GB2187774A

GB2187774A - Core-drilling tool

Info

Publication number: GB2187774A
Application number: GB08705653A
Authority: GB
Inventors: Philippe Gueroult; Franck Weyland
Original assignee: Soletanche SA
Current assignee: Soletanche SA
Priority date: 1986-03-11
Filing date: 1987-03-10
Publication date: 1987-09-16
Also published as: FR2595751B1; FR2595751A1; GB2187774B; GB8705653D0

Abstract

The invention relates to a core- drilling tool of the type comprising an inner tube receiving the core sample and outer tube (1) for driving in rotation radially projecting cutting members 4 mounted at the front end of the outer tube, an annular channel being provided between the said inner and outer tubes for conveying a drilling fluid. A downwardly extending ring 5 having vents 6 is provided for concentating the flow of drilling fluid at the front end of the said blades in relation to the direction of rotation of the tool. <IMAGE>

Description

SPECIFICATION Core-drilling tool The present invention relates to a core-drilling tool, more particularly such a tool intended for the core-drilling in air of cohesive fine soils, such as clays, loams, marls or chalks.

In core-drilling, a column of soil is taken by means of a hollow cylindrical tool, before a borehole is made, and is subsequently extracted from the borehole for examination and or analysis in the laboratory.

There are already known core-drilling tools which comprise an inner tube for receiving the core sample and an outer tube for driving in rotation cutting members mounted at the front end of the said outer tube, an annular channel being provided between the said inner and outer tubes for conveying a drilling fluid.

The drilling fluid, which can be a liquid, such as clear water or water laden with bentonite, is intended for cooling and lubricating the cutting members and for raising the soil elements cut and broken up as a result of the work of the cutting members.

Such tools have already been used with air as the drilling fluid. This proves useful when core samples with a content of natural water are to be obtained, for example for detecting possible inflows of water or wet passages during the advance of the drilling operation.

However, air core-drilling by means of conventional core-drilling tools has generally proved unsatisfactory.

The object of the invention is to provide a core-drilling tool which can be used in air and which is especially effective in cohesive fine soils.

To achieve this, the subject of the invention is a core-drilling tool of the type comprising an inner tube for receiving the core sample and an outer tube for driving in rotation cutting members mounted at the front of the said outer tube, an annular channel being provided between the said inner and outer tubes for conveying a drilling fluid, characterized in that it has a plurality of cutting blades distributed on the periphery of the front end of the said outer tube, the said blades projecting radially beyond the outer surface of the said tube, and means for concentrating the flow of drilling fluid at the front of the said blades in relation to the direction of the rotation of the tool.

Particularly effective cooling and lubrication of the cutting blades are obtained in this way.

Moreover, the latter, since they project from their supporting tube, provide an annular space which is located between this tube and the wall of the borehole and via which the waste is carried off.

In a particular embodiment of the invention, the said means for concentrating the flow of drilling fluid comprise a ring mounted at the end of the said outer tube, the said ring having vents located in front of each blade in relation to the direction of rotation of the tool.

The ring can be mounted set back from the outer surface of the said outer tube and can extend in front of the end of this tube by substantially the same amount as the said cutting blades.

Thus, the drilling fluid cannot escape at the front of the borehole and is forced to pass through the vents located in front of the cutting blades.

In a particular embodiment, the core-drilling tool according to the invention has three cutting blades arranged at 1200.

Moreover, it has been found that satisfactory results are obtained when the cutting blades project radially by an amount which is of the order of 10% of the diameter of the borehole.

The particular embodiment of the invention will now be described by way of non-limiting example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a perspective view of a coredrilling tool according to the invention, and Figure 2 is a view in axial section of this tool in operation.

The core-drilling tool according to the invention comprises, in a known way, an outer tube 1 connected to a set of drill rods for driving it in rotation.

An inner tube 2 is mounted concentrically relative to the tube 1, so that it can pivot freely relative to the latter. Thus, when a core sample is taken, the tube 2, retained by the frictional forces exerted by the core sample.

remains substantially fixed in terms of rotation.

The clearance between the outer surface of the tube 2 and the inner surface of the tube 1 provides an annular channel 3, by which the drilling fluid, particularly air, is conveyed from the set of rods.

Three cutting blades 4 are fastened to the front end of the tube 1. The cutting blades 4 project beyond the tube 1, on the one hand axially towards the front at 4' and on the other hand radially at the sides at 4".

The three blades 4 are uniformly spaced from one another at 1 200 at the periphery of the tube 1. A ring 5 is also mounted at the front of the tube 1. This ring is substantially in line with the inner surface of the tube 1 and is consequently set back from the outer surface of this tube. The ring 5 projects at the front of the tube 1 by an amount substantially equal to the projecting length at the part -4' of the blades 4, so that the blades 4 and the ring 5 terminate substantially at the same level.

The ring 5 has three orifices or vents 6 formed just in front of the cutting blades 4 in the direction of rotation indicated by the arrow F in Fig. 1.

Reinforcements can be provided behind the cutting blades opposite the vents 6.

The cutting blades 4, since they project radially beyond the tube 1, for example by an amount corresponding to approximately 10% of the diameter of the borehole, provide between the outer wall of the tube 1 and the wall 7 of the borehole an annular space 8 which makes it easier to remove the waste.

Fig. 2 shows the core-drilling tool according to the invention in operation, in the process of making the borehole and extracting a core sample 9 which penetrates into the tube 2 serving as a receptacle for it.

Air is blown into the annular space 3 and follows the path indicated by the arrow 10 through the vents 6 and then into contact with the blades 4 which are thus cleaned and cooled. The air subsequently carries off the waste into the annular space 8.

Of course, the preceding description can contain various alternatives and modifications, without thereby departing from the scope or spirit of the invention.

Claims

1. Core-drilling tool of the type comprising an inner tube for receiving the core sample and an outer tube for driving in rotation a plurality of cutting blades distributed on the periphery of the front end of the said outer tube, the said blades projecting radially beyond the outer surface of the said tube, and an annular channel being provided between the said inner and outer tubes for conveying a drilling fluid, characterized in that it has means for concentrating the flow of drilling fluid at the front of the said blades in relation to the direction of rotation of the tool.

2. Core-drilling tool according to Claim 1, chatracterized in that the said means for concentrating the flow of drilling fluid comprise a ring mounted at the end of the said outer tube, the said ring having vents located in front of each blade in relation to the direction of rotation of the tool.

3. Core-drilling tool according to Claim 2, characterized in that the said ring is mounted set back from the inner surface of the said outer tube, and in that it extends in front of the end of this tube by substantially the same amount as the said cutting blades.

4. Core-drilling tool according to any one of Claims 1 to 3, characterized in that it has three cuttng blades arranged at 1200.

5. Core-drilling tool according to any one of Claims 1 to 4, characterized in that the said cutting blades project radially by an amount which is of the order of 10% of the diameter of the borehole.

8. Core-drilling tool substantially as hereinbefore described with reference to the accompanying drawing.