The invention relates to an excavation installation comprising excavation means. The excavation installation is suited to excavate a substantially horizontal sea bed or lake floor.

US 2006/0032094 describes a machine for dredging having a substantially vertical cutting front. This machine is suited for digging a trench.

WO2014153494 describes an excavation installation for deep sea mining. The installation shows multiple rows each having two rotatable mining drums. The installation can be lowered to the sea bed by means of a cable. Although the installation may be suited for deep sea mining it is not suited for dredging a defined part of the sea bed.

Excavation installations comprising excavation means are for example described in

US4084334. This document describes a dredger with a cutter head for dredging the bottom of a body of water. In order to do this, a vessel is positioned by means of anchors. A ladder is rotatably connected to the vessel, and at the end of the ladder the cutter head is positioned. This cutter head can excavate the bottom under the ship. The problem that needs to be solved according to this published document is as follows. In case of swell, the vessel moves on top of the waves. The consequence of this is that the pressure with which the cutter head is positioned onto the bottom fluctuates. Moreover, it is difficult to dredge the prescribed trail. The danger also exists that the cutter head will be damaged. This published patent tackles these drawbacks by proposing varying the length of the ladder in the longitudinal direction. By doing this, the cutter head stays resting on the bottom in a substantially constant position while the vessel moves up and down and/or back and forth.

WO2010/066757 describes a drag head of a trailing suction dredger provided with drag heads. A problem with the prior art excavation installations is that they are less suited for dredging with a controlled vertical pressure force working on the excavating means. This is especially desired when dredging relative more cohesive and harder soil types. The limiting factor of the vertical pressure is limited by the weight of the underwater dredging unit.

The following excavation installation does not present such a drawback.

Excavation installation comprising excavation means in which more than one excavation means is positioned next to another in a row of excavation means, in which multiples of such rows of excavation means are positioned behind one another, and in which the excavation means of a particular row are offset with regard to the excavation means of an adjacent row, such that in use the excavation installation may excavate a horizontal bottom of water in a direction that is perpendicular to the direction of the rows of excavation means,

in which the excavation means are connected to a rigid construction positioned vertically above the excavation means by means of a resilient connection in order to absorb the vertical impact loads on the excavation means and to transmit these impacts to the rigid construction, and

in which the rigid construction is resiliently connected to a bridge that is positioned vertically above the rigid construction, in which the bridge is connected to the rigid construction by means of linear actuators, in such a way that, during use, the linear actuators exert an adjustable and vertical pressing force onto the excavation means.

The excavation installation according to the invention enables one to control and even enhance the vertical pressure of the excavation means on the bottom of water. Furthermore, the vertical impact loads on the individual excavation means are absorbed and transferred to the rigid construction. This offers the advantage that irregularities of the bottom of water can be accounted for by this construction. This means that the different excavation means of the excavation installation can function with comparable vertical pressing force, which implies that each excavation means shall realise a comparable production. The bridge is

advantageous because it can be incorporated in a relatively fixed position from where, in use, an adjustable and vertical pressing force can be exerted onto the excavation means. A further advantage is that the excavation installation according to the invention enables one to use multiple excavation means simultaneously, which means that a larger surface of a bottom of water can be excavated simultaneously. During use, the excavation installation is moved over the bottom of water in a direction that is perpendicular to the direction of the rows of excavation means. By applying an offset to the excavation means in a particular row with regard to those of the adjacently positioned row, the bottom of water can be excavated in the most efficient way possible. Parts of the bottom of water that are situated between excavation means and that therefore cannot be excavated efficiently by the particular row of excavation means, shall then be excavated by the excavation means of the adjacently positioned row.

In this description terminology shall be used such as "horizontal", "vertical ^* ', "longitudinal", "above", and "under" for describing the invention and the preferred embodiments thereof.

One thereby presupposes the invention in its normal position under normal use, for example, during use thereof to excavate a horizontal bottom of water. By "bottom of water" one understands any surface under water that consists of a solid material. This can be a seabed or a lakebed. When using the term "longitudinal", one refers to the direction in which the rows of excavation means are moved over a bottom of water. When using the term "transversal", "transverse force", or "transverse direction", one refers to a direction that is perpendicular to the longitudinal direction, and that is situated in the horizontal plane. By using the term "submersible", one refers to the fact that a submersible construction element can be lowered to the bottom of water and can rise again to the water surface.

The excavation installation can be used to excavate part of a bottom of water, for example in order to increase the water depth and/or to extract soil or minerals.

The number of rows of excavation means can be quite large. For example, three and preferably two rows of excavation means are positioned behind one another. The rows of excavation means are positioned behind one another and are positioned in a parallel way. A row of excavation means comprises preferably at least 2, better at least 3, and preferably at least 4 excavation means. The maximum number of excavation means per row will depend on what is mechanically possible. The maximum number can for example be 50 excavation means per row, and preferably 30 excavation means per row. Examples of suitable excavation means are excavation wheels, cutters, drum cutters, trailing dragheads, cutters and/or ploughs.

The advantages of the invention are notably realised when the excavation means are rotating excavating elements, in which the excavation means comprise wheels that rotate around a substantially horizontal axis. Examples of such excavation means are excavation wheels and drum cutters. These rotating axes of the excavation means are positioned in the transverse direction. More preferably, the axes of these devices that are positioned in one row will be positioned coaxially. It is even more to be preferred that such rotating excavation means are positioned pairwise in a row. The excavation means preferably comprise wheels that rotate around a substantially horizontal axis, in which the excavation means are positioned pairwise in a row, and in which the rotating wheel of the first excavation means of a pair, during use, possesses a rotation direction that is contrary to that of the rotating wheel of the second excavation means of the pair. Preferably the wheels in a row alternate in rotation direction. The direction of the substantially horizontal axis will be the direction of the row which comprises the pairs.

The rotation direction of a wheel of the excavation means in such a pair is preferably contrary to that of the other wheel of the same pair. The excavation means of such a pair preferably comprise a combination of undercutting and overcutting excavation wheels. Such implementation offers the advantage that the relatively large bending moment per excavation wheel is compensated for at the rigid construction by the opposite moment of the other excavation wheel of the pair. Moreover, the required force for moving a row of such excavation means over the bottom of water in the longitudinal direction is relatively small in comparison with a situation in which all wheels move in the same direction.

