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Title:
HOLE ENLARGEMENT PROCEDURE AND APPARATUS FOR THE IMPLEMENTATION THEREOF
Document Type and Number:
WIPO Patent Application WO/2019/021042
Kind Code:
A1
Abstract:
Hole enlargement procedure and apparatus for the implementation thereof The subject of the invention is the procedure for the enlargement of a hole drilled into the ground, during the preparatory phase of which a drill pipe, driven through the pilot bore hole, is connected to the drilling unit located at one end of the pilot bore hole, and then, a ram piston reamer is connected to the other end of the drill pipe, and in the enlargement phase, the reamer is pulled to the drilling unit, while the pilot bore hole is enlarged to its final size, or to an interim size, and, during this process, drilling liquid is discharged from the reamer both in the direction of enlargement (1) and in the direction opposite to the direction of enlargement (2). It is characterized in that cutting operation is carried out at any time during the operation at or within the limits of the reamer's projection onto a plane that is perpendicular to the direction of enlargement (1), and the undesired mixing of the drilling liquids released in the direction of enlargement (1) and the direction opposite to the direction of enlargement (2) is prevented. The ram piston reamer apparatus implementing this procedure is also a subject of this invention.

Inventors:
SZIGETVARI CSABA (HU)
WAGNER ANDRAS (HU)
Application Number:
PCT/IB2017/055329
Publication Date:
January 31, 2019
Filing Date:
September 05, 2017
Export Citation:
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Assignee:
CONSTRUCTEAM ZRT (HU)
International Classes:
E21B7/28; E21B10/00; E21B10/26; E21B10/46; E21B10/60
Domestic Patent References:
WO1988008480A11988-11-03
Foreign References:
DE102008053239B32010-08-19
CN204457441U2015-07-08
DE102012013119A12014-01-02
DE19610239C11997-07-17
US4117895A1978-10-03
US5979573A1999-11-09
US6386299B12002-05-14
US6926100B12005-08-09
DE20203143U12002-06-13
NL1004632C21998-05-28
CA1307519C1992-09-15
CN102587836A2012-07-18
KR101249257B12013-04-01
CN204457441U2015-07-08
CN103527092B2015-10-14
CN202810662U2013-03-20
CN102003140B2012-10-17
US6668946B22003-12-30
Attorney, Agent or Firm:
PINTZ, Gyorgy (HU)
Download PDF:
Claims:
CLAIMS

1. Procedure for the enlargement of a hole drilled into the ground, during the preparatory phase of which a drill pipe, driven through the pilot bore hole, is connected to the drilling unit located at one end of the pilot bore hole, and then, a ram piston reamer is connected to the other end of the drill pipe, and in the enlargement phase, the reamer is pulled to the drilling unit, while the pilot bore hole is enlarged to its final size, or to an interim size, and, during this process, drilling liquid is discharged from the reamer both in the direction of enlargement (1) and in the direction opposite to the direction of enlargement (2), characterized in that cutting operation is carried out at any time during the operation at or within the limits of the reamer's projection onto a plane that is perpendicular to the direction of enlargement (1), and the undesired mixing of the drilling liquids released in the direction of enlargement (1) and the direction opposite to the direction of enlargement (2) is prevented.

2. The procedure according to claim 1 , characterized in that, during the preparatory phase, the drill pipe is connected to the reamer with a threaded connection, and then a pipe is connected to the reamer, and the pipe is pulled after the reamer during the enlargement phase, and it is disconnected from the reamer at the end of the enlargement phase.

3. Any of the procedures according to claims 1 and 2, where, during the preparatory phase, cutters (8) pointing into the direction of enlargement (1) and the direction opposite to the direction of enlargement (2) are installed onto the reamer, characterized in that the projection of the cutters (8) onto the plane perpendicular to the direction of enlargement (1) falls within the limits of the reamer's projection onto the plane perpendicular to the direction of enlargement (1).

4. Any of the procedures according to claims 1 to 3, characterized in that, during the preparatory phase, a connecting unit (4) of the reamer, is fitted with a wear-resistant component (9), and the connecting unit (4) is used to plug the hole during the enlargement phase, thereby preventing the mixing of drilling liquids discharged in the direction of enlargement (1) and the direction opposite to the direction of enlargement (2).

5. Ram piston reamer apparatus for implementing the procedure according to claim 1, which includes a back support unit (3), a front support unit (5), a connecting unit (4) between the back and front support units (3, 5), a mounting unit (6) for the front support unit (4), and at least one nozzle (7) that is capable of discharging drilling liquid and at least one cutter (8) on each of the back and front support unit (3, 5), characterized in that the connecting unit (4) includes all points of the apparatus that are farthest from the centre of gravity of the apparatus on the apparatus' projection onto the plane perpendicular onto the direction of enlargement (1), and the projection of the cutters (8) onto the plane perpendicular to the direction of enlargement (1) falls within the limits of the apparatus' projection onto the plane perpendicular to the direction of enlargement (1).

