1. The bridge pier underpinning method is characterized in that the underpinning process of the original bridge pier during road widening and reconstruction is carried out according to the following steps:

1) according to the road widening requirement, a new pier is built on the outer side of the original pier, the new pier is provided with a cantilever cover beam extending towards the original pier, and a certain height is reserved between the top surface of the cantilever cover beam and the bottom surface of the box girder; a wedge-shaped hole which vertically penetrates through the cantilever capping beam is reserved at the position, aligned with the central axis of the original pier, of the cantilever capping beam, so that the original pier is wrapped outside the cantilever capping beam but is not contacted with the cantilever capping beam;

2) a temporary support with adjustable height and measurable force is arranged on the top surface of the cantilever cover beam;

3) jacking the temporary support step by step to transfer the load on the upper part of the bridge from the original support to the temporary support;

4) dismantling the original pier;

5) pouring a wedge-shaped hole reserved in the cantilever bent cap to form a post-pouring wedge-shaped body, constructing a new support on the top surface of the wedge-shaped body, and installing a new support with adjustable height and capable of measuring force on the new support;

6) unloading the temporary support step by step to transfer the load on the upper part of the bridge from the temporary support to a new support;

7) and (5) removing the temporary support.

2. The bridge pier underpinning method according to claim 1, characterized in that: for the original pier with the double-column or multi-column provided with the tie beam, before a new pier is built, a temporary tie beam is newly built below the tie beam of the original pier to replace the original tie beam, so that the original pier is guaranteed to have reliable transverse connection during subsequent construction.

3. The bridge pier underpinning method according to claim 1, characterized in that: the cantilever bent cap starts from the middle section of the new bridge pier and extends upwards and slantways towards the original bridge pier, so that the bottom surface of the cantilever bent cap forms an inclined surface, and the wedge-shaped hole vertically penetrates from the top surface of the cantilever bent cap to the inclined surface; the wedge-shaped hole is of a structure with a large upper part and a small lower part, the clear distance between the lower port and the original bridge pier is 5-15cm, the clear distance between the upper port and the original bridge pier is 30-50cm, and reserved steel bars needed in secondary wedge body pouring are reserved in the wedge-shaped hole.

4. The bridge pier underpinning method according to claim 1, characterized in that: a plurality of temporary supports are arranged around the support of the original pier, the temporary supports are arranged along the periphery of a wedge-shaped hole on a cantilever bent cap, and the temporary supports are arranged below a box girder web or below a box girder middle cross beam to ensure the stress safety of the box girder.

5. The bridge pier underpinning method according to claim 4, wherein when the temporary support is installed:

(1) constructing a temporary strut on the top surface of the cantilever bent cap, wherein the temporary strut is of a steel pipe concrete column structure, a steel pipe is connected with a foundation bolt pre-embedded in the cantilever bent cap through a flange, and self-compacting concrete is poured into the steel pipe;

(2) mounting a temporary support on the temporary support, wherein the temporary support is internally provided with a jacking device and a force measuring device, and after the temporary support is mounted in place, adjusting the height of the temporary support to enable the temporary support to be closely attached to the bottom of the box girder;

(3) the temporary support is jacked in a grading manner, and the load of the upper structure is transferred to the temporary support from the original support; the jacking force is predetermined according to theoretical bearing counter force of the temporary support, jacking is carried out in five stages, the jacking load is 20%, 40%, 60%, 80% and 100% of the jacking force of each stage in sequence, and the final jacking force of the temporary support is determined on the basis of completely disengaging the original support; meanwhile, the jacking height of the bottom of the box girder is synchronously monitored in the grading jacking process, and the final jacking height of the bottom of the box girder is controlled within 5 mm;

(4) after the temporary support is jacked, waiting for 1-2 months, during the period, a newly-built lower structure shrinks and creeps concrete and deforms soil body creep, the upper structure is downwarped and contacts the original support, partial counter force is transferred to the original support, the counter force reading of the temporary support changes, and if the counter force reading of the temporary support changes greatly, jacking is carried out according to the step (3);

(5) and (4) repeating the steps (3) to (4) for 2-3 times until the change value of the reading of the bearing reaction force of the temporary support is less than 5% so as to ensure that the time-varying effects of concrete shrinkage, creep, soil body creep and the like of the new bridge pier reach a relatively stable state.

