GB2270329A - Forming a hole in the ground - Google Patents

Abstract

An apparatus for forming a hole in the ground comprises one or more rotary drilling or boring tools 5, 24, 25 mounted in a casing 4 which is arranged not to rotate with the tool or tools and which has a profile which determines the shape of the hole. <IMAGE>

Description

FORMATION OF HOLES IN THE GROUND This invention relates to the formation of holes in the ground, and in particular, but not exclusively, to holes of non-circular cross-section.

In the field of civil engineering, it is often necessary to build extensive underground structures, for example foundation elements such as piles or structural diaphragm walls. Other below ground structures, which are designed to prevent flow of water, are called cut-offs.

The installation of such structures generally involves the excavation of a hole or trench in the ground, which may subsequently be filled with grout or concrete. In some soils it may be necessary to stabilise the soil by use of a metal casing, and/or filling the hole with water or a drilling fluid.

Hitherto excavation of trenches and holes of rectangular profile has generally been accomplished by use of a "back-hoe" (i.e. a mechanical digger with a hydraulically powered arm on which is fitted a bucket), or a purpose built grab, or even by dragline bucket.

Additionally, reverse circulation milling machines can be used.

All the aforementioned methods have limitations.

For example, with a back-hoe, because of the articulation of the digging arm, it is very difficult to excavate a trench which is rectilinear in elevation.

It is similarly difficult to perform this excavation with a dragline bucket. Although purpose built grabs can be used to form rectilinear holes, the output is low. The aforementioned milling machines also provide for rectilinear holes in suitable soils, and at a greater output than grabs. However, they are difficult to use in mixed soils (e.g. cohesive soils interbedded with non-cohesive strata, or even boulders or rock formations.) Additionally, because all the soil is removed from the trench by means of a flushing fluid when milling machines are used, there is a requirement for a large fluid cleaning plant (a desanding unit).

It is known to use drills or boring machines to form holes in the ground. However, drilling or boring machines currently in use create holes which (in plan) are generally described by the outer perimeter of the rotating drills or bores, and are therefore essentially circular. In contrast, the present invention allows for the formation of holes with plan sections which do not have to be circular.

According to one aspect of this invention, there is provided an apparatus for forming a hole in the ground, which apparatus comprises one or more rotary drilling or boring tools mounted in a casing which casing is arranged not to rotate with the tool or tools and which has a profile determining the shape of the hole.

According to a second aspect of this invention, there is provided an apparatus for forming a hole in the ground, which apparatus comprises one or more rotary drilling or boring tools mounted in a casing which casing has a non-circular profile determining the shape of the hole.

In embodiments where more than one drilling or boring tool is mounted in an assembly, the tools may all rotate in one direction, or in opposed directions.

The tools may be synchronised or rotated at differing rates.

In preferred embodiments, said one or more drilling or boring tools project below said casing when said apparatus is in use.

The casing may comprise compartments for housing boring or drilling tools individually, or in groups In embodiments where the drilling or boring tools are not individually housed, it is advantageous for there to be some degree of overlap between the tools and for the tools to rotate in synchrony.

The casing may be constructed from steel, plastics, or any other material suitable for entering the ground without rotation as the tool or tools rotate, in which case means may be provided for coupling the casing to the tool or tools in a relatively rotatable manner.

Preferably, the one or more drilling or boring tools are augers, which may have one or more cutting plates at their working ends and one or more flights.

In some embodiments, the one or more cutting plates are provided with teeth. The cutting profile of such teeth may exceed the dimensions of the casing profile in order to provide clearance for the casing.

The apparatus may be suspended from a crane or lifting device. Alternatively, the apparatus may be fixed to a kelly or on a mast arrangement which allows the apparatus to be raised and lowered. The drilling or boring tools may be rotated by various means, including a hydraulic drive, compressed air, electrical motor, or a mechanical drive.

In use, the apparatus is allowed to rest on the soil. As the drilling or boring tools are rotated, the tools and casing enter the soil. The penetration into the soil may be assisted by applying a constant or intermittent force which may often be (but not necessarily) in the direction of penetration. The apparatus may also be fitted with adjustable guides to control the inclination of the hole. Alternatively or in addition, the casing may be provided with remotely actuated thrust plates which enable the inclination of the apparatus to be adjusted while excavation is in progress.

In one mode of operation, the apparatus is withdrawn after a certain depth of penetration has been achieved, and the soil contained within the casing is removed. This may be carried out either by withdrawing the drilling tools from the casing, opening the casing "box", or by using a special cleaning apparatus which is drawn down when the auger is rotated in reverse mode. The apparatus may then be re-inserted into the hole and the excavating cycle repeated until the required depth of penetration is achieved. Depending on the nature of the soil, the hole may be left as an open hole, or may be filled with a drilling fluid such as bentonite which is introduced during withdrawal of the apparatus. One or more hollow-stem augers may be used to introduce the drilling fluid into the hole below the drilling or boring tools during extraction of the apparatus.Alternatively or in addition, in embodiments where the plan shape of the casing noncircular, one or more pipes may be run down the inside of the casing in such a way that they do not obstruct the drilling or boring tools. These pipes may be adapted to introduce drilling fluid into the hole below the drilling or boring tools during extraction of the apparatus.

