WO2011075045A1

WO2011075045A1 - An arrangement for joining double-walled drill rods and double-walled drill rod

Info

Publication number: WO2011075045A1
Application number: PCT/SE2010/051354
Authority: WO
Inventors: Peter F Johansson; Magnus HÖRMAN
Original assignee: Wassara Ab
Priority date: 2009-12-18
Filing date: 2010-12-09
Publication date: 2011-06-23
Also published as: SE0950989A1; SE534395C2

Abstract

The invention concerns an arrangement for the joining of double-walled drill rods that, consisting of two rods (3, 4) one inside the other, limits a central inner channel (5) in which a first fluid can be led, an annular outer channel (6) located between the walls of the inner and outer rods through which a second fluid can led, whereby the arrangement for axial joining of the drill rods at their ends comprises a threaded outer connector (15) that in a fluid-tight manner allows the connection of the opposing outer rods (4) at a joint, and an inner connector (16) that in a similar fluid-tight manner allows connection of the two opposing inner rods 3 at a joint. In order to avoid mixing of fluids, the end of one inner rod is at an inner connector (16) at a joint provided with an arrangement (40) that limits axial passage of driving fluid through the joint, while allowing radial or sideways directed passage of driving fluid through the joint without significant resistance. The invention also concerns a double-walled drill rod.

Description

An arrangement for joining double-walled drill rods and double-walled drill rod

The present invention concerns an arrangement for the joining of double-walled drill rods according to the introduction to claim 1. It concerns in particular an arrangement to avoid the mixing of fluids when joining drill strings intended to be used during soil stabilisation in a process known as "jet grouting". The invention concerns also a double- walled drill rod according to the introduction to claim 10.

During soil stabilisation, it is normal to use a stabilisation arrangement that comprises a rock drilling arrangement with a drill string that consists of a number of drill rods connected coaxially at their ends. A down-the-hole hammer drill provided with a drill bit is fixed at the front end of the drill string. The load capacity of roads and similar civil engineering structures can be significantly improved through soil stabilisation, which is the term used to describe the stabilisation of soil layers with a binding agent such as cement. In order to carry out the soil stabilisation, what is known as a "monitor" or "injector head" is arranged between the down-the-hole hammer drill itself and the drill string. This monitor has one or several grouting openings known as "nozzles", out through which a grouting mixture can be caused to flow. A driving fluid in the form of water is led down to the drill hammer with the aid of a central channel in the drill string in order to carry out the drilling operation. The grouting mixture is led via the annular outer channel down to the grouting openings in the monitor. It is normal that the grouting mixture is constituted by a solution of cement and water. When the drill bit has reached its predetermined position in the drill-hole, jet grouting of the soil can begin, whereby the drill string is withdrawn back up the hole while being rotated. During jet grouting, an outwardly directed stream of grouting mixture that flows out from the grouting nozzles will be mixed with soil that is available within a diameter of up to 1 metre, and will produce a pillar or column that is approximately as high as the depth of the drilled hole. The drill string is completely withdrawn from the drilled hole following the stabilisation operation, and is thereafter ready to be used in a further drill and stabilisation cycle.

Drill rods of double-walled type, i.e. consisting of two rods concentrically arranged relative to each other (one inside the other), are used in order to be able to lead two different media independently of each other. A central inner channel is limited by the wall of the inner rod and an outer annular channel is limited between the walls of the outer rod and the inner rod. New drill rods are joined onto the drill string, and the drill string becomes longer as the hole becomes deeper. The joining of new drill rods to the drill string involves problems during the actual operation of joining since there is a risk when the drill string has been divided and is open that grouting mixture, which is led in the outer channel of the drill string, will spill over and contaminate driving fluid that is led in the central inner channel of the drill string. It is to be understood in this respect that cement residual from the grouting mixture of previously performed grouting that spills over from the outer to the central inner rod can accompany the driving fluid (water) down into the hammer drill and there cause an interruption in its operation or, in the worst case, its failure.

Against the background of the large number of drill rods that are reused and handled during the joining of a drill string in association with drilling and soil stabilisation, it will be readily understood that the said problem with the risk of contamination of the driving fluid means that the joining operation becomes both complicated and time-consuming. It is easy to appreciate that there will be a striving to minimise as far as possible the risk of spill from the grouting mixture to the driving fluid during the joining operation of drill strings.

