Method for repairing and reinforcing underwater piers of bridges in tidal zones

Abstract

Disclosed is a low-cost and safe method for repairing and reinforcing underwater piers of bridges in tidal zones, including: installing a steel boxed cofferdam and reinforcing concrete of a pier column, where during the step of installing the steel boxed cofferdam, a lower internal bracing is first fixed onto a top surface of a pile cap, then side plates of the steel boxed cofferdam are connected to the lower internal bracing, and subsequently, hydraulic jacks are used to push a waterstop work platform; and during the step of reinforcing the concrete of the pier column, spacers are arranged between an inner surface of glass fiber reinforced plastic formwork and an outer surface of the pier column, a bottom outer edge of the glass fiber reinforced plastic formwork is sealed with mortar, and once the mortar reaches a certain strength, reactive powder concrete is placed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The application claims priority to Chinese patent application No. 202310470529.9, filed on Apr. 26, 2023, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

[0002] This disclosure relates to a method for repairing and reinforcing underwater piers of bridges in tidal zones.BACKGROUND

[0003] With the rapid development of large-scale transportation systems such as modern highways and urban expressways, an increasing number of cross-river and cross-sea bridges have emerged. While these bridges facilitate transportation, the loads borne by the piers have been rising annually, and early signs of deterioration have emerged in the pier foundations. This is particularly severe for cross-sea bridges with navigation requirements, where piers are subjected to combined adverse effects including seawater erosion in tidal zones, vessel impacts, or scraping. The resulting damages are especially serious, including corrosion-induced expansion, concrete loss, vessel impact marks, and issues at the connections between pile caps and pier columns, posing significant safety hazards. Therefore, repair and reinforcement measures for the piers are necessary. Underwater piers in the substructure of a cross-sea bridge include pile foundations, pile caps, and pier columns. The repair and reinforcement of the substructure differ from the construction of new bridge substructures. Factors such as bridge clearances, existing structures, seawater tides, and navigation requirements impose constraints on the repair and reinforcement work, thereby increasing the difficulty of the work.SUMMARY

[0004] This disclosure is intended to overcome the deficiencies in the prior art by providing a method for repairing and reinforcing underwater piers of bridges in tidal zones, which features low cost and high safety, can effectively alleviate corrosion of rebar in the underwater piers, and improves the service life of the pier structure.

[0005] The objective of this disclosure is achieved as follows: a method for repairing and reinforcing underwater piers of bridges in tidal zones, using an open-bottom steel boxed cofferdam for water enclosure and including the following steps: trimming an underwater pile cap, installing the steel boxed cofferdam, sealing the steel boxed cofferdam, installing a sacrificial anode protection system, reinforcing concrete of a pier column, and removing the steel boxed cofferdam;

[0006] during the step of trimming the underwater pile cap, divers clean top and side surfaces of the pile cap in conjunction with high-pressure water jets, ensuring the top surface of the pile cap is level and there is no accumulated silt on the side surface;

[0007] during the step of installing the steel boxed cofferdam, the steel boxed cofferdam is rectangular in plan view and is an open-bottom type, with its inner wall provided with a lower internal bracing, a middle waling, and an upper waling sequentially from bottom to top; a bottom surface inside the lower internal bracing is connected to a steel anchor plate; an outer end of the lower internal bracing is connected to a bracket fixed on a side plate of the steel boxed cofferdam, with a connection between the bracket and the lower internal bracing made via a flange; a bottom of each of four side plates of the steel boxed cofferdam is provided with a waterstop work platform, which is located within a guide channel formed by a pressure plate and a base plate, and an inner end of the waterstop work platform is provided with a mounting groove for embedding a GINA waterstop; a plurality of hydraulic jacks are spaced apart between an outer end of the waterstop work platform within the guide channel and the side plates of the steel boxed cofferdam; and when the steel boxed cofferdam is installed, first, a surveyor measures and sets out a position of the lower internal bracing of the steel boxed cofferdam on the top surface of the pile cap, taking into account a tidal difference, then post-installed rebar holes are drilled according to the set-out on the top surface of the pile cap and filled with epoxy resin adhesive, anchor bolts connected to the steel anchor plate of the lower internal bracing are embedded into the post-installed rebar holes, and after the epoxy resin adhesive cures, the lower internal bracing is fixed onto the top surface of the pile cap, next, the brackets on the side plates of the steel boxed cofferdam are connected to the corresponding lower internal bracing via flange bolts, and finally, the hydraulic jacks on the outer side of the waterstop work platform simultaneously apply pressure to the work platform, pushing it along the guide channel towards the pile cap until the GINA waterstop is in close contact with the side surface of the pile cap;

[0008] during the step of sealing the steel boxed cofferdam, first, communication holes on the steel boxed cofferdam are plugged, and then water is pumped out to create a dry working environment;

[0009] during the step of installing the sacrificial anode protection system, zinc blocks, which are higher in a galvanic series, are installed on corroded rebar of the pier column to act as sacrificial anodes, protecting the iron rebar lower in the galvanic series, thereby establishing the sacrificial anode protection system, including the following sub-steps:

[0010] 1) chipping away concrete at areas of corrosion-induced spalling on the pier column to expose the rebar, then derusting and applying anti-rust treatment to the exposed rebar; and

[0011] 2) electrically connecting several galvanized iron straps at intervals to the exposed rebar, with ends of the galvanized iron straps extending below a designed low water level, then installing the zinc blocks using bolts at the ends of the galvanized iron straps, and finally connecting the several zinc blocks in series electrically;

[0012] the step of reinforcing the concrete of the pier column includes the following sub-steps:

[0013] 1) inside the steel boxed cofferdam, removing unsound mortar from a concrete surface of the pier column, removing loose attachments and harmful contaminants, and roughening a surface of a to-be-reinforced area using a concrete scabbler or manually, with a roughening depth of at least 10 mm;

[0014] 2) hoisting and placing permanent glass fiber reinforced plastic formwork in sections using a crawler crane assisted by workers, where cross-sectional dimensions of the glass fiber reinforced plastic formwork are larger than those of the pier column; arranging spacers between an inner side surface of the glass fiber reinforced plastic formwork and an outer surface of the pier column; and after the glass fiber reinforced plastic formwork is fixed, sealing a bottom outer edge of the glass fiber reinforced plastic formwork with mortar, and once the mortar reaches a certain strength, placing reactive powder concrete; and

[0015] 3) preparing the reactive powder concrete by mixing silica powder, cement, reactive powder concrete-specific admixtures, water, and chemical admixtures; placing the mixed reactive powder concrete within 30 min; placing structural members continuously, with a maximum interval not exceeding 6 min; and upon completion of the placement of the reactive powder concrete, curing the concrete by covering it and sprinkling with water for not less than 7 days;

[0016] during the step of removing the steel boxed cofferdam, first, the pressure applied to the waterstop work platform is released, allowing seawater to enter the steel boxed cofferdam, then the bolt connections between the four side plates of the steel boxed cofferdam are disconnected using the crawler crane assisted by the divers underwater section by section, and unit side plates are removed one by one.

[0017] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones as described above, where during the step of installing the steel boxed cofferdam, the four side plates of the steel boxed cofferdam all employ a double-wall structure, and each of the side plates is formed by splicing two of the unit side plates together using high-strength bolts, with a rubber waterstop plate arranged on a splicing surface of every two of the unit side plates; each of the unit side plates includes an inner steel plate, an outer steel plate, and horizontal stiffening plates and vertical bulkhead plates connected between the inner steel plate and the outer steel plate; and the steel boxed cofferdam is provided with an operational platform arranged circumferentially at a top thereof and a ladder for entry and exit by construction personnel.

[0018] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones as described above, where during the step of installing the steel boxed cofferdam, the waterstop work platform is made of stainless steel, and polytetrafluoroethylene plates are arranged both between a top surface of the waterstop work platform and the pressure plate of the guide channel, and between a bottom surface of the waterstop work platform and the base plate of the guide channel.

[0019] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones as described above, where during the step of installing the steel boxed cofferdam, a chain hoist is used to fine-tune positions of the side plates of the steel boxed cofferdam; precise positioning of the side plates is achieved via guide holes and frustum-shaped guide rods pre-installed on flange mating surfaces connecting the brackets to the lower internal bracing, after which the flange bolts are tightened; and top openings of the side plates are temporarily fixed using channel steel onto clamps pre-installed on the pier column.

[0020] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones as described above, where during the step of reinforcing the concrete of the pier column, the reactive powder concrete is placed by grouting, with one grouting pipe arranged on each of four sides of the pier column, and the grouting is performed in a symmetrical sequence to ensure pressure balance around the glass fiber reinforced plastic formwork.

[0021] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones provided by this disclosure has the following characteristics:

[0022] 1) it employs the retractable waterstop work platform composed of the GINA waterstop and hydraulic jacks; by applying pressure to the waterstop work platform via the jacks, a sealing effect is achieved between the steel boxed cofferdam and the pile cap, preventing seawater from entering the steel boxed cofferdam and providing a dry working environment for the repair of the pier column; and by utilizing the existing pile cap as the construction work platform, the need for a bottom plate on the steel boxed cofferdam is eliminated, reducing cost investment;

[0023] 2) the lower internal bracing of the double-walled steel boxed cofferdam is fixed onto the pile cap by embedding anchor bolts into the top surface of the pile cap, and these anchor bolts are embedded into the post-installed rebar holes filled with epoxy resin adhesive; the upper side plates of the steel boxed cofferdam use two levels of waling as internal bracing, which prevents the bottom of the steel boxed cofferdam from resting on the seabed, providing a full-section construction environment for the pier column, reducing interference from steel bracing attached to the pier column, and facilitating construction;

[0024] 3) it establishes the sacrificial anode protection system by installing sacrificial anodes (zinc), which are higher in the galvanic series, onto the corroded rebar of the existing pier, thereby protecting the rebar (iron), which is lower in the galvanic series, thereby effectively mitigating rebar corrosion and enhancing the service life of the pier column; and

[0025] 4) it adds a layer of reactive powder concrete to the external surface of the original pier column, which effectively repairs damage on the underwater pier column in the tidal zone, reduces erosion caused by seawater to the rebar of the underwater pier column, and extends the service life of the pier.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a longitudinal elevation view of a steel boxed cofferdam used in a according to this disclosure;

[0027] FIG. 2 is a transverse elevation view of the steel boxed cofferdam used in the method for repairing and reinforcing the underwater piers of bridges in the tidal zones according to this disclosure;

[0028] FIG. 2A is a view taken in an A-A direction of FIG. 2;

[0029] FIG. 2B is a view taken in a B-B direction of FIG. 2;

[0030] FIG. 2C is a view taken in a C-C direction of FIG. 2;

[0031] FIG. 2D is a view taken in a D-D direction of FIG. 2;

[0032] FIG. 3 is an enlarged view of a portion P in FIG. 2;

[0033] FIG. 4 is a schematic structural diagram when the steel boxed cofferdam is installed according to the method of this disclosure;

[0034] FIG. 5 is another schematic structural diagram when the steel boxed cofferdam is installed according to the method of this disclosure;

[0035] FIG. 5A is a top view of FIG. 5;

[0036] FIG. 6 is a schematic structural diagram when a sacrificial anode protection system is installed according to the method of this disclosure;

[0037] FIG. 7 is a schematic structural diagram when concrete of a pier column is reinforced according to the method of this disclosure; and

[0038] FIG. 7A is a view taken in an E-E direction of FIG. 7.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] This disclosure will be further described below with reference to the accompanying drawings.

[0040] Referring to FIGS. 1-7a, this disclosure provides a method for repairing and reinforcing underwater piers of bridges in tidal zones, using an open-bottom steel boxed cofferdam for water enclosure and including the following steps: trimming an underwater pile cap, installing the steel boxed cofferdam, sealing the steel boxed cofferdam, installing a sacrificial anode protection system, reinforcing concrete of a pier column, and removing the steel boxed cofferdam.

[0041] During the step of trimming the underwater pile cap, divers clean top and side surfaces of the pile cap in conjunction with high-pressure water jets, ensuring the top surface of the pile cap is level and there is no accumulated silt on the side surface;

[0042] during the step of installing the steel boxed cofferdam, the plan of the steel boxed cofferdam 100 corresponds to the plan structure of the pile cap 301 and is therefore rectangular and an open-bottom type; four side plates 10 of the steel boxed cofferdam 100 all employ a double-walled structure, and each of the side plates 10 is formed by splicing two unit side plates together using M20 high-strength bolts, with a 1-cm-thick rubber waterstop plate arranged on a splicing surface of every two unit side plates; each unit side plate includes an inner steel plate, an outer steel plate, and horizontal stiffening plates and vertical bulkhead plates connected between the inner steel plate and the outer steel plate; the steel boxed cofferdam 100 is provided with an operational platform arranged circumferentially at a top thereof and a ladder for entry and exit by construction personnel; an inner wall of the steel boxed cofferdam 100 is provided with a lower internal bracing 101, a middle waling 102, and an upper waling 103 sequentially from bottom to top; a bottom surface inside the lower internal bracing 101 is connected to a steel anchor plate 10A; a rear end of the lower internal bracing 101 is connected to a bracket 11 fixed on the side plate 10, with a connection between the bracket 11 and the lower internal bracing 101 made via a flange 12; a bottom of each of the four side plates 10 of the steel boxed cofferdam is provided with a waterstop work platform 200, which is located within a guide channel formed by a pressure plate 201 and a base plate 202 fixed onto an inner side surface of the side plate 10 of the steel boxed cofferdam; an inner end of the waterstop work platform 200 is provided with a mounting groove for embedding a GINA waterstop 20; the waterstop work platform 200 is made of stainless steel, and to facilitate smooth sliding of the waterstop work platform 200 within the guide channel, polytetrafluoroethylene plates are arranged both between a top surface of the waterstop work platform 200 and the pressure plate 201 of the guide channel, and between a bottom surface of the waterstop work platform 200 and the base plate 202 of the guide channel; and a plurality of hydraulic jacks 30 are spaced apart between an outer end of the waterstop work platform 200 within the guide channel and the side plates 10 of the steel boxed cofferdam;

[0043] when the steel boxed cofferdam is installed, first, a surveyor measures and sets out a position of the lower internal bracing 101 of the steel boxed cofferdam 100 on the top surface of the pile cap 301, taking into account a tidal difference, then post-installed rebar holes are drilled according to the set-out on the top surface of the pile cap 301 and filled with epoxy resin adhesive, φ20 anchor bolts 10B connected to the steel anchor plate 10A of the lower internal bracing 101 are embedded into the post-installed rebar holes, and after the epoxy resin adhesive cures, the lower internal bracing 101 is fixed onto the top surface of the pile cap 301; next, the brackets 11 on the side plates 10 of the steel boxed cofferdam 100 are connected to the corresponding lower internal bracing 101 via flange bolts; and finally, the hydraulic jacks 30 on the outer side of the waterstop work platform 200 simultaneously apply pressure to the waterstop work platform 200, pushing it along the guide channel towards the pile cap 301 until the GINA waterstop 20 is in close contact with the side surface of the pile cap 301. The joints between every two sections of the GINA waterstop 20 are filled with rubber blocks, and two φ32 fine-rolled threaded steel bars 104 are symmetrically tensioned at the bottoms of the four side plates 10 of the steel boxed cofferdam 100 to enhance the bottom connection performance of the steel boxed cofferdam 100. When the side plates 10 of the steel boxed cofferdam are installed, a chain hoist is used to fine-tune positions of the side plates 10; precise positioning of the side plates 10 is achieved via guide holes 13 and frustum-shaped guide rods 14 pre-installed on flange mating surfaces connecting the brackets 11 to the lower internal bracing 101, after which the flange bolts are tightened; and to prevent the side plates 10 from overturning, top openings of the side plates 10 are temporarily fixed using channel steel 15 onto clamps 16 pre-installed on the pier column 302;

[0044] during the step of sealing the steel boxed cofferdam, first, communication holes on the steel boxed cofferdam 100 are plugged, and then water is pumped out to create a dry working environment;

[0045] during the step of installing the sacrificial anode protection system, zinc blocks 42, which are higher in a galvanic series, are installed on corroded rebar of the pier column 302 to act as sacrificial anodes, protecting the iron rebar 40 lower in the galvanic series, thereby establishing the sacrificial anode protection system, effectively alleviating corrosion of the rebar, and improving the service life of the structure, including the following sub-steps:

[0046] 1) chipping away concrete at areas of corrosion-induced spalling on the pier column 302 to expose the rebar 40, then derusting and applying anti-rust treatment to the exposed rebar 40; and

[0047] 2) electrically connecting several galvanized iron straps 41 at intervals to the exposed rebar 40, with ends of the galvanized iron straps 41 extending below a designed low water level, then installing the zinc blocks 42 using bolts at the ends of the galvanized iron straps 41, and finally connecting the several zinc blocks 42 in series electrically;

[0048] the step of reinforcing the concrete of the pier column includes the following sub-steps:

[0049] 1) inside the steel boxed cofferdam 100, removing unsound mortar from a concrete surface of the pier column 302, removing loose attachments and harmful contaminants, and roughening a surface of a to-be-reinforced area using a concrete scabbler or manually, with a roughening depth of at least 10 mm, to ensure effective bonding between reactive powder concrete and the structural base;

[0050] 2) hoisting and placing permanent glass fiber reinforced plastic formwork 50 in sections using a crawler crane assisted by workers, where cross-sectional dimensions of the glass fiber reinforced plastic formwork 50 are 10 cm larger than those of the pier column 302; arranging spacers 51 with a thickness of 5 cm between an inner side surface of the glass fiber reinforced plastic formwork 50 and an outer surface of the pier column 302; forming the glass fiber reinforced plastic formwork 50 by bringing together two formwork members with a U-shaped plan and then locking them with fastening bolts 52; and after the glass fiber reinforced plastic formwork 50 is fixed, sealing a bottom outer edge of the glass fiber reinforced plastic formwork 50 with mortar, and once the mortar reaches a certain strength, placing the reactive powder concrete to prevent bottom grout leakage; and

[0051] 3) preparing the reactive powder concrete by mixing silica powder, cement, reactive powder concrete-specific admixtures, water, and chemical admixtures; placing the mixed reactive powder concrete within 30 min; placing structural members continuously, with a maximum interval not exceeding 6 min; and upon completion of the placement of the reactive powder concrete, curing the concrete by covering it and sprinkling with water for not less than 7 days;

[0052] the reactive powder concrete is placed by grouting using grouting equipment; since the reactive powder concrete is in a thick, paste-like state during the placement and the plan structure of the pier column 302 is rectangular, the reactive powder concrete has relatively poor fluidity at corners of the pier column 302; therefore, one grouting pipe is arranged on each of the four sides of the pier column 302, and grouting is performed in a symmetrical sequence to ensure pressure balance around the glass fiber reinforced plastic formwork 50; and

[0053] during the step of removing the steel boxed cofferdam, first, the pressure applied to the waterstop work platform 200 is released, allowing seawater to enter the steel boxed cofferdam 100 to balance internal and external pressures, then the bolt connections between the four side plates 10 of the steel boxed cofferdam 100 are disconnected using a 50T crawler crane assisted by the divers underwater section by section, and unit side plates are removed one by one.

[0054] The above embodiments are used merely to illustrate this disclosure rather than to limit it. Those skilled in the art may make various modifications or alterations without departing from the spirit and scope of this disclosure. Therefore, all equivalent technical solutions should also fall within the scope of this disclosure, as defined by the appended claims.

Examples

Embodiment Construction

[0039]This disclosure will be further described below with reference to the accompanying drawings.

[0040]Referring to FIGS. 1-7a, this disclosure provides a method for repairing and reinforcing underwater piers of bridges in tidal zones, using an open-bottom steel boxed cofferdam for water enclosure and including the following steps: trimming an underwater pile cap, installing the steel boxed cofferdam, sealing the steel boxed cofferdam, installing a sacrificial anode protection system, reinforcing concrete of a pier column, and removing the steel boxed cofferdam.

[0041]During the step of trimming the underwater pile cap, divers clean top and side surfaces of the pile cap in conjunction with high-pressure water jets, ensuring the top surface of the pile cap is level and there is no accumulated silt on the side surface;[0042]during the step of installing the steel boxed cofferdam, the plan of the steel boxed cofferdam 100 corresponds to the plan structure of the pile cap 301 and is the...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The application claims priority to Chinese patent application No. 202310470529.9, filed on Apr. 26, 2023, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

[0002] This disclosure relates to a method for repairing and reinforcing underwater piers of bridges in tidal zones.BACKGROUND

[0003] With the rapid development of large-scale transportation systems such as modern highways and urban expressways, an increasing number of cross-river and cross-sea bridges have emerged. While these bridges facilitate transportation, the loads borne by the piers have been rising annually, and early signs of deterioration have emerged in the pier foundations. This is particularly severe for cross-sea bridges with navigation requirements, where piers are subjected to combined adverse effects including seawater erosion in tidal zones, vessel impacts, or scraping. The resulting damages are especially serious, including corrosion-induced expansion, concrete loss, vessel impact marks, and issues at the connections between pile caps and pier columns, posing significant safety hazards. Therefore, repair and reinforcement measures for the piers are necessary. Underwater piers in the substructure of a cross-sea bridge include pile foundations, pile caps, and pier columns. The repair and reinforcement of the substructure differ from the construction of new bridge substructures. Factors such as bridge clearances, existing structures, seawater tides, and navigation requirements impose constraints on the repair and reinforcement work, thereby increasing the difficulty of the work.SUMMARY

[0004] This disclosure is intended to overcome the deficiencies in the prior art by providing a method for repairing and reinforcing underwater piers of bridges in tidal zones, which features low cost and high safety, can effectively alleviate corrosion of rebar in the underwater piers, and improves the service life of the pier structure.

[0005] The objective of this disclosure is achieved as follows: a method for repairing and reinforcing underwater piers of bridges in tidal zones, using an open-bottom steel boxed cofferdam for water enclosure and including the following steps: trimming an underwater pile cap, installing the steel boxed cofferdam, sealing the steel boxed cofferdam, installing a sacrificial anode protection system, reinforcing concrete of a pier column, and removing the steel boxed cofferdam;

[0006] during the step of trimming the underwater pile cap, divers clean top and side surfaces of the pile cap in conjunction with high-pressure water jets, ensuring the top surface of the pile cap is level and there is no accumulated silt on the side surface;

[0007] during the step of installing the steel boxed cofferdam, the steel boxed cofferdam is rectangular in plan view and is an open-bottom type, with its inner wall provided with a lower internal bracing, a middle waling, and an upper waling sequentially from bottom to top; a bottom surface inside the lower internal bracing is connected to a steel anchor plate; an outer end of the lower internal bracing is connected to a bracket fixed on a side plate of the steel boxed cofferdam, with a connection between the bracket and the lower internal bracing made via a flange; a bottom of each of four side plates of the steel boxed cofferdam is provided with a waterstop work platform, which is located within a guide channel formed by a pressure plate and a base plate, and an inner end of the waterstop work platform is provided with a mounting groove for embedding a GINA waterstop; a plurality of hydraulic jacks are spaced apart between an outer end of the waterstop work platform within the guide channel and the side plates of the steel boxed cofferdam; and when the steel boxed cofferdam is installed, first, a surveyor measures and sets out a position of the lower internal bracing of the steel boxed cofferdam on the top surface of the pile cap, taking into account a tidal difference, then post-installed rebar holes are drilled according to the set-out on the top surface of the pile cap and filled with epoxy resin adhesive, anchor bolts connected to the steel anchor plate of the lower internal bracing are embedded into the post-installed rebar holes, and after the epoxy resin adhesive cures, the lower internal bracing is fixed onto the top surface of the pile cap, next, the brackets on the side plates of the steel boxed cofferdam are connected to the corresponding lower internal bracing via flange bolts, and finally, the hydraulic jacks on the outer side of the waterstop work platform simultaneously apply pressure to the work platform, pushing it along the guide channel towards the pile cap until the GINA waterstop is in close contact with the side surface of the pile cap;

[0008] during the step of sealing the steel boxed cofferdam, first, communication holes on the steel boxed cofferdam are plugged, and then water is pumped out to create a dry working environment;

[0009] during the step of installing the sacrificial anode protection system, zinc blocks, which are higher in a galvanic series, are installed on corroded rebar of the pier column to act as sacrificial anodes, protecting the iron rebar lower in the galvanic series, thereby establishing the sacrificial anode protection system, including the following sub-steps:

[0010] 1) chipping away concrete at areas of corrosion-induced spalling on the pier column to expose the rebar, then derusting and applying anti-rust treatment to the exposed rebar; and

[0011] 2) electrically connecting several galvanized iron straps at intervals to the exposed rebar, with ends of the galvanized iron straps extending below a designed low water level, then installing the zinc blocks using bolts at the ends of the galvanized iron straps, and finally connecting the several zinc blocks in series electrically;

[0012] the step of reinforcing the concrete of the pier column includes the following sub-steps:

[0013] 1) inside the steel boxed cofferdam, removing unsound mortar from a concrete surface of the pier column, removing loose attachments and harmful contaminants, and roughening a surface of a to-be-reinforced area using a concrete scabbler or manually, with a roughening depth of at least 10 mm;

[0014] 2) hoisting and placing permanent glass fiber reinforced plastic formwork in sections using a crawler crane assisted by workers, where cross-sectional dimensions of the glass fiber reinforced plastic formwork are larger than those of the pier column; arranging spacers between an inner side surface of the glass fiber reinforced plastic formwork and an outer surface of the pier column; and after the glass fiber reinforced plastic formwork is fixed, sealing a bottom outer edge of the glass fiber reinforced plastic formwork with mortar, and once the mortar reaches a certain strength, placing reactive powder concrete; and

[0015] 3) preparing the reactive powder concrete by mixing silica powder, cement, reactive powder concrete-specific admixtures, water, and chemical admixtures; placing the mixed reactive powder concrete within 30 min; placing structural members continuously, with a maximum interval not exceeding 6 min; and upon completion of the placement of the reactive powder concrete, curing the concrete by covering it and sprinkling with water for not less than 7 days;

[0016] during the step of removing the steel boxed cofferdam, first, the pressure applied to the waterstop work platform is released, allowing seawater to enter the steel boxed cofferdam, then the bolt connections between the four side plates of the steel boxed cofferdam are disconnected using the crawler crane assisted by the divers underwater section by section, and unit side plates are removed one by one.

[0017] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones as described above, where during the step of installing the steel boxed cofferdam, the four side plates of the steel boxed cofferdam all employ a double-wall structure, and each of the side plates is formed by splicing two of the unit side plates together using high-strength bolts, with a rubber waterstop plate arranged on a splicing surface of every two of the unit side plates; each of the unit side plates includes an inner steel plate, an outer steel plate, and horizontal stiffening plates and vertical bulkhead plates connected between the inner steel plate and the outer steel plate; and the steel boxed cofferdam is provided with an operational platform arranged circumferentially at a top thereof and a ladder for entry and exit by construction personnel.

[0018] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones as described above, where during the step of installing the steel boxed cofferdam, the waterstop work platform is made of stainless steel, and polytetrafluoroethylene plates are arranged both between a top surface of the waterstop work platform and the pressure plate of the guide channel, and between a bottom surface of the waterstop work platform and the base plate of the guide channel.

[0019] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones as described above, where during the step of installing the steel boxed cofferdam, a chain hoist is used to fine-tune positions of the side plates of the steel boxed cofferdam; precise positioning of the side plates is achieved via guide holes and frustum-shaped guide rods pre-installed on flange mating surfaces connecting the brackets to the lower internal bracing, after which the flange bolts are tightened; and top openings of the side plates are temporarily fixed using channel steel onto clamps pre-installed on the pier column.

[0020] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones as described above, where during the step of reinforcing the concrete of the pier column, the reactive powder concrete is placed by grouting, with one grouting pipe arranged on each of four sides of the pier column, and the grouting is performed in a symmetrical sequence to ensure pressure balance around the glass fiber reinforced plastic formwork.

[0021] The method for repairing and reinforcing the underwater piers of bridges in the tidal zones provided by this disclosure has the following characteristics:

[0022] 1) it employs the retractable waterstop work platform composed of the GINA waterstop and hydraulic jacks; by applying pressure to the waterstop work platform via the jacks, a sealing effect is achieved between the steel boxed cofferdam and the pile cap, preventing seawater from entering the steel boxed cofferdam and providing a dry working environment for the repair of the pier column; and by utilizing the existing pile cap as the construction work platform, the need for a bottom plate on the steel boxed cofferdam is eliminated, reducing cost investment;

[0023] 2) the lower internal bracing of the double-walled steel boxed cofferdam is fixed onto the pile cap by embedding anchor bolts into the top surface of the pile cap, and these anchor bolts are embedded into the post-installed rebar holes filled with epoxy resin adhesive; the upper side plates of the steel boxed cofferdam use two levels of waling as internal bracing, which prevents the bottom of the steel boxed cofferdam from resting on the seabed, providing a full-section construction environment for the pier column, reducing interference from steel bracing attached to the pier column, and facilitating construction;

[0024] 3) it establishes the sacrificial anode protection system by installing sacrificial anodes (zinc), which are higher in the galvanic series, onto the corroded rebar of the existing pier, thereby protecting the rebar (iron), which is lower in the galvanic series, thereby effectively mitigating rebar corrosion and enhancing the service life of the pier column; and

[0025] 4) it adds a layer of reactive powder concrete to the external surface of the original pier column, which effectively repairs damage on the underwater pier column in the tidal zone, reduces erosion caused by seawater to the rebar of the underwater pier column, and extends the service life of the pier.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a longitudinal elevation view of a steel boxed cofferdam used in a according to this disclosure;

[0027] FIG. 2 is a transverse elevation view of the steel boxed cofferdam used in the method for repairing and reinforcing the underwater piers of bridges in the tidal zones according to this disclosure;

[0028] FIG. 2A is a view taken in an A-A direction of FIG. 2;

[0029] FIG. 2B is a view taken in a B-B direction of FIG. 2;

[0030] FIG. 2C is a view taken in a C-C direction of FIG. 2;

[0031] FIG. 2D is a view taken in a D-D direction of FIG. 2;

[0032] FIG. 3 is an enlarged view of a portion P in FIG. 2;

[0033] FIG. 4 is a schematic structural diagram when the steel boxed cofferdam is installed according to the method of this disclosure;

[0034] FIG. 5 is another schematic structural diagram when the steel boxed cofferdam is installed according to the method of this disclosure;

[0035] FIG. 5A is a top view of FIG. 5;

[0036] FIG. 6 is a schematic structural diagram when a sacrificial anode protection system is installed according to the method of this disclosure;

[0037] FIG. 7 is a schematic structural diagram when concrete of a pier column is reinforced according to the method of this disclosure; and

[0038] FIG. 7A is a view taken in an E-E direction of FIG. 7.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] This disclosure will be further described below with reference to the accompanying drawings.

[0040] Referring to FIGS. 1-7a, this disclosure provides a method for repairing and reinforcing underwater piers of bridges in tidal zones, using an open-bottom steel boxed cofferdam for water enclosure and including the following steps: trimming an underwater pile cap, installing the steel boxed cofferdam, sealing the steel boxed cofferdam, installing a sacrificial anode protection system, reinforcing concrete of a pier column, and removing the steel boxed cofferdam.

[0041] During the step of trimming the underwater pile cap, divers clean top and side surfaces of the pile cap in conjunction with high-pressure water jets, ensuring the top surface of the pile cap is level and there is no accumulated silt on the side surface;

[0042] during the step of installing the steel boxed cofferdam, the plan of the steel boxed cofferdam 100 corresponds to the plan structure of the pile cap 301 and is therefore rectangular and an open-bottom type; four side plates 10 of the steel boxed cofferdam 100 all employ a double-walled structure, and each of the side plates 10 is formed by splicing two unit side plates together using M20 high-strength bolts, with a 1-cm-thick rubber waterstop plate arranged on a splicing surface of every two unit side plates; each unit side plate includes an inner steel plate, an outer steel plate, and horizontal stiffening plates and vertical bulkhead plates connected between the inner steel plate and the outer steel plate; the steel boxed cofferdam 100 is provided with an operational platform arranged circumferentially at a top thereof and a ladder for entry and exit by construction personnel; an inner wall of the steel boxed cofferdam 100 is provided with a lower internal bracing 101, a middle waling 102, and an upper waling 103 sequentially from bottom to top; a bottom surface inside the lower internal bracing 101 is connected to a steel anchor plate 10A; a rear end of the lower internal bracing 101 is connected to a bracket 11 fixed on the side plate 10, with a connection between the bracket 11 and the lower internal bracing 101 made via a flange 12; a bottom of each of the four side plates 10 of the steel boxed cofferdam is provided with a waterstop work platform 200, which is located within a guide channel formed by a pressure plate 201 and a base plate 202 fixed onto an inner side surface of the side plate 10 of the steel boxed cofferdam; an inner end of the waterstop work platform 200 is provided with a mounting groove for embedding a GINA waterstop 20; the waterstop work platform 200 is made of stainless steel, and to facilitate smooth sliding of the waterstop work platform 200 within the guide channel, polytetrafluoroethylene plates are arranged both between a top surface of the waterstop work platform 200 and the pressure plate 201 of the guide channel, and between a bottom surface of the waterstop work platform 200 and the base plate 202 of the guide channel; and a plurality of hydraulic jacks 30 are spaced apart between an outer end of the waterstop work platform 200 within the guide channel and the side plates 10 of the steel boxed cofferdam;

[0043] when the steel boxed cofferdam is installed, first, a surveyor measures and sets out a position of the lower internal bracing 101 of the steel boxed cofferdam 100 on the top surface of the pile cap 301, taking into account a tidal difference, then post-installed rebar holes are drilled according to the set-out on the top surface of the pile cap 301 and filled with epoxy resin adhesive, φ20 anchor bolts 10B connected to the steel anchor plate 10A of the lower internal bracing 101 are embedded into the post-installed rebar holes, and after the epoxy resin adhesive cures, the lower internal bracing 101 is fixed onto the top surface of the pile cap 301; next, the brackets 11 on the side plates 10 of the steel boxed cofferdam 100 are connected to the corresponding lower internal bracing 101 via flange bolts; and finally, the hydraulic jacks 30 on the outer side of the waterstop work platform 200 simultaneously apply pressure to the waterstop work platform 200, pushing it along the guide channel towards the pile cap 301 until the GINA waterstop 20 is in close contact with the side surface of the pile cap 301. The joints between every two sections of the GINA waterstop 20 are filled with rubber blocks, and two φ32 fine-rolled threaded steel bars 104 are symmetrically tensioned at the bottoms of the four side plates 10 of the steel boxed cofferdam 100 to enhance the bottom connection performance of the steel boxed cofferdam 100. When the side plates 10 of the steel boxed cofferdam are installed, a chain hoist is used to fine-tune positions of the side plates 10; precise positioning of the side plates 10 is achieved via guide holes 13 and frustum-shaped guide rods 14 pre-installed on flange mating surfaces connecting the brackets 11 to the lower internal bracing 101, after which the flange bolts are tightened; and to prevent the side plates 10 from overturning, top openings of the side plates 10 are temporarily fixed using channel steel 15 onto clamps 16 pre-installed on the pier column 302;

