A construction method for a cofferdam with PLC method piles

Abstract

The present invention belongs to the technical field of pile cofferdam construction, in particular to a construction method for a PLC method pile cofferdam. Step 1: Measuring and lofting. Pilot holes are used for lofting, and the positioning of the pilot holes is completed by a total station. After lofting, pilot hole construction is carried out. After the pilot hole construction is completed, steel sheet piles are driven. After the pilot hole construction is completed, precise lofting of the steel sheet piles is carried out again. For this construction method of the PLC method pile cofferdam, through this device, the PLC program automatically controls the winch drive motor to perform winding or releasing operations, drives and controls the ring plate to move up or down inside the steel pipe pile, and cooperates with proximity switches, tension sensors, inclination sensors, and rotary encoders to automatically control the measurement reading counting and calculation, realizing the intelligentization of steel cofferdam construction, improving construction efficiency and quality, accurately measuring the height of the concrete surface, and reducing the adverse effects caused by inaccurate existing measurements, such as increasing the chiseling work and reducing the subsequent construction of the bearing platform.

Description

Technical Field

[0001] The present invention relates to the technical field of pile cofferdam construction, and particularly relates to a construction method for a PLC method pile cofferdam. Background Art

[0002] For pile cofferdam construction, before driving steel pipe piles and steel sheet piles, pilot holes need to be drilled for pile planting, the bottom is sealed, and then the water is pumped out for anti-seepage treatment to form a dry working environment. In actual construction, the construction of the steel pipe pile bite and the bottom-sealing concrete is crucial.

[0003] In the construction of the traditional cofferdam bottom-sealing concrete, when pouring the bottom-sealing concrete, a sounding rope is used to measure the height of the concrete surface. During the measurement, a counterweight is added to one end of the rope and placed inside the steel pipe pile. Since the self-weight of the counterweight itself is likely to sink into the concrete during the measurement, the measured value is inaccurate. In addition, when the counterweight is inclined and touches during the lowering process, it will also cause a large deviation in the measured size, resulting in low efficiency and large errors. It is not easy to control the elevation of the top surface of the bottom-sealing concrete, which increases the chiseling work or affects the effective thickness of the bottom-sealing concrete, bringing adverse effects to the subsequent construction of the bearing platform.

[0004] Based on the above existing technical problems, a construction method for a PLC method pile cofferdam is needed. Summary of the Invention

[0005] Based on the existing technical problems, the present invention proposes a construction method for a PLC method pile cofferdam.

[0006] A construction method for a PLC method pile cofferdam proposed by the present invention includes: Step 1, surveying and setting out. Pilot hole piles are used for setting out, and the positioning of the pilot hole piles is completed by a total station. After the setting out is completed, pilot hole construction is carried out. After the pilot hole construction is completed, steel sheet piles are driven. After the pilot hole construction is completed, another precise setting out of the steel sheet piles is carried out;

[0007] Step 2, guiding equipment. To ensure the verticality of the steel sheet pile driving, before driving, steel sheet pile positioning piles are driven first. Brackets are welded on the positioning piles, and a guide beam is installed to form a frame-type cofferdam as the guiding equipment for pile driving. The guiding frame is set in two layers up and down, and the boundaries of each sheet pile are marked on the guiding frame to correct the deviation while driving during the pile driving process to prevent large deviations;

[0008] Step 3, pile planting and closing;

[0009] Step 4, backfilling of the pilot hole, a. Cleaning and filling the hole, b. Backfilling the outer groove hole of the cofferdam, c. Backfilling the inner groove hole of the cofferdam;

[0010] Step 5: Installation of the support system and anti-leakage measures. The steel sheet pile support system mainly consists of double-piled H450mm steel sections of Q345 to form the waling and supports. The first layer of waling is horizontally installed 1.4m below the top of the cofferdam, and the second layer of waling is installed 4.1m from the top of the cofferdam. After the cofferdam is closed, while pumping water, the internal supports are installed layer by layer. The internal supports are arranged from top to bottom and installed while pumping water.

[0011] Step 6: Backfilling of the foundation pit; after the installation of the waling, according to the positional relationship between the bottom-sealing concrete and the riverbed top, the inside of the steel sheet pile cofferdam needs to be backfilled. The dump truck loads pebble river sand and transports it to the cofferdam through the construction trestle and unloads it at the bottom of the cofferdam, and the 25m long-arm excavator is used for preliminary leveling. Then, the filling height is measured. When the filling height meets the requirements, the grab or long-arm excavator is used to level the bottom of the pit, and the bottom is measured with a sounding rope at intervals of 50 - 100cm to ensure the flatness of the base.

[0012] Step 7: Pouring of the bottom-sealing concrete. The bottom-sealing concrete is constructed by the underwater bottom-sealing method. Before construction, the height of the concrete surface is quickly detected through a height measuring mechanism to assist the construction of the bottom-sealing concrete.

[0013] Step 8: Erection of the bottom-sealing platform. The bottom-sealing platform utilizes the already erected drilling platform. A conduit support is erected on the top of the drilling platform, and a footboard is laid on it to form a pedestrian passage and a conduit pouring platform. Railings and corresponding protective nets are set on the platform to ensure the safety of personnel during construction.

[0014] Preferably, the height measuring mechanism in Step 7 includes steel pipe piles and an equipment placement platform. The equipment placement platform is located above the water. On one side of the top of the equipment placement platform, a hoist support seat is fixedly installed. On the opposite surfaces of the two hoist support seats, a hoist shaft is rotatably connected through bearings. On the arc surface of the hoist shaft, a roller is fixedly installed. A steel wire rope is wound and connected to the surface of the roller.

[0015] Preferably, a hoist drive motor is fixedly installed on one side of one of the hoist support seats. The output shaft of the hoist drive motor is fixedly installed on the opposite surface of the hoist shaft through a coupling. On one side of the other hoist support seat, a connecting plate is fixedly installed. Above the connecting plate, a rotary encoder is fixedly installed. One side of the rotary encoder is fixedly installed on the opposite end of the hoist shaft through a coupling.

[0016] Preferably, on the other side of the top of the equipment placement platform, a hinge seat is fixedly installed. At one end of the top of the hinge seat, a connecting rod is hinged. At the top of the connecting rod, a wire unwinding seat is fixedly installed. On the U-shaped opposite inner walls of the wire unwinding seat, a wire unwinding shaft is rotatably connected through bearings. On the arc surface of the wire unwinding shaft, a wire wheel is fixedly installed. The inner wall of the groove of the wire wheel is slidably inserted into the arc surface of the steel wire rope.

[0017] Preferably, a tension sensor is fixedly installed at the bottom of the steel rope. A buckle is fixedly installed below the tension sensor through a rope. A sleeve is clamped at the bottom of the buckle. A control ring plate is threadedly connected to the bottom of the sleeve. A proximity switch is fixedly installed on the inner top wall of the sleeve.

[0018] Preferably, guide holes are formed in the top of the control ring plate. The four guide holes are annularly arrayed on the surface of the control ring plate. Guide posts are slidably inserted into the inner walls of the guide holes. Trigger ring plates are fixedly installed at the bottoms of the four guide posts. Air bags are fixedly installed on the arc surfaces of the trigger ring plates.

[0019] Preferably, a limit hole is formed in the center of the top of the control ring plate. A plug hole is formed in the inner bottom wall of the limit hole. A limit ring is slidably inserted into the inner wall of the limit hole. A sliding rod is fixedly installed at the bottom of the limit ring. The arc surface of the sliding rod is slidably inserted into the inner wall of the plug hole. The top of the limit ring is in contact and extrusion with the contact point of the proximity switch. The bottom of the sliding rod is fixedly installed with the center of the top of the trigger ring plate.

