JP2015034430A - Suction structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure sufficient pull-out resistance even for the sand ground.SOLUTION: A suction anchor 1 comprises a cylindrical peripheral wall part 3 and a top plate part 2 which closes one end thereof, and while the cylindrical peripheral wall part 3 is formed cylindrically, and the top plate part 2 is formed circularly. A drain hole 5 is formed in the top plate part 2, and water spreading in the inside space 6 enclosed with the cylindrical peripheral wall part 3 and top plate part 2 can be drained by connecting a tip of a suction hose 7 to the drain hole and also placing a suction pump (not illustrated) connected to a base end side thereof in operation. A flange-like projection 4 as a projection part is extended outward at the other end of the cylindrical peripheral wall part 3, namely, at the end on the opposite side from the top plate part 2.

Description

  The present invention relates to a suction structure that is mainly laid on a seabed ground as a suction anchor or a skirt suction foundation.

  In order to hold a floating offshore structure at a predetermined position on the sea, it is moored to an anchor on the seabed via a mooring line or mooring chain composed of wires and chains, or via a tension line called tendon. Although it is necessary to moor at the ship, a suction anchor is known as such an anchor.

  The suction anchor uses a suction structure composed of a cylindrical peripheral wall portion and a top plate portion that closes one end thereof as an anchor, and when set up, the opening side of the cylindrical peripheral wall portion is downward. After the suction structure is installed on the seabed, the water in the cylindrical peripheral wall is drained to create a water pressure difference inside and outside, and the cylindrical pressure wall can be penetrated into the seabed ground using the water pressure difference as a pushing force. As long as there is a hoisting ship for installing the suction structure and a drainage pump that gives suction power, it can be constructed without using special construction machines, and horizontal For the force, the passive earth pressure from the seabed that acts on the outer peripheral surface of the cylindrical peripheral wall becomes the resistance force, so the construction period can be shortened and the oil drilling of the North Sea oil field is an anchor method with excellent strength characteristics. The It has been adopted by such Ttohomu.

Japanese Patent Laid-Open No. 10-25738

  Nowadays, there is an urgent need to secure a new energy source that can suppress greenhouse gas emissions and is excellent in safety. In Japan, offshore wind power generation is considered promising. Since the water depth in the surrounding sea area is relatively large, the introduction of floating bodies using suction anchors has been studied.

  However, conventional suction anchors are mainly supposed to be set on viscous ground, and the seabed ground around Japan is often composed of sandy ground, and there is a concern that the pullout resistance is not sufficient compared to viscous ground. There was a problem that there was.

  On the other hand, the above-described suction structure is used as the foundation of a harbor structure such as a breakwater. After the suction structure is installed on the sea floor in the same manner as described above, a caisson is installed on the suction structure. If this is the case, compared to the conventional construction method in which the caisson is placed after the rubble mound has been laid in advance on the sea floor, construction and strength can be improved in the short construction period, as with the suction anchor. Even in the foundation, in order to resist a fall caused by a horizontal force caused by waves, winds, earthquakes, etc., a sufficient pulling resistance is required for the suction structure, and thus the same concern as a suction anchor arises.

  The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a suction structure capable of ensuring sufficient pulling resistance even in sandy ground.

In order to achieve the above object, the suction structure according to the present invention comprises a cylindrical peripheral wall portion and a top plate portion that closes one end thereof, and a drain hole is formed in the top plate portion. In the suction structure
When a pulling force is applied in a state in which the cylindrical peripheral wall portion is penetrated into the water bottom ground, the peripheral surface of the cylindrical peripheral wall portion has a bowl shape so that a resistance force against the pulling force acts from the water bottom ground. Ribbed, spiral or other convex portions are provided.

  In the suction structure according to the present invention, the convex portion is provided in the vicinity of the other end of the cylindrical peripheral wall portion.

  Moreover, the suction structure which concerns on this invention provides the said convex part in the outer peripheral surface at least among the surrounding surfaces of the said cylindrical surrounding wall part.

  In the suction structure according to the present invention, a connecting portion capable of connecting the mooring means is provided on the upper surface of the top plate portion.

  In the suction structure according to the present invention, the top surface of the top plate is configured such that a seawall, a breakwater, a main tower of a bridge, and other port structures or marine structures can be placed thereon.

