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(11) | EP 0 367 479 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Depositing reinforced matrix |
| (57) In order to deposit in a speedy manner an even layer of sand reinforced with randomly
mixed small mesh pieces of high flexural recovery (4), a tracked vehicle 1 is used.
The vehicle has a hopper 3 for the reinforced matrix 4, from which the matrix 4 is
fed by a feed conveyor 5 to a vertically reciprocating transverse blade 12; on each
stroke, the blade 12 penetrates the top surface to push the mesh pieces down into
the layer. The layer then passes down between parallel runs of two belts 9,10, is
deposited from the lower belt 10 onto the soil, and is subsequently smoothed by a
vibrating plate 11. |
Background of the Invention.
[0001] GB-A-2 120 475 describes a method of reinforcing a particulate matrix such as soil using relatively small pieces of plastic mesh which have a high flexural recovery. The reinforced matrix is highly intractable. It cannot be readily compressed and it resists shear, and these two qualities are the reason for its success. However, these qualities make it very difficult to lay the reinforced matrix. The invention is however also applicable to other reinforced matrices, for instance sand reinforced with fibres, but for convenience, the invention is described mainly in relation to the reinforced matrix of GB-A-2 120 475.
[0002] Laying the reinforced matrix has been extremely difficult. It has been possible to lay the matrix using dump trucks which deliver individual loads to the site, which are then spread evenly using back-acting buckets modified to have smooth under-surfaces. Although a reasonable end result is achieved, it requires considerable time and experience. It is very hard to produce an even surface, and the reinforcing pieces stick up from the surface so that a top dressing, say 20 mm thick, must be applied in order to cover the reinforcing pieces and provide an even surface. Because of the intractable nature of the matrix, screws and augers do not work well. If one deposits a layer using a strickler, the strickler tries to shear the matrix and pulls out the reinforcing pieces.
[0003] Because of these difficulties, it was desirable to find a method that removed the requirement for experienced labour, reduced variations in the thickness of the layer deposited, produced a flat surface with a minimum of pieces projecting, could reduce the necessity for applying a top dressing, and carried out the operation more quickly.
The Invention
[0004] The present invention provides a machine for depositing a layer of matrix which includes random reinforcement, the machine comprising means for feeding the reinforced matrix. According to a first aspect, there is at least one pusher member arranged to make repeated up-and-down movements and positioned so that the feeding means feeds the matrix beneath the pusher member, and as the matrix is fed beneath the pusher member, the pusher member passes down into the matrix so as to push the reinforcement beneath the level of the top of the matrix. According to a second aspect, there is a belt for feeding the layer of matrix towards a recipient, and a moving member above the belt for engaging the top surface of the layer of matrix.
[0005] The invention also provides a method of depositing a layer of matrix which includes random reinforcement, comprising feeding a layer of the reinforced matrix. According to a first aspect, the layer is fed beneath a pusher member which is repeatedly passed down into the matrix, thereby pushing the reinforcement beneath the top of the matrix. According to a second aspect, the layer is fed between a gap formed between a lower moving belt for supporting the layer and a moving member above the belt for engaging the top surface of the layer.
[0006] In the first aspect of the invention, the pusher member penetrates the top surface of the matrix, and pushes the reinforcement down into the body of the matrix. Voids can be reduced or largely eliminated, and the reinforcement can be kept below the top surface. This avoids the necessity for applying a top dressing in many circumstances, and enables the matrix to be spread evenly across the deposited width.
[0007] The pusher member should be sufficiently thin to pass into the matrix without undue compression, but should be sufficiently thick to avoid cutting the reinforcement - in practice, the pusher member should be as thick as conveniently possible so that e.g. the reciprocation need not be very rapid in order to cover a reasonable proportion of the whole surface. A suitable thickness is about 3 mm.
[0008] The pusher member need only penetrate a little into the surface, say not less than about 5 or 10% or not more than about 20 or 30%, of the layer thickness. For instance, for a 150 mm layer, the pusher member need only penetrate about 25 mm.
[0009] The word cover is used herein in the following sense - if the pusher member or members engaged the whole of the surface of the layer as the layer passes underneath them, with no overlap, there is 100% cover. Ideally, there should be 100%, but 100% cover is not essential, and 50% or 25% cover may be satisfactory. It is however desirable that each reinforcing element adjacent the top surface should be pressed down, and preferable that it should be pressed down several times. A suitable cover can be achieved using staggered pusher members.
