Segment joint structure

Abstract

To provide a segment joint structure that can suitably join a K segment and a B segment and also suitably resist a force acting on the K segment in the direction of slipping out.SOLUTION: This segment joint structure includes a cantilever spring-like anti-slip member 13 whose base end is supported on a bottom surface of a recess 11 and whose tip end extends at an angle toward the inside of a female joint member 12, and a tip of the anti-slip member 13 engages with an engagement recess 14 formed on a tip surface portion of a male joint member 10, so that relative movement in a direction in which the female joint member 12 and the male joint member 10 separate from each other in the axial direction of the segment ring is prevented.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a joint structure of segments for connecting between segments used for the internal lining of a tunnel, particularly to a joint structure of segments for connecting a B segment and a K segment that is finally connected.

Background Art

[0002] In tunnel construction by the shield method, a plurality of segments are connected in the circumferential direction along the inner peripheral surface of the excavation hole on the rear side of the shield excavator to assemble segment rings 1, 1..., and these segment rings 1, 1... are successively connected in the tunnel axis direction as the shield excavator advances, so that the lining 2 is formed in the tunnel.

[0003] As shown in FIG. 8, the segment ring 1 is assembled by successively connecting arc-shaped normal segments (hereinafter referred to as A segments) 3, 3... in the circumferential direction, and then joining segments (hereinafter referred to as B segments) 4, 4 having inclined surfaces inclined in the segment axis direction at one end in the circumferential direction at both ends in the circumferential direction, and finally incorporating a K segment (key segment) 5 between both B segments 4, 4 from the face side.

[0004] The joining of the K segment 5 and the B segment 4 in the circumferential direction of the segment generally has a structure joined by bolts. However, for the purpose of shortening the construction period, reducing costs, and coping with automatic assembly, for example, a cone connector type joint structure, a hook type joint, etc. have been developed (see, for example, Patent Document 1 and Patent Document 2).

[0005] In the conventional segment joint structure, a segment joint provided with a male joint member protruding from the end face of the circumferential joint portion of one segment and a female joint member disposed in a recess opened in the end face of the other joint portion is used. The male joint member is inserted into the recess, and the segments are relatively slid in the segment axis direction, so that the male and female joint members are engaged with each other to join between the two segments.

[0006] Furthermore, to join the segments 1, 1, a ring joint is used, which consists of a pin-shaped male ring joint member 6 protruding from one end face of the joint and a female ring joint member 7 embedded in the other end face of the joint. By inserting the male ring joint member 6 into the female ring joint member 7, the male and female ring joint members 6 and 7 engage, and the connection of the male and female ring joint members 6 and 7 joins adjacent segments in the segment axis direction. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2009-019460 [Patent Document 2] Japanese Patent Publication No. 2007-056555 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, when assembling a new segment ring, the jacks supporting the face-side end face of segment K 5 are removed, and as a result, a force acts on segment K 5 that pushes it toward the face-side, being pressed against the joint end faces of both B segments 4, 4 by the compressive force acting circumferentially on segment ring 1.

[0009] On the other hand, in conventional inter-segment joints, when the male and female joint members engage with each other in a wedge-like manner as the K segment 5 slides relative to the B segment 2, if the engagement strength between the male and female joint members is high, the resistance to insertion in the segment axial direction for the K segment 5 increases accordingly, which may hinder insertion between the two B segments 4, 4. Therefore, the male and female joint members were formed with sufficient engagement strength to ensure that the K segment could be reliably inserted between the two B segments.

[0010] Therefore, conventional segment joints, due to their structure, cannot withstand the pull-out force described above, and as a result, there was a risk that a large load would be placed on the ring joints 6 and 7 connecting the K segment 5 and the existing segment ring 1 by the pull-out force.

[0011] On the other hand, to address the problems described above, conventional methods have been employed, as shown in Figure 9, in which a rod 8, such as a tie rod, is placed between the K segment 5 and an existing segment 2 adjacent in the segment axis direction, and this rod 8 is used to counteract the force acting on the K segment 5 in the pushing direction, and the tie rod 8 is removed after the assembly of the new segment ring is completed. However, this method has the problem that the work of installing and removing the tie rod or other rod 8 is very time-consuming.

