GB2214539A

GB2214539A - Locating devices for soil displacement hammers

Info

Publication number: GB2214539A
Application number: GB8727218A
Authority: GB
Inventors: David Edward Holloway
Original assignee: HOLLOWAY EQUIPMENT SALES LIMIT
Current assignee: HOLLOWAY EQUIPMENT SALES LIMIT
Priority date: 1987-04-02
Filing date: 1987-11-20
Publication date: 1989-09-06
Anticipated expiration: 2007-11-20
Also published as: GB2214539B; GB8727218D0; GB8707936D0

Abstract

The locating device comprises a cylindrical, radio-transparent housing 12 which is releasably connected between an airline for the soil displacement hammer (or mole) and the hammer itself so as to permit air communication through the housing. Mounted along the axis of the housing is a cylindrical radio-transmitter 18, such that, when the hammer is driven through the ground by repeated pnumatic impact, its location under the ground can be detected at the surface. <IMAGE>

Description

Locating Devices for Soil Displacement Hammers Ihe present invention relates to locating devices for soil displacement hammers.

Soil displacement hammers (commonly referred to as "moles") are increasingly employed for laying underground pipes, cables or conduits underneath a roadway or the like, without the need for excavating a continuous trench and therefore without disturbing the surface or causing disruption to traffic.

Conventional soil displacement hammers are powered by compressed air and operate as follows. A pit or trench is dug at one side of the area to be bored under and the soil displacement hammer is set up and aimed in the direction of the desired cable or pipe run. Compressed air is applied such that the mole bores the cable or pipe hole. Retrieval of the mole may be achieved by digging a corresponding pit at the opposite side of the area being traverse.

Soil displacement hammers of this type are described in, for example, G.B. Specifications 2134152 and 2147035, and PC1 Specification ;087/03924.

Soil displacement hammers are intended to be driven through the ground by repeated pneumatic impact (with, typically 400 to 700 pneumatic impacts per minute in use).

They are not intended to be rotatably driven nor to transmit torque, and therefore cannot function as drilling bits.

(Drilling bits are, of course, alternative tools for boring underground tunnels or the like.) While soil displacement hammers operate extremely effectively, and will normally cope with small obstructions such as tree roots, stones and the like, larger obstructions can deflect the tool from its predicted course making it difficult to retrieve. One proposal for overcoming the problem has been to attach a radio sonde to the compressed air hose behind the mole by means of waterproof tape or hose clips. However, in practice, such a sonde is not the complete answer since its shape and the fact that it is asymmetrically located on the hose, give rise to obstruction problems.

The use of a radio transmitter within a housing provided in line with a rotatably driven boring bit has been previously proposed in, for example,.S. Patent 3746106.

However, such a boring bit locator cannot easily be adapted for use in a soil displacement hammer, as will now be explained.

The only major requirements for the bit locator for a rotatably driven boring bit are that it should be capable of transmitting rotary motion and should permit passage of water to facilitate the cutting action of the boring bit. In contrast, a radio transmitter within a housing provided in line with a soil displacement hammer would be required to permit air to flow therethrough with little or no constriction or disturbance to the air flow, in order that the pneumatic drive transferred to the striker or anvil of the hammer is not adversely affected.

It is probably for this reason that the previously proposed solution to the problem of using a radio transmitter with a soil displacement hammer has been to attach the transmitter externally to the compressed air hose.

The present invention seeks to provide an improved locating device for a soil displacement hammer; according to the present invention therefore, there is provided a locating device for a soil displacement hammer which comprises a substantially axially symmetrical, radio transparent housing adapted to be fitted between an airline for the hammer and the hammer itself so as to permit air communication through said housing, said housing having mounted therein, substantially along the axis thereof, an axially symmetrical radio transmitter.

The housing would generally be cylindrical in shape and would conveniently be of the same external diameter as the airline to which it is to be attached. Preferably it will have end fittings allowing it to be releasably connected, at one end to the mole itself, and the other end to the airline.

The material from which the housing is made is not critical provided that it will meet the two requirements that it is sufficiently durable for the conditions it will be exposed to, and yet be sufficiently transparent to radio waves to allow the signal generated by the transmitter to be detected above the surface of the ground. For these reasons stainless steel is the preferred material.