The purpose of the present invention, therefore, is to achieve an arrangement for the joining of double-walled drill rods, in particular to avoid the contamination of the driving fluid when joining drill strings that are intended to be used for soil stabilisation through jet grouting. The arrangement is intended to facilitate the joining on of new sections for the extension of the drill string. In particular, the invention aims to minimise the problem with disturbances in operations of the drill equipment caused by spill between the channels of the drill rod when joining on new drill rods, and thus also interruptions in operation caused by the grouting mixture entering the impact drill hammer as an accompaniment to the driving fluid. A second purpose of the invention is to achieve a double-walled drill rod that solves the problems described above.

These purposes of the invention are achieved by an arrangement for the joining of double-walled drill rods for the formation of drill strings that demonstrates the distinctive features and characteristics that are specified in claim 1 and a double-walled drill rod with the distinctive features and characteristics that are specified in claim 10. Other advantages of the invention are made clear by the non-independent claims 2-9.

The invention will be described in more detail below in the form of a non-limiting embodiment with reference to the attached drawings in which:

Figure 1 shows a longitudinal section through the forward end of a fluid-driven down-the-hole hammer drill attached at the forward end of a drill string with drill rods of concentric double-walled type,

Figure 2 shows a longitudinal section through an arrangement in order to avoid the mixing of fluids when joining double-walled drill rods according to the invention, shown as part of a connection between two adjacent sections of drill rod,

Figure 3 shows a cross-section through the arrangement according to the invention viewed along the line Ill-Ill in Figure 2, and Figure 4 shows a side view of the arrangement according to the invention displayed as part of the connection between two adjacent sections of drill rod that have been separated from each other.

Figure 1 shows a drill string 1 that is positioned inside an essentially vertical drill hole 2. The drill string 1 is of the type that has double channels or passages for leading fluid, such as liquids or gases, independently of each other. The drill string 1 consists of a number of sections of drill rod connected coaxially at their ends, each one of which sections is of double-walled type. This means that they comprise two rods 3, 4 concentrically position with each other (the first, inner rod 3 inside the second, outer rod 4), demonstrating a central inner channel 5 through which driving fluid can be led and an outer annular channel 6 located between the walls of the outer and the inner rods through which a water-based cement- containing grouting mixture can be led. In order for it to be possible to extend the drill string 1 through the joining on of further drill rod sections, the rod sections that are connected with the drill string are connected by means of a connector arrangement 10 at adjacent ends in a manner that allows their release.

The drill string 1 is provided at its forward end, which is located down inside the drill hole, with a down-the-hole hammer drill 1 1 that is equipped with a drill bit 12, which drill string is so designed that it form channel-formed extensions of the inner channel 5 of the drill string, such that the driving fluid in the form of water can be led through the parts when driving the hammer drill 1 1. The hammer drill 11 has a machine housing in which there is housed a percussion mechanism that is driven by pressurised fluid and arranged to provide blows against the drill bit 12, which in turn is mounted in a manner that allows reciprocating motion inside a chuck. The machine housing has a central supply line for driving liquid and channels in the drill bit 12 (not shown in the drawings) through which channels used driving liquid can flow out, and through the influence of this drill cuttings, generated during the drilling operation, are driven backwards along the outer surface of the machine housing and onwards up out from the drill hole 2 along the outer surface of the drill string 1.