[0012] Therefore, in view of these conventional problems, the present invention aims to provide a segment joint structure that can suitably join K segments and B segments and can also suitably resist pull-out forces acting on the K segments. [Means for solving the problem]

[0013] The features of the invention described in claim 1 for solving the conventional problems described above are, between the arc-shaped segments that are joined to each other in the circumferential direction and constitute an annular segment ring, The circumferential joining end face of one segment to be joined in the segment ring axis direction forward and the circumferential direction of the other segment to be joined in the segment ring axis direction backward A male joint member protruding from the joint end face, and the aforementioned The circumferential joining end face portion of the other segment to be joined in the segment ring axial direction, and the circumferential joining end face portion of the one segment to be joined in the segment ring axial direction, and the segment ring axial end It is formed in Circumferential direction The male joint member comprises a female joint member positioned in a recess opening on the joint end face side and the segment ring axial end face side, into which the male joint member is inserted from one end side in the segment ring axial direction in accordance with the relative movement of both segments in the segment ring axial direction, and the male joint member but Insert into the recess from the axial end face side of the segment ring. So By moving the two segments relative to each other in the segment ring axis direction, the female joint member and the male joint member EngagementIn a segment joint structure in which two segments adjacent to each other in the circumferential direction are joined so as not to be separated in the circumferential direction, the recess Segment circumferential direction The base end is supported on the bottom surface, and the tip end is in the segment ring axial direction within the female joint member. The opposite side of the opening on the axial end face side of the segment ring. It is equipped with a cantilevered spring-shaped anti-slip member that extends inclined toward, By moving the two segments relative to each other in the segment ring axis direction, The tip of the anti-slip member is the male joint member Projection direction tip surface or The segment ring axial end face side The female joint member and the male joint member engage with an engaging recess formed on the side surface, and in the segment ring axial direction, the female joint member and the male joint member support each other via the anti-detachment member, thereby preventing relative movement of the segments in the direction of separation in the segment ring axial direction.

[0014] The feature of the invention described in claim 2 is that, in addition to the configuration of claim 1, a biasing member is provided between the anti-slip member and the bottom surface of the recess or the bottom plate of the female joint member to bias the tip side of the anti-slip member toward the male joint member.

[0015] The feature of the invention described in claim 3 is that, in addition to the configuration of claim 1 or 2, the female joint member is provided with a support portion for the anti-dislodgement member that extends along the bottom surface of the recess integrally with the bottom plate, and the base end of the anti-dislodgement member is fixed to the support portion for the anti-dislodgement member.

[0016] The feature of the invention described in claim 4 is that, in addition to the configuration of claim 1 or 2, the base end of the anti-loosening member is fixed to an anchor reinforcement embedded in the segment.

[0017] The feature of the invention described in claim 5 is that, in addition to the configuration of claim 1 or 2, the segment has inclined surfaces at both circumferential ends that are inclined in the direction of the segment ring axis, and is a K-segment inserted in the direction of the segment ring axis between a pair of segments constituting the segment ring. [Effects of the Invention]

[0018] The joint structure of the segment according to the present invention can resist the force acting in the extraction direction of the segment by having the configuration of claim 1.

[0019] Also, in the present invention, by having the configuration of claim 2, the fixing condition of the free end of the cantilever spring-shaped extraction prevention member is changed, and the allowable compressive force of the extraction prevention member against the force in the extraction direction of the K segment can be increased by buckling restraint.

[0020] Also, in the present invention, by having the configuration of claim 3, the female joint member and the extraction prevention member are integrated, and segment production can be performed efficiently.

[0021] Also, in the present invention, by having the configuration of claim 4, the extraction prevention member can be firmly fixed to the segment, and the relative positional relationship between the extraction prevention member and the female joint member can be finely adjusted.

[0022] Also, in the present invention, by having the configuration of claim 5, when a compressive force acts in the circumferential direction on the segment ring and is pressed against the joint end face of the B segment so that a force in the extraction direction acts on the key segment, the force in the extraction direction can be dispersed to the joint portion between segments to resist it, reducing the burden on the ring joint, and also eliminating the need for a rod such as a tie rod, thereby reducing the construction period and cost.

