increased by an embodiment of the device wherein the male coupling part is situated on a lower side of the second part. A casing tube is thus obtained wherein a first part can be extended relative to a second part. Because a casing tube is generally lowered into the substrate from a fixed position on land or at sea, the first part is in these embodiments generally situated lower than the second part, i.e. closer to the substrate than the second part.
In a further embodiment of the device the female coupling part comprises a peripheral part provided with a recess, wherein the male coupling part preferably comprises a protrusion which can engage in a recess of the female coupling part for the purpose of coupling the two parts. A recess of the female coupling part is for this purpose preferably accessible on a lower side of the peripheral part in the longitudinal direction to a protrusion of the male coupling part. In order to obtain a coupling which is fixed in the longitudinal direction of the parts, in an embodiment the recess can have a laterally extending lateral branch behind which the male protrusion can be slid by a relative rotation of the first and second part. When a rotation is performed in the other direction, the male protrusion slides from the lateral branch into the recess running along the longitudinal direction, whereby the two parts can be uncoupled.
An embodiment of the device is characterized in that the second part comprises a stop edge which in the extended position in which the parts are coupled lies against a stop edge of the first part. The stop edge of the first part preferably forms a lower edge of the female coupling part.
The ground parts dislodged by the drilling means must be discharged. An embodiment of the device suitable for this purpose comprises means for maintaining a flushing agent column in the casing tube, which flushing agent column maintains a flow in an annular space between the casing tube and the preferably hollow drill string for the purpose of discharging the dislodged ground material. The flushing agent column which is arranged in the casing tube, and which otherwise extends into the space between the casing tube and the drilling means which is lowered into the casing tube and is disposed substantially coaxially with the casing tube, provides for a pressure difference between the upper side of the discharge means for dislodged ground material connected to the drill string and the lower side of the drill string, wherein the pressure is of course higher on the lower side. A flow is hereby maintained in an annular space between the casing tube and the (hollow) drill string, and thus also in the discharge means connected to the annular space, in which flow the dislodged ground material is discharged to the upper side of the discharge means, which comprise for instance a discharge hose connected to an upper side of the annular space. The flushing agent (for instance water, mud, air, foam, ...) coming from the flushing agent column provides for the flushing away of the dislodged ground material. In order not to lose water pressure unnecessarily, the casing tube is preferably arranged in a manner such that it admits substantially no water on its lower side. The casing tube is generally placed for this purpose on or in the (underwater) substrate, so creating a good seal and water sealing at the lower outer end of the casing tube.
Because the drilling means must be received in the casing tube during drilling, the casing tube has somewhat greater transverse dimensions than the drilling means. The casing tube preferably takes a cylindrical form, wherein a preferably also substantially cylindrical drilling means can be lowered into the casing tube in a direction corresponding to the longitudinal direction of the casing tube.
In order to be able to maintain a flow for the discharge of the dislodged ground material it is advantageous for the intermediate space between the drilling means and an inner surface of the casing tube to be relatively small, particularly on a lower side of the casing tube. An embodiment of the device which contributes hereto has the feature that the first part has a smaller diameter than the second part and can be slid partially into the second part.
In order to prevent ground parts and/or flushing agent coming to lie between jacket surfaces of the first and the second part, in an embodiment of the device an upper edge of the first part comprises a seal for an intermediate space between jacket surfaces of the first and the second part.
Optionally being able to move the drill head out of the casing tube allows ground layers lying deeper than the underside of the casing tube to be provided with a shaft. Because the structure of the substrate is weakened at this position, the casing tube can penetrate more easily into the substrate. If desired, use can be made of a so-called underreamer. In underreaming the drill string is provided on the drill head outer end with a construction having radially fold-out side arms. When drilling is carried out with the arms in the folded-out position a borehole will be created which is wider than the diameter drilled by the drill head. The substrate directly beneath the casing tube is hereby drilled away and the casing tube can be moved deeper into the substrate. Underreaming is also applied when a wider foot must be drilled in order to obtain extra pile bearing capacity or anchoring.
The device comprises means with which the casing tube can be arranged in the substrate, and means for setting the drilling means into rotation. An embodiment of the device provides a device wherein these means comprise a rotary motor. Suitable means for arranging the casing tube in the substrate comprise a rotary motor, a pile-driver and/or an oscillator. In an embodiment the second part of the telescopic casing tube is driven by the means for arranging the casing tube in the substrate. By coupling the first and second part in non-rotatable and non-translatable manner in the extended position the first part is also driven. In the uncoupled position the second part can in principle be driven while the first part remains substantially stationary.
