A DRILLING METHOD AND BIT ASSEMBLY TO REALIZE THE METHOD

Abstract: A method to drill a hole in the soil by a bit assembly and a bit assembly comprising a ring-shaped bit (2) to drill the outer circle of the hole and to which a protection tube system (4), mounted in the hole while drilling, is coupled, and a cylindric inner bit (1) to drill the center portion of the hole, from which bit at least the rotative motion is transmitted to the outer bit (2). Drilling by the outer bit (2) and pulling out the protection tube (4) are disconnected upon need by reverse rotation of the inner bit, whereafter drilling is continued with the inner bit (1) only.

Description: A DRILLING METHOD AND BIT ASSEMBLY TO REALIZE THE METHOD This invention relates to a method according to the introduction part of patent claim 1 and to a bit assembly according to the introduction part of patent claim 5 to realize the method on drilling a hole or tunnel in the soil and to a drill bit accord¬ ing to patent claim 8. Previously known are, for instance from patent specifications FI 933074 and GB 2 255 365, double bit assemblies where the inner bit that drills the centre hole can be pulled out from the hole, while the ring bit that drills the outer hole circle is left in the bore. However, in these examples the inner bit can be pulled out from the hole after drilling and also reinstalled if dril¬ ling is continued. On drilling a hole in the soil, the most general case is that the first portion of the hole is made in soft soil, whereby a protection tube is pulled into the drilled hole. Eventually, on hitting rock, the protection tube is not needed anymore. Dril¬ ling can then be continued without a protection tube if change of the drilling procedure is easy. The problem is the difficulty to change the way of drilling. The inner bit must then be pulled out from the hole and replaced by a bit that drills a hole with a smaller diameter. At this replacement, the complete drilling equipment is pulled out from the hole and reinstalled furnished with a new rock-drilling bit. This takes time and money, especi¬ ally if the first bore in the soil is long. By means of a method and bit assembly with a proper bit accord¬ ing to this invention a surprising improvment of this disadvant¬ age is achieved and the invention is characterized in what is presented in the patent claims. The advantage of this invention is that a hole requiring a pro¬ tection tube is drilled with the same bit assembly as a hole into rock. When the protection tube is not needed, drilling proceeds nonstop with the inner bit only. In case drilling is stopped in a dead end, the inner bit can be pulled out through the outer bit. Even the outer bit can be pulled out from the bore on condition that also the protection tube is pulled out simultaneously. The bit assembly and the method can be applied to drilling by hammering but also to bits rotating only. The groove in the bayonet joint that opens in both of the axial directions is favourably arranged as a flow channel for flushing medium, whereat the joint is a simple construction. In the following the invention is disclosed with reference to the enclosed drawing, where Fig. 1 shows a section of the bit assembly along line A-A. Fig. 2 shows the bit assembly viewed from the front. Fig. 3 shows the inner bit surface viewed from one side. Fig. 4 shows a section of bore, where drilling proceeds by the inner bit only. Fig. 5 shows a cross-section of the ring bit. Figure 1 illustrates a section of the bit assembly including a cylindric inner bit 1 fastened to the head of hammer 7, a ring- shaped outer bit 2 around the inner bit and a protection tube 4 mounted in the hole while drilling and reaching the outer shell of outer bit 2. The inner bit 1 and outer bit 2 are intercon¬ nected by a bayonet joint, where rotation is transmitted to the outer bit by the inner bit. The inner bit 1 also transmits the hammer impacts to outer bit 2. Outer bit 2 pulls protection tube 4 into the hole by means of the joint lap between them, which has restriction for the mutual axial motion. Figure 2 shows that in the circle between bits 1 and 2 three bayonet joints are placed, where in the inner bit 1 three axial grooves 6 are formed to run through the bit. Correspondingly, there are in inner bit 2 three projecting parts with the same spacing and moving in grooves 6. Sidewards from grooves 6 in bit 1 surface, as per figure 3, there are notches for projecting parts 3, into which the projecting parts are guided due to the mutual rotation of the bits. Thereby, bits 1 and 2 are in locked state and bit 2 is rotated by bit 1, while the locking is re¬ tained. The locking is opened by reverse rotation. Projecting parts 3 are square in order to receive by a bigger face the impacts from the inner bit and to transmit them to the outer bit. Groove 6 of bit 1 is also a flow channel for the flushing medium, whose direction of flow, in this case, is backward in the channel. In figure 4 drilling has advanced to a location, where ring bit 2 and protection tube 4 have been left. Drilling has proceeded only by bit 1. For demounting of the inner bit from the outer bit, the rotation of the drill assembly has been reversed. Hammer 7 transmits the rotation to bit 1. Reverse rotation of bit 1 opens the bayonet joint in such a way that projecting part 3 turns in groove 8 and enters groove 6, whereafter, drilling further by reverse rotation, projecting parts 3 glide out from grooves 6 to the front side of the ring bit, whereat the ring bit stops to rotate and remains totally immobile. The inner bit drills rock or other hard ground that does not collapse into the hole. If drilling is stopped at a wanted depth or length, bit 1 and the drilling equipment are pulled out from the hole. Bit one passes ring bit 2 in running through it, when the bit is turned into a position where projecting parts 3 hit grooves 6 and glide through bit 2. Figure 5 illustrates an example of ring bit 2 with several pro¬ jecting parts 3 for several sequentially arranged axial bayonet joints, by means of which construction a face to transmit impacts to ring bit 2 is produced. Likewise, the protection tube is pulled with several sequential shoulder faces. On using many sequential bayonet joints and pulling shoulders of protection tube 4, it is possible to make ring bit 2 thinner and yet strong enough for drillings of longer duration. By means of a method and a bit assembly as per this invention it is possible to carry out, advantageously, s.c. anchoring dril¬ ling, whereat drilling is done by the outer bit till hitting rock and a certain distance by the inner bit in the rock. Since reversed flushing is used for removal of drill waste, whereby there is through inner bit 1 a straight channel tube up to the surface, an anhcor wire rope can be taken through the channel to the bottom of the bore and, for instance, on pulling up the bit, concrete can be poured through the channel into the hole. When the hole is filled and bit 1 pulled out to the level of ring bit 2, the outer bit and even the protection tube are then pulled out and the hole is filled with concrete at the same time. If during drilling the ring bit and the protection tube have been left in the hole at a too early stage, the inner bit can be pulled up to the ring bit and locked and drilling continued. In order to carry out properly the mutual rotation of bits 1 and 2 necessary for locking, it is worth to record on the ground the mutual depth position of protection tube and the drill rod in¬ side it, when bits 1 and 2 are locked, so that relocking could be made in the same position. This is of great significance, especially if there are several sequential bayonet lockings between the bits as shown in figure 5. The inner bit 1 according to this investion is characterized in that on its outer shell there are transvers ring grooves 8 ending in a vertikal wall 9. The groove 8 flanks function as faces transmitting impacts to ring bit 2 and the face 9 as rotation-transmitting means. The outer shell of bit 1 lacks stepped impact-transmitting shoulders known from previous designs. By means of a method and bit assebmly according to this invent¬ ion both vertical as well as horizontal holes can be drilled. Likewise, the axial groove of the bayonet joint can be also in the ring bit and the projecting part in the inner bit.