  In the suction structure according to the present invention, when a pulling force is applied in a state where the cylindrical peripheral wall portion is inserted into the water bottom ground, the resistance of the cylindrical peripheral wall portion is such that a resistance force against the pulling force acts from the water bottom ground. The peripheral surface is provided with projections such as bowls, ribs, spirals, etc., and when settling on the bottom of the water bottom, it is installed on the bottom of the water so that the opening side of the cylindrical peripheral wall is downward as in the past. Thereafter, the internal water is drained through drain holes formed in the top plate.

  In this way, the weight of the suction structure (excluding buoyancy) and the difference in water pressure between the inside and outside of the suction structure becomes the pushing force when penetrating the cylindrical peripheral wall into the water bottom ground. The perimeter of the cylindrical peripheral wall part extends from the bottom of the water to the bottom of the cylindrical peripheral wall part and creates an osmotic flow in the bottom of the water, thereby reducing the effective stress of the ground. Since the penetration resistance at the lower end of the part is reduced, there is no possibility that the convex part provided on the peripheral surface of the cylindrical peripheral wall part hinders penetration into the water bottom ground.

  On the other hand, after the drainage operation is stopped with the completion of the rooting of the cylindrical peripheral wall portion into the water bottom ground, the above-described osmotic flow disappears and the water bottom ground returns to the original state.

  Therefore, when a pulling force acts on the suction structure in such a state, in the configuration in which the convex portion is provided on the inner peripheral surface of the cylindrical peripheral wall portion, the bottom of the bottom soil is filled in the cylindrical peripheral wall portion. Therefore, the weight of the earth and sand filled in the cylindrical peripheral wall part is added as a new resistance compared to the case where the earth and sand are not filled in the ground but left on the bottom of the bottom. The surface friction force is excluded), and the strength of the suction structure against pulling can be improved to some extent.

  Moreover, in the structure which provided the convex part in the outer peripheral surface of the cylindrical peripheral wall part, since the surrounding earth and sand are integrated with the outer peripheral surface of the cylindrical peripheral wall part by the convex part, the outer peripheral surface of the cylindrical peripheral wall part is separated from the water bottom ground. Compared to the case of the conventional configuration in which it is pulled out and pulled out, the weight of the ground area integrated on the outer peripheral surface of the cylindrical peripheral wall part is added as a new resistance force, but the boundary between the ground area and the surrounding water bottom ground The frictional force on the surface (shear surface) has a sufficient magnitude, and this frictional force is added as a new resistance force. Even if the peripheral frictional force of the configuration is subtracted, the proof stress of the suction structure against pulling out is greatly improved.

Specifically, as the peripheral surface of the cylindrical peripheral wall portion provided with the convex portion,
(a) Inner peripheral surface only
(b) Outer surface only
(c) Although three forms of the inner peripheral surface and the outer peripheral surface are assumed, in the conventional configuration in which there is no convex portion, when pulling and breaking in the form that only the cylindrical peripheral wall portion is pulled out from the water bottom ground at the time of extraction (hereinafter referred to as In addition, the pulling failure mode I), the peripheral surface frictional force acting on the inner peripheral surface and the outer peripheral surface, and the own weight of the suction structure only become a resistance force against the pulling.

  In this case, if the configuration of (a) is selected, the pull-out failure mode is a mode in which the cylindrical peripheral wall portion is pulled out from the bottom bottom ground in a state where the sediment of the bottom bottom ground is filled in the inside of the cylindrical peripheral wall portion (hereinafter, Since the transition to the pulling failure mode II) and the weight of the earth and sand filled in the cylindrical peripheral wall as described above is added as a new resistance force (excluding the peripheral frictional force on the inner peripheral surface), the suction against the pulling out The yield strength of the structure can be improved to some extent, and since the convex portion is not formed on the outer peripheral surface of the cylindrical peripheral wall, the overall size of the suction structure can be suppressed, and transportation and other handling are facilitated. be able to.