Brief Description of the Drawings

[0023] [Figure 1] It is a partial development view of a segment ring showing an example of an embodiment of the joint structure of the segment according to the present invention. [Figure 2] It is an enlarged side view of the K segment described above. [Figure 3] It is an enlarged cross-sectional view corresponding to the position viewed in the direction of arrow A-A in FIG. 2 showing the joint structure portion of the segment described above. [Figure 4] It is an enlarged cross-sectional view showing the male joint member described above. [Figure 5]This is an enlarged cross-sectional view showing the female joint member shown above. [Figure 6] This is an enlarged cross-sectional view showing the state of the same segment during the joining process. [Figure 7] This is an enlarged cross-sectional view showing another embodiment of the segment joint structure according to the present invention. [Figure 8] This is a perspective view showing an overview of tunnel lining using the shield tunneling method. [Figure 9] This is a partial unfolded diagram of the segment ring to explain the relationship between the K-segment and B-segment and the state of the forces acting on the key segment. [Modes for carrying out the invention]

[0024] Next, embodiments of the segment joint structure according to the present invention will be described based on the examples shown in Figures 1 to 6.

[0025] Furthermore, the same reference numerals are used to denote the same configuration as in the conventional example described above. In the figure, reference numeral 3 is a normal arc-shaped segment formed from concrete (hereinafter referred to as A segment), reference numeral 4 is a segment having an inclined surface 4a at one end in the circumferential direction that is inclined in the segment axis direction (hereinafter referred to as B segment 4), and reference numeral 5 is a K segment 5. A ring-shaped segment ring 1 is assembled by sequentially connecting multiple A segments 3, 3... in the circumferential direction, joining B segments 4, 4 to both ends in the circumferential direction, and then wedging the K segment 5 between these two B segments 4, 4 from one side in the segment axis direction (the face side). ru.

[0026] Furthermore, after advancing the shield excavator while applying jack reaction force to the end face of the existing segment ring 1, the jacks are retracted and new segment ring 1 are installed in a series in the direction of the tunnel axis, thereby sequentially creating the tunnel lining 2.

[0027] In the following explanation, using segment ring 1 as the reference, the circumferential direction of segment ring 1 for each segment is defined as the segment circumferential direction, the radial direction of segment ring 1 as the segment thickness direction, and the central axis direction of segment ring 1 as the segment axis direction. The direction in which segment K 5 is inserted between segments B 4, 4, from the face side in the segment axis direction is described as the front.

[0028] The K segment 5 is formed in an arc shape from concrete and has inclined surfaces 5a, 5a at both ends in the circumferential direction of the segment that are aligned with the joint end faces 4a of the B segments 4 that are joined to each other, and are inclined in the segment axis direction.

[0029] As shown in Figures 1 and 3, the segment joint structure connecting segment B 4 and segment K 5 comprises a male joint member 10 protruding from one of the joining end faces 4a (or 5a) that are joined together, and a female joint member 12 positioned in a recess 11 formed in the other joining end face 5a (or 4a). By butting the two joining end faces 4a and 5a together and inserting the male joint member 10 into the recess 11, and by moving both segments 4 and 5 relative to each other in the segment axis direction, the male and female joint members 10 and 12 are connected in accordance with the relative movement of segment B 4 and segment K 5 in the segment axis direction, thereby joining segment K 5 and segment B 4 in the segment circumferential direction.

[0030] Furthermore, the joint structure of this segment includes a cantilever spring-shaped anti-slip member 13 whose base end is supported on the bottom surface of the recess 11 and whose tip extends inclined toward the female joint member 12. The tip of the anti-slip member 13 engages with an engagement recess 14 formed on the tip surface of the male joint member 10, thereby preventing relative movement between the female joint member 12 and the male joint member 10 in the direction of separation in the segment ring axis direction.

[0031] In this embodiment, as shown in Figure 2, a female joint member 12 is positioned in front of the K segment 5 in the segment axis direction, and a male joint member 10 is positioned behind it. Correspondingly, a male joint member 10 is positioned in front of the B segment 4 in the segment axis direction, and a female joint member 12 is positioned behind it. As the two segments move relative to each other in the segment axis direction, the male and female joint members move relative to each other in the connection direction, and the male joint member 10 is inserted into the female joint member 12 through the recess 11. Note that the arrangement of the male and female joint members is not limited to this embodiment; the male joint member 10 may be positioned on the K segment 5 and the female joint member 12 on the B segment 4, or vice versa.

