CN115288021A - Construction method of underpass high-speed bridge - Google Patents

Abstract

The invention discloses a construction method of a underpass high-speed bridge, which comprises the following steps: s1, leveling a bridge construction site, backfilling a pond in the bridge construction site to form a working surface, and reinforcing existing structures around the bridge; s2, performing bored pile construction on the working face; s3, after the construction of the cast-in-situ bored pile is completed, constructing a ground tie beam; s4, after the construction of the ground tie beam is finished, constructing the pier stud; s5, after the construction of the pier stud is completed, sequentially performing the construction of a top tie beam; and S6, after the construction of the top tied beam is finished, carrying out cast-in-place box beam construction. The invention provides a construction method of a underpass high-speed bridge, which ensures the construction safety and quality.

Description

Construction method of underpass high-speed bridge

Technical Field

The invention relates to the field of bridge construction. More particularly, the invention relates to a construction method of a underpass high-speed bridge.

Background

With the rapid development of economic construction in China and the continuous development of expressways, the situation of 'dividing' cities and roads by expressways is increasingly obvious, and meanwhile, the construction of high-speed railway lines in road crossing operation is more and more. For example, in the infrastructure project of the backbone traffic network around the destination station suitable for high-speed filtration in the new three rivers, a section (south) of road engineering in the longitudinal road is one single project, six south roads are used for the line, the current situation of downward crossing is suitable for high-speed filtration, the upward crossing port-entering railway is about 793m long, and the route is a secondary city main road. Under the project design, the user can wear under the Maanshan bridge at a speed of Lu, but a pond is arranged under the Maanshan bridge, and the area of the water area is about 6473.98 m ² The water depth of the construction bridge position area is about 2 meters, the bridge needs to be erected to be penetrated and the speed is high, but a construction method special for penetrating the high-speed bridge is lacked at present.

Disclosure of Invention

The invention aims to provide a construction method of a bottom-penetrating high-speed bridge.

To achieve these objects and other advantages in accordance with the purpose of the invention, there is provided a method for constructing an underpass high speed bridge, comprising the steps of:

s1, leveling a bridge construction site, backfilling a pond in the bridge construction site to form a working surface, and reinforcing existing structures around the bridge;

s2, performing bored pile construction on the working face;

s3, after the construction of the cast-in-situ bored pile is completed, constructing a ground tie beam;

s4, after the construction of the ground tie beam is completed, constructing the pier stud;

s5, after the construction of the pier stud is completed, sequentially performing the construction of a top tie beam;

and S6, after the construction of the top tied beam is finished, carrying out cast-in-place box beam construction.

Preferably, in the construction method of the underpass high-speed bridge, the step of performing bored pile construction on the working face in step S2 includes the following steps:

s2.1, pile position lofting;

firstly discharging the pile center on a working face, guiding the pile center to the periphery, inserting and driving a positioning pile, then determining the pile casing position, installing an inserting and driving pile casing, and re-measuring the pile center position after the pile casing is vibrated and sunk to the position;

s2.2, embedding the pile casing;

backfilling a soil layer, finishing embedding of pile casings, coinciding the central lines of the pile casings and the central lines of the pile casings, wherein the allowable error of the plane is not more than 5cm, and the inclination of a vertical line is not more than 1%;

s2.3, forming holes in the pile foundation;

adjusting the drilling machine to enable the center of the drill bit and the center of the pile hole to be on the same vertical line, wherein the drilling machine drills at a low speed, the drill bit is uniformly lifted and lowered in the drilling process, and meanwhile, slurry is continuously supplemented into the hole to maintain the height of a water head in the hole;

s2.4, forming a hole and checking the hole;

after the drilling machine finishes drilling, detecting the aperture, the hole shape, the hole verticality and the hole depth of a formed hole, and cleaning Kong Dezuan slag to form a final hole after the detection is qualified;

s2.5, lowering a pile foundation reinforcement cage;

after the final hole is formed, timely lowering a pile foundation reinforcement cage, and installing a concrete pouring guide pipe for preparing concrete pouring;

s2.6, constructing pile foundation concrete;

constructing by adopting an underwater concrete pouring mode, detecting the quality of formed holes and cleaning the holes before constructing, and continuously pouring concrete after the formed holes are qualified until the concrete construction is finished;

s2.7, pile foundation detection;

and when the poured pile concrete reaches proper strength, respectively detecting the quality of the pile body concrete and the defects of the pile body, and finishing the construction of the cast-in-situ bored pile after the detection is qualified.