[0020] Preferably, an L-shaped mounting plate is fixedly installed on one side surface of the connecting rod. A fixed seat is fixedly installed on one side of the unwinding seat. A first adjusting shaft is rotatably connected to one side of the fixed seat and the surface of the opposite L-shaped mounting plate through bearings. A first winding wheel is fixedly installed on the arc surface of the first adjusting shaft. A first pulling rope is wound and connected to the surface of the first winding wheel. A first adjusting motor is fixedly installed on one side of the L-shaped mounting plate. The output shaft of the first adjusting motor is fixedly installed with the opposite surface of the first adjusting shaft through a coupling.

[0021] Preferably, a second adjusting shaft is rotatably connected to the other side of the fixed seat and the surface of the opposite L-shaped mounting plate through bearings. A second winding wheel is fixedly installed on the arc surface of the second adjusting shaft. A second pulling rope is wound and connected to the surface of the second winding wheel. A second adjusting motor is fixedly installed on one side of the L-shaped mounting plate. The output shaft of the second adjusting motor is fixedly installed with the opposite surface of the second adjusting shaft through a coupling.

[0022] Preferably, the bottom ends of the first pulling rope and the second pulling rope are both fixedly installed on the top of the control ring plate. An inclination sensor is fixedly installed on the top of the control ring plate. The two inclination sensors and the bottom ends of the first pulling rope and the second pulling rope are annularly arrayed on the top of the control ring plate.

[0023] The beneficial effects in the present invention are as follows:

[0024] The PLC program automatically controls the winch drive motor through this device to perform winding or releasing operations, driving and controlling the ring plate to move up or down inside the steel pipe pile. In cooperation with proximity switches, tension sensors, inclination sensors, and rotary encoders, automatic control measurement reading, counting, and calculation are carried out to realize the intelligentization of steel cofferdam construction, improve construction efficiency and quality, accurately measure the height of the concrete surface, and reduce the adverse effects caused by inaccurate existing measurements, such as increased chiseling work and subsequent adverse effects on the construction of the following bearing platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of a construction method for a PLC method pile cofferdam;

[0026] Figure 2 It is an exploded view of a construction method for a PLC method pile cofferdam;

[0027] Figure 3 It is a Figure 2 magnified view of the structure at position B in a construction method for a PLC method pile cofferdam;

[0028] Figure 4 It is a three-dimensional view of the reel structure of a construction method for a PLC method pile cofferdam;

[0029] Figure 5 It is a sectional view of the casing structure of a construction method for a PLC method pile cofferdam;

[0030] Figure 6 It is a Figure 2 magnified view of the structure at position A in a construction method for a PLC method pile cofferdam.

[0031] In the figure: 1, steel pipe pile; 2, equipment placement platform; 3, winch support seat; 4, winch shaft; 5, reel; 6, steel wire rope; 7, winch drive motor; 8, connecting plate; 9, rotary encoder; 10, hinge seat; 11, connecting rod; 12, unwinding seat; 13, unwinding shaft; 14, reel; 15, tension sensor; 16, buckle; 17, casing; 18, control ring plate; 19, proximity switch; 20, guide hole; 21, guide post; 22, trigger ring plate; 23, airbag; 24, limit hole; 25, insertion hole; 26, limit ring; 27, sliding rod; 28, L-shaped mounting plate; 29, fixed seat; 30, first adjusting shaft; 31, first winding wheel; 32, first pulling rope; 33, first adjusting motor; 34, second adjusting shaft; 35, second winding wheel; 36, second pulling rope; 37, second adjusting motor; 38, inclination sensor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0033] Referring to Figures 1-6 , a construction method for a PLC method pile cofferdam. Step 1: Measurement and lofting. Pilot holes are used for lofting, and the positioning of the pilot holes is completed by a total station. After lofting, pilot hole construction is carried out. After the pilot hole construction is completed, sheet pile driving is carried out. After the pilot hole construction is completed, precise lofting of the sheet piles is carried out again.

