A rigid frame thin-walled pier passive underpinning construction method

Abstract

This application relates to a passive underpinning construction method for rigid frame thin-walled piers, comprising the following steps: S1: reinforcement of the bottom of the enlarged foundation of the rigid frame thin-walled pier; S2: construction of underpinning piles; S3: excavation of the foundation pit; S4: installation of emergency safety supports; S5: rebar installation on the rigid frame thin-walled pier; S6: construction of the underpinning beam; S7: grouting reinforcement of the underpinning pile bottom; S8: grouting reinforcement around the underpinning pile. This passive underpinning construction method is simple, has a short construction period, and expands its application in pile foundation underpinning projects for continuous beam bridges.

Description

Technical Field

[0001] This invention relates to the field of underpinning construction technology, and in particular to a passive underpinning construction method for rigid thin-walled piers. Background Technology

[0002] Currently, thin-walled continuous rigid frame bridges are widely used in urban elevated sections due to their smooth and continuous driving surface, slender and aesthetically pleasing structure, and low cost. However, the construction of underground rail transit inevitably damages the pier foundations, causing settlement and deformation, threatening the normal use of the elevated bridge. Domestically and internationally, urban underground rail transit construction has led to damage to various building foundations. Common solutions include pile foundation replacement and pile foundation reinforcement. Compared to complete demolition, bridge pile foundation replacement and reinforcement methods demonstrate significant advantages, resulting in a substantial reduction in construction time and costs.

[0003] Pile foundation underpinning is divided into active underpinning and passive underpinning. Active underpinning has the advantage of controlling the final deformation value of the superstructure; however, it requires high precision monitoring during the lifting process and necessitates the design of auxiliary measures to strictly control lateral displacement of the structure. The underpinning process carries certain risks and is mainly suitable for situations with large foundation loads and strict deformation requirements for the superstructure, such as foundation underpinning of continuous beam bridges and foundation underpinning of displacement-sensitive buildings. Passive underpinning has the advantage of a clear force transmission mechanism in the underpinned structure and simple construction with a short construction period; however, it suffers from larger structural deformation, complex secondary soil deformation, and the inability to accurately calculate the displacement value of the superstructure settlement. It is mainly suitable for situations with small foundation loads and lower deformation requirements for the structure, such as pile foundation underpinning of simply supported beam bridges and foundation underpinning of non-displacement-sensitive buildings.

[0004] Considering the technical characteristics and applicability of both active and passive underpinning, active underpinning technology is often chosen for pile foundation underpinning of thin-walled rigid frame piers. However, many projects face tight schedules. Passive underpinning offers advantages such as simple construction and short construction period, but its requirements for controlling structural deformation are not stringent, limiting its application to structures such as continuous beam bridges. Therefore, it is necessary to further improve the passive pile foundation underpinning technology for thin-walled pier continuous rigid frames, enhance its deformation control measures, expand its application in pile foundation underpinning projects for continuous beam bridges, and actively leverage the advantages of simple construction and short construction period of passive underpinning. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a passive underpinning construction method for rigid frame thin-walled piers.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is: a passive underpinning construction method for rigid frame thin-walled piers, comprising the following steps: S1: Reinforcement of the enlarged foundation bottom of rigid frame thin-walled pier; S2: Pile replacement construction; S3: Excavation of the foundation pit; S4: Install emergency safety supports; S5: Reinforcing steel bars are installed on rigid thin-walled piers; S6: Construction of beam replacement; S7: Grouting reinforcement of the bottom of the underpinning pile; S8: Grouting reinforcement around the replacement pile.

[0007] Furthermore, in step S1, the enlarged foundation includes a first enlarged foundation and a second enlarged foundation located at the lower end of the first enlarged foundation. Grouting is performed to reinforce the stratum at the bottom of the enlarged foundation, and quick-drying concrete is used to seal the opening after the grouting is completed.

[0008] Furthermore, in step S2, a hole is drilled on the construction ground and a steel casing is driven in. Then, a steel cage is hoisted into the pile hole. An acoustic logging pipe is installed inside the steel cage, and underwater concrete is poured through the guide pipe to form a replacement pile.

[0009] Furthermore, in step S3, a foundation pit is excavated around the rigid thin-walled pier, with the bottom of the foundation pit flush with the lower end of the first enlarged foundation.

[0010] Furthermore, the safety support in step S4 includes a Bailey beam, with a steel column at the upper end of the Bailey beam, steel plates at the upper and lower ends of the steel column, the steel plate at the lower end of the steel column being fixed to the Bailey beam, and an I-beam at the upper end of the steel column, with a wedge-shaped wooden block at the upper end of the I-beam. Step S4 includes the following steps: S41: Construction of capping beams: Construct capping beams on both sides of the foundation pit; S42: Bailey beam installation: After the capping beam construction is completed, at least three Bailey beams are installed on the upper end of the capping beam. The two ends of the Bailey beams are fixed to the upper part of the capping beam and arranged parallel to the rigid thin-walled pier. S43: Steel column installation: Two steel columns are erected on each Bailey beam. The steel columns are symmetrically arranged along the central axis of the thin-walled pier, and steel plates are welded to the upper and lower ends of the steel columns respectively. S44: Beam installation: I-beams are laid out continuously above the steel columns on the same Bailey bridge.

[0011] Furthermore, step S5 includes the following steps: S51: Surface treatment of rigid thin-walled pier and first enlarged foundation: The rigid thin-walled pier has a grooved section near its bottom. The surface of the grooved section is roughened into the first toothed groove. The surface of the first enlarged foundation is roughened into the second toothed groove. After cleaning with a wire brush, it is cleaned with a blower. S52: Rebar installation: Use an electric drill to drill two rows of 12 rebar installation holes on the grooved section. After removing impurities from the drill holes, fill the holes with rebar installation adhesive and then use a positioning bracket to assist in the installation of the threaded rebar.

[0012] Furthermore, in step S52, the positioning bracket includes a large-diameter support steel pipe, an implanted rebar limiting steel pipe sleeved inside the large-diameter support steel pipe, and an implanted rebar positioning support rod set at the lower end of the large-diameter support steel pipe. The locking threaded rebar can be inserted into the implanted rebar limiting steel pipe. The large-diameter support steel pipe is provided with a rebar fixing bolt for locking the threaded rebar. The rebar fixing bolt is provided with a large-diameter steel pipe top locking welding nut. The large-diameter steel pipe top locking welding nut abuts against the outer wall of the large-diameter support steel pipe. The large-diameter support steel pipe is provided with a limiting steel pipe inclination measuring groove on the outside. A dual-axis electronic digital display angle meter is provided in the limiting steel pipe inclination measuring groove. The embedded rebar positioning support rod includes a height adjustment stud, a lower connecting pipe, and an upper connecting pipe that is slidably installed in the lower connecting pipe. The bottom of the lower connecting pipe is provided with a tapered support foot for the support rod. The lower end of the height adjustment stud extends into the upper connecting pipe and is threadedly connected to the upper connecting pipe. The upper connecting pipe has a limit welding nut for threaded connection with the height adjustment stud at its upper end. The height adjustment stud has a stud limit welding nut and a top limit plain round steel bar at its upper end. The large-diameter support steel pipe has a support rod angle adjustment groove at its lower end. The limit plain round steel bar is rotatably set in the support rod angle adjustment groove. Support rod limit hoops for wrapping the top limit plain round steel bar are set on both sides of the support rod angle adjustment groove. The top limit plain round steel bar can rotate relative to the support rod limit hoops. The upper connecting pipe has multiple height adjustment through slots along its axial direction. The lower connecting pipe has a connecting pipe height adjustment slot and a connecting pipe height adjustment bolt. The connecting pipe height adjustment bolt passes through the height adjustment through slots and the connecting pipe height adjustment slot and is locked with a height adjustment nut.

[0013] Furthermore, in step S6, a concrete interface treatment agent is applied to the surface of the grooved section and the first enlarged foundation. Four hours after application, concrete is poured around the grooved section and the first enlarged foundation to form a support beam around the grooved section and the first enlarged foundation. The grooved section, the threaded steel bars embedded in the grooved section, the first enlarged foundation, the support beam, and the support pile together constitute the passive support foundation.

[0014] Furthermore, in step S7, grouting is performed at the bottom of the replacement pile through the sonic logging tube inside the reinforcement cage of the replacement beam, and a grouting zone is formed at the bottom of the replacement pile, with a grouting pressure of 3-5 MPa.

[0015] Furthermore, in step S8, grouting holes are added on both sides of the adjacent replacement pile. Holes are opened at the 4th to 5th ring after the shield segment exits the shield tail. Grouting in the transverse tunnel is carried out through the grouting holes, and the grouting pressure is controlled at 0.3 to 0.4 MPa.

[0016] The beneficial effects of this application are as follows: 1. This application is applicable to complex construction environments. The emergency safety support concrete foundation uses the capping beam at the top of the foundation pit, eliminating the need for separate construction of the emergency support foundation. This is convenient, quick, cost-effective, and effectively shortens the construction period.

[0017] 2. The positioning bracket of this application is simple to disassemble and assemble, easy to use, economical to maintain and replace, and highly applicable. By setting up upper connecting pipe, lower connecting pipe and height adjustment stud, it can meet the needs of different adjustment conditions, ensure the positional accuracy of the inserted steel bar, reduce the cumbersome procedure of bracket adjustment, and greatly improve construction efficiency.

[0018] 3. This application adopts a comprehensive grouting reinforcement technology for bridge pier foundations, which involves grouting reinforcement at the bottom of the enlarged foundation of the rigid frame thin-walled pier, grouting reinforcement at the bottom of the replacement pile, and grouting reinforcement around the replacement pile. This technology strengthens the existing bridge pier foundation and the replacement foundation in succession, enhances the bearing capacity of both, and achieves the effect of "supporting without replacing" the foundation.

[0019] 4. An emergency safety support system is added, consisting of a concrete foundation, Bailey bridge beams, steel pipe columns, and crossbeams. By setting wedge-shaped wooden blocks, when the bridge deformation exceeds the limit, the settlement deformation at the bottom of the bridge can be actively controlled through adjustment of the wedge-shaped wooden blocks. The emergency safety support system can be adjusted based on the feedback from the pile foundation deformation to control the settlement of the piers. This method of combining passive underpinning with active deformation control of the emergency safety support system makes up for the deficiency of passive underpinning in that it cannot actively control deformation, and improves the application scope of passive underpinning technology. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the structure of the replacement beam of the present invention; Figure 3 This is a schematic diagram of the rebar installation structure of the present invention; Figure 4 This is a schematic diagram of the emergency safety bracket of the present invention; Figure 5 This is a schematic diagram of the positioning bracket; Figure 6 This is a top view of the positioning bracket; Figure 7 A schematic diagram of the structure for implanting the rebar positioning support rod; Figure 8 This is a schematic diagram of the comprehensive grouting process of the present invention; Figure 9 This is a settlement curve diagram of the rigid frame thin-walled pier shield tunneling of the present invention.

[0021] Markings in the diagram: 1. Continuous bridge; 2. Rigid frame thin-walled pier; 201. Grooved section; 202. First groove; 3. Emergency safety support; 301. Bailey bridge; 302. Steel column; 303. Steel plate; 304. I-beam; 305. Wedge-shaped wooden block; 4. Crown beam; 5. Foundation pit; 6. Underpinning beam; 7. Spread foundation; 701. First spread foundation; 702. Second spread foundation; 703. Second groove; 8. Underpinning pile; 9. Threaded steel bar; 10. Ground grouting area; 11. Underpinning pile bottom grouting area; 12. Underpinning pile grouting area inside the tunnel during shield tunneling; 13. Shield tunnel segment; 14. Dual-axis electronic digital display angle. Instrument, 15. Rebar fixing bolt, 16. Large diameter steel pipe top locking welding nut, 17. Large diameter support steel pipe, 18. Inserted rebar limiting steel pipe, 19. Support rod angle adjustment groove, 20. Support rod limiting hoop, 21. Inserted rebar positioning support rod, 211. Top limiting plain round rebar, 212. Height adjusting stud, 213. Stud limiting welding nut, 214. Upper connecting pipe limiting welding nut, 215. Upper connecting pipe, 216. Lower connecting pipe, 217. Connecting pipe height adjusting bolt, 218. Connecting pipe height adjusting slot, 219. Support rod tapered support foot, 22. Limiting steel pipe inclination measuring groove. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that, in the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] Please see Figure 1-9 This invention provides a passive underpinning construction method for rigid thin-walled piers, comprising the following steps: S1: Reinforcement of the bottom of the enlarged foundation 7 of the rigid thin-walled pier 2; S2: Construction of pile replacement 8; S3: Excavation of foundation pit 5; S4: Install emergency safety bracket 3; S5: Install rebar for the rigid thin-walled pier 2; S6: Construction of beam replacement 6; S7: Grouting reinforcement at the bottom of pile 8; S8: Grouting reinforcement around the replacement pile 8.

[0024] In step S1, the enlarged foundation 7 includes a first enlarged foundation 701 and a second enlarged foundation 702 located below the first enlarged foundation 701. Grouting is performed to reinforce the stratum at the bottom of the enlarged foundation 7. After grouting, quick-drying concrete is used to seal the opening. S12: The drilling rig is positioned and drilling is performed. Step S1 includes the following steps: S11: Construct a construction platform and mark out hole positions around the second enlarged foundation 702; S12: The drilling rig is positioned, the orientation and inclination are corrected, and the Ф108 casing is used to follow the drilling process. The hole position is marked according to the drilling layout diagram, and the drill is drilled to the designed depth. S13: Configuring casing material: Use water, ash, and soil in a ratio of 1.6:1:1 to configure casing material. Immediately after drilling, replace the mud in the hole with casing material through the drill rod. S14: Insertion and Hole Reservation: Insert the PVC plastic sleeve valve tube to the designed depth, with the top of the sleeve valve tube protruding 20cm above the ground. Drill a set of 4Ф6mm injection holes every 33cm on the sleeve valve tube, and drill 3 sets of injection holes per meter. Wrap the injection holes with rubber sleeves. S15: Grouting control: The grouting material for the sleeve valve pipe is cement grout with a ratio of 1:1. The grouting pressure is controlled within 0.3-0.5MPa, and the pressure stabilization time is not less than 30 minutes. The sleeve valve pipes are arranged in a quincunx pattern with a spacing of 1.5m.

[0025] S16: Grouting and sealing: The ground grouting area at the bottom of the expanded foundation 7 is 12m×9.2m×3.0m. After the grouting is completed, the grouting holes are immediately sealed with quick-drying concrete.

[0026] In step S2, a hole is drilled on the construction ground and a steel casing is driven in. Then, a reinforcing cage is hoisted into the pile hole. A sonic logging tube is installed inside the reinforcing cage, and underwater concrete is poured through a guide pipe to form the underpinning pile 8. Step S2 includes the following steps: S21: Ground hardening: The sixth-generation crawler hydraulic high-power reverse circulation drilling rig KYZ10-180 is selected for drilling. Before construction, the site within the construction area is located and inspected. The site is hardened with concrete to ensure that the ground bearing capacity meets the safe driving requirements of large equipment such as drilling rigs, truck cranes, and concrete mixer trucks. S22: Site layout: Temporary wall protection mud pits and slag pits shall be set up within the site; S23: Drilling Rig Positioning and Construction: The replacement pile has a diameter of 1.0m and a length of 24.9m. The bottom is embedded 7.0m deep into the moderately weathered mudstone layer. Before construction, the pile should be positioned, and the drilling rig should be positioned and drilled. During drilling and hole formation, ensure sufficient mud in the hole, with the mud level 15cm higher than the top of the artificial wall to prevent collapse. During hole formation, monitor the hole depth, diameter, verticality, hole wall integrity, and sediment thickness. S24: Reinforcing cage fabrication and installation: The main reinforcement of the reinforcing cage uses 34 25 threaded steel bars, the stiffening stirrups use 27 25 threaded steel bars, and the spiral stirrups use φ12@100 / 200 steel bars. Three sonic logging tubes are arranged in an isosceles triangle inside the reinforcing cage for grouting. The sonic logging tubes have a diameter of 57mm and a wall thickness of 3mm. After the reinforcing cage is fabricated, it is hoisted into the hole. S25: Conduit installation: The conduit uses φ25-30 steel pipe. The installation sequence of conduit sections is as follows: the middle section should be 2m long, the bottom section can be 4m, and the conduit below the funnel should be 1m long. S26: Underwater Concrete Pouring: C35 grade underwater concrete is poured using a tanker truck and a tremie pipe to form 8 replacement piles. The slump is controlled between 180 and 220 mm. During the pouring process, the height of the concrete surface in the hole is measured in a timely manner, and the lifting and removal of the tremie pipe are properly directed. The burial depth of the tremie pipe should be controlled at about 2 m. The position of the concrete surface in the hole should be measured frequently, and the burial depth of the tremie pipe should be adjusted in time. The removal of the tremie pipe should be done quickly, with a removal time of less than 15 minutes. An additional 1.0 m of concrete should be poured above the design elevation of the pile top.

[0027] In step S3, foundation pit 5 is excavated around the rigid thin-walled pier 2, and the bottom of foundation pit 5 is flush with the lower end of the first enlarged foundation 701. Step S2 includes the following steps: S31: Excavation of foundation pit 5: Foundation pit 5 is 5.48m deep. It is excavated in stages with slope ratios of 1:0.5 and 1:0.75. The top of foundation pit 5 is set with a width of 1m. When the foundation pit is excavated to 50cm above the base, the bottom of foundation pit 5 is flush with the lower end of the first enlarged foundation 701. At this time, the excavation is stopped and the excavation is carried out manually and mechanically to the design elevation to confirm that the bearing capacity of the base meets the design requirements. S32: Soil nailing installation: The slope protection for the foundation pit is a soil nailing wall. Holes are drilled on the excavated slope surface at point 5 of the foundation pit using mechanical drilling or a Luoyang shovel. Soil nail anchors, 3m long, are inserted into the holes using φ16 threaded steel arranged in a 2.0m × 2.0m staggered pattern. L-shaped hooks are installed at 2m intervals on the outer ends, welded with centering supports to prevent eccentricity. The grouting pipes are tied to the main reinforcement bars, 0.5m from the bottom of the hole. S33: Grouting: Grouting of soil nail anchor pipes, starting from the bottom, grouting while pulling out the pipe, high pressure grouting at the opening and finally sealing the hole, grouting pressure is maintained at 0.4mpa~0.6mpa, flow rate is not greater than 5L / min, cement grout usage is 25Kg / m~30Kg / m, after grouting, the grouting pipe is cleaned in time; S34: Install steel mesh: Tie φ10@200×200mm steel mesh, stagger adjacent steel bar joints by 500mm, weld connecting bars for each layer of soil nails, and press the steel mesh with threaded steel bars in a grid pattern.

[0028] S35: Shotcrete: C20 early-strength concrete is sprayed in two layers, each layer is 5cm thick, sprayed vertically from bottom to top on the slope, and the spraying distance is controlled between 0.6-1.0m.

[0029] The safety support in step S4 includes a Bailey beam 301, with a steel column 302 at the upper end of the Bailey beam 301. Steel plates 303 are respectively installed at the upper and lower ends of the steel column 302. The steel plate 303 at the lower end of the steel column 302 is fixed to the Bailey beam 301. An I-beam 304 is installed at the upper end of the steel column 302, and a wedge-shaped wooden block 305 is installed at the upper end of the I-beam 304. Step S4 includes the following steps: S41: Construction of Crown Beam 4: C30 concrete beams are constructed on both sides of the foundation pit, with a cross-sectional dimension of 1.0m × 0.8m; S42: Bailey beam 301 installation: After the cap beam 4 is constructed, at least three 321 type Bailey beams 301 are installed on the upper end of the cap beam 4. The length of Bailey beam 301 is 15.9m. Both ends of Bailey beam 301 are fixed to the upper part of the cap beam 4 and extend 0.9m from each end. Bailey beam 301 is arranged parallel to the rigid frame thin-walled pier 2. S43: Installation of steel column 302: Two φ609×16mm steel columns 302 are erected on each Bailey beam 301. The steel columns 302 are symmetrically arranged along the central axis of the rigid thin-walled pier 2. 80mm×80mm steel plates 303 are welded to the upper and lower ends of the steel columns 302 respectively. S44: Crossbeam Installation: 50a I-beams 304 are installed above the steel columns. Each 15.9m I-beam 304 is laid out continuously. The steel columns are spaced 3.5m x 3.5m apart in both the longitudinal and transverse directions. The I-beams 304 are spaced along the bridge direction and fixed above the steel columns 302, contacting the bottom of the bridge deck. They support the continuous bridge 1 and play a supporting role in controlling settlement. The vertical temporary supports do not contact the bridge deck. A vertical distance of 2-3mm is reserved. Depending on the settlement situation, wedge-shaped wooden blocks 305 can be installed within the reserved distance to apply active support in a timely manner.

