CN116291471A - Construction Method and Excavation Equipment of Large Diameter Shaft in Upper Soft and Lower Hard Ground - Google Patents

Abstract

The invention relates to the technical field of shaft construction, and discloses a construction method and tunneling equipment for a large-diameter shaft with a soft upper stratum and a hard lower stratum. Aims at solving the technical problems that the construction diameter of a vertical shaft is smaller, the applicable stratum is single, and the construction steps are difficult to synchronously implement in the prior art. The construction method comprises the steps of splicing the cutting edge angle with the cylindrical well wall, excavating rock and soil, discharging the mixture of excavated dregs and slurry to the ground, sinking the cutting edge angle and the cylindrical well wall. The tunneling equipment comprises a large-size expanding drill bit, a slag discharging pipeline, a drill rod and a rotary drive. The invention not only can excavate soft soil and soft rock stratum, but also can excavate hard rock stratum; and synchronous implementation of shaft excavation and well wall installation is realized.

Description

Construction Method and Excavation Equipment of Large Diameter Shaft in Upper Soft and Lower Hard Ground

technical field

The invention relates to the technical field of shaft construction, in particular to a large-diameter shaft construction method and excavation equipment in upper soft and lower hard strata.

Background technique

At present, there are many types of equipment and construction methods for mechanical excavation of shaft shafts, and shaft excavation equipment for blind shaft shafts includes shaft boring machines and shaft drilling rigs.

In the field of prior art, in the invented Chinese patent documents: 202011314104.1 invented a sinking shaft boring machine and its well-forming method. The sinking shaft boring machine includes a main engine, a sinking system, a pipeline system and a main engine recovery system . The well-forming method of the sinking shaft boring machine includes excavation and slag discharge, lining installation, sinking, and structural bottom sealing. In the invented Chinese patent literature: 202011238787.7 invented a sinking shaft boring machine suitable for soft soil layers, including segment, traction mechanism, excavation mechanism, lifting mechanism, and mud pipeline conveying mechanism. The above scheme adopts the cantilever-type washing head for excavation, which is only suitable for the excavation of soft soil and soft rock, and when the uniaxial compressive strength of the rock exceeds 100 MPa, it is almost impossible to excavate.

In the prior art field, in the invented Chinese patent literature: 202010645876.7 invented a full-face shaft boring machine, including a cutter head, a muck transfer mechanism and a slag discharge mechanism; Cross-section cutterhead excavation is suitable for rock formations, and soft soil formations are prone to partial wear of hobs and sticky cutterheads, and are not suitable for soft soil formations.

In the field of prior art, in the invented Chinese patent literature: 201110412546.4 invented a shaft forward and reverse shaft comprehensive sinking method, including using a shaft drilling rig to drill to the bedrock section, and lifting the liquid during the drilling process by using a shaft drilling rig. The generated mud containing cuttings is discharged to the ground at high speed; the well walls of each section are prefabricated on the ground; counterweight water is added to the drilling well, and the well wall of each section is slowly sunk into the wellbore of the topsoil section by using the buoyancy of the mud during drilling to the well wall and welded in sequence; fill grouting between the well wall and the rock side outside the well wall, the lowest layer is filled with cement slurry, and then filled with cement slurry and gravel alternately step by step upward to obtain the topsoil section for drilling; lower the raise drilling rig And fix it to the bottom of the topsoil section drilling; use the raise drilling machine to reversely ream the hole to form a slip hole; brush it to the predetermined diameter of the wellbore. In this scheme, the mud wall is used to temporarily support the surrounding rock when the wellbore is excavated, and the wellbore is installed by suspending and sinking after the excavation is completed. The installation and excavation of the diameter wellbore and well wall are not synchronized, which may easily lead to the collapse of the surrounding rock.

Therefore, in shaft construction, how to simultaneously adapt to soft soil formation and hard rock formation, so as to realize the synchronous implementation of shaft wall installation and shaft excavation is an urgent problem to be solved in this technical field.

Contents of the invention

In view of the above technical problems, the present invention provides a large-diameter shaft construction method and excavation equipment in upper soft and lower hard strata, which solves the technical problems in the prior art that the shaft construction diameter is small, the applicable stratum is single, and the construction steps are difficult to implement synchronously. The invention can excavate not only soft soil and soft rock formations, but also hard rock formations; the simultaneous implementation of shaft excavation and shaft wall installation is realized.

