[0001] The invention relates to a method for loading a dredging vessel with dredged material.
The invention likewise relates to a dredging vessel particularly equipped for performing
the invented method.
[0002] During dredging with a dredging vessel, such as for instance a trailing suction hopper
dredger, a mixture of dredged material and water is suctioned up in known manner via
a drag head connected to a suction conduit and moving over the water bottom, and carried
via an inlet into a hold (or hopper) of the dredging vessel until the hold is completely
filled. The maximum filling height of the hold is determined by the height position
of an overflow which is present in the hold of the dredging vessel and which forms
an open connection with the water, for instance via the underside of the dredging
vessel.
[0003] The heavier dredged material particles collected in the hold will settle after a
period of time and thus form in the hold a settled layer of more or less closely packed
coarser particles, this layer increasing in height as the dredging progresses. On
top of the settled layer forms a non-settled layer of substantially finer particles
free-floating in water. In the known method the overflow is placed in a highest position
to enable maximum possible filling of the hold and to avoid non-settled particles
re-entering the water via the overflow. This latter must be avoided because there
is the chance of the turbidity of the water then increasing too much. This has an
adverse effect on the flora and fauna at the location.
[0004] As soon as the level of the suctioned-up dredged material/water mixture reaches the
upper side of the overflow, mixture runs via the overflow back to the water. During
overflow the draught of the dredging vessel can however still increase since an increasing
number of heavier particles settle while a mixture of finer particles and water disappears
through the overflow. In the known method, as described in
US 4 245 932 A and
US 4 172 617 A for instance, the overflow remains for a while in the highest position until the
trailing suction hopper dredger has reached its maximum allowable draught (also referred
to as dredge mark). From this moment the dredge mark is kept constant by optionally
lowering the overflow. Dredging is ended at the moment there is no further net settlement
of material. The same amount of material then disappears through the overflow as is
added to the hold. The dredged material/water mixture entering the water via the overflow
can, depending for instance on the current, settle once again (fall back onto the
water bottom), erode (fall back onto the water bottom and then be carried away by
the current) and/or be transported (carried away by the current without settling).
As stated above, it is necessary to ensure that the turbidity of the water is not
allowed to increase too much.
[0005] US 4 365 509 A discloses a method for measuring the amount of mire and mud present in a dredged
mixture collected in the hold of a dredger. The method comprises measuring the height
of the settled sand laver of the mixture by a plump weight and measuring the position
of the upper surface of the mixture with an acoustic level guide. By combining this
(volume) measurement with a number of density measurements taken over the height of
the mixture, the total amount of mire is obtained in the dredged mixture.
[0006] US 4 206 057 A discloses a dredging vessel, the overflow of which is equipped with a telescopically
arranged level-adjustable outlet conduit provided under the vessel. When the head
water is polluted, the telescopical part is extended to underneath the main current
such that polluted sludge remains on the bottom and is not carried away with the current.
[0007] NL 9 201 853 A discloses a method for loading a dredging vessel wherein the dredged slurry is partly
contaminated. Dredged slurry collected in the holds is allowed to phase separate in
a heavy (clean) fraction and a light (contaminated) fraction. The light fraction is
then off-loaded to one dumping site and the heavy fraction to another.
[0008] Although the known method delivers a maximum dredging efficiency, the quality of
the dredged material which settles in the hold is open to improvement, in particular
being not readily controllable.
[0009] The present invention has for its object to provide a method for loading a dredging
vessel with dredged material which does not have this and other drawbacks, or does
so to lesser extent. Another object is to provide a dredging vessel particularly equipped
for performing the improved method.
[0010] This object is achieved according to the invention by providing a method
according to claim 1. According to the invention, a method for loading a dredging vessel with
dredged material in a hold provided for this purpose and having a height-adjustable
overflow is provided, wherein a dredged material/water mixture is carried via an inlet
into the hold and forms a settled layer therein due to settling of the heavier dredged
material particles, and wherein the height position of the overflow above the settled
layer is adjusted subject to a value of a control parameter measured during filling
of the hold. It has been found that by defining a suitable control parameter the quality
of the dredged material settled in the hold can be favourably affected. This can be
understood as follows. In contrast to the known method, in the method according to
the invention the overflow will not be placed in the highest position at the start
of dredging, but rather in a lower position. Dredged material mixture, and in particular
the finer fraction of the dredged material mixture (since the heavier fraction settles),
will hereby overflow via the overflow at a relatively early stage after the start
of dredging. It has been found that by adjusting the height position of the overflow
the average particle size of the dredged material mixture which overflows via the
overflow can be influenced, and therefore also the average particle size of the dredged
mixture remaining behind in the hold. Settled material is in this way obtained with
a better controlled particle size distribution, in particular a higher average particle
size and/or narrower particle size distribution, than is the case in the known method.
Such a material has an improved quality. The invented method has the additional advantage
that the degree of contamination of the dredged material in the hold and/or of the
overflowing dredged material can be influenced. The height position of the overflow
is preferably set subject to the momentary value of the control parameter.
[0011] A preferred embodiment of the method is characterized in that the height position
of the overflow above the settled layer is adjusted so that the measured value of
the control parameter remains substantially constant. This embodiment allows a dredged
material remaining behind in the hold to be obtained with a predetermined desired
average particle size.
[0012] According to the invention, the control parameter for use in the method comprises
the average horizontal velocity of the non-settled dredged material/water mixture
above the settled layer between the inlet and the overflow. It has been found that
this control parameter has a high sensitivity to the average particle size of the
dredged material mixture overflowing via the overflow, and therefore also for the
average particle size of the settled dredged material remaining behind in the hold.
In the case of a fixed height position of the overflow above the settled layer it
is found for instance that at a higher average horizontal velocity dredged material
mixture of a higher average particle size is flushed away via the overflow. A typical
average horizontal velocity of the non-settled dredged material/water mixture in the
hold amounts to in the order of magnitude of 1 m/sec. The invention is however not
limited to such velocities. The average horizontal velocity of the non-settled dredged
material/water mixture in the hold is preferably adjusted within a range of 0.1 to
5 m/sec, more preferably within a range of 0.3 to 3 m/sec, and most preferably within
a range of 0.5 to 1.5 m/sec.
[0013] The invention is based on the insight that the dredged material particles carried
via the inlet into the hold will settle (sediment) partially and form a settled layer
and, subject to the strength of the current generated above the settled layer, will
partially erode (fall back onto the settled layer and then be carried away by the
current) and/or will be transported (carried away by the current to the overflow without
settling).
[0014] The horizontal velocity above the settled layer of the non-settled mixture flowing
from the inlet to the overflow can be determined in simple manner by measuring the
incoming flow rate of the suctioned-up mixture and dividing it by the width of the
hopper and the height of the non-settled mixture. This horizontal velocity is preferably
compared to the average fall velocity of the solid particles in the suctioned-up mixture.
This fall velocity can easily be determined experimentally, for instance by a sedimentation
measurement. It is in principle possible in this way to determine which particles
will flow out via the overflow and which particles will settle at the set height (or
horizontal velocity of the mixture).
[0015] According to the invention the average horizontal velocity V is preferably defined
by the following formula:
wherein
Q is the flow rate of the dredged material/water mixture measured at the position of
the inlet,
B is the width of the hold and
h is the height position of the overflow above the settled layer. The flow rate
Q at the position of the inlet can be measured in known manner by incorporating a flow
meter, for instance in the inlet. The flow rate
Q can be controlled by adjusting the dredge pump which pumps the dredged material/water
mixture up from the water bottom.
[0016] A further preferred embodiment of the method according to the invention is characterized
in that the height position
h of the overflow above the settled layer is adjusted to a substantially constant value,
and that the flow rate
Q is adjusted so that the average horizontal velocity V acquires the desired value.
The flow rate
Q can be adjusted by providing a feedback of the measured flow rate
Q to the control of the dredge pump which pumps the dredged material/water mixture
up from the water bottom.
[0017] An alternative preferred embodiment of the method according to the invention is characterized
in that the flow rate
Q is adjusted to a substantially constant value (by the pump control), and that the
height position
h of the overflow above the settled layer is adjusted so that the average horizontal
velocity V acquires the desired value. According to the invention the overflow is
generally not placed in the highest position at the start of dredging in the method
according to the invention, but rather in a lowest position of the overflow. The lowest
position of the overflow corresponds to a low load factor of the hold, preferably
25%, more preferably 20%, still more preferably 15%, still more preferably 10% and
most preferably 5%. It will be apparent that the lowest position of the overflow will
preferably not be lower than the water level outside the dredging vessel, since otherwise
water from outside could flow into the hold.
[0018] Because contaminants in dredged material are generally bound mainly to the finer
particles, for instance to particles with a dimension < 63 µm, and these are preferably
discharged according to the invention via the overflow, the settled layer of dredged
material comprises fewer contaminants. An additional advantage of the invented method
is that the preferably discharged smaller particles are generally carried away more
easily with the current, so that they do not settle but, on the contrary, are carried
away with the current by erosion and/or transport. The invented method provides the
option of adjusting the particle size of the dredged material discharged via the overflow
such that such an erosion and/or transport can take place taking into account the
strength of the current at the location. In areas with strong current it will generally
be possible to discharge an average larger particle size via the overflow without
this resulting in an unacceptable increase in turbidity. In areas with a weak current
the height of the overflow will preferably be set such that dredged material of an
average smaller particle size is discharged via the overflow.
[0019] In a preferred embodiment of the method the hold is filled with water to the level
of the overflow in the lowest position before dredging begins. Dredged material/water
mixture will hereby overflow via the overflow almost immediately after dredging has
started.
[0020] It is advantageous that in the method according to the invention the control parameter
relates to the height of the settled layer and that the overflow is kept above the
settled layer, and is more preferably kept at substantially constant height above
the settled layer. In this variant the overflow as it were co-displaces with the height
of the settled layer, whereby a mixture with well controlled particle size distribution
remains behind in the hold. The constant height depends on the conditions at the location
and can, if desired, be determined experimentally. It is also possible to arrive at
a suitable value for the constant height on the basis of theoretical considerations.
The height of the settled layer can be measured in a number of ways. The simplest
methods are by measuring the draught of the dredging vessel and/or using a dipstick.
It is however also possible to apply other methods.
[0021] Yet another preferred embodiment of the method has the feature that the control parameter
relates to the particle size distribution of the overflowing mixture close to the
overflow. The particle size distribution of a dredged material/water mixture can be
determined in different ways. Suitable methods include concentration measurement by
photography or film, particle distribution determination of samples taken by means
of screening and/or sedimentation scales, x-ray extinction measurement, extinction
measurement of light with one or more wavelengths and/or by means of sound waves.
[0022] The method according to the invention is preferably characterized in that the control
parameter relates to the density of the overflowing mixture close to the overflow.
The density can be measured in a manner known to the skilled person, for instance
with an extinction measurement. In such a measurement a radioactive source is placed
on one side of the mixture flow. A (-detector placed on the other side of the mixture
flow measures the amount of radiation passing through the mixture. The (-radiation
detected depends on the quantity of solid particles between the source and the detector
counter. Devices for measuring density in this way are commercially available, for
instance from the firm Berthold Technologies N.V. of Vilvoorde, Belgium.
[0023] In a particularly advantageous method the turbidity of the overflowing mixture close
to the overflow is applied as control parameter. The turbidity can also be easily
measured by means of a density measurement as briefly described above. Turbidity resulting
from the removal of the silt has a great ecological effect. Owing to the turbidity
less light penetrates to the bottom of the water. The flora and fauna present on the
bottom hereby have less opportunity to develop. A very common requirement in dredging
operations is that the turbidity during dredging may not rise above 1000 mg per litre.
The method according to the present preferred variant provides the option of adjusting
the overflow height such that the turbidity (increase) remains below a determined
desired value.
[0024] It will be apparent that it is likewise possible to apply as control parameter a
combination of the above stated control parameters. The position of the overflow can
for instance thus be determined in first approximation by the height of the settled
layer, wherein corrections to this first approximation are made subject to the value
of another control parameter, such as for instance the measured mixture density at
inlet and overflow.
[0025] For even better control of the particle size distribution of the overflowing mixture,
and therefore also of the settled mixture, the overflow is preferably provided with
a filter of predetermined mesh width, preferably for the purpose of sampling the particle
size distribution of the outflowing mixture.
[0026] The invention likewise relates to a dredging vessel adapted to perform the method
according to the invention. Particularly provided is a dredging vessel which is provided
with a hold with height-adjustable overflow for loading with a dredged material/water
mixture, wherein the dredging vessel is further provided with means for measuring
a control parameter, as well as with a control device which adjusts the height position
of the overflow subject to the measured value of the control parameter. According
to the invention, said control parameter relates to the average horizontal velocity
of the non-settled dredged material/water mixture above the settled layer between
the inlet and the overflow. The advantages of the dredging vessel according to the
invention have already been elucidated at length above with reference to the invented
method, and will not therefore be repeated here.
[0027] In a preferred variant of the dredging vessel according to the invention the measuring
means are chosen from the group comprising means for measuring the height of the settled
layer, means for measuring the average horizontal velocity of the non-settled mixture
between the inlet and the overflow, means for measuring the particle size distribution
of the suctioned-up mixture close to the inlet and/or the particle size distribution
of the overflowing mixture close to the overflow, means for measuring the density
of the suctioned-up mixture close to the inlet and/or the density of the overflowing
mixture close to the overflow, means for measuring the turbidity of the overflowing
mixture close to the overflow and/or in the water, or combinations of the above stated
measuring means.
[0028] A particularly advantageous preferred variant relates to a dredging vessel, the measuring
means of which comprise a densimeter disposed at the position where the overflowing
mixture runs into the overflow.
[0029] The method and dredging vessel according to the invention will now be further elucidated
on the basis of the following figure, without the invention being limited thereto.
Figure 1 shows a schematic side view of a dredging vessel according to the invention;
and
Figure 2 shows schematically the particle size distribution of a dredged material
mixture obtainable with the invented method and dredging vessel, compared to the particle
size distribution of a dredged material mixture obtainable with the known method.
[0030] The trailing suction hopper dredger according to the invention comprises a vessel
1 with a hold 2 and a suction conduit which is constructed from a loading pipe 3 debouching
into hold 2, a pump 4, and a suction pipe 5 which is pivotable about an axis 30 relative
to vessel 1 and which has on its bottom end a drag head 6 and which is dragged over
the bottom 8 located under water 7 while vessel 1 sails in the direction of arrow
9 and bottom material 16, for instance sand, is suctioned up together with water 7
as a suspension from bottom 8 via conduit 5 and carried into hold 2. Drag head 6 is
provided with a visor 12 which can be pivoted about a shaft 11 relative to drag head
6 by means of a hydraulic cylinder 13.
[0031] Hold 2 is suitable for receiving the mixture of water bottom material and water suctioned
up through conduit 5 by means of pump 4. After a time the mixture present in hold
2 will settle and form herein a settled layer 20 with a height 40 relative to the
bottom of hold 2. Present on settled layer 20 is a layer 21 comprising an aqueous
suspension of non-settled bottom material. The height 41 of layer 21 is determined
by the height position of a height-adjustable overflow 10 with conical upper outer
end 14. Overflow 10 has an open lower outer end 15 along which mixture overflowing
in the direction of arrow 31 can be carried in the direction of arrow 32 to the water
7 via the underside of the trailing suction hopper dredger.
[0032] The variant of a trailing suction hopper dredger according to the invention shown
in figure 1 is further provided with means for measuring a control parameter, subject
to which value the height position of overflow 10 is adjusted. The measuring means
comprise a first densimeter 25 which is arranged in the vicinity of the inlet or loading
pipe 3 and there measures the density of the suctioned-up mixture. A per se known
flow meter 28 is also arranged at substantially the same position. This measures the
flow rate of the suctioned-up water, from which the average horizontal velocity of
the non-settled part 21 can be determined. The densimeter comprises a radioactive
concentration meter obtainable from the firm Berthold Technologies N.V. of Vilvoorde,
Belgium. A second densimeter 26 of the same type is arranged at the position of overflow
10 and measures the density of the overflowing mixture. If desired, a third densimeter
27 can be arranged in the water in the vicinity of the trailing suction hopper dredger
in order to enable measurement of the turbidity of the overflowing mixture or of the
surrounding water. The signals from the above mentioned measuring means are stored
in a central computer (not shown), this computer forming part of the control equipment
of the trailing suction hopper dredger.
