JPS596998B2 - culvert joint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to connection of cylindrical culverts made of concrete or steel, and cylindrical culverts assembled from a plurality of segments, such as sewerage, water supply, public ditches, underground passages, etc. This relates to joints for underdrains used in

Conventionally, as a joint for an underdrain, a short cylindrical flexible member made of rubber or synthetic resin was installed along the inner peripheral surface of the underdrain, and both ends of the flexible member were anchored to the inner peripheral wall of the underculvert to be connected. Alternatively, a bolt is installed on the back of the flexible member, and a cylindrical flex member is suspended by the bolt, and the distortion of the flex member due to the difference in water pressure between the inside and outside of the culvert is suppressed to a small amount. The flexible member is designed to stop water and absorb relative displacement between the joints of opposing underdrains.

However, when using any type of culvert joint, if the two connected culverts move away from each other in the axial direction due to uneven ground subsidence or relative displacement of the ground during an earthquake, a large amount of gap will be created between the culverts. Sediment from outside the culvert enters through the gap and deforms the flexible member inward, resulting in decreased durability and damage to the flexible member, as well as obstructing the flow inside the culvert and There was a problem of damage to internal piping and structures.

In order to solve these problems, the applicant of this patent has
An anchoring member having a seat in the center and a body at each of the outer peripheral positions is attached to the opposing end surfaces of the underdrain to be connected, and a flexible member is installed between the seats of the anchoring member. At the same time,
A large number of rod-shaped load-bearing members are arranged in parallel at the same positions inside and outside the flexible member, with both ends of the rod-shaped load-bearing members inserted into the casing of the anchoring member so as to be movable within a certain range but not detachable; An underdrain joint OS has been proposed which allows appropriate displacement between both underdrains, prevents separation of the joint, and prevents harmful deformation of the flexure member.

In other words, the proposed culvert joint prevents the intrusion of earth and sand into the area where the culvert is installed, and also connects a group of parallel load-bearing members to the culvert to prevent excessive relative displacement between the two culverts to be connected. It had a structure in which it was installed at each of the inner and outer positions.

However, since load-bearing member groups require a considerable amount of work to assemble and are expensive, providing two groups of them around the flexible member would greatly increase the amount of work required to assemble the culvert joint itself. In addition, the structure of the casing of the anchoring member that supports both ends of the load-bearing member also requires a considerable amount of space, so it is difficult to provide a casing inside or outside the joint. The size of the fitting itself increases, which increases the cost.
Problem 03 was that it led to an increase in the amount of excavation required to install joints for the culvert.

In the present invention, when one flexible member for the purpose of water stopping between the inside and outside of a culvert in a culvert joint is provided between anchoring members, both the inner and outer sills are applied to the flexible member. A load-bearing member must be provided at the same location on the inside and outside of the flexible member, but
When two flexible members are provided, by providing a group of load-bearing members between them, the inner circumferential flexible member receives only the inner wall, and the outer load-bearing member receives only external pressure, so that each deforms only in one direction. Focusing on the fact that it is sufficient to regulate the load-bearing member with a load-bearing member, this joint for an underdrain solves the above-mentioned conventional problem by configuring a structure in which a flexible member is provided at each outer circumferential position of one group of load-bearing members. The purpose is to provide

The present invention further provides another flexible member that protects the inner and outer flexible members at the inner and outer circumferential positions of the inner and outer flexible members, so that the flow of water in the culvert is improved. The purpose of the present invention is to provide a joint for an underdrain which solves the above-mentioned conventional problems while preventing the obstruction of the joint and preventing the function of the joint of the underdrain from being impaired due to the intrusion of earth and sand from the outside.

Below, practical examples of the dark joint of the present invention will be explained with reference to the drawings.

In Figure 1, the culverts to be connected are the primary covered sewer culverts A, A'l)5, which are divided into multiple pieces in the solid direction.
It is shown.

However, culvert A. The shape and type of A' are not limited to a circular shape or for use in a sewer, but may be other shapes such as a square, or other types such as a water supply or an underground passage.

Between the culverts A and A' to be connected, culvert joints Bb3 are interposed as necessary via joint segments A, , A; (not necessary), but usually this culvert joint Bb3
is placed in places where uneven ground subsidence is expected, such as culverts near vertical shafts.

