Ground compaction

Abstract

The apparatus (10) is a weighted body (12). The first regions (20) taper at a first taper angle, such as 5°. Second regions (22) taper at a greater angle, such as 60°. The ground is compacted by dropping the apparatus (10) on the ground, so that the nose (18) penetrates the ground. The relatively low taper angle of the first regions (20) tends to result in deeper penetration. The relatively high taper angle of the regions (22) tends to create some bounce on impact, helping to free any tendency for the first regions (20) to stick. The second regions (22) also create greater downward compaction.

Description

This application is based on GB 0712329.2 filed with United Kingdom Patent Office on Jun. 26, 2007, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to improvements in or relating to methods and apparatus for ground compaction.

SUMMARY OF THE INVENTION

Embodiments of the invention provide ground compaction apparatus comprising:

a weighted ground impact body with an outer surface which reduces in width to a nose;

the outer surface having a plurality of first regions which taper at a first taper angle, and

at least one second region between first regions, the second region tapering at a second taper angle which is greater than the first taper angle.

The body may be generally conical. The body may be substantially circular in section. The body may be substantially polygonal in section. The body may be substantially hexagonal or octagonal in section.

The or each second region may be a band around the body.

Each first region may be a band around the body. At least one first region may be separated from a neighbouring first region by a band providing a second region.

There may be a plurality of second regions. The spacing of second regions may be non-uniform. The second regions may be spaced more closely nearer the nose than further from the nose.

The radial extent of the or each second region may be substantially equal to the radial extent of a neighbouring first region.

The first taper angle may be in the range 0° to 15°. The first taper angle may be substantially 5°. The second taper angle may be greater than 45°. The second taper angle may be substantially 60°.

The weight of the body may be at least 1 tonne and may be 12 tonnes or more.

Embodiments of the invention also provide a method of ground compaction, in which a ground compaction apparatus as defined above is dropped onto the ground to be compacted.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present invention will now be described in more detail, by way of example only, and with reference to the accompanying drawings, in which:

FIG. 1 is an elevation of ground compaction apparatus in accordance with one embodiment of the present invention;

FIG. 2 is a simplified, diagrammatic section through the apparatus of FIG. 1;

FIG. 3 is a diagram illustrating taper angles;

FIG. 4 is an enlarged partial view corresponding with FIG. 2, illustrating ground compaction forces; and

FIG. 5 is a diagrammatic view of the apparatus in use.

DETAILED DESCRIPTION

The drawings illustrate an example of ground compaction apparatus 10. This may be used, for example, for preparing ground prior to building work, foundation work, piling or other operations. It may also be used as a foundation element in its own right, for example as a stanchion base.

The apparatus 10 comprises a weighted ground impact body 12. This is mounted to the underside of a plate 14 which carries lifting eyes 16 on its upper surface, allowing the apparatus 10 to be slung from lifting apparatus, for use.

The body 12 has an outer surface which reduces in width to a nose indicated generally at 18, as can be seen in FIG. 1.

The outer surface has a plurality of first regions 20, and second regions 22. The first regions 20 taper at a first taper angle (as defined below). The second regions 22 are located between first regions 20 and taper at a second taper angle. The second taper angle (of the second regions 22) is greater than the first taper angle (of the first regions 20).

FIG. 2 illustrates the shape of the apparatus 10 more diagrammatically, for ease of understanding of the geometry. The apparatus 10 has a central axis 24, which is normally vertical during use, and perpendicular to the plate 14, which is normally horizontal in use. The section of the apparatus 10, taken perpendicular to the axis 24, has the same shape at any position along the axis 24, such as at the section line X-X in FIG. 2. The section may be substantially circular or substantially polygonal, such as substantially hexagonal or substantially octagonal. Accordingly, the sectional shape, together with the width reduction toward the nose 18, gives the apparatus 10 a generally conical form.

Each first region 20 is a band around the body 12, centred on the axis 24. Each second region 22 is similarly a band around the body 12, centred on the axis 24. First regions 20 and second regions 22 alternate along the axis 24, from the plate 14 to the nose 18. Accordingly, each first region 20 is separated from a neighbouring first region 20 by a band providing a second region 22. There is a plurality of second regions 22 between the plate 14 and the nose 18. The axial spacing of second regions 22, along the axis 24, is not uniform, as can be seen from FIG. 1. The second regions 22 are axially spaced more closely nearer the nose 18 than further from the nose 18.

The radial extent of each second region 22 (that is, the difference in radius, from the axis 24, of the outermost extremity of the region 22 and the innermost extremity of the region 22) is substantially equal to the radial extent of each neighbouring first region 20.

Each region 20, 22 has a taper angle relative to the axis 24. A taper angle is diagrammatically illustrated in FIG. 3. In FIG. 3, the surface of a region 20, 22 is illustrated by dotted lines 26 to either side of the axis 24. Lines 28, parallel with the dotted lines 26, intersect the axis 24 at a point 30. An angle 32 can be drawn to either side of the axis 24, between the axis 24 and one of the lines 28. The angle 32 is the same to either side of the axis 24. The angle 32 is here termed the taper angle of the surface indicated by the lines 26.