6. The apparatus according to claim 5, characterized in that the connecting unit (4) is rotationally symmetric, and it includes at least one wear-resistant component (9), and the wear- resistant component (9) is a hard metal frame, a welding joint, hard surface cover, nitrided surface component, or cemented surface component, and the wear-resistant component (9) goes along the total length of the connecting unit (4).

7. Any of the apparatus according to claims 5 to 6, characterized in that the mounting unit (6) includes an internal or external threaded shape.

8. Any of the apparatus according to claims 5 to 7, characterized in that the apparatus includes a holding unit (10), and the holding unit (10) is connected to the back support unit (3) and is suitable for receiving a pipe, and the holding unit (10) is a rotating head, which is connected to the back support unit (3) through a bearing that allows it to rotate relatively.

Description:
Hole enlargement procedure and apparatus for the implementation thereof

The subject of the invention is the enlargement of holes drilled into the ground. In the preparatory phase of the procedure, a drill pipe, driven through the pilot bore hole, is connected to the drilling unit located at one end of the pilot bore hole, and a ram piston reamer is connected to the other end of the drill pipe. In the enlargement phase of the procedure, the reamer, with or without the conduit to be pulled in, is pulled toward the drilling unit, while the pilot bore hole is enlarged to its final size, or to an interim size, and drilling liquid is discharged from the reamer both in the direction of enlargement and in the direction opposite to the direction of enlargement. The ram piston reamer implementing this procedure is also a subject of this invention.

The apparatus includes a back support unit, a front support unit, a connecting unit between the back and front support units, a mounting unit, at least one nozzle suitable to discharge drilling liquid and at least one cutter on the back and front support units.

The following solutions form part of the state of art.

A principle followed when describing the design and operation of devices used for hole enlargement and/or the pulling of conduits during horizontal directional drilling (hereinafter: HDD technology) is that the mixture of drilling liquid and the produced cuttings (mud) is moving in the drilling channel in a direction opposite to the direction of travel of the reamer. It is also assumed in such descriptions that the cut soil forms a homogenous mix with the drilling liquid, which is usually a water-based mixture of water or betonite, and sometimes other viscosity improving materials are also added (special polymer and other filler materials). According to the basic principle of such operational descriptions, the flow of the mud removes from the drilling channel all solid blocks of various sizes (stones, clay blocks etc.) that are not mixed in the mud in a liquid-like manner. In currently applied drilling machines, the emerging relatively low flow speeds (up to 1 to 3 m/min) usually do not remove such solid blocks from the drilling channel completely. The mud speed would need to be increased by approximately 100 times to safely remove such solid blocks, which would require a corresponding increase in storage and pump capacity, not to mention the need to dispose or recycle to increased amount of mud (which is often qualified as hazardous waste). The factors would make the use of current drilling machines unfeasible from a technical and financial perspective. According to the laws of physics, the direction and speed of flow of liquids between two points is fundamentally determined by the difference in pressure at the given points, as well as the hydraulic resistance between the two points.

During the pilot drilling, the mud flows in the space between the pilot bore hole, which is larger than the drill-rod, and the drill-rod in a direction opposite to the direction of travel of the drill head due to the pressure difference between the nozzles of the drill head and the beginning of the pilot bore hole.

At the commencement of the enlargement, the hydraulic resistance between the nozzles of the reamer and the hole's end opposite to the direction of movement of the reamer is considerably smaller, than at the other end of the hole, meaning that the mud, according to the currently accepted operating principle, will flow in a direction opposite to the direction of movement of the reamer. However, at some point the hydraulic resistance between the reamer and the two ends of the hole will be the same. The emergence of this balance depends on when and where the solid blocks behind the reamer pile up and form an obstacle to the flow due to the insufficient speed of flow. In practice, this situation is absolutely unpredictable. Due to the equal hydraulic resistance, the mud flows in both directions, but the volume and speed of the mud flowing backward (i.e. in the direction opposite to the direction of travel of the reamer) is reduced due to the liquid also flowing forward. With its speed of flow being reduced, the mud's ability to remove the soil parts cut by the reamer becomes reduced. The situation deteriorates even further as the reamer keeps moving forward: the cut soil parts keep piling up behind the reamer, and the drilling liquid flows forward with increasing speed and being less and less mixed with the soil, i.e. without any use technically.

