An integrated underpinning structure and construction method for a bridge in a deep foundation pit of an urban tunnel

Abstract

The present invention relates to an integrated underpinning structure for a bridge within a deep foundation pit of an urban tunnel, comprising: an original bridge cap, an expanded cap, and a top plate of the tunnel; the original bridge cap, the expanded cap, and the top plate of the tunnel are fixedly connected in sequence from the inside out to form an integrated structure; the integrated structure serves as both a bridge underpinning and force transmission structure, as well as the top plate of a newly constructed tunnel, and as the primary support for the retaining structure of the tunnel's deep foundation pit; the upper portion of the original bridge cap comprises, from bottom to top, piers and the bridge structure, and the lower portion comprises the original bridge piles; the bottom of the expanded cap is provided with reinforcement piles, and a temporary buttress is provided on the top during construction; the top surface of the temporary buttress is provided with a jack to assist in controlling the settlement of the bridge structure within a safe range during tunnel construction; the top plate of the tunnel extends along the cross-sectional direction of the foundation pit on both sides to the top ring beam of the tunnel and is connected to the top ring beam. The present invention provides an underpinning structure that serves as both a bridge underpinning and force transmission structure and a top plate of a newly constructed tunnel.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel construction, and in particular relates to an integrated underpinning structure and a construction method for a bridge in a deep foundation pit of an urban tunnel. Background Art

[0002] As urban tunnel construction in my country expands, planned tunnel routes often require passing under urban bridges. Existing bridge abutments and pile foundations hinder deep tunnel excavation. Currently, bridge pile foundation underpinning generally employs a one-time force transfer method. This involves using an underpinning system to transfer the affected bridge foundation to a newly constructed foundation outside the tunnel excavation. After removing the existing bridge pile foundation and piers, the main tunnel structure is constructed. Each component requires separate construction, resulting in complex construction processes, long construction times, high project costs, and significant space requirements.

[0003] For example, a river crossing connection project connects a river tunnel with an urban expressway, designed to pass beneath the city's main roads and elevated bridges in the form of a tunnel. Due to restrictions imposed by the surrounding construction environment, the abutments and pile foundations of the main bridge and ramp bridges are located within the tunnel's deep foundation pit, severely impacting deep foundation pit construction. Replacement is necessary, and after replacement, the bridge foundations can only be located within the pit. This bridge is a major urban artery with heavy traffic, requiring uninterrupted traffic and strict control over bridge deck deformation. The bridge was built relatively recently, resulting in fragile concrete and irregular shapes for the abutments. The tunnel pit excavation is deep, and the pit edge is very close to the surrounding bridge piers, necessitating strict control over deformation of the tunnel retaining structure. The clearance under the bridge is less than 6 meters, making it impossible for large machinery to operate underneath. Summary of the Invention

[0004] (1) Technical issues to be solved

[0005] In response to the existing technical problems, the present invention provides an integrated underpinning structure and construction method for a bridge in a deep foundation pit of an urban tunnel.

[0006] (2) Technical solution

[0007] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] An integrated underpinning structure for a bridge in a deep foundation pit of an urban tunnel, characterized by comprising: an original bridge cap, an expanded cap, and a top plate of the tunnel;

[0009] The original bridge cap, the expanded cap and the tunnel top plate are fixedly connected in sequence from the inside to the outside to form an integrated structure;

[0010] The integrated structure serves as both the bridge support and force transmission structure, the roof of the newly constructed tunnel, and the primary support for the tunnel's deep foundation pit retaining structure.

[0011] The upper part of the original bridge cap is composed of bridge piers and bridge structure from bottom to top, and the lower part is the original bridge pile;

[0012] The bottom of the expanded cap is provided with reinforcement piles, and the top is provided with temporary piers during construction;

[0013] The top surface of the temporary pier is provided with a jack, which is used to assist in controlling the settlement of the bridge structure within a safe range during tunnel construction;

[0014] The top plate of the tunnel is extended to the top ring beam of the tunnel on both sides along the cross section of the foundation pit and is connected to the top ring beam, and is connected to the tