JP2000087330A - Construction method for marine structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To construct a foundation rubble-mound on a superposing sheet member and arranging a deformable heavy mat member at the ends of the superposing sheet to prevent scouring of the bottom of the sea by the mat member and stably support a structure when the structure is constructed on a soft bottom ground of the sea. SOLUTION: When a caisson 1 is constructed, a superposing sheet member 10 is laid on the bottom ground 7 of the sea and mat members 15 are integrally disposed at both sides and then, a foundation rubble-mound 4 is constructed. The ends of the foundation rubble-mound 4 are placed on the superposed part of the superposing sheet member and the mat member to prevent influence against the rubble mound by deforming the mat member so as to cover the slope face of the scoring part even when the scoring has arisen in the bottom ground of the sea.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the protection of the ground in places where the seabed is susceptible to drafts and scours, such as artificial reefs, submerged breakwaters, breakwaters and jetties. Regarding members.

[0002]

2. Description of the Related Art When constructing marine structures such as breakwaters, quays, seawalls, etc., in general, the ground on the seabed is leveled, and a foundation rubble embankment having a predetermined height is constructed thereon. A caisson-like structure is installed on the upper surface of a rubble dike and constructed. When the foundation rubble dike is constructed, if the ground is soft, the ground improvement work is performed, and then the foundation rubble dike is constructed on the ground,
A caisson is placed on the foundation rubble dike. As the structure, a concrete box-type or steel structure, a hybrid caisson in which a steel structure is coated with concrete having a predetermined thickness on its surface, and the like are used. Further, the caisson is constructed on land, floated on the sea, towed to the construction site, or transported in a state of being suspended by a crane, etc., submerged in the sea surface at the structure construction site, and placed on the foundation rubble dike Is placed.

[0003] For example, a breakwater exemplified as a general marine structure is constructed as shown in FIG. 13, and a foundation rubble dike 4 made of rubble is constructed on a seabed ground 7, and its upper surface is made flat. A structure such as a caisson 1 is placed on the leveled upper surface to construct the structure. A mat 3 for increasing friction is arranged between the upper surface of the foundation rubble dike 4 and the bottom plate 2 of the structure 1 such as a caisson. The mat 3 is used when the caisson is manufactured on land. The bottom plate 2 is often integrally attached to the lower surface of the bottom plate 2.

The basic rubble dike for supporting the caisson is constructed on the seabed ground where the above-mentioned ground improvement has been performed. However, where the construction site of the marine structure is easily affected by tidal currents and waves. However, there is a problem that the seabed is sucked out or scoured. Therefore, conventionally, asphalt mats, fiber sheet members, etc. are laid on the foundation ground of the basic rubble dike to protect the ground such as sandy ground from sucking and scouring, and stabilize the basic rubble dike supporting the structure. Such means are used. As a method of protecting the seabed and a sheet-like protective member used for the method,
For example, as shown in Japanese Patent Application Laid-Open No. 7-82719, it is known to use a polymer sheet in which a synthetic fiber sheet having water permeability but not allowing sand or the like to pass through and a wire mesh are stacked. And by protecting the seafloor ground using the superposed sheet, the sand or the like of the ground is not sucked out or scoured by the influence of waves or tidal currents, and can favorably perform the supporting action on the base rubble embankment. At the same time, in the case of constructing a basic rubble dike by dumping rubble on the seabed via a superposed sheet member, the characteristic that the basic rubble dike can be stably constructed on the soft submarine ground can be exhibited.

[0005]

As described in the prior art,
When a base rubble dike is constructed on the seabed ground 7 on which the superposed sheet member is arranged, in order to protect the submarine ground located at the end of the base rubble dike from scouring, the construction site of the structure is It is necessary to set the laying range of the superposed sheet member in accordance with the geology of the seabed. In this regard,
In the conventional example, the projecting length of the overlapped sheet member from the end of the foundation rubble dike is set to a length that can prevent scouring, and a weight band is arranged at the tip end of the overlapped sheet member, whereby the seabed ground is When scouring occurs, it is shown that the weight band arranged at the end of the superposed sheet member enters the scouring section together with the superposed sheet member so as to prevent scouring of a certain value or more from occurring. I have.

