FR2486562A1 - FOUNDATION DEVICE FOR STRUCTURE, SUCH AS A PLATFORM, INCLUDING SELF-LIFTING, BASED ON A SUB-MARINE BASE, AND PLATFORMS OF THIS TYPE - Google Patents

Abstract

THE INVENTION CONCERNS A FOUNDATION DEVICE FOR A STRUCTURE INTENDED TO BE BASED ON AN UNDERWATER BOTTOM, SUCH AS A PLATFORM, IN PARTICULAR OF A SELF-ELEVING TYPE. THE FOUNDATION DEVICE INCLUDES AT LEAST ONE BOX 3 WITH OPEN BOTTOM, WITH SIDE WALLS 5 SENSITIVELY VERTICAL, AND WHOSE UPPER FACE SHOWS AT LEAST ONE PASSAGE ORIFICE 3, FOR THE WATER THAT IS DISCHARGED FROM BOX 3 WHEN THE LATTER IS ' PRESSED THROUGH ITS SIDE WALLS 5 INTO THE SEA BOTTOM, OR FOR THE WATER THAT IS INJECTED INTO BOX 3 TO RELEASE THIS FROM THE SEA BOTTOM. APPLICATION TO STABILIZATION ON AN UNDERWATER BOTTOM OF STRUCTURE, ESPECIALLY OF DRILLING AND EXPLOITATION PLATFORM.

Description

The subject of the present invention is a device

  foundation for the equipment of a structure des-

  designed to rest on an underwater floor, such as a platform, in particular a self-elevating platform, and also for platforms equipped with such a device

foundation.

  Structures, such as platforms each resting on an underwater floor via at least one pile integral with a foundation device, have been used for many years, in particular for research, drilling and on offshore oil fields, commonly referred to as

English "off-shore".

  In addition, some of these platforms have been

  designed to be able to move according to the locality

  geographical location of the work to be done. Thus, since about 1953, so-called "self-elevating" platforms have been used, consisting of a resting barge, during operation, on the selected submarine bottom, through piles. equipped at their lower end with a foundation device, the cells being mounted movably

  in the vertical direction on the barge, so that this

  can transport them, in raised position relative to the barge, to the chosen site, where the piles are

  descended to provide support on the underwater ground.

  The stability of platforms based on submarine bottoms depends on the adaptation of the

  foundation of their pile (s) to the nature and characteristics

  mechanical ticks of the sea floor. Different types of dis-

  positive foundations are currently used. Some

  platforms rest on piles terminated by

  substantially cylindrical, or caissons, whose face

  inferior is conical, these devices being habitually

  referred to as "spud cans". Another type of foundation device consists of a single sole, of dimensions comparable to those of the platform, which is then usually qualified by

  the English terms of "mat-supported".

  Depending on the bearing capacity of the soil, that is to say the seabed, these foundation devices either rest on the bottom or are sunk into the seabed.

  In the first case,

  currently used do not pose a problem.

  In the second case the use of devices

  known poses many unsolved problems.

  In particular, it is then necessary to move significant amounts of materials from the sea floor, and the depression of the device of

  foundation is a phenomenon that can be

  completely or completely, in a brutal manner, capable of

  to question the stability of the whole structure.

  Moreover, taking into account, on the one hand, the rules and

  safety standards and the risk of apprehending

  the very dynamic dynamic load structure

  than static forces (the weight of the structure

  ture), because of natural phenomena such as waves, laterally soliciting the piles and, consequently, their foundation devices, one is forced to apply on the structure vertical forces at least 3D equal to the maximum foreseeable forces, what is done

  by a battery charge operator, commonly referred to

  English terms of "pre loading", by ballasting in particular, which presents risks, causes a loss of time, and makes more expensive the installation of the

platform.

  Finally, and more particularly for self-elevating platforms, which, as already stated, are

  moved according to the work to be done.

  killing, one of the most delicate moments in the use of the platforms resting on the sea bottom, is when it comes to clearing the foundation device of the seabed. Indeed, after penetration of the foundation device inside the seabed, the latter "heals" above the bases or boxes that constitutes it, and it is then very difficult to bring out. In the case of a platform resting on the sea bed via several piles, such a release of the foundation device at the level of certain piles can be attempted by taking advantage of

  other batteries, which is to apply to these

  very important efforts, with the risk of concentrating

  on a small number of batteries

  of them, because of the displacement of the center of gravity.

  This results in the risk of breakage of batteries that are too

  tees and overturning the platform. Another solution

  tion, which can be used in particular in the case of

  on the bottom by means of a single battery,

  is to release the training device by chasing the

  materials (earth or sand), covering and solidari-

  underwater underwater application of water jets

  under pressure Along the walls of the bases or caissons.