[0030] The erection of steel column 302 was carried out using a JKW-95 log grabber with an arc-shaped grab head. The grab head can rotate 360°. At the same time, the log grabber also served as a temporary support for steel column 302 during its use, ensuring the stability of the column. The steel columns in the same row were reinforced by welding 400×400×13×21H steel, which made the construction convenient and quick, and effectively saved the construction period.

[0031] The erection positions of steel columns 302 are pre-determined. Two log grappling machines are required for erecting steel columns 302 in the same row. The temporary support for the steel columns 302 includes the following steps: Step 1, one log grappling machine grips a horizontally placed steel column 302; Step 2, the gripping machine is raised and rotated 180°; Step 3, the steel column 302 is erected and placed upright on the Bailey beam 301, ensuring that the positional deviation is within the allowable range during placement; Step 4, the above steps—up to Step 3—are repeated to erect the other steel column 302 in the same row, with the gripping machine maintaining a tight grip during the erection process; Step 5, the two steel columns 302 in the same row are welded together using structural steel, with both log grappling machines maintaining a tight grip during the welding process; Step 6, after the structural steel welding is completed, one log grappling machine is removed, while the other remains in a supporting position, serving as temporary support for the steel columns 302 during the pile foundation replacement construction.

[0032] Specifically, step S5 includes the following steps: S51: Surface treatment of rigid thin-walled pier 2 and first enlarged foundation 701: The rigid thin-walled pier 2 has a grooved section 201 near its bottom. The surface of the grooved section 201 is roughened into a first toothed groove 202, and the surface of the first enlarged foundation 701 is roughened into a second toothed groove 703. After cleaning with a wire brush, it is cleaned with a blower. The groove size of the first toothed groove 202 and the second toothed groove 703 is 20mm×60mm (depth×width).

[0033] S52: Rebar installation: Drill two rows of 12 rebar installation holes on the grooved section 201 using an electric drill. After removing impurities from the drill holes, fill the holes with rebar installation adhesive and then insert the threaded rebar 9 with the assistance of a positioning bracket.

[0034] In step S52, the positioning bracket includes a large-diameter support steel pipe 17, an implanted rebar limiting steel pipe 18 sleeved inside the large-diameter support steel pipe 17, and an implanted rebar positioning support rod 21 set at the lower end of the large-diameter support steel pipe 17. The locking threaded rebar 9 can be inserted into the implanted rebar limiting steel pipe 18. The large-diameter support steel pipe 17 is provided with a rebar fixing bolt 15 for locking the threaded rebar 9. The rebar fixing bolt 15 is provided with a large-diameter steel pipe top locking welded nut 16. The welding nut 16 abuts against the outer wall of the large-diameter support steel pipe 17. A limiting steel pipe inclination measuring groove 22 is provided on the outside of the large-diameter support steel pipe 17. A dual-axis electronic digital display angle gauge 14 is installed inside the limiting steel pipe inclination measuring groove 22. The embedded rebar positioning support rod 21 includes a height adjustment stud 212, a lower connecting pipe 216, and an upper connecting pipe 215 slidably disposed within the lower connecting pipe 216. A support rod tapered support foot 219 is provided at the bottom of the lower connecting pipe 216. The lower end of the height adjustment stud 212 extends into the upper connecting pipe 215. 15 is threadedly connected to the upper connecting pipe 215. The upper end of the upper connecting pipe 215 is provided with an upper connecting pipe limiting welded nut 214 that is threadedly connected to the height adjusting stud 212. The height adjusting stud 212 is provided with a stud limiting welded nut 213. The upper end of the height adjusting stud 212 is provided with a top limiting plain round steel bar 211. The lower end of the large-diameter support steel pipe 17 is provided with a support rod angle adjustment groove 19. The limiting plain round steel bar is rotatably set in the support rod angle adjustment groove 19. The two sides of the support rod angle adjustment groove 19 are respectively A support rod limiting hoop 20 is provided for wrapping the top limiting plain round steel bar 211. The top limiting plain round steel bar 211 can rotate relative to the support rod limiting hoop 20. The upper connecting pipe 215 is provided with multiple height adjustment through slots along its axial direction. The lower connecting pipe 216 is provided with a connecting pipe height adjustment slot 23. The lower connecting pipe 216 is also provided with a connecting pipe height adjustment bolt 217. The connecting pipe height adjustment bolt 217 passes through the height adjustment through slot and the connecting pipe height adjustment slot 23 and is locked with a height adjustment nut.

