WO2001015969A1

WO2001015969A1 - Mobile barge with tensioned struts for nautical works at medium depths

Info

Publication number: WO2001015969A1
Application number: PCT/FR2000/002423
Authority: WO
Inventors: Pierre Blanc; Alain Horeo
Original assignee: Vinci Construction Grands Projets
Priority date: 1999-09-01
Filing date: 2000-09-01
Publication date: 2001-03-08
Also published as: FR2797843A1; AU7296800A; EP1208034A1; KR20020042821A; FR2797843B1

Abstract

The invention concerns a barge for nautical works comprising a deck (7) for receiving equipment for executing works such as a crane, said barge (1) comprising ballast (3), linking means (4) connecting the deck (7) to each ballast (3), at least three of said ballast (3) being set on the ground (2) when the barge (1) is operating, said barge being such that in combination, when operational: the ballast (3) are not rigidly fixed to the ground (2), the linking means (4) are maintained tensioned, the barge (1) is maintained in a substantially constant position relative to the ground (2), the effects of the surge, the waves and the loading movements on the barge (1) and the effects of current being absorbed by the linking means (4); said barge (1) being capable of shifting from an operational state to a neutral state wherein it can move freely, the ballast (3) being then suspended above the ground (2). Such a barge, useful for nautical works at medium depths, can be obtained by reversible transformation of a standard self-propelled elevating platform.

Description

Mobile barge with straight legs for nautical works at medium depths

The invention relates to an anchoring device for floating structures, in particular for platforms used for various nautical works, such as for example dredging, embankment or pile driving of submerged piles.

Numerous designs of anchoring devices for floating structures are already known in the prior art with a view to keeping them in a good position relative to the work location, in particular despite the effects of the swell.

To maintain this position, various solutions have been envisaged, such as in particular: - permanent fixing relative to the seabed, by concrete or steel structures. Such a method is sometimes used for so-called rigid base oil platforms, suitable for shallow seas. For this first type of anchoring, reference may be made, for example, to the following document: EP -A- 0 640 522; - mooring lines connected to a mooring turret and distributed around the axis of the turret so as to oppose its drift under the effect of transverse forces exerted on the floating structure. The floating structure, rotatably mounted relative to the turret, can thus rotate around the axis of this turret. For this second type of anchoring, reference may be made, for example, to the following documents: WO -A- 99/17983, WO -A- 99/17982, WO -A- 96/30524, WO -A- 98 / 34829, EP -A- 0 921 061, FR -A- 2 771 703; maintenance with respect to a single or more mooring points, by means of mooring lines which are not necessarily vertical and which are not necessarily held in tension. For this third type of anchoring, reference may be made, for example, to the following documents: EP -A- 0 796 784, WO -A- 98/35874, WO -A- 99/02394, WO -A- 99 / 10228, US -A- 3,865,064; funicular anchoring by taut lines which extend, most often vertically, towards a base anchored on the seabed. This method is used in particular for a large number of so-called oil platforms with straight feet (leg platform tension or TLP), particularly suitable for deep-sea drilling, between 500 m and 2000 m.

For this fourth type of anchoring, reference may be made, for example, to the following documents: FR -A- 2,755,091, FR -A- 2,729,635, FR -A- 2,703,021,

FR -A- 2 624 089, EP -A- 0 716 011, JP -A- 60163786, JP -A- 60045494, JP -A- 59128086, EP -A- 0 575 288, EP -A- 0 441 413, EP -A- 0 360 364, EP -A- 0 328 196, EP -A- 0 323 392, EP -A- 0 319 419, EP -A- 0 311 398, EP - A- 0 311 397, EP - A- 0 311 396, EP -A- 0 302 546, WO -A- 95/29839, WO -A- 96/40548, WO -A- 96/21797, WO -A- 97/45318, WO -A- 97/29942, WO -A-

99/00293.

Turret anchors, if they are well suited to certain underwater works such as drilling, allow a rotation of the floating structure relative to the axis of the turret, a movement which is undesirable for certain works under -marins.

Rigid base platforms placed directly on the seabed, barges or semi-submersible platforms with catenary anchoring, especially for shallow seas, certainly offer more stability in position than turret anchors by report to an underwater site for the machines they support.

However, they generally cannot be easily and quickly moved from one job site to another while being kept in a substantially stable position at each job site.

It has been proposed in the prior art to remedy this defect by proposing floating structures anchored by stretched cables and which can be towed.

Document FR -A- 2 248 192 thus describes an ocean-going device used for well operations. The device is held in place by at least two taut anchor or mooring lines, generally vertical. The anchoring means can be lowered by filling their internal compartment, to be placed on the seabed. The device can be towed, the anchoring means being emptied and able to support themselves during towing.

