1. Technical Field ,

The invention relates to the forming and installing of a ballasted mat for stabilization of the ground. Typical applications of the invention are: Pre¬ vention or control of scour along sul-marine pipelines and also ballasting of these, shore and river bank protection, prevention of shoaling up of naviga¬ tional channels, stabilization of the ground tinder roads, prevention of land slides, and the like.

2. Background Art

Several means have been devised for fixing the soil or for covering it. How¬ ever, these present solutions often are of relatively high cost and are some¬ what complex in construction while not always giving the desired protective results.

For anchoring of underwater pipelines a continuous durrfcfoell tube system is disclosed by the Murphy US Patent No. 3,779,027. However, this tube system extends only a short distance away from the pipeline and thereby has too nar¬ row width to prevent undermining of the pipeline. Furthermore, the filling of the tubular envelope with ballast material takes place a f t e r the tubular envelope has 'been installed over the pipeline. This method of filling which does not utilize gravity cannot and is not supposed to totally fill out the cross-section of the tube.

Similar disadvantages has the Keith US Patent No. 3,793,845. Another existing, so called Gabion system is used for shore protection, har¬ bour construction, road construction, and the like. The area to be stabilized

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is covered with separate,side-by-side boxes of wire mesh which are filled manually with stones. Eecause of the large required volume of stones and the extensive use of labour work involved, this system is very expensive. 3. Disclosure of Invention

It is therefore an object of the present invention to provide a method and apparatus for producing and laying a ballasted mat for ground stabilization which will overcome the inherent limitations and disadvantages of the known prior systems.

It is another object of the present invention to provide a ballasted mat having an economical cost per unit area factor.

Depending on the purpose of the mat, the mat-producing machine is mounted either on a vehicle, e g supplied with caterpillars fit for moving on land, or on a surface vessel or on a platform supplied with movable legs by means of which the platform can "walk", or on a underwater vehicle, e g supported on and driven forward by longitj linally extending rotating tubes supplied with screw threads on their outer surfaces.

The -sheet material used for forming the mat preferably is provided in two op¬ posite rolls, each having the proper width, or alternatively, in more, shor¬ ter rolls. The material from either roll is fed through a system of parallel, adjacent rollers which spread out the sheets and by means of brakes control the speed of laying the mat.

A certain distance below the last roller which either sheet passes over, the sheet is seamed together with the other sheet by means of a row of horizont¬ ally -spaced seaming devices. Hereby a continuous mat containing vertical pa¬ rallel compartments like those of a ribbed eider down is formed. Particulate-matter forming ballast is simultaneously fed through pipes or hoses between the seaming devices into the compartments of the mat. The lower ends of the hoses or pipes are below the seaming devices, but above the ground, so that the weight of the ballast oontiπuously pulls the mat down to the ground, as the mat-forming machine is continuously advanced. At the completion of the section of mat, the cctipartments of the mat are closed by seaπiing crosswise the end of the section in a horizontal line below the lower ends of the hoses or pipes. A parallel seam a little distance above this first seam is produced to close the foremost end of the next section of mat to be produced, and finally the mat is cut between the two seams. 4. Brief Description of Drawings

While the fields of application of the present invention cover uses above as well as under water, a full and cαπplete understanding of the invention may

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be had by reference to the description of preferred embodiments relating to one example: protection of submarine pipelines as set forth hereinafter and as may be seen in the accompanying drawings in which:

Fig. 1 is a plan view of the mat-forming system of the present invention and shows the system mounted on a surface vessel and continuously forming and laying the mat over the pipeline,

Fig. 2 is a cross-section taken along the line I-I in Fig. 1 and shows the pipeline covered by the mat.

Fig. 3 is an enlarged cross-section taken along the line II-II in Fig. 1 and shows a schematic cross-section of the Brat-forming and -laying systsn, Fig. 4 is an enlarged cross-section taken along the line III-III in Fig. 3, Fig. 5 is a cross section taken along the line IV-IV in Fig. 3 of the com ^¬ pleted mat,

Fig. 6 is a cross-section of an alternative shape of the mat, and Fig. 7 is a schematic cross-section of a submarine barrier involving use of the present "type of mat.

