A single shield TBM hoisting installation method

Abstract

The present application relates to the technical field of shield machine hoisting, in particular to a single shield TBM hoisting installation method, step S1, starting guide table, guide hole and empty push guide table construction are carried out, step S2, first, the front shield is lowered into the well and pre-tightened, the front shield is located at the front end of the starting guide table, so that the front end face of the front shield is located above the ring welding channel, step S3, the cutterhead and the front shield are pushed forward along the starting guide table, the rear end face of the front shield is located above the ring welding channel, the middle shield is lowered into the well in turn and connected with the front shield, the ring welding channel is reserved between the starting guide table and the empty push guide table, the shield body is given way by using the front push form, so that the shield body hoisting is realized in the limited working well space, the assembly can be completed by only setting one ring welding channel, and the construction difficulty of the guide table can be effectively reduced. The shield body posture control is realized by using the guide rail and the sliding block, the cumbersome pipe piece disassembly and assembly is avoided, and the construction efficiency is greatly improved.

Description

Technical Field

[0001] This invention belongs to the technical field of tunnel boring machine (TBM) hoisting, specifically relating to a method for hoisting and installing a single-shield TBM. Background Technology

[0002] Tunnel boring machine (TBM) construction is currently widely used in tunnel construction. When encountering confined spaces, TBMs typically need to excavate and push tunnels in the tunnel from the starting shaft. The TBM is first hoisted into the starting shaft, and then pushed into the tunnel for launch. In existing technologies, a concrete guide platform is poured inside the tunnel, and the shield body is assembled on the platform. This requires a certain diameter for the starting shaft. In addition, to ensure the shield body's posture during push-out, negative ring segments need to be assembled and then filled with gravel. This method has limited control over the shield body's posture and is quite cumbersome, making construction difficult.

[0003] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a method for hoisting and installing a single-shield TBM.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for hoisting and installing a single-shield TBM includes:

[0007] Step S1: Construct the launching platform, pilot tunnel, and empty propulsion platform; harden the ground outside the working shaft using mixing piles.

[0008] The air-launching platform is located inside the guide tunnel, with its rear end extending out of the guide tunnel. A gap is left between the air-launching platform and the launching platform to serve as a circumferential welding channel. Longitudinal welding channels corresponding to the shield body are provided on both sides of the launching platform.

[0009] Step S2: Divide both the middle shield and the front shield into six lifting blocks. Name the top lifting block of the middle shield as Middle Lifting Block 1, and name the remaining lifting blocks of the middle shield in clockwise order as Middle Lifting Block 2, Middle Lifting Block 3, Middle Lifting Block 4, Middle Lifting Block 5, and Middle Lifting Block 6. Name the top lifting block of the front shield as Front Lifting Block 1, and name the remaining lifting blocks of the front shield in clockwise order as Front Lifting Block 2, Front Lifting Block 3, Front Lifting Block 4, Front Lifting Block 5, and Front Lifting Block 6.

[0010] First, hoist the front lifting blocks three, four, and five into the well and pre-tighten them. The front shield is located at the front end of the launching guide platform so that the front face of the front shield is above the circumferential welding channel. After welding the cutter head, turn it over and lower it to the rear end of the empty thrust platform so that the cutter head and the front lifting blocks three, four, and five are pre-tightened through the circumferential welding channel.

[0011] Step S3: Push the cutterhead and front shield forward along the starting guide platform so that the rear end face of the front shield is above the circumferential welding channel. Then, lower the middle lifting blocks three, four, and five into the well and connect them to the front shield. After the main drive is lowered into the well, connect it to the cutterhead. Then, lower the front lifting blocks two, six, one, two, six, and one into the well in sequence.

[0012] Step S4: Push forward and then lower and connect the cross beam and the shield tail in sequence. After connecting the external hydraulic pump station, push the shield forward. Then, lower and connect the trailer in sequence. After the pipeline connection is debugged, push the shield to the starting excavation position.