The rows of excavation means shall be part of an excavation installation. The excavation means are connected to a rigid construction that is positioned vertically above the excavation means. The rigid construction can be a box construction and preferably a lattice construction. The excavation means are connected to this rigid construction by means of a resilient connection, in order to absorb the vertical impact loads on the individual excavation means, and to transfer this to the rigid construction. This offers the advantage that irregularities of the bottom of water can be accounted for by this construction. This means that the different excavation means of the excavation installation can function with comparable vertical pressing force, which implies that each excavation means shall realise a comparable production. The excavation means themselves can also comprise means that transfer the local irregularities of the bottom of water to individual excavation means. This excavation means can then, independently of the other excavation means, move in an upward direction. In this way a local irregularity can be avoided without the complete row of excavation means being blocked in the longitudinal movement direction. Such a compensator for bottom irregularities can preferably be added to each of the excavation means. Rotating excavation means such as excavation wheels and drum cutters are preferably equipped with a compensator for bottom irregularities, with a spherical screen that by means of bearings can be rotated around the rotation axis of the wheel of the excavation means, and is resiliently positioned relative to the rigid construction, which means that, when relatively large or extreme obstacles are encountered on the bottom, the excavation means will be lifted up. Another possibility for avoiding large and/or extreme obstacles on the bottom of water is to connect the excavation means to the rigid construction in such a way that it may pivot around an axis in the transverse direction and/or around an axis in the longitudinal direction. The pivot

connections preferably comprise torsion springs to bring the excavation means back to their initial positions. If the excavation means are positioned pairwise, as described above, it is advantageous when the pairs of excavation means are connected pairwise to a rigid construction that is positioned vertically above the excavation means and is connected to the pairs of excavation means by means of a resilient connection in order to absorb the vertical impact loads and the continuously varying and fluctuating loads on the pairs of excavation means, and to transfer these to the rigid construction.

The invention also relates to an excavation installation comprising a row of rotating excavation means that are positioned pairwise in the row, and in which the excavation means of a pair, during use, rotates in an opposite direction, as can be seen from the figures and as will be described hereafter more in detail. These rotating excavation means preferably are excavation wheels or drum cutters. The excavation means are preferably removably connected to the rigid construction. This permits one to simply replace a less well -functioning excavation means with a better functioning excavation means. It is also possible to for example replace the excavation wheels with drum cutters, or the drum cutters with excavation wheels. The excavation wheels or the drum cutters can also be replaced by a trailing draghead or vice versa.

The rotating wheels of the excavation wheels and drum cutters are preferably removably connected to the drive/drive shaft. Less well functioning wheels of the excavation wheels or drum cutters can thereby easily be replaced. The wheels can also be mutually exchanged.

Because of this construction a relatively large space is needed on both sides of the wheel for the axis and drives. Underneath this space, a row of excavation means will excavate no or less soil. However, because a row of excavation means is positioned behind or in front of this row with a certain offset, soil shall be excavated by this adjacently positioned row.

Each of the excavation means can be connected to a suction tube that discharges the mixture of soil and water that is excavated by the excavation means. For realizing a well balanced flow of soil/water mixture, preferably every suction tube per excavation means is connected to the suction side of a separate pump. In case of dredging in relatively shallow water depths the pumps are preferably fixed to the rigid construction such to limit the distance between pump and excavating means such to prevent cavitation of the pump.

At the extremities of a row or of every row preferably a freestanding excavation means is foreseen. This excavation means can for example be a wheel of drum cutters that is driven by the engine of the extreme excavation wheel and/or drum cutter of the row. The function of this excavation means is to prevent the excavation installation from seizing up in the trench that is being dug by the excavation installation itself. This excavation means is preferably devoid of hoods that are present on the other excavation means for discharging the soil/water mixture. In order to create a less inclined downward slope at both sides of the trench that is being dug by the excavation installation, it is to be preferred to also equip the excavation installation with an excavation means that is horizontally e tendable in the direction of the row. This excavation means is positioned above the row of excavation means and is preferably part of the rigid construction. The excavation means is preferably an excavation wheel or a drum cutter. If the rows of excavation means excavate the same surface of the bottom of water more than once, the rigid construction and the excavation means will move in a downward direction. By moving the horizontal excavation means at each downward movement in the direction of the rigid construction a less inclined downward slope will be created.

The aforementioned rigid construction is resiliently connected to a bridge that is positioned vertically above the rigid construction. The bridge can comprise a lattice framework. If the bridge forms part of a submersible excavation installation it preferably consists of a box construction. The box construction can for example be filled with a gas in order to be able to float or raise the excavation installation from the bottom of water. The bridge is preferably connected to the rigid construction by means of multiple linear actuators, amongst which are hydraulic cylinders, in such a way that, during use, an adjustable and vertical pressing force can be exerted onto the excavation means. The spring constant of one or more springs by which the excavation means are resiliently connected to the rigid construction is preferably smaller than the spring constant of one or more springs by which the rigid construction is connected to the bridge.

Such a bridge can be part of the floating vessel, in which the bridge is resiliently connected to the floating vessel by means of multiple linear actuators that extend in a downward direction from the floating vessel and towards the bridge. The bridge is thus substantially fixed relative to the bottom of water and the vertical pressing force that may be exerted onto the bottom of water by the excavation means will relate to the submersed weight of the vessel. The extremities of these actuators are preferably connected to the bridge and to the floating vessel by means of ball joints and springs. Preferably, the longitudinal direction of the row of excavation means is also the direction in which the floating vessel moves. Preferably, the bridge is connected by means of at least four linear actuators, the extremities of which are connected to the floating vessel and to the bridge by means of a ball joint. This connection comprises at least one spring. The connection with the floating vessel is preferably movably connected in the transverse direction in order to compensate for the rolling movement of the floating vessel. The connection, preferably a ball joint, is preferably movably connected by means of a linear actuator. This actuator can maintain the actuator that extends towards the bridge as much as possible in a vertical position. By moving the floating vessel in a direction that is perpendicular to the rows of excavation means it is possible to excavate a clearly defined part of the bottom of water.