Figure 2 shows the cross-sectional configuration of the culvert Tsujisen B. In the figure, symmetrical members are indicated by adding a dash to the reference numeral of one member, so that the other member can be easily distinguished from the other member. Omit the explanation as necessary.

In Figure 2, culvert Tsujisen B is connected to culvert A,
A pair of anchoring members 10.10' anchored to the end face of A', a large number of load-bearing members 20 arranged in parallel between the pair of anchoring members 10.10', and outer peripheral positions of the load-bearing members 20. An inner circumferential flexible member 30 and a Togawa-cho flexible member 40 made of rubber or synthetic resin are installed astride the anchoring member 10.10', and the anchoring member 10. 10'
and a cover means 60 installed astride the anchoring member 10, 10' at the inner peripheral position of the Uchikawa town flexible member 30.

The anchoring member 10 includes a housing part 12 having an opening 11 on one side, and an end plate 13 extending from the same position on the outside of the housing part 12 toward the outer circumferential direction of the joint to form a joint part with the end surface of the dark IA. As shown in FIG. 3, in the direction of the joint cylinder, a plurality of segments are assembled into a cylinder shape in the same direction as the joint.

This assembly in the joint (self) direction is performed by a connecting portion 14 provided on the underdrain A side of the housing portion 12 as a part of the anchoring member 10.

That is, the connecting portion 14 has an end plate 15 extending in the joint axial direction on the joint circumferential end face of the segment, and the end plate 15 is formed to match the end plate of the connecting portion of the adjacent segment. This is done by inserting a bolt 17 into the bolt hole 16 and tightening the segments together.

An insertion hole 18 for inserting the load-bearing member 20 is opened on the underdrain A' side of the housing portion 12'.
Then, the load-bearing member 20 is sequentially moved between the anchoring members 10 and 10' with both ends thereof inserted into the housing part 12 through the opening 11.11' having a notch opening partially enlarged in the circumferential direction of the joint. This allows it to be loaded.

The insertion hole 18 has a plate 19θ that closes the insertion hole 18.
It is tightened and fixed with 5 bolts.

Note that the insertion hole 18 only needs to be provided in at least one of the housing parts 12 and 12'.

In addition, the load-bearing member 20 can be inserted between the anchoring members 10 and 10' by making a part of the housing part 12 and 12' removable, and after removing this detachable part and inserting the load-bearing member 20. , you can also do this by attaching the detachable part).

On the end face of the casing 12 of the anchoring member 10 facing the anchoring member 10', there are a seat part 12a for coupling the inner flexible member 30 and a seat part 12a for connecting the outer peripheral flexible member 40 at the inner and outer peripheral positions of the opening 11, respectively. A coupling seat 12bf)'5 is provided.

The seat portions 12a, 12b may be formed directly on the end surface of the housing portion 12, or, as will be described later, water stop means or cover means O may be provided on the inside, further inside the Togawa-machi flexible member, or on the Togawa surface. '3 When provided, even if it is indirectly formed at the same position inside and outside the opening 11 by supporting the water stop means or cover means, or by being formed on the surface of the holding member. good.

The anchoring member 10 is attached to the culvert A in the same manner as before.
b5 In the case of an underdrain made of concrete, the anchor 14a provided on the end face of the anchoring member 10 on the underdrain A side is embedded in the underdrain A, or the underdrain is made of segments made of concrete or steel. In this case, this is done by bolting the anchoring member 10 to the culvert A.

The load-bearing member 20 installed astride between the anchoring members 10 and 10' is
It consists of a rod-shaped body whose both ends are inserted into the housing part 12.12' through the opening 11.11' so as to be movable within a certain range but not to be removed.

A large number of load-bearing members 20 are arranged in parallel between the anchoring members 10 and 10', and the load-bearing members # form a kind of cylindrical body b5.

A protrusion 21 is formed at the end of the load-bearing member 20, and by making the height h1 of the protrusion 21 smaller than the height h2 of the opening 11 of the casing 12 of the anchoring member 10, the joint shaft This is intended to prevent it from coming off in any direction.

Adjacent load-bearing member 20. The spacing between the joints 20 in the same direction is regulated so that they are biased and a large gap is created between the load-bearing members 20, 20.