[0034] Step 2: Guide equipment. To ensure the verticality of sheet pile driving, positioning piles for sheet piles are driven before driving. Brackets are welded on the positioning piles, and a guide beam is installed to form a frame-type cofferdam as the guide equipment for pile driving. The guide frame is set in two layers, upper and lower. The boundaries of each sheet pile are marked on the guide frame to facilitate deviation correction during pile driving and prevent large deviations.

[0035] Step 3: Pile planting and closure.

[0036] Step 4: Backfilling of the pilot holes. a. Cleaning and filling the holes. b. Backfilling the outer trench holes of the cofferdam. c. Backfilling the inner trench holes of the cofferdam.

[0037] Step 5: Installation of the support system and anti-leakage measures. The sheet pile support system is mainly composed of Q345 double-ply H450mm steel sections to form the waling and supports. The first layer of waling is horizontally installed 1.4m below the top of the cofferdam, and the second layer of waling is installed 4.1m from the top of the cofferdam. After the cofferdam is closed, while pumping water, the internal supports are installed layer by layer. The internal supports are arranged from top to bottom and installed while pumping water.

[0038] Step 6: Foundation pit backfilling; after the installation of the waling, according to the position relationship between the bottom seal concrete and the riverbed top, the inside of the sheet pile cofferdam needs to be backfilled. The dump truck loads pebble river sand and transports it to the cofferdam through the construction trestle and unloads it at the bottom of the cofferdam. The 25m long-arm excavator is used for preliminary leveling. Then, the filling height is measured. When the filling height reaches the requirement, the bottom of the pit is leveled with a grab bucket or a long-arm excavator, and measured with a sounding rope at intervals of 50 - 100cm to ensure the flatness of the foundation bottom.

[0039] Step 7: Pouring of the bottom seal concrete. The bottom seal concrete is constructed by the underwater bottom seal method. Before construction, the height of the concrete surface is quickly detected through a height measuring mechanism to assist in the construction of the bottom seal concrete.

[0040] In order to quickly detect the height of the concrete surface through the height measuring mechanism during the back cover concrete pouring, the height measuring mechanism in Step 7 includes a steel pipe pile 1 and an equipment placement platform 2. The equipment placement platform 2 is located above the water. On one side of the top of the equipment placement platform 2, a hoist support seat 3 is fixedly installed. On the opposite surfaces of the two hoist support seats 3, a hoist shaft 4 is rotatably connected through bearings. On the arc surface of the hoist shaft 4, a roller 5 is fixedly installed. A steel rope 6 is wound and connected to the surface of the roller 5.

[0041] During use, during measurement, the rotation of the roller 5 is controlled to drive the release of the steel rope 6 wound on its surface, and the measurement operation is carried out from below the measurement device to the bottom of the steel pipe pile 1.

[0042] In order to automatically count the height, a hoist drive motor 7 is fixedly installed on one side of a hoist support seat 3. The output shaft of the hoist drive motor 7 is fixedly installed on the opposite surface of the hoist shaft 4 through a coupling. On one side of the other hoist support seat 3, a connecting plate 8 is fixedly installed. Above the connecting plate 8, a rotary encoder 9 is fixedly installed. One side of the rotary encoder 9 is fixedly installed on the opposite end of the hoist shaft 4 through a coupling.

[0043] By setting the installation operation of the rotary encoder 9 and the hoist shaft 4, when the hoist shaft 4 rotates to release the steel rope 6, the rotary encoder 9 starts to count the number of turns of the released steel rope 6 to count the released length.

[0044] On the other side of the top of the equipment placement platform 2, a hinge seat 10 is fixedly installed. At one end of the top of the hinge seat 10, a connecting rod 11 is hinged. At the top of the connecting rod 11, a pay-off seat 12 is fixedly installed. On the opposite U-shaped inner walls of the pay-off seat 12, a pay-off shaft 13 is rotatably connected through bearings. On the arc surface of the pay-off shaft 13, a reel 14 is fixedly installed. The inner wall of the groove of the reel 14 is slidably inserted into the arc surface of the steel rope 6.