In order to compensate all six kinematic motions of freedom of the floating vessel the bridge is connected by means of at least four linear actuators, the extremities of which are respectively connected to the floating vessel by means of three or more automatic controlled actuators and a ball joint and connected with the bridge by means of a ball joint. The three or more automatic controlled actuators are preferably controlled to keep the topside of the linear actuator, coupled with the bridge, at such a position in space that the linear actuator always remains at its vertical position.

By using the aforementioned connection to the floating vessel it becomes possible to maintain the pressing force of the excavation means on the bottom of water at a reasonably constant and high level in situations in which the vessel moves under the influence of the swell and/or in cases of a bottom of water with irregularities. By moving back and forth the floating vessel can excavate a bottom of water by means of the excavation installation according to the invention. This is particularly interesting in cases in which the vessel cannot turn around because of the limited width of the fairway. Such a floating vessel, as described above and as can be seen in the figures, can also be implemented with just one row of excavation means. For this reason the invention also relates to a floating vessel that is connected to a rigid construction by means of linear actuators, comprising a row of 3 to 30 excavation means, and in which the rigid construction is positioned underneath the floating vessel, and in which the linear actuators may be connected to the floating vessel by means of a ball joint and spring, and to the rigid construction by means of a ball joint. The rigid construction preferably comprises the aforementioned bridge and rigid construction with the row of excavation means that are connected thereto, as described in this application. Preferably the excavation means are trailing dredging heads, also referred to as dragheads or trailing dragheads. For trailing dredging heads less space will be present between the excavation means and therefore less need for an additional row of offset excavation means in order to effectively excavate a bottom of water.

The aforementioned linear actuators can be electromechanical actuators and preferably hydraulic cylinders.

The propulsion of the aforementioned vessel is realized in using thrusters fixed to the vessel. To prevent the bridge and the herewith connected excavation means to be dragged by the vessel thrusters, preferably additional thrusters are fixed to the rigid construction. These additional thrusters will push the excavation means forward in longitudinal direction in addition to the drag force exercised by the vessel. A problem that occurs when connecting the bridge to a floating vessel is that the vertical pressing force that is being exerted onto the bottom of water by the excavation means cannot be larger than the submersed weight of the vessel. Hereafter will follow the description of an embodiment that allows a larger vertical pressing force. In this embodiment the movable bridge can move horizontally and longitudinally along in the longitudinal direction positioned and parallel framework beams that, in combination with two transverse beams, compose a rectangular framework. By fixing such a frame to the bottom of water it becomes possible to exert a larger vertical pressing force onto the bottom of water than that which is possible with a floating vessel. Moreover, it is possible to work in deeper waters than with an excavation means that during the excavation is in some way connected to a floating vessel.

Such a frame comprises four corners. The term "corner" refers to any construction that is suitable for being connected to the framework beams and to the transverse beams. The construction is preferably also suitable for being equipped with supporting means and with anchoring means. The connection to the corners can for example be a box construction or a lattice construction. Box constructions are interesting because they can possibly be filled with water and gas in order to float, submerse, or raise the framework. The corners of the rectangular frame therefore preferably comprise means for anchoring the frame to the soil. These means are preferably screw anchors or suction anchors.

The corners of the rectangular frame moreover preferably comprise a supporting means. Such supporting means are preferably one or more wheels, caterpillar tracks, or a sled. The supporting means are preferably connected to the comers by means of linear actuators with an adjustable length. By means of these actuators the frame can be placed in the desired position relative to the bottom of water, for example horizontally. By using the supporting means the framework can be moved over the bottom of water while it remains in the submersed position. This is interesting in cases in which the excavation installation is done with the excavation off the surface of the bottom of water that lies under the installation. The excavation installation can then be moved in a simple way to a surface of the bottom of water that still needs excavating. For the displacement it can be interesting that the excavation installation also comprises one or more means for moving the rectangular frame horizontally. These means can preferably be so-called thrusters and/or the aforementioned caterpillar tracks and/or driven wheels. If the frame is connected to a floating vessel, it is interesting to make use of the propulsion of the floating vessel and of the means that are present on the frame for the displacement. The movable bridge is preferably connected to the two transverse beams by means of winch cables that permit a horizontal movement of the movable bridge along the two parallel framework beams. By applying tension to the winch cables it becomes possible to move the movable bridge. Once the tension is applied, the winch cables also stabilise the form of the rectangular framework. This an advantage not only when the framework is being used during the excavation of a bottom of water, but also during the vertical and horizontal transport of the framework.

Each of the extremities of the movable bridge preferably comprises a guiding tube. One of the two parallel framework beams pass through the opening of each of the tubes, in such a way that the movable bridge can move in the longitudinal direction of the framework beams. The guiding tubes preferably comprise on their inner side resilient wheel sets and/or resilient rollers that, during use, can give the framework beams six kinematic degrees of freedom relative to the guiding tube. Such an implementation is interesting for preventing the movable bridge from seizing up during the displacement along the framework beams. The guiding tubes can comprise at their lower parts supporting means to avoid deflection of the framework beams. Such supporting means are preferably one or more wheels, caterpillar tracks, or sleds.

The extremities of the framework beams and the extremities of the transverse beams are preferably resiliently and by means of a ball joint connected to a corner on each of the four corners of the framework. The result of this is that the forces on the excavation means are being transferred not only by the resilient wheel sets in the bridge part, but also by the springs between the framework beams and the transverse beams and corners. If the framework is fixed to the bottom of water by means of the aforementioned anchors a framework is created with a very stable form, maintaining the six kinematic degrees of freedom. In this anchored position the extreme loads on the excavation means and/or on the movable bridge can be absorbed or taken over by the framework. The optional supporting means are also resiliently connected to the corners to absorb impact loads when the framework lands on the bottom of water. The combination of the springs and of the ball joints in the connections with the corners and the resilient supporting means results in a framework that is capable of following a bottom of water with irregularities, when the framework is being transported over the bottom of water. Also during the horizontal transportation of the framework over the bottom of water the framework maintains six kinematic degrees of freedom, which is interesting in order to absorb the forces that are then exercised on the framework. The stable form of the framework during the horizontal transportation over the bottom of water is realised by prestressing the winch cables on both sides of the bridge and by the resilient guiding means that are part of the bridge part.