6. The bridge pier underpinning method according to claim 5, characterized in that: when the original bridge pier is dismantled, firstly, a manual hoist is arranged at the top of the cantilever cover beam to temporarily fix the original bridge pier segment wrapped by the cantilever cover beam, then the original bridge pier is cut below the cantilever cover beam and the original bridge pier segment below the cantilever cover beam is dismantled, and finally the manual hoist is used for lowering and dismantling the original bridge pier segment wrapped by the cantilever cover beam;

and after the original bridge pier is dismantled, adjusting the height of the temporary support to ensure that the height of the beam bottom at the original support is adjusted to be consistent with the existing state before underpinning of the bridge pier.

7. The bridge pier underpinning method according to claim 3, wherein when the reserved wedge-shaped hole of the cantilever capping beam is poured:

(1) the bottom die of the hanging basket is arranged at the bottom of the cantilever capping beam, the connecting steel bars of the wedge-shaped body are bound, the hanging basket bottom die and the reserved steel bars of the cantilever capping beam are welded, then the wedge-shaped hole is poured to form a post-pouring wedge-shaped body, the post-pouring wedge-shaped body has a self-locking effect after being stressed, and reliable force transmission between post-pouring concrete and existing concrete is guaranteed;

(2) constructing a new pillar on the top surface of the post-cast wedge body, wherein the new pillar is of a steel pipe concrete pillar structure, the steel pipe is connected with foundation bolts pre-embedded in the wedge body through flanges, and self-compacting concrete is poured in the steel pipe;

(3) mounting a new support on the new support, wherein the new support adopts a height-adjustable force-measuring support, and a jacking device and a force-measuring device are arranged in the new support; after the new support is installed in place, adjusting the height of the new support to enable the new support to be closely attached to the bottom of the box girder;

(4) unloading the support reaction force of the temporary support in five stages according to 20%, 40%, 60%, 80% and 100%, and transferring the upper structure load from the temporary support to a new support; after each stage of unloading is finished, checking and adjusting the new support reaction force increment to ensure that the temporary support reaction force unloading amount is completely transferred to the new support reaction force increment; meanwhile, the displacement of the beam bottom at the new support is synchronously monitored, and the variable quantity of the displacement of the beam bottom at the new support before and after load transfer is ensured to be less than 2 mm.

8. The bridge pier underpinning method according to claim 7, characterized in that: and after the unloading of the supporting reaction force of the temporary support is finished, the temporary support is removed, then the temporary support is removed and connected with the foundation bolt of the cantilever cover beam, and the temporary support is chiseled.

9. The utility model provides a pier underpins structure which characterized in that: the new bridge pier built on the outer side of the original bridge pier is provided with a cantilever cover beam extending towards the original bridge pier, and a certain height is reserved between the top surface of the cantilever cover beam and the bottom surface of the box girder; a wedge-shaped hole which vertically penetrates through the cantilever capping beam is reserved at the position, aligned with the central axis of the original pier, of the cantilever capping beam, so that the original pier is wrapped outside the cantilever capping beam but is not contacted with the cantilever capping beam; and after the original pier is dismantled, concrete is poured into the wedge-shaped hole to form a post-pouring wedge-shaped body, a new support is constructed on the top surface of the wedge-shaped body, a new support with adjustable height and capable of measuring force is installed on the new support, and the box girder is supported through the new support.

10. The bridge pier underpinning structure of claim 9, wherein: the cantilever bent cap starts from the middle section of the new bridge pier and extends upwards and slantways towards the original bridge pier, so that the bottom surface of the cantilever bent cap forms an inclined surface, and the wedge-shaped hole vertically penetrates from the top surface of the cantilever bent cap to the inclined surface; the wedge-shaped hole is of a structure with a large upper part and a small lower part, the clear distance between a lower port and an original bridge pier is 5-15cm, the clear distance between an upper port and the original bridge pier is 30-50cm, and reserved steel bars required for secondary wedge body pouring are reserved in the wedge-shaped hole; and a new pile foundation is built in the foundation below the new bridge pier, a new bearing platform is built on the new pile foundation, and the new bridge pier is supported by the new bearing platform.

Background

With the advance of city upgrading and transformation and urbanization construction in China, the traffic flow of urban roads is increasing day by day, a lot of existing roads can not meet the increasing traffic flow demand, and a large quantity of urban roads are in urgent need of widening and transformation. Among the roads to be widened, some roads pass through bridges under and are close to existing piers, and in this case, if the roads are to be widened, the adjacent piers are first underpinned to leave enough road widening space.

