EP0299118A1

EP0299118A1 - Method and device for compacting soil

Info

Publication number: EP0299118A1
Application number: EP87202420A
Authority: EP
Inventors: Hans Günther Schnell; Tjako Aaldrik Wolters
Original assignee: Ballast Nedam Groep NV
Current assignee: Ballast Nedam NV
Priority date: 1987-07-14
Filing date: 1987-12-04
Publication date: 1989-01-18
Also published as: NL8701654A

Abstract

Ground is compacted by dropping a weight onto the top surface of the ground. In order to effectively transfer the energy onto the ground the drop weight (36) is guided relatively to guide means (12).

Description

The invention relates to a method for compacting ground whereby a drop weight is dropped onto the ground.
Such method is known from DE-A-2351713. A drop weight is thereby allowed to fall freely onto the ground from a high level.
The invention has for its object to provide a different method for compacting ground, whereby the compacting result of the blows is better. To this end according to the invention the drop weight is guided relative to guiding means anchored to the ground. The result of this guiding is that the drop weight repeatedly comes down on the ground at the same location and in the same position. The compacting strokes which are substantially directed in the same direction have a good depth effect, even in the case that the drop weight comes loose of its guide while still above the ground. Preferably however, the drop weight is also guided by guiding means during the period in which the energy of the drop weight is transferred to the ground. The compacting result is then even better because any slight tilting of the drop weight when it makes contact with the ground is then prevented. Tilting of the drop weight could disturb the desired directed transmission of energy into the ground.
In order to decrease even further the compacting energy required, not only strokes with a small impact surface having a compacting result at considerable depth over only a small width, but also strokes with a larger impact surface having a compacting result to a smaller dpeth but over a greater width are applied according to the invention to each of a plurality of selected positions distributed over the ground at a distance from each other. The aim with this method is not to compact the ground packet homogeneously to a great depth, but to ensure a sufficiently homogeneous and acceptable settling over the entire surface. To this end, mushroom-like compacted ground packets distributed over the ground are as it were formed, which provide the ground as a whole with a considerable bearing capacity, while the energy transferred to the ground, which corresponds virtually to the volume of the compacted ground packets, is very low compared to the energy required for a homogeneous compaction. The method according to the invention has of course the advantage that with the compacting apparatus available the compacting work can be completed much more quickly.
The invention likewise relates to and provides an apparatus for performing the method according to the invention, as stated in claim 8.
Mentioned and other characteristics of the invention will now be elucidated in the description following hereinafter with reference to a drawing.
In the drawing in schematic form:

Fig. 1 shows a preferred embodiment of an apparatus according to the invention;
Fig. 2 shows on a larger scale detail II from fig. 1;
Fig. 3 shows on a larger scale detail III from fig. 1;
Fig. 4 is a view corresponding to fig. 3 in a different position;
Fig. 5 shows on a larger scale a variant of detail V from fig. 1;
Fig. 6 shows on a larger scale a part of a variant of detail VI of the apparatus from fig. 1;
Fig. 7, 8 and 9 each show a schematic view of a variant of detail VII from fig. 1;
Fig. 10 and 11 each show a schematic view of in each case a different apparatus according to the invention; and
Fig. 12 and 13 are each top views of two different foundations manufactured according to the invention.