  The implementation of this process, known by the term "jetting", is long and expensive, and often proves to be insufficient, because the foundation devices sometimes sink several meters when the seabed is underwater. soft. This operation is not free of dangers, since it is during this operational phase

  that self-elevating platforms were damaged.

  Whatever the process used, the release

  Such platforms of the underwater bed on which they lie can only be realized if we develop tearing efforts which can be very important, which leads to extra operating costs, and makes

  significant risks to the structure and personnel

  identified. By the present invention, it is proposed to overcome these disadvantages, by means of a foundation device, for a structure intended to rest on a seabed, which is characterized in that it comprises at least one bottom box. open, with substantially vertical sidewalls and the upper part of which has at least

  a passage opening, especially for water, which is chas-

  the caisson when it sinks through its side walls in the seabed, or that is injected into the box to release the latter from the seabed. Thus, the foot of each pile, or the common foot, affects the shape of a corer. This immediately results in a significant advantage. Indeed, the driving force depends only on the "pointed" surface of the vertical walls of the box

  and friction along its vertical walls,

  that the water, which has been trapped during the descent of the caisson, may escape through the orifice (s) provided for in

its upper face.

  Advantageously, a pipe provided with a valve is connected to at least one of the passage orifices. According to the invention, it is possible to provide a

  single valve on a single pipe in which

  close different branches connected to the different through holes, or a pipe and a valve for each through hole. In this way, by controlling the opening of the valve or valves, it is possible to vary the water passage section, and therefore to control

  the evacuation of the water out of the box, and it is enough

  shutting down the valve (s) to stop immediately

  the depression of the rotation device in the bottom sub-

  marine. Another advantage of the present invention is that it is possible to increase the depression of a

  foundation device in the seabed, that is,

  to exceed the depression normally obtained under the simple effect of the weight of the structure, thanks to means, connected to the passage orifices via the pipes which are connected to it, and making it possible to ensure in the caisson a depression relative to the

  hydrostatic pressure on the sea floor.

  Similarly, to promote the release of the box, and therefore of the entire foundation device, out of the seabed, the device according to the invention advantageously comprises means, also connected to the through openings via the pipelines that connect to it, and to ensure in the box

  a relative overpressure with respect to the hydrostatic pressure

  tick on the seabed. The foundation device is thus released from the sea floor by reaction on the latter. To fix ideas, the load that is applied to the batteries may be 100 tons for example, but the surface of the set of feet may itself be of the order of 100 m, so that overpressure or Relatively low relative pressures make it possible to obtain

  significant maneuvering efforts.

  The invention also relates to platforms for resting on an underwater seabed

  through at least one battery integral with a disc

  positive foundation of the invention. According to a first embodiment, a platform according to the invention is

  such that all of its batteries are in solidarity with a

  positive foundation with a single compartment

  open-bottomed, with each compartment having a passage opening to which a pipe

equipped with a valve.

  According to a second exemplary embodiment, a platform according to the invention is such that each pile corresponds to an open bottom box of a foundation device, the pile of which is integral, each box having a through hole on which connect a

pipe with a valve.

  According to the invention, the self-raising type platforms, that is to say the stacks of which are designed to support a barge on which they are movably mounted in the vertical direction, are characterized in that the valves are mounted on the barge. Furthermore,

  these valves are preferably connected to a pump group.

  page, also mounted on the barge, and acting as a means ensuring a depression or an overpressure in the or

the caissons.

  Other features and benefits

  of the invention will become apparent during the description, which

  will follow, embodiments of the invention with regard to the figures which represent:

Figure 1 a self-supporting platform

  lift mounted on a single box.

Figure 2 a self-supporting platform

  lift on which each battery is supported by

an independent open box.

  FIG. 3 a platform mounted on a single caisson, and whose passage orifices

  are connected to a system of pipes and valves.

  Figure 4 a platform of the same

  type as that of Figure 3, but with an independent box

by stack.

  And figure 5 a top view of a

  box to support all the batteries of a platform

shape, and of partitioned type.

  In the figures, only two stacks per platform have been shown, but this can not constitute

line any limitation.

  In FIG. 1, it can be seen that the barge 1 of the self-elevating platform is supported by lattice piles 2, which rest on a single caisson 3, open at its lower part, and which has on its upper face a a set of passage orifices 3 ', onto which are connected pipes 7 provided with valves 4, advantageously controlled from the

barge 1.