[0044] during the step of sealing the steel boxed cofferdam, first, communication holes on the steel boxed cofferdam 100 are plugged, and then water is pumped out to create a dry working environment;

[0045] during the step of installing the sacrificial anode protection system, zinc blocks 42, which are higher in a galvanic series, are installed on corroded rebar of the pier column 302 to act as sacrificial anodes, protecting the iron rebar 40 lower in the galvanic series, thereby establishing the sacrificial anode protection system, effectively alleviating corrosion of the rebar, and improving the service life of the structure, including the following sub-steps:

[0046] 1) chipping away concrete at areas of corrosion-induced spalling on the pier column 302 to expose the rebar 40, then derusting and applying anti-rust treatment to the exposed rebar 40; and

[0047] 2) electrically connecting several galvanized iron straps 41 at intervals to the exposed rebar 40, with ends of the galvanized iron straps 41 extending below a designed low water level, then installing the zinc blocks 42 using bolts at the ends of the galvanized iron straps 41, and finally connecting the several zinc blocks 42 in series electrically;

[0048] the step of reinforcing the concrete of the pier column includes the following sub-steps:

[0049] 1) inside the steel boxed cofferdam 100, removing unsound mortar from a concrete surface of the pier column 302, removing loose attachments and harmful contaminants, and roughening a surface of a to-be-reinforced area using a concrete scabbler or manually, with a roughening depth of at least 10 mm, to ensure effective bonding between reactive powder concrete and the structural base;

[0050] 2) hoisting and placing permanent glass fiber reinforced plastic formwork 50 in sections using a crawler crane assisted by workers, where cross-sectional dimensions of the glass fiber reinforced plastic formwork 50 are 10 cm larger than those of the pier column 302; arranging spacers 51 with a thickness of 5 cm between an inner side surface of the glass fiber reinforced plastic formwork 50 and an outer surface of the pier column 302; forming the glass fiber reinforced plastic formwork 50 by bringing together two formwork members with a U-shaped plan and then locking them with fastening bolts 52; and after the glass fiber reinforced plastic formwork 50 is fixed, sealing a bottom outer edge of the glass fiber reinforced plastic formwork 50 with mortar, and once the mortar reaches a certain strength, placing the reactive powder concrete to prevent bottom grout leakage; and

[0051] 3) preparing the reactive powder concrete by mixing silica powder, cement, reactive powder concrete-specific admixtures, water, and chemical admixtures; placing the mixed reactive powder concrete within 30 min; placing structural members continuously, with a maximum interval not exceeding 6 min; and upon completion of the placement of the reactive powder concrete, curing the concrete by covering it and sprinkling with water for not less than 7 days;

[0052] the reactive powder concrete is placed by grouting using grouting equipment; since the reactive powder concrete is in a thick, paste-like state during the placement and the plan structure of the pier column 302 is rectangular, the reactive powder concrete has relatively poor fluidity at corners of the pier column 302; therefore, one grouting pipe is arranged on each of the four sides of the pier column 302, and grouting is performed in a symmetrical sequence to ensure pressure balance around the glass fiber reinforced plastic formwork 50; and

[0053] during the step of removing the steel boxed cofferdam, first, the pressure applied to the waterstop work platform 200 is released, allowing seawater to enter the steel boxed cofferdam 100 to balance internal and external pressures, then the bolt connections between the four side plates 10 of the steel boxed cofferdam 100 are disconnected using a 50T crawler crane assisted by the divers underwater section by section, and unit side plates are removed one by one.

[0054] The above embodiments are used merely to illustrate this disclosure rather than to limit it. Those skilled in the art may make various modifications or alterations without departing from the spirit and scope of this disclosure. Therefore, all equivalent technical solutions should also fall within the scope of this disclosure, as defined by the appended claims.

Examples

Embodiment Construction

[0039]This disclosure will be further described below with reference to the accompanying drawings.

[0040]Referring to FIGS. 1-7a, this disclosure provides a method for repairing and reinforcing underwater piers of bridges in tidal zones, using an open-bottom steel boxed cofferdam for water enclosure and including the following steps: trimming an underwater pile cap, installing the steel boxed cofferdam, sealing the steel boxed cofferdam, installing a sacrificial anode protection system, reinforcing concrete of a pier column, and removing the steel boxed cofferdam.

[0041]During the step of trimming the underwater pile cap, divers clean top and side surfaces of the pile cap in conjunction with high-pressure water jets, ensuring the top surface of the pile cap is level and there is no accumulated silt on the side surface;[0042]during the step of installing the steel boxed cofferdam, the plan of the steel boxed cofferdam 100 corresponds to the plan structure of the pile cap 301 and is the...