[0045] Through the hinge setting of the hinge seat 10 and the connecting rod 11, it is convenient to control the angle change of the connecting rod 11, so as to facilitate the adjustment of the effect of moving the measurement device above the steel pipe pile 1.

[0046] At the bottom of the steel rope 6, a tension sensor 15 is fixedly installed. Below the tension sensor 15, a buckle 16 is fixedly installed through a rope. At the bottom of the buckle 16, a sleeve 17 is clamped. At the bottom of the sleeve 17, a control ring plate 18 is threadedly connected. At the inner top wall of the sleeve 17, a proximity switch 19 is fixedly installed.

[0047] By setting the tension sensor 15, during the release, the tension sensor 15 generates the tension of the self-weight of the measurement device. When the tension is offset and the measurement device reaches the measurement position, the count of the rotary encoder 9 is read, and the effect of controlling the hoist drive motor 7 to stop operating is achieved through the proximity switch 19.

[0048] The top of the control ring plate 18 is provided with guide holes 20. The four guide holes 20 are annularly arrayed on the surface of the control ring plate 18. A guide post 21 is slidably inserted into the inner wall of the guide hole 20. Trigger ring plates 22 are fixedly installed at the bottoms of the four guide posts 21. An airbag 23 is fixedly installed on the arc surface of the trigger ring plate 22.

[0049] By arranging the airbag 23, when the trigger ring plate 22 is lowered into the steel pipe pile 1, it plays a buoyancy role to prevent the gravity of the measuring mechanism itself from causing it to dive into the wet concrete, resulting in inaccurate measurement height. And by slidably inserting the guide post 21 into the inside of the guide hole 20, the trigger ring plate 22 can be controlled to slide up and down.

[0050] A limit hole 24 is opened at the center of the top of the control ring plate 18. A plug hole 25 is opened at the inner bottom wall of the limit hole 24. A limit ring 26 is slidably inserted into the inner wall of the limit hole 24. A sliding rod 27 is fixedly installed at the bottom of the limit ring 26. The arc surface of the sliding rod 27 is slidably inserted into the inner wall of the plug hole 25. The top of the limit ring 26 is in contact and extrusion with the contact point of the proximity switch 19. The bottom of the sliding rod 27 is fixedly installed with the center of the top of the trigger ring plate 22.

[0051] After the trigger ring plate 22 is lowered into the steel pipe pile 1 and contacts the top of the wet concrete, a reverse thrust is generated to block the trigger ring plate 22 from moving downward. When the control ring plate 18 continues to move downward to control the top of the limit ring 26 to squeeze the trigger point of the proximity switch 19, the winch drive motor 7 is controlled to stop operating through the proximity switch 19. By sliding the limit ring 26 inside the limit hole 24, when the trigger ring plate 22 is being lowered, the limit ring 26 is controlled to leave the proximity switch 19 under its own weight.

[0052] An L-shaped mounting plate 28 is fixedly installed on one side surface of the connecting rod 11. A fixed seat 29 is fixedly installed on one side of the unwinding seat 12. A first adjusting shaft 30 is rotatably connected to the surfaces of the fixed seat 29 on one side and the opposite L-shaped mounting plate 28 through bearings. A first winding wheel 31 is fixedly installed on the arc surface of the first adjusting shaft 30. A first pulling rope 32 is wound and connected to the surface of the first winding wheel 31. A first adjusting motor 33 is fixedly installed on one side of the L-shaped mounting plate 28. The output shaft of the first adjusting motor 33 is fixedly installed with the opposite surface of the first adjusting shaft 30 through a coupling.

[0053] By arranging the first pulling rope 32, when the control ring plate 18 moves downward inside the steel pipe pile 1, when the control ring plate 18 is tilted horizontally, the vertical horizontal plane of the first pulling rope 32 is adjusted by pulling or releasing the first pulling rope 32, so as to adjust the horizontal level.