Document FR -A- 2 698 605 describes an underwater self-elevating platform that can be towed and includes means for pulling cables from the platform towards the bottom to a submerged position where its legs are in support on the bottom, and means for adjusting the position of each leg relative to the deck of the platform so that it is at a predetermined height relative to the bottom, four legs sliding vertically in sleeves arranged in the bridge .

We also know self-elevating barges with a multiplicity of feet on which a floating structure can be supported and raised. Reference may be made, for example, to document WO -A- 92/08849.

Mention will also be made of American patents 3982492, 3540396, 4048945, 4062313, 3919957, 3780685, 3976021, 3983828, 2972973, 2399656.

All these documents describe the floating platforms connected to the seabed by stretched cables. These platforms have an upper structure located significantly above sea level and a lower structure located significantly below this level, these two structures being interconnected by vertical columns of relatively small section.

As a result, variations in sea level due to the tide have little effect on the buoyancy pressure exerted on the structure.

Such platforms have a complex and costly structure completely different from that of barges. Indeed, the barges have a generally parallelepiped shape whose height is small compared to the other dimensions.

As a result, the slightest variation in sea level modifies Archimedes' thrust, in considerable proportions. It follows that the means disclosed by the prior art of the platforms are not sufficient to stabilize the barges.

The invention aims to provide a mobile barge called with stretched legs, that is to say comprising weights suspended from cables or anchor chains, this barge being obtainable in a completely reversible manner from a platform. self-elevating, and not requiring anchorage by anchor lines.

This barge must in particular be able to remain at a substantially invariable level despite the tidal range, the swell or the load variations linked to the operation of machines such as crane carried by said barge.

This barge must also be suitable for nautical work, of maritime or river type, at shallow depth, of the order of a few tens of meters to 150 m for example, including for areas where the seabed is at low lift and in steep slope.

This barge must be economical and simple in design and use.

To achieve the above objectives, the invention relates, according to a first aspect, to a barge for nautical works comprising a bridge capable of receiving machines for carrying out work such as a crane, this barge comprising ballast weights, connecting means connecting the deck at each ballast, at least three of the said ballasts being placed on the ground when the barge is in active state, said barge being such that, in combination:

• when the barge is in active state:

- the weights are not rigidly fixed to the ground;

- The connecting means are kept under tension; - The barge is kept in a substantially constant position relative to the ground, the effects of swell, waves, load movements on the barge and the effects of current being absorbed by the connecting means;

• the barge can pass from an active state, to an inactive state in which it is free to move, the ballasts then being suspended above the ground. An active state of the barge corresponds in particular to its use perpendicular to a given site.

An inactive state of the barge corresponds for example to its conveying or to its movement between two sites.

In a particular embodiment, the lifting means of the barge connecting means are at least partly similar to those used for lifting the legs of a self-elevating platform.

Said barge can thus be obtained by reversible transformation of the structure of a conventional jack-up platform.

The invention relates according to a second aspect to the application of a barge as presented above for carrying out nautical works such as dredging of foundations, placement of inclusions, embankment, pile driving, setting up ballast mat place, for depths of a few tens of meters.

Other objects and advantages of the invention will appear during the following description of embodiments, which description will be made with reference to the accompanying drawings in which: Figure 1 is a block diagram of the operation of the anchoring of the barge with stretched legs according to the invention; Figure 2 is a front view of a barge obtainable by reversible transformation of a jack-up platform according to one embodiment; Figure 3 is a side view of the barge of Figure 2; - Figure 4 is a detail view of the device for lifting the legs of a self-elevating platform before its reversible transformation into a barge with stretched legs; FIG. 5 is a detailed view of the device for lifting the chains of the straight leg barge, a device which can be obtained by transformation reversible of the lifting device for the legs of the self-lifting platform as shown in FIG. 4.

We first refer to Figure 1.

The meaning of the symbols used in Figure 1 is as follows: PA: Archimedes push;

PB: weight of barge 1, including any mobile loads; R1, R2: reactions of the soil 2 with respect to the weights 3; T1, T2: voltage of the connecting means 4 connecting the barge 1 to the weights 3; Δh: difference between water level at high tide 5a and initial level 5b.

For simplification: only two weights 3 are shown in Figure 1. It is understood, however, that more than two tests can be provided; sof 2 is considered to be substantially horizontal. Those skilled in the art will however understand that the reasoning below made with reference to FIG. 1 can be transposed to the case of non-horizontal soil.

The basic work surface 6 defined by the barge 1 is at a substantially constant distance from the ground 2 both in general (on the left in FIG. 1) and during a rising tide (middle of FIG. 1), than when moving a load on the barge (right in Figure 1).