Preferably, in the construction method of the underpass high-speed bridge, after the concrete pouring guide pipe in S2.6 is installed, a water tightness test is firstly carried out on the concrete pouring guide pipe to check whether a waterproof rubber mat is intact, meanwhile, in the concrete pouring process of pile foundations, a guide pipe water tightness test is carried out according to 3-5 sections before each pile foundation is poured, and whether the guide pipe is clean is checked before the guide pipe is put down.

Preferably, in the construction method of the underpass high-speed bridge, the construction of the ground tie beam in S3 includes the following steps:

s3.1, excavating a tie beam foundation pit;

after the pit bottom of the tie beam foundation pit is leveled, leveling the pit bottom by using concrete as a foundation pit cushion layer;

s3.2, pile head processing;

adopting a circular cutting method to break off the pile head of the cast-in-situ bored pile, embedding a reinforcement cage of the reserved cast-in-situ bored pile into the tie beam part, finishing the reserved reinforcement of the cast-in-situ bored pile after the pile head is chiseled off, and performing nondestructive testing on the pile foundation;

s3.3, binding the ground tie beam reinforcing steel bars;

pre-processing the reinforcing steel bars of the ground tie beam, and binding the reinforcing steel bars of the ground tie beam after the foundation pit cushion concrete is formed and hardened after the nondestructive testing of the pile foundation is qualified;

s3.4, installing a ground tie beam template;

after the ground tie beam steel bars are bound, mounting a ground tie beam template, wherein a concrete cushion layer of a ground tie beam foundation pit is used as a tie beam bottom die, a tie beam side die is formed by combining shaped steel dies, binding a steel bar framework on the ground tie beam on the prefabricated bottom die, and separating the periphery of the ground tie beam template by using prefabricated concrete or mortar cushion blocks to ensure an enough steel bar protective layer, and erecting the side die after the ground tie beam steel bars are bound;

s3.5, pouring concrete into the ground system beam;

after the foundation tie beam formwork support and the foundation tie beam steel bars are checked and accepted, the concrete can be poured after dirt and sundries in the formwork are removed from the foundation tie beam steel bars;

s3.6, removing the mold;

when the strength of the ground tie beam concrete reaches 2.5MPa, the lateral side ground tie beam template without bearing can be disassembled, the ground tie beam concrete is maintained after the ground tie beam template is disassembled, the surface is covered by plastic cloth to prevent moisture evaporation, for the dry and hard concrete, uninterrupted sprinkling is ensured to the ground tie beam to provide additional moisture to prevent the surface from generating shrinkage cracks, and the whole maintenance period lasts for at least 7 days.

Preferably, in the construction method of the underpass high-speed bridge, the pier construction in the step S4 comprises the following steps:

s4.1, manufacturing and installing pier stud steel bars;

prefabricating pier column reinforcing steel bars, and welding the pier column reinforcing steel bars and a pile foundation reinforcement cage;

s4.2, installing a pier stud template;

the pier stud template is a semicircular template, is polished before installation, and is uniformly coated with a release agent; after the template is installed, checking and adjusting the size and the verticality of the template by using a suspension wire, and rechecking the plane position and the elevation of the template;

s4.3, pouring concrete of the pier column;

before pouring, sealing the bottom opening of the pier column template by cement mortar to prevent the concrete from being separated in the falling process;

s4.4, curing and demolding;

and when the strength of the pier column concrete reaches 2.5MPa, the pier column template starts to be dismantled.

Preferably, in the construction method of the underpass high-speed bridge, the construction of the top tie beam in the step S5 includes the following steps:

s5.1, installing a top tied beam supporting system;

the top tied beam construction platform adopts a form of using a through steel bar as a support;

s5.2, measuring and lofting;

after the top tied beam supporting system is adjusted, firstly, reserving extended steel bars at the top of the straight pier column, forming the extended reserved steel bars according to the shape required by the design, and during top tied beam construction, firstly, lofting and positioning the axis point and the four corner points of the top tied beam by using a total station coordinate lofting method through a ground control point to serve as datum points for installation and template erection;

s5.3, constructing top tied beam steel bars;

when the top tie beam reinforcement frameworks are bound, the protective layer cushion blocks on the bottom plate are ensured to be not less than 6 per square meter, and the protective layer cushion blocks on the side surfaces are ensured to be not less than 4 per square meter;

s5.4, constructing a top tied beam template;

installing a top tie beam bottom die, then installing top tie beam side dies, connecting adjacent top tie beam templates by bolts, and arranging mortar or a water-stopping adhesive tape at the joint of the lower opening of the top tie beam template and the joint of the bottom die and a pier body;

s5.5, constructing top tie beam concrete;

the top tie beam adopts an integral vertical mold and is cast and constructed at one time, the top tie beam is distributed in a horizontal layering mode from the middle to two sides when concrete is cast, the layering thickness is not more than 30cm, the top tie beam is cast to the top surface of the top tie beam layer by layer, and the periphery of the template is distributed firstly;

s5.6, curing the top system Liang Ningtu;

after the top tie beam concrete is poured, timely plastering and collecting slurry, and curing the top tie beam concrete, wherein the watering curing time of the top tie beam concrete is not less than 7 days;

s5.7, removing the mold;

and when the design value of the compressive strength of the top tied beam concrete reaches 2.5MPa, the top tied beam formwork is removed, and the side die and the bottom die are removed firstly.

The invention aims at the field environment, adjusts the construction method of the bridge, provides a construction method of a bottom-crossing high-speed bridge, and ensures the construction safety and quality.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Drawings

FIG. 1 is a flow chart of a cast-in-situ bored pile construction process according to the present invention;

FIG. 2 is a flow chart of the construction process of the tie-beam according to the present invention;

FIG. 3 is a flow chart of the construction process of the cylindrical pier according to the present invention;

FIG. 4 is a flow chart of a top tied beam construction process according to the present invention;

FIG. 5 is a flow chart of the construction process of the cast-in-place box girder.

Detailed Description

The present invention is further described in detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description text.

It should be noted that in the description of the present invention, the terms "lateral", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.

As shown in fig. 1 to 5, an embodiment of the present invention provides a method for constructing a high-speed underpass bridge, including the following steps:

s1, leveling a bridge construction site, backfilling a pond in the bridge construction site to form a working surface, and reinforcing existing structures around the bridge;

s2, performing bored pile construction on the working face;

specifically, in the step S2, when the cast-in-place bored pile is constructed on the working face, the method includes the following steps:

s2.1, pile position lofting;

firstly discharging the pile center on a working face, guiding the pile center to the periphery, inserting and driving a positioning pile, then determining the pile casing position, installing an inserting and driving pile casing, and re-measuring the pile center position after the pile casing is vibrated and sunk to the position;

s2.2, embedding the pile casing;

backfilling a soil layer, completing embedding of pile casings, enabling the center lines of the pile casings to coincide with the center line of the pile, enabling the plane tolerance error to be not more than 5cm, and enabling the vertical line to be inclined to be not more than 1%;

s2.3, pile foundation hole forming;

adjusting the drilling machine to enable the center of the drill bit and the center of the pile hole to be on the same vertical line, wherein the drilling machine drills at a low speed, the drill bit is uniformly lifted and lowered in the drilling process, and meanwhile, slurry is continuously supplemented into the hole to maintain the height of a water head in the hole;

s2.4, forming a hole and checking the hole;

after the drilling machine finishes drilling, detecting the aperture, the hole shape, the hole verticality and the hole depth of a formed hole, and cleaning Kong Dezuan slag to form a final hole after the detection is qualified;

s2.5, lowering a pile foundation reinforcement cage;

after the final hole is formed, timely lowering a pile foundation reinforcement cage, and installing a concrete pouring guide pipe to prepare for concrete pouring;

s2.6, constructing pile foundation concrete;

constructing by adopting an underwater concrete pouring mode, detecting the quality of formed holes and cleaning the holes before constructing, and continuously pouring concrete after the formed holes are qualified until the concrete construction is finished;

specifically, after the concrete pouring guide pipe in S2.6 is installed, firstly, a water tightness test is carried out on the concrete pouring guide pipe, whether a waterproof rubber mat is intact is checked, meanwhile, in the concrete pouring process of the pile foundations, a guide pipe water tightness test is carried out according to 3-5 sections before each pile foundation is poured, and whether the guide pipe is clean is checked before the guide pipe is lowered.