[0035] More specifically, the large-diameter support steel pipe 17 has a diameter of 108mm, a thickness of 3mm, and a length of 400mm; the inserted rebar limiting steel pipe 18 has a diameter of 48mm, a thickness of 2mm, and a length of 300mm; the upper connecting pipe is 25mm thick, 2mm long, and 800mm long; the lower connecting pipe has a diameter of 34mm, a thickness of 2mm, and a length of 1000mm; the connecting pipe height adjusting bolt 217, the rebar fixing bolt 15, and the height adjusting stud 212 have a diameter of M20; the top limiting plain round rebar 211 has a diameter of 22mm and a length of 60mm; the limiting steel pipe tilt measuring groove 22 has a length of 50mm and a width of 30mm; the dual-axis electronic digital display angle gauge 14 is a DP-160SS type.

[0036] In addition, the installation of rebar using the positioning bracket includes the following steps: Step 1: After drilling is completed, a positioning bracket is set up on each side of the grooved section 201 of the rigid thin-walled pier 2. The threaded steel bar 9 is passed through the implanted steel bar limiting steel pipe 18 to keep the threaded steel bar 9 at the center of the borehole. The height of the rebar hole from the ground or platform supported by the positioning bracket is measured, and the height of the large-diameter support steel pipe 17 is calculated. Step 2: Based on the height of the large-diameter support steel pipe 17 from the ground or platform, assemble the upper connecting pipe 215 and the lower connecting pipe 216. After adjustment, the connecting pipe height adjusting bolt 217 passes through the height adjusting through groove and the connecting pipe height adjusting slot 23, and is locked with the height adjusting nut. Step 3: Connect the upper connecting pipe 215 to the height adjustment stud 212. Insert the top limiting plain round steel bar 211 into the large diameter support steel pipe 17 through the support rod angle adjustment groove 19, and insert both ends of the top limiting plain round steel bar 211 into the support rod limiting hoop 20. Adjust the support angle of the embedded steel bar positioning support rod 21 through the support rod angle adjustment groove 19. Step 4: First, place the positioning bracket on one side, and place the threaded steel bar 9 inside the implanted steel bar limiting steel pipe 18. Ensure that the threaded steel bar 9 is in full contact with the bottom of the implanted steel bar limiting steel pipe 18. Check the position of the implanted steel bar inside the implanted steel bar limiting steel pipe 18. Try to tighten the steel bar fixing bolt 15 to check whether it can contact and fix the threaded steel bar 9. If the deflection angle is too large, adjust the vertical deflection angle of the upper connecting pipe 215 by adjusting the height adjustment stud 212 to achieve better limiting and fixing conditions.

[0037] Step 5: Use a dual-axis electronic digital display angle meter 14 to check whether the horizontal inclination angle of the threaded steel bar 9 meets the design limits and engineering requirements. If it does not meet the requirements, adjust the intermediate height adjustment stud 212 to make it meet the requirements.

[0038] Step Six: Based on the already adjusted position of the threaded steel bar 9, set up the other side positioning bracket, ensuring that the threaded steel bar 9 is in full contact with the bottom of the implanted steel bar limiting tube 18. Use a dual-axis electronic digital display angle meter 14 to measure the tilt angle of the implanted steel bar limiting tube 18 in the vertical and horizontal directions. Adjust the left and right sides and the middle height adjustment studs 212 to ensure that the implanted steel bar limiting tube 18 meets the limiting fixation and design requirements in the vertical and horizontal directions. Then fix the positioning brackets on both sides in place and remove the threaded steel bar 9. Step 7: Inject anchoring adhesive into the hole, insert one side of the threaded rebar 9 into the anchoring rebar limiting steel pipe 18, and insert it into the anchoring hole along the anchoring rebar limiting steel pipe 18. Insert the other side through the anchoring hole into the anchoring rebar limiting steel pipe 18 on the other side, ensuring full contact between the threaded rebar 9 on both sides and the anchoring rebar limiting steel pipe 18. Use a dual-axis electronic digital display angle meter 14 to re-measure the vertical and horizontal tilt angles of the anchoring rebar limiting steel pipe 18, and fine-tune the height of the stud 212 according to the results.

[0039] Step 8: After the dual-axis electronic digital display angle meter 14 re-measures and meets the conditions, tighten the steel bar fixing bolts 15. After the anchoring adhesive has solidified, remove the positioning brackets on both sides.

[0040] The anchoring adhesive should be tested in advance to observe the curing time and effect. When anchoring the rebar, first fill the hole with anchoring adhesive, and then insert the threaded rebar 9. Do not disturb the threaded rebar 9 before the anchoring adhesive cures. After construction, check whether the threaded rebar 9 in each hole is loose. If it is loose, take remedial measures in time.

[0041] In step S6, a concrete interface treatment agent is applied to the surface of the grooved section 201 and the first enlarged foundation 701. Four hours after application, concrete is poured around the grooved section 201 and the first enlarged foundation 701 to form a support beam 6 around the grooved section 201 and the first enlarged foundation 701. The grooved section 201, the threaded steel bar 9 embedded in the grooved section 201, the first enlarged foundation 701, the support beam 6, and the support pile 8 together constitute a passive support foundation.