  On the other hand, if the configuration of (c) is selected, the pulling failure mode is a state in which the sediment of the bottom bottom is filled in the inside of the cylindrical peripheral wall and the soil of the bottom bottom is integrated on the outer peripheral surface of the cylindrical peripheral wall. In addition to the action of the configuration of (a), the outer peripheral surface of the cylindrical peripheral wall portion is shifted to the pulling failure mode (hereinafter referred to as the pulling failure mode III) in which the cylindrical peripheral wall portion is pulled out from the bottom ground. Not only does the weight of the ground area integrated into the surface add a new resistance, but the frictional force at the boundary surface (shear surface) between the ground area and the surrounding water bottom ground is sufficiently large. Since this frictional force is added as a new resistance force, it is possible to greatly improve the proof stress of the suction structure against pulling.

  Also, in the conventional configuration where there is no convex portion, when the pulling failure mode is the pulling failure mode II, if the configuration (b) is selected, the pulling failure mode shifts to the pulling failure mode III. Not only does the weight of the ground area integrated into the outer peripheral surface of the peripheral wall part add as a new resistance force, but also the frictional force at the boundary surface (shear surface) between the ground area and the surrounding water bottom ground is sufficiently large Since this frictional force is added as a new resistance force, it is possible to sufficiently improve the proof stress of the suction structure against drawing.

  As long as the pulling force acts on the suction structure when the pulling force acts on the suction structure, it can be arbitrarily configured as long as the resistance against the pulling force acts from the bottom of the ground. However, it is not always necessary to continuously form the entire circumference, and it may be arranged discretely.

  Further, the convex portion may be provided in an intermediate portion of the cylindrical peripheral wall portion except for the vicinity of the end portion, but the end located near the other end of the cylindrical peripheral wall portion, that is, on the opposite side of the top plate portion. If the structure is provided in the vicinity of the part, since the convex part is always located at the place where the effective stress reduction due to the permeation flow is the largest during the penetration work by the suction, the penetration resistance is surely reduced. In addition, when the penetration is completed, the convex portion is buried at the deepest position from the bottom of the water, so the weight of the surrounding earth and sand integrated into the cylindrical peripheral wall portion is maximized, and the resistance to pulling out. Can be sufficiently increased.

  The suction structure according to the present invention can be submerged in the bottom of the lake, including the seabed.

  Further, the suction structure according to the present invention is applicable to all structures that need to be sunk in the bottom of the ground with sufficient resistance to horizontal force and pulling force. Is assumed to be applied to a suction anchor or a skirt suction foundation. In the former case, a connecting part to which the mooring means can be connected is provided on the top surface of the top plate part, and in the latter case, the top part is provided. What is necessary is just to comprise the upper surface of a board part so that harbor structures or marine structures, such as a seawall, a breakwater, and the main tower of a bridge, can be mounted in the form of a caisson, for example.

It is the figure of the suction anchor 1 which concerns on this embodiment, (a) is a vertical sectional view, (b) is the arrow line view seen from the AA line direction. The construction drawing which showed a mode that the suction anchor 1 which concerns on this embodiment was sunk. Explanatory drawing which showed the effect | action of the suction anchor 1 which concerns on this embodiment by the comparison with the conventional suction anchor. The vertical sectional view which showed another example about the range of the bearing pressure which the hook-shaped protrusion 4 exerts on the seabed ground 14. FIG. Explanatory drawing which showed the suction anchor 1b which concerns on a modification, and its effect | action by the comparison with the conventional suction anchor. Explanatory drawing which showed the suction anchor 1c which concerns on a modification, and its effect | action by the comparison with the conventional suction anchor. The figure which showed the modification of the hook-shaped protrusion 4. FIG. It is a figure of the skirt suction foundation 73, (a) is a vertical sectional view, (b) is a vertical sectional view along the BB line.

  Hereinafter, embodiments of a suction structure according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an example in which a suction structure according to the present invention is applied to a suction anchor. As can be seen in the figure, the suction anchor 1 according to the present embodiment is composed of a cylindrical peripheral wall portion 3 and a top plate portion 2 that closes one end thereof, and the cylindrical peripheral wall portion 3 is cylindrical and has a top plate. The parts 2 are each formed in a circular shape.

  The suction anchor 1 can be appropriately composed of reinforced concrete, prestressed concrete, steel, and other materials, and has a diameter of, for example, about several m to 10 m depending on strength and proof strength required for horizontal force and pulling force. The height may be set to about 3 to 4 times the height.