2, 4, and 5 show this load-bearing member 20. 2
The case where the interval regulation of 0 is achieved by attaching comb-shaped plate pieces 23 to the casing part 12 with bolts and inserting and supporting an appropriate number of load-bearing members 20 (two in the figure) between the comb teeth. It is shown.

However, the spacing regulation of the load-bearing members is not limited to this illustrated example; for example, as shown in FIG. 2
A joint material 24 made of rubber, synthetic resin, asphalt, caulking material, etc. may be interposed between the holes to regulate the spacing, and the load-bearing member may be a load-bearing member with a protrusion and a hole. Consists of two types of load-bearing members: a load-bearing member with holes,
The mutual positional relationship may be regulated by inserting the protrusions into the holes, and the spacing regulating means may be arbitrarily selected.

Anchoring members 10, 10' are installed at the internal fixed position of the 20 groups of load-bearing members.
In between, an internally fixed flexible member 30b5 made of rubber or synthetic resin is straddled.

The inner flexible member 30 is formed of a short cylindrical body having a wave-shaped cross section, for example, so as to be able to sufficiently follow the relative displacement between the underdrains A and A'.

The end portion of the flexible member 30 is formed in a shape that follows the end surface of the housing portion 12, and this end portion is held between the seat portion 12a of the housing portion 12 and the presser plate 31 and tightened with the bolt 32. It is fixed to the anchoring member 10 in a watertight manner.

As a result, watertightness between the inside and outside of the culvert is maintained regardless of the presence or absence of relative displacement between the culverts A and A'.

Since the Togawa-machi flexible member 40 is present, the inner peripheral flexible member 30
tJ3 receives only internal pressure, and the deflection of the inner flexible member 30 due to the internal pressure is supported by the force-bearing member 20 group.

At the outer periphery of the force-bearing member 20 group, an outer flexible member 40 made of rubber or synthetic resin is provided to straddle between the anchoring members 10 and 10', similar to the inner fixed flexible member 30.

The outer circumference flexible member 40, like the inner (4) town flexible member 30, is made of a short cylindrical body formed, for example, in a wave-shaped cross section so as to be able to sufficiently follow the relative displacement between the culverts A and A'. .

The end of the Sodomachi flexible member 40 is formed in a shape that follows the end surface of the seat 12b disposed on the outer periphery of the opening 11 of the housing 12, and this end is formed between the seat 12b and the presser plate 41. By clamping and tightening with bolts 42, the anchoring member 10 is fixed in a watertight state.

By providing the inner peripheral flexible member 30, the outer peripheral flexible member 40
Although only external pressure is applied to , the bending is supported by the force-bearing member 20 group due to the external pressure of the Sodomachi bending member 40 .

This configuration ensures a double water stop between the inside and outside of the underdrain.

Next, a case will be described in which a cover means, a water stop means, etc. are provided at the inner and outer positions of the inner and outer Togawa-machi flexible members.

On the inner surface of the joint of the end plate 13 of the housing part 12, there is an anchoring plate 70b5 extending in the same direction as the joint, which is a component of the underdrain A.
The end plate 1 is assembled using bolts, nuts 71, etc. while the segments are assembled into a cylinder in the same direction as the joints.
3 is assembled into one piece.

Further, on the inner side of the joint of the anchoring plate 70, a water stop member 5 outside the town flexure is provided.
A holding member 80 for supporting both ends of the bolt and
It is fixed to the housing end plate 13 with a nut 71.

The holding member 80 includes a plate body 81 that has a shape that follows the surface of the anchoring plate 70 and is divided into a plurality of parts in the direction of the joint station, and a plate body 81 that extends from the plate body 81 in the joint axis direction and toward the opposing anchoring member 10' side. It has a seat part 82 that is provided at a distance, and a horizontally extending part 83 that connects the outer peripheral position of the plate body 81 and the same position on the outside of the seat part 82.

In this case, a seat portion 12b for coupling the Togawa-machi flexible member 40 is formed on the end surface of the plate body 81 of the holding member 80 fixed to the end plate 13 of the housing portion 12 on the anchoring member 10' side.

At the outer position of the Togawa flexible member 40 and the holding member 80.80
Between the seat parts 82 and 82', an outer water stop member 50 made of rubber or synthetic resin with a reinforcing material embedded therein is installed astride.

The flexible external water stop member 50 is attached to the underdrain A. In order to prevent water leakage and intrusion of earth and sand from the outside when assembling the joint between A', and to prevent intrusion of water and earth and sand by following the relative displacement between dark IA and A' after assembly. It is provided to prevent this, and is made of, for example, a short cylindrical body with a bent cross-sectional shape.

The end portion of the flexible external water stop member 50 is connected to the seat portion 8 of the holding member 80.
2, and is firmly fixed to the holding member 80 in a watertight manner by sandwiching this end portion between the seat portion 82 and the holding plate 51 and tightening it with the bolt 52.

At the outer (4) position of the anchoring member 10.10', there is an extension part 83.
A skin plate 84 made of a thin steel plate is fixed by welding or the like to the outside of the extension portion 8 3 and 8 3 ′.

The skin plate 84 is mainly provided to prevent water leakage and intrusion of earth and sand from the outside, similar to the flexible outer circumferential water stop member 50 described above, when assembling the joint. It is constructed so that when a relative displacement occurs between A', it breaks and allows relative displacement freely.

However, even in this state, the flexible outer water stop member 50 maintains its strength and can deform to follow the displacement, so intrusion of earth and sand and water leakage are prevented, and the inner and outer Togawa Town flexible members 30. 40 maintains a sound watertight condition inside and outside the culvert.

Further inside the inner peripheral flexible member 30, there is an inner rigid flexible member 3.
A cover sheet 60 is provided as a cover made of rubber, synthetic resin, etc., covering the underdrains A and A' from the inside and at the same height as the inner peripheral surfaces of the underdrains A and A'.

The cover sheet 60 is provided to prevent dirt and other impurities from entering from inside after the joints between the underdrains A and A' are assembled, and to allow the water in the underdrains A to flow smoothly without being obstructed. It is something that was given.

The cover sheets 60 are joined together at the joint intermediate portion with their ends overlapping each other, and these ends are connected to the anchoring member 1.
It is cylindrically fastened with bolts (not shown) to metal fittings 61 attached to the inner peripheral positions of 0 and 10'.

FIG. 7 and FIG. 8 show other examples of actual sheets, and parts having configurations similar to those of the aforementioned example of actual sheets are designated by the same reference numerals as those of the aforementioned example of actual sheets. The explanation will be omitted.

In FIG. 7, an injection nozzle 90 with a removable cap is provided on the underdrain A side of the casing 12 constituting the anchoring member 10. A filler such as a foamable urethane resin is injected into the space as necessary.

This can prevent dirt and the like from entering the housing portion 12 and impairing the functionality of the load-bearing member 20 group.

In the example shown in FIG. 7, a cover sheet 6 is used as a cover made of rubber, synthetic resin, etc. at the inner peripheral position of the anchoring member 10.
0' is the anchoring member 10. 10' is made into an integral piece with no joint in the middle part so as to cover the internally fixed flexible member 30 which is installed astride between 10' and 10'.

FIG. 8 shows yet another example of leprosy, in which the anchoring member 1
Inner and outer bending members installed across 0.10' 30. 4
0 is formed into a triangular waveform cross-section, and the cover means 60 is formed into a cross-sectional waveform.

By making the cover sheet 60'' into a corrugated shape, the culvert A
, A' can be sufficiently tracked, but the flow resistance inside the culvert is slightly sacrificed.

Next, the function of the joint B of the underdrain will be explained.

Before a relative displacement occurs between the culverts A and A', the skin plate 84 and the cover sheet 60. 6 0',
60 is functioning normally, water is stopped between the inside and outside of the underdrain, and the intrusion of earth, sand, dirt, etc. into the joint B of the underdrain is prevented.

In addition, the water in the culvert can flow smoothly.

If a relative displacement occurs between dark IA and A' due to uneven settlement, earthquake, etc., only the skin plate 84 will be damaged while the displacement is small, and the flexible external water stop member 50 and cover sheath 1-6 will be damaged.
0.60' and 60'' are functioning normally and water is stopped between the inside and outside of the culvert.

The flexible outer water stop member 50 is reinforced with cloth or the like, so it has sufficient strength against the intrusion of earth and sand, but even if it is damaged by the intrusion of earth and sand, the Togawa Town flexible member 40 Since it is deformed and supported by the load-bearing member 20, the outer circumferential flexible member 40 will not be damaged and water-tightness will be maintained sufficiently.