S2.7, pile foundation detection;

and when the poured pile concrete reaches proper strength, respectively detecting the quality of the pile body concrete and the defects of the pile body, and finishing the construction of the cast-in-situ bored pile after the detection is qualified.

S3, after the construction of the cast-in-situ bored pile is completed, constructing a ground tie beam;

specifically, the construction of the ground tie beam in S3 includes the following steps:

s3.1, excavating a tie beam foundation pit;

after the pit bottom of the tie beam foundation pit is leveled, leveling the pit bottom by using concrete as a foundation pit cushion layer;

s3.2, pile head processing;

adopting a circular cutting method to break off the pile head of the cast-in-situ bored pile, embedding a reinforcement cage of the reserved cast-in-situ bored pile into the tie beam part, finishing the reserved reinforcement of the cast-in-situ bored pile after the pile head is chiseled off, and performing nondestructive testing on the pile foundation;

s3.3, binding the ground tie beam reinforcing steel bars;

pre-processing the reinforcing steel bars of the ground tie beam, and binding the reinforcing steel bars of the ground tie beam after the foundation pit cushion concrete is formed and hardened after the nondestructive testing of the pile foundation is qualified;

s3.4, installing a ground tie beam template;

after the ground tie beam steel bars are bound, mounting a ground tie beam template, wherein a concrete cushion layer of a ground tie beam foundation pit is used as a tie beam bottom die, a tie beam side die is formed by combining shaped steel dies, binding a steel bar framework on the ground tie beam on the prefabricated bottom die, and separating the periphery of the ground tie beam template by using prefabricated concrete or mortar cushion blocks to ensure an enough steel bar protective layer, and erecting the side die after the ground tie beam steel bars are bound;

s3.5, pouring concrete into the ground system beam;

after the foundation tie beam formwork supports and the foundation tie beam steel bars are checked and accepted, the concrete can be poured after dirt and sundries in the formwork on the foundation tie beam steel bars are removed;

s3.6, removing the mold;

when the strength of the ground tie beam concrete reaches 2.5MPa, the side ground tie beam template without bearing is disassembled, the ground tie beam concrete is cured after the ground tie beam template is disassembled, the surface is covered by plastic cloth to prevent water from evaporating, the ground tie beam is continuously sprinkled with water to provide external water to prevent the surface from shrinking cracks for the dry and hard concrete, and the whole curing period lasts for at least 7 days.

S4, after the construction of the ground tie beam is finished, constructing the pier stud;

specifically, the construction of the pier stud in the step S4 comprises the following steps:

s4.1, manufacturing and installing pier stud steel bars;

prefabricating pier column reinforcing steel bars, and welding the pier column reinforcing steel bars and a pile foundation reinforcement cage;

s4.2, installing a pier stud template;

the pier stud template is a semicircular template, is polished before installation, and is uniformly coated with a release agent; after the template is installed, checking and adjusting the size and the verticality of the template by a suspension wire, and rechecking the plane position and the elevation of the template;

s4.3, pouring concrete of the pier column;

before pouring, sealing the bottom opening of the pier column template by cement mortar to prevent the concrete from being separated in the falling process;

s4.4, curing and demolding;

and when the strength of the pier column concrete reaches 2.5MPa, the pier column template starts to be dismantled.

S5, after the construction of the pier stud is completed, sequentially performing the construction of a top tie beam;

specifically, the construction of the top tie beam in the step S5 includes the following steps:

s5.1, installing a top tied beam supporting system;

the top tied beam construction platform adopts a form of using a through steel bar as a support;

s5.2, measuring and lofting;

after the top tie beam supporting system is adjusted, firstly, reserving extended steel bars at the top of a straight pier column, forming the extended reserved steel bars according to the shape required by the design, and during top tie beam construction, firstly, lofting and positioning the axis point and the four corner points of the top tie beam by using a total station coordinate lofting method through a ground control point to serve as datum points for installation and template erection;

s5.3, constructing top tied beam steel bars;

when the top tie beam reinforcement frameworks are bound, the protective layer cushion blocks on the bottom plate are ensured to be not less than 6 per square meter, and the protective layer cushion blocks on the side surfaces are ensured to be not less than 4 per square meter;