In another mode of operation, the spoil may be removed as a slurry from the area of the drilling or boring tools by means of pumping; that is, by direct or reverse circulation. The slurry may be removed via one or more hollow-stem augers and/or by one or more pipes which may be run down the inside of the casing in embodiments in which the casing is non-circular.

In a further mode of operation, the casing (which may be of a length less than or greater than the depth of the hole) may be left in position either temporarily or permanently.

Regardless of whether any casing is left in the hole, either temporarily or permanently, the hole may be cleared of any residual detritus and then filled with reinforcement concrete or the like, thus forming a foundation element. The method of cleaning any residual detritus may be by conventional piling or diaphragm walling techniques. Alternatively the apparatus itself can be used, with the casing position progressively adjusted until the tools do not project below the casing.

The casing profile may take a variety of noncircular forms, such as square, rectangular or other substantially polygonal forms, according to the first aspect. In other words, this aspect envisages any profile which, when engaging the ground, acts to tend to prevent rotation of the casing with the tool or tools.

According to another aspect of this invention, the casing may be of circular profile. In this aspect, means such as a kelly bar or any other means may be provided to prevent the casing rotating with the drilling or boring tool or tools, which are directly driven by a drive unit rather than being driven through the kelly. In operation, the apparatus of this aspect is lowered to the ground and the drilling or boring tools are rotated, thus penetrating the soil. After a predetermined time, the rotation of the drilling tools is stopped, and the apparatus is withdrawn from the ground. While the apparatus is being withdrawn, the resultant borehole may be filled with water or drilling fluid if necessary in order to ensure stability.Once the apparatus has been withdrawn, spoil contained therein is removed in a manner previously mentioned, and the apparatus may be reintroduced into the borehole. These steps may be repeated until the required depth of penetration is reached. Once the required depth has been reached, the entire apparatus may be withdrawn.

Alternatively, only the drilling or boring tools are withdrawn, leaving behind the casing. In the latter case, spoil may be withdrawn with the drilling tools, leaving behind a fully or partially cased hole.

The fully or partially cased hole may then be filled with concrete, grout, drilling fluid or any other suitable material. In the embodiment where the cased hole is filled with a drilling fluid, reinforcing steel may then be placed in the cased hole, and concrete or other suitable materials may then be inserted.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: FIGURE 1 shows a side view of a lifting device carrying a boring apparatus; FIGURE 2 shows a front view of the boring apparatus of Figure 1; FIGURE 3a shows a plan view from below of the boring apparatus of Figures 1 and 2; FIGURE 3b shows a plan view from below of an alternative embodiment of a boring apparatus; FIGURE 4 shows in cross-section the shape of a hole excavated by the boring apparatus of Figures 1, 2 and 3a; FIGURES 5 to 10 show six stages in excavating a hole; FIGURE 11 shows a horizontal cross-section through an embodiment of the boring apparatus comprising a hollow-stem auger;; FIGURE 12 shows a horizontal cross-section through an embodiment of the boring apparatus incorporating a pipe which is run down the inside of the casing; FIGURE 13 shows a section through an embodiment of the boring apparatus which includes thrust plates; FIGURE 14 shows a plan view onto Section A-A in Figure 13; and FIGURE 15 shows a boring apparatus with a casing of circular cross-section suspended from a lifting device.

Referring now to Figure 1 of the drawings, there is shown a lifting device 1 bearing a kelly 2 to which a boring apparatus 3 is attached. The kelly 2 and the boring apparatus 3 are disposed so as to be able to move up or down while being driven. The kelly is rotated by a drive unit 23 which may be powered by hydraulic, pneumatic, electrical or mechanical means.

The boring apparatus 3 comprises a casing 4 which is shown cut away to reveal one auger 5 out of three and a gearing arrangement 6.

Figure 2 shows a front elevation of the boring apparatus 3, showing the casing 4, a central auger 5, and two peripheral augers 24 and 25. In the depicted embodiment only the central auger 5 is directly driven via the kelly 2, the peripheral augers 24 and 25 being rotated through the gearing arrangement 6 (shown in Figure 1). A plan view from below of this boring apparatus is shown in Figure 3a. The base plates 32 of the augers are provided with teeth, represented at 33.

Figure 3b shows an alternative embodiment of-a boring apparatus comprising six boring tools 34 mounted in a casing 35.

In both Figures 3a and 3b, there are shown internal partitions 39 which separate the boring tools within the casing.

A hole excavated by the boring apparatus Figures 1, 2 and 3a will have a horizontal cross-section of the shape shown in Figure 4.

Turning now to Figure 5, the boring apparatus 3 is brought to the ground 7 to be excavated. Drive unit 23 (shown in Figure 1), via kelly 2, rotates auger 5, which in turn rotates peripheral augers 24 and 25 through gearing arrangement 6 (shown in Figure 1), and the apparatus 3, by virtue of its weight and the rotation of the augers 5, 24 and 25, enters the ground as shown in Figure 6. Once a predetermined depth d has been reached, the apparatus 3 is withdrawn, as shown in Figure 7. The spoil contained within the casing 4 is removed. Some spoil 8 is left at the bottom of the partial excavation 9.