  A drain hole 5 is formed in the top plate portion 2, and the tip of the suction hose 7 is connected to the drain hole and a suction pump (not shown) connected to the base end side thereof is operated to The water spreading in the inner space 6 surrounded by the peripheral wall portion 3 and the top plate portion 2 can be drained.

  On the other end of the cylindrical peripheral wall 3, that is, on the end opposite to the top plate 2, a hook-like projection 4 as a convex portion is extended outward.

  FIG. 2 is a construction diagram showing a state in which the suction anchor 1 according to the present embodiment is sunk in the seabed ground 14. In order to sink the suction anchor 1 to the seabed ground 14, first, the suction anchor 1 is installed on the seabed 11 so that the opening side of the cylindrical peripheral wall portion 3 is downward as shown in FIG.

  For the installation work, a crane (not shown) mounted on the hoist ship 12 may be appropriately used.

  Next, the water spreading in the inner space 6 of the suction anchor 1 is drained by connecting the drain hole 5 of the top plate 2 and the suction pump 13 through the suction hose 7 and operating the suction pump.

  In this way, the water in the inner space 6 of the suction anchor 1 and the suction hose 7 communicating with the water is lowered by δh from the surrounding sea area, and the water pressure difference δP corresponding to the lowering of the water level is Together with its own weight (excluding buoyancy), it becomes a pushing force that penetrates the cylindrical peripheral wall portion 3 of the suction anchor 1 into the seabed ground 14.

  Here, the water pressure difference δP simultaneously causes an osmotic flow in the seabed ground 14 from the seabed 11 spreading around the cylindrical peripheral wall part 3 to the bottom of the cylindrical peripheral wall part toward the inner seabed, Thereby, the effective stress of the seabed ground 14 is lowered, and the penetration resistance at the lower end of the cylindrical peripheral wall portion 3 is reduced.

  Therefore, the cylindrical peripheral wall 3 is penetrated into the submarine ground 14 as shown in FIG. 5B without being obstructed by the hook-like protrusion 4 extending outward from the outer peripheral surface of the lower end.

  After the penetration of the cylindrical peripheral wall portion 3 into the seabed ground 14 is completed, the drainage operation by the suction pump 13 is finished, but the above-described osmotic flow disappears accordingly, so the seabed ground 14 returns to its original state. .

  In addition, after the drainage by the suction pump 13 is completed, the drainage hole 5 is closed so that the suction anchor 1 does not communicate with the outside from the side other than the opening side of the cylindrical peripheral wall 3.

  FIG. 3 is an explanatory view showing the action of the suction anchor 1 when a pulling force acts on the suction anchor 1 after the suction anchor 1 is laid down. As shown in FIG. 2A, a connecting portion 32 is provided on the top surface of the top plate portion 2 of the suction anchor 1, and a floating structure such as offshore wind power generation (not shown) is provided on the connecting portion. A mooring line 31 as a mooring means extending from) is connected, and the suction anchor 1 functions as a mooring anchor for a floating structure.

  Here, when the floating structure is subjected to wave force or wind force, a tensile force acts on the suction anchor 1 via the mooring line 31. Of the tensile force, a horizontal peripheral component is a cylindrical peripheral wall portion. The passive earth pressure from the seabed ground 14 acting on the outer peripheral surface 3 becomes a resistance force, and holds the suction anchor 1 stably.

  On the other hand, with respect to the vertically upward component, that is, the pulling force, the outer diameter of the cylindrical peripheral wall portion 3 is an inner diameter that is an area extending above the hook-shaped protrusion 4 provided at the lower end of the cylindrical peripheral wall portion 3, A cylindrical ground region 33 whose outer diameter is the diameter of the hook-shaped protrusion 4 is integrated with the cylindrical peripheral wall 3.

  That is, in the case of the conventional configuration in which the hook-like protrusions 4 do not exist, when the mode at the time of breakage due to pulling is the pulling breakage mode II, as shown in FIG. In any case, in the case of the present embodiment, as shown in FIG. 3C, the cylindrical ground region 33 is excluded. Are integrated into the cylindrical peripheral wall portion 3, and the pulling failure mode shifts to the pulling failure mode III.