The above described excavation installation comprising the framework can be connected to a floating vessel by means of linear actuators comprising ball joints and springs that connect the corners of the framework to the floating vessel. The excavation installation comprising the framework can also be used independently, for example in shallow water. In shallow water the framework can be fixed to the bottom of water by means of screwing anchors, and can subsequently jack itself up. The transverse beams and the framework beams can in that situation be located above the water surface and the rows of excavation means can excavate the shallow bottom of water.

An excavation installation comprising the framework as described above is preferably submersible if the depth of water makes the use of a floating vessel less attractive and/or if a larger and/or constant pressing force on the excavation means is necessary. Therefore the framework beams, the transverse beams, the corners, and the movable bridge preferably comprise compartments that can be filled with gas and/or water in order to be able to float or submerse the excavation installation. During the lowering and rising of the framework, thrusters can preferably be used to maintain the framework in the desired orientation and to give it sufficient stability. An excavation installation comprising the submersible framework can be used in shallow water, at normal dredging depths, and in very deep waters. Because the framework is flexible, it can be transported very easily. Moreover, the excavation means can simply be replaced by another type of excavation means. The application of such an excavation installation has not yet been described and is a clear improvement over the existing installations.

A spare excavation means can be foreseen to replace an excavation means that no longer functions properly. Therefore, preferably on both sides of the rows of excavation means, one or more excavation means are present that can be positioned in the place of the no longer functioning excavation means. The positioning can take place by means of cables or rails.

The energy that is needed to drive the excavation means and other elements such as anchors, thrusters, and actuators can be electrical energy that is transported from the mainland or from a mother vessel on the surface of the water by means of cables. The electrical energy can also be generated on a floating vessel by means of generators. Electricity can also be generated on the spot, under water, by using a fuel cell that can for example use hydrogen or other suitable means for fuel cells. The hydrogen can be present in pressurised reservoirs. If such a pressurised reservoir has to be changed this can be simply done by lowering a reservoir from the surface of the water to the excavation installation that is resting on the bottom of the water, and by replacing the reservoirs on the spot. The energy can also be hydraulic energy. Therefore, the excavation installation preferably comprises a pressurised reservoir that can feed the necessary gas under high pressure to the systems. These reservoirs can comprise compartments with gas under pressure. By using the compartments separately, it is possible to deliver a more constant gas pressure to the different systems. Also these pressurised reservoirs can be replaced by newly pressurised reservoirs. The used reservoirs can be filled by means of compressors that are present at the water surface or can be transported over from the mainland. On the mainland the reservoirs can be filled more efficiently with pressurised gas. The pressurised reservoirs containing gas can also be used to fill the compartments in the framework beams, the transverse beams, the corners, and the movable bridge with gas, as described before. The gas is preferably air but can also be nitrogen or carbon dioxide.

The excavation installation shall now be described in further detail, referring to the attached drawings.

Figure 1 shows a side view of a possible embodiment of the excavation installation according to the invention, with two rows (34,35) of excavation wheels as excavation means (1, 2). The excavation wheels can optionally comprise teeth. The excavation means (1 , 2) are connected to a lattice construction (3) as the rigid construction by means of a resilient construction comprising columns (43) resiliently connected to rigid lattice construction (3) by means of springs (45) as can be seen in greater detail in figure 5. The lattice construction (3) is positioned vertically above the excavation means (1, 2). The excavation means (1, 2) are connected to a suction tube (4) that is used to discharge the mixture of soil and water that is being excavated by the excavation means ( 1 , 2). The lattice construction (3) is connected to a boxlike bridge (5). The boxlike bridge (5) is positioned vertically above the lattice construction (3) and connected by means of columns (6) and hydraulic cylinders (7). The hydraulic cylinders (7) and the thereto attached columns (6) permit a vertical displacement of the lattice construction (3). Therefore, the columns (6) are connected at the bottom side to the lattice construction (3), and the columns (6) are vertically displaceable relative to the boxlike bridge (5) by guiding them through openings (8) in the bridge (5). The hydraulic cylinders (7) are fixed to the bridge (5). The upper end of the column (6) is connected to the upper ends of the hydraulic cylinders (7) by means of a spring construction (10). The spring construction (10) is interesting for absorbing possible impact loads on the excavation means ( 1 , 2). This spring construction ( 10) can be seen in further detail in figure la, and comprises an upper plate (1 1 ) that is connected to the upper end of the column (6), and also comprises two springs (12) that are connected to the upper ends of hydraulic cylinders (7). The hydraulic cylinders (7) are at their lower parts connected to the boxlike bridge (5). By means of the hydraulic cylinders (7) the rows of excavation means (1, 2) and the thereto connected lattice construction (3) can be vertically moved as can be seen in figures 5a and 5b. The length of the hydraulic cylinders (7) is chosen in such a way that the desired vertical movement of the excavation means (1, 2) and the lattice construction (3) is feasible.

The construction shown in figure 1 has the advantage that lateral forces and bending moments, initiated by the forces originating from the soil on the excavation means (1 , 2), are being transferred via the lattice construction (3) and the thereto connected vertical columns

(6) to the bridge (5) that in this case has a boxlike construction. Because the bending stiffness of the columns (6) is much larger than the bending stiffness of the hydraulic cylinder rods

(7) , the lateral forces and moments shall be absorbed more or less completely by the columns (6).

Figure 2 shows the construction of figure 1 in combination with a submersible and rectangular framework (15). The framework (15) consists of two parallel framework beams (16,17) positioned in the longitudinal direction and two transverse beams (18, 19). The bridge (5) is movably connected to the framework (15) by means of a bridge part (22) comprising two guiding tubes (20, 21) as well as a partially shielded space (22a) in which the excavation means (1, 2) and the lattice construction (3) can move vertically. The bridge part (22) is connected to the two transverse beams (18, 19) by means of winch cables (23) that permit a horizontal movement of the bridge part (22) and thus of the bridge (5) along the two parallel framework beams (16, 17). The framework beams (16, 17) pass through the guiding tubes (20, 21), as can be seen in further detail in figures 7a-c. By means of four hydraulic cylinders (5b) the bridge (5) can be moved vertically upwards relative to the bridge part (22). By doing this the excavation wheels can be moved upwards, for example for carrying out maintenance work.