After the apparatus 3 has been emptied, it is reintroduced into the partial excavation and penetrates the ground further as shown in Figure 8. Again, when the apparatus has penetrated the ground to a predetermined depth d + d', it is withdrawn as shown in Figure 9 and spoil contained within the apparatus is removed.

This procedure may be repeated until the final depth of excavation has been achieved. At this point, any residual spoil 8 at the bottom of the excavation is removed, as shown in Figure 10.

The spoil may be removed by lowering the casing over the drilling tool or tools until the casing contains the residual spoil. Alternatively, a hollowstem auger 10 as shown in Figure 11 may be used. In this case, spoil is removed via hole 11 by means of direct or reverse circulation. A further alternative, depicted in Figure 12, involves running a pipe 12 down the inside of the casing 13 in such a way that it does not obstruct the drilling tool 15. Spoil may then be removed via pipe 12 by means of direct or reverse circulation. It is also possible to remove the spoil by means of a clam-shell grab (not shown) or by means of a diaphragm wall grab (not shown).

Turning now to Figure 13, there is shown an embodiment of a casing 16 which incorporates thrust plates 17 mounted in holders 26 from which they may be extended (shown at 17' and 26') or into which they may be retracted (shown at 17" and 26") by hydraulic, pneumatic or electric means. The holders 26 are attached to the casing 16. The thrust plates 17 are generally disposed as diametrically opposed pairs.

Only one pair is shown in Figure 13, but it is to be understood that further pairs may be located at different positions on the casing 16. By extending and retracting the thrust plates 17, it is possible to adjust the angle of penetration during excavation, rather than being restricted to a predetermined initial boring angle. Figure 14 is a plan view onto Section A A of Figure 13, showing attachment means 27 for attaching the holders 26 to the casing 16.

Figure 15 shows a side view of a lifting device 29, having a boring apparatus 30 comprising a casing 18 of circular cross-section. The casing 18 is suspended from a kelly 19, both of which are prevented from rotating by the provision of a kelly guide 20. A single auger 28 is driven by means of a rotary drive unit 21 powered by pneumatic, hydraulic, electrical or mechanical means through power cable 22. The rotary drive unit 21 is fixed to the bottom of kelly 19 and to the casing 18. Through these means, the auger 28 may be rotated independently of the kelly 19 and the casing 18, which both remain rotationally fixed. The boring apparatus 30 may be raised or lowered by means of cable 36 which passes over pulley arrangement 31 to winch 38.

Claims (19)

CLAIMS:

1. An apparatus for forming a hole in the ground, which apparatus comprises one or more rotary drilling or boring tools mounted in a casing which casing is arranged not to rotate with the tool or tools and which has a profile determining the shape of the hole.

2. An apparatus as claimed in claim 1, wherein said casing has a non-circular profile.

3. An apparatus as claimed in claim 1, wherein said casing has a circular profile.

4. An apparatus as claimed in claim 1, 2 or 3, wherein said one or more tools project below said casing when said apparatus is in use.

5. An apparatus as claimed in any preceding claim, wherein said casing comprises compartments which house said one or more tools individually.

6. An apparatus as claimed in any preceding claim, wherein said casing comprises compartments which house said one or more tools in groups.

7. An apparatus as claimed in claim 6, wherein said one or more tools exhibit a predetermined degree of overlap and, in use, rotate in synchrony.

8. An apparatus as claimed in any preceding claim, wherein said one or more tools are augers.

9. An apparatus as claimed in claim 8, wherein said augers are provided with one or more cutting plates at their working ends.

10. An apparatus as claimed in claim 9, wherein said cutting plates are provided with teeth.

11. An apparatus as claimed in claim 10, wherein said teeth have a cutting profile which exceeds the cross-sectional area of the casing.

12. An apparatus as claimed in claim 8, wherein said augers are hollow-stem augers adapted to convey drilling fluid.

13. An apparatus as claimed in any preceding claim, wherein said apparatus is fitted with adjustable guides adapted to control the angle of penetration.

14. An apparatus as claimed in any preceding claim, wherein said casing is provided with remotely actuated thrust plates.

15. A method of forming a hole in the ground, which method consists of the application to the ground of an apparatus comprising one or more rotary drilling or boring tools mounted in a casing which casing is arranged not to rotate with the tool or tools and which has a profile determining the shape of the hole.

16. A method according to claim 15, wherein said apparatus is suspended from a crane or lifting device.

17. A method according to claim 15 or 16, wherein said apparatus is fixed to a kelly or on a mast arrangement which allows the apparatus to be raised and lowered.

18. A method according to any of claims 15 to 17, wherein the penetration of said apparatus into the soil is assisted by the application of a force to said apparatus.

19. A method according to claim 18, wherein said force is applied in the direction of penetration.