[0013] Preferably, the upper surfaces of the air thruster platform and the launching platform are arc-shaped corresponding to the shield body, and interconnected air thruster tracks are laid on the air thruster platform and the launching platform. The air thruster tracks are fixed to the air thruster platform and the launching platform by embedded parts, and lubricating oil is applied to the air thruster tracks.

[0014] Preferably, the tail shield is installed in four parts. When the bottom block of the tail shield is installed, its center line is aligned with the center line of the middle shield, and its front end is aligned with the tail section of the middle shield. Then, the left block, right block and top block are installed in sequence. During the installation of the tail shield, a total station is used to measure the position of the tail shield and the distance from the inner circle of the bottom block to the center line. The overall roundness of the tail shield and its coaxiality with the middle shield are adjusted in a timely manner as needed.

[0015] Preferably, after the tail shield welding is completed, the tail shield brushes are assembled. The starting points of the welding of the four tail shield brushes must be 1m apart, and the welds of the second, third, and fourth tail shield brushes are located in the middle of the previous tail shield brush.

[0016] Preferably, reaction grooves are provided on both sides of the launching guide platform and the empty thrust platform. A reaction seat is installed in the reaction groove in a detachable manner. The reaction seat is connected to a hydraulic cylinder, and the hydraulic cylinder is connected to the outer wall of the shield body in a hinged manner.

[0017] Preferably, anti-torsion pads are welded on both sides of the outer wall of the shield, and the lower end of the anti-torsion pads is provided with rollers, which are supported on the flat surfaces on both sides of the air push platform or the starting platform.

[0018] Preferably, an anti-buoyancy mechanism corresponding to the shield body is provided in the guide tunnel. The anti-buoyancy mechanism includes guide rails and slide blocks. No less than two guide rails extend along the large mileage direction of the guide tunnel. Multiple slide blocks are slidably assembled in the guide rails. A top rod is provided in the slide block. The end of the top rod is provided with an arc-shaped support plate corresponding to the outer wall of the shield body.

[0019] Preferably, the guide rails are evenly distributed in the upper half of the guide tunnel and are evenly distributed around the circumference of the guide tunnel. One end of the guide rail extends to the shield working face, and the other end extends out of the guide tunnel and into the working shaft.

[0020] As the shield enters the pilot tunnel, multiple sliding blocks are placed sequentially at intervals in each guide rail. The sliding blocks are supported on the outer wall of the shield by top rods and slide with the shield within the guide rail.

[0021] Preferably, multiple positioning detection points are evenly distributed on the shield body. The positioning detection points are monitored by a total station to obtain the shield body attitude, and the shield body attitude is adjusted by adjusting the length of the top rod.

[0022] Beneficial effects: By reserving a circumferential welding channel between the launching platform and the air thrust platform, and using a forward-pushing method to make way for the shield body, the shield body can be hoisted within the limited working shaft space. Only one circumferential welding channel is needed to complete the assembly, which can effectively reduce the construction difficulty of the launching platform.

[0023] By using guide rails and sliders to control the shield's attitude, the tedious process of disassembling and assembling tunnel segments is avoided, greatly improving construction efficiency. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0025] Figure 1 This is a schematic diagram showing the distribution of the anti-buoyancy mechanism in a specific embodiment provided by the present invention;

[0026] Figure 2 This is a simplified structural diagram of the anti-buoyancy mechanism in a specific embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the shield body's central shield block in a specific embodiment of the present invention.

[0028] In the diagram: 1. Working shaft; 2. Launching guide platform; 3. Empty propulsion platform; 4. Circumferential welding channel; 5. Shield body; 6. Guide rail; 7. Sliding block; 8. Guide tunnel; 9. Sliding block; 10. Top rod; 11. Arc-shaped support plate. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0030] In the description of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "connected" and "linked" used in this invention should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0031] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0032] like Figure 1 As shown, a single-shield TBM hoisting and installation method includes the following steps: Step S1, construction of the starting guide platform 2, guide tunnel 8 and empty propulsion platform 3, hardening of the ground outside the working well 1 by mixing piles, the mixing piles are mainly distributed on the travel trajectory of the hoisting equipment, and then the outside of the working well 1 is hardened as a whole by concrete. Due to the limited assembly site, the single-shield TBM hoisting and lowering channel has only one well opening, and it is planned to use a 650T gantry crane and a 500T crawler crane for hoisting and assembly.