[0054] On the other side of the fixed seat 29 and on the surfaces of the opposite L-shaped mounting plates 28, second adjusting shafts 34 are rotatably connected through bearings. On the arc surface of the second adjusting shaft 34, a second winding wheel 35 is fixedly installed. A second pulling rope 36 is wound and connected to the surface of the second winding wheel 35. On one side of the L-shaped mounting plate 28, a second adjusting motor 37 is fixedly installed. The output shaft of the second adjusting motor 37 is fixedly installed on the opposite surface of the second adjusting shaft 34 through a coupling.

[0055] By setting the second pulling rope 36 to control the downward movement of the control ring plate 18 inside the steel pipe pile 1, when the horizontal plane of the control ring plate 18 is inclined, the vertical horizontal plane of the second pulling rope 36 is adjusted by pulling or releasing the second pulling rope 36, so as to achieve the effect of adjusting the horizontal plane.

[0056] The bottom ends of the first pulling rope 32 and the second pulling rope 36 are both fixedly installed on the top of the control ring plate 18. An inclination sensor 38 is fixedly installed on the top of the control ring plate 18. The two inclination sensors 38, the bottom end of the first pulling rope 32, and the bottom end of the second pulling rope 36 are annularly arranged on the top of the control ring plate 18.

[0057] By setting the inclination sensor 38, the horizontal effects of the control ring plate 18 in the transverse and longitudinal directions are monitored in real time, which is convenient for the trigger ring plate 22 to maintain horizontal contact when contacting the inner wall of the concrete or the drilled hole below, enhancing the accuracy of measuring the height, and preventing the measurement accuracy from being inaccurate due to inclination.

[0058] Measurement working principle: Before measurement, the hoisting drive motor 7 works to drive the hoisting shaft 4 to rotate, so that the steel rope 6 on the surface of the roller 5 is wound and taken up, thereby driving the control ring plate 18 at one end of the steel rope 6 to move upward to reach the initial H position at the top;

[0059] After the construction of the hole inside the steel pipe pile 1 is completed, the hoisting drive motor 7 is reversed to release the steel rope 6. Then, under the self-weight of the control ring plate 18, it moves downward and makes a free fall. During the downward movement of the control ring plate 18, the horizontal angle is monitored by two inclination sensors 38 above the control ring plate 18. When an inclination occurs, the first adjusting motor 33 and the second adjusting motor 37 work to drive the first pulling rope 32 and the second pulling rope 36 to wind or release, so as to adjust the horizontal plane. When the bottom of the trigger ring plate 22 contacts the inner bottom wall of the pile hole, the control ring plate 18 continues to move downward to drive the limit plate to squeeze the proximity switch 19, so as to provide a signal to control the hoisting drive motor 7 to stop operating. At the same time, after the trigger ring plate 22 stops, the control ring plate 18 also stops under the condition of the limit ring 26, so as to offset the downward gravity, thereby reducing the tension of the tension sensor 15. Then, the PLC module is used to control the counting of the rotary encoder 9 to record the total depth H at this time;

[0060] When measurement is required after pouring concrete, the trigger ring plate 22 is controlled to move downward to contact the poured concrete, and the buoyancy is increased by the air bags 23 around it to prevent it from sinking into the concrete by its own weight. When the bottom of the trigger ring plate 22 contacts the poured concrete, the first height H at this time is recorded, and the poured concrete height at this time is calculated by H total depth - H first height = H.

[0061] Step eight, build the bottom platform. The bottom platform uses the already built drilling platform. Set up the conduit bracket on the top of the drilling platform, and lay scaffolding on it to form a human-shaped passage and conduit pouring platform. Set up railings and corresponding protective nets on the platform to ensure the safety of construction personnel.