However, merely arranging a gabion or the like as the above-mentioned heavy band may not be able to prevent scouring from progressing to the tip of the foundation rubble dike, and may not be able to hold down wide scouring scouring. Often required. In addition, especially in the sea area where the tidal current is fast, the sea area where the waves are rough, the tip of a basic rubble embankment facing the open sea such as a breakwater, and the seabed is sandy or soft stratum, sufficient In many cases, it is required to adopt appropriate countermeasures, and in order to stably install marine structures, higher durability than conventional construction methods is required.

The present invention is to improve the stability of the conventional structure as described above, in which a mat layer of an arbitrary length is integrally attached to the tip of the superposed sheet member, and the mat layer is formed on the seabed ground. The purpose of the present invention is to provide a construction method of an offshore structure capable of easily curving against scouring and preventing the progress of scouring, and stably protecting a foundation rubble dike supporting a caisson. I have.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a polymerization method which has flexibility and toughness and which allows water to pass through but not sand or the like on a submarine ground surface and on a foundation rubble dike constructed on the submarine ground surface. A marine structure constructed in such a manner that a sheet member and a mat member connected to an end of the superposed sheet member via a superposed portion are provided and provided, and an end of a foundation rubble embankment is placed on the mat member. About. The invention according to claim 1 of the present invention is characterized in that the mat member is arranged by arranging unit mats via an overlapping portion, and using a connecting means provided on the unit mat, connection with the superposed sheet member is performed. I do.

In the present invention, as described above, in the present invention, the superposed sheet member is formed by superposing a fiber layer and a wire mesh layer, and a mat member is integrally formed at an end of the superposed sheet member. By providing, when a scour part is formed in the seabed ground, it is easily deformed along the slope of the scour part, so that the scouring action can be prevented from reaching the base of the foundation rubble dike The foundation rubble dike can be supported in a stable state, and the structure can be prevented from collapsing. Further, the fixing of the mat member to the superposed sheet member is performed using the superposed portion and the connection wire, and the mat member is provided so as to cover a predetermined range of the mat member from the superposed portion so as to cover the end of the foundation rubble dike. Can be prevented from separating from the superposed sheet member even when the end of the member is bent toward the scouring portion.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A construction method of an offshore structure according to the present invention will be described with reference to the illustrated example. The example shown in FIG. 1 is a case where, as shown in FIG. 13, the foundation rubble dike 4 is constructed on the seabed ground 7 and the caisson 1 is installed on the foundation rubble dike 4 to construct an offshore structure. Is shown. In this embodiment, when constructing the basic rubble dike 4, the superposed sheet member 10 is arranged on the seabed ground 7 so as to cope with the dumping of the rubble at the basic rubble dike. A mat member 15 having a predetermined length (width) is arranged on each side of the member 10, and the superposed sheet member 10 and the mat member 15 are integrated. Further, the mat members 15 arranged on both sides of the superposed sheet member 10 are, like the friction increasing members arranged on the lower surface of the caisson, etc., asphalt mastic having a reinforcing member integrally incorporated therein to a predetermined thickness. What was constituted as the formed mat member is used.

The structure shown in FIG. 1 will be described with reference to the plan view of FIG. 2. A foundation rubble dike 4 is constructed within a predetermined range on both sides of a caisson 1 installation site.
The overlapped portion 17 of the overlapped sheet member 10 and the mat member 15 is provided within a predetermined range slightly inside the end of the sheet. The end of the basic rubble embankment 4 is arranged so as to act as a holding member with respect to the overlapping portion 17, and the base of the mat member 15 is fixed and held. In this embodiment, the length L of the mat member 15 protruding from the end of the foundation rubble dike 4 is set to be substantially the same. However, the mat member 15 has a matte member between the rough open sea side and the calm inland sea side. May be made different, and the protrusion length L can be arbitrarily set according to the predicted occurrence of scouring. Also, if scouring is expected to occur only on one side, such as on the open sea side of the structure, the projecting length of the mat member on the inland sea side is formed very short, and the construction unit price of the mat member is reduced. It is also possible.

As shown in the example of FIG. 3, the end of the superposed sheet member 10 covering the seabed ground 7 is located inside the end of the foundation rubble dike 4, and the end of the foundation rubble dike 4 On the other hand, the end portion of the mat member 15 is provided so as to extend outside the foundation rubble dike by a length L in a state where the end portion enters. And
A superposed portion 17 in which the superposed sheet member 10 and the mat member 15 are overlapped is set by L1, and at a predetermined position of the superposed portion 17, the mat member 15 is locked to a wire mesh layer to integrate the two members. I have. Further, in the basic rubble dike 4, a rubble layer 5 having a predetermined thickness is formed on the superposed sheet member 10 and the superposed portion, and a coating stone layer 6 covering the surface is formed with a predetermined thickness. However, this structure is constructed in the same way as a general foundation rubble dike.

As shown in FIG. 3, the base of the mat member 15 is inserted into the lower part of the foundation rubble dike, and the wire mesh layer 1 is formed.
In the case where the means for locking and holding at the end portion 0 is used, FIG.
As shown in (1), the resistance of the mat member to scouring can be favorably exhibited. That is, when the seabed 7 is scoured and the scouring portion 8 is formed, the end of the mat member is bent toward the scouring portion 8 in accordance with the change in the shape of the ground, and the tip portion 15a is formed. Enters the hole. Then, as described above, the tip portion 15a is bent and falls so as to cover the slope of the scouring portion, so that the mat member 15
Even when a force is applied such that the leading end of the sheet is pulled outward, the overlapping portion 17 and the locking members of the two sheets prevent the mat member from moving, so that the mat member does not come off from the wire mesh layer and slip out. Be able to hold.

The superposed sheet member 10 and the mat member 15 arranged below the foundation rubble embankment are configured as shown in FIG. 5, and the superposed sheet member 10 has a fiber layer 11 disposed on the lower surface. The wire mesh layer 12 is disposed on the upper surface thus formed, and the two are integrated by using a fixing member, so that two types of sheet-shaped members are superposed. A mat member 15 arranged and fixed on both sides of the superposed sheet member 10 is
The superposed sheet member 10 via the superposed portion 17 and the fixing portion 16
So that the mat member can resist even if a force is applied to move the mat member outward and away from the superposed sheet member. As the fixing portion 16, any fixing means can be used. For example, an eggplant ring or other one which can be fixed by one touch can be used, and is provided so as to protrude from the end of the mat member. Using a locking wire or the like as a locking means, the wire is locked to the wire of the wire mesh layer via a fixing portion provided at an end of the wire. In the mat member 15, the fixing portions 16 disposed between the mat member 15 and the superposed sheet member can be provided at arbitrary intervals.

In the mat member 15, a rectangular unit mat 20 is provided so as to be continuous with an adjacent unit mat via an overlapping portion 21, so that a large number of unit mats 20 are formed. Even if it is arranged, it can act as a single mat member. Also,
As the unit mat 20, a member similar to an asphalt mat conventionally used for harbor construction is used, and the unit mat is configured to have a width of 5 m and a length of 10 m or more, for example. I have. When a mat member is formed by combining a large number of the unit mats, when a scouring portion of the seabed occurs at a position corresponding to a part of an end of the mat member, the unit mat at the corresponding position is formed. The end of the sword is deformed corresponding to the scouring part, and bends into the scouring part, thereby acting to prevent scouring and suction from progressing.

If one unit mat is deformed, it is supposed that a deviation occurs at an overlapping portion between adjacent unit mats. However, such a local deformation of the end of the unit mat may occur. Even if it occurs, the whole continuity of the mat member is not hindered. Further, when the mat member 15 is constructed by combining the unit mats as described above and is arranged around the superposed sheet member, even if scouring occurs in a wide range at the front end of the mat member, each unit mat is 4 is deformed in the state as shown in FIG. 4 to cover the slope of the scouring portion, so that the ground portion covered by the unit mat can be protected. And, since scouring is prevented from progressing to the base of the base rubble dike, scouring does not progress to the portion of the superposed sheet member, and the basic rubble dike can be held in a stable state.

In a general unit mat, as shown in FIG. 6, a large number of cargo handling wires 23 parallel to the width direction are used.
Are arranged, and an eye portion 24 formed at the end of the cargo handling wire is engaged with a hanging device to be used for cargo handling of the unit mat. Therefore, in this embodiment, a connection wire 25 as shown in FIG. 7 is attached to an end of the cargo handling wires 23 arranged on the unit mat 20 to connect the wire to the wire mesh layer. Is composed. In the example shown in FIG. 7, like the connection wire indicated by reference numeral 25, the base fixing portion 26
And the connecting portion 27 can be arranged at the protruding end.

In addition to the connection to one cargo handling wire, a connecting wire 25a fixed to each of the two cargo handling wires at the ends buried in the mat by using base fixing portions 26a. It can also be configured as Furthermore, as shown as connection wires 25b, they are arranged in a state of being orthogonal to the cargo handling wires in the length direction of the unit mat,
A base fixing portion 27 provided at an end of the loading wire 25b
Means for fixing to the wire mesh layer via b can also be used. The connection method using the connection wires uses means capable of stably holding the mat member using the connection wires against a tensile force estimated to be applied to the mat member, and is used to construct a structure. It can be arbitrarily selected according to the conditions of the sea area.

The connecting wires as connecting means as shown in FIG. 7 are attached to the unit mat body as disclosed in FIGS. 8 to 10, respectively. In the example shown in FIG. The connection to the wire netting layer can be dealt with by exposing the connection to the mat via the connection portion 27 toward the upper surface of the mat and extending the free end of the connection wire to an arbitrary length. To do. Further, as shown by a chain line in FIG. 8, the connection wires 25 can be projected from the lower surface of the mat, but the connection wires are exposed at arbitrary positions above and below the mat. It is arbitrarily selected according to the construction conditions.

The example shown in FIG. 9 shows a case where the connecting wires are exposed from the ends of the unit mat, and the connecting wires are buried from the cargo handling wires at the ends to the ends of the unit mat. Accordingly, there is an advantage that the connection wire can be held by the asphalt layer. In the example shown in FIG. 10, a long connection wire 25b is buried and provided so as to be orthogonal to the cargo handling wire 23, and this is shown in a cross section corresponding to the connection wire 25b in FIG.

As described above, the unit mat 20 described in the present embodiment has an internal reinforcing member between the asphalt layers to be cast in two layers similarly to the asphalt mat used in the conventional marine construction. 22 and loading wire 23
... are arranged and integrated with each other. As the internal reinforcing member, a material such as a glass cloth or a wire mesh is used, and the upper and lower asphalt layers are connected via the internal reinforcing member, so that even when a hanging load is applied to the cargo handling wire, the material is unloaded. The wire is held so that it does not come off. And when the end of the connection wire is fixed to the cargo handling wire as described above,
Since the base fixing portion is fixed and held in the asphalt layer, the connection wire does not come off the mat even when a tensile force is applied to the connection wire. Further, as shown in each of FIGS. 7 to 9, the connection wire is connected to the cargo handling wire at one or a plurality of locations via the base fixing portion, whereby the holding action of the unit mat by the connection wire is achieved. It will be possible to ensure that it is fully demonstrated.

In the example shown in FIG. 11, instead of connecting the connecting wires as shown in the above embodiments to the cargo handling wires and providing them, a rope net 30 is provided at the end of the unit mat 20.
Are provided integrally, and the connection wires 32 are arranged using the end ropes 31 of the rope net 30. As the rope net 30, as in the case of a wire net conventionally used for cargo handling, a wire net formed by weaving a wire rope into a net shape can be used. As the wire used for the rope net, Can be of any thickness. In the example of FIG. 11, as shown in FIG. 10, the rope net 30 is disposed so as to overlap with the internal reinforcing member of the unit mat 20, and the end rope 31 of the rope net 30 is united by a predetermined length. Expose from the end of the mat.

By fixing the end rope 31 and the superposed sheet using an arbitrary connecting member, the end of the unit mat is connected to the superposed sheet. Because of the connection of the wire or the wire, the connection can be easily made even by using a simple clip or the like. When a rope net buried in the unit mat is used, the connection means with the superposed sheet can be connected at any position, and can be connected to the magnitude of the force applied to the unit mat. The connection point can be selected.

FIG. 12 shows an example in which a rope net 30 having substantially the same size as the internal reinforcing member of the unit mat 20 is used, and a cargo handling wire and a connection wire are attached via the rope net 30. I have. In this embodiment, a rope net 30 can be used in place of a conventionally used reinforcing wire or reinforcing bar as an internal reinforcing member of a unit mat, and a rope disposed around the unit mat With respect to the end rope 31 of the net, a connecting wire 32... And a cargo handling wire 35... Provided with an eye member 36 at the end can be connected and provided.

Since the connection wire and the cargo handling wire can be connected to the end of the crossed wire of the rope net and arranged, the tension given to the cargo handling wire during cargo handling can be reduced. On the other hand, the vertical wires of the rope net correspond to each other, and the horizontal wires of the rope net correspond to the tension applied to the connection wires after connection with the superposed sheet. Therefore, when the rope net is used by being buried integrally inside the unit mat, the rope net itself serves as a reinforcing member and, at the same time, has two tensions, one for cargo handling and one for connection. It becomes possible to function as a burden member.

Instead of the rope net, in the unit mat shown in this embodiment, a net-shaped member such as a wire net can be used.
It is possible to arrange in the same manner as in the example of the rope net 30 and integrally form with the unit mat, and attach the connection wire and the cargo handling wire respectively. Further, in addition to the wire net, it is also possible to use a net member made of synthetic fiber and to be provided integrally with the unit mat in the same manner as the rope net. And the cargo handling wire can be arranged at the respective ends.

Further, instead of the rope net, a high-strength resin net called "geogrit" or "polymer grid" can be used. The resin net is formed as a net having high strength by forming a hole in a thick sheet such as polypropylene or high-density polyethylene and stretching it while heating in a uniaxial or biaxial direction. Then, the resin net is replaced with the resin net shown in FIG.
By burying and arranging inside the unit mat as shown in 1 and 12 and connecting and arranging the connecting wire and the cargo handling wire, respectively, the same operation as the rope net can be borne. .

When the resin net is used, a large force is not applied to the connection with the superposed sheet as in the case of cargo handling. Therefore, even if the connection wire is directly connected to the resin net. Considered good. On the contrary,
When it is expected that a large tension is applied to the position where the cargo handling wire is connected, a cargo handling wire provided with an eye member at the end as shown in FIG. 6 or the like may be attached and used for cargo handling. It is also possible to prevent the weight of the unit mat from being applied to the resin net when the unit mat is lifted and laid.

In each of the above embodiments, a case has been described in which an offshore structure is constructed by installing an existing structure such as a caisson on a foundation rubble dike. However, the method of constructing an offshore structure of the present invention is as follows. It can also be applied to structures such as breakwaters and submerged breakwaters for wave extinction. In the structure such as the submerged levee, the basic rubble dike 4 as shown in FIG. 1 is constructed to a position slightly lower than the sea surface, and the covering stone layer of the basic rubble dike is constructed with a large one. Also, a general wave-dissipating block will be constructed on the foundation rubble dike in a turbulent pile. And even when constructing a submerged levee without protruding above the sea surface like the caisson, scouring of the seabed ground by the mat member can be prevented, and the submerged levee can be maintained in a stable state.

It should be noted that the unit mat having the above-described structure is not only fixedly connected to the superposed sheet member through the connection wire but also when a large number of unit mats are arranged to form the mat member. It is also possible to connect the unit mats to be connected or between arbitrary unit mats using a cargo handling wire. Connecting the unit mats via the cargo handling wires is effective in integrating the mat members without separating many unit mats individually, and is particularly effective in sea areas with rough waves or washing. For submarine ground where digging is easy to proceed, the mat members are prevented from being individually lifted, preventing the base rubble embankment from becoming unstable due to scouring of the submarine ground, and maintaining a caisson stable Can be done.

In the above embodiment, any size of the superposed sheet member can be used. For example, the size of the unit of the superposed sheet member is limited by the convenience of cargo handling and laying work. In this case, a plurality of polymerized sheet member units can be connected on the seabed ground to form a polymerized sheet member of a predetermined size. In order to connect the polymerized sheet member unit, a wire mesh layer can be connected, but any other connecting means can be used. Further, the unit body of the superposed sheet member is arranged so that the ends overlap with a predetermined width, and a tension member such as a long wire or a wire is arranged over a plurality of wire mesh layers, and the end portion of the tension member is disposed. When a means for connecting the connection wires of the unit mat is used, the integration of the mat member and the superposed sheet member can be set better.