[0033] In a preferred method the above described trailing suction hopper dredger is employed
to dredge material present in or on water bottom 8. In the method a mixture of water
bottom material and water is suctioned up via drag head 6 connected to suction conduit
5 and moving over water bottom 8, and carried into hold 2 via the inlet or suction
pipe 3. In a preferred method overflow 10 is set in the lowest position at the start
of the method. This preferably corresponds to a load factor of hold 2 of about 10%
(of the overall available load in m
3). In figure 1 the lowest position of overflow 10 is indicated schematically by the
level 100 of the top side of overflow 10. At this position 100 a relatively large
amount of suctioned-up mixture will be carried in the direction of arrow 31 through
overflow 10 in the direction of arrow 32 to the water 7. This overflow is formed particularly
by the finer particles of the suctioned-up mixture, since the coarser fraction has
already moved below level 100 under the influence of gravitational force and remains
behind in hold 2 as settled layer 20. During dredging the height 40 of settled layer
20 will gradually increase. In the shown variant the height position of overflow 10
is adjusted subject to the height 40 of settled layer 20, this such that overflow
10 is kept at substantially constant height above settled layer 20. This means that
the height 41 will have a constant value during a great part of the dredging. The
precise value depends on the conditions on location and can amount to for instance
0.75 m. If the suction flow rate measured by flow meter 28 is held constant, the average
horizontal velocity of the non-settled part 21 will then also be substantially constant.
[0034] Because the height 40 of settled layer 20 increases over time, the height of overflow
10 will also rise until overflow 10 reaches the highest position 101. The highest
position 101 is reached when the trailing suction hopper dredger has reached its maximum
allowable draught or dredge mark. This situation is shown in figure 1.
[0035] The invented method is particularly suitable for dredging access channels for urban
areas which run out into the sea or other large stretch of water, and/or for dredging
sand, more preferably fine sand, and most preferably fine silt-containing sand. Sand
has 65% by volume of particles larger than 63 µm and 50% by volume of particles smaller
than 2 mm. Fine sand has between 5-15% by volume of particles with a grain size lying
between 2 and 63 µm. Using the invented method more bottom material, and particularly
the finer fraction thereof, runs back via the overflow to the water at a low load
factor of the hopper than is the case in the known method. This so-called agitation
process can be controlled well with the invented method, this being a great advantage
in respect of the requirements set for the turbidity of the water. The overflowed
finer fraction can be carried away by the current in the access channel from the location
of the dredging operations to for instance the sea. In addition, the settled material
in the hold has a higher quality, so that it can advantageously be used for sand supply
and the like, optionally in the immediate vicinity of the dredging location.
[0036] Figure 2 shows schematically the particle size distribution (50) of a dredged material
mixture obtained using the invented method and dredging vessel. The obtained particle
size distribution is compared to the particle size distribution (51) of a dredged
material mixture obtained using the known method. In the shown graphic representation
a percentage by weight (52) is plotted against the particle size (53). By allowing
a part (54) of the supplied particle size distribution (51) to overflow via overflow
(10) during dredging a particle size distribution (50) is obtained which not only
has a narrower distribution but also has a larger average particle size (55) than
the supplied particle size distribution (56).
[0037] The invention is not limited to the above described exemplary embodiments, and modifications
can be made hereto to the extent they fall within the scope of the appended claims.
1. Method for loading a dredging vessel (1) with dredged material in a hold (2) provided
for this purpose and having a height-adjustable overflow (10), wherein a dredged material/water
mixture is carried via an inlet (3) into the hold (2) and forms a settled layer (20)
therein due to settling of the heavier dredged material particles, and wherein the
height position of the overflow (10) above the settled layer (20) is adjusted subject
to a value of a control parameter measured during filling of the hold (2), characterized in that the control parameter relates to the average horizontal velocity of the non-settled
dredged material/water mixture above the settled layer (20) between the inlet (3)
and the overflow (10).