[0033] The empty propulsion platform 3 is located inside the guide hole 8. The rear end of the empty propulsion platform 3 extends out of the guide hole 8 by a certain distance, which is adapted to the thickness of the cutter head. A gap is left between the empty propulsion platform 3 and the launching guide platform 2 to serve as a circumferential welding channel 4. Longitudinal welding channels corresponding to the shield body 5 are provided on both sides of the launching guide platform 2.

[0034] Step S2: Divide both the middle shield and the front shield into six lifting blocks, naming the top lifting block of the middle shield "Middle Lifting Block One," as follows: Figure 3 As shown, the remaining lifting blocks of the middle shield are named in clockwise order as Middle Lifting Block 2, Middle Lifting Block 3, Middle Lifting Block 4, Middle Lifting Block 5, and Middle Lifting Block 6; the top lifting block of the front shield is named Front Lifting Block 1, and the remaining lifting blocks of the front shield are named in clockwise order as Front Lifting Block 2, Front Lifting Block 3, Front Lifting Block 4, Front Lifting Block 5, and Front Lifting Block 6. First, Front Lifting Block 3, Front Lifting Block 4, and Front Lifting Block 5 are lowered into the well and pre-tightened. The bottom block assembly lifting cylinder of the shield body 5 is set at the starting guide platform 2. It consists of 4 lifting cylinders and is used to adjust the position and height difference during the assembly of the bottom block of the shield body 5.

[0035] The front shield is located at the front end of the launching guide platform 2, so that the front end face of the front shield is above the circumferential welding channel 4. Then, the hydraulic cylinder and reaction seat corresponding to the front shield are installed. Specifically, reaction grooves are set on both sides of the launching guide platform 2 and the empty thrust platform 3, with the opening of the reaction groove facing upward. The reaction grooves are formed by pre-embedded metal grooves during the casting process. The reaction seat is installed in the reaction groove in a detachable manner. The reaction seat is a block shape corresponding to the reaction groove and is welded from steel plates. The reaction seat is connected to the hydraulic cylinder, and the hydraulic cylinder is connected to the outer wall of the shield body 5 in a hinged manner, thereby realizing the advancement of the shield body 5.

[0036] After welding, the cutter head is flipped and lowered to the rear end of the empty pusher platform 3, thus supporting the cutter head through the empty pusher platform 3. At this time, the gap between the cutter head and the front shield is located at the circumferential welding channel 4. The cutter head and the front lifting blocks three, four and five are pre-tightened through the circumferential welding channel 4. Two limit blocks are welded on both sides of the front lifting block four along the outer side of the track to prevent the bottom block from sliding during the installation of other sub-blocks. Sealing strips are installed on the sub-block connecting surfaces and flat sealant is applied. Pre-tightened sub-block connecting bolts are installed.

[0037] In step S3, the cutterhead and front shield are pushed forward along the starting guide platform 2 so that the rear end face of the front shield is above the circumferential welding channel 4. Then, the middle lifting blocks 3, 4, and 5 are sequentially lowered into the well and connected to the front shield, thereby welding and fixing the front shield and the middle shield. After the main drive is hoisted into the well, it is connected to the cutterhead. Then, the front lifting blocks 2, 6, 1, 2, 6, and 1 are sequentially hoisted into the well. The middle shield, main drive, front shield, and cutterhead are connected as one unit through assembly.

[0038] In this embodiment, as the shield body 5 is pushed forward, corresponding hydraulic cylinders and reaction seats are installed on the outside of the middle shield and the tail shield respectively. Multiple reaction grooves on both sides of the launching guide platform 2 and the empty thrust guide platform 3 are evenly distributed along the large mileage direction. In this way, the hydraulic cylinder can be reciprocated by adjusting the position of the reaction seat during the forward pushing process, thereby continuously pushing the shield body 5 forward.