According to one aspect of the present invention, a method for constructing a large-diameter shaft in upper soft and lower hard formations is provided, and the construction steps include:

S1 Assembling the edge angle and the cylindrical shaft wall: at the beginning of the work step, determine the assembly edge angle and the cylindrical shaft wall size, the predetermined working distance of the shaft wall suspension device according to the predetermined shaft size and the geological information of the survey, and the assembled The outer diameter of the cylindrical shaft wall is smaller than the inner diameter of the shaft;

S2 ground breaking: excavating rock and soil vertically downward from the surface using shaft excavation equipment equipped with large-size expanding drill bits;

S3 balanced excavation: mud is filled above the shaft excavation equipment, and the shaft excavation equipment is equipped with a mud-water circulation system, the inlet of the mud-water circulation system is at the bottom of the shaft excavation equipment, and the mud-water circulation system passes through the shaft excavation equipment The rear outlet is connected to the ground, so that the excavated slag and mud mixture can be discharged from the ground through the slag discharge pipeline by means of the mud water circulation system;

S4 The bottom of the shaft is formed and the shaft wall is placed at the same time: after the excavation reaches the predetermined distance, at the same time as the excavation, the steel strand is lowered by the shaft wall suspension device, so that the pre-assembled edge and the cylindrical shaft wall sink, and irrigation is added between the two. become muddy to maintain balance;

S5 Shaft Construction Forming: Repeat steps S2~S4 to synchronize the shaft excavation and shaft wall installation until the entire shaft construction is completed; in repeating steps S2~S4, the large-size expanding drill bit is replaced with a hob or cutter according to the hardness of the rock formation. knife.

In some embodiments of the present invention, the mud circulation system adopts a compressed air reverse circulation flushing method to improve the slag absorption capacity of the mud circulation system.

In some embodiments of the present invention, in the construction step S3, filling the mud above the shaft excavation equipment also includes injecting mud into the shaft to maintain the stability of the surrounding rock of the shaft; Thixotropic mud is injected into the rock gap to stabilize the surrounding rock and lubricate the sinking of the well wall.

In some embodiments of the present invention, in the construction step S3, filling the mud above the shaft excavation equipment further includes injecting mud into the shaft to maintain the stability of the surrounding rock of the shaft.

In some embodiments of the present invention, the construction step S4 further includes injecting thixotropic mud into the gap between the well wall and the surrounding rock to stabilize the surrounding rock and lubricate the well wall to sink.

According to another aspect of the present invention, there is provided a large-diameter shaft excavation equipment in upper soft and lower hard strata, which realizes the above-mentioned large-diameter shaft construction method in upper soft and lower hard stratum, and is installed on a frame, including a large-size expanding drill bit, a Slag pipeline, drill pipe, rotary drive; the large-size expanding drill bit includes a drill body and at least one expanding cutter movably connected thereto, so as to realize the diameter expanding of the shaft, and the lower end of the drill pipe is connected to the large-sized The diameter-expanding drill bit is connected to the rotary drive at the upper end; the slag discharge pipe is located inside the drill pipe, the lower end is connected to the bottom of the large-sized diameter-expanding drill bit, and the upper end is connected to the ground.

In some embodiments of the present invention, the drill bit is a rotary body, the bottom of which is provided with a multi-stage cutter head capable of cutting rock and soil, and its side wall is provided with connecting elements capable of connecting expanding cutters.

In some embodiments of the present invention, the expanding cutter includes a fixed plate, a connecting rod set, an expanding cutter head and a hydraulic adjustment element, one end of the connecting rod set is connected to the fixing plate, and the other end is connected to the expanding cutter head One end of the hydraulic adjustment element is connected to the connecting rod group, and the other end is hinged and connected to the side wall of the drill bit; the connecting rod group includes an active rod and a passive rod, one end of the passive rod is connected to the fixed plate, and the other end is connected to the expanding diameter The cutter head, the middle part of the active rod is connected to the hydraulic adjustment element to realize rotation, the driven rod is provided with an adjustment groove to realize length adjustment, and the connecting rod group drives the opening and closing of the expanding cutter .