[0032] As shown in Figure 4, the male joint member 10 comprises a flat male joint member body 20, one end of which is embedded in the circumferential end of the segment 5 and the other end of which protrudes from the joint end face with its surface facing the segment thickness direction, and male engaging portions 21, 21 that protrude in the segment axis direction from both surfaces of the male joint member body 20.

[0033] The male joint member body 20 is formed in the shape of a rectangular flat plate from cast iron or the like, with its longitudinal direction facing the circumferential direction of the segment and its surface facing the thickness direction of the segment. In this state, one end is embedded in the circumferential end of the segment, and the other end protrudes from the joint end face with its surface facing the thickness direction of the segment. Reference numeral 22 in the figure indicates a reinforcing bar whose tip is fixed to the surface of the male joint member body 20.

[0034] Furthermore, an engagement recess 14 is formed on the tip surface of the male joint member body 20, and the tip of the cantilever spring-shaped anti-slip member 13 engages with this engagement recess 14, thereby preventing relative movement of the female joint member 12 and the male joint member 10 in the direction of separation in the segment ring axis direction.

[0035] The engaging recess 14 is formed in a L-shape in plan view by a tip contact surface 14a located on the female joint member 12 side (forward in the sliding direction of the male joint member 10) and a stopper surface 14b that is perpendicular to the tip contact surface 14a and inclined from its lower end toward the rear tip in the sliding direction of the male joint member 10.

[0036] The male engaging portions 21, 21 are formed from a rigid material such as cast iron in a continuous rectangular cross-section and are firmly fixed by welding at a predetermined distance from the joint end face 5a on the surface of the male joint member body 20, with their longitudinal direction oriented in the segment axis direction.

[0037] Furthermore, the male engagement portions 21, 21 are arranged so that the front side in the sliding direction of the male joint member 10 is inclined toward the tip side of the male joint member body 20, in accordance with the inner surface shape of the female joint member 12.

[0038] On the other hand, as shown in Figure 5, the female joint member 12 is fixed in a position shifted to the front in the sliding direction of the male joint member 10 within the recess 11 formed at the circumferential end of the segment 5 (or 4).

[0039] The recesses 11 are located in the segment axis direction forward of segment K segment 5 and in the segment axis direction rear of segment B segment 4, and each has a groove shape that opens on the joint end face side and the segment axis direction end face side, respectively.

[0040] The female joint member 12 comprises a main body 31 having a pair of support plate portions 30, 30 that are spaced apart from each other and facing each other in the segment thickness direction, and a pair of female engaging portions 32, 32 that protrude from the inner surfaces of each support plate portion 30, 30.

[0041] The main body 31 comprises a pair of support plate portions 30, 30 arranged vertically apart from each other, a bottom plate 33 positioned to span between the two support plate portions 30, 30, and an end plate 34 positioned on the closed end side of the recess 11. The bottom plate 33, the end plate 34, and the two support plate portions 30, 30 form a hollow structure with an open side into which the male joint member 10 is inserted. The outer surfaces of the end plate 34, the bottom plate 33, and the two support plate portions 30, 30 are fitted into the recess 11, facing each other's inner surfaces.

[0042] Furthermore, the bottom plate 33 is positioned at a certain distance from the tip surface of the inserted male joint member 10, and the tip side of the anti-slip member 13 is inserted between the tip of the male joint member 10 and the bottom plate 33, and a space is formed that allows for a certain amount of elastic deformation (bending).

[0043] On the outside of each support plate portion 30, 30, there are multiple reinforcing bars 35, 35 embedded in the segment in a parallel arrangement spaced apart in the segment axis direction, and the ends of the reinforcing bars are fixed to the outer surface of the support plate portion 30, 30 by welding, and the female joint member 12 is fixed to the segment 5 (or 4) via the anchor members 35, 35.

[0044] Furthermore, the main body 31 is provided with a support portion 36 for the anti-loosening member that extends along the bottom surface of the recess 11 toward the end opening of the recess 11, integrally with the bottom plate 33, and the base end of the anti-loosening member 13 is fixed to the support portion 36 for the anti-loosening member.

[0045] The anti-slip member support portion 36 extends from the edge of the bottom plate 33 inward at a predetermined angle towards the bottom of the recess 11 and is positioned on the bottom surface of the recess 11.