Another important factor is that the forward speed of the reamer is comparable to the speed of the mud, meaning that this speed reduces the mud's absolute backward speed of flow, relative to the wall of the hole. Thus, no accurate information is available at the end of the enlargement as to whether or not the mud left in the hole is liquid-like and free of solid blocks.

At the time of pulling in the conduit, the solid blocks in the hole may pile up along and in front of the conduit in an unpredictable manner. In addition to interfering with the mud's flow, they may also deform the plastic pipe to be pulled in, even if the external pressure on the pipe is increased only slightly. (E.g. an external pressure of 1.3 bar is enough to deform a polyethylene plastic pipe with a nominal pressure of 6 bar.) If the solid blocks pile up in front of the plastic or steel pipe to be pulled in, they may result in the pipe being stuck permanently, thereby possibly causing significant financial losses. Currently applied reamers can be divided into two categories according to their shape. Reamers with a coned body are commonly fitted with cutters that extend beyond the largest diameter of the cone, and the cone body is notched, the diameter of which increases going backward, in order to channel the mud backward. In recent years, some coned reamers are produced without any mud channelling notches, where the relatively large cutters considerably extend beyond the largest diameter of the cone. Certain machines are fitted with fixed cutters, while other machines are fitted with external rotating cutters.

As for reamers with a not cone-shaped body, the beginning of the body is usually cone shaped, primarily to help the reamer to align with the centre of the pilot bore hole. Otherwise, the body may have various shapes. For example, it may be fitted with three wings, or three front-and-back props. During the rotation of such reamers, the mud in the space of the reamer is not forced backward by any mechanical means, not even by solutions similar to the notches on cone-shaped reamers.

For the purposes of HDD technology, the types of grounds can be classified as follows: 1. Clay and sludge (granulation: 0 to 0.06 mm), 2. Sand (granulation: 0.06 to 2 mm), 3. Pebble (granulation: 2 to 60 mm), 4. Rolling stone (granulation: above 60 mm), and rock. Rolling stones and rocks can be drilled using special rock drills /Felsbohrkopfe/ and can be reamed using special rock reamers / Grundo-Rock-Ream/. The following paragraphs do not apply to this kind of ground.

As for the application of the HDD technology, there are about 50 kinds of reamers in circulation, recommended for different - not rocky - grounds. In the United States, cone- shaped and not-cone-shaped reamers are recommended for various types of ground, depending on their design. This fact raises the question if it is justified to offer reamers with various designs, as well as the problem of selecting a reamer that is most suitable for the ground at hand. In Europe, using reamers in clay and sludge, sand, and pebbles requires different equipment. Using different reamers in clay and sludge, and in sand and pebble is recommended. This often leads to difficulties regarding the enlargement of pilot bore holes and the selection of the appropriate reamer when the composition of the ground changes mid-drilling (clay ground or sandy ground). Other problems arise when enlarging bore holes in urban environments. In such cases, clay, sand, and embedded hard objects (concrete, stone, bricks etc.) may appear during the same drilling, and there is no established practice of selecting the appropriate reamer for such grounds. The above considerations give rise to the need to design a universal and ground-independent reamer that can be used in any kind of ground other than rocks, to be applied primarily with the HDD technology.

Canadian patent document No. CA 1307519 C, dated in 1988, describes HDD technology, including pilot bore hole drilling, bore hole enlargement and pulling in a conduit, using a bidirectional drill bit (Figure 12), and with the mud moving in the traditional direction, i.e. opposite direction of travel of the reamer. The device described for enlarging the bore hole is a two-sided coned tool, where one side is shaped as a closed cone, and the other side includes a cone with nozzles in order to facilitate the traditional removal of the mud, i.e. in opposite direction of travel of the reamer.

Chinese publication application No. CN 102587836 A describes a two-way reamer design, including coned rock cutters that are rotated by the flow of liquids. The essence of the invention is that, unlike previous solutions, it includes not one, but two usual rock cutting reamers placed in front of each other, so that the reamer can be pushed back in the opposite direction, if it is clamped during its movement forward. This rock reamer is unsuitable for expanding holes in other kind of soils, while the present invention can be used in any kind of soil, except rock.

Korean patent document No. KR 101249257 Bl describes a reamer, which can be operated in hammering mode and is operated by a pneumatic cylinder. Compressed air is supplied through a pie connected to the back end of the reamer device. The drill liquid enters through the drill bits connected to the front end of the reamer. In the front coned part of the reamer, compressed air driven driving blocks drive the hammers. The drill liquid flows from the holes on these hammers. The solution can be used in rocky soils primarily, and another disadvantage is that it requires a complex supporting apparatus, and another disadvantage is that this reamer cannot be used to pull in the conduit to be installed.

Chinese utility model No. CN 204457441 U also describes a bidirectional HDD drill, where both sides have the same design. On both sides of the reamer, there are detecting rods that detect the working direction of the reamer through pressing, and the apparatus controls the opening and closing of the drilling liquid released through the nozzles according to the direction of the reamer. A disadvantage of the solution is that the reamer does not release any drilling liquid behind the reamer when moving forward, and that the detecting rods are probably vulnerable in rocky soils.

Chinese patent document No. CN 103527092 B describes a reamer apparatus, which removes the mud, i.e. the mixture of drilling liquid and cuttings, through a pipe connected to the reamer using the suction effect created by a nozzle inside the reamer. The mud is cleaned at the end of the pipe, and the cleaned liquid is returned to the enlarged hole. A disadvantage of this solution is that, in the course of the enlargement process, one more pipe needs to be connected to the continuously forward-moving reamer and the mud cleaning apparatus at the end of the hole, and that, as a consequence, the bore cannot pull in the conduit to be installed.

Chinese utility model No. CN 202810662 U describes a similar solution, where the mud is removed from the hole through the drill bits connected behind the reamer. There is a nozzle in the reamer, and the suction effect thereof sucks in the mud, i.e. the mixture of drilling liquid and the cuttings, from the vicinity of the reamer. When used in rocky soils, even clean water can be used as drilling liquid. A disadvantage of the solution is that it can be used for enlargement only in soils where the pilot bore hole cannot collapse, since the drilling liquid or mud used in this technology does not fill the bore, and such soils are typically rocky soils, and another disadvantage is that this reamer cannot be used to pull in the conduit to be installed due to the drill bits connected behind the reamer.

Chinese patent document No. CN 102003140 B describes a solution where the mud, i.e. the mixture of drilling liquid used for directional drilling and the cuttings, is removed from the suitably designed reamer bit through a pipe using a special mud pump. A disadvantage of the solution is that one more pipe needs to be connected to the continuously forward-moving reamer and the mud pump at the end of the hole, and that, as a consequence, the reamer cannot pull in the conduit to be installed.

American patent document No. US 6668946 B2 describes a reamer that can be steered using a hydraulic cylinder. The relative direction of the reamer to the carrier frame can be changed by the cylinder, so that the pilot bore can be followed as accurately as possible, even if larger rocks are other obstacles are in the way. Any change to the direction of the reamer caused by a collision is detected through the carrier frame, and the cylinder is used to perform gradual path adjustment. The pilot bore can be followed, for example, using a laser positioning system, or a digital gyroscope and a compass.

The purpose of the invention is to eliminate the shortfalls of known solutions, and to provide a procedure and an apparatus implementing that procedure, through which the speed of the mud generated during the enlargement is increased and is made steadier, thereby achieving continuous debris removal, and, as a consequence, the speed of the enlargement apparatus (i.e. the speed of the enlargement operation) is increased. Another purpose of the invention is to maximize the safety of the conduit pulling process, i.e. the final objective of the HDD technology, by ensuring that the hole is filled by a drilling liquid that is free from solid blocks in the vicinity of the conduit, and not by mud and/or solid soil blocks in the mud. The inventive step is based on the recognition that an invention that is more advantageous than the previous solutions can be achieved by implementing the enlargement procedure according to claim 1. The inventive step is based on the recognition that the mud may flow in the same direction as the reamer, if the necessary difference in pressure is ensured in the space between the pilot bore hole and the drill pipe, which may be achieved through the hydraulic separation of the drilling liquid released from the reamer in the direction of enlargement (forward) from the liquid released in the direction opposite to the direction of enlargement (backward), so that the permanent pressure of the drilling liquid released in the direction of enlargement ensures the difference in pressure necessary for the mud to move forward. The inventive step also includes the recognition that the absolute speed of flow of the mud moving in the direction of enlargement (forward), relative to the wall of the hole, is further increased by the forward movement of the reamer - which is comparable to the mud's speed of flow -, unlike in the case of the mud moving in the direction opposite to the direction of enlargement (backward). The inventive step also includes the recognition that, unlike in the case of common practice, the largest possible reamer should be applied directly after the pilot drilling, taking into account the torque and pulling power of the reamer and the capacity of the drilling liquid pump, so that the speed of the mud flowing forward due to the movement of the reamer closing the drilling channel in the back, like a hydraulic piston, is increased significantly and in proportion to the free cross-sections of the reamer and the pilot bore hole. The inventive step also includes the recognition that the removal of solid blocks from the hole is supported by the mechanic cleaning effect of the reamer closing the cross-section of the hole, i.e. by the way the reamer, while moving forward, pushes such parts to its edges and presses them into the wall of the hole. This way, not only does the hole become free of solid blocks as the reamer moves forward, but we have also recognized that, as a secondary but very important effect, the wall of the hole becomes denser, which is very important for the stability of the hole. This recognition goes against current practices, which seek to avoid the collapse of holes drilled in unstable and collapsible grounds by mixing large volumes of bentonite and special filling materials into the drilling liquid and/or increasing the density of the mud flowing backward; in such situations, the increased hydraulic resistance of the mud, as an undesirable side-effect, interfered with the backward movement of the mud. The inventive step also includes the recognition that the pressing of the hole wall makes it possible to avoid the collapse of the hole even if the drilling liquid is significantly less dense than the mud. The inventive step also includes the fundamental recognition that, in the course of pulling in the conduit, the need for pulling power is mostly due to the resistance generated by the solid blocks located in the hole - working as a mechanic obstacle to the pulling of the conduit - and to the frictional resistance caused by the liquid in the hole pressing upward the conduit to be pulled in. The buoyant force may be countered by filling the conduit with water, but the optimal situation - i.e. the conduit floating in the liquid - may not be reached with this solution unless the density of the liquid in the hole is approximately the same as the density of water; the clean drilling liquid meets this requirement, but the mud, which also contains cut soil parts, does not.