[0042] Step S6 includes the following steps: S61: Reinforcement Layout: A reinforcement mesh is laid around the grooved section 201 and the first enlarged foundation 701. First, the upper surface reinforcement and some of the diagonal bottom reinforcement are tied to form a reinforcement skeleton. Then, reinforcement is laid symmetrically from the middle to both sides from top to bottom to finally form a tight reinforcement mesh. S62: Template addition: Templates are set up around the steel mesh frame. The templates are made of 15mm thick composite bamboo plywood. The supports are made of 90mm×90mm square timber. The vertical back ribs of the templates are set at 30cm intervals, and the horizontal back ribs are set at 60cm intervals. S63: Layered concrete pouring: Pour C35 micro-expansion concrete, use ground formwork on the bottom surface, pour a 100mm thick C20 plain concrete pad to the design elevation of the beam bottom, pour C35 concrete in layers, the vibration of the upper layer of concrete should be inserted into the lower layer of concrete by 50mm, the moving distance should not be greater than 1.5 times the effective radius of the vibrator, and control the temperature during pouring and curing. S64: Curing and Formwork Removal: After pouring, cover with plastic film or geotextile. Spray water on the formwork and film for curing according to the temperature. The curing time is more than 14 days. When the concrete strength reaches more than 80% of the design strength or 80% of the compressive strength of the test block under the same conditions, the formwork can be removed, and the replacement beam 6 will be formed. The dimensions of the replacement beam 6 are 13.5m×3.2m×2.5m (length×width×height).

[0043] In step S7, grouting is performed at the bottom of the replacement pile 8 through the sonic logging tube inside the reinforcing cage of the replacement beam 6, forming a grouting zone 11 at the bottom of the replacement pile 8. The grouting uses 42.5 grade cement with a water-cement ratio of 0.7. The grouting pressure is controlled within 3-5 MPa, and the grouting volume is 3 m³.3 / root.

[0044] In step S8, grouting holes are added on both sides of the adjacent replacement pile 8. Holes are opened at the 4th to 5th rings after the shield segment 13 exits the shield tail. One hole is opened every 2 rings of tunneling. The lateral grouting range is a radius of 3m outside the tunnel on the side closest to the pile foundation, and the longitudinal grouting range is a range of 5m in front of and behind the pile foundation. Grouting in the transverse tunnel is carried out through the grouting holes. The grouting pressure is controlled at 0.3 to 0.4MPa. The grouting pipe is a φ42×3.5mm steel perforated pipe with a length not exceeding 35m.

[0045] During the grouting process in step S8, there should be an air vent. The air vent is located on the pre-grouting hole and a one-way check valve for grouting is installed. When the grouting pressure reaches the set value (0.3MPa) and the grouting volume reaches more than 90% of the design value, the quality requirements can be considered met.

[0046] In addition, such as Figure 5 The settlement curve shows that the maximum settlement of the bridge pier was 2.94 mm, which did not exceed the warning value of 6.7 mm throughout the entire process. The maximum settlement rate of 2.54 mm / d occurred on September 26, exceeding the warning value of 2 mm / d for daily deformation. Emergency safety supports were adjusted to provide emergency support for the bridge, controlling the deformation of the bridge within a safe range and achieving good deformation control results. The entire method is easy to operate and the process is clear, providing good technical support for the pile foundation replacement technology of thin-walled pier continuous rigid frame and other continuous beam bridge pier structures.