The existing bridge pier underpinning is generally passive underpinning, and the underpinning process is approximately as follows: building a temporary support upper structure of the temporary pier → building a new portal pier (wrapping the top of the existing pier to form a whole), cutting off the part below the existing pier along the junction surface of the portal pier and the existing pier → unloading the temporary pier support load, and transferring the upper structure load to the new portal pier. After the newly-built portal pier system is stressed, the upper structure is passively warped downwards due to the compression deformation of the lower pile foundation and the soil body and the bending deformation of the portal pier, and the typical passive underpinning is achieved.

Underpinning the pier underpinning project that the road under-crossing widened and involved, often need be in order to reserve the road and widen the space to the pier offset along the bridge direction, newly-built pier passes through cantilever bent cap support superstructure. Under the condition, the cantilever bent capping beam causes the eccentric stress of the newly-built foundation, the pier and other lower structures, and then the time-varying effects of concrete shrinkage creep, soil body creep and the like are superposed, so that the total downward deflection at the supporting point is obvious. If the existing underpinning method is adopted, the upper structure generates larger downwarping, which is very unfavorable for the stress of the main beam of the hyperstatic system. In addition, the existing bridge pier underpinning method usually needs to build a temporary pier supporting upper structure, and traffic control is needed in the process, so that the influence on the road traffic protection on the existing bridge and the road traffic protection under the bridge is large, the cost is high, and certain construction risk also exists.

Disclosure of Invention

The invention aims to solve the technical problem of the prior art, and provides a bridge pier underpinning method and an underpinning structure which can solve the problem of girder deformation in the underpinning process of a bridge pier, improve the underpinning safety of the bridge pier, reduce the construction risk, avoid the need of building a temporary pier and save the construction cost.

In order to solve the technical problems, the invention adopts the following technical scheme: a bridge pier underpinning method is characterized by comprising the following steps: the underpinning process of the original pier during road widening and reconstruction is carried out according to the following steps:

1) according to the road widening requirement, a new pier is built on the outer side of the original pier, the new pier is provided with a cantilever cover beam extending towards the original pier, and a certain height is reserved between the top surface of the cantilever cover beam and the bottom surface of the box girder; a wedge-shaped hole which vertically penetrates through the cantilever capping beam is reserved at the position, aligned with the central axis of the original pier, of the cantilever capping beam, so that the original pier is wrapped outside the cantilever capping beam but is not contacted with the cantilever capping beam;

2) a temporary support with adjustable height and measurable force is arranged on the top surface of the cantilever cover beam;

3) jacking the temporary support step by step to transfer the load on the upper part of the bridge from the original support to the temporary support;

4) dismantling the original pier;

5) pouring a wedge-shaped hole reserved in the cantilever bent cap to form a post-pouring wedge-shaped body, constructing a new support on the top surface of the wedge-shaped body, and installing a new support with adjustable height and capable of measuring force on the new support;

6) unloading the temporary support step by step to transfer the load on the upper part of the bridge from the temporary support to a new support;

7) and (5) removing the temporary support.

For the original pier with the double-column or multi-column provided with the tie beam, before a new pier is built, a temporary tie beam is newly built below the tie beam of the original pier to replace the original tie beam, so that the original pier is guaranteed to have reliable transverse connection during subsequent construction.

The cantilever bent cap starts from the middle section of the new bridge pier and extends upwards and slantways towards the original bridge pier, so that the bottom surface of the cantilever bent cap forms an inclined surface, and the wedge-shaped hole vertically penetrates from the top surface of the cantilever bent cap to the inclined surface; the wedge-shaped hole is of a structure with a large upper part and a small lower part, the clear distance between the lower port and the original bridge pier is 5-15cm, such as 10cm, the clear distance between the upper port and the original bridge pier is 30-50cm, such as 40cm, and reserved steel bars needed in secondary wedge body pouring are reserved in the wedge-shaped hole.

A plurality of temporary supports are arranged around the support of the original pier, the temporary supports are arranged along the periphery of a wedge-shaped hole on a cantilever bent cap, and the temporary supports are arranged below a box girder web or below a box girder middle cross beam to ensure the stress safety of the box girder.