The totality of the above recognitions - i.e. the existence of a hole that is free of solid blocks at the time of pulling in the conduit, a dense hole wall that does not tend to collapse, and the presence of small density drilling liquid in the hole at the time of pulling in the conduit - contributes to the achievement of the final objective of the invention, that is pulling in the conduit, with maximum safety.

Another part of the inventive step is that if the reamer is designed to implement the procedure according to the invention, the reamer can be pushed back with absolute safety if there is any obstacle in the previously enlarged hole, if the reamer hits an obstacle (rock, concrete etc.) during the enlargement process that prevents it from moving forward, since the cutter units - when the reamer is observed from the direction of enlargement - do not extend beyond the back coned part of the reamer, and drilling liquid discharging nozzles are also available on this part, as well as cutter units that can remove any obstacle that may be left in the hole, thereby avoiding significant financial losses. Another part of the inventive step is that, unlike in current practice (where the volume of the drilling liquid is about 3 to 4 times the volume of the cut soil, so that the somewhat thin mud can flow back easily), dense mud should be produced to implement the solution according to the invention, since the dense mud, flowing forward at high speed, is much more capable of picking up the solid soil blocks than any thinner and slower mud flowing backward. To this end, and depending on the type and density of the ground, the volume of the drilling liquid should be 0.75 to 1 time of the volume of the cut soil. In comparison to the use of known reamers, the final volume of mud will be significantly lower, because a considerable part of the produced thick mud (depending on the ground structure) will be pressed into the wall of the hole. In line with the set objective, the most general implementation form of the application according to the invention may be implemented according to claim 1. The most general form of the apparatus implementing the application is described in the main structural claim. The various implementation forms and described in the sub-claims.

Procedure for the enlargement of a hole drilled into the ground, during the preparatory phase of which a drill pipe, driven through the pilot bore hole, is connected to the drilling unit located at one end of the pilot bore hole. Then, a ram piston reamer, and optionally a conduit to be pulled in is connected to the other end of the drill pipe. In the enlargement phase, the reamer is pulled to the drilling unit, while the pilot bore hole is enlarged to its final size, or to an interim size. During this process, drilling liquid is discharged from the reamer both in the direction of enlargement and in the direction opposite to the direction of enlargement. A distinctive feature of the procedure is that cutting operation is carried out at any time during the operation at or within the limits of the reamer's projection onto a plane that is perpendicular to the direction of enlargement. The cutting operation can be performed by any kind of cutting unit or cutter fitted onto the reamer by moving the reamer.

Another distinctive feature is that the undesired mixing of the drilling liquids released in the direction of enlargement and the direction opposite to the direction of enlargement is prevented, distinctively by using hydraulic insulation between the front and back support units of the reamer, or by applying hydraulic resistance. Preventing the mixing of drilling liquids may also mean that at least one uninterrupted perimeter of the wall of the reamer is touching the hole wall during the entire enlargement section.

In another application form, during the preparatory phase, the drill pipe is connected to the reamer with a threaded connection, and then the pipe to be pulled in is connected to the reamer, and the pipe is pulled after the reamer during the enlargement phase, and it is disconnected from the reamer at the end of the enlargement phase, meaning that the pipe is pulled in at the same time as the enlargement is performed. The pipe may be connected using a threaded or other releasable connection, but, distinctively, the connection method allows the pipe to turn relative to the reamer, for example, the connection of the pipe and the reamer includes bearings.