In some embodiments of the invention, the multi-stage cutter head includes cutting tools or hobs.

In some embodiments of the invention, the expanding cutter head comprises a cutting tool or a hob.

In some embodiments of the present invention, the drill bit body further includes a central fixed cutterhead and an edge telescopic cutterhead, wherein the edge telescopic cutterheads are evenly distributed around the middle fixed cutterhead, and the edge telescopic cutterheads are The disc is provided with a telescopic element between the drill body, and the telescopic element is connected with an electric control element/hydraulic element to drive it to expand and contract.

In some embodiments of the present invention, a hinged connection is provided between the telescopic arm and the outer wall of the drill bit, and a hinged connection is provided between the telescopic arm and the fixing plate.

The beneficial effects of the present invention are:

The drill bit is equipped with a multi-stage cutter head including cutting tools and hobs, which can excavate not only soft soil and soft rock formations, but also hard rock formations;

After the shaft is excavated to a certain distance, the shaft wall suspension device is used to sink the bevel and the cylindrical shaft wall, so that the shaft excavation and shaft wall installation can be implemented simultaneously;

Inject the treated mud into the well to realize the rapid stabilization of the surrounding rock of the newly excavated wellbore;

Inject thixotropic mud into the gap between the well wall and the surrounding rock to stabilize the surrounding rock and lubricate the well wall to sink;

The mud circulation system adopts the compressed air reverse circulation washing method to improve the slag absorption capacity of the mud circulation system;

Set expansion cutters to realize the expansion of shaft construction;

Set the telescopic arm, which can move the position of the expanding cutter;

The expansion plate is set to facilitate the adjustment of the force point of the drill bit construction, and the construction efficiency is high;

The telescopic arm is equipped with a hinge connection, which is convenient for adjusting the direction of the expansion cutter.

Description of drawings

Fig. 1 is the sectional view of large-diameter shaft construction in upper soft and lower hard formations of the present invention;

Fig. 2 is a schematic diagram of the structure of large-diameter vertical shaft excavation equipment in upper soft and lower hard formations;

Fig. 3 is a structural schematic diagram of a large-size expanding drill bit protruding from the expanding cutter;

Fig. 4 is a schematic diagram of the structure of a large-size expanding drill bit shrinking and expanding cutter;

The names of the components in the figure: 1. Rack; 2. Large-size expanding drill bit; 20. Drill body; 21. Expanding cutter; 22. Multi-stage cutter head; 23. Drill side wall; 24. Movable components; 25 , expansion cutter head; 26, telescopic arm; 27, fixed plate; 28, telescopic plate; 29, hinge support connection; 3, slag discharge pipeline; 4, drill pipe; 5, rotary drive; 6, edge angle; 7, Cylindrical well wall; 8. Well wall suspension device.

Detailed ways

The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

Example 1

This example invents a method for constructing a large-diameter shaft in upper soft and lower hard formations, referring to Fig. 1, including a method for constructing large-diameter shafts in upper soft and lower hard formations, and the construction steps include:

S1 Assembling the edge angle and the cylindrical shaft wall: at the beginning of the work step, determine the assembly edge angle and the cylindrical shaft wall size, the predetermined working distance of the shaft wall suspension device according to the predetermined shaft size and the geological information of the survey, and the assembled The outer diameter of the cylindrical shaft wall is smaller than the inner diameter of the shaft;

S2 ground breaking: excavating rock and soil vertically downward from the surface using shaft excavation equipment equipped with large-size expanding drill bits;

S3 balanced excavation: mud is filled above the shaft excavation equipment, and the shaft excavation equipment is equipped with a mud-water circulation system, the inlet of the mud-water circulation system is at the bottom of the shaft excavation equipment, and the mud-water circulation system passes through the shaft excavation equipment The rear outlet is connected to the ground, so that the excavated slag and mud mixture can be discharged from the ground through the slag discharge pipeline by means of the mud water circulation system;

S4 The bottom of the shaft is formed and the shaft wall is placed at the same time: after the excavation reaches the predetermined distance, at the same time as the excavation, the steel strand is lowered by the shaft wall suspension device, so that the pre-assembled edge and the cylindrical shaft wall sink, and irrigation is added between the two. become muddy to maintain balance;

S5 Shaft Construction Forming: Repeat steps S2~S4 to synchronize the shaft excavation and shaft wall installation until the entire shaft construction is completed; in repeating steps S2~S4, the large-size expanding drill bit is replaced with a hob or cutter according to the hardness of the rock formation. knife.