s5.4, constructing a top tied beam template;

installing a top tie beam bottom die, then installing top tie beam side dies, connecting adjacent top tie beam templates by bolts, and arranging mortar or a water-stopping adhesive tape at the joint of the lower opening of the top tie beam template and the joint of the bottom die and a pier body;

s5.5, constructing top tie beam concrete;

the top tie beam adopts an integral vertical mold and is cast and constructed at one time, the top tie beam is distributed in a horizontal layering mode from the middle to two sides when concrete is cast, the layering thickness is not more than 30cm, the top tie beam is cast to the top surface of the top tie beam layer by layer, and the periphery of the template is distributed firstly;

s5.6, curing the top system Liang Ningtu;

after the top tie beam concrete is poured, timely plastering and collecting slurry, and curing the top tie beam concrete, wherein the watering curing time of the top tie beam concrete is not less than 7 days;

s5.7, removing the mold;

and when the design value of the compressive strength of the top tied beam concrete reaches 2.5MPa, the top tied beam formwork is removed, and the side die and the bottom die are removed firstly.

And S6, after the construction of the top tied beam is finished, carrying out cast-in-place box beam construction.

In the embodiment, before construction, a site in a bridge range is leveled, a pond is backfilled to form a working surface, the right filling range is controlled according to the outward expansion 10m of a projection surface of the bridge, and the elevation 303 is filled. The filling material is selected from sandstone broken materials, the grain diameter is controlled within 30cm, the filling speed is controlled during filling so as to prevent the water surface elevation from rapidly rising, and the water surface elevation is always kept below 302.8 (the elevation of the river starting point bottom is changed to be 302.2). After the field is filled, dug and leveled, the construction of the cast-in-situ bored pile can be carried out.

After the construction of the pile foundation is finished, the construction of a bearing platform and a ground tie beam can be carried out, and because the bearing platform and the ground tie beam are embedded deeply (about 7-9 m), the peripheral underground water level is high, the distance is short, the large-range excavation risk is large, the construction is carried out by adopting steel sheet pile support in order to reduce the disturbance to the peripheral structures. After the construction of the bearing platform and the ground tie beam is finished, the construction of the pier column and the tie beam can be carried out in sequence.

The cast-in-place box girder adopts a full framing construction process. Because the elevation of the No. 1 right beam bottom is 304.84, the elevation of the No. 2 right beam bottom is about 305.20, and in order to ensure that the beam bottom has enough support erection height, the water surface elevation of a pond needs to be reduced, the precipitation is pumped and drained by a high-power water pump, the water surface elevation is reduced to 300.5, and the elevation of a bridge bottom platform is controlled at 301.5. And excavating the part 301.5 higher than the bottom of the 2 nd span bridge after the precipitation is finished, replacing and filling the soft foundation by adopting rubbles, building a full support in a 20cm concrete hardening field after the replacement and filling are finished, and performing cast-in-place box girder construction. The construction process has no influence on the normal operation of the highway.

Due to the fact that the terrain is low at the bridge of the Maanshan, and in order to guarantee safety of the bridge, the ground elevation cannot be raised through filling soil, and flood storage needs to be carried out to an elevation higher than 302.2m to discharge flood by combining with the situation of newly opening a river channel. According to 20 years of flood defense, the highest water level of an under-bridge pond reaches 303.85m, a west 9# abutment and a bridge pile foundation are both arranged in weakly weathered bedrock, water storage basically has no influence on the structure safety, an east abutment base is arranged in a strongly weathered layer, soil layer mechanical parameters are weakened after water is taken under the bridge, and certain influence is brought to the local stability of the abutment and the overall stability of the whole slope.

After water storage, the parameters of the east 0# abutment base are reduced, the anti-sliding safety coefficient of the abutment base is reduced (but the abutment base can be ensured to be stable), and grouting reinforcement treatment is performed on the front covering layer and the strongly weathered layer of the abutment, and reinforcement is performed through grouting. Grouting points are arranged according to a 1.2-1.2m square grid, an SH-30 type drilling machine is adopted for construction, the hole forming depth is determined according to geological conditions, and the hole bottom enters a weakly weathered rock stratum by 0.5m and is about 7m deep. And arranging a reinforcing mesh on the grouting ground surface, fixing the reinforcing mesh on a grouting pipe through reinforcement, and finally spraying C20 concrete with the thickness of 20cm on the surface to seal the reinforcing mesh.