Claims: PATENT CLAIMS 1. A method to drill a hole in the soil by a bit assembly com¬ prising a ring-shaped drill bit (2) to drill the outer circle of the hole and to which a protection tube system is coupled, which is mounted in the hole when the drilling advances and a cylind- ric inner bit (1) to drill the center portion of the hole and from which at least the rotative motion is transmitted to the outer bit (2) characterized in that drilling by the outer bit (2) and pulling out the protection tube (4) are stopped by dis- connetion of the outer bit (2) from the inner bit (1) in a wanted spot, whereafter drilling is continued with the inner bit (1) only. 2. A method according to patent claim 1 characterized in that drilling is carried out by hammering bits (1,2), while the inner bit (1) transmits the impacts to the outer bit (2) by means of projecting parts (3) in the bayonet joint. 3. A method according to patent claims 1 and 2 characterized in that the inner bit (1) can be pushed through the outer bit (2) in each direction and, upon need, the outer bit can be locked to the inner bit. 4. A method according to any of the above patent claims 1 - 3 characterized in that the first portion of the hole is drilled by the complete bit assembly (1,2), the second portion by the inner bit (1) and the inner bit removed from the hole either alone or together with ring bit (2) and protection tube (4). 5. A bit assembly including an inner bit (1) drilling the hole center and a ring bit (2) drilling the hole outer circle and at least a rotation-transmitting joint between said bits, and a protection tube, mounted in the bore during drilling, is coupled to the outer bit (2), characterized in that the inner bit (1) can be threaded through the outer bit (2) from each direction, locked to the outer bit (2) by inter-rotation of both bits and in which locking at least one bit (2) is rotating and moving along with the other bit (1). 6. A bit assembly according to patent claim 5 characterized in that between the bits (1,2) there is one or more sequential bayonet joints, and projecting parts (3) in these joints trans¬ mit the rotative motion and drilling force, i.e. the impacts, to the outer bit (2). 7. A bit assembly according to patent claims 5 and 6 character¬ ized in that axial groove (6) in one of bits (1) or (2) of the bayonet joint is also the flow channel of flushing medium. 8. An inner bit forming with ring bit (2), that drills the hole outer circle, a united bit assembly to drill a hole or tunnel in the soil characterized in that there is on the cylindric outer shell of inner bit 1 transversal grooves (8) with regard to the axial direction, the side faces of which extrude in the direct¬ ion of inner bit (1) radius and transmit impacts and/or rotation to ring bit (2) . 9. An inner bit according to patent claim 8 characterized in that there is on its shell or more axial grooves (6). 10. An inner bit according to patent claims 8 and 9 charact¬ erized in that there are several sequentially arranged axial ring-shaped grooves (8) on the shell and that the grooves end in wall (9).

Inventors: ILOMAEKI VALTO, ILOMAEKI, VALTO
Applicants: ILOMAEKI VALTO, ILOMAEKI, VALTO
Application year: 1995
Main classification: E21B7
IPC codes: E21B3, E21B7, E21B10, E21B17