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.

What is claimed is: 
     
         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, where
 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;   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; and   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;   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; and   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;   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.