Claims

1. A method for repairing and reinforcing underwater piers of bridges in tidal zones, using an open-bottom steel boxed cofferdam for water enclosure and comprising the following steps: trimming an underwater pile cap, installing the steel boxed cofferdam, sealing the steel boxed cofferdam, installing a sacrificial anode protection system, reinforcing concrete of a pier column, and removing the steel boxed cofferdam, whereduring the step of trimming the underwater pile cap, divers clean top and side surfaces of the pile cap in conjunction with high-pressure water jets, ensuring the top surface of the pile cap is level and there is no accumulated silt on the side surface;during the step of installing the steel boxed cofferdam, the steel boxed cofferdam is rectangular in plan view and is an open-bottom type, with its inner wall provided with a lower internal bracing, a middle waling, and an upper waling sequentially from bottom to top; a bottom surface inside the lower internal bracing is connected to a steel anchor plate; an outer end of the lower internal bracing is connected to a bracket fixed on a side plate of the steel boxed cofferdam, with a connection between the bracket and the lower internal bracing made via a flange; a bottom of each of four side plates of the steel boxed cofferdam is provided with a waterstop work platform, which is located within a guide channel formed by a pressure plate and a base plate, and an inner end of the waterstop work platform is provided with a mounting groove for embedding a GINA waterstop; a plurality of hydraulic jacks are spaced apart between an outer end of the waterstop work platform within the guide channel and the side plates of the steel boxed cofferdam; and when the steel boxed cofferdam is installed, first, a surveyor measures and sets out a position of the lower internal bracing of the steel boxed cofferdam on the top surface of the pile cap, taking into account a tidal difference, then post-installed rebar holes are drilled according to the set-out on the top surface of the pile cap and filled with epoxy resin adhesive, anchor bolts connected to the steel anchor plate of the lower internal bracing are embedded into the post-installed rebar holes, and after the epoxy resin adhesive cures, the lower internal bracing is fixed onto the top surface of the pile cap, next, the brackets on the side plates of the steel boxed cofferdam are connected to the corresponding lower internal bracing via flange bolts, and finally, the hydraulic jacks on the outer side of the waterstop work platform simultaneously apply pressure to the work platform, pushing it along the guide channel towards the pile cap until the GINA waterstop is in close contact with the side surface of the pile cap;during the step of sealing the steel boxed cofferdam, first, communication holes on the steel boxed cofferdam are plugged, and then water is pumped out to create a dry working environment;during the step of installing the sacrificial anode protection system, zinc blocks, which are higher in a galvanic series, are installed on corroded rebar of the pier column to act as sacrificial anodes, protecting the iron rebar lower in the galvanic series, thereby establishing the sacrificial anode protection system, comprising the following sub-steps:1) chipping away concrete at areas of corrosion-induced spalling on the pier column to expose the rebar, then derusting and applying anti-rust treatment to the exposed rebar; and2) electrically connecting several galvanized iron straps at intervals to the exposed rebar, with ends of the galvanized iron straps extending below a designed low water level, then installing the zinc blocks using bolts at the ends of the galvanized iron straps, and finally connecting the several zinc blocks in series electrically;the step of reinforcing the concrete of the pier column comprises the following sub-steps:1) inside the steel boxed cofferdam, removing unsound mortar from a concrete surface of the pier column, removing loose attachments and harmful contaminants, and roughening a surface of a to-be-reinforced area using a concrete scabbler or manually, with a roughening depth of at least 10 mm;2) hoisting and placing permanent glass fiber reinforced plastic formwork in sections using a crawler crane assisted by workers, wherein cross-sectional dimensions of the glass fiber reinforced plastic formwork are larger than those of the pier column; arranging spacers between an inner side surface of the glass fiber reinforced plastic formwork and an outer surface of the pier column; and after the glass fiber reinforced plastic formwork is fixed, sealing a bottom outer edge of the glass fiber reinforced plastic formwork with mortar, and once the mortar reaches a certain strength, placing reactive powder concrete; and3) preparing the reactive powder concrete by mixing silica powder, cement, reactive powder concrete-specific admixtures, water, and chemical admixtures; placing the mixed reactive powder concrete within 30 min; placing structural members continuously, with a maximum interval not exceeding 6 min; and upon completion of the placement of the reactive powder concrete, curing the concrete by covering it and sprinkling with water for not less than 7 days;during the step of removing the steel boxed cofferdam, first, the pressure applied to the waterstop work platform is released, allowing seawater to enter the steel boxed cofferdam, then the bolt connections between the four side plates of the steel boxed cofferdam are disconnected using the crawler crane assisted by the divers underwater section by section, and unit side plates are removed one by one.

2. The method for repairing and reinforcing the underwater piers of bridges in the tidal zones of claim 1, wherein during the step of installing the steel boxed cofferdam, the four side plates of the steel boxed cofferdam all employ a double-wall structure, and each of the side plates is formed by splicing two of the unit side plates together using high-strength bolts, with a rubber waterstop plate arranged on a splicing surface of every two of the unit side plates; each of the unit side plates comprises an inner steel plate, an outer steel plate, and horizontal stiffening plates and vertical bulkhead plates connected between the inner steel plate and the outer steel plate; and the steel boxed cofferdam is provided with an operational platform arranged circumferentially at a top thereof and a ladder for entry and exit by construction personnel.

3. The method for repairing and reinforcing the underwater piers of bridges in the tidal zones of claim 1, wherein during the step of installing the steel boxed cofferdam, the waterstop work platform is made of stainless steel, and polytetrafluoroethylene plates are arranged both between a top surface of the waterstop work platform and the pressure plate of the guide channel, and between a bottom surface of the waterstop work platform and the base plate of the guide channel.

4. The method for repairing and reinforcing the underwater piers of bridges in the tidal zones of claim 1, wherein during the step of installing the steel boxed cofferdam, a chain hoist is used to fine-tune positions of the side plates of the steel boxed cofferdam; precise positioning of the side plates is achieved via guide holes and frustum-shaped guide rods pre-installed on flange mating surfaces connecting the brackets to the lower internal bracing, after which the flange bolts are tightened;and top openings of the side plates are temporarily fixed using channel steel onto clamps pre-installed on the pier column.

5. The method for repairing and reinforcing the underwater piers of bridges in the tidal zones of claim 1, wherein during the step of reinforcing the concrete of the pier column, the reactive powder concrete is placed by grouting, with one grouting pipe arranged on each of four sides of the pier column, and the grouting is performed in a symmetrical sequence to ensure pressure balance around the glass fiber reinforced plastic formwork.

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