[0039] Step S4: After pushing the shield body 5 forward, the cross beam and shield tail are lowered and connected through the circumferential welding channel 4. Emergency airbags and articulated seals are installed. Before installing the seals, the articulated rings must be welded in advance, and the welds must be ground smooth. After connecting the hydraulic pump station to the shield body 5, the shield body 5 is pushed forward by the hydraulic cylinder. Then, the trailer is lowered and connected in sequence, and the top-level equipment is installed. After the pipeline connection is debugged, the shield body 5 is pushed to the starting excavation position.

[0040] In this embodiment, the air-propellant platform 3 and the launching platform 2 are pre-cast concrete platforms with an upper surface that corresponds to the arc shape of the shield body 5. The centerlines of the air-propellant platform 3 and the launching platform 2 coincide with the centerline of the tunnel, and the axial deviation cannot exceed ±20mm. Interconnected air-propellant tracks are laid on the air-propellant platform 3 and the launching platform 2. The air-propellant tracks can be I-beams and are fixed to the air-propellant platform 3 and the launching platform 2 by embedded parts. Lubricating oil is applied to the top of the air-propellant tracks. Specifically, two 120kg steel rails are arranged on each side of the air-propellant platform 3 and the launching platform 2, welded to steel plates embedded in the concrete of the platform, to provide tracks for the single-shield TBM to advance. The reaction seat is designed as a 500*500*30mm steel plate in both vertical and horizontal directions. A 400*400*1100mm vertical barrel groove is welded to the rear of the vertical steel plate and reinforced with a triangular rib plate. It is inserted into the embedded part of the guide platform. The horizontal steel plate is welded to the embedded part on the guide platform.

[0041] In one optional embodiment, the cutterhead is transported to the construction site in sections for assembly and welding. During cutterhead welding, the connecting welds between the side blocks and the center block are welded first, followed by the welds on the secondary cutter beams, and finally the welds on the large circular ring and other welds. Insulation measures are implemented during welding. After the overall cutterhead welding is completed, the tooling is removed. The shield tail is installed in four sections. When installing the bottom block, its centerline is aligned with the centerlines of the front and middle shields, and its front end is aligned with the tail section of the middle shield. Then, the left, right, and top blocks are installed sequentially. During the shield tail installation process, the anti-deformation support of the shield tail cannot be removed prematurely to prevent deformation of the thin-walled cylinder. A total station is used throughout the process to measure whether there is any deviation in the placement of the tail shield, and to measure the distance from the inner circle of the bottom block to the centerline. Adjustments are made promptly as needed to ensure the overall roundness of the shield tail and its coaxiality with the middle and front shields.

[0042] After the tail shield welding is completed, the tail shield brushes are assembled. The starting points of the welding of the four tail shield brushes must be 1m apart, and the welds of the second, third, and fourth tail shield brushes must be in the middle of the previous tail shield brush.

[0043] The main drive uses a tilting lug and a tilting support. The tilting lug is installed on the housing assembly facing upwards, and the tilting support is installed on the ground side. They are then tightened and secured with bolts.

[0044] In an optional embodiment, to prevent the shield 5 from twisting during the air thrusting process, anti-twist pads are welded at the contact position between the shield 5 and the rail. The lower end face of the anti-twist pads is provided with rollers. Flat platforms are provided on both sides of the air thrusting guide platform 3 or the starting guide platform 2 for material transportation and personnel walking. The rollers are supported on the flat platforms on both sides of the air thrusting guide platform 3 or the starting guide platform 2 to avoid the shield 5 from rotating due to uneven force. Preferably, 6 anti-twist pads are welded to the middle shield and the front shield, and 2 anti-twist pads are welded to the tail shield.