  The barge 1 itself carries means 6 for drilling or production. When box 3 arrives on

  surface A, of the sea floor, the sidewalls

  5 of the box 3 penetrate into the latter, and the initially trapped water escapes through the passage openings 3 'and the pipes 7, as long as they remain open. As soon as the valves 4 are closed, the water which is possibly still trapped in the box 3, remains locked inside the latter, and a downward movement thereof is immediately stopped. It should be noted that the lift of the foundation is at this moment equal to

  that of a sole of the same section, based on the lower

  reached by box 3, and takes a high value

  greater than the effort required to sink the box in the case where the valves 4 are open. The quantity of

  displaced material, corresponding to the volume of the vertical walls

  wedges of the caisson, is therefore weak, and the depression of the

  sound does not cause any material movement on a large

  ladder under the foundation. This is a welcome advantage

  table in relation to the case of caissons or solid soles,

  which can only penetrate the soil by breaking and

  placement thereof, which leads to a weakening of the mechanical strength of the sea floor, which can be

reveal detrimental.

  When the depression of the caisson 3 is completed, the lift presented is much greater than the static load, so that the dynamic overloads can be

  supported with adequate security factors.

  FIG. 1 therefore represents either the caisson at the neck: s of its depression in the seabed, or at the end of depression in an intermediate position, the valves 4 being closed while the caisson is not

completely embedded in the ground.

  In FIG. 2, each of the stacks 2 of the platform is mounted on an individual box 3, the upper face of which has two through-holes 3 ', without

  that it is planned of channeling or valve.

  In FIG. 3, the batteries 2 are again mounted on a single box 3, but valves 4 are arranged on the bar 1, and each connected with a

  part of several through-holes 3 'of the upper surface

  top of the caisson 3, through the pipes 7 and

  on the other hand, to a pumping group 12, which allows

  to draw a depression inside the box 3, to promote the depression thereof, or to produce an overpressure in the box 3 to allow its release

from the sea bottom.

In FIG. 4, each stack 2 is

  supported by an individual box 3, whose upper face

  rieure is placed in communication, by the pipes 7 and 8, each connected to a passage opening 3 ', with the valves 4 carried by the barge 1. Of course, these valves 4 are preferably connected, as previously,

  to a pumping group (not shown).

  FIG. 5 shows, in plan view, a box according to the invention, of circular and compartmentalized shape. This box is divided into sectors by solid edges 9 and 10, said sectors being themselves

  divided substantially into two parts by a ring 11.

  This division is carried out for reasons of resistance

  obvious mechanical properties. Each of the compartments thus formed is provided as explained above, with a passage opening on which is connected a pipe provided with

  a valve, preferably controlled from the barge 1.

  This allows, by an appropriate control of the valves, to ensure

a uniform depression of the box.

  It goes without saying that changes may

  The above-described embodiments may be made, in particular by substitution of equivalent technical means, without departing from the scope of the present invention.

Claims (9)

R E V E N D I C A T IO N S   1.- foundation device for structure intended to rest on a seabed, characterized in that it comprises at least one box 3 open bottom, with side walls 5 substantially vertical, and whose upper face has at least one passage orifice 3 ', especially for water, which is driven from the box 3, when the latter is sinking by its side walls 5 in the seabed A, or that is injected into the box 3, for remove the latter from the seabed A.   2.- Foundation device according to the claim   1, characterized in that a pipe 7 provided with a   valve 4 is connected to at least one of the age 3 '.   3.- Foundation device according to the   cation 2, characterized in that it comprises connected means   to the through-holes 3 'through the channeling   7 which are connected to it, and make it possible to ensure in the box 3 a relative depression with respect to the pressure   hydrostatic on the seabed A, to favor the darkness of the casing 3.   4.- Foundation device according to any one   of claims 2 and 3, characterized in that   includes means, also connected to the passenger orifices   ge 3 'through the pipes 7 which connect   tooth, and to ensure in the box 3 a surprise-   relative to the hydrostatic pressure on the submarine bottom A, to promote the release of the box 3 out of the bottom subsea A. 5.- Platform intended to rest on a sea floor via at least one stack 2 secured   of a foundation device, characterized in that this last   deny is a device according to any one of the cations 1 to 4 above.   6. Platform according to claim 5,   characterized in that the set of cells 2 is integral with a foundation device comprising a single compartment 3 compartmentalized open bottom, each compartment presents   a passage opening 3 'to which a channel 7, 8 equipped with a valve 4.   7. Platform according to claim 5, characterized in that each cell 2 corresponds to a box 3 open bottom of a foundation device, the stack 2 is secured, each box 3 having a hole of passage 3 ', on which is connected a pipe 7, 8 equipped with a valve 4.   8. Platform according to any one of the claims   6 and 7, self-elevating type, whose batteries 2 are de-   designed to support a barge 1 on which they are   moving heads in the vertical direction, characterized in that   the valves 4 are mounted on the barge 1.   9. Platform according to claim 8, characterized in that the valves 4 are connected to a pumping unit 12, also mounted on the barge 1, and acting as means ensuring a vacuum or an overpressure in the box or boxes) 3.