Figure 2 also shows that the four corners (24-27) of the framework (15) comprise screw anchors (33a) for anchoring the framework (15) to the bottom of the water. Each corner (24, 25, 26, 27) also comprises a sled (33) as supporting means, as well as thrusters (28) that can be used to help move the framework (15). The screw anchors (33a) are driven by an engine (not represented), and are connected to the framework (15) by means of a column (29). The column (29) is at its upper extremity connected to hydraulic cylinders (30) by means of a plate (31). The column (29) passes movably through an opening (32) in the corner (24). Hydraulic cylinders (30) are at their lower part connected to the corner (24).

Figure 3 shows the excavation installation of figure 2, seen from the bottom upwards. The reference numbers refer to the same parts as in figure 2. The two rows (34, 35) of excavation means (1, 2) each consist of nine drum cutters. The two rows (34, 35) are positioned adjacently. In other words the rows (34, 35) are parallel and positioned next to one another. One can see that the nine excavation wheels of a row (34) of excavation means are offset relative to the nine excavation wheels of an adjacent row (35). By doing this a continuous surface of the bottom of water will be excavated during use when the bridge (5) is moved by means of winches (23) from a position at the transverse beam (18) in the direction of the transverse beam (19) (or vice versa).

Figure 4 shows the bridge (5) of figure 1. The reference numbers refer to the same parts as in figure 1. This figure shows how the gaps between the excavation means (1) in the row (34) are filled up with the offset excavation means (2) of the adjacent row (35). A continuous row of drum cutters can be seen, formed by the row (34) and by parts of the row (35). This figure also shows how the different suction tubes (36) are integrated into the lattice construction (3) and connected to the lattice construction (3). The suction tubes (36) are resiliently connected to the individual excavation means ( 1 ). The suction tubes (36) converge in suction tubes (4) then in turn converge in a central suction tube (37a). These suction tubes (4 and/or 36) are preferably completely or partially flexible, such that, when the rows (34, 35) of excavation means (1 , 2) and the lattice construction (3) are hoisted up to the bridge (5) or are being lowered, the suction tubes (4) can be shortened or extended. This can be done by the suction tubes (4 and 36) comprising two telescopically sliding parts, in such a way that the suction tubes are in possession of an adjustable length . An alternative is to have the suction tubes comprise a flexible part, for example a part with a U-form, that can absorb the vertical displacement of the suction tube.

Figure 4 also shows a freestanding cutter wheel (34a, 35a) at both extremities of the rows (34, 35), meant to avoid the excavation installation seizing up in its own excavated trench. Moreover, there are two horizontally extendable excavation means (36a) at the top side of the lattice construction (3), which can be moved outwardly and inwardly by means of hydraulic cylinders (36b), in order to realise a plane downwardly sloping surface.

The mixture of water and solid material that is discharged via the suction tube can be transported directly to the water surface or via a tube, for example to be collected in a vessel. The mixture can also be transported to a storage tank that is positioned on the bottom of water. The thus stored mixture can then be transported from this tank or possibly in this tank to the surface. Figure 5a shows how the excavation wheel (38) is resiliently connected to the lattice construction (3) and also shows the integrated suction tube (36). Figure 5b is a cross-section along line A-A of figure 5a. As each excavation wheel (38) is resiliently connected to the complete lattice construction (3) it is possible that the excavation wheels (38) can move independently of one another in a vertical direction relative to the lattice construction (3). Figure 5b is a cross-section through the excavation wheel (38) from figure 5a. The suction tube (36) comprises a part (37) with a smaller diameter, a part that extends right up to the excavation wheel (38). The part (37) of the suction tube can move vertically in the opening of the suction tube (36). The part (37) of the suction tube passes through and is connected to a boxlike construction (39). A hood (40) enhances the flow of the soil/water mixture, limits the pressure losses, and can be controlled and turned at the required angle by means of hydraulic cylinders (41) that comprise biasing springs (42). The construction is such that the hood (40) can be turned in the direction that is opposite to the direction of movement of the row of excavation means. In other words, this is when the bridge arrives at one side of the frame and subsequently returns to the opposite transverse beam. Moreover, a plunger (47) is foreseen that is used to adjust the excavation depth of the excavation wheels (38).

On top of the boxlike construction (39) four columns (43) are foreseen per excavation wheel (38) that extend upwardly. The columns (43) pass movably through a tube like opening (44) in the lattice construction (3). Above and below the tube like opening (44) a column (43), comprising springs (45), is clamped between flanges (46). By removing the upper flanges (46) that are positioned above the lattice construction (3) and that are connected to the columns (43), the excavation wheel (38), the part (37) of the suction tube, the box like construction (39), and the columns (43) can be easily dismantled, for example to be replaced by another type of excavation means, such as the already mentioned draghead, cutter, drum cutter, or plough.

Figure 5c shows a cross-section of a possible drive of a rotating excavation wheel or drum cutter (1), in which the excavation wheel is driven by two driving shafts (139) that are suspended on both extremities by means of bearings (133) and are connected to

synchronously rotating engines (131), in which the engines (131) as well as the bearings (133) are fixed to the water permeable box like construction (39) by means of plate elements (130). The wheels (1) can be replaced in a very simple way by loosening the bolts of the fixed flanged connections (136, 135). This way, the engine and/or the bearings do not need to be replaced. A problem with this construction is that the relatively large space remains present between the excavation wheels ( 1 ). Thanks to the configuration with the offset, as can be seen in figure 6b, this problem is solved and the excavation means can be assembled in such a way as to allow it to excavate a rectangular surface of the bottom of water. The part of the bottom of water that is not excavated by row 34 shall then be excavated by row 35.