The connector arrangement 10 for the coaxial connection of the drill rod sections one after the other is shown in more detail in Figures 2 and 3. The connector arrangement 10 comprises a threaded outer connector 15 that connects in a fluid-tight manner the opposing outer rods 4, and an inner connector 16 that in a similar fluid-tight manner connects the two opposing inner rods 3. The sections 3, 4 of drill rod can be connected through the said two connectors 15, 16 and the said grouting mixture and driving fluid can be led down through the drill string 1. With respect to the said fluids, it is a case of (in addition to the driving fluid in the form of water for the impact hammer that is led through the inner channel 5) a cement- containing grouting mixture for jet grouting, which is led through the outer channel 6. It is preferable that the threads of the outer connector 15 become smaller in the direction towards the free end of the rod. The outer rods 4 are at their threaded opposing ends provided with a surrounding shoulder 20 and a contact surface 21 that, through interaction and an achieved contact, limit the tightening of the screw connection and ensure that a fluid-tight connection between the rod ends is achieved. In order to form the internal connection 16, the two coaxial opposing inner rod ends are arranged such that they are absorbed telescopically displaced in each other (one inside the other) with interacting glide surfaces. The dimensional exactitude and precision that are required are obtained in respect of this through the two inner rods 3 having been manufactured from steel of high quality, for example, cold-drawn steel. For reasons associated with the manufacture, each one of the inner rods 3 is provided at its opposing ends with annular end pieces 25 and 26, which, forming the opposing ends of the inner rods at the connection, are attached to the appropriate end of the rod by means of shrinkage fitting, or in combination with welding.

As is made most clear by Figure 2, the two inner rod ends can be coaxially introduced into each other (one introduced into the other). To be more precise, the said relevant end pieces 25 and 26 have been given such a form that one end piece 25 (which in Figure 2 is the upper end piece) can be displaced down into the opposing second end piece 26 (which in Figure 2 is the lower end piece). When introduced one inside the other, the first end piece 25 surrounds the second end piece 26, in a manner that ensures sealing, along the surrounding region of contact and in which the two interacting rods ends are provided with sealing sections 28 that interact with each other in a manner that provides sealing at rod ends that have been coaxially brought together. For the purpose of the said sealing function, there is a groove with a sealing ring 29, for example an O-ring, at the second end piece 7. The said sealing ring 29 is so arranged that it is in sealing interaction in the region of contact between opposing wall surfaces of the two end pieces 25, 26.

Figure 3 shows in more detail the construction of each drill rod section. The inner rod 3 is attached at its upper end to the outer rod 4 with a bracing, and located concentrically in the said outer rod. The bracing comprises three spacer elements 30 evenly distributed around the circumference, with a pre-determined radial and axial extent. It is appropriate that the said spacer elements 30 are pre-mounted on the inner rod 3 before it is fixed in place in the outer rod 4, whereby it is appropriate that the union take place by means of welding at 31. The spacer elements 30 of the inner rod 3 are treated externally before the final assembly such that their external dimensions agree exactly with the internal diameter of the outer rod 4, after which the inner rod is finally mounted through being inserted into the outer rod and united with this by welding at 32.

With reference to Figures 2 and 4, the arrangement according to the invention is shown in more detail, and drawings make clear that one inner rod end of the inner connection is, at for every lower drill rod section in a joint 10, provided with an arrangement 40, the task of which is to limit axial passage of driving fluid through the joint. [The arrangement,] however, allows radial, or sideways directed passage of the driving fluid through the joint without significant resistance, as is illustrated by the flow arrows 41 in Figure 2. The terms "radial" and "sideways directed" are here used to denote directions at an angle to, or perpendicular to, the axial direction of the united inner ends 3 of the rods. Due to the fact that the arrangement 40 limits axial passage and does not limit radial passage of driving fluid through the joint 10, it functions as drip protection, in which the drill string that has been divided in order to allow the joining on of a new upper drill section prevents any possible spillage of grouting fluid from entering the central inner channel 5 for driving fluid of a lower drill rod section. The arrangement for this purpose comprises a protective cover 42 that is supported by a holder 43 attached at one end of the inner rod 3. The protective cover 42 has been arranged by the holder 43 at a position that is somewhat axially advanced from the end of the inner rod 3 and thus is located at a distance from the said end of the rod.

