SYSTEM FOR EXCAVATING A TRENCH IN SUBMERGED GROUND AND ASSOCIATED EXCAVATION METHOD

Abstract

A system for excavating a trench in ground submerged in water is described. The system includes an excavation device comprising moving means capable of moving the excavation device on the submerged ground and excavation means capable of being supplied with pressurized water and excavating the submerged ground using the pressurized water, The system also includes control means configured to control the moving means and supply means configured to supply pressurized water to the excavation means, where the supply means can include at least one water-jet turbine.

Description

TECHNICAL FIELD

The present invention relates to the general field of burial and in particular concerns a system for excavating a trench in ground submerged in water, for example a sea floor.

The invention particularly, but not exclusively, applies to the excavation of a trench in ground submerged in shallow waters, typically a sea floor located less than fifty metres from the surface of the water (for example in the area around a shore line).

PRIOR ART

In known manner, the burying of an undersea pipeline is obtained by means of a system particularly comprising an excavation device capable of excavating trenches in the sea floor.

More specifically, said excavation device is able to travel over the sea floor whilst excavating the sea floor using pressurized water to excavate a trench.

The excavation device is supplied with pressurized water by a pump positioned on the deck of a ship, a feedline connecting the excavation device to the pump.

However, said system is little adapted to the burying of a pipeline in shallow waters. Having regard to the size thereof, a ship on which the pump is positioned is unable to navigate in shallow waters and must remain offshore. In this case, a long feedline must be used, which implies loss of excavating efficiency.

There is therefore a need for a solution allowing a trench to be efficiently excavated on a sea floor in shallow waters.

DESCRIPTION OF THE INVENTION

The present invention concerns a system for excavating a trench in ground submerged in water, said system comprising an excavation device comprising:

• • locomotion means able to move said excavation device over the submerged ground,
  • excavating means able to be supplied with pressurized water and to excavate the submerged ground using the pressurized water,said system further comprising control means configured to control the locomotion means, and supply means configured to supply pressurized water to the excavating means,characterised in that the supply means comprise at least one turbine of water-jet type, said at least one turbine of water-jet type being positioned on floating means adapted to position a water intake of said at least one turbine of water-jet type immersed in the water.

The high power of the turbine of water-jet type enables the excavation device to perform efficient excavation of the submerged ground. In addition, the dimensions of the turbine of water-jet type allow use thereof in shallow waters.

The turbine of water-jet type can therefore be positioned close to the excavation device, even in shallow waters, which allows better transmittal of the power of the turbine of water-jet type.

In one particular embodiment, the excavation device comprises at least one watercraft comprising said at least one turbine of water-jet type and the floating means.

The watercraft is common equipment, light (about 300 kilograms), manoeuvrable and easily transported. In addition, the watercraft allows positioning of the turbine of water-jet type close to the excavation device even in shallow waters, thereby allowing better transmittal of the power of the turbine of water-jet type.

In one particular embodiment, the excavation system further comprises detection means, able to detect a pipeline positioned on the submerged ground, the control means being able to control the locomotion means so that the submerged ground can be excavated underneath the pipeline.

In one particular embodiment, the excavation system further comprises:

• • first acquisition means able to obtain the position of the excavation device,
  • second acquisition means able to obtain the depth of the water at said position of the excavation device, via the transmission and reception of acoustic waves,the control means being able to control the locomotion means as a function of the obtained position and/or obtained depth.

Measurement of depth by acoustic waves, permitted by the shallow depth of the water, enables the control means to exert efficient control over the locomotion means of the excavation device.

In one particular embodiment:

• • the control means are positioned on a vessel,
  • the second acquisition means are positioned on the surface of the water at the position of the excavation device,the second acquisition means being able to transmit the obtained depth to the control means via radio waves.

In one particular embodiment, the excavation device is a trencher.

In one particular embodiment, the excavation system comprises first connection means able to connect the excavation means to the turbine of water-jet type, in the form of piping having a length of less than thirty metres.

The short length of the piping allows limited power losses between the turbine and the excavating means.

The invention further concerns a method for excavating a trench in ground submerged in water, comprising the following steps:

• • controlling, by control means, the locomotion means of an excavation device, to move said excavation device over the submerged ground,
  • supplying pressurized water, by supply means, to the excavating means of said excavation device, the submerged ground being excavated by the excavating means using the pressurized water, the supply means comprising at least one turbine of water-jet type, said at least one turbine of waterjet type being positioned on floating means adapted to position a water intake of said at least one turbine of water-jet type immersed in the water.