The mud circulation system adopts the compressed air reverse circulation washing method to improve the slag absorption capacity of the mud circulation system.

In the construction step S3, filling the mud above the shaft excavation equipment also includes injecting mud into the shaft to maintain the stability of the surrounding rock of the shaft.

The construction step S4 also includes injecting thixotropic mud into the gap between the well wall and the surrounding rock to stabilize the surrounding rock and lubricate the well wall to sink.

Among them, thixotropic mud is a kind of mixed liquid, which contacts the soil under pressure and penetrates into the soil layer, slowly spreads out, and forms a whole with the surrounding soil. As the amount of infiltration increases, the soil and mud will form a layer of dense seepage blocks. At the same time, under the action of the mud pressure, the blocks are tightly combined with each other, thus forming a stable mud and soil around the pipeline. A mud jacket made of a combination of bodies. Grouting can play the role of lubricating, reducing drag and supporting the soil; thixotropic mud has fluidity in the process of conveying and pouring, and it is a glue-packed liquid, which changes the dry friction between the outer wall of the pipeline and the soil layer into wet friction, reducing the friction. little friction. After standing still for a certain period of time, the mud consolidates into a gel form, which can support the soil, balance the soil pressure, stabilize the soil around the pipeline, and prevent ground subsidence. Attention should be paid to the grouting construction: the uniformly stirred mud should be allowed to stand for a certain period of time before grouting; before grouting, the grouting equipment should be checked by water injection, and grouting can only be done after confirming that the equipment is normal; the grouting flow rate and pressure during the grouting process It is adjusted according to the soil quality and covering soil depth; the pressure of grouting is greater than the pressure of the mud bin; the principle of "synchronous grouting for jacking, grouting along the line, and 1:1 arrangement of grouting pipes" should be followed; during synchronous grouting, The amount of grout injected must be 1.5 times greater than the overbreak of the cutter head; the jacking speed must match the amount of grout injected to form the drag-reducing lubrication of the slurry sleeve. Thixotropic mud is made by mixing bentonite, water and admixture in a certain proportion. In order to strengthen the consolidation of the thixotropic mud after the jacking is completed, a coagulant (lime paste) can be added, but in order to maintain fluidity during construction, a retarder (industrial hexasaccharide) and a plasticizer must also be added (sodium abietate). The grouting process goes round and round throughout the entire jacking process.

Among them, the working principle of the compressed air reverse circulation well cleaning method is to send the compressed air to the gas-water mixing chamber downhole through the gas supply pipeline, and make the compressed air mix with the circulating fluid in the drill pipe, thereby forming a liquid with a density higher than that of the liquid outside the drill pipe. Small column of mixed liquid. Under the effect of the pressure difference inside and outside the pipe, the mixed liquid rises along the inner cavity of the drill pipe and is discharged to the sedimentation tank through the slag discharge pipe. The circulating liquid after sedimentation flows continuously into the annular gap in the well in a self-flowing manner, forming a reverse circulation. Drilling efficiency is high by adopting air reverse circulation continuous sampling. The circulating medium is first pumped (flowed) into the drill bit at the bottom of the hole from the inner and outer pipe annulus of the double-walled drill pipe or the annular space of the drill hole, and then returns to the surface from the central passage of the drill pipe (or the central passage of the inner pipe of the double-walled drill pipe). , to complete the well flushing function. The back passage of the flushing medium has a small cross-section, fast flow rate, strong carrying capacity for cuttings (including rock samples that can be used by the geological department), greatly reduces the phenomenon of repeated breakage at the bottom of the hole, and has a good flushing effect; The scouring is small, which is conducive to the stability of the drilling and reduces the accidents in the hole such as buried drill and broken drill pipe; the flushing medium has a good cooling effect on the drill bit, the drilling speed is fast, and the service life of the drill bit is long; it can realize drilling and sampling at the same time. Know the situation of the drilled formation at any time. The core collection rate is high, the representativeness is strong, and the geological record and the real description of the stratum are convenient; when the air is used as the circulating medium, water-saving drilling can be realized, and the advantages of construction in arid and water-deficient areas are more prominent.