[0010] The pusher member can be of any suitable type, for instance: flexible blades which bend on withdrawal so that they in effect pass in and out at 90° to the surface of the layer; spaced disc rotating about a transverse axes or axes, in which case it is the consecutive peripheral parts which make the repeating up-and-down movements; rod-like members; a blade or blades in general. The preferred pusher members is a transverse blade, used singly or in association with other transverse blades. The use of multiple pusher members enables power requirements to be reduced in that most power is required when pushing the pusher members into the matrix - by suitably staggering the cycles of the multiple pusher members, the power requirement curve is evened out. A simple arrangement is to have two or more transverse blades, aligned across the machine, working out of phase with one and other.
[0011] In the second aspect of the invention, the belt and the moving member act as an extrusion die with moving walls, and postively determine the thickness of the layer. If, as is preferred, the pusher members have already acted on the matrix, or the matrix otherwise has an unreinforced top layer, the belt and the moving member level the top of the unreinforced matrix both longitudinally and transversely, and make the density more constant. The distance apart of the moving member and the belt can be adjusted to alter the thickness of the layer.
[0012] It is preferred that the moving member should be another belt. The belts should be long enough to ensure a positive feed. If the belts are substantially parallel, there is no compression or other change in cross-sectional area as the layer travels between the belts, and no shear is applied. However, some slight convergence, say a reduction in thickness along the length of the belts of 10% or less, or 5% or less, may be beneficial as it applies slight compression to the matrix.
[0013] It is particularly useful if the pusher member applies positive feed to the layer as the layer enters between the moving member and the belt.
[0014] As an alternative to using the pusher member to prepare the layer of matrix before it reaches the entry between the moving member and the belt, a vibrating plate could be used to prepare the layer of matrix.
[0015] In theory, it is possible to deposit the layer on a moving surface as a final recipient, in a manufacturing process. However, the recipient is preferably stationary, e.g. the ground, with the depositing means moving along it.
Preferred Embodiment
[0016] The invention will be further described, by way of example, with reference to the accompanying drawing, which is a schematic side view of a machine for depositing on the ground sand reinforced with mesh pieces in accordance with GB-A-2 120 475.
[0017] The machine 1 is a track-laying, self-propelled vehicle. It is suitable for working on soil surfaces; it has smooth-surfaces tracks 2 (which could be in the form of flat rubber belts). The tracks 2 are of large surface area, the preferred footprint pressure being 20-40 KPa.
[0018] The machine has a holding hopper 3 into which the pre-mixed reinforced matrix 4 is loaded. The hopper 3 has a moving lower feed surface provided by a feed conveyor 5 whose speed is controlled to feed the reinforced matrix at a predetermined rate, closely related to the rate at which the matrix is to be finally deposited on the ground. At the exit from the hopper 3, there is a spreading auger 6 and a thickness gate 7, which give a crude intial distribution. The matrix tips over the end of the feed conveyor 5 onto a short slide 8 and then onto a lower belt 9, subsequently entering between parallel runs of lower and upper belts 9, 10 which move at the same speed and which carry the matrix, now formed into a layer, down to the ground. The belts 9, 10 preferably have knurled surfaces to increase the tractive force on the layer. At the end of the lower belt 9, there is a short free-fall, but the layer then lies on the ground. The layer is finished with vibrating means in the form of a light-weight, vibrating plate 11, which finishes the surface to a trowelled consistency. The speed of advance of the machine 1 is equal to the resolved speed of the belts 9, 10 so that the layer as it is deposited is not moving with respect to the ground.
[0019] As the matrix is fed towards the belts 9, 10, it is fed past a single reciprocating pusher member or transverse blade 12 which is repeatedly pushed down into the reinforced matrix, thereby pushing the reinforcement, ie the mesh pieces, beneath the level of the top of the matrix layer. The blade 12 has a crank drive, ie. a quasi-sinusoidal movement, and for about half its stroke, it is above the matrix layer. As can be seen in the drawing, the blade 12 moves vertically whilst the layer is moving downwards, and the speed of the blade 12 is roughly co-ordinated to the movement of the layer so that as the blade 12 passes into the layer, its speed is roughly the same as that of the layer; as the blade 12 comes out of the layer, it is withdrawn completely, and thus carries out no substantial strickling action. The blade 12 is positioned immediately before the entry to the gap between the belts 9, 10, and as the blade 12 is effectively moving forward at the same speed as the layer of reinforced matrix as the blade 12 descends, it applies positive feed to the layer, ie. positively assists entry of the reinforced matrix into the gap between the belt 9, 10.
[0020] The total width of the feed conveyor 5 is equal to the width of the blade 12 and to the width of the belts 9, 10, this width defining the width of the layer to be deposited. The layer can have any suitable width, but in practice the width may be 2 metres, 3 metres or 4 metres.