The advantages set forth for the excavation system such as previously described can be directly transposed to the excavating method.

In one particular embodiment, the method further comprises the following step:

• • detecting a pipeline positioned on the submerged ground,the locomotion means being controlled so that the excavating means excavate the submerged ground underneath the pipeline.

In one particular embodiment, the method further comprises the following steps:

• • obtaining the position of the excavation device,
  • obtaining the depth of the water at said position of the excavation device, via transmission and receiving of acoustic waves,the controlling of the locomotion means being performed as a function of the obtained position and/or obtained depth.

In one particular embodiment,

• • the control means are positioned on a vessel,
  • depth obtention is obtained by acquisition means called second acquisition means positioned on the surface of the water at the position of the excavation device,the method further comprising transmission of the depth measured by the second acquisition means to the control means via radio waves.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention will become apparent from the description given below, with reference to the appended drawings illustrating an example of embodiment thereof that is by no means limiting. In the Figures:

FIG. 1 schematically illustrates an excavation system according to one example of embodiment of the invention.

FIG. 2 schematically illustrates a turbine of water-jet type in an excavation system according to one example of embodiment of the invention.

FIG. 3 in the form of a flow chart shows the main steps of an excavation method according to one example of embodiment of the invention.

FIG. 4 schematically illustrates an excavation system according to another example of embodiment of the invention.

FIG. 5 schematically illustrates the excavation system in FIG. 4.

FIG. 6 schematically illustrates an excavation device of an excavation system according to one example of embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

The invention concerns a system for excavating a trench in ground submerged in water, for example a sea floor.

The invention particularly, but not exclusively, applies to the excavation of a trench in ground submerged in shallow waters, typically a sea floor located at less than fifty metres from the surface of the water (for example in the area around a shore line).

FIG. 1 schematically illustrates an example of embodiment of an excavation system 100 of the invention.

The excavation system 100 comprises an excavation device 110. This excavation device 100 is adapted to be immersed in water E and to be positioned against the submerged ground S.

An example of excavation device 110 is schematically illustrated in FIG. 6.

The excavation device 100 comprises locomotion means 112 able to move said excavation device 110 over the submerged ground S.

The locomotion means 112 for example comprise one or more wheels, one or more caterpillar tracks and/or one or more skids.

In addition, the excavation device 110 comprises excavating means 116 able to be supplied with pressurized water and to excavate the submerged ground S using this pressurized water.

The excavating means 116 typically comprise one or more nozzles, each nozzle being adapted to concentrate a pressurized water jet, the water jet allowing the submerged ground S to be excavated.

The excavation device 110 may also comprise detection means 114 configured to detect a pipeline C (for example a cable) positioned on the submerged ground S. For example, the detection means 114 comprise a TSS sensor (Turbidity, Suspended Solids).

The excavation device 110 is typically a trencher or a robot of sledge type.

The excavation system 100 further comprises control means 120 configured to control the locomotion means 112 of the excavation device 110.

The control means 120 may comprise a control station 1112 which can be positioned on a vessel B. The vessel B is positioned in deep water i.e. typically at a distance of more than 50 metres or 100 metres from the shore R.

In addition, the control means 120 typically comprise a motor 124, the motor possibly being positioned on the shore R (see FIGS. 4 and 5) typically when the excavation device 110 is a robot of sledge type, or on the vessel B, or on the excavation device 110 (typically when the excavation device 110 is a trencher).

According to other embodiments, the control means 120 can be housed in a control station positioned on land, for example on a beach.

In addition, the excavation system 100 comprises supply means 130 configured to supply the excavating means 116 with pressurized water.

The supply means 130 comprise at least one turbine 140 of water-jet type. It is considered in the remainder of the description that the supply means 130 comprise a turbine 140 of water-jet type. However, the supply means 130 could comprise one or more additional turbines 140 of water-jet type, the turbines 140 of water-jet type of the supply means 130 being coupled together by duct connecting means.

As shown in FIG. 2, the turbine 140 of water-jet type typically comprises a duct 141 in which there is positioned a propeller 142 linked to a motor 143 by a transmission shaft 144. The duct 141 comprises a water inlet 145 and leads into a nozzle 146. The nozzle 146 comprises a water outlet 147, the diameter of the water outlet 147 being smaller than the diameter of that part of the nozzle 146 connected to the duct 141.