Figure 6a shows a cluster of four excavation wheels (50), in which two excavation wheels (51 , 52) are connected as a pair (50a, 50b) to a water permeable box like construction (53), whereas the two remaining excavation wheels (54, 55) are connected as a pair to a separate water permeable box like construction (56) via plates (58). For wheel (55) a motor (57) is shown. The excavation wheels are in possession of a horizontal rotating axis. The boxlike constructions (53, 56) are in turn connected to the lattice construction (3) via a resilient connection (43) in order to absorb the impact loads and the continuously varying and fluctuating loads on the pair of excavation means and to transmit these impact loads to the rigid construction (3). Such a connection is comparable to those of figures 1 -5. Per pair one of the excavation wheels is overcutting, whereas the other excavation wheel is undercutting with angular velocities ω in opposite directions but preferably with the same magnitude. With the exception of the over- and undercutting fonn of the cutting elements, the geometry and the positions of the cutting elements of the excavation wheels (51, 52, 54, 55) are preferably identical. The velocity V is the velocity with which the row of excavation wheels is moved and is directed in the same longitudinal x-direction for the whole lattice

construction and thus for all excavation wheels. The resulting tangential forces (soil reaction), respectively Ftl and Ft4, are supposed to be substantially identical with regard to magnitude and direction. In the same way the tangential forces Ft2 and Ft3 are supposed to be substantially identical with regard to magnitude and direction. All the resulting radial forces (soil reaction), respectively Frl, Fr2, Fr3, and Fr4, are supposed to be substantially identical with regard to magnitude and direction.

The resulting forces and moments that are being exerted onto the lattice construction (3) are as follows:

• the moment in the XZ-plane: Mxz = Ftl * Y0 = Ft2 * YO, in which Y0 is the distance in the Y-direction from the centrelines of the respective excavation wheels 51 , 52 (or between the excavation wheels 54 and 55)

• the resulting force in the radial direction, Fr = 2 * Frl = 2 * Fr2 = 2 * Fr3 = 2 * Fr4 • the resulting bending moment around the Y-axis: My = (Frl +Fr2+Fr3+Fr4)*Z-gv = 4*Frl*Z~gv, in which Z-gv is the distance in Z-direction from the centreline in Y-direction of the excavation wheels (51,52,54 and 55) and the centreline of the bottom part of the lattice construction (3).

The resulting forces and moments that are being exerted onto the lattice construction (3) are identical with regard to magnitude and direction, with the exception of the moment Mxz in the XZ-plane, which works in opposite directions via the boxlike constructions (53, 56).

The resulting bending moment that is exerted onto the associated boxlike constructions via the excavation wheels by the resulting soil reaction Ftl = Ft2 = Ft3 = Ft4 is reduced with regard to the order of magnitude to a value of My = Ftl * Z-gd * sin a = Ft4 * Z-gd* sin a, and the oppositely oriented bending moments -My = Ft2 * Z-gd* sin a = Ft3 * Z-gd * sin a (see figure 6). The distance Z-gd is equal to the vertical distance between the centre line of the excavation wheels (51 , 52, 54, 55) and the centre line of the boxlike constructions (53, 56). The angle a is equal to the angle between the tangential soil reaction force Ft l and the vertical.

The resulting bending moment on the lattice construction due to the tangential soil reaction forces (Ftl , Ft2, Ft3, Ft4) is negligibly small. The resulting horizontal force upon the lattice construction (3) and upon the bridge part (22) that has to be exerted onto the bridge part (22) by the winch cables (23) due to the forces on the excavation wheels is equal to Fx = 4 * Frl * sin a, which represents a relatively small value.

Figure 6b shows a pair of excavation means of row (34), as well as a pair of excavation means of row (35), seen from beneath. The reference numbers have the same meaning as in the foregoing figures. The beam (3e) is a protective construction. The figure shows how parts of the bottom of water that are situated between the excavation means of row (34), and therefore cannot be excavated efficiently by the row (34), can then be excavated by the excavation means of the adjacent row (35). Figure 7a shows a guiding tube (20) of the bridge part (22) through which the framework beam (16) passes, as can be seen in figure 2. In the figure the framework beam (16) is represented somewhat withdrawn, in such a way that the inner side of the guiding tube (20) is visible. The inner side of the guiding tube (20) comprises resilient wheel sets (60) that permit a displacement of the bridge part (22) along the framework beam (16) in the longitudinal direction. The wheel sets (60, 64) are implemented in such a way that they also, during use, permit six kinematic degrees of freedom from the guiding tube (20) in the radial, tangential, and rotational (around the vertical axis) direction relative to the framework beam (16). Such a degree of freedom for the guiding tube (20) with regard to the framework beam (16) is important and avoids clamping forces when the bridge part (22) that can be seen in figure 2 is moved along the framework beams (18, 19) by the winches (23). The framework beam (16) is composed of three parallel tubes ( 1 ) that form a triangular cross-section and a rigid entity. The outside of these combined tubes (61) comprises a flat plate (62) that comprises a rail (59) on which the wheel sets (60) can roll. The three tubes (61 ) and the flat plate (62) together form a cross-section that resembles the triangle of the framework beams (16).

Figure 7b shows a cross-section of the framework beam (16) and of the guiding tube (20), in which the interaction between the guiding tracks/rails (59) that are uniformly distributed along the circumference of the framework beam (16) and connected thereto, and the resilient wheel sets (60, 64) can be seen. The flat plates on which the point load of the guiding wheels is being exerted can be strengthened by using radial plate elements (59a) or tubes (59b) that fit in the open spaces of the circumference of the framework beam (16) and the combined tubes (61). Figure 7c shows a cross-section of the framework beam (16) and of the guiding tube (20). The resilient wheel sets are in this case resilient rollers (69a) that are resiliently suspended from a wheelset, as can be seen from figure 8c.

Figure 8a shows the wheel sets (60, 64) of figure 7 in further detail. The wheelset (60) comprises a U-form baseplate (62). The baseplate (62) is fixed by its bottom side to the inner side of the guiding tube (20), in such a way that the raised extremities of the U-form baseplate are directed towards the inner sides of the guiding tube (20). Between the raised extremities of the U-form baseplate (62) a system (63) with four wheels is resiliently clamped by means of springs (65). The system (63) with four wheels in turn forms the basis of a wheelset (64) of which the wheels (67) are perpendicular to the direction of the wheels of the system (63) with four wheels. The wheelset (64) of which a wheel (67) is part, is fixed onto the stationary axes (66) of the system (63) with four wheels, and is, thanks to the vertical springs (65a) of the wheelset (64), capable of absorbing a movement in the radial direction. The wheel (67) of the wheelset (64) makes contact with the guiding rails (59) that are fixed to the outside of the framework beam (16), as can be seen from figure 7a, and permits, during use, a passage in the X-direction. Thanks to the resilient suspension of the system with four wheels upon which the wheelset (64) is positioned, the wheelset (64) can carry out a small displacement in a substantially tangential direction (Y-direction in figure 8a) relative to the inner side of the guiding tube (20) on which the wheelset (60, 64) is mounted.