5. Best Mode of Carrying Out the Invention

Referring to Figs. 1-6 of the drawings, there is depicted an apparatus 16 of the present invention for forming and installing a ballasted mat 15 over a pipeline 1. 16 is mounted on a sea going vessel which may be in the form of a barge out over the side of which 16 is overhanging, or in the form of a barge supplied with a iroonpool through which 15 can pass on its way to the seabed, or in the form of two barges 17 coupled together by means of beams 18 an the over*- and/or underside of 17.

The vessel 17 may be moved forwards by means of winches 21 pulling the vessel along the warps 19 which are anchored to warp anchors 20.

The vessel 17 may ^' include compartments for storing a particulate ballast ma¬ terial 3 and sheet material 2 utilized in forming the mat 15. Both kinds of material may transported from shore to the vessel by supply boats 24 and un¬ loaded by a crane 23.

The ballast material 3 may cαπprise any suitable weighty particulate material such as stones, pebbles, -sand, pieces of concrete and the like. The grain size must be larger than the size of any perforation of the sheet material 2, but smaller than about 1/3 of the diameter of the hoses or pipes 8. Otherwise the ballast material may get stuck in the hoses or pipes.

The sheet material 2 may be a continuous, woven or extruded sheet consisting for instance of plastic or natural fibres resistant to the eroding and dete¬ riorating factors of the environment. Alternatively, it nay be a net, in which

the mesh width is smaller than the grain size of the ballast material 3. The net may be made of plastic, natural fibres, aluminium or steel which may be galvanized and/or coated with plastic.

The two layers of sheet 2 forming the mat 15 may be made of the same material or i_wo different kinds of material, they may have different mesh widths and other differences. For example, in the cross-section of the mat shown in Fig. 5 the straight sheet 30 may be a coated steel wire mesh or a strong plastic net, e g reinforced with aromatic polyamide, and the buckled sheet 31 may be a thinner or weaker net made for instance of plastic.

The rolls 10 supported on bearing rollers 13 feed the sheet material 2 to the seaming devices 4 via a suitable number of rollers, for instance three: 5, 6 and 7. The functions of the rollers are to stretch out the sheet in its trans¬ verse direction and to control the speed of laying of the mat. If for instance the sheet material is a plastic net and therefore is very elastic, its width has a tendency to contract because of the longitudinal drag force due to the weight of the ballast 3. To counteract such tendency of a sheet 30 which is supposed to be straightened out when it leaves the roller 5, one of the rol¬ lers, e g 7, on its surface may be supplied with two screw threads 25. Either thread occupies half of the length of the roller 7, and the two threads have opposite directions of pitch. The surface of the roller 7 turns in the direc¬ tion 32 against the direction 33 ^' of movement of the sheet 2, and when 7 ro¬ tates, either screw thread tends to stretch out the .sheet 2 in direction away from the middle of the roller 7 toward the outer end of the thread. The surfaces of the rollers 6 and 5 turn in the same directions as the direc¬ tion of movement of the sheet 2. The surface of at least the roller 5, which carries the weight of the suspended length of the mat 15, has a high frictio- nal resistance, obtained for instance by means of the raised edges of longi¬ tudinally extending slits cut in a steel plate cylinder making up the surface of 5.

The roller 6 may be supported in slide bearings and by means of spring or rubber πeans continuously pressed against 5. The weight of 15 thereby is car¬ ried by the rollers 5; a d by brake means acting on the periphery or the axle of 5, the speed of descending the mat can be controlled.

At a suitable level below 5, guiding merrbers 11 make the two sheets meet, so that the sheets can be seamed together in each line between the upper and lower parts of each guiding merrber 11. The meπbers 11 may be vertical plates, as shown in the drawing, and should have thickness corresponding to the width of the seaming devices 4. Depending on the desired contour of the cross-sec-

tion of the mat, the guiding edges of the eπbers 11 are placed in line with the centerlines of the hoses o pipes 8, cf. Fig. 6, or asyπm≥trically as shewn in Fig. 3. In the latter case the seams of the mat, Fig. 5, become less strained by the ballast during and after laying of the mat.

Preferably the guiding members 11 are mounted slidably on horizontal beams 35, so that their mutual spacing can be regulated in accordance with the desired thickness of the mat.