Example 2

This example invents a large-diameter vertical shaft excavation equipment for upper soft and lower hard formations, as shown in Fig. 2 to Fig. 4, which is installed on the frame 1 and includes a large-size expanding drill bit 2, a slag discharge pipeline 3, a drill pipe 4, and a rotary drive 5 The large-size expanding drill bit 2, referring to Fig. 3 and Fig. 4, comprises a drill body 20 and at least one expanding cutter 21 movably connected thereto, so as to realize the expanding diameter of the shaft, and the lower end of the drill pipe 4 is connected to the large-sized expanding diameter The upper end of the drill bit 2 is connected to the rotary drive 5; the slag discharge pipe 3 is located inside the drill pipe 4, the lower end is connected to the bottom of the large-size enlarged diameter drill bit 2, and the upper end is connected to the ground. The drill bit body 20 is a revolving body, the bottom is provided with a multi-stage cutter head 22 capable of cutting rock and soil, and the drill bit side wall 23 is provided with connecting elements capable of connecting the expanding cutter 21 . The expansion cutter comprises a fixed plate 27, a connecting rod group 24, an expanding cutter head 25 and a hydraulic adjustment element 26. One end of the connecting rod group 24 is connected to the fixing plate 27, and the other end is connected to the expanding diameter cutter head 25; one end of the hydraulic adjustment element 26 is Connect the connecting rod group 24, and the other end is hinged to connect the connecting element of the drill bit side wall 23; The middle part of the hydraulic adjustment element 26 is connected to realize rotation, and the driven rod is provided with an adjustment groove to realize length adjustment, and then the connecting rod group 24 drives the expansion cutter 25 to open and close. The multi-stage cutter head 22 includes cutting tools or hobs. Expanding cutter head 25 includes cutting tools or hobs. The drill body 20 also includes a central fixed cutterhead 28 and an edge telescopic cutterhead 22, wherein the edge telescopic cutterhead 22 is evenly distributed around the middle fixed cutterhead 28 in a ring, and the edge telescopic cutterhead 22 is provided with a telescopic element between the drill body 20, The telescopic element is connected with the electric control element/hydraulic element/spring to drive it to expand and contract. A hinge connection 29 is provided between the telescopic arm 26 and the side wall 23 of the drill bit, and a hinge connection 29 is provided between the telescopic arm 26 and the fixed plate 27 .

While a few preferred embodiments of the invention have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of this application and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (10)

1. A construction method of a large-diameter vertical shaft with soft upper stratum and hard lower stratum is characterized by comprising the following steps: the construction steps comprise:

s1, splicing the cutting edge angle and the cylindrical well wall, namely, at the beginning of a working step, determining the splicing cutting edge angle, the size of the cylindrical well wall and the working preset distance of a well wall suspension device according to preset shaft size and surveyed geological information, wherein the outer diameter of the spliced cylindrical well wall is smaller than the inner diameter of the shaft;

s2, breaking the earth, namely excavating rock and soil from the earth surface vertically downwards by adopting shaft tunneling equipment with a large-size expanding drill bit;

s3, balanced excavation, namely filling slurry above shaft tunneling equipment, wherein a slurry circulation system is arranged in the shaft tunneling equipment, an inlet of the slurry circulation system is positioned at the bottom of the shaft tunneling equipment, and an outlet of the slurry circulation system is communicated with the ground after penetrating through the shaft tunneling equipment so as to discharge an excavated mixture of slag and slurry out of the ground through a slag discharging pipeline by using the slurry circulation system;

s4, forming the bottom of the vertical shaft and simultaneously placing a shaft wall, namely, after the vertical shaft is excavated to a preset distance, simultaneously, adopting a shaft wall suspension device to lower a steel strand so that a pre-assembled cutting edge angle and a cylindrical shaft wall are sunk, and adding thixotropic slurry between the pre-assembled cutting edge angle and the cylindrical shaft wall to keep balance;

s5, shaft construction molding, namely repeating the steps S2-S4, and synchronously carrying out shaft excavation and shaft wall installation processes until the whole shaft construction is completed; and in the repeated steps S2-S4, the large-size expanding drill bit is replaced by a hob or a cutter according to the hardness of the rock stratum.