When the temporary support is installed:

(1) constructing a temporary strut on the top surface of the cantilever bent cap, wherein the temporary strut is of a steel pipe concrete column structure, a steel pipe is connected with a foundation bolt pre-embedded in the cantilever bent cap through a flange, and self-compacting concrete is poured into the steel pipe;

(2) mounting a temporary support on the temporary support, wherein the temporary support is internally provided with a jacking device and a force measuring device, and after the temporary support is mounted in place, adjusting the height of the temporary support to enable the temporary support to be closely attached to the bottom of the box girder;

(3) the temporary support is jacked in a grading manner, and the load of the upper structure is transferred to the temporary support from the original support; the jacking force is predetermined according to theoretical bearing counter force of the temporary support, jacking is carried out in five stages, the jacking load is 20%, 40%, 60%, 80% and 100% of the jacking force of each stage in sequence, and the final jacking force of the temporary support is determined on the basis of completely disengaging the original support; meanwhile, the jacking height of the bottom of the box girder is synchronously monitored in the grading jacking process, and the final jacking height of the bottom of the box girder is controlled within 5 mm;

(4) after the temporary support is jacked, waiting for 1-2 months, during the period, a newly built lower structure (comprising a new bridge pier, a new bearing platform and a new pile foundation) shrinks and slowly deforms concrete and a soil body, the upper structure is then downwarped and contacted with the original support, part of counterforce is transferred to the original support, the counterforce reading of the temporary support changes, and if the counterforce reading changes greatly, jacking is carried out according to the step (3);

(5) and (4) repeating the steps (3) to (4) for 2-3 times until the change value of the reading of the bearing reaction force of the temporary support is less than 5% so as to ensure that the time-varying effects of concrete shrinkage, creep, soil body creep and the like of the new bridge pier reach a relatively stable state.

When the original bridge pier is dismantled, firstly, a manual hoist is arranged at the top of the cantilever cover beam to temporarily fix the original bridge pier segment wrapped by the cantilever cover beam, then the original bridge pier is cut below the cantilever cover beam and the original bridge pier segment below the cantilever cover beam is dismantled, and finally the manual hoist is used for lowering and dismantling the original bridge pier segment wrapped by the cantilever cover beam;

and after the original bridge pier is dismantled, adjusting the height of the temporary support to ensure that the height of the beam bottom at the original support is adjusted to be consistent with the existing state before underpinning of the bridge pier.

When the reserved wedge-shaped hole of the cantilever bent cap is poured:

(1) the bottom die of the hanging basket is arranged at the bottom of the cantilever capping beam, the connecting steel bars of the wedge-shaped body are bound, the hanging basket bottom die and the reserved steel bars of the cantilever capping beam are welded, then the wedge-shaped hole is poured to form a post-pouring wedge-shaped body, the post-pouring wedge-shaped body has a self-locking effect after being stressed, and reliable force transmission between post-pouring concrete and existing concrete is guaranteed;

(2) constructing a new pillar on the top surface of the post-cast wedge body, wherein the new pillar is of a steel pipe concrete pillar structure, the steel pipe is connected with foundation bolts pre-embedded in the wedge body through flanges, and self-compacting concrete is poured in the steel pipe;

(3) mounting a new support on the new support, wherein the new support adopts a height-adjustable force-measuring support, and a jacking device and a force-measuring device are arranged in the new support; after the new support is installed in place, adjusting the height of the new support to enable the new support to be closely attached to the bottom of the box girder;

(4) unloading the support reaction force of the temporary support in five stages according to 20%, 40%, 60%, 80% and 100%, and transferring the upper structure load from the temporary support to a new support; after each stage of unloading is finished, checking and adjusting the new support reaction force increment to ensure that the temporary support reaction force unloading amount is completely transferred to the new support reaction force increment; meanwhile, the displacement of the beam bottom at the new support is synchronously monitored, and the variable quantity of the displacement of the beam bottom at the new support before and after load transfer is ensured to be less than 2 mm.

And after the unloading of the supporting reaction force of the temporary support is finished, the temporary support is removed, then the temporary support is removed and connected with the foundation bolt of the cantilever cover beam, and the temporary support is chiseled.