2. Method as claimed in claim 1, characterized in that the height position of the overflow (10) above the settled layer (20) is adjusted
so that the measured value of the control parameter remains substantially constant.
3. Method as claimed in claim 1 or 2,
characterized in that the average horizontal velocity v is defined by the following formula:
wherein
Q is the flow rate of the dredged material/water mixture measured at the position of
the inlet (3),
B is the width of the hold (2) and
h is the height position of the overflow (10) above the settled layer (20).
4. Method as claimed in claim 3, characterized in that the height position h of the overflow (10) above the settled layer (20) is adjusted to a substantially
constant value, and that the flow rate Q is adjusted so that the average horizontal velocity v acquires the desired value.
5. Method as claimed in claim 3, characterized in that the flow rate Q is adjusted to a substantially constant value and that the height position h of the overflow (10) above the settled layer (20) is adjusted so that the average
horizontal velocity v acquires the desired value.
6. Method as claimed in any of the foregoing claims, characterized in that the control parameter further relates to the particle size distribution of the overflowing
mixture close to the overflow (10).
7. Method as claimed in any of the foregoing claims, characterized in that the control parameter further relates to the density of the overflowing mixture close
to the overflow (10).
8. Method as claimed in any of the foregoing claims, characterized in that the control parameter further relates to the turbidity of the overflowing mixture
close to the overflow (10) or in the water (7).
9. Method as claimed in any of the foregoing claims, characterized in that the control parameter is a combination of the stated control parameters.
10. Dredging vessel provided with a hold (2) with height-adjustable overflow (10) for
loading with a dredged material/water mixture, wherein the dredging vessel is further
provided with means (25, 26, 27, 28) for measuring a control parameter and with a
control device which adjusts the height position of the overflow (10) subject to the
measured value of the control parameter, characterized in that the control parameter relates to the average horizontal velocity of the non-settled
dredged material/water mixture above the settled layer (20) between the inlet (3)
and the overflow (10).
11. Dredging vessel as claimed in claim 10, characterized in that the measuring means are chosen from the group comprising means for measuring the
height of the settled layer, means for measuring the average horizontal velocity of
the non-settled mixture between the inlet and the overflow, means for measuring the
particle size distribution of the suctioned-up mixture close to the inlet and/or the
particle size distribution of the overflowing mixture close to the overflow, means
for measuring the density of the suctioned-up mixture close to the inlet and/or the
density of the overflowing mixture close to the overflow, means for measuring the
turbidity of the overflowing mixture close to the overflow and/or in the water, or
combinations of the above stated measuring means.
12. Dredging vessel as claimed in claim 11, characterized in that the measuring means comprise a densimeter disposed at the position where the overflowing
mixture runs into the overflow (10).
1. Verfahren zum Beladen eines Baggerschiffs (1) mit Baggergut in einem Frachtraum (2),
der zu diesem Zweck bereitgestellt wird und mit einem höhenverstellbaren Überlauf
(10) ausgestattet ist, wobei eine Mischung aus Baggergut und Wasser über einen Einlass
(3) in den Frachtraum (2) befördert wird, die darin aufgrund des Absetzens der schwereren
Baggergutpartikel eine Setzschicht (20) ausbildet, und wobei die Höhenposition des
Überlaufs (10) über der Setzschicht (20) in Abhängigkeit eines Werts eines Steuerparameters,
der beim Befüllen des Frachtraums (2) gemessen wird, eingestellt wird, dadurch gekennzeichnet, dass sich der Steuerparameter auf die durchschnittliche horizontale Geschwindigkeit der
ungesetzten Mischung aus Baggergut und Wasser oberhalb der Setzschicht (20) zwischen
dem Einlass (3) und dem Überlauf (10) bezieht.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Höhenposition des Überlaufs (10) über der Setzschicht (20) so eingestellt wird,
dass der Messwert des Steuerparameters im Wesentlichen konstant bleibt.