Figure 8b shows in further detail how the wheelset (64) from figure 8a can undergo an angular displacement Ψ in the radial direction, in such a way that the forces on the wheels (67) and on the guiding rails (59) of the framework beam (16) are strongly reduced. Figure 8c shows a roller (69a) that is resiliently connected to two wheel sets (60) by means of springs (65a), as discussed with regard to figure 8a.

Figure 9 schematically shows how the extremities of the framework beams (16, 17) and the extremities of the transverse beams (18, 19) are resiliently connected to a corner in each of the four corners (24,25,26,27) of the rectangular frame (15). The sleds (33) are resiliently (73) connected to the corners (24,25,26,27), in such a way that, when the rectangular frame ( 15) is anchored to the bottom of water, the rectangular frame (15) comprises a resilient geometry with six kinematic degrees of freedom. The resilient connection of the framework beams and the transverse beams with the corners is realised by means of a ball joint (70), a connector (71), and a spring (72). The ball joints (70) permit limited angular displacements (<p2, Θ2, ψ2) of the framework beams ( 16, 17) and of the transverse beams (18, 19) relative to the corners (24,25,26,27). The displacements of the corners (24,25,26,27) in the horizontal XY-plane are made possible by compressing or extending spring elements (72) and by the angular displacements of the ball joints (70). In order to permit the sleds (33) to follow the contours of the bottom of water properly, the sleds have kinematic degrees of freedom (x, y, z, φ, θ, ψ) that can be realised by means of a spring (73), a hydraulic cylinder (74), ball joints (70), and the springs (72) of the comers (24, 25, 26, 27). Because of the kinematic degrees of freedom (x, y, z, φ, θ, ψ) of the sleds (33) the sleds are capable of, in case of horizontal displacements of the framework (15), following the contours of the bottom of water properly. Moreover, the moments at the comers (24, 25, 26, 27) will be strongly reduced by the flexibility of the framework (15). The displacements (Y7, Z7) and the angular displacements (cp7, Θ7, ψ7) of the bridge part (22) are realised by the translating and rotating resilient wheel sets (60, 64) that can be seen in figure 7a~c, and a longitudinal displacement (X7) by means of the winches (23). The applicant has found that, when such a framework (15) is anchored to the bottom of water, a very rigid and form stable framework is obtained that permits an unhindered displacement of the bridge part (22) along the framework beams (16, 17).

Figure 10-13 shows a possible embodiment of a bridge (84). In order to realise a large vertical displacement of the rows of excavation means relative to the framework (15), the rows of excavation means (34, 35), the lattice construction (3), and the boxlike construction (5) are part of a telescopic construction. Figure 10 shows this construction, in which the rows (34, 35) are completely lifted by means of the winch cables (80), the hydraulic cylinders (81), the hydraulic cylinders (82), and the hydraulic cylinders (7). The winch cables (80) can move the lattice construction (3) and the therewith connected rows of excavation means (34, 35) in a vertical direction relative to a bridge part (84). The winch cables (80) also provide a rotational stability for the boxlike construction (5) around the axis that passes through the boxlike construction, from the framework beam (16) to the framework beam (17) (see figures 1 and 2).

The bridge part (84) is a modified bridge part (22) and also comprises guiding tubes (not represented) to be able to move along the framework beams. The bridge part (84) comprises hydraulic cylinders (81) that can vertically move a boxlike construction (85). The boxlike construction (85) is open at its top side and at its bottom side. The boxlike construction (5) comprises four upright walls (86) that in turn comprise resilient guiding wheels (87) for guiding the inner wall of the open boxlike construction (85). The inner walls (88) of the rectangular opening in the bridge part (84) also comprise resilient guiding wheels (89) for guiding the external wall of the open boxlike construction (85).

Figure 1 1 shows the open boxlike construction (85), which has been moved downwardly by retracting the hydraulic cylinders (81). Figure 12 shows the boxlike construction (5), which has been moved downwardly by extending the hydraulic cylinders (82).

Figure 13 shows the lattice construction (3) and the therewith connected rows (34, 35) of excavation means that have been moved downwardly by retracting the hydraulic cylinders (7). Such a bridge, as can be found in figures 10-13, can be part of a submersible framework (15) as a movable bridge part. The framework beams and the transverse beams can be filled with air in order to move the framework (15) from the bottom of water to the water surface.

Figures 14a-d show an excavation installation according to the invention in which the bridge (5) is resiliently connected to a floating vessel (90) by means of four hydraulic cylinders (91), at the top side comprising springs that extend downwardly from the floating vessel (90) to the bridge (5). Figures 14a-d show a single row (34) of excavation means. The excavation means shown in Figures 14a-b are trailing dredging head (34c). The bridge (5) can also be a telescopic bridge, as can be seen in figures 10-13. Each of the four hydraulic cylinders (91) is at the top side connected to the vessel (90) by means of a ball joint (92), and at the bottom side connected to the bridge (5) by means of a ball joint (93). A lattice framework (100) is connected to the vessel (90).