[0062] Through this device, the PLC program automatically controls the winch drive motor 7 to perform winding or releasing operations, drives the control ring plate 18 to move up or down inside the steel pipe pile 1, and cooperates with the proximity switch 19, the tension sensor 15, the inclination sensor 38 and the rotary encoder 9 to automatically control the measurement reading counting and calculation, so as to realize the intelligent construction of steel cofferdams, improve construction efficiency and quality, accurately measure the height of the concrete surface, reduce the existing inaccurate measurement that leads to increased chiseling work and reduce the adverse effects of subsequent foundation construction.

[0063] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A construction method for a PLC diaphragm wall cofferdam, characterized in that: Step 1. Measurement and lofting. The pilot hole piles are used for lofting, and the positioning of the pilot hole piles is completed by a total station. After lofting, the pilot hole construction is carried out. After the pilot hole construction is completed, the steel sheet piles are inserted, and after the pilot hole construction is completed, the steel sheet piles are accurately lofted again. Step 2. Guide equipment. To ensure the verticality of the insertion of the steel sheet piles, before insertion, the positioning piles of the steel sheet piles are driven first. The corbels are welded on the positioning piles, and the guide beams are installed to form a frame-type cage as the guide equipment for pile insertion. The guide frame is set in two layers, upper and lower. The boundaries of each sheet pile are marked on the guide frame so as to correct the deviation while driving the piles during the pile driving process and prevent large deviations. Step 3. Pile planting and closure. Step 4. Backfilling of the pilot hole. a. Cleaning and filling the hole. b. Backfilling the slot hole outside the cofferdam. c. Backfilling the slot hole inside the cofferdam. Step 5. Installation of the support system and anti-leakage measures. The steel sheet pile support system is mainly composed of double-ply H450mm steel sections of Q345 to form the waling and supports. The first layer of waling is horizontally installed 1.4m below the top of the cofferdam, and the second layer of waling is installed 4.1m from the top of the cofferdam. After the cofferdam is closed, while pumping water, the internal supports are installed layer by layer. The internal supports are arranged from top to bottom and are installed while pumping water. Step 6. Foundation pit backfilling. After the installation of the waling is completed, according to the position relationship between the bottom-sealing concrete and the riverbed top, the inside of the steel sheet pile cofferdam needs to be backfilled. The dump trucks loaded with pebble sand are transported to the cofferdam through the construction trestle and unloaded at the bottom of the cofferdam, and are initially leveled by a 25m long-boom excavator. Then the filling height is measured. When the filling height meets the requirements, the bottom of the pit is leveled by a grab bucket or a long-boom excavator, and the bottom is measured with a sounding rope at intervals of 50 - 100cm to ensure the flatness of the foundation bottom. Step 7. Pouring of the bottom-sealing concrete. The bottom-sealing concrete is constructed by the underwater bottom-sealing method. Before construction, the height of the concrete surface is quickly detected by a height measuring mechanism to assist the construction of the bottom-sealing concrete. The height measuring mechanism in Step 7 includes a steel pipe pile (1) and an equipment placement platform (2). The equipment placement platform (2) is located above the water. On one side of the top of the equipment placement platform (2), a hoist support seat (3) is fixedly installed. On the opposite surfaces of the two hoist support seats (3), a hoist shaft (4) is rotatably connected through bearings. On the arc surface of the hoist shaft (4), a roller (5) is fixedly installed. A steel wire rope (6) is wound and connected to the surface of the roller (5). On one side of one of the hoist support seats (3), a hoist driving motor (7) is fixedly installed. The output shaft of the hoist driving motor (7) is fixedly installed on the opposite surface of the hoist shaft (4) through a coupling. On one side of the other hoist support seat (3), a connecting plate (8) is fixedly installed. Above the connecting plate (8), a rotary encoder (9) is fixedly installed. One side of the rotary encoder (9) is fixedly installed on the opposite end of the hoist shaft (4) through a coupling. A hinged seat (10) is fixedly installed on the other side of the top of the equipment placement platform (2), a connecting rod (11) is hingedly connected to one end of the top of the hinged seat (10), a reeling seat (12) is fixedly installed on the top of the connecting rod (11), the U-shaped relative inner walls of the reeling seat (12) are rotatably connected to the reeling shaft (13) through bearings, a reel (14) is fixedly installed on the arc surface of the reeling shaft (13), and the inner wall of the groove of the reel (14) is slidably plugged into the arc surface of the steel rope (6); A tension sensor (15) is fixedly mounted on the bottom of the steel rope (6), a buckle (16) is fixedly mounted below the tension sensor (15) via a rope, a sleeve (17) is clamped at the bottom of the buckle (16), a control ring plate (18) is threadedly connected to the bottom of the sleeve (17), and a proximity switch (19) is fixedly mounted on the inner top wall of the sleeve (17); A guide hole (20) is provided on the top of the control ring plate (18), and four of the guide holes (20) are arranged in a ring array on the surface of the control ring plate (18). A guide column (21) is slidably inserted into the inner wall of the guide hole (20), and a trigger ring plate (22) is fixedly installed on the bottom of the four guide columns (21), and an air bag (23) is fixedly installed on the arc surface of the trigger ring plate (22); A limit hole (24) is provided at the top center of the control ring plate (18), a plug-in hole (25) is provided at the inner bottom wall of the limit hole (24), a limit ring (26) is slidably plugged into the inner wall of the limit hole (24), a sliding rod (27) is fixedly installed at the bottom of the limit ring (26), the arc surface of the sliding rod (27) is slidably plugged into the inner wall of the plug-in hole (25), the top of the limit ring (26) is in contact and pressed with the contact point of the proximity switch (19), and the bottom of the sliding rod (27) is fixedly installed at the top center of the trigger ring plate (22); Step eight, build the bottom platform. The bottom platform uses the already built drilling platform. Set up the conduit bracket on the top of the drilling platform, and lay scaffolding on it to form a human-shaped passage and conduit pouring platform. Set up railings and corresponding protective nets on the platform to ensure the safety of construction personnel.