2. The construction method of the large-diameter vertical shaft of the upper soft and lower hard stratum as claimed in claim 1, wherein the construction method comprises the following steps: the mud circulation system adopts a compressed air reverse circulation well washing method to improve the slag sucking capacity of the mud circulation system.

3. The construction method of the large-diameter vertical shaft of the upper soft and lower hard stratum as claimed in claim 1, wherein the construction method comprises the following steps: in the construction step S3, filling slurry above the shaft tunneling equipment further comprises injecting slurry capable of maintaining stability of surrounding rock of the shaft into the shaft; the construction step S4 further comprises the step of injecting thixotropic slurry into a gap between the well wall and the surrounding rock so as to stabilize the surrounding rock and lubricate the sinking of the well wall.

4. The utility model provides a go up soft lower hard stratum major diameter shaft tunnelling equipment, realizes the upper soft lower hard stratum major diameter shaft construction method of claim, installs on the frame, its characterized in that: comprises a large-size expanding drill bit, a slag discharging pipeline, a drill rod and a rotary drive; the large-size expanding drill bit comprises a drill bit body and at least one expanding cutter movably connected with the drill bit body so as to realize the expanding of a vertical shaft, wherein the lower end of the drill rod is connected with the large-size expanding drill bit, and the upper end of the drill rod is connected with the rotary drive; the slag discharging pipeline is positioned in the drill rod, the lower end of the slag discharging pipeline is communicated with the bottom of the large-size expanding drill bit, and the upper end of the slag discharging pipeline is communicated with the ground.

5. The large-diameter vertical shaft tunneling apparatus for upper soft and lower hard strata as claimed in claim 4 wherein: the drill bit is a revolving body, the bottom is provided with a multi-stage cutterhead capable of cutting rock and soil, and the side wall of the drill bit is provided with a connecting element capable of being connected with a diameter-enlarging cutter.

6. The large-diameter vertical shaft tunneling apparatus for upper soft and lower hard strata as claimed in claim 4 wherein: the expanding cutter comprises a fixed plate, a connecting rod group, an expanding cutter disc and a hydraulic adjusting element, wherein one end of the connecting rod group is connected with the fixed plate, and the other end of the connecting rod group is connected with the expanding cutter disc; one end of the hydraulic adjusting element is connected with the connecting rod group, and the other end of the hydraulic adjusting element is hinged with the side wall of the drill bit; the connecting rod group includes initiative pole and passive pole, the fixed plate is connected to the one end of passive pole, and the expanding blade disc is connected to the other end, the middle part of initiative pole is connected hydraulic pressure adjusting element is in order to realize rotating, be equipped with the adjustment tank on the driven pole in order to realize length adjustment, and then the connecting rod group drives opening and shutting of expanding cutting tool.

7. The large-diameter vertical shaft tunneling apparatus for upper soft and lower hard strata as claimed in claim 5, wherein: the multi-stage cutterhead includes a cutting tool or hob.

8. The large-diameter vertical shaft tunneling apparatus for upper soft and lower hard strata as claimed in claim 6 wherein: the expanding cutterhead comprises a cutting tool or a hob cutter.

9. The large-diameter vertical shaft tunneling apparatus for upper soft and lower hard strata as claimed in claim 4 wherein: the drill bit body further comprises a middle fixed cutter disc and edge telescopic cutter discs, wherein the edge telescopic cutter discs are annularly and uniformly distributed around the middle fixed cutter disc, telescopic elements are arranged between the edge telescopic cutter discs and the drill bit body, and the telescopic elements are connected with an electric control element/a hydraulic element to drive the electric control element/the hydraulic element to stretch.

10. The large-diameter vertical shaft tunneling apparatus for upper soft and lower hard strata as claimed in claim 4 wherein: the telescopic arm is connected with the outer wall of the drill bit through a hinge, and the telescopic arm is connected with the fixing plate through a hinge.

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