The ball joints (92) can, via the lattice framework (100) by means of a cylinder (101), move in a parallel way to the direction of the row of excavation means. Thus, the direction of the cylinder (91) relative to the bridge (5) can be kept substantially in a vertical position when the floating vessel rolls due to swell. The length of the cylinders (101 and 91 ) shall be adjusted in response to or anticipation of the movement of the floating vessel in such a way that the excavation means can be pressed onto the bottom of water with a substantially constant vertical force. The spring at the top of the cylinder (91) is preferably in possession of a smaller spring constant than that of the hydraulic cylinder. Using this construction, one obtains a complete decoupling of the movements of the floating vessel (90) from the bridge (5), but the necessary vertical pressing force on the excavation means is maintained. The other extremity of hydraulic cylinders (91) is connected to the bridge (5) by means of ball joints (93). By means of the cylinders (91) the aforementioned bridge (5), the therein integrated hydraulic cylinders (7), the columns (6), and one or two rows of excavation means (34 and/or 35) can be lifted off the bottom of water (102) or positioned on the bottom of water (102). The water surface (103) is also drawn in the figures. The bridge (5) comprises four upright walls (104) that, using multiple springs (107, 109) and roll bearings (105, 108), are enclosed along the walls in an opening (106) of the floating vessel (90). Thanks to this resilient suspension of the bridge (5) small rolling and pitching movements of the vessel (90) due to the swell can be absorbed.

Figures 14e-f show an excavation installation according to the invention in which the bridge (5) is resiliently connected to a floating vessel (90) by means of four hydraulic cylinders (91 ), from which each hydraulic cylinder (91) is connected to a horizontal plate (91b), which is connected to three hydraulic cylinders (91 a). For decoupling the motions of the vessel (90) and the bridge (5) the three cylinders (91b) at each corner of the bridge (5) are connected to both the horizontal plates (91b) and the portal of the vessel (100a) by means of ball joints (93a). The three hydraulic cylinders (91a) preferably will be in a vertical direction and will be controlled in such a way that the position of the horizontal plate (91b) in the horizontal x- y plane, within a narrow deviation, is equal to the position in the x-y plane of the bottom of the hydraulic cylinder (91 ), which is connected to the bridge (5). The hydraulic cylinders (91) are connected to the horizontal plates (91b) and the bridge (5) by means of ball joints (93b). All hydraulic cylinders (91a) and the hydraulic cylinders (91) should be able to withstand the resulting vertical force initiated by the excavating means (1,2) in rows (34,35) and the vessel (90) motions related to the bridge (5) position. The propulsion propellers (145) of the vessel (90) are synchronized with the propulsion propellers (146) connected to the lattice (3) in such a way that the velocity of the vessel (90) equals the velocity of the lattice (3). Connected to both sides of the bridge (5) are excavating means (34a, 35a), which are connected to lattices (3a) and can be displaced vertically using columns (6a) which are connected to hydraulic cylinders (7a). The function of both excavating means (34a, 35a) is to stabilize the excavated trench on both sides in transverse y-direction. Such means (34a,35a) may also be used in combination with a frame (15) as in Figure 2.

The suction of the soil/water mixture of the excavation means (1,2) in rows (34,35), especially in shallow waters, is realized using centrifugal pumps (144) which are connected to the lattice (3). Also the flow of the soil/water mixture of side excavation means (34a, 35a) is realized using centrifugal pumps (not presented in the figure), which are connected to the lattices (34a) and are connected to a vertical displaceable suction tube (4a), in a way similar to the suction tubes (4) of the excavation means (1,2). Figure 15 shows how the submersible and rectangular framework (15) of figure 2 is anchored by means of screw anchors (33a) to the bottom of water (102) and at a large depth below the water surface (103). In figure 15a one can see how the bridge part (22) is moved from right to left by means of winch cables (23). In doing this, the rows (34, 35) of excavation means create a trench (104). In figure 15b one sees the bridge part (22) in its uttermost left position after which, from a stationary position, the excavation means are given a small vertical initial movement by the force of the hydraulic cylinders on the lattice construction (3), after which the direction is reversed and the excavation means, the hydraulic cylinders, the columns, and the bridge part (22) are moved to the right by means of the winch cables (23). The next layer of the bottom of water is then excavated and a deeper trench (104) is created, as can be seen in figure 15c. The dashed lines in figure 15 indicate which compartments are filled with water, in which the fine dashed lines in the framework beam (16) indicate that air is present in the two upper tubes (61 ) and water in the bottom tube (16).

Figure 16 shows how the rectangular framework (15) from figure 2 can be connected to a floating vessel ( 1 10) by means of a framework (111) and four cylinders (112). The four cylinders are connected to the corners (24, 25, 26, 27) and to the framework (11 1) in the same way as can be seen in figure 2. In the figure the anchors and the supporting means are represented. It should be absolutely clear that these anchors and supporting means in this embodiment have no function. However, it is not impossible for the framework (15) to be alternatively used in the embodiment according to figure 16 and in the embodiment according to figure 15. By decoupling the cylinders (1 12) in the corners (24, 25, 26, 27) the framework can be easily submersed and moved away and positioned under the floating vessel (1 10).

Figure 16 also shows two floating barges (1 14) in which the excavated soil can be collected. By means of pipes and tubing (113) the excavated soil can be transported to these barges by means of pumps (not represented) in the framework (15) or fixed to the lattice construction (3).

Figure 17 shows an excavation wheel (1 ) that comprises a bottom compensator that is made up of two spherical hoods (121 ) that are pivotably connected to the rotation axis of the wheel (1). If the excavation wheel encounters an obstacle on the bottom of water, as is represented in figure 17 by means of the force Fg, the spherical configuration of the hood (121 ) shall impart an upwardly directed force onto the excavation wheel. Part of this force will be absorbed by springs (120) with which the hood at its upper end is connected to the box like construction (39).

Figure 18a shows how an excavation wheel (1 ) is connected to the lattice construction (3), rotatable around the axis in the transverse direction. For this, the lattice construction (3) comprises a rigid part (3a) and a pivotable part (3b). The pivotable part (3b) is in turn connected to the excavation wheel (38), as can also be seen in figure 5a. The rotatable axis (141) comprises rigid torsion springs (140).

Figure 18b shows how an excavation wheel (38) is connected to the lattice construction (3) by means of a cardan joint. The excavation wheel is now rotatable around an axis (141) in the transverse direction, and also rotatable around an axis (143) in the longitudinal direction, and is connected to the lattice construction (3). The axes (141, 143) comprise rigid torsion springs (respectively 140 and 142), in such a way that the pivotable parts (3b and 3c) of the lattice construction are returned to their horizontal position, for example after an impact on the excavation wheel (1).