3. Verfahren nach Anspruch 1 oder 2,
dadurch gekennzeichnet, dass die durchschnittliche horizontale Geschwindigkeit durch folgende Formel definiert
ist:
wobei
Q die Fließgeschwindigkeit der Mischung aus Baggergut und Wasser gemessen an der Position
des Einlasses (3),
B die Breite des Frachtraums (2) und
h die Höhenposition des Überlaufs (10) oberhalb der Setzschicht (20) ist.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass die Höhenposition h des Überlaufs (10) oberhalb der Setzschicht (20) auf einen im Wesentlichen konstanten
Wert eingestellt wird und die Fließgeschwindigkeit Q so eingestellt wird, dass die durchschnittliche horizontale Geschwindigkeit v den
Sollwert erreicht.
5. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass die Fließgeschwindigkeit Q auf einen im Wesentlichen konstanten Wert eingestellt wird und dass die Höhenposition
h des Überlaufs (10) oberhalb der Setzschicht (20) so eingestellt wird, dass die durchschnittliche
horizontale Geschwindigkeit v den Sollwert erreicht.
6. Verfahren nach allen vorherigen Ansprüchen, dadurch gekennzeichnet, dass sich der Steuerparameter weiterhin auf die Partikelgrößenverteilung der überlaufenden
Mischung nahe am Überlauf (10) bezieht.
7. Verfahren nach allen vorherigen Ansprüchen, dadurch gekennzeichnet, dass sich der Steuerparameter weiterhin auf die Dichte der überlaufenden Mischung nahe
am Überlauf (10) bezieht.
8. Verfahren nach allen vorherigen Ansprüchen, dadurch gekennzeichnet, dass sich der Steuerparameter weiterhin auf die Trübung der überlaufenden Mischung nahe
am Überlauf (10) oder im Wasser (7) bezieht.
9. Verfahren nach allen vorherigen Ansprüchen, dadurch gekennzeichnet, dass der Steuerparameter eine Kombination der aufgeführten Steuerparameter ist.
10. Baggerschiff, das mit einem Frachtraum (2) mit höhenverstellbarem Überlauf (10) bereitgestellt
wird, um mit einer Mischung aus Baggergut und Wasser befüllt zu werden, wobei das
Baggerschiff weiterhin mit Mitteln (25, 26, 27, 28) zur Messung eines Steuerparameters
und mit einer Steuereinheit bereitgestellt wird, die in Abhängigkeit des Messwerts
des Steuerparameters die Höhenposition des Überlaufs (10) einstellt, dadurch gekennzeichnet, dass sich der Steuerparameter auf die durchschnittliche horizontale Geschwindigkeit der
ungesetzten Mischung aus Baggergut und Wasser oberhalb der Setzschicht (20) zwischen
dem Einlass (3) und dem Überlauf (10) bezieht.
11. Baggerschiff nach Anspruch 10, dadurch gekennzeichnet, dass das Messmittel aus der Gruppe ausgewählt wird, die das Mittel zur Messung der Setzschichthöhe,
das Mittel zur Messung der durchschnittlichen horizontalen Geschwindigkeit der ungesetzten
Mischung zwischen dem Einlass und dem Überlauf, das Mittel zur Messung der Partikelgrößenverteilung
der aufgesaugten Mischung nahe am Einlass und/oder der Partikelgrößenverteilung der
überlaufenden Mischung nahe am Überlauf, das Mittel zur Messung der Dichte der aufgesaugten
Mischung nahe am Einlass und/oder der Dichte der überlaufenden Mischung nahe am Überlauf,
das Mittel zur Messung der Trübung der überlaufenden Mischung nahe am Überlauf und/oder
im Wasser oder Kombinationen aus den oben aufgeführten Messmitteln umfasst.
12. Baggerschiff nach Anspruch 11, dadurch gekennzeichnet, dass das Messmittel ein Densimeter umfasst, das dort angebracht ist, wo die Überlaufmischung
in den Überlauf (10) läuft.