[0045] Furthermore, to prevent the shield body 5 from buoyancy during air thrusting, this application does not use negative pressure segments, but instead provides a corresponding anti-buoyancy mechanism for the shield body 5 within the guide tunnel 8. The anti-buoyancy mechanism includes guide rails 6 and sliding blocks 7. At least two guide rails 6 extend along the mileage direction of the guide tunnel 8. In this application, five guide rails 6 are provided, evenly distributed in the upper half of the guide tunnel 8 and circumferentially. Specifically, one of the five guide rails 6 is located at the arch, and the other four guide rails 6 are symmetrically distributed within a 180° range on both sides of the arch. The guide rails 6 can be dovetail grooves, and multiple sliding blocks 7 are slidably mounted within the guide rails 6. Each sliding block 7 has a dovetail-shaped slider 9 corresponding to the dovetail groove. Figure 2 As shown, the slide block 7 is equipped with a push rod 10, which can be a pneumatic cylinder or a hydraulic cylinder. The side of the guide rail 6 has evenly distributed hooks corresponding to the hydraulic cylinder's hydraulic pipes, allowing for the arrangement and storage of the hydraulic pipes. The end of the push rod 10 is equipped with an arc-shaped support plate 11 corresponding to the outer wall of the shield body 5. The arc-shaped support plate 11 is adapted to the outer wall of the shield body 5. One end of the guide rail 6 extends to the shield working face, and the other end protrudes from the guide hole 8 to facilitate the insertion of the slide block 7. During the advancement of the shield body 5, the anti-buoyancy mechanism enters the guide hole 8 synchronously with the shield body 5. Specifically, according to the advancement progress, multiple slide blocks 7 are sequentially and spaced within each guide rail 6, providing multiple anti-buoyancy mechanisms along the length of the shield body 5. The mechanism is evenly distributed. The slide block 7 is supported on the outer wall of the shield body 5 by the top rod 10 and slides synchronously with the shield body 5 in the guide rail 6, thereby providing anti-buoyancy support for the upper part of the shield body 5. Multiple positioning detection points are evenly distributed on the shield body 5. The positioning detection points are monitored by a total station to obtain the attitude of the shield body 5. The attitude of the shield body 5 is adjusted by adjusting the length of the top rod 10 based on the attitude of the shield body 5, thereby ensuring the stability of the shield body 5 during air thrust. When the excavation begins, the slider 9 abuts against the end of the guide tunnel 8, thereby sliding relative to the shield body 5 and then separating from the shield body 5. Furthermore, the shield body 5 can be adjusted when it begins to enter the tunnel, ensuring the accuracy of the shield body 5 entering the tunnel.