In addition, the supply means 130 comprise floating means 132 on which there is positioned the turbine 140 of water-jet type. The floating means 132 are adapted to position and to hold in place the water intake 145 of the turbine 140 immersed in the water. When the turbine is in operation, the water intake 145 is typically positioned at a distance from the water surface by a minimum distance of about 20 cm. It is therefore possible to position the turbine 140 close to the excavation device even in shallow waters, the minimum depth of water required for operating of the turbine being about 20 cm. Evidently, as a function of the turbine used, the minimum water depth may vary.

In one embodiment, the excavation system 100 comprises a watercraft 150 known as a «Jet Ski» (registered trademark). The watercraft 150 then comprises the supply means 130 and hence the turbine 140 of water-jet type and the floating means 132, the hull of the water craft 150 forming the floating means 132.

The excavation system 100 may additionally comprise first connecting means 160 able to connect the excavating means 116 of the excavation device 110 to the turbine 140 of water-jet type.

The first connecting means 160 can be in the form of a line such as a flexible hose for example. A first end of the line 160 is connected to the water outlet 147 of the turbine 140 and a second end is connected to a water intake of the excavating means 116.

The length of the line is typically less than thirty metres and for example is 20 metres. This short length of line allows limiting of power losses between the turbine 140 and the excavating means 116.

The excavation system 110 may also comprise second connecting means 170 able electrically to connect the control means 120 to the excavation device 110. The second connecting means 170 are typically in the form of a cable comprising one or more electrical wires and/or optical fibres and called an «umbilical cord».

The excavation system may comprise first acquisition means 180 able to obtain the position of the excavation device 110 and/or second acquisition means 190 able to obtain the depth of the water at the position of the excavation device 110.

The first acquisition means 180 are typically attached to the excavation device 110 and can be a camera for example.

The second acquisition means 190 are a transmitter-receiver for example of acoustic waves, adapted to be positioned on the surface of the water above the excavation device 110.

The first acquisition means 180 and/or the second acquisition means 190 are configured respectively to transmit the position obtained and/or the depth obtained to the control means 120, the control means 120 then being able to determine the progress of the excavation device 110. The control means 120 are configured to control the locomotion means 112 of the excavation device 110 as a function of the position and/or depth obtained, and as a function of the position of the detected pipeline. The instructions transmitted to the locomotion means 112 are determined from this information, in particular because the response of the excavation device 110 to received instructions differs according to whether it is fully submerged or whether it is starting to emerge from the water and to climb on shore.

The first acquisition means 180 are typically configured to transmit the position obtained to the control means 120 via a wire connection, for example via an optical fibre of the second connecting means 170.

The second acquisition means 190 are typically configured to transmit the obtained depth to the control means 120 via radio waves.

FIG. 3 illustrates a method for excavating a trench in ground S submerged in water such as a sea floor. This method is implemented by an excavation system conforming to an example of embodiment of the invention such as the excavation system 100 in FIG. 1.

The excavation method is typically carried out after the implementation of a method for laying a pipeline C on the submerged ground S, the pipeline C being adapted to be buried in the ground S (embedded).

At a step E300, the excavation device 110 is immersed in water E to be positioned against the submerged ground S.

At a step E310, the detection means 114 of the excavation device 110 detect the pipeline C that has previously been laid on the ground S. The detection means 114 can then transmit one or more data items on the positioning of the pipeline C to the control means 120, typically via the second connecting means 170.

In addition, at a step E320, the first acquisition means 180 obtain the position PO of the excavation device 110. The obtained position is then typically transmitted to the control means 120 via the second connecting means 170, for example via an optical fibre of the second connecting means 170.

At a step E330, the second acquisition means 190 obtain the depth PR of the water E, at the position PO of the excavation device 110, typically the position PO obtained at step E320.

Acquisition of the depth PR is obtained for example by a transmitter-receiver 190 of acoustic waves positioned on the surface of the water E above the excavation device 110. The transmitter-receiver 190 transmits an acoustic wave and receives the acoustic wave reflected by the ground S, the time elapsed between transmission of the acoustic wave and reception of the reflected acoustic wave allowing calculation of the depth PR of the water E.

The depth obtained PR is then transmitted to the control means 120, typically via radio waves.