  And in this embodiment, not only the weight of the ground area | region 33 integrated with the outer peripheral surface of the cylindrical surrounding wall part 3 is added as a new resistance force but the boundary of this ground area | region and the seabed ground 14 of the circumference | surroundings around it. The frictional force on the surface (shear surface) has a sufficient magnitude, and this frictional force is added as a new resistance force.

  In FIGS. 3 (b) and 3 (c), the state after the pulling failure is drawn so that the difference between the pulling failures can be clearly understood. The relationship between the pulling force and the resistance force in response thereto is shown in FIG. (The same applies hereinafter).

  As described above, according to the suction anchor 1 according to the present embodiment, not only the weight of the ground region 33 integrated with the cylindrical peripheral wall portion 3 by the hook-shaped protrusion 4 but also the ground region 33 and its surroundings. Since the amount obtained by subtracting the peripheral surface friction force on the outer peripheral surface from the friction force on the boundary surface (shear surface) with the seabed ground 14 is added to the resistance force at the time of extraction, the proof stress of the suction anchor 1 against extraction is sufficiently improved. It becomes possible.

  As a result, the height and number of the suction anchors 1 can be suppressed, and the cost from manufacturing to transportation and further sinking can be greatly reduced.

  Further, according to the suction anchor 1 according to the present embodiment, the hook-like protrusion 4 is provided in the vicinity of the other end of the cylindrical peripheral wall portion 3, that is, in the vicinity of the end portion located on the opposite side of the top plate portion 2. During the penetration work by suction, the hook-like projections 4 are always located at locations where the effective stress drop due to osmotic flow is greatest, so that the penetration resistance can be reliably reduced and the penetration is completed. In this state, since the bowl-shaped protrusion 4 is buried at the deepest position from the seabed 11, the weight of the ground region 33, which is the peripheral earth and sand integrated into the cylindrical peripheral wall portion 3, and the ground region 33 and its The frictional force at the boundary surface with the surrounding seabed ground 14 is maximized, and thus the resistance to drawing can be sufficiently increased.

  In the present embodiment, the shear surface formed in the seabed ground 14 is formed vertically upward from the tip edge portion of the hook-shaped protrusion 4 at the time of pulling failure. 4 is considered to be limited to the range of the bearing pressure to the seabed ground 14 only above the hook-shaped protrusion 4 and extends obliquely upward from the tip edge of the hook-shaped protrusion 4 as shown in FIG. When it can be considered that the bearing pressure is applied to the surface, the ground region integrated with the cylindrical peripheral wall portion 3 at the time of the pulling failure is not the cylindrical ground region 33 but the inverted truncated cone-shaped ground region 33 ′. In this case, the resistance to pulling is greatly increased.

  Further, in the present embodiment, it is assumed that the pulling failure mode in the conventional configuration is the pulling failure mode II, but the pulling failure mode in the conventional configuration is the pulling failure mode I, that is, only the cylindrical peripheral wall portion at the time of the pulling failure is the seabed ground. In the mode of being pulled out from the pipe, instead of the suction anchor 1, as shown in FIG. 5 (a), the cylindrical peripheral wall portion 3 and a top plate portion 2 that closes one end of the cylindrical peripheral wall portion 3 are formed. It is possible to use a suction anchor 1b in which a hook-like protrusion 4 is extended outwardly at the other end of the same and an annular protrusion 4b as a convex part is extended inwardly.

  In the case of the conventional configuration in which the hook-like protrusion 4 and the annular protrusion 4b do not exist, when the mode at the time of breakage due to pulling is the pulling breakage mode I, as shown in FIG. ) And the peripheral frictional force acting on the inner and outer peripheral surfaces is only a resistance force against pulling, but in the case of this modification, as shown in FIG. Since the earth and sand of the submarine ground 14 is held in the inner space 6 of the portion 3 as the middle-filled earth and sand, and the cylindrical ground region 33 is integrated with the cylindrical peripheral wall 3 by the hook-like projections 4, the pulling failure mode Shifts to pull-out failure mode III.

  Therefore, the weight of the earth and sand packed in the cylindrical peripheral wall portion 3 by the annular protrusion 4b is added as a new resistance force, and is integrated into the cylindrical peripheral wall portion 3 by the hook-shaped protrusion 4 as in the above-described embodiment. Not only the weight of the ground region 33 but also the frictional force at the boundary surface (shear surface) between the ground region 33 and the surrounding seabed 14 is subtracted from the peripheral surface frictional force at the outer peripheral surface as resistance during pulling out. Since it is added, the yield strength of the suction anchor 1 against pulling out can be greatly improved.