If a larger relative displacement occurs between the dark IA and A', the displacement is restrained by the force-bearing member 20.

In other words, the displacement b5 in the culvert axis direction between culverts A and A'
When this occurs, the tip of the force-bearing member 20 comes into contact with the wall surface of the casing 12 to prevent further displacement of the culverts A and A' in the case of approaching direction, and the force-bearing member 20 in the case of displacement in the direction of moving away from each other.
The protrusion 21b5 engages with the edge of the opening 11 of the housing portion 12 to prevent further displacement of the underdrains A and A'.

Further, when a displacement occurs between the underdrains A and A' in the direction perpendicular to the underdrain axis direction, the state in which the load-bearing members 20 groups are arranged side by side changes from the state shown in FIG. 9 to the state shown in FIG. 10, and the load-bearing members 20. 20
The gap e, bj, and e' between the side surfaces of the comrades becomes small and eventually reaches zero, and further progress of displacement is restrained.

Therefore, by the 20 groups of load-bearing members, the culverts A, A
The displacement between ' is limited within a certain range both in the axial direction of the joint and in the direction perpendicular to the axial direction of the joint.

For this reason, a large displacement occurs and the water stop member 50 outside the town sill,
Even if the cover sheets 60', 60', and 60'' are damaged, the inner Togawa-machi flexure members 30 and 40 will not be forced to deform to the extent that they will be damaged, and the culverts A.A' will be deformed by an appropriate amount. This means that the watertight state of the inner and outer peripheries of the culvert is always maintained while being restrained by the relative displacement of the culvert.

The above-mentioned functions and actions are mainly performed by the 20 groups of load-bearing members in one stage and the outer flexible members 30 and 40 of the two stages, which are respectively provided on the inner and outer peripheries of the 20 groups of load-bearing members. Therefore, although the load-bearing member group is arranged at the inner and outer peripheral positions of the conventional one-stage flexible member, that is, the load-bearing member group is provided at the inner and outer circumferential positions of the conventional one-stage flexible member, the function and action are comparable to the case where two-stage load-bearing member group is provided. By removing one stage of members, the underdrain joint can be easily assembled, and the underdrain joint can be made more compact, and the amount of excavation required to install the underdrain joint can be reduced accordingly. 6 and 03, when using the underdrain joint according to the present invention, there is an effect in addition to the underdrain joint between the anchoring members that have a casing and are attached to the end face of the underdrain to be connected. f) 3 A large number of load-bearing members are movably supported within a certain range and cannot be removed, and among these, the inner and outer flexible members are installed at the Togawa position, respectively. , only internal pressure is applied to the internally fixed flexible member,
If only external pressure is applied to the Togawa-machi flexible members, their deformation will always be supported by the load-bearing member, and even if there is a relative displacement in the culvert to be connected, it will follow it and ensure the watertightness of the culvert. In addition to being able to secure the required amount of space, it also saves space, is smaller, is easier to assemble, reduces costs, and reduces the amount of excavation compared to conventional culverts.

In addition to the above-mentioned effects, if a cover means is provided at the inner and outer circumferential positions of the inner and outer flexible members, in addition to the above-mentioned effects, the flow resistance of running water in the culvert can be reduced, and the It is possible to prevent functional deterioration of the underdrain joints due to the intrusion of earth and sand.

[Brief explanation of drawings]

FIG. 1 is a front view schematically showing a partially sectional view of the underdrain joint of the present invention used for connecting an underdrain; FIG. 2 is a partially enlarged cross-sectional view of the underdrain joint of FIG. 1; Figure 3 shows I of Figure 2.
4 is a front view showing the load-bearing member shown in FIG. 2, and FIG. FIG. 6 is an enlarged sectional view showing another practical example of the load-bearing member of the present invention, and FIGS. 7 and 8 are another practical example of the present invention. FIG. 9 is a side view of the load-bearing member before the relative displacement 03 occurs between the culverts, and FIG. f)
FIG. 3 is a side view of the load-bearing member portion after the load-bearing member is applied. A, A'-...Culture to be connected, B-...-
・・Underdrain joint, 10.10'-・・・Anchoring member, 1
1. 1 1'-. ．． ．． −． Opening, 1 2.
1 2'----- Housing part, 12a, 12a', 12
b, 12b'... Seat part, 13.13'...
...End plate, 14.14'--Connection part, 1 5
．． 1 5'-... End plate, 20-... Load-bearing member, 30... Inner periphery flexible member, 40-...
・Togawa town flexure member, 50--... Town flexure external water stop member, 8
0.80'...Holding member, 84-...Skin plate.