When the tide is rising or the water level changes for any other reason, the values PA and T1, T2 increase, while the values R1, R2 decrease.

When moving a load, for example from left to right (Figure 1, right), the tension of the connecting means 4 and the values of the reactions R1, R2 on the weights 3 vary accordingly, the weights 3 remaining at the ground 2 and the tension of the connecting means 4 not canceling out. To obtain such stability characteristics of barge 1, the following general conditions are applied.

The weight in water of the weights 3 is determined by the following condition:

Plest> = ΣTmin + Psmin + ΔPA

• minTmin being the sum of the minimum voltages of the connecting means 4 such as chains or equivalent, voltages measured at the bottom; • Psmin being the minimum total weight to be transferred to the ground to compensate for the lateral thrusts exerted on the barge - for example under the effect of currents or wind - and to also compensate for any variations in slope of the ground 2;

• ΔPA being the variation of the Archimedes thrust under the effect of the swell.

The effect of waves and movements of the load on the barge 1 results in voltage variations on the connecting means 4.

In one embodiment, the variations in water level can be accommodated, within a certain range of variation, by the elastic deformation of the connection means 4, without the tension of these connection means being canceled.

This range of water level variations can correspond to the values of the tidal coefficients predicted during the duration of the work.

As a variant, the length of the connection means 4 can be modified so as to keep them in a non-zero voltage range but less than a threshold value, making it possible to avoid any risk of deterioration of these connection means, or of excessive reduction soil reactions R1, R2.

According to another embodiment, the effect of the tides is at least partially offset by ballasting the barge, so as to attenuate or even reduce zero the elastic deformation of the connecting means induced by these tides for an unballasted barge.

The effect of the current is compensated by the return force of the connecting means 4.

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The weight of the weights 3 is determined in particular so as to avoid a drift of the barge under the effect of the currents encountered in the area of the site under consideration.

We now refer to Figures 2 and 3. 0

The bridge 7 of the barge 1 comprises four stretched feet 8 formed by connecting means 4 between the ballasts 3 and the bridge 7.

The bridge 7 has an upper work surface 6 on which work machines can be placed.

In the embodiment shown: a Manitowoc 888 Ringer type hoist with a capacity of 180 T at 40 m and 75 m of boom is mounted on barge 1; 0 - the weights 3 are placed on the ground 2 at 65 m below the water level 5; the width of the barge, measured in the horizontal direction D1 in FIG. 2, is of the order of 40 m; the length of the barge 1, measured in the horizontal direction D2 in FIG. 3, is of the order of 55 m; 5 - each ballast 3 has a submerged weight of 750 T; the connecting means 4 are chains of 168 mm, with a breaking load of the order of 2360 T; the distance, measured along direction D1, between the two front chains is substantially equal to the distance measured along this direction D1, between 0 the two rear chains and is of the order of 27 m; similarly, the distance measured in direction D2 between the two right side chains is substantially equal to the distance measured in this direction D2 between the two left side chains and is of the order of 35 m. The lifting device represented in FIGS. 2 and 3 is used for placing inclusions 9 using a threshing hammer, a storage area for these inclusions being visible in FIG. 3, at the rear. of the arrow of the craft.

These inclusions can be, for example, metal tubes two meters in diameter and 25 to 30 meters in length, to be placed in the ground under the foundation of the piles.

It is understood that the dimensions and type of work machine mentioned above are given only by way of example of embodiment.

Other work equipment, such as dredging, backfilling, pile driving can be considered.

For example, the barge can be used for the installation of a ballast mat on a surface of the order of 120 m in diameter, leveled to the nearest 5 centimeters to a depth of the order of 65 m

Barge 1 can have three, four or more than four weights.

When the barge has more than four weights, some of these weights may not rest on the ground 2 when the barge is in use on site when the dimensioning of the weights 3 placed on the ground, carried out in the general manner described above, ensures stability sufficient for the barge.

The stretched legs 8 are advantageously made using chains or stranded steel cables.

Other materials can be envisaged by those skilled in the art, taking into account the efforts to be accommodated.

The weights 3 can be made of concrete, for example heavy concrete or concrete based on quality cement taken from the sea to avoid degradation by sulfates contained in sea water, the masses preferably having rounded angles.

In a particular mode of implementation, the weights comprise at least one compartment allowing, by the water inlet or outlet, to vary their weight.

We now refer to Figures 4 and 5.

In Figure 4 is shown a detail view of a self-elevating platform leg.

The leg 10 is keyed, in a manner known per se, by a movable keying block 11 connected to a fixed keying block 12 by jacks 13.

In FIG. 5 is shown a chain lifting device obtained by reversible modification of the structure shown in FIG. 4.