In another application form, during the preparatory phase, cutters pointing into the direction of enlargement and the direction opposite to the direction of enlargement are installed onto the reamer. A distinctive feature of this application form is that the projection of the cutters onto the plane perpendicular to the direction of enlargement falls within the limits of the reamer's projection onto the plane perpendicular to the direction of enlargement, meaning that the cutters do not extend beyond the perimeter of the reamer when the reamer is viewed from the direction of enlargement, i.e. from the direction of movement of the reamer (from the direction of the current movement vector).

In yet another application form, during the preparatory phase, a connecting unit of the reamer, advantageously a pipe, is fitted with a wear-resistant component to slow down the wearing of the reamer, because, this connecting unit is used to plug the hole during the enlargement phase, meaning that it creates the hydraulic resistance between the direction of enlargement and the direction opposite to the direction of enlargement. In other words, this connecting unit prevents the mud forming in front of the reamer from mixing with the drilling liquid behind the reamer.

The apparatus applied during the implementation of the invention can be applied in the course of all kinds of ground and underground drillings, and it can be applied especially advantageously as a reamer in the course of horizontal directional drilling (HDD), and it can be applied as an apparatus to pull in a pipe in certain application forms.

In general, the apparatus is a ram piston reamer, which includes a back support unit, a front support unit, a connecting unit between the back and front support units, a mounting unit for the front support unit, and at least one nozzle that is capable of discharging drilling liquid and at least one cutter on each of the back support unit and the front support unit. In other words, in total, at least two nozzles and cutters are needed to implement the invention. The back and front support unit is advantageously shaped as a cone, and the connecting unit between the back and front support unit is advantageously a pipe. The nozzle may be a simple hole on the support units.

The apparatus may be divided into parts according to the direction of travel, meaning that the part facing the direction of enlargement may be called the front part, and the part facing the direction opposite to the direction of enlargement may be called the back part. The back support unit, the connecting unit, the front support unit, and the mounting unit may be realized, for example, by bending a single sheet, meaning that they form one single sheet part, but advantageously they are separate, pre-manufactured cone-shaped and pipe components that are connected to each other by welding along edges.

A distinctive feature of the apparatus is that the connecting unit includes all points of the apparatus that are farthest from the centre of gravity of the apparatus on the apparatus' projection onto the plane perpendicular onto the direction of enlargement, and the projection of the cutters onto the plane perpendicular to the direction of enlargement falls within the limits of the apparatus' projection onto the plane perpendicular to the direction of enlargement.

In another implementation form, the connecting unit is rotationally symmetric, and it includes at least one wear-resistant component. The wear-resistant component may be a hard metal frame, a welding joint, hard surface cover, nitrided surface component, or cemented surface component, and, advantageously, it goes along the total length of the connecting unit. In certain cases, it may be located only on certain narrow parts of the connecting unit, for example on the expected or empirically main wearing areas.

In another implementation form, the mounting unit includes an internal or external threaded shape, so that the drill pipe may be connected to it using an appropriate internal or external threaded shape. Advantageously, the mounting unit is a pipe.

In another implementation form, the apparatus includes a holding unit, and the holding unit is connected to the back support unit and is suitable for receiving a pipe, and the holding unit is a rotating head. The holding unit may be connected to the back support unit by welding, using a threaded shape, by using any other traditional mechanical means, or by a non- releasable joint, and the same applies to the above-mentioned connections between the connecting unit and the front and back support units, as well as the mounting unit and the front support unit. The rotating unit is advantageously connected to the back support unit through a bearing that allows it to rotate relative to the back support unit.

The invention is presented in more detail below with regard to one implementation form using a drawing.

Figure 1 shows a section drawing of the apparatus, shown from above.