[0047] It should be noted that the above embodiments are only used to illustrate the present invention, but the present invention is not limited to the above embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A rigid thin-walled pier passive underpinning construction method, characterized in that, Includes the following steps: S1: Reinforcement of the bottom of the enlarged foundation (7) of the rigid thin-walled pier (2); S2: Construction of the replacement pile (8); S3: Excavation of the foundation pit (5); S4: Install emergency safety brackets (3); S5: Reinforcing bars are installed on the rigid thin-walled pier (2); S6: Construction of the replacement beam (6); S7: Grouting reinforcement of the bottom of the replacement pile (8); S8: Grouting reinforcement around the replacement pile (8); In step S1, the enlarged foundation (7) includes a first enlarged foundation (701) and a second enlarged foundation (702) located at the lower end of the first enlarged foundation (701). Grouting is performed to reinforce the stratum at the bottom of the enlarged foundation (7). After the grouting is completed, quick-drying concrete is used to seal the opening. Step S5 includes the following steps: S51: Surface treatment of rigid thin-walled pier (2) and first enlarged foundation (701): The rigid thin-walled pier (2) has a grooved section (201) near its bottom. The surface of the grooved section (201) is roughened into a first toothed groove (202), and the surface of the first enlarged foundation (701) is roughened into a second toothed groove (703). After cleaning with a wire brush, it is cleaned with a blower. S52: Rebar installation: Drill holes in the grooved section (201) using an electric drill. After drilling, fill the holes with rebar adhesive and then insert the threaded rebar (9) with the help of a positioning bracket. In step S52, the positioning bracket includes a large-diameter support steel pipe (17), an implanted rebar limiting steel pipe (18) sleeved inside the large-diameter support steel pipe (17), and an implanted rebar positioning support rod (21) set at the lower end of the large-diameter support steel pipe (17). The locking threaded rebar (9) can be inserted into the implanted rebar limiting steel pipe (18). The large-diameter support steel pipe (17) is provided with a rebar fixing bolt (15) for locking the threaded rebar (9). The rebar fixing bolt (15) is provided with a large-diameter steel pipe top locking welding nut (16). The large-diameter steel pipe top locking welding nut (16) abuts against the outer wall of the large-diameter support steel pipe (17). The large-diameter support steel pipe (17) is provided with a limiting steel pipe inclination measuring groove (22). The limiting steel pipe inclination measuring groove (22) is provided with a dual-axis electronic digital display angle meter (14). The embedded rebar positioning support rod (21) includes a height adjustment stud (212), a lower connecting pipe (216), and an upper connecting pipe (215) that is slidably disposed in the lower connecting pipe (216). The bottom of the lower connecting pipe (216) is provided with a support rod tapered foot (219). The lower end of the height adjustment stud (212) extends into the upper connecting pipe (215) and is threadedly connected to the upper connecting pipe (215). The upper end of the upper connecting pipe (215) is provided with an upper connecting pipe limiting welded nut (214) that is threadedly connected to the height adjusting stud (212). The height adjusting stud (212) is provided with a stud limiting welded nut (213). The upper end of the height adjusting stud (212) is provided with a top limiting plain round steel bar (211). The lower end of the large diameter support steel pipe (17) is provided with a support rod angle adjustment groove (19). The limiting plain round steel bar is rotatably set in the support rod angle adjustment groove (19). Support rod limiting hoops (20) for wrapping the top limiting plain round steel bar (211) are provided on both sides of the support rod angle adjustment groove (19). The top limiting plain round steel bar (211) can rotate relative to the support rod limiting hoop (20). The upper connecting pipe (215) is provided with multiple height adjustment slots along its axial direction, the lower connecting pipe (216) is provided with a connecting pipe height adjustment slot (23), and the lower connecting pipe (216) is also provided with a connecting pipe height adjustment bolt (217). The connecting pipe height adjustment bolt (217) passes through the height adjustment slots and the connecting pipe height adjustment slot (23), and is locked with a height adjustment nut.

2. The passive underpinning construction method for rigid frame thin-walled piers according to claim 1, characterized in that: In step S2, a hole is drilled on the construction ground and a steel casing is driven in. Then, a steel cage is hoisted into the pile hole. A sonic logging pipe is installed inside the steel cage. Underwater concrete is poured through the guide pipe to form a replacement pile (8).

3. The rigid frame thin-walled pier passive underpinning construction method according to claim 2, characterized in that: In step S3, a foundation pit (5) is excavated around the rigid thin-walled pier (2), and the bottom of the foundation pit (5) is flush with the lower end of the first enlarged foundation (701).

4. The rigid frame thin-walled pier passive underpinning construction method according to claim 3, characterized in that: The safety support in step S4 includes a Bailey beam (301), a steel column (302) at the upper end of the Bailey beam (301), steel plates (303) at the upper and lower ends of the steel column (302), the steel plate (303) at the lower end of the steel column (302) is fixed on the Bailey beam (301), an I-beam (304) at the upper end of the steel column (302), and a wedge-shaped wooden block (305) at the upper end of the I-beam (304). Step S4 includes the following steps: S41: Construction of the cap beam (4): Concrete beams are constructed on both sides of the foundation pit (5); S42: Bailey beam (301) installation: After the capping beam (4) is completed, at least three Bailey beams (301) are installed on the upper end of the capping beam (4). The two ends of the Bailey beams (301) are fixed to the upper part of the capping beam (4) and arranged parallel to the rigid thin-walled pier (2). S43: Steel column (302) installation: Steel column (302) is erected on Bailey beam (301), and steel plate (303) is welded to the upper and lower ends of steel column (302); S44: Beam installation: Install I-beams (304) on top of steel columns (302).

5. The passive underpinning construction method for a rigid thin-walled pier according to claim 1, characterized in that: In step S6, a concrete interface treatment agent is applied to the surface of the grooved section (201) and the first enlarged foundation (701). Four hours after application, concrete is poured around the grooved section (201) and the first enlarged foundation (701) to form a support beam (6) around the grooved section (201) and the first enlarged foundation (701). The grooved section (201), the threaded steel bar (9) embedded in the grooved section (201), the first enlarged foundation (701), the support beam (6), and the support pile (8) together form a passive support foundation.

6. The passive underpinning construction method for a rigid thin-walled pier according to claim 5, characterized in that: In step S7, grouting is performed at the bottom of the replacement pile (8) through the sonic logging tube inside the reinforcing cage of the replacement beam (6), and a grouting zone (11) is formed at the bottom of the replacement pile (8), with a grouting pressure of 3-5 MPa.

7. The method of claim 6, wherein: In step S8, grouting holes are added on both sides of the adjacent replacement pile (8), and holes are opened in the 4th to 5th rings of the shield segment (13) after it comes out of the shield tail. Grouting in the transverse tunnel is carried out through the grouting holes, and the grouting pressure is controlled at 0.3 to 0.4 MPa.

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