While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable to various fields of endeavor for which the invention may be embodied with additional modifications as would be readily apparent to those skilled in the art, and the invention is therefore not limited to the details given herein and to the embodiments shown and described without departing from the generic concept as defined by the claims and their equivalents.

Claims (6)

1. A construction method of a high-speed bridge penetrating downwards is characterized by comprising the following steps:

s1, leveling a bridge construction site, backfilling a pond in the bridge construction site to form a working surface, and simultaneously treating reinforcement of an existing structure at the periphery of the bridge;

s2, performing bored pile construction on the working face;

s3, after the construction of the cast-in-situ bored pile is completed, constructing a ground tie beam;

s4, after the construction of the ground tie beam is finished, constructing the pier stud;

s5, after the construction of the pier stud is completed, sequentially performing the construction of a top tie beam;

and S6, after the construction of the top tied beam is finished, carrying out cast-in-place box beam construction.

2. The construction method of the underpass high-speed bridge, according to claim 1, wherein the step of performing bored pile construction on the working face in step S2 comprises the following steps:

s2.1, pile position lofting;

firstly discharging the pile center on a working face, guiding the pile center to the periphery, inserting and driving a positioning pile, then determining the pile casing position, installing an inserting and driving pile casing, and re-measuring the pile center position after the pile casing is vibrated and sunk to the position;

s2.2, embedding the pile casing;

backfilling a soil layer, finishing embedding of pile casings, coinciding the central lines of the pile casings and the central lines of the pile casings, wherein the allowable error of the plane is not more than 5cm, and the inclination of a vertical line is not more than 1%;

s2.3, pile foundation hole forming;

adjusting a drilling machine to enable the center of a drill bit and the center of a pile hole to be on the same vertical line, wherein the drilling machine drills at a low speed, and in the drilling process, the drill bit is uniformly lifted and lowered, and meanwhile, slurry is continuously supplemented into the hole, and the height of a water head in the hole is maintained;

s2.4, forming a hole and checking the hole;

after the drilling machine finishes drilling, detecting the aperture, the hole shape, the hole verticality and the hole depth of a formed hole, and cleaning Kong Dezuan slag to form a final hole after the detection is qualified;

s2.5, lowering a pile foundation reinforcement cage;

after the final hole is formed, timely lowering a pile foundation reinforcement cage, and installing a concrete pouring guide pipe to prepare for concrete pouring;

s2.6, constructing pile foundation concrete;

constructing by adopting an underwater concrete pouring mode, performing pore-forming quality detection and pore cleaning detection before construction, and continuously pouring concrete after the construction is qualified until the concrete construction is finished;

s2.7, detecting a pile foundation;

and when the poured pile concrete reaches proper strength, respectively detecting the quality of the pile body concrete and the defects of the pile body, and finishing the construction of the cast-in-situ bored pile after the detection is qualified.

3. The underpass high-speed bridge construction method of claim 2, wherein after the concrete pouring guide pipe is installed in S2.6, the concrete pouring guide pipe is subjected to a water tightness test to check whether the waterproof rubber mat is intact, and meanwhile, in the pile foundation concrete pouring process, the guide pipe water tightness test is performed in groups of 3-5 sections before each pile foundation is poured, and whether the guide pipe is clean is checked before the guide pipe is lowered.

4. The construction method of the underpass high-speed bridge as claimed in claim 1, wherein the construction of the ground tie beam in S3 comprises the following steps:

s3.1, excavating a tie beam foundation pit;

after the pit bottom of the tie beam foundation pit is leveled, leveling the pit bottom by using concrete as a foundation pit cushion layer;

s3.2, pile head processing;

adopting a circular cutting method to break away the pile head of the cast-in-situ bored pile, embedding a reinforcement cage of the reserved cast-in-situ bored pile into the tie beam part, finishing the chiseling of the pile head, arranging the reserved reinforcement of the cast-in-situ bored pile, and carrying out nondestructive testing on the pile foundation;

s3.3, binding the ground tie beam reinforcing steel bars;