[0032]

As described above, the polymerized sheet member is constituted by polymerizing a fiber layer and a wire mesh layer, and a mat member is integrally provided at an end portion of the polymerized sheet member. It can counter the dumping of rubble, etc., and can prevent suction of sand and the like from the seabed. In addition, the mat member disposed at the end of the superposed sheet member easily deforms along the slope of the scouring portion when the scouring portion is formed on the seabed ground, so that the scouring operation has a basic rubble dike. The base rubble dike can be supported in a stable state, and the structure can be prevented from collapsing. Further, the fixing of the mat member to the superposed sheet member is performed using the superposed portion and the connecting wire, and the mat member is provided so that the end of the base rubble dike covers a predetermined range of the mat member from the superposed portion. Can be prevented from separating from the superposed sheet member even when the end of the member is bent toward the scouring portion. Also, in the case where the means for protecting the undersea ground of the present invention is applied to a submerged embankment, similarly to the case of the above-mentioned structure, the protection of the foundation rubble dike against scouring and suction can be performed well.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a construction state of a marine structure of the present invention.

FIG. 2 is a plan view of FIG.

FIG. 3 is an explanatory diagram of an arrangement state of a superposed sheet member and a mat member with respect to an end of a foundation rubble dike.

FIG. 4 is an explanatory diagram when scouring occurs at an end of a mat member.

FIG. 5 is an explanatory view showing a configuration of a superposed sheet member and a mat member.

FIG. 6 is an explanatory diagram of a configuration of a general asphalt mat.

FIG. 7 is an explanatory diagram of an example of attaching a connection wire to a unit mat.

FIG. 8 is an explanatory diagram showing an attached state of a connection wire.

FIG. 9 is an explanatory diagram of another example of a state of attachment of connection wires.

FIG. 10 is an explanatory diagram of another example of a state of attachment of connection wires.

FIG. 11 is an explanatory diagram of an example in which a rope net is used as a connection unit.

FIG. 12 is an explanatory diagram of an example in which a large-sized rope net provided integrally with a unit mat is used.

FIG. 13 is an explanatory diagram of a construction state of a general offshore structure.

[Explanation of symbols]

1 caisson, 2 bottom plate, 3 mat member,
4 foundation rubble mound, 5 rubble stone layer, 6 covering stone layer, 7 submarine ground, 8 scouring section, 10 polymer sheet material, 11 fiber layer, 12 wire mesh layer, 1
5 mat member, 20 unit mat, 21 overlapping portion, 22 internal reinforcing member, 23 cargo handling wire, 25 connection wire, 30 rope net,
31 end rope, 32 connecting wire.

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 000230711 Nihon Marine Construction Co., Ltd. 2-10-9 Akasaka, Minato-ku, Tokyo (72) Inventor Tatsu Waki 1-2-29-4 Tsurugamine, Asahi-ku, Yokohama-shi, Kanagawa Inside World Engineering Co., Ltd. (72) Inventor Masami Orikasa 1-29-4 Tsurugamine, Asahi-ku, Yokohama, Kanagawa Prefecture Inside World Engineering Co., Ltd. (72) Inventor Mitsuru Nonotada 2-11-20 Tamagawa, Ota-ku, Tokyo No. Japan Road Co., Ltd. (72) Inventor Takahiko Ito 3-13-1 Kyobashi, Chuo-ku, Tokyo Inside Taisei Rotec Co., Ltd. (72) Inventor Katsuo Matsuzaki 2-10-9 Akasaka, Minato-ku, Tokyo Nippon Marine Construction Co., Ltd. (72) Inventor Hiroshi Nakano 2-10-9 Akasaka, Minato-ku, Tokyo Nippon Marine Construction Co., Ltd. F-term (reference) 2D018 BA12 DA02

Claims (1)

[Claims] 1. A polymer sheet member having flexibility and toughness and allowing water to pass through but not sand, etc., on a seabed ground surface and a lower surface of a foundation rubble dike constructed on the seabed ground surface. And a mat member connected to the end portion of the rubble embankment via a superposed portion, and the mat member is a unit mat. Are arranged side by side via a superposed portion, and are connected to a superposed sheet member using connection means provided on the unit mat.