The utility model provides a pier underpins structure which characterized in that: the new bridge pier built on the outer side of the original bridge pier is provided with a cantilever cover beam extending towards the original bridge pier, and a certain height is reserved between the top surface of the cantilever cover beam and the bottom surface of the box girder; a wedge-shaped hole which vertically penetrates through the cantilever capping beam is reserved at the position, aligned with the central axis of the original pier, of the cantilever capping beam, so that the original pier is wrapped outside the cantilever capping beam but is not contacted with the cantilever capping beam; and after the original pier is dismantled, concrete is poured into the wedge-shaped hole to form a post-pouring wedge-shaped body, a new support is constructed on the top surface of the wedge-shaped body, a new support with adjustable height and capable of measuring force is installed on the new support, and the box girder is supported through the new support.

Furthermore, the cantilever bent cap rises from the middle section of the new bridge pier and extends towards the original bridge pier in an inclined manner, so that the bottom surface of the cantilever bent cap forms an inclined surface, and the wedge-shaped hole vertically penetrates from the top surface of the cantilever bent cap to the inclined surface; the wedge-shaped hole is of a structure with a large upper part and a small lower part, the clear distance between the lower port and the original bridge pier is 5-15cm, such as 10cm, the clear distance between the upper port and the original bridge pier is 30-50cm, such as 40cm, and reserved steel bars required for secondary wedge body pouring are reserved in the wedge-shaped hole; and a new pile foundation is built in the foundation below the new bridge pier, a new bearing platform is built on the new pile foundation, and the new bridge pier is supported by the new bearing platform.

The technical effects of the invention comprise:

1. a wedge-shaped hole is reserved in the position, aligned to the central axis of the original bridge pier, of the cantilever capping beam of the newly-built bridge pier, so that the original bridge pier is wrapped outside the cantilever capping beam and is not in contact with the cantilever capping beam. Because the new pier is not in contact with the original pier, the newly-built lower part structure is stressed in advance through the temporary support system before the new support system is stressed, and the deformation stable state is achieved. Therefore, when a new support system is stressed, the deformation of the lower structure is basically stable, and the passive downwarping of the upper structure cannot be caused, so that the problem of girder deformation in the conventional bridge pier underpinning method is solved, the girder is always in a safe and controllable state in the bridge pier underpinning process, and the bridge pier underpinning safety is improved.

2. After the load of the upper structure is transferred to the temporary support system, the original pier support system can still be used as a second safety barrier during the deformation stability of the newly-built lower structure, and the pier underpinning safety is improved.

3. The temporary support and the new support are height-adjustable force-measurable supports, the jacking and unloading precision of the supports is powerfully guaranteed, so that the deformation of a main beam in the load transfer process is controlled within a small range, and the underpinning safety of the bridge pier is improved.

4. Through the ingenious structural design of the bent cap, a temporary pier is not required to be built in the construction process, and the temporary support system is directly arranged on the cantilever bent cap, so that the construction convenience is improved, the construction risk is reduced, and the construction cost is saved.

5. The cantilever bent cap top surface has reserved a take the altitude apart from the case bottom of the girder for the bent cap top surface can be simultaneously as the operation platform of follow-up construction, has reduced setting up of interim construction platform, has improved the construction convenience and ease nature, has reduced the construction risk, has practiced thrift construction cost.

Drawings

FIG. 1 is a schematic diagram showing the comparison of the present invention before and after the reconstruction of a pier;

FIG. 2 is a schematic view of the original state of a bridge;

FIG. 3 is a schematic diagram of the first step of the new pier underpinning process of the present invention;

FIG. 4 is a schematic diagram of a second step of the new pier underpinning process of the present invention;

FIG. 5 is a schematic diagram of a third step corresponding to the new bridge pier underpinning process of the present invention;

FIG. 6 is a schematic diagram of the fourth step corresponding to the new bridge pier underpinning process of the present invention;

FIG. 7 is a schematic diagram of the fifth step of the new pier underpinning process of the present invention;

FIG. 8 is a schematic diagram of the new pier underpinning process of the present invention corresponding to the sixth step;

fig. 9 is a schematic view of the seventh step corresponding to the new bridge pier underpinning process of the present invention, i.e., the final state after the bridge pier underpinning is completed;

FIG. 10 is a detailed view of the new pier corresponding to the sixth step;

FIG. 11 is a schematic plan view of the temporary support and the new support corresponding to the sixth step;

FIG. 12 is a schematic view of a steel bar connection for casting a wedge;

fig. 13 is a detailed view of the new pier in the final state.