pre-processing the reinforcing steel bars of the ground tie beam, and binding the reinforcing steel bars of the ground tie beam after the foundation pit cushion concrete is formed and hardened after the nondestructive testing of the pile foundation is qualified;

s3.4, installing a ground tie beam template;

after the binding of the ground tie beam steel bars is finished, installing a ground tie beam template, wherein a concrete cushion layer of a foundation pit of the ground tie beam is used as a bottom tie beam mould, a side tie beam mould is formed by combining shaping steel moulds, a steel bar framework is bound on the ground tie beam on the prepared bottom mould, prefabricated concrete or mortar cushion blocks are used for separating the periphery of the steel bar framework from the ground tie beam template to ensure an enough steel bar protective layer, and the side mould is erected after the ground tie beam steel bars are bound;

s3.5, pouring concrete into the ground system beam;

after the foundation tie beam formwork supports and the foundation tie beam steel bars are checked and accepted, the concrete can be poured after dirt and sundries in the formwork on the foundation tie beam steel bars are removed;

s3.6, removing the mold;

when the strength of the ground tie beam concrete reaches 2.5MPa, the lateral side ground tie beam template without bearing can be disassembled, the ground tie beam concrete is maintained after the ground tie beam template is disassembled, the surface is covered by plastic cloth to prevent moisture evaporation, for the dry and hard concrete, uninterrupted sprinkling is ensured to the ground tie beam to provide additional moisture to prevent the surface from generating shrinkage cracks, and the whole maintenance period lasts for at least 7 days.

5. The construction method of the underpass high-speed bridge as claimed in claim 1, wherein the construction of the pier stud in S4 comprises the following steps:

s4.1, manufacturing and installing pier stud steel bars;

prefabricating pier column reinforcing steel bars, and welding the pier column reinforcing steel bars and a pile foundation reinforcement cage;

s4.2, installing a pier stud template;

the pier stud template is a semicircular template, is polished before installation, and is uniformly coated with a release agent; after the template is installed, checking and adjusting the size and the verticality of the template by a suspension wire, and rechecking the plane position and the elevation of the template;

s4.3, pouring concrete of the pier column;

before pouring, sealing the bottom opening of the pier column template by cement mortar to prevent the concrete from being separated in the falling process;

s4.4, curing and demolding;

and when the strength of the pier column concrete reaches 2.5MPa, the pier column template starts to be dismantled.

6. The construction method of the underpass high-speed bridge as claimed in claim 1, wherein the construction of the top tie beam in S5 comprises the following steps:

s5.1, installing a top tied beam supporting system;

the top tied beam construction platform adopts a form that a through steel bar is used as a support;

s5.2, measuring and lofting;

after the top tie beam supporting system is adjusted, firstly, reserving extended steel bars at the top of a straight pier column, forming the extended reserved steel bars according to the shape required by the design, and during top tie beam construction, firstly, lofting and positioning the axis point and the four corner points of the top tie beam by using a total station coordinate lofting method through a ground control point to serve as datum points for installation and template erection;

s5.3, constructing top tied beam steel bars;

when the top tie beam reinforcement frameworks are bound, the protective layer cushion blocks on the bottom plate are ensured to be not less than 6 per square meter, and the protective layer cushion blocks on the side surfaces are ensured to be not less than 4 per square meter;

s5.4, constructing a top tied beam template;

installing a top tied beam bottom die, then installing a top tied beam side die, connecting adjacent top tied beam templates by bolts, and arranging mortar or a water-stopping adhesive tape at the joint of the lower opening of the top tied beam template and the joint of the bottom die and a pier body;

s5.5, constructing top tie beam concrete;

the top tie beam adopts an integral vertical mold and is cast and constructed at one time, the top tie beam is distributed in a horizontal layering mode from the middle to two sides when concrete is cast, the layering thickness is not more than 30cm, the top tie beam is cast to the top surface of the top tie beam layer by layer, and the periphery of the template is distributed firstly;

s5.6, curing the top system Liang Ningtu;

after the top tie beam concrete is poured, timely plastering and collecting slurry, and curing the top tie beam concrete, wherein the watering curing time of the top tie beam concrete is not less than 7 days;

s5.7, removing the mold;

and when the design value of the compressive strength of the top tied beam concrete reaches 2.5MPa, the top tied beam formwork is removed, and the side die and the bottom die are removed firstly.

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