At a step E340, the control means 120 send instructions to the locomotion means 112 of the excavation device 110, to move the excavation device 110 over the ground S, typically as a function of the positioning datum or data on the cable or pipeline transmitted at step E310, of the position of the excavation device 110 transmitted at step E320 and/or of the water depth transmitted at step E330.

The locomotion means 112 then move the excavation device 110 typically along the detected pipeline.

At a step E350, implemented concomitantly with step E340, the supply means 130 supply pressurized water to the excavating means 116 of the excavation device 110. The ground S is then excavated by the excavating means 116 using the pressurized water.

More specifically, the motor 143 of the turbine 140 of water-jet type is set in operation and drives the propeller 142 in rotation via the transmission shaft 144. Rotation of the propeller causes suction of water E via the water intake 145 and the water is propelled towards the nozzle 146. The configuration of the nozzle 146 (i.e. the diameter of the water outlet 147 that is smaller than the diameter of that part of the nozzle 146 connected to the duct 141) accelerates the velocity of the water E circulating in the nozzle 146 (application of Bernoulli's principle).

The water E exits via the water outlet 147 and circulates through the first connecting means 160 to arrive at the water intake of the excavating means 116, the excavating means using this water E to excavate the ground S.

The power of the turbine 140 is typically 310 hp (horsepower) i.e. about 228 kW, a power of 620 hp (and hence about 456 kW) possibly being obtained in the event that two turbines 140 are coupled together. The excavation depth is typically two metres from the surface of the ground S.

The travel of the excavation device 110 concomitantly with excavation of the ground S allows the excavation of a trench typically along the detected pipeline C and underneath the detected pipeline C, the ground S possibly also being excavated around the pipeline C so that the pipeline C is able to be lower itself into the trench without causing friction on the sides of the trench.

Claims

1. A system for excavating a trench in ground submerged in water, said system comprising: an excavation device comprising: locomotion means able to move said excavation device over the submerged ground, andexcavating means able to be supplied with pressurized water and to excavate the submerged ground using the pressurized water,control means configured to control the locomotion means, andsupply means configured to supply pressurized water to the excavating means, wherein the supply means comprise at least one water-jet turbine, said at least one water-jet turbine being positioned on floating means adapted to position a water intake of said at least one water-jet turbine immersed in the water.

2. The system of claim 1, further comprising at least one watercraft comprising said at least one water-jet turbine and the floating means.

3. The system of claim 1, further comprising detecting means able to detect a pipeline positioned on the submerged ground, wherein the control means are able to control the locomotion means to obtain excavation of a portion of the submerged ground underneath the pipeline.

4. The system of claim 1, further comprising: first acquisition means able to obtain a position of the excavation device, andsecond acquisition means able to obtain a depth of the water at said position of the excavation device, via transmission and reception of acoustic waves, wherein the control means are able to control the locomotion means as a function of the position obtained and/or the depth obtained.

5. The system of claim 4, wherein: the control means are positioned on a vessel,the second acquisition means are positioned on a surface of the water at the position of the excavation device, wherein the second acquisition means are able to transmit the depth obtained to the control means via radio waves.

6. The system of claim 1, wherein the excavation device is a trencher.

7. The system of claim 1, further comprising first connecting means able to connect the excavating means to the at least one water-jet turbine, in the form of a line having a length shorter than thirty meters.

8. A method for excavating a trench in ground submerged in water, the method comprising: controlling, by control means, locomotion means of an excavation device, to move said excavation device over the submerged ground, andsupplying pressurized water, by supply means, to the excavating means of said excavation device, the submerged ground being excavated by the excavating means using the pressurized water, the supply means comprising at least one water-jet turbine, said at least one water-jet turbine being positioned on floating means adapted to position a water intake of said at least one water-jet turbine immersed in the water.

9. The method of claim 8, further comprising detecting a pipeline positioned on the submerged ground, the locomotion means being controlled so that the excavating means excavate a portion of the submerged ground underneath the pipeline.

10. The method of claim 8, further comprising: obtaining a position of the excavation device, andobtaining a depth of the water at said position of the excavation device, by transmitting and receiving acoustic waves, wherein the controlling of the locomotion means is performed as a function of the position obtained and/or the depth obtained.

11. The method of claim 8, wherein: the control means are positioned on a vessel, andacquisition of the depth is obtained by second acquisition means, positioned on a surface of the water at the position of the excavation device,the method further comprising transmission of the depth measured by the second acquisition means to the control means via radio waves.