The seams may be continuous, so that completely separated tube-like compart¬ ments between the two sheets 2 are formed. Aternatively, the seaming process may be stopped at intervals, while the sheets continue on their way dσwr&rards, whereby the resulting connections between the ccnpart ents are left open. The intervals may be staggered between neighbouring seams.

The seaming together of the two sheets 2 is effected by means of well-known seaming devices 4. These devices may be in the form of heating means, if pla¬ stic sheet material is being utilized. Alternatively, seaming means may be in the form of any suitable apparatus for sewing, stapling or gluing the sheets together, so that sufficiently strong joints are produced with lasting quali¬ ties for the environment within which the mat will be placed. If the sheets 2 are nets with suffiently large mesh widths, the well-known seaming devices 4 schematically shewn in Fig. 3 may be appropriate. Each de¬ vice includes an electrically heated melt of polyester which is pumped . through a nozzle so that a squirt 34 is formed. If in each line to be seamed two opposite devices 4 pump squi-rts 34 against eachother, preferably under an angle, the two squirts will fuse in the openings between the threads of the nets 2 and eπforace the threads on their outward sides, so that a continuous, ^• strong seam is formed.

The lower row or parts of the guiding meπbers 11 are placed so far below the seaming devices 4 that the πelted polyester gets time enough to harden before it readies the lower rcw-or parts of the guiding meπbers. The crosswise seaming of the end of each section of mat appropriately may be done by means of stapling means.

Between the guiding meπfoers 11, hoses or pipes 8 lead the ballast material 3 into the continuous ccnpartments formed between the two sheets 2. The lower ends of 8.are below the lower guiding neπfoers 11, but above the ground, so that gravity can be utilized.

An even distribution of the ballast material 3 over all of the width of the . mat 15 may be obtained by means of a well-knσwn distribution plant 9, 12, 13 and 14. 9 is a horizontal tank to the perforated bottom of which the hoses or

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pipes 8 are attached. A conveyer belt 12 on bearing rollers 13 transports the ballast material 3 from a filling station at the end of the belt, and a car 14 on tracks,driven by the belt 12, moves to and fro and distributes the ballast material over the entire length of the tank 9.

In some cases an uneven distribution is desirable. For example, in a mat con¬ sisting of two layers of net for covering a submarine pipeline, the net ope¬ nings allowing for flow through the centre portion of the mat may be kept open. Such uneven distribution may be obtained by regulating the supply of ballast material frcm the filling station and/or from the car 14, and/or by closing more or less the centre hoses or pipes 8.

The speed of laying the mat 15 must be correlated with the speed of the sur- . face vessel 17 and with the speed of supply of the ballast material 3. This correlation may be obtai ed by manual regulation. Alternatively, the said three speeds may be correlated by means of mechanical couplings 22 between the winches 21 and the rollers 5 and the conveyer belt 12, or between two of these three components, only. 6..Industrial Applicability

In the above-mentioned fields of application of the invention the mat 15 nor¬ mally is placed directly on the ground above or under water. Besides this way of applying the mat, it may be used for construction of a barrier on land or in a body of water. Exaπples are: Road or railway construc¬ tion, sea or river dikes, submarine barriers for coastal protection or pre¬ vention of siltation in water ways, and the like.

The core of the barrier may be solid and consist of fill material such as sand, gravel or other granular material. Or it may consist of a shell-formed struc¬ ture 37 forming at least part of the desired cross-section of the barrier, cf. Fig. 7. The surface of the barrier is made up of a the ballasted mat 15. In submarine barriers the mat protects the core against undermining and adds weight to prevent removal of the barrier due to waves and currents. The structure 37, for example, may consist of concrete, plastic, wood or metal. The syπrnetrical side portions of 37 may be hinged or rigidly interconr- nected, and their lower edges may be interconnected by horizontal ties 38. The structure 37 may be a continuous plate, which may be provided with aper¬ tures allowing for vertical flew of water. Alternatively, the structure may be made up of separate or interconnected transversely exten i g supporting πsπbers perpendicular or oblique to the longitudi al direction of the barrier. The structure 37 may be attached to the mat 15, before the mat is laid.

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