GB2324820A - Device for widening an earth borehole - Google Patents

Abstract

A device for widening an earth borehole comprises at least one broaching spiral (5) fitted at the end of a tubular linkage (2) connected to a rotary-tractive drive (not shown), said spiral having a conical envelope and a direction of conveying of the excavated soil counter to the direction of advance. The broaching spiral (5) is connected to a widening cone (3) which is attached to the tubular linkage (2) by a connecting piece (1). The broaching spiral is positioned on a tubular core (4) which is mounted rotatably in a bearing member in the form of a swivel (6). This swivel is connected by radial struts to a smoothing ring (8) and to a coupling (9) to which a follower pipe or cable can be attached. Large passage openings between the struts permit the removal of excavated soil. Nozzles (12, 13, 14, 15, 16, 17) are provided at various locations and angles on the tubular core and widening cone.

Description

V 2324820, 1 "Device for widening an earth borehole."

The invention relates to a device for widening earth boreholes, for example a pilot borehole produced by means of a percussion boring machine or a pipeline laid in the ground which is destroyed at the same time as it is widened.

It is known to provide self-propelled percussion boring machines at the front or rear end with a widening cone which displaces the soil surrounding the pilot borehole sideways as the machine advances, thereby causing considerable compaction of the soil surrounding the borehole. However, difficulties arise if the soil contains obstructions and/or cannot be sufficiently compacted. In any event, however, the expenditure of energy in respect of the work of compaction which has to be performed is considerable, and when obstructions are present in the ground the directional stability is poor.

To counter this, it is further known to drive the widening cone through the ground not only by means of the percussion boring machine, but at the same time to pull it by means of a cable passed through the pilot bore or the pipeline and a winch positioned in the target pit. While in this way the rate of working can be increased and the directional stability improved, the work of compaction for the enlargement of the initial bore must nevertheless still be performed.

From US patent specification 4 925 344 another method of operation is known in which at the end of a tubular linkage a drill head in the form of a relatively slim cone fitted with a cutting spiral is fitted, with which a traction cable engages.

The cutting spiral serves as a tool for the destruction of a pipeline laid in the ground and at the same time to carry away the fragments of the pipe and the soil excavated in the widening of the earth borehole.

Between the turns of the spiral there are outlet openings which are supplied with a lubricant through the tubular linkage.

This lubricant serves both to cool the highly stressed cutting spiral and in addition to reduce the friction between the drill 2 head and the cutting spiral on the one hand and the pipeline to be destroyed and the surrounding or won soil on the other hand. Furthermore the lubricant lowers the frictional resistance of the soil surrounding the widened borehole and thereby facilitates the subsequent or even simultaneous drawing in of a new pipeline.

An important disadvantage of the procedure described above is that the excavated soil must be conveyed away in the direction of boring or of advance, i.e. through the cross-section of the old pipeline, which is small relative to the volume of the soil excavated during the widening and of the fragments of the old pipeline. Consequently the drill head constantly pushes a more or less compact volume of won soil along in front of it. As a result of the friction with the rotating drill head, and dependent on the mass of soil which accumulates, this requires a considerable expenditure of energy.

It is therefore the object of the invention to make faster progress in boring possible and especially to lower the amount of energy which has to be expended for conveying away the excavated soil and, in the case of the destruction of a pipeline laid in the ground, the fragments of pipe.

To this end, the invention provides a widening device wherein at least one broaching spiral having a conical envelope surface and having a direction of conveying for the excavated soil and any fragments of an old pipeline, if there is one, which is counter to the direction of advance is fitted at the end of a linkage connected to a rotary-tractive drive. In this way the soil to be conveyed away is very quickly moved out of the vicinity of the broaching spiral so that the ground can be excavated substantially unhindered by loose soil and possible fragments of pipe.

In the device in accordance with the invention two spirals can also run parallel to one another. In addition the broaching spiral can take the form of a passage for a flushing liquid: it then consists of U-shaped plates welded to one another and has a rectangular cross-section standing on one narrow side.

3 At least between the linkage and the spiral, nozzles can be positioned which are directed in and/or counter to the direction of advance. Some or all of the nozzles can be made such that the jets issuing from them also perform excavating work, but in any case such that they facilitate the carrying off of the loose soil. Furthermore, nozzles with the same or similar effect can also be provided in a tubular core carrying the broaching spiral, arranged at an acute angle to the axis of the pipe. The tubular core preferably has a diameter which is small relative to the envelope surface, so as to provide a relatively large free space for the excavated soil between the envelope surface and the tubular core. This is particularly the case if the included angle between the axis of the tubular core and the envelope surface amounts to 5 to 60', and is preferably 25 to 40'. 15 Between the linkage and the broaching spiral a widening cone can be placed which, depending on its contour, widens the pilot borehole by lateral displacement of the soil before the broaching spiral excavates soil and thus further enlarges the section of the widened borehole. 20 The nozzles may be arranged in the widening cone, which performs a certain amount of widening work before the broaching spiral becomes effective. Behind the broaching spiral in the direction of advance a smoothing ring can be provided which smooths the walls of the earth borehole widened by the broaching spiral and leads to a certain amount of compaction of the soil in a more or less narrow zone, according to its composition, and at the same time improves the directional stability.