[0046] Each female engaging portion 32, 32 is provided protruding from the mutually opposing inner surfaces of each support plate portion 30, 30. As the two segments slide relative to each other, the male joint member body 20 is inserted between the two female engaging portions 32, 32, and the male engaging portions 21, 21 move relative to the female engaging portions 32, 32. The male engaging portions 21, 21 engage wedge-shaped with the inside of the female engaging portions 32, 32, and the movement of both segments 4, 5 away from each other in the circumferential direction is restricted while the joint end faces of segment B 4 and segment K 5 are attracted to each other and butt together.

[0047] The anti-loosening member 13 is formed from spring steel such as SUP6 in the shape of a strip plate with a certain thickness, and its base end is fixed along the anti-loosening member support portion 36 by welding or bolting, forming a cantilevered leaf spring shape that extends diagonally from the bottom of the recess 11 toward the female joint member 12.

[0048] The length, width, and thickness of the anti-detachment member 13 are set such that they are pressed against the axial side and tip surface of the segment of the male joint member 10, allowing a certain amount of deflection to the bottom of the recess 11, and then elastically return to engage with the engaging recess 14, and that they have sufficient strength to prevent buckling due to the force acting on the K segment 5 that is received via the male joint member 10 in the direction of detachment after engagement.

[0049] Furthermore, a biasing member 37 may be provided between the anti-dislodgement member 13 and the bottom surface of the recess 11 or the bottom plate 33 of the female joint member 12, which biases the tip side of the anti-dislodgement member 13 toward the male joint member 10.

[0050] The biasing member 37 can be, for example, a cylindrical or spherical rubber material, a coil spring, a leaf spring, etc., and is preferably positioned to support the tip of the anti-detachment member 13.

[0051] By using this biasing member 37, the fixing conditions of the free end of the cantilever spring-shaped anti-pull-out member 13 can be changed, and the allowable compressive force of the anti-pull-out member 13 against the force in the pull-out direction of the K segment 5 can be increased by buckling constraint.

[0052] In the joint structure of the segment configured in this way, when the K segment 5 is fitted between the two B segments 4, 4 from one side in the segment axis direction (face side), the male and female joint members 10, 12 move relative to each other, and the male joint member 10 is inserted into the recess 11 from the end opening side in the segment axis direction, and the male joint member 10 is inserted into the female joint member 12 from one end side.

[0053] In this case, as shown in Figure 6, the male joint member body 20 is inserted between the two female engaging portions 32, 32 of the female joint member 12, and the male engaging portions 21, 21 move relative to the female engaging portions 32, 32, so that the male engaging portions 21, 21 engage in a wedge shape inside the female engaging portions 32, 32, and the B segment 4 and the K segment 5 are joined together with their joint end faces attracting each other, and the movement of both segments away from each other in the circumferential direction is restricted.

[0054] Furthermore, when the relative movement of the male and female joint members 10 and 12 progresses by a certain amount, the tip of the male joint member 10 comes into contact with the anti-dislodgement member 13, and as the movement progresses further, the cantilever spring-shaped anti-dislodgement member 13 is pressed by the male joint member 10 and elastically deforms and bends.

[0055] Then, as the relative movement of the male and female joint members 10 and 12 progresses further, and the male engaging parts 21 and 21 engage in a wedge-like manner with the inside of the female engaging parts 32 and 32, the anti-dislodgement member 13 elastically returns to its original position, and its tip engages with the engaging recess 14.

[0056] Furthermore, the male ring joint member 6 is inserted into the female ring joint member 7 of the segment constituting the existing segment ring 1, and the K segment 5 is joined to the existing segment ring 1 in a state where the segment axial end faces abut each other.

[0057] In this state, when the jack supporting the face-side end face of segment K 5 is removed and a compressive force is applied to segment ring 1 in the circumferential direction, a force acts on segment K 5 in a direction that causes it to be pressed against the joint end faces 4a, 4a of both B segments 4 and pull it out toward the face.

[0058] In this case, the tip of the anti-pull-out member 13 engages with the engaging recess 14 formed on the tip surface of the male joint member 10, so that the force acting on the K segment 5 in the pull-out direction acts as a compressive force on the anti-pull-out member 13 via the male joint member 10, and the anti-pull-out member 13 acts like a prop and can resist the force in the pull-out direction.

