GB2197902A

GB2197902A - Process for the production of an accumulation of granular material

Info

Publication number: GB2197902A
Application number: GB8727476A
Authority: GB
Inventors: Johan Hendrik Volbeda
Original assignee: Hollandsche Beton Groep NV
Current assignee: Hollandsche Beton Groep NV
Priority date: 1986-11-27
Filing date: 1987-11-24
Publication date: 1988-06-02
Also published as: GB8727476D0; DE3739045A1

Description

PROCESS FOR THE PRODUCTION OF

AN ACCUMULATION OF GRANULAR MATERIAL The invention relates to a process for the production of an accumulation of granular material by pumping the material together with a fluid onto a substrate at the place where the accumulation is to be formed and according to the layout or shape of the accumulation to be made, such as a dam or dyke. It is known to make such accumulations in the form of dams, dykes, heaps of bulk material and the like by pumping the mixture onto a substrate, which can be under water or above water. For example, it is known to raise the level of sites with a mixture of water and sand, from which the water separates off and flows away. It is also known to do this under water, in which case the separation between the sand pumped in and the transporting water is more difficult, because the separation has to take place in an environment formed by water. It is also known to transport dry granular material with a gaseous medium, for example air or an inert gas. In all these cases, the problem is that on leaving the transporting line the mixture spreads out, so that the separation between the fluid and the granular material takes place in a manner which was hitherto always accepted as normal, but which is fairly arbitrary. In a mixture of sand and water which is pumped freely onto a site, the water runs away in a fairly arbitrary manner along the path of least resistance. A compact accumulation of desired shape is therefore difficult to achieve. A finishing-off operation is necessary in many cases. When this mixture is placed under water, there is such a spread of the granular material that an accumulation can be made only at relatively high cost and with relatively great effort. When a mixture of dry material is pumped together with a gaseous medium, there is generally very great dust formation.Dust is not only a nuisance in the environment, but also means a loss of material. The object of the invention is now to produce a simple process by means of which it is possible to eliminate the above-mentioned disadvantages. This object is achieved according to the invention in that the mixture of granular material and fluid is pumped into a space which is bounded by a cloth or sheet which is fixed at least along part of its periphery to the substrate, and whose effective surface area is no less than an area of the surface of the substrate bounded by the fixed periphery. By introducing the mixture in one suitable way or another under the cloth or sheet, that is, into the space which is bounded by the cloth or sheet, and which is bounded by the substrate and has one or more openings for the fluid to escape, the separation between granular material and fluid will take place within this space, so that the fluid is forced to disappear through the openings, while the material separated off remains within the space which is bounded by the cloth or sheet. This cloth or sheet is larger in area than the surface of the substrate, which means that on completion of the process an embankment of granular material which is closed at the top by the cloth or sheet is obtained. The escape opening for the fluid can be formed by keeping one point of the periphery of the cloth free of the substrate. The infeed can also take place through this point.. The cloth or sheet may instead be permeable to the fluid. The cloth or sheet can be fixed in a simple manner by loose bulk material, such as stones or ballast, which is deposited on the periphery. The cloth may have strips for bulk material disposed at least along part of its periphery such as bags for receiving stones or sand. The cloth may be provided with withes or blocks at the edges or provided with metal wires woven in, which serve to reinforce the cloth and function as ballast. If such a cloth or sheet is placed on the substrate with the correct distance between the edges, a calming of the mixture flow fed in will always occur, irrespective of whether this is now a mixture of granular material with a liquid below a liquid level or such a mixture above a liquid level or in the dry, while also in the transportation of granular material with a gaseous fluid the spread is limited and the formation of dust clouds is prevented. A process according to the invention may be carried out under water. The accumulation on a sea or lake bed using a mixture jet of, for example, water and sand is not simple, because the sand spreads with the spread of the water jet and it takes quite a long time, longer than in the case of a flow in air, before the sand has separated from the water. With a process according to the invention, it is now possible to produce an accurately determined shape of the accumulation:under water and extending above water if necessary..By making a suitable choice of the position of injection points and ballast distribution on the cloth, it is:possible to control the place where the granular material settles.The mass of the material loads the substrate, which can lead to sagging and slipping, in ^particular if the substrate has little bearing power= This can now be remedied by placing a layer of geotextile, for example, a sheet of synthetic material under the cloth or sheet. The cloth is thus placed above-,'the geotextile and fixed at the periphery..The layer of geotextile, generally a fabric of plastics fibres, then ensures distribution of the load. A specially effective embodiment is obtained if the periphery'of the geotextile and of the cloth or sheet are fattened to each other and the dimensions of the geotextile are no greater than those of the cloth or sheet. This means that after placing the geotextile on the substrate and pulling it taut in the lengthwise and crosswise direction, one can be sure that the bottom layer is properly positioned and the cloth, which is of course larger, will ensure the correct shaping of the embankment to be formed. In addition, it means that forces exerted by deposited bulk material such as ballast and stones, which have transverse components, and transverse forces exercised by'the slope action are absorbed by the geotextile. If desired, a hardening and binding material can be added to the mixture, for example cement in the case of a mixture of water and sand, for after separation of the solids from the surplus of water a mixture which has sufficient water to ensure hardening and binding of the sand through the cement remains. In the case of other materials other binding agents could be of importance. An embodiment of the invention will now be described by way of example and with reference to the drawing, which shows schematically the making of a dam embankment under water. Reference number 1 indicates a sea or lake bed. Placed on that substrate is a sheet 2 of geotextile. Placed on this sheet is a cloth 3, which may or may not be permeable, and the periphery or edges 4 and 5 of which coincide with the periphery or edges 6 and 7 of the geotextile. If desired, the edges 4 and 6 and 5 and 7 can be joined to each other. The cloth 3 is also sealed off of an edge from the lake or sea bed at its end which can be assumed to be at the top right of the drawing. The edges can be ballasted with stones 8, or with sand-filled tubular strips 9, or with blocks 10 fixed in a suitable manner. The cloth 3 can be ballasted in the same way, with such a distribution that the desired shape is obtained. Reference number 11 indicates a pipe with a mouth 12 out of which the mixture 13 can flow. In the initial state the cloth 3 will lie in a loosely folded state on the sheet of geotextile 2. On insertion of the pipe 11 and infeed of the mixture near the end, a sand embankment will be built up there, so that the water which is fed in flows backwards and flows out through the opening 14 or flows away through the top cloth 3. If the pipe 11 is gradually pulled back, a dam embankment then forms under the cloth, acquiring the shape which is indicated in the drawing. The sheet 2 of geotextile can be fixed with anchor cables 15 and/or with pins 16. The pipe 11 can be guided through loops 17 which are fixed to the sheet 2. On the cloth 3 there can be a distribution of ballast by means of blocks 18 to influence the final shape and to protect against 'mechanical damage and the effect of waves and current. The ballasted edges 4 can be very wide, so that a great surface area of friction is obtained and there is protection against erosion. The edges of the cloth can be fixed to the sheet, for example at 19. To fill jute or plastics sausage-shaped bags with sand by injecting a mixture of water and sand is knoWn. On closure of the bags, one then obtains long, sausage-shaped bags of oval cross section which can be used as a bank protection. These are bags which must.be able to be .moved after filling, and they are thus relatively small, although they are often much larger than ordinary sandbags. With a process according to the invention a basic embankment which is not movable is built up in one go. This embankment can be of triangular or trapezoidal cross-section. The shape is determined by the distribution of the ballast and by the sheet of geotextile. A process according to the invention has a number of advantages. For example, an accurately shaped dam embankment or other embankment can be produced under water. However, the invention is not limited to this, for even above water some of the advantages obtained with the cloth remain. The losses through turbulence, such as those with the known process, are substantially reduced. The mixture can be introduced in many ways, for example at a number of injection points, that is, openings in the cloth to which a mixture infeed opening can be connected. A rigid cloth which has little stretch, but which is sufficiently supple, can be used; an elastic cloth can also be used. During the production and also thereafter, the embankment obtained is insensitive to the eroding action of waves and currents. The density of the packing obtained in the cloth is greater, which mainly is obtained by the impulse of the outflowing material and the outflowing conveying fluid upon the previously deposited material. Through the use of a permeable cloth, mixing with ambient water is avoided, and the speed of settling is increased. A steeper slope is possible also if the cloth, after accumulation, is removed. The position of the pipe under the cloth can be "controlled" by inserting the pipe through loops which are fastened to the cloth or the geotextile. The large density achieved with a process according to the invention is of importance for the stability of the body obtained. Said density is obtained in that the flow of mixture remains concentrated. The sand grains settle down in a highly turbulent environment with the result of high packing density. The slope formed is less sensitive to aquafunction which is indeed the case with freely settling of soil in water.