Claims (1)

[Claims] 1. A casing portion with an opening on one side, and a seat portion 03 for coupling a flexible member at an outer circumferential position on both sides of the opening of the casing portion.
a pair of anchors installed on opposite end surfaces of the underdrain to be connected, with the openings of the housing portions facing each other and a plurality of segments assembled in a cylindrical shape in the circumferential direction of the joint; a load-bearing member inserted between the pair of anchoring members so as to be movable within a certain range into the casing through the opening at end b5 and not to be removed from the casing; ; the end portions are respectively connected to the seats disposed at the inner and outer circumferential positions of the opening of the casing, and the ends are respectively connected to the inner and outer circumferential positions close to the load-bearing member, and between the pair of anchoring members; A joint for an underdrain characterized by having a short cylindrical inner and outer circumferential flexible member that is provided astride. 2 It has a casing part with an opening on one side, and a seat part for connecting the flexible members is arranged on the outer periphery between the openings of the casing part, and the openings of the casing parts are facing each other and A plurality of segments are assembled in a cylindrical shape in the circumferential direction of the joint, and a pair of anchoring members is provided to be attached to each of the opposing end surfaces of the underdrain to be connected; between the pair of anchoring members, an end portion is provided. includes a force-bearing member that is inserted into the housing portion through the opening so as to be movable within a certain range and cannot be removed from the housing portion; at each of the inner and outer circumferential positions close to the load-bearing member, End portion O'5 A short cylindrical inner and outer circumferential portion connected to a seat portion disposed on the inner and outer periphery of the opening of the casing portion and provided astride between the pair of anchoring members. Comprising a member: A short cylindrical flexible outer water stop member is provided at an outer peripheral position of the outer circumferential flexible member between the pair of anchoring members, and is installed to straddle between the holding members attached to both the anchoring members. A culvert joint characterized by comprising: 3 It has a casing part with an opening on one side b3, and a seat part for connecting the flexible members is arranged on the outer periphery between the openings of the casing part, and the openings of the casing parts face each other. and a pair of anchoring members attached to each of the opposing end surfaces of the underdrain to be connected, with the plurality of segments assembled in a cylindrical shape in the circumferential direction of the joint; between the pair of anchoring members, an end Part b5 includes a force-bearing member that is inserted into the casing through the opening so as to be movable within a certain range and cannot be removed from the casing; , a short cylindrical inner and outer circumferential flexible member whose end portions are respectively coupled to seat portions disposed at inner and outer circumferential positions of the opening of the housing portion, and which is provided astride between the pair of anchoring members; At the outer circumferential position of the outer circumferential flexible member between the pair of anchoring members, a short cylindrical outer water-stopping member installed between the holding members attached to both anchoring members is provided. Provided: A cover means is provided at an inner peripheral position of the inner circumferential flexible member between the pair of anchoring members, spanning between both anchoring members and covering the inner circumferential flexible member. culvert joint. 4. It has a casing part that is open on one side, and a seat part for connecting the flexible members is arranged on the outer periphery between the openings of the casing part, and the openings of the casing parts are facing each other and A plurality of 10 segments are assembled in a cylindrical shape in the circumferential direction of the joint, and a pair of anchoring members are attached to each of the opposite end faces of the underdrain to be connected; between the pair of anchoring members, an end a force-bearing member inserted into the casing through the opening so as to be movable within a certain range and not to be removed from the casing; , a short cylindrical inner and outer circumferential flexible member whose end portions are respectively coupled to seat portions disposed at inner and outer circumferential positions of the opening of the housing portion and which are provided astride between the pair of anchoring members; A short cylindrical outer water stop member is provided at an outer circumferential position of the outer circumferential flexible member between the pair of anchoring members, and is installed to straddle between the holding members attached to both the anchoring members. a cover means is provided at an inner circumferential position of the inner circumferential flexible member between the pair of anchoring members; a cover means is provided spanning between both the anchoring members and covering the inner circumferential flexible member; A joint for an underdrain, characterized in that a skin plate is provided at an outer peripheral position of the member to cover the flexible external water stop member.