[0046] In this embodiment, the length of the guide rail 6 extending into the working well 1 is adapted to the length of the slide block 7. The guide rail 6 can extend to the outer periphery of the guide hole 8, and the part extending out of the outer periphery of the guide hole 8 transitions into the hole through an arc or an incline, thereby facilitating the installation of the slide block 7. The middle part of the slide block 7 is provided with a mounting hole corresponding to the top rod 10, and the diameter of the mounting hole is adapted to the top rod 10.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for hoisting and installing a single-shield TBM, characterized in that, include: Step S1: Construct the launching platform, pilot tunnel, and empty propulsion platform; harden the ground outside the working shaft using mixing piles. The air-launching platform is located inside the guide tunnel, with its rear end extending out of the guide tunnel. A gap is left between the air-launching platform and the launching platform to serve as a circumferential welding channel. Longitudinal welding channels corresponding to the shield body are provided on both sides of the launching platform. Step S2: Divide both the middle shield and the front shield into six lifting blocks. Name the top lifting block of the middle shield as Middle Lifting Block 1, and name the remaining lifting blocks of the middle shield in clockwise order as Middle Lifting Block 2, Middle Lifting Block 3, Middle Lifting Block 4, Middle Lifting Block 5, and Middle Lifting Block 6. Name the top lifting block of the front shield as Front Lifting Block 1, and name the remaining lifting blocks of the front shield in clockwise order as Front Lifting Block 2, Front Lifting Block 3, Front Lifting Block 4, Front Lifting Block 5, and Front Lifting Block 6. First, hoist the front lifting blocks three, four, and five into the well and pre-tighten them. The front shield is located at the front end of the launching guide platform so that the front end face of the front shield is above the circumferential welding channel. After welding the cutter head, turn it over and lower it to the rear end of the empty propulsion platform so that the cutter head and the front lifting blocks three, four, and five are pre-tightened through the circumferential welding channel. Step S3: Push the cutterhead and front shield forward along the starting guide platform so that the rear end face of the front shield is above the circumferential welding channel. Then, lower the middle lifting blocks three, four, and five into the well and connect them to the front shield. After the main drive is lowered into the well, connect it to the cutterhead. Then, lower the front lifting blocks two, six, one, two, six, and one into the well in sequence. Step S4: Push forward and then lower and connect the cross beam and shield tail in sequence. After connecting the external hydraulic pump station, push the shield forward. Then lower and connect the trailer in sequence. After the pipeline connection is debugged, push the shield to the starting excavation position. The shield tail is installed in four sections. When the bottom block of the shield tail is installed, its center line is aligned with the center line of the middle shield, and its front end is aligned with the cross section of the tail of the middle shield. Then the left block, right block and top block are installed in sequence. During the installation process, a total station is used to measure the position of the shield tail, measure the distance from the inner circle of the bottom block to the center line, and adjust the overall roundness of the shield tail and its coaxiality with the middle shield as needed. After the tail shield welding is completed, the tail shield brushes are assembled. The starting points of the welding of the four tail shield brushes must be 1m apart, and the welds of the second, third, and fourth tail shield brushes are located in the middle of the previous tail shield brush.

2. The single-shield TBM hoisting and installation method according to claim 1, characterized in that, The upper surfaces of the air thruster platform and the launch platform are arc-shaped corresponding to the shield body. Interconnected air thruster tracks are laid on the air thruster platform and the launch platform. The air thruster tracks are fixed to the air thruster platform and the launch platform by embedded parts. Lubricating oil is applied to the air thruster tracks.

3. The single-shield TBM hoisting and installation method according to claim 1, characterized in that, Reaction grooves are set on both sides of the launching guide platform and the empty thrust platform. Reaction seats are installed in the reaction grooves in a detachable manner. The reaction seats are connected to hydraulic cylinders, which are connected to the outer wall of the shield body by hinges.

4. The single-shield TBM hoisting and installation method according to claim 1, characterized in that, Anti-torsion pads are welded on both sides of the outer wall of the shield. Rollers are provided on the lower end face of the anti-torsion pads, and the rollers are supported on the flat surfaces on both sides of the air propulsion platform or the starting platform.

5. The single-shield TBM hoisting and installation method according to claim 1, characterized in that, An anti-buoyancy mechanism corresponding to the shield body is provided in the guide tunnel. The anti-buoyancy mechanism includes guide rails and slides. No less than two guide rails extend along the large mileage direction of the guide tunnel. Multiple slides are slidably assembled in the guide rails. A top rod is provided in the slide. The end of the top rod is provided with an arc-shaped support plate corresponding to the outer wall of the shield body.

6. The single-shield TBM hoisting and installation method according to claim 5, characterized in that, The guide rails are evenly distributed in the upper half of the guide tunnel and are evenly distributed around the circumference of the guide tunnel. One end of the guide rail extends to the shield working face, and the other end extends out of the guide tunnel and into the working shaft. As the shield enters the pilot tunnel, multiple sliding blocks are placed sequentially at intervals in each guide rail. The sliding blocks are supported on the outer wall of the shield by top rods and slide with the shield within the guide rail.

7. The single-shield TBM hoisting and installation method according to claim 5, characterized in that, Multiple positioning detection points are evenly distributed on the shield body. The positioning detection points are monitored by a total station to obtain the shield body's attitude. The shield body's attitude is adjusted by adjusting the length of the top rod.

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