Claims

CLAIMS:

1. Process for the production of an accumulation of granular material by pumping the material together with a fluid onto a substrate, characterised in that the mixture of granular material and fluid is pumped into a space which is bounded by a cloth or sheet which is fixed at least along part of its periphery to the substrate, and whose effective surface area is no less than an area of the surface of the substrate bounded by the fixed periphery.

2. Process according to Claim 1, characterised in that the cloth or sheet is fixed to the substrate in such a way that it has one or more openings for the fluid to escape.

3. Process according to Claim 1 or 2, characterised in that the cloth or sheet is permeable.

4. Process according to any preceding claim, characterised in that the cloth or sheet is fixed by loose material, such as stones, being deposited on the periphery.

5. Process according to any preceding claim, characterised in that the cloth has strips for receiving bulk material disposed at least along part of its periphery.

6. Process according to Claim 5, characterised in that withes or blocks are fastened to the cloth.

7. Process according to any preceding claim, characterised in that the cloth is reinforced with wires woven in of a material with high strength and high density.

8. Process according to any preceding claim, characterised in that the substrate is under water.

9. Process according to any preceding claim, characterised in that a layer of geotextile is placed on the substrate under the cloth or sheet.

10. Process according to Claim 9, characterised in that the periphery of the geotextile and of the cloth or sheet are fastened to each other and the dimensions of the geotextile are no greater than those of the cloth or sheet.

11. Process according to any preceding claim, characterised in that a hardening and binding material is added to the mixture.

12. Process substantially as herein described with reference to the accompanying drawing.