[0021] The rate of feed of the feed conveyor 5 is adjusted so that the volume feed is that required by the belts 9,10; this can be done using automatic overfeed sensors for sensing the thickness of the matrix in the layer immediately before blade 12. For the layer shown, which is 150 mm thick, the blade 13 can have a 40 mm stroke and penetrate 25 mm into the layer of reinforced matrix. The width of the blade can equal the width of the layer deposited, or multiple blades 12 can be used. The thickness of the blade can be 3 mm with a flat end and slight radiusing at the edges. The frequency of reciprocation of the blade 12 should be suitably adjusted to the speed of the layer. If the blade reciprocates at 1000 r.p.m., 100% surface cover can be achieved at the preferred feed rate, which is 3 metres/minute.
[0022] Any suitable matrix can be layed in this way, but the invention is particularly useful where the matrix is an intractable reinforced matrix. The intractability of a matrix is measured by its shear resistance, there being a considerable increase in shear resistance when compared to the same matrix without reinforcement. A simple test is to try and strickle or scrape over the top - if this cannot be done without pulling out pieces of reinforcement, the matrix can be considered to be intractable.
Example
[0023] A suitably graded sand was reinforced with mesh pices generally as described in GB-A-2 120 475. Specific details were as follows:
| Mesh material | - polypropylene |
| Mesh weight | - 40 g/m² |
| Mesh pitch | - 10 x 10 mm |
| Mesh piece size | - 100 x 50 mm |
| Mesh/sand ratio | - 6 Kg/m³ |
| Pieces per unit volume | - 30,000 pices/m³ |
| Thickness of layer | - 150 mm |
| Pieces per m² surface | - 4500 pieces/m² |
1. A machine (1) for depositing a layer of matrix (4) which includes random reinforcement,
and comprising means (5) for feeding the matrix, characterised in that there is at least one pusher member (7) arranged to make repeated up-and-down movements
and positioned so that the feeding means feeds the matrix beneath the pusher member,
and as the matrix is fed beneath the pusher member, the pusher member passes down
into the matrix so as to push the reinforcement beneath the level of the top of the
matrix.
2. The machine of Claim 1, wherein the pusher member (7) is a transverse blade.
3. The machine of Claim 1 or 2, wherein the pusher member (7) applies positive feed
to the layer of matrix (4).
4. The machine of any of the preceding claims, and comprising a belt (9) for feeding
the layer of matrix (4) away from the pusher member (7).
5. The machine of Claim 4, and comprising a moving member (10) above the belt (9)
for engaging the top surface of the layer of matrix (4).
6.The machine of both Claim 3 and Claim 5, wherein the pusher member (7) is immediately
adjacent the entry between the moving member (10) and the belt (9), and applies positive
feed to the layer of matrix (4) as it enters between the moving member and the belt.
7. A machine (1) for depositing a layer of matrix (4) which includes random reinforcement,
and comprising means (5) for feeding the matrix, characterised in that there is a belt (9) for feeding the layer of matrix towards a recipient, and a moving
member (10) above the belt for engaging the top surface of the layer of matrix.
8. The machine of any of claims 5 to 7, when the moving member (10) is a belt.
9. The machine of Claim 8, wherein the two belts (9, 10) have substantially or nearly
parallel runs, the layer of matrix (4) being arranged to pass between the runs.
10. The machine of any of the preceding Claims, and comprising vibrating means (11)
for contacting the surface of the layer of matrix (4) after it has been deposited.
11. The machine of any of the preceding Claims, and being a travelling machine (1)
for depositing the layer of matrix (4) on a stationary recipient.
12. The machine of Claim 11, and being a track laying vehicle (1) for depositing the
layer of matrix (4) on a soil surface.
13. A method of depositing a layer of matrix (4) which includes random reinforcement,
characterised in that a layer of the reinforced matrix is fed beneath a pusher member (7) which is repeatedly
passed down into the matrix, thereby pushing the reinforcement beneath the top of
the matrix.
14. A method of depositing a layer of matrix (4) which includes random reinforcement,
characterised in that a layer of the reinforced matrix is fed between a gap formed between a lower moving
belt (9) for supporting the layer and a moving member (10) above the belt for engaging
the top surface of the layer.
15. The method of Claim 13 or 14, wherein the matrix (4) is soil, reinforced with
small mesh pieces of high flexural recovery.
16. The method of Claim 15, wherein the soil is sand.
17. The method of any of Claims 13 to 16, and carried out in the machine of any of
Claims 2 to 12.