The apparatus 1 from fig. 1 consists of a lifting gear 2, a chassis 4 of which can swivel round a vertical axis 6 relative to a sub-frame 5 with caterpillar tracks 3 which support on the ground 21. A jib 7 can swivel on a horizontal axis 8. At the top end of jib 7, a guide bushing 9 can pivot on a horizontal shaft 11 in which bushing a vertically guided tubular pole 12 is arranged for sliding. Two pulleys 13 are mounted for pivoting on guide bushing 9 on either side of pole 12 for guiding two lifting cables 14 which carry a gripper member 16. The gripper member 16 comprises a lifting frame 17 guided round pole 12, on which two gripping elements 18 are mounted for pivoting on horizontal shafts 19. Suspension links 20 of the lifting cables 14 grip onto shafts 19.
Each gripping element 18 has an open jaw 22 at its outer end, and a stop roller 23 at its inner end. A draw spring 24 is arranged between a pin 25 of the lifting frame 17 and a pin 26 of the outer end of the gripping element 18 such that a gripping element 18 in the release position shown in fig. 4 remains stable in this release position, since the draw spring 24 is then located under shaft 19. A locking member 27 which is vertically displaceable relative to lifting frame 17, has on its outer parts locking members 28 with vertical locking faces which co-operate with the stop rollers 23 of the gripping element 18, as can be seen in the lifting position from fig. 3.
Locking member 27 has a stop console 30 arranged on a sliding rod. Accommodated between console 30 and lifting frame 17 are pre-tensioned compression springs 31 which force locking member 27 upward into the locking position, which is determined by a cross pin 32 of the sliding rod 29 striking against a flange 33 of lifting frame 17.
In the lifting position from fig. 3, the jaws 22 of the gripping elements 18 grip on horizontal tubes 34 of suspension frames 35 which are attached to the top part of a drop weight 36. When drop weight 36 has been lifted to the required height of 10 or 15 m for example, the stop console 30 strikes up against a stop ring 38 attached to pole 12 at that point by means of cross pins 37 and gripping round pole 12 with the result that the compression springs 31 are pressed in, and the lifting frame 17 moves upward slightly further relative to locking member 27, until spring guide bushings 40 of compression springs 31 strike against each other. During the relative upward displacement of lifting frame 17 relative to the locking member 27, the stop rollers 23 and consequently the gripping elements come free of the locking elements 28 and then pivot into the release position shown in fig. 4 because of the drop weight 36 hanging from it, as a result of which drop weight 36 falls down to the ground 21. The gripper member 16 can now be lowered down again by paying out lifting cables 14, whereby gripping elements 18 remain in their release position because of draw springs 24. In this release position they then grip on the tubes 34. As a result of the weight of the lifting frame 17, which is in the order of 900 kg, the gripping elements 18 tilt into the lifting position, whereby the stop rollers 23 press locking member 27 downward. After stop rollers 23 have passed on, the compression springs 31 press locking member 27 into the locking position, after which the lifting of drop weight 36 for the next stroke cycle can begin.
In order to move pole 12 from one compacting location to another, a cross pin 90 is inserted through transverse openings in the pole 12 above lifting frame 17, so that when lifting frame 17 is lifted by means of lifting cables 14, pole 12 can be pulled out of the ground, lifted and set down at another location on the ground. Cross pin 90 is then removed, lifting frame 17 is lifted slightly further and cross pin 90 is again inserted under lifting frame 17 into the pole 12. The lifting frame 17 with the drop weight 36 hanging from it is subsequently lowered, so that pole 12 with this drop weight is pushed 1 to 2 m into the ground 21. It has been found that with the drop weight 36 guided by the pole 12 anchored in the ground 21, a considerably more efficient compacting action is obtained compared with an uncontrolled fall of a drop weight.
Pole 12 can also be used to measure the ground reaction occurring as a result of the blow. A measurement recorder 42 is fitted to the lower end of pole 12 for this purpose in the variant from fig. 5. This consists of a vertically downward directed pin 43 with four acceleration recorders 44 distributed over the periphery and an acceleration recorder 44 arranged on the bottom surface. The pin 43 can be driven as plunger of a hydraulic cylinder 45 downward into the ground and be withdrawn again. Cylinder 45 is elastically mounted with a rubber lining relative to pole 12.
Pole 12 can also be used to set the ground 21 into vibration, while drop weight 36 is being dropped. In the variant from fig. 6, a vibration unit 47 is arranged for this purpose on the top end of pole 12, which unit may be loaded with a mass 49 via springs 48. Preferably arranged on the bottom end of pole 12 which penetrates into the ground 21 are resonance plates 50.
The drop weight 36 weighs for example 15,000kg.
The drop weight 51 can as according to the variant from fig. 7 consist of three drop weight members 52 which are linked to one another by means of lugs 53 and pins 54.
The drop weight 36 has for instance a stepped impact surface as in fig. 8 with a central bottom impact surface of for example 2 m² and a surrounding higher impact surface 80 likewise of for example 2 m².
As a result the drop weight 36 strikes the ground first with the small impact surface 69 and, because of the comparatively small impact surface 69, has an effect to a substantial depth q over a small width r (fig. 12 and 13). With the first, for example six, strokes a compacted ground packet 82 is formed reaching down to for example 10 m. With the seventh stroke for example the uppermost impact surface 80 lands on the ground surface 81, as a result of which the ground is subjected to the total impact surface of 4 m². Formed as a result on the seventh and following strokes with a small depth effect is the ground packet 83 with a width s which is greater than the width r but a depth t which is smaller than the depth q. With this second series of strokes the first ground packet 82 may increase slightly in depth.
Also conceivable is the forming first with a large impact surface of the ground packet 83 for compacting, and the forming of the compacted ground packet 82 later by employing in the first instance a drop weight member 56 and by coupling a second drop weight 57 underneath the latter by means of coupling means 85 at a later stage. It has been found that a very effective compaction can be realized if the ground is struck repeatedly at the same selected positions located at a distance from each other first with a large surface area of the drop weight and later with a surface area that is substantially smaller, for example a quarter part. Mushroom-like ground packets as it were are then compacted. In this way a foundation is formed which is as it were arch-shaped. Placed over this is a top layer 140 which compacted in another, conventional manner. The whole then forms a good foundation, whereby at least the minimal required quantity of ground is compacted, for which only little energy is required.
Fig. 9 shows another form of a drop weight 58.
It is however conceivable that other, for example smaller or greater masses, are used and that a somewhat smaller or greater dropping height is applied. With a smaller bottom surface of the drop weight a greater depth will be achieved. The number of strokes required can be determined experimentally and/or by acceleration measurement.
In the apparatus 59 from fig. 10 a drop weight 60 is fastened to a swivel arm 61 which is arranged for pivoting on a pole 62 anchored in the ground, whereby the drop weight 60 is raised by means of a lifting cable 63 and then abruptly released by paying out a relevant winch.
In the apparatus 70 from fig. 11 a drop weight 71 is guided into a tubular pole 72 which is anchored in the ground, and is lifted by means of a lifting cable 74 of a winch (not shown), which is paid out abruptly to cause the drop block to fall.
Although drop weight 36 is usually guided preferably by disposing pole 12 vertically, it is also possible to anchor pole 12 slantwise in the ground 21.
It is remarked, that the present invention relates particularly to the compaction of ground to a considerable depth, for example 10 to 20 m. The top layer 79 is afterwards levelled and compacted in another way.
The undersurface of the drop weight may be of a flat or a concave shape, depending on whether it is desired to counter or stimulate the sideward radiation of energy. Generally speaking a depth compaction and a limiting of the sideward radiation will be aimed for.
An acceleration recorder can also be fitted to the drop weight in addition to the pole 12.
In the case ground under water is being compacted, the drop weight is raised to a greater height to compensate for the braking effect of the water, a slimmer drop weight with a small surface area of the undersurface is employed and/or more strokes are applied to the ground per compaction location.

Claims

1. Method for compacting ground whereby a drop weight is dropped on the ground, characterized in that said drop weight is guided relative to guiding means anchored on the ground.

2. Method as claimed in claim 1, characterized in that the drop weight is guided relative to guiding means inserted into the ground, preferably a pole inserted into the ground.

3. Method as claimed in any of the foregoing claims, characterized in that the ground is set into vibration while the drop weight is dropped onto said ground.

4. Method as claimed in any of the foregoing claims, characterized in that the drop weight is guided relative to the ground, while its energy is transferred to the ground.

5. Method as claimed in any of the foregoing claims, characterized in that after a compaction of ground with a drop weight a supplementary ground compacting is performed with a larger drop weight and/or a drop weight which has a different, preferably smaller, undersurface and/or with a drop weight having an undersurface of a different form.

6. Method as claimed in any of the foregoing claims, characterized in that measurings are performed on the ground during the compacting by means of measuring means carried into the ground on the guiding means.

7. Method as claimed in any of the foregoing claims, characterized in that not only strokes with a small impact surface having a compacting result at considerable depth over only a small width, but also strokes with a larger impact surface having a compacting result to a smaller depth but over a greater width are applied to each of a plurality of selected positions distributed over the ground at a distance from each other.

8. Apparatus for compacting ground according to the method from any of the foregoing claims, comprising a lifting device and a drop weight, characterized by guiding means anchorable on the ground for guiding said drop weight.

9. Apparatus as claimed in claim 8, characterized in that the guiding means consist of at least one guide member inserted into the ground, preferably a pole inserted into the ground, around which the drop weight is arranged.

10. Apparatus as claimed in either of the claims 8 or 9, characterized in that the vibrating means are fitted on the guiding means.

11. Apparatus as claimed in any of the claims 8-10, characterized in that the drop weight is assembled from a plurality of weight elements which can be coupled to one other.

12. Apparatus as claimed in any of the foregoing claims, characterized by a plurality of weight elements having undersurfaces of different sizes.

13. Apparatus as claimed in any of the claims 8-12, characterized by at least one gripper member which is carried by at least one lifting cable and is movable from a lifting position into a release position, which gripper member can preferably be locked in its lifting position by a locking member which co-operates during lifting of the gripping element to a determined level with a stop member attached to the guiding means to be adjusted into an unlocking position.

14. Apparatus as claimed in any of the claims 8-13, characterized by measuring means arranged on the guiding means for recording the ground reaction occurring during a blow.

15. Apparatus as claimed in any of the claims 8-14, characterized in that at least one resonance plate is arranged at the lower end of the guiding means.