2. The construction method for a PLC diaphragm wall cofferdam according to claim 1, characterized in that: An L-shaped mounting plate (28) is fixedly mounted on one side surface of the connecting rod (11), a fixing seat (29) is fixedly mounted on one side of the unwinding seat (12), a first adjusting shaft (30) is rotatably connected to one side of the fixing seat (29) and a surface opposite to the L-shaped mounting plate (28) via a bearing, a first winding wheel (31) is fixedly mounted on the arc surface of the first adjusting shaft (30), a first pull rope (32) is wound around the surface of the first winding wheel (31), a first adjusting motor (33) is fixedly mounted on one side of the L-shaped mounting plate (28), and an output shaft of the first adjusting motor (33) is fixedly mounted to a surface opposite to the first adjusting shaft (30) via a coupling.

3. The construction method for a PLC diaphragm wall cofferdam according to claim 2, characterized in that: On the other side of the fixed seat (29) and on the surface of the opposite L-shaped mounting plate (28), a second adjusting shaft (34) is rotatably connected through bearings. A second winding wheel (35) is fixedly installed on the arc surface of the second adjusting shaft (34). A second pulling rope (36) is wound and connected to the surface of the second winding wheel (35). A second adjusting motor (37) is fixedly installed on one side of the L-shaped mounting plate (28). The output shaft of the second adjusting motor (37) is fixedly installed on the opposite surface of the second adjusting shaft (34) through a coupling.

4. The construction method for a PLC diaphragm wall cofferdam according to claim 3, characterized in that: The bottom ends of the first pulling rope (32) and the second pulling rope (36) are both fixedly installed on the top of the control ring plate (18). An inclination sensor (38) is fixedly installed on the top of the control ring plate (18). The two inclination sensors (38), the bottom end of the first pulling rope (32), and the bottom end of the second pulling rope (36) are annularly arranged on the top of the control ring plate (18).

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