  Note that it is also possible to omit the hook-like protrusion 4 of the modification shown in FIG. 5 and employ the suction anchor 1c shown in FIG.

  In such a configuration, the pulling failure mode only shifts from the pulling failure mode I to the pulling failure mode II. However, as described above, the weight of the earth and sand packed in the cylindrical peripheral wall portion 3 is added as a new resistance force. For this reason (excluding the peripheral frictional force on the inner peripheral surface), it is possible to improve the yield strength of the suction structure against pulling out to some extent, and since no convex portion is formed on the outer peripheral surface of the cylindrical peripheral wall portion 3, the suction anchor It becomes possible to suppress the overall size of 1c and to facilitate handling and other handling.

  In the present embodiment, the hook-like protrusion 4 is extended in a direction orthogonal to the cylindrical peripheral wall portion 3, but instead of this, as shown in FIG. 7 (a), it is opposite to the cylindrical peripheral wall portion 3. Although not shown, the hook-shaped protrusion 4c extending obliquely on the same side as the cylindrical peripheral wall portion 3 may be employed. is there.

  Further, in the present embodiment, the hook-like protrusion 4 is provided over the entire circumference of the cylindrical peripheral wall portion 3, but instead of this, as shown in FIG. You may make it extend in multiple outward along the outer peripheral surface of the lower end of the cylindrical surrounding wall part 3 so that it may mutually space apart.

  In addition, while the above-described modified example in which the convex part is configured to extend obliquely and the above-described modified example in which the convex part is configured with a plurality of projecting pieces can be similarly applied to the annular protrusion 4b, These modifications can be arbitrarily combined.

  Further, in the present embodiment and its modified examples, the case where the suction structure according to the present invention is used as a suction anchor has been described. However, the above-described suction anchors 1, 1b, 1c and their modified examples are all skirt suctions. It can be used as a basis.

  FIG. 8 shows an example in which a skirt suction foundation 73 having the same configuration as the suction anchor 1c is sunk in the seabed ground 14 in the same manner as in the above-described embodiment, and a plurality of skirt suction foundations 73 are arranged in a row. A caisson 71 is placed on the top plate part 2 along the arrangement row of the skirt suction foundations as a breakwater, and the caisson 71 is the top plate part 2 of the skirt suction foundation 73 and stands on the land side. The leg part is made to contact | abut to the made stopper 72. FIG.

  Even in such a configuration, the skirt suction foundation 73 has a large resistance to pulling out, like the suction anchor 1c, and thus can prevent the caisson 71 from falling over due to waves.

1,1b, 1c Suction anchor (suction structure)
2 Top plate part 3 Cylindrical peripheral wall part 4 Hook-like projection (convex part)
4b Annular protrusion (convex part)
4c Spider-like protrusion (convex part)
4d Projection (convex part)
5 Drainage hole 14 Seabed ground (waterbed ground)
31 Mooring line (Mooring means)
32 Connecting part 73 Skirt suction foundation (suction structure)

Claims (5)

In the suction structure formed with a cylindrical peripheral wall portion and a top plate portion that closes one end thereof, and formed a drainage hole in the top plate portion,
When a pulling force is applied in a state in which the cylindrical peripheral wall portion is penetrated into the water bottom ground, the peripheral surface of the cylindrical peripheral wall portion has a bowl shape so that a resistance force against the pulling force acts from the water bottom ground. A suction structure having ribs, spirals, or other convex portions. The suction structure according to claim 1, wherein the convex portion is provided in the vicinity of the other end of the cylindrical peripheral wall portion. The suction structure according to claim 1 or 2, wherein the convex portion is provided on at least the outer peripheral surface of the peripheral surface of the cylindrical peripheral wall portion. The suction structure according to any one of claims 1 to 3, wherein a connecting portion to which the mooring means can be connected is provided on an upper surface of the top plate portion. The suction structure according to any one of claims 1 to 3, wherein the top surface of the top plate portion is configured so that a seawall, a breakwater, a main tower of a bridge, and other port structures or marine structures can be placed thereon. body.

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