In the figure, 1 is a box girder, 2 is a new bridge pier, 21 is a cantilever capping beam, 22 is a wedge-shaped hole, 23 is an inclined plane, 3 is a new bearing platform, 4 is a new pile foundation, 5 is a new supporting column, 6 is a new supporting seat, 7 is a wedge-shaped body, 8 is a reserved steel bar, and 9 is a connecting steel bar.

Detailed Description

The invention will be further illustrated by the following specific examples in conjunction with the accompanying fig. 1-13:

the technical scheme of the invention is described by taking a three-span prestressed continuous box girder bridge as an example. As shown in fig. 1 and 2, a bridge is penetrated under an existing road, and the road needs to be widened and reformed according to planning requirements, so that two original piers on two sides of the road need to be underpinned to reserve a road widening space.

The technical scheme of the invention mainly comprises the following steps:

the method comprises the following steps: new temporary replacement tie beam

As shown in fig. 3, a temporary substitute tie beam is newly built below the tie beam of the original pier so as to ensure that the original pier has reliable transverse connection during subsequent construction.

Step two: demolish the original tie beam of pier

As shown in fig. 4, since the original pier tie beam collides with the spatial position of the cantilever bent cap 21 of the new pier 2, the original pier tie beam is removed after the temporary replacement tie beam reaches the design strength.

Step three: newly-built bridge pier

And building a new pier 2 outside the original pier according to the road widening requirement. Firstly, a new pile foundation 4 is built in a foundation below the new pier, then a new bearing platform 3 is built on the new pile foundation 4, and finally a new pier 2 is built on the new bearing platform 3. A wedge-shaped hole 22 is reserved in the axial line position of the cantilever bent cap 21 of the new pier 2, so that the cantilever bent cap 21 covers the original pier without contacting with the original pier. The ingenious structural design is one of the main innovation points of the bridge pier underpinning method and is the biggest difference between the bridge pier underpinning method and the existing bridge pier underpinning method. On one hand, because the new pier 2 is not in contact with the original pier, the newly-built lower structure is stressed in advance through the temporary support system before the new support system is stressed, and a certain deformation stable state is achieved. Therefore, when a new support system is stressed, the deformation of the lower structure is basically stable, and the passive downward deflection of the upper structure cannot be caused, so that the problem of deformation of the main beam in the existing bridge pier underpinning method is solved. On the other hand, through the ingenious structural design of the cantilever bent cap 21, the technical scheme of the invention does not need to build a temporary pier, and the temporary support system is directly arranged on the cantilever bent cap 21. After the load of the upper structure is transferred to the temporary support system, the original pier support system can still be used as a second safety barrier during the deformation stability of the newly-built lower structure.

In addition, a certain height is reserved between the top surface of the cantilever bent cap 21 and the bottom of the box girder 1, so that the top surface of the cantilever bent cap 21 can be used as an operation platform for subsequent construction, and the erection of a temporary construction platform is reduced.

The cantilever bent cap 21 rises from the middle section of the new bridge pier 2 and extends obliquely towards the original bridge pier, so that the bottom surface of the cantilever bent cap 21 forms an inclined surface 23, and the wedge-shaped hole 22 vertically penetrates from the top surface of the cantilever bent cap 21 to the inclined surface 23; the cantilever capping beam 21 is reserved with a wedge-shaped hole 22 with a large upper part and a small lower part, the distance between a lower port and an original bridge pier is 10cm, the distance between an upper port and the original bridge pier is 40cm, and reserved steel bars 8 required in secondary wedge body pouring are reserved in the hole.

Step four: installing temporary supports and transferring superstructure loads to temporary support systems

4 temporary supports are arranged around each original support, the temporary supports are arranged along the periphery of the cover beam reserved wedge-shaped hole 22, and in order to ensure the stress safety of the box beam 1, the temporary supports are arranged below a box beam web plate or below a box beam middle cross beam.

(1) The temporary support column is constructed on the top surface of the cantilever bent cap 21 and adopts a steel pipe concrete column structure, the steel pipe is connected with the foundation bolt pre-buried in the cantilever bent cap 21 through a flange, and self-compacting concrete is poured in the pipe.