Returning to FIG. 2, the surface of one first region 20 is continued by a dotted line 34 until intersecting the central axis 24. Similarly, the surface of one second region 22 is continued by a long dotted line 36. It can readily be seen from FIG. 2 that the taper angle of the first region 20 is smaller than the taper angle of the second region 22. In examples, the first taper angle may be in the range between 0° and 15°. In one example, the taper angle of the first regions 20 is substantially 5°. The taper angle of the second regions 22 is, in one example, greater than 45° and may be substantially 60°. Accordingly, when the apparatus 10 is hanging with the axis 24 vertical, the surfaces of the first regions 20 are closer to the vertical than to the horizontal orientation, while the second regions 22 are oriented closer to the horizontal than the vertical orientation.

In use, the apparatus 10 is lifted above the ground and then dropped onto the ground, penetrating the ground by virtue of the generally tapered shape, and causing ground compaction by the impact. The compaction forces which result are schematically illustrated in FIG. 4. In impacts between a dropped body and the ground, impact forces can generally be considered as being perpendicular (normal) to the surface of the body. Accordingly, two orientations of compaction forces arise. Compaction forces 38a are closer to the horizontal than to the vertical orientation and arise from the first regions 20 impacting the ground 40 around the apparatus 10. Second impact forces 38b are closer to the vertical than to the horizontal and arise from impact of the second regions 22 with the ground 40.

When the apparatus 10 is dropped onto the ground 40, the ground 40 is subjected to compaction forces at both of these angles 38a, 38b, as illustrated schematically in FIG. 5.

The apparatus 10 described above is expected to provide enhanced ground compaction performance, for reasons which may include the following. If a simpler apparatus is envisaged, with a surface which has a constant taper angle, then the apparatus will have a short, squat conical form in the event of a large taper angle, or a long, thin conical form in the event of a small taper angle. Using a small taper angle results in deep penetration into the ground, so that compaction is achieved at deeper levels. However, a long cone with small taper angle is prone to sticking in some ground conditions. Friction between the surface of the cone and the surrounding ground may grip the weight, hindering removal for a further dropping operation.

In an alternative with a large taper angle, the impact surface is closer to the horizontal, creating enhanced downwardly directed compaction forces and also tending to provide some bounce at the time of impact, which helps prevent the apparatus sticking in the ground. However, the shorter, squatter form tends to result in less penetration and less deep ground compaction.

In the examples described above, the relatively low taper angle of the first regions 20 result in a long cone which provides deep penetration. However, the greater taper angle of the second regions 22 creates some bounce on impact, helping to free the first regions 22 to prevent the apparatus 10 sticking. The second regions 22 also create greater downward compaction. Accordingly, it is desirable to have the second regions 22 spaced more closely nearer the nose 18 than further from the nose 18, so that there is a greater contribution to downward compaction, at the greater penetration depth.

In use, it is envisaged that the apparatus 10 will be lifted by a suitable crane 42 (FIG. 5). The crane 42 may be purpose built or general purpose. The apparatus 10 is then dropped to penetrate into the ground 40 and create compaction, as has been described. The apparatus 10 may be dropped once or repeatedly at the same position. In many situations, an area of ground may be treated by using the apparatus 10 at different points across the ground, such as at lattice points of a square grid, or other geometry.

In the example described above, the total weight of the apparatus 10 may be in the region of at least 1 tonne and may be as much as 12 tonnes or more. The length of the apparatus 10 along the axis 24 may be approximately 3 m. The diameter of the body 12, at the plate 14, may be approximately 2 m or more.

Many variations and modifications can be made to the apparatus described above, without departing from the scope of the present invention. In particular, many different weights, heights, widths, taper angles, dimensions and relative dimensions can be chosen, particularly according to the degree of compaction required, the nature of the ground being compacted, and the like.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. Ground compaction apparatus comprising:

a weighted ground impact body with an outer surface which reduces in width to a nose;

the outer surface having a plurality of first regions which taper at a first taper angle, and

at least one second region between first regions, the second region tapering at a second taper angle which is greater than the first taper angle.

2. Apparatus according to claim 1, wherein the body is generally conical.

3. Apparatus according to claim 1, wherein the body is substantially circular in section.

4. Apparatus according to claim 1, wherein the body is substantially polygonal in section.

5. Apparatus according to claim 4, wherein the body is substantially hexagonal or octagonal in section.

6. Apparatus according to claim 1, wherein the or each second region is a band around the body.

7. Apparatus according to claim 1, wherein each first region is a band around the body.

8. Apparatus according to claim 1, wherein at least one first region is separated from a neighbouring first region by a band providing a second region.

9. Apparatus according to claim 1, wherein there are a plurality of second regions.

10. Apparatus according to claim 9, wherein the spacing of second regions is non-uniform.

11. Apparatus according to claim 10, wherein the second regions are spaced more closely nearer the nose than further from the nose.

12. Apparatus according to claim 1, wherein the radial extent of the or each second region is substantially equal to the radial extent of a neighbouring first region.

13. Apparatus according to claim 1, wherein the first taper angle is in the range 0° to 15°.

14. Apparatus according to claim 13, wherein the first taper angle is substantially 5°.

15. Apparatus according to claim 1, wherein the second taper angle is greater than 45°.

16. Apparatus according to claim 15, wherein the second taper angle is substantially 60°.

17. Apparatus according to claim 1, wherein the weight of the body is at least 1 tonne.

18. Apparatus according to claim 17, wherein the weight of the body is at least 12 tonnes.

19. A method of ground compaction, in which a ground compaction apparatus, the apparatus comprising a weighted ground impact body with an outer surface which reduces in width to a nose, the outer surface having a plurality of first regions which taper at a first taper angle, and at least one second region between first regions, the second region tapering at a second taper angle which is greater than the first taper angle, is dropped on the ground to be compacted.

20-22. (canceled)