The invention will be described further, by way of example, with reference to the accompanying drawings in which: Figure 1 is an axial sectional view of a first embodiment of a locating device according to the invention; Figure 2 is a side elevation of a modification of the device of Figure 1; Figure 3 is a more detailed view showing the radio transmitter and its mounting in the embodiment of Figure 2; and Figure 4 is a more detailed sectional view of the housing for the radio transmitter in the embodiment of Figure 2.

Referring to Figure 1, a locating device generally designated 10 comprises a cylindrical housing 12 adapted to be connected to a horizontal soil displacement hammer (not shown in the drawings) by male end fitting 14 and to a compressed air line by female end fitting 16 having a central bore 17.

Within the housing 12 is a radio transmitter or signal unit 18 mounted on a central boss 20, which is itself mounted at the end 22 of an air conduit 24 so as to close the end 22. A series of apertures 26 are arranged around the end 22 of conduit 24; in the embodiment illustrated, there would be four such apertures, arranged at 909 spacings (that is, symmetrically around the axis of conduit 24).

In use, air from the compressor passes into the housing 12 via bore 17, around the radio transmitter 18 and boss 20; then through apertures 26 into conduit 24; and then to the soil displacement hammer or mole.

In Figures 2 to 4, parts like those in Figure 1 are denoted by like reference numerals. In Figure 2, the radio transmitter 18, boss 20 and air conduit 24 are shown in phantom lines. Two apertures 26 are provided in conduit 24, these being spaced by 180ç. The apertures have bevelled ends 28 which taper outwardly in the direction of the radio transmitter 18 (that is, in the upstream direction relative to the predominant direction of air flow through the housing 12 and conduit 24); the bevelled ends 28 can be seen more clearly in Figure 3. Conduit 24 has a section 30 of enlarged diameter towards the downstream direction.

Referring to Figure 4, the enlarged diameter section 30 of conduit 24 engages an annular'rubber seal 32 provided internally of the housing 12. The housing 12 has a main, generally cylindrical portion 34 (of stainless steel, for example) having a close-fitting sheath 36 of, for example, heat-shrunk plastics material (such as a heat-shrunk polyethylene tube).

In the embodiment of Figures 2 to 4, the female end fitting 16 is provided with an internal thread 38, while male end fitting 14 is provided with an external thread 40.

In use, the compressed air hose is disconnected from the mole and the locating device 10 connected to the mole following which the compressed air line is connected to the locating device 10. The mole is then used in the conventional manner. The position of the mole can be located at the ground surface using a suitable receiver, of which many are available commercially. If desired the depth of mole can be monitored to ensure that it will not conflict with existing drains or other utilities and, should the mole be defected in use, its position can be determined so that an appropriate retrieval trench can be dug.

The locating device according to the invention is simple to use and does not involve problems of obstruction in the hole being bored.

Claims

CLAIMS:

1. A locating device for a soil displacement hammer, which comprises a substantially axially symmetrical, radio-transparent housing adapted to be fitted between an airline for the hammer and the hammer itself so as to permit air communication through said housing, said housing having mounted therein, substantially along the axis thereof, an axially symmetrical radio transmitter.

2. A locating device according to claim 1, in which the housing is substantially cylindrical in shape.

3. A locating device according to claim 1 or 2, in which the housing has substantially the same external diameter as the airline to which it is to be attached.

4. A locating device according to any of claims 1 to 3, in which said housing is provided with end-fittings such that it can be releasably connected at one end to the soil displacement hammer and at the other end to the airline.

5. A locating device according to any of claims 1 to 4, in which said housing is of stainless steel.

6. A locating device according to any of claims 1 to 5, in which said radio transmitter is mounted at the blind end of an air conduit secured in an airtight manner at one end of said housing, said conduit having a series of symmetrically spaced apertures permitting air communication between the interior of said housing and said air conduit.

7. A locating device according to claim 6, in which each of said apertures has a chamfered edge arranged to be substantially parallel to flow of air from said housing to said air conduit.

8. A locating device according to claim 6 or 7, in which said air conduit is arranged for connection to said hammer.

9. A locating device according to any of claims 1 to 8, in which said housing is provided with a replaceable wear-resistant sleeve.

10. A locating device for a soil displacement hammer, substantially as described herein with reference to Figure 1 or Figures 2 to 4 of the accompanying drawings.