[0059] Therefore, the force acting on the K segment 5 in the pull-out direction is distributed and applied to the inter-ring joints 6 and 7 and the pull-out prevention member 13, reducing the load on the inter-ring joints 6 and 7, and effectively preventing the K segment 5 from coming loose.

[0060] In the above embodiment, a support portion 36 for the anti-loosening member is provided, which extends along the bottom surface of the recess 11 integrally with the bottom plate 33, and the base end of the anti-loosening member 13 is fixed to the support portion 36. However, as shown in Figure 7, the anti-loosening member 13 may be fixed to an anchor reinforcing bar 40 embedded in the segment 5. Reference numeral 41 in the figure indicates a fixing bolt.

[0061] Furthermore, the configuration of the male and female coupling members is not limited to the embodiments described above, and can accommodate a variety of configurations. For example, the male and female coupling members may be integrally formed from cast iron or the like.

[0062] Furthermore, although the above-described embodiment explained an example in which the segment joint structure according to the present invention was applied to the joining of B segment 4 and K segment 5, it may also be applied to the joining of A segments 3, 3 or A segment 3 and B segment 4. [Explanation of Symbols]

[0063] 1 Segment Ring 2. Lining 3 A segment 4. B-segment 5K segment 6 Male ring joint member 7 Female ring joint member 10 Male joint member 11 recess 12 Female joint member 13 Anti-detachment component 14 Engagement recess 20 Male joint component body 21 Male engagement part 22 Reinforcement bars 30 Support plate part 31 Main body 32 Female engagement portion 33 Bottom plate 34 End plate 35 Reinforcement bars 36 Support part for preventing detachment 37. Biasing member 40 Anchor reinforcing bars 41 volts

Claims

1. The annular segment ring comprises a male joint member protruding from the circumferential joint end face of one of the joined segments in the segment ring axis direction forward and from the circumferential joint end face of the other joined segment in the segment ring axis direction backward, and a female joint member formed at the circumferential joint end face of the other joined segment in the segment ring axis direction forward and from the circumferential joint end face of the one joined segment in the segment ring axis direction backward, and at the segment ring axis direction end, and disposed within a recess opening on the circumferential joint end face side and the segment ring axis direction end face side, into which the male joint member is inserted from one end in the segment ring axis direction in accordance with the relative movement of the two segments in the segment ring axis direction, In a segment joint structure in which the male joint member is inserted into the recess from the segment ring axial end face side, and the female joint member and the male joint member are connected by engagement by moving the two segments relative to each other in the segment ring axial direction, thereby joining the two adjacent segments in the circumferential direction in a way that prevents them from separating in the circumferential direction, A segment joint structure characterized in that a cantilever spring-shaped anti-slip member is provided, the base end of which is supported on the circumferential bottom surface of the segment of the recess, and the tip end of which is inclined and extends toward the opposite side of the opening on the segment ring axis direction end face side of the female joint member, and by moving the two segments relative to each other in the segment ring axis direction, the tip of the anti-slip member engages with an engagement recess formed on the protruding tip surface of the male joint member or on the side surface on the segment ring axis direction end face side, so that the female joint member and the male joint member support each other in the segment ring axis direction via the anti-slip member, and relative movement of the segments in the direction of separation in the segment ring axis direction is prevented.

2. The segment joint structure according to claim 1, further comprising a biasing member between the anti-slip member and the bottom surface of the recess or the bottom plate of the female joint member, which biases the tip side of the anti-slip member toward the male joint member.

3. The segment joint structure according to claim 1 or 2, wherein the female joint member is provided with a support portion for preventing dislodgement of a member that extends along the bottom surface of the recess integrally with the bottom plate, and the base end of the dislodgement prevention member is fixed to the support portion for preventing dislodgement of a member.

4. The segment joint structure according to claim 1 or 2, wherein the base end of the anti-detachment member is fixed to an anchor reinforcement embedded in the segment.

5. The segment joint structure according to claim 1 or 2, wherein the segment has inclined surfaces at both circumferential ends that are inclined in the direction of the segment ring axis, and is a K-segment inserted in the direction of the segment ring axis between a pair of segments constituting the segment ring.

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