1. Procédé pour charger de matériau dragué un bâtiment de dragage (1), dans une cale
(2) prévue à cet effet et ayant un trop-plein réglable en hauteur (10), étant entendu
qu'un mélange matériau dragué/eau est amené par une admission (3) dans la cale (2)
et y forme une couche décantée (20) suite à la sédimentation des particules les plus
lourdes du matériau dragué, et étant entendu que la position en hauteur du trop-plein
(10) au-dessus de la couche décantée (20) est réglée en fonction de la valeur d'un
paramètre de régulation mesuré pendant le remplissage de la cale (2), caractérisé en ce que le paramètre de régulation concerne la vitesse horizontale moyenne du mélange matériau
dragué/eau non décanté au-dessus de la couche décantée (20) entre l'admission et le
trop-plein (10).
2. Procédé selon la revendication 1, caractérisé en ce que la position en hauteur du trop-plein (10) au-dessus de la couche décantée (20) est
réglée de telle sorte que la valeur mesurée du paramètre de régulation reste sensiblement
constante.
3. Procédé selon la revendication 1 ou 2,
caractérisé en ce que la vitesse horizontale moyenne v est définie par la formule suivante :
où
Q est le débit du mélange matériau dragué/eau mesuré au niveau de l'admission (3),
B est la largeur de la cale (2) et
h est la position en hauteur du trop-plein (10) au-dessus de la couche décantée (20).
4. Procédé selon la revendication 3, caractérisé en ce que la position en hauteur h du trop-plein (10) au-dessus de la couche décantée (20) est réglée sur une valeur
sensiblement constante et en ce que le débit Q est réglé de telle sorte que la vitesse horizontale moyenne v prenne la valeur voulue.
5. Procédé selon la revendication 3, caractérisé en ce que le débit Q est réglé sur une valeur sensiblement constante et en ce que la position en hauteur h du trop-plein (10) au-dessus de la couche décantée (20) est réglée de telle sorte
que la vitesse horizontale moyenne v prenne la valeur voulue.
6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le paramètre de régulation concerne par ailleurs la distribution granulométrique
du trop-plein du mélange à proximité du trop-plein (10).
7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le paramètre de régulation concerne par ailleurs la densité du trop-plein du mélange
à proximité du trop-plein (10).
8. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le paramètre de régulation concerne par ailleurs la turbidité du trop-plein du mélange
à proximité du trop-plein (10) ou dans l'eau (7).
9. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le paramètre de régulation est une combinaison des paramètres de régulation cités.
10. Bâtiment de dragage pourvu d'une cale (2) à trop-plein réglable en hauteur (10) pour
le chargement d'un mélange matériau dragué/eau, étant entendu que le bâtiment de dragage
est par ailleurs pourvu de moyens (25, 26, 27, 28) pour mesurer un paramètre de régulation
et d'un dispositif de régulation qui règle la position en hauteur du trop-plein (10)
en fonction de la valeur mesurée du paramètre de régulation, caractérisé en ce que le paramètre de régulation concerne la vitesse horizontale moyenne du mélange matériau
dragué/eau non décanté au-dessus de la couche décantée (20) entre l'admission (3)
et le trop-plein (10).
11. Bâtiment de dragage selon la revendication 10, caractérisé en ce que les moyens de mesure sont choisis dans le groupe comprenant un moyen pour mesurer
la hauteur de la couche décantée, un moyen pour mesurer la vitesse horizontale moyenne
du mélange non décanté entre l'admission et le trop-plein, un moyen pour mesurer la
distribution granulométrique du mélange aspiré à proximité de l'admission et/ou la
distribution granulométrique du trop-plein du mélange à proximité du trop-plein, un
moyen pour mesurer la densité du mélange aspiré à proximité de l'admission et/ou la
densité du trop-plein du mélange à proximité du trop-plein, un moyen pour mesurer
la turbidité du trop-plein du mélange à proximité du trop-plein et/ou dans l'eau,
ou des combinaisons des moyens de mesure cités ci-dessus.
12. Bâtiment de dragage selon la revendication 1 l, caractérisé en ce que les moyens de mesure comprennent un densimètre placé à l'endroit où le trop-plein
du mélange se déverse dans le trop-plein (10).