A smoothing ring which has proved particularly satisfactory is one comprising a hollow cylindrical section which is connected by radial struts to a bearing member. The openings formed between the radial struts serve for the passage of the soil to be conveyed away: together they are large enough to allow unhindered removal of the soil.

In order to minimise the friction between the smoothing ring and the soil, the broaching spiral should be mounted rotatably 4 in the bearing member, so that the smoothing ring does not rotate and the broaching spiral can perform its work independently of the smoothing ring.

In any case the bearing member can be provided with a coupling for attaching a follower pipe which is drawn in simultaneously with the widening of the earth borehole and in addition facilitates the removal of the soil through the interior of the pipe. The coupling for the follower pipe can also be located on the smoothing ring, provided this does not rotate.

The invention will now be described in more detail, by way of example, with reference to an embodiment shown in the accompanying drawings, in which: Fig. 1 is a side view of a spiral broach, longitudinal section, and partly in Fig. 2 is a plan view of the spiral reamer shown in Fig. 1.

The spiral broach consists essentially of a connecting piece 1 to which is attached a tubular linkage 2, connected to a rotary-tractive drive (not shown), a widening cone 3 and a tubular core 4 having at least one broaching spiral 5. The spiral can be in the form of a hollow body and have outlet openings for a flushing liquid. The conical surface of the widening cone 3 in practice constitutes an extension of the envelope surface of the broaching spiral, with the result that the broaching spiral 5 does not eat into the soil, but merely scales off a more or less thin layer of the soil surrounding the pilot borehole. This soil then fills the relatively large free space between the envelope surface and the tubular core 4, which has a relatively small diameter.

The free end of the tubular core 4 is mounted rotatably in a bearing member in the form of a swivel 6. This swivel is connected by radial struts 7 to a smoothing ring 8 and to a coupling 9, for example for a follower pipe or cable (not shown).

Between the struts 7 there are relatively large passage openings for the soil excavated by the broaching spiral.

The tubular linkage 2 is connected to a longitudinal bore in the spiral broach from which a number of nozzles 12, 13, 14, 15, 16, 17 proceed in various directions. Through these nozzles a flushing liquid, for example a bentonite/water suspension, can be supplied, in order to facilitate the conveying away of the soil which has been won, to stabilise the surrounding soil and to decrease the friction between the soil and the spiral broach. The nozzles can be of different dimensions. Thus for example individual nozzles can have such a small cross-section that cutting jets issue from them which excavate the soil, while other nozzles, in particular the backward-pointing nozzles 13, 14, 15, 16, 17, merely supply flushing liquid. However, according to the composition of the ground only conveying flushing liquid or excavating cutting jets can issue from all the nozzles.

Since the tubular linkage 2, together with the connecting piece 1, the widening cone 3 and the tubular core 4, is mounted rotatably in the swivel 6, the smoothing ring 8 stands still during the boring operation. Its task is to smooth the walls of the earth borehole widened by the broaching spiral 5 and to stabilise the position of the spiral broach or to centre the broaching spiral so as to avoid directional deviations.

6

Claims (1)

1. Claims

   Device for widening an earth borehole, comprising at least one broaching spiral fitted at the end of a linkage connected to a rotary-tractive drive, said spiral having a conical envelope surface and a direction of conveying of the excavated soil counter to the direction of advance.

   2. Device as claimed in claim 1, wherein the broaching spinal is fitted on a cylindrical core.

   Device as claimed in claim 1 or claim 2, wherein a widening cone is fitted between the linkage and the broaching spiral.

   Device as claimed in any of claims 1 to 3, wherein nozzles are provided at least between the linkage and the broaching spiral.

   5. Device as claimed in claim 4, wherein the axes of the nozzles run at an acute angle to the longitudinal axis of the broaching spiral.

   6. Device as claimed in claim 4 or claim 5, wherein at least some of said nozzles are located in a widening cone.

   Device as claimed in one of claims 4 to 6, wherein said nozzles point in different directions.

   8. Device as claimed in one of claims 1 to 7, wherein the broaching spiral is connected to a smoothing ring.

   Device as claimed in claim 8, wherein the smoothing ring consists of a hollow cylindrical section and is connected by radial struts to a bearing member.

   7 10. Device as claimed in claim 9, wherein the head end of the broaching spiral is rotatably mounted in said bearing member.

   11. Device as claimed in claim 9 or claim 10, wherein said bearing member is connected to a follower pipe.

   12. Device as claimed in one of claims 1 to 11, wherein the included angle between the envelope surface of the broaching spiral and the axis of the tubular core amounts to 5 to 6C.

   13. Device as claimed in one of claims 1 to 12, wherein th broaching spiral is in the form of a hollow body.

   is 14. Device as claimed in claim 11, wherein the broaching spiral is provided with outlet openings for a flushing liquid.