The chain lifting system, said stretched legs, is locked on a movable false leg 14 provided with a chain blocker 15, a fixed false leg 16, placed in alignment with and below the movable false leg 14 also being fitted with a chain blocker 17, lower.

The main traction on the chain 8 is exerted in the vertical direction parallel to the direction of the false legs 14,16 by the action of the jacks 13 on the false leg 14 and the chain blocker 15.

Direction F is the winding direction of the excess chain after deflection on the drum 18.

During this pulling, the upper chain blocker 15 of the mobile false leg 14 is locked, the lower chain blocker 17 of the fixed false leg 16 being unlocked, the false mobile leg being raised using the jacks 13. The mode of operation of the lifting system, for barge 1, is therefore such that the general structure of the lifting system of the legs of a self-lifting platform can be reversibly changed, so as to allow the transformation of this platform in towable barge with straight legs.

A chain guiding device 19 and chain storage equipment, not shown, complete the lifting system.

We will now describe the method of placing and moving the barge from one site to another.

The weights 3 being above the ground 2 such as a seabed for example, the barge is towed by any suitable means to the right of a first site.

During this towing, the internal compartments, if any, of the barge are preferably deballasted so as to give the barge a buoyancy suitable for its towing.

When the barge is substantially at the right of the first site, the driving means are actuated so as to allow the ballasts 3 to descend to the bottom 2.

As was said above, when the weights rest on the ground 2, a certain level of tension is maintained in the connecting means such as chains

If necessary, the weights can have a support face on the ground provided with projections or a coating increasing the friction of the weights on the ground and facilitating the maintenance in position of the barge against winds and currents.

Where appropriate, at least partial deballasting of the internal compartments of the barge is carried out so as to increase the average tension of the connecting means. By the design of the weights presented above, the barge can be maintained at a substantially constant level under predetermined conditions of use, the design of the weights taking into account for example the tidal range, the swell or the load variations linked to the displacement of the machines they support, for the site under consideration.

The possibility of transforming a self-elevating platform into a barge with straight legs as presented above is advantageous in more than one way: the self-elevating platforms conventionally used in maritime works are not designed for construction sites nautical to depths of a few tens of meters; the use of an elevating platform out of water leads, in the case where the ground is at low lift to the realization of wide skids which, moreover, must be articulated when the ground is in steep slope. In such types of work sites, the use of lifting platforms out of water becomes very complex and expensive, the weight exerted by the legs of the platforms also risks causing a landslide.

Claims

1. Barge for nautical works comprising a bridge (7) capable of receiving work execution machines such as a crane, this barge (1) comprising ballast weights (3), connecting means (4) connecting the bridge (7 ) at each ballast (3), at least three of the said ballasts (3) being placed on the ground (2) when the barge (1) is in active state, characterized in that in combination, • when the barge is in active state: the weights (3) are not rigidly fixed on the ground (2); the connecting means (4) are kept under tension; the barge (1) is kept in a substantially constant position relative to the ground (2), the effects of swell, waves, load movements on the barge (1) and the effects of current being absorbed by the connecting means ( 4);

• the barge (1) can pass from an active state to an inactive state in which it is free to move, the weights (3) then being suspended above the ground (2).

• the barge further comprising internal ballasts, capable of compensating for the effect of the tides when the barge (1) is in active state, these tides therefore not causing any variation in voltage of the connecting means (4).

2. Barge according to claim 1, characterized in that the weight in the water of the ballasts (3) is determined by the following condition: Plest> = ΣTmin + Psmin + ΔPA

• minTmin being the sum of the minimum voltages of the connecting means (4), voltages measured at the bottom;

• Psmin being the minimum total weight to be transferred to the ground to compensate for the lateral thrusts exerted on the barge, for example under the effect of currents or wind, and to also compensate for any variations in slope of the ground (2);

3. Barge according to any one of claims 1 or 2, characterized in that the connecting means (4) between the weights (3) and the bridge (7) are chosen from the group comprising chains, braided cables, twisted cables made of steel or any other equivalent material.

4. Barge according to any one of the preceding claims, characterized in that at least one of the weights (3) comprises at least one compartment allowing, by the inlet or outlet of water, to vary its weight.

5. Barge according to any one of the preceding claims, characterized in that the lifting system of the connecting means is locked on a movable false leg (14) provided with a blocker (15), a fixed false leg (16) placed in alignment with and below the movable false leg (14) being also provided with a blocker (17).

6. Barge according to claim 5, characterized in that the lifting means of the connecting means (4) are at least partly similar to those used for lifting the legs of a self-elevating platform.

7. Application of a barge according to any one of claims 1 to 6, for carrying out nautical works such as dredging of foundations, installation of inclusions (9), embankment, pile driving, installation of ballast mat, for depths of a few tens of meters.