(2) A temporary support is arranged on the temporary support column, the height-adjustable force-measuring support is adopted as the temporary support, and a jacking device and a force-measuring device are arranged in the temporary support column. And after the temporary support is installed in place, adjusting the height of the support to enable the support to be closely attached to the beam bottom.

(3) And (4) jacking the temporary support in a grading manner, and transferring the load of the upper structure from the original support to the temporary support. The jacking force is predetermined according to the theoretical supporting counter force of the support, jacking is carried out in five stages, the jacking load is 20%, 40%, 60%, 80% and 100% of the jacking force of each stage in sequence, and the final jacking force of the support is determined on the basis of completely disengaging the original support. Meanwhile, the jacking height of the beam bottom is synchronously monitored in the grading jacking process, and the final jacking height of the beam bottom is controlled within 5mm (the final jacking height of the beam bottom mainly considers the rebound deformation of a bridge lower structure, and the separation of an upper support plate and a lower support plate of an original support is taken as a control standard in actual operation).

(4) After the jacking of the temporary support is completed, waiting for 1-2 months, during the period, the concrete shrinkage, creep and soil body creep deformation of a newly-built lower structure (comprising a new pier 2, a new bearing platform 3 and a new pile foundation 4) occur, the upper structure can be in downwarping contact with the original support, partial counter force is transferred to the original support, the counter force reading of the temporary support can be changed, and if the counter force reading of the temporary support is changed greatly, the temporary support is jacked according to the step (3) of the step.

(5) And (4) repeating the steps (3) to (4) for 2-3 times until the change value of the reading of the support reaction force of the temporary support is less than 5%.

The key points of the steps (4) and (5) are to make the newly-built substructure hold load for a period of time after being stressed, so that the time-varying effects of concrete shrinkage, creep, soil body creep and the like of the substructure reach a relatively stable state.

Step five: demolish former pier

(1) Firstly, an original pier segment wrapped by the cantilever cover beam 21 is temporarily fixed by the hand hoist at the top of the cantilever cover beam 21, then the original pier segment under the cantilever cover beam 21 is cut and removed, and finally the original pier segment wrapped by the cantilever cover beam 21 is lowered and removed by the hand hoist.

(2) And after the original bridge pier is dismantled, adjusting the height of the temporary support to ensure that the height of the beam bottom at the original support is adjusted to be consistent with the existing state before underpinning of the bridge pier.

Step six: pouring a reserved hole of the bent cap, installing a new support, and transferring the load of the upper structure to a support system of the new support

(1) The bottom of the cantilever bent cap 21 is provided with a hanging basket bottom die, wedge-shaped body steel bars are bound, the extending connecting steel bars 9 are welded with the reserved steel bars 8 of the cantilever bent cap 21, the wedge-shaped holes 22 are poured to form the post-pouring wedge-shaped body 7, the self-locking effect is achieved after the wedge-shaped body 7 is stressed, and reliable force transfer between post-pouring concrete and existing concrete is guaranteed.

(2) And constructing a new strut 5 on the top surface of the post-cast wedge body 7, wherein the new strut 5 adopts a steel pipe concrete column structure, a steel pipe is connected with a foundation bolt pre-embedded in the wedge body 7 through a flange, and self-compacting concrete is poured into the steel pipe.

(3) A new support 6 is arranged on the new support column 5, the new support 6 adopts a height-adjustable force-measuring support, and a jacking device and a force-measuring device are arranged in the new support 6. After the new support 6 is installed in place, the height of the support is adjusted to be in close contact with the beam bottom (the new support bears 10% of theoretical support reaction and is used as a standard for being in close contact with the beam bottom).

(4) The temporary support reaction force is unloaded in five stages of 20%, 40%, 60%, 80% and 100%, and the superstructure load is transferred from the temporary support to the new support 6. And after each stage of unloading is finished, checking and adjusting the counter force increment of the new support 6 to ensure that the temporary support counter force unloading amount is completely transferred to the counter force increment of the new support 6. Meanwhile, the displacement of the beam bottom at the new support 6 is synchronously monitored, and the variable quantity of the displacement of the beam bottom at the new support 6 before and after load transfer is ensured to be less than 2 mm.

Step seven: removing temporary supports

After the temporary support bearing reaction force is unloaded, the temporary support can be detached. The temporary support is then removed from the anchor bolt connection with the cantilever capping beam 21 and the temporary support column is chiseled off.

The present invention has been described in detail, and it should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.