The protective cover 42 is shown in more detail in Figure 4, together with the way in which it protrudes from one end of an inner rod 3 of the relevant drill rod section. In order to limit axial passage of driving fluid through the inner joint 16, the protective cover 42 is taken up into the end of an opposing inner rod 3 such that a passage 44 is limited between the inner surface of the opposing rod end and the peripheral edge of the protective cover 42. The protective cover 42 has a top cover 45 that is radially extended relative to the axial direction of the inner rod 3, and a surrounding side wall 46 that forms at the same time a part of the holder 43. The surrounding side wall 46 limits a circularly cylindrical part with a diameter that increases in steps, in which the cylindrical part is broader at a lower part 47 than it is at an upper part. The diameter of the narrower cylindrical upper part is so chosen relative to the internal diameter of the opposing inner rod that an annular gap-shaped passage 48 is limited between the said surrounding side wall and the inner surface of the opposing rod end. The lower part 47 has been given such an external diameter that it can be inserted into one end of an inner rod 3 of a relevant drill rod section and attached in a suitable manner, for example by welding. As a more detailed study of Figure 2 will show, the broader lower part 47 of the protective cover 42 is attached immediately at the second end part 26. In order to allow radial passage of driving fluid, the upper side wall 46 of the protective cover 42, which upper side wall is narrower in its surrounding diameter, is provided with a number of holes 50, or openings, through which driving fluid, passing the annular gap 48, is led without noticeable resistance between the connected inner rod 3 of the inner joint and thus down to a subsequent lower drill section of the drill string 1.

The present invention is not limited to what has been described above and shown in the drawings: it can be changed [misspelt in the Swedish] and modified in several different ways within the scope of the innovative concept defined by the attached patent claims.

Claims

An arrangement for the joining of double-walled drill rods during the formation of a drill string for soil stabilisation by jet grouting, and where each drill rod comprise two rods (3, 4) one inside the other that together limit a central inner channel (5) in which a first fluid for the driving of a down-the-hole hammer drill is intended to be led through the rod, and an annular outer channel (6) located between the walls of the inner and outer rods through which a second fluid including a grouting mixture for jet grouting is intended to be led in the rod, and where each drill rod includes a joint between opposing rod ends that comprises a threaded outer connector (15) that in a fluid-tight manner allows the connection of the opposing outer rods (4) at a joint, and an inner connector (16) that in a similar fluid-tight manner allows connection of the two opposing inner rods (3) at a joint, c h a r a c t e r i s e d in that at an inner connection (16) at opposing rods that meet at a joint one end of the inner rod (3) is arranged through the influence of an end wall (45) to allow only radial or sideways directed passage of driving fluid through the joint, whereby the end wall is arranged such that it protrudes from the end of one of the inner rods in the joint.

The arrangement according to claim 1 , whereby the end wall (45) forms part of a protective cover (42) that is radially extended from the axial direction of the inner rod and is supported by a holder attached at the said inner rod.

The arrangement according to claim 2, whereby the protective cover 42 is located taken up in such a manner into the rod end of an opposing second inner rod (3) at the joint that a passage (44) is limited between the periphery of the protective cover and the inner surface of the opposing second rod end.

The arrangement according to claim 3, whereby the protective cover (42) has a radially extended top cover (45) and a surrounding side wall (46) that limit the circularly cylindrical part.

The arrangement according to claim 4, whereby the circularly cylindrical part of the protective cover (42) is broader at the bottom than at the top and is by means of its broader lower part (47) inserted into and fixed at the rod end of the opposing inner rod (3) that meets the connector.

6. The arrangement according to claims 4-5, whereby the surrounding side wall (46) is provided with a number of holes (50) or openings that allow fluid to pass radially through the joint.

7. The arrangement according to claims 1-6, whereby both rod ends of the inner

opposing rods (3) in the joint can be coaxially introduced into each other (one into the other).

8. The arrangement according to claim 7, whereby the ends of the two inner rods (3) in the joint are provided with a separate end piece (25, 26) attached at the relevant end, which end pieces have been given such a mutual design that one end piece (26) can be introduced into the second end piece (25).

9. The arrangement according to claim 8, whereby the protective cover (42) is with its circularly cylindrical broader part (47) attached immediately at one of the said end pieces (26).

10. A double-walled drill rod that, consisting of two rods (3, 4) laid one inside the other, limits a central inner channel (5) in which a first fluid can be led, an annular outer channel (6) located between the walls of the inner and outer rods in which a second fluid can be led, and which drill rod is intended to form a drill string through axial joining, in particular a drill string of the type that can be used during soil stabilisation by jet grouting, characterised in that one end of the central inner rod (3) has a protective cover (42) demonstrating a top cover (45) that extends in the radial axial direction, and that by means of a holder (43) attached to the said rod end is supported in a manner such that it protrudes outwards from the said rod end.