Figure 1 shows a section of a characteristic implementation form of the apparatus. The body of the reamer includes two hollow, cone-shaped (truncated cone) body facing each other. This means that the back support unit 3 is typically shaped as a cone, and the front support unit 5 is also a shaped as a cone. The back and front support units 3, 5 are connected to each other by a connecting unit 4, which is typically a pipe. This connecting unit 4 provides the largest transversal expansion of the apparatus. Advantageously, the back and front support units 3, 5 and the connecting unit 4 share the same rotational axis, meaning that the body itself is rotationally symmetric. Nozzles 7 and cutters 8 are installed onto the back and front support units 3, 5 of the body, so that the cutters 8 do not extend beyond the endless cloak defined by the projection of the connection unit 4 onto the plane perpendicular to the direction of enlargement into the direction of enlargement, meaning that the farthest point (edge) of the cutters 8 located on the largest diameter from the rotational axis of the apparatus falls, advantageously, onto that very endless cloak. Advantageously, the nozzles 7 are evenly distributed on the cone cloak of the front support unit 5 along its length and diameter. One end of the apparatus ends in a mounting unit 6, which is typically implemented as a pipe with external or internal threading, to which a drill pipe may be connected with an appropriate internally or externally threaded part. Generally, the drill pipe is also a set of pipe sections connected to each other with threaded connections, and it connects the apparatus to the surface drilling unit. Advantageously, a holding unit 10 is also located on the other end of the apparatus, which may be, for example, a holed rotating head on a bearing. This means that, advantageously, the rotating head is capable of performing rotating movements relative to the apparatus that performs rotating movements during the drilling (typically HDD) operation, and along the same axis. During a two-step HDD operation, the conduit to be pulled in may be connected to this holding unit 10 at the beginning of the enlargement operation, on the surface end of the pilot bore hole that is opposite to the drilling unit. If the holding unit 10 is shaped as a rotating head, the conduit to be pulled in follows the reamer with a translation movement. While the apparatus is being pulled toward the drilling unit during the enlargement operation, the pilot bore hole is enlarged by the cutters 8 to its final diameter, in case of a two-step HDD, or to an interim diameter, in case of a multi-step HDD operation. In the course of the enlargement, drilling liquid is fed to the apparatus from the direction of the drilling unit, that is backward, meaning that a liquid flowing in the direction opposite to the direction of enlargement 2 is supplied through the drill pipe connected to the mounting unit 6. The drilling liquid is discharged, on the one hand, backward through the nozzles 7 of the back support unit 3 in the direction opposite to the direction of enlargement 2, and, on the other hand, through the nozzles 7 of the front support unit 5 in the direction of enlargement 1. Since the external diameter of the connecting unit 4 is the same as, or is bigger than, the largest enlargement diameter defined by the edges of the cutters 8, the apparatus separates the enlarged hole section from the hole section yet to be enlarged, and acts is a hydraulic piston in the hole. The connecting unit 4 solidifies the hole wall 11, but the continuous friction means increased tear and wear, which is countered by the wear-resistant component 9 of the connecting unit 4. In its most characteristic implementation form, the wear-resistant component 9 is a protruding frame-like component on the entire length of the surface. Characteristically, the wear-resistant components 9 are evenly distributed along the perimeter of the connecting unit 4. The cutters 8 located on the back cone make allow for changing the working direction of the apparatus.

The below calculation shows the main advantages of the invention. The examinations apply to mud speeds when enlarging a pilot bore hole that was pre-enlarged to a diameter of 200mm to a 600mm diameter hole using an RX33xl20 drill in a medium density, not rocky ground and without pulling in any conduit.

Technical details required for calculations:

- Cross-section area of the pre-enlarged hole (200mm)

- Cross-section area of the enlarged hole (600mm)

- Cross-section area of the drill pipe (73mm)

- Maximum drilling liquid volume

- Volume of forward flowing drilling liquid in a ram piston reamer

qi um. iKib i 4,0 \ 10 " ' | m 7mi n |

- Volume of backward flowing drilling liquid in a ram piston reamer

qf ,ro,hdb2 = 5,0 x 10 "2 | m 7mi n |

- Drilling liquid / soil mixture ratio

- Currently known reamers ri = 3,5 [-]

- Ram piston reamer r 2 = 7,5 x 10 "1 [-]

When calculating the mud's volume increase, it is to be taken into account that the excavated soil, after mixing with the drilling liquid, will increase the mud's volume by about half of its original volume.

Currently available reamers:

- Soil excavation speed qfeid,i = qfuro,o / Π = 1,29 x 10 "1 [m /min]

- Reamer speed \ box it . i = qioid. i / (A b , 0 - A a .„) 5, 12 \ 10 " ' [m/min]

- Generated mud volume q Z agy,i = qmro,o + qfeid,i / 2 = 5, 14 x 10 "1 [m /min]

- Relative backward flow speed of the mud v re i,i = q za gy,i / Ab, 0 = 1,82 [m/min]

- Absolute backward flow speed of the mud v a b S ,i = v re i,i - Vb6vit6,i = 1,31 [m/min]

Ram piston reamer:

- Soil excavation speed • qfoid,2 = qftro,hdbi / r 2 = 5,33 x 10 "1 [m /min]

- Reamer speed Vb6vit6,2 = qfoid,2 / (A b , 0 - A a ,o) = 2,12 [m/min] - Generated mud volume q Z agy,2 = qfur6,hdbi + qfeid,2 / 2 = 6,67 x 10 "1 [m /min]

- Relative forward flow speed of the mud, compared to the reamer

v re i,2 = q Z agy,2 / (A u - A t |.„) = 2,39 | m/min |

- Absolute forward flow speed of the mud, compared to the wall of the enlarged (600mm) hole Vabs(6oo),2 = Vb6vit6,2 + v re i, 2 = 4,51 [m/min]

- Absolute forward flow speed of the mud, compared to the wall of the pre-enlarged (200mm) hole Vabs(2oo),2 = Vabs(6oo),2 (A b , 0 / Α 3;0 ) = 40,6 [m/min]

As the example shows, the ram piston reamer has the following significant advantages in comparison to currently available reamers: when performing the same enlargement task using a currently available reamer, the mud flowing in the direction opposite to the direction of pulling the reamer with a speed of 1.31 m/min, relative to the hole wall, is thinned by 3.5 times, i.e. the mud is quite thin, while experience has shown that this speed may reduce to as low as zero during the enlargement process due to the increasing hydraulic resistance building up behind the reamer. When using the invention, the generated mud is thinned by 0.75 times, i.e. it is much denser, and it flows forward in the pilot bore hole at a speed of 40.6 m/min, i.e. more than 30 times faster, and this speed does not change while pulling the reamer. Furthermore, the generated mud's volume is proportionate to the mixing ratio of the drilling liquid and the soil forming the mud. This also determines the quantity of the generated mud. Thus, when applying the invention, 3.5/0.75=4.7 times less mud is generated. It should be noted that, as experience has also confirmed, the apparatus according to the invention has the extraordinary effect of solidifying the ground - current reamers do not have this effect. It is not possible to calculate this impact in advance, as it depends on the density of the ground to the enlarged, the pulling speed of the reamer, and the thickness of the generated mud. In practice, 10 to 50% of the mud's calculated quantity can be pressed into the walls, thereby reducing the mud's quantity possibly by 10 to 20 times in comparison to current reamers. In soft grounds, it happens often that no mud is generated during the process. The calculated pulling speed of the reamers is also significantly different: in the above case, the ram piston reamer can be pulled more than four times faster (2.12/0.512=4.14). In practice, it is advantageous to exploit the extraordinary ground solidifying effect of the invention in soft grounds, which works best at high pulling speeds. In certain cases, even a pulling speed of 5 to 10 m/min can be reached, which speed, in the above case, means working ca. 10 to 20 times faster than currently available reamers. The procedure and apparatus described above has numerous other advantages as well. It is an advantage of the invention that the reamer does not need to be changed if different types of soils - e.g. sand and sludge - appear during the same drill, as all enlargement and pipe pulling tasks can be performed applying a reamer implementing the procedure according to the invention and the recommended technology in any kind of ground other than rock. Consequently, the number of reamers to be kept on stock is significantly reduced, and there is no need to perform costly ground mechanical exploratory drillings before the drilling. Another advantage is that, during the application according to the invention and due to the fact that the cutters do not extend beyond the largest diameter of the apparatus according to the invention, the mud flowing before the reamer with high speed leaves the drilling channel through the pilot bore hole or the enlarged hole. If the hole before the reamer becomes blocked temporarily, it is possible that the mud passes through the gap between the largest diameter of the reamer and the ground and leaves backward. In such a situation, the solid soil blocks become pressed into the ground, and only liquid mud can get behind the reamer. As the reamer moves forward, the blockage in the hole in front of the reamer is removed in normal course. The thick mud behind the reamer leaves the drilling channel when the reamer is pushed back. In contrast to known solutions, tasks relating to the HDD technology can be performed within a shorter period of time, generating significantly less waste, and, essentially, with 100% safety (avoiding pipes getting stuck or becoming deformed) - in other words, more efficiently, economically, and safely. The application according to the invention, and the recommended reamer implementing it, is not sensitive to the viscosity of the drilling liquid, while determining the optimal viscosity thereof is a considerable challenge when using currently known reamers, depending on the composition and characteristics of the ground. Furthermore, as the reamer - designed with the right cone angle - moves forward, it presses some of the solid soil blocks into the wall of the hole, thereby increasing its density and stability significantly. The solidified hole wall makes the addition of expensive and environmentally harmful additives (polymers, filling substances) to the drilling liquid unnecessary. Thus, another advantage of the invention is that, in case of working in non- rocky grounds, the use of drilling liquids of 40 to 50 sec/1 MARSH viscosity is sufficient.

The field of application of the invention includes the enlargement of any pilot bore hole made with any kind of drilling technology, including the pulling in of any conduit using the reamer, when drilling liquid is supplied to the reamer through a pipe, and the reamer is pulled while rotating. In addition to the above examples, the invention may be implemented in other forms and with other production procedures within the scope of protection.