The device can be used both on land and on water. The advantages of the invention become particularly manifest in use of the device at sea. For this purpose an embodiment provides a floating device which is provided with a device according to the invention. The floating device can for instance comprise a lifting platform which is anchored in the vicinity of the shafts to be formed. In an embodiment such a lifting platform comprises an adjustable outboard frame (an 'outrigger') provided with the means for arranging the casing tube in the substrate, such as preferably a rotary motor. It is also possible to configure the means for arranging the casing tube in the substrate such that the casing tube is arranged in the substrate at an angle other than zero to the vertical direction. This can for instance be achieved by connecting the rotary motor to the frame for pivoting around a substantially horizontal axis so that the rotary motor can be tilted at an angle other than zero to the horizontal direction. In the context of the present application the vertical direction designates the direction running substantially perpendicularly of the water surface. In the context of the present application the horizontal direction designates the direction running substantially parallel to the water surface.
The drill head can if desired be provided with substantially radially outward directed nozzles connected to feed lines and configured to inject a fluid into the substrate at the position of the drill head under a high pressure of at least 200 bar, more preferably at least 350 bar, and most preferably at least 500 bar. Such an embodiment renders the use of an underreaming construction unnecessary, whereby the casing tube can be moved in relatively simple manner to a greater depth. The fluid can comprise any injectable substance, although particularly suitable is water to which additives, such as for instance abrasives and other abrading means, are added if desired.
It may also be useful to equip the device with means connected to feed lines and configured to inject a transport fluid into the hollow drill string of the drilling means at the position of the drill head under a pressure of a maximum of 50 bar, more preferably a maximum of 30 bar, and most preferably a maximum of 20 bar. The transport fluid preferably has a lower density than water, causing this transport fluid to rise upward in the drill string, whereby the upward flow of the flushing agent is further supported. A particularly suitable transport fluid comprises air.
An aspect of the invention relates to a method for drilling a shaft in a substrate consisting of rock, clay and/or related materials. The method comprises of arranging a casing tube in the substrate, wherein prior thereto a first part of the casing tube was displaced telescopically relative to a second part of the casing tube along a common axis, extending in a longitudinal direction of both parts, into an extended position, coupling the parts in the extended position, lowering a drilling means provided with cutting tools into the casing tube, uncoupling the parts, and setting the drilling means into rotation in order to drill the shaft.
In an embodiment of the method the first part and the second part are coupled and uncoupled by a rotation of at least one of the parts, preferably the second part, about the common axis.
The method is preferably applied in situations in which the substrate is situated under water and the method is performed from a floating device, preferably a jack-up platform. The telescopic casing tube can be brought into the uncoupled position during drilling, wherein the first and second parts of the casing tube can slide telescopically relative to each other along a common axis extending in a longitudinal direction of both parts. The casing tube can here accommodate the effects of swell, and in this situation acts as swell compensator for the drilling device.
Finally, it is stated that the embodiments of the invention described in this patent application can be combined in any possible combination of these embodiments, and that each embodiment can individually form the subject-matter of a divisional patent application.

BRIEF DESCRIPTION OF THE FIGURES

Other details and advantages of the invention will become apparent from the following description of a device and method for drilling a shaft in a substrate consisting of rock, clay and/or related materials. This description is given solely by way of example, without the invention being limited thereto. The reference numerals relate to the accompanying figures. In the figures:

figure 1 shows a schematic side view of an embodiment of the device according to the invention in a coupled state (left) and an uncoupled state (right);
figure 2 shows a schematic perspective detail view of coupling means according to an embodiment of the invention; and finally
figures 3A-3H show a number of successive steps of an embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to figure 1, a device 1 is shown for drilling a shaft 2 in a ground layer 3. Ground layer 3 preferably comprises rock, but may also comprise clay and/or related materials. The ground layer 3 may be covered with a top layer 3a, or overburden, which generally comprises somewhat more loosely packed stone. Device 1 comprises a casing tube 4 which can be arranged over at least part of its length in overburden 3a, and optionally also in substrate 3, by means of for instance pile-driving, oscillation or vibration. The diameter of casing tube 4 can in principle be chosen within wide limits. Because casing tube 4 supports on its underside on or in ground layer 3, a substantially water-impermeable sealing is achieved, though this may depend to some extent on the properties of ground layer 3 and is not therefore essential to the invention. In the shown embodiment casing tube 4 comprises a thick-walled steel tube which is suitable for withstanding the forces exerted during insertion of casing tube 4 into ground layer 3 and the drilling.
According to the invention, casing tube 4 comprises a first part 4a and a second part 4b. The parts (4a, 4b) are telescopically displaceable relative to each other along a common axis 4c extending in a longitudinal direction 40 of both parts (4a, 4b) between an extended position, shown in the lefthand drawing of figure 1, in which the parts (4a, 4b) are coupled with coupling means (5, 6), and a retracted position, shown in the right-hand drawing of figure 1, wherein the parts (4a, 4b) are uncoupled and the first part 4a can be moved telescopically in second part 4b over a distance 40.
Referring to figure 2, the coupling means (5, 6) comprise a female coupling part 5 connected to first part 4a and a male coupling part 6 connected to second part 4b. In order to be able to achieve a maximum length in the extended position the female coupling part 5 is situated on an upper side 41 of first part 4a, while the male coupling part 6 is situated a relatively short distance from an underside 42 of second part 4b. Because in the shown embodiment the first part 4a has a diameter 43 smaller than the inner diameter 44 of the second part 4b, first part 4a can be slid at least partially into second part 4b.
Referring to figure 2, the female coupling part 5 comprises a peripheral part 50 provided with two recesses 52 distributed regularly over a peripheral direction 51 of peripheral part 50. Peripheral part 50 is preferably connected to a jacket surface 46 of first part 4a by means of welding. Recesses 52 have on an underside thereof an open outer end 52a and a lateral branch 52b running substantially in the peripheral direction of the peripheral part. Four protrusions arranged on an internal jacket surface 45 of second part 4b and protruding in a radial direction 53 form the male coupling part 6. The protrusions are preferably welded onto an internal surface 45 of the second part 4b. It is also possible to use a different manner of connection, for instance a releasable connection for the purpose of easy replacement following wear. It is noted that outer part 4b is shown in transparent view in figure 2. The number of recesses 52 and protrusions 6 can in principle be chosen freely and be adjusted to the diameter of the casing tube, wherein the number of at least two can be increased in the case of for instance larger diameters.
By displacing first part 4a relative to second part 4b in longitudinal direction 40, wherein recesses 52 are aligned with protrusions 6, these latter can be slid into recesses 52 and engage therein for the purpose of coupling the two parts (4a, 4b). In order to obtain a fixed coupling in the longitudinal direction 40 of the parts (4a, 4b) the second part 4b is rotated about the longitudinal axis 4c in counter-clockwise direction as according to arrow 54, while first part 4a remains stationary. Male protrusions 6 hereby slide into the laterally directed lateral branches 52b of recesses 52, whereby the connection between the parts (4a, 4b) is a fixed connection both in the longitudinal direction 40 and in the rotation direction in counter-clockwise direction 54. When second part 4b of casing tube 4 is rotated in counter-clockwise direction 54 by a rotary motor 7b, for instance in order to drive casing tube 4 into the substrate (3, 3a), the parts (4a, 4b) will rotate collectively and the casing tube parts (4a, 4b) act as one whole. In order to uncouple the parts (4a, 4b) the second part 4b is rotated in clockwise direction 55, wherein first part 4a is once again held stationary. The male protrusions hereby slide from lateral branches 52b into the recesses 52 running in the longitudinal direction 40, whereby the two parts (4a, 4b) can be uncoupled by a relative translation in longitudinal direction 40. An embodiment in which the above stated rotation directions are reversed (clockwise becoming counter-clockwise and vice versa) is also possible.
In order to centre first casing part 4a relative to second casing part 4b the internal jacket surface 45 of second part 4b is provided on an underside 42 thereof with a stop 60 with stop edge 60a. In the extended position in which the parts (4a, 4b) are coupled the stop edge 60a lies against a lower edge 50a of the peripheral part 50 of female coupling part 5, wherein lower edge 50a serves as stop edge. Stop 60 does not continue along the whole peripheral direction (not 360°) in order to prevent dislodged material accumulating between the two parts (4a, 4b).
In order to further prevent material from being able to accumulate between an inner wall 45 of second part 4b and an outer wall 46 of first part 4a the upper edge 41 of coupling part 5 (which coincides with an upper edge of first part 4a) is provided with a seal in the form of a rubber ring 56 which is mounted with bolts 57 on upper edge 41 and which seals the intermediate space between the jacket surfaces (46, 45) of the first and the second part. In another embodiment rubber ring 56 is replaced by two plastic shell parts received (similarly to stop parts 60) in the intermediate space between first casing part 4a and second casing part 4b. The plastic shell parts extend over about 180° in the peripheral direction and lie with edges running in longitudinal direction 40 against each other. The shell parts are preferably arranged removably (not mechanically connected) in the intermediate space and can be easily removed and replaced by new ones by carrying the (inner) first casing part 4a out of the (outer) second casing part 4b on an upper side, wherein the shell parts are released. Casing tube 4 is sufficiently large to provide space for a drilling means, which can be lowered into casing tube 4 to a position at the height of the underside 47 of casing tube 4. The drilling means comprises a hollow drill string 10 which is provided on the side facing toward the substrate 3 with a drill head 8 with cutting tools, for instance a so-called Down The Hole hammer (DTH). The invention is however not limited to a determined type of drill head 8.
Drill string 10 is driven by means in the form of a rotary motor 7a for setting drill string 10 (and so also drill head 8) into rotation and translation. Discharge means (not shown) for dislodged ground material can be connected to the, if desired hollow, drill string 10. The translating of drill string 10 in longitudinal direction 40 of casing tube 4 can likewise be realized by motor 7a, wherein drill head 10 can be moved out of or retracted into casing tube 4. It will be apparent that the driving of drill string 10 and of casing tube 4 takes place in known manner, wherein the equipment required for this purpose is assumed to be present.
By setting drill string 10 into rotation and translation on the upper side thereof the drill head 8 is likewise set into rotation and translation in longitudinal direction 40 of casing tube 4, this direction 40 also being the drilling direction, wherein the substrate (3, 3a) is crushed by the action of cutting tools and a shaft 2 is formed. Although casing tube 4 and drill string 10 run substantially vertically in the shown figures, they can be adjusted to any angle other than zero to the vertical direction, for instance from a jack-up platform or pontoon, or from the shore when the device forms part of for instance a vehicle.
Device 1 can also be provided with means (not shown) for maintaining a water column in casing tube 4, for instance in the form of a pump with sufficient rise height and flow rate so as to maintain the highest possible water level in casing tube 4. The water column provides for a pressure difference between the upper side of casing tube 4 and the lower side of drill string 10 at the position of drill head 8, wherein the pressure is of course higher on the lower side. Owing to this pressure difference, and because casing tube 4 is open on the underside so that a throughfeed is possible to the annular space between drill string 10 and casing tube 4 (4a, 4b), water and dislodged ground material flow into the annular space, where they are entrained with a flow directed upward as according to arrow P in the annular space lying between drill string 10 and casing tube 4 and are discharged on an upper side of device 1. The dislodged ground material can optionally also be discharged via a cavity 10a arranged in drill string 10. If desired, the upward flow as according to arrow P is aided by blowing air bubbles into it from below. In an embodiment casing tube 4, particularly first casing part 4a and/or second casing part 4b, is provided with openings distributed over the length of casing tube 4 to enable discharged ground material parts to be discharged to the surrounding water.
Shown with reference to figures 3A-3H is a pontoon 30 which is provided with a device 1 according to the invention. Such a floating embodiment is particularly suitable for drilling holes in underwater bottoms in which explosives may be arranged after removal of the drill string.
The shown pontoon 30 is provided with a drilling mast 32 and, if desired, with other auxiliary means. Device 1, comprising at least the rotary motors (7a, 7b) and the casing tube 4 and drill string 10 connected thereto, can be lifted and lowered along drilling mast 32. Device 1 is supported here by an adjustable outboard frame 33 (also referred to with the term outrigger).
Referring to figure 3A, a casing tube 4 with drill string 10 is first brought into a desired position, wherein the casing tube/drill string combination (4, 10) is situated at the top of drilling mast 32. Drill string 10 is situated in casing tube 4, the two parts (4a, 4b) of which are coupled. A first part 4a is here extended relative to second part 4b.
According to figure 3B, the casing tube/drill string combination (4, 10) is then moved downward along drilling mast 32 until the underside 47 of the first part 4a of the casing tube reaches the overburden 3a.
As shown in figure 3C, casing tube 4 is then driven into the overburden 3a by rotating the casing tube, for instance driven by rotary motor 7b, in counter-clockwise direction 54 until the desired depth is reached, for instance the depth of the substrate 3.
In a subsequent step shown in figure 3D the two parts (4a, 4b) of casing tube 4 are uncoupled by rotation of second part 4b in clockwise direction 55, driven by rotary motor 7b, through an angle of about 45 degrees. An underside of casing tube 4 rests here on substrate 3. At the insertion depth of casing tube 4 the substrate 3 is preferably a hard layer such as rock, limestone, hard clay or highly compacted sand. Overburden 3a usually comprises more easily penetrable ground such as for instance weathered rock, clay, peat, loosely compacted sand or combinations thereof.
Drill string 10 is subsequently set into rotation with rotary motor 7a and driven further into the substrate 3, wherein a shaft 2 is formed (figure 3E). The casing tube parts (4a, 4b) are uncoupled so that second part 4b can be moved relatively freely in longitudinal direction 40 over a distance 41 relative to the first part 4a positioned on the substrate 3. Rocking motions of pontoon 30 due to swell are hereby for instance accommodated. During drilling the dislodged ground material can if desired be discharged via an upward water flow maintained in hollow drill string 10.
In the method step shown in figure 3F drill string 10 is then retracted into casing tube 4 by rotary motor 7a into a position in which rotary motor 7a of drill string 10 is situated at the top of drilling mast 32. Drill string 10 has here been out of pulled wholly out of casing tube 4.
Figure 3G shows schematically a possible subsequent step of the method, in which explosives are loaded into a detonator, the detonator and a pump hose for the explosives are then carried downward into the substrate 3 through the still uncoupled casing tube 4, explosives are carried through the conduit to a lower side of shaft 2, and the charge is detonated.
Finally, the casing tube parts (4a, 4b) are coupled by a combined translation in longitudinal direction 40 and rotation in counter-clockwise direction 54 of second part 4b relative to the stationary first part 4a, after which casing tube 4 is lifted upward using drilling mast 32. A possible detonator cable 35 is hauled in and the pontoon 30 provided with the device 1 is moved to a subsequent drilling position, where the above described method is repeated.
The invented device and method are particularly suitable for drilling shafts in a substrate on which a top layer or overburden is present, wherein the depth of the substrate is not always well known. Making use of the invented telescopic casing tube saves a lot of time because the length of the casing tube adjusts automatically to the depth of the substrate. The telescopic casing tube also functions as swell compensator.
The invention is not limited to the embodiment described here, and many modifications could be made thereto, to the extent these modifications fall within the scope of the appended claims.

Claims

Device (1) for drilling a shaft (2) in a substrate (3) consisting of rock, clay and/or related materials, comprising a casing tube (4) and means for arranging the casing tube (4) in the substrate (3); and further a drilling means (8, 10) which can be lowered into the casing tube (4) and is provided with a drill head (8) with cutting tools, and means (7a) for setting the drilling means (8, 10) into rotation; wherein the casing tube (4) comprises a first and a second part (4b) which are telescopically displaceable relative to each other along a common axis, extending in a longitudinal direction of both parts, between an extended position, in which the parts are coupled with coupling means (5, 6), and a retracted position.
Device (1) according to claim 1, wherein the coupling means (5, 6) comprise a female coupling part (5) connected to the first part (4a) and a male coupling part (6) connected to the second part (4b).
Device (1) according to claim 2, wherein the female coupling part (5) is situated on an upper side of the first part (4a).
Device (1) according to any one of the foregoing claims, wherein the male coupling part (6) is situated on a lower side of the second part (4b).
Device (1) according to any one of the foregoing claims, wherein the first part (4a) has a smaller diameter than the second part (4b) and can be slid partially into the second part (4b).
Device (1) according to any one of the foregoing claims, wherein the female coupling part (5) comprises a peripheral part provided with a recess.
Device (1) according to claim 6, wherein the male coupling part (6) comprises a protrusion which can engage in a recess of the female coupling part (5) for the purpose of coupling the two parts.
Device (1) according to any one of the foregoing claims, wherein the second part (4b) comprises a stop edge which in the extended position in which the parts are coupled lies against a stop edge of the first part (4a).
Device (1) according to claim 1, wherein the stop edge of the first part (4a) forms a lower edge of the female coupling part (5).
Device (1) according to any one of the foregoing claims, wherein an upper edge of the first part (4a) comprises a seal for an intermediate space between jacket surfaces of the first and the second part (4b).
Floating device (1) provided with a device (1) according to any one of the claims 1-10.
Method for drilling a shaft (2) in a substrate (3) consisting of rock, clay and/or related materials, comprising of arranging a casing tube (4) in the substrate (3), wherein prior thereto a first part (4a) of the casing tube (4) was displaced telescopically relative to a second part (4b) of the casing tube (4) along a common axis, extending in a longitudinal direction of both parts, into an extended position, coupling the parts in the extended position, lowering a drilling means (8, 10) provided with cutting tools into the casing tube (4), uncoupling the parts, and setting the drilling means (8, 10) into rotation in order to drill the shaft (2).
Method according to claim 12, wherein the first part (4a) and the second part (4b) are coupled and uncoupled by a rotation of at least one of the parts about the common axis.
Method according to claim 12 or 13, wherein the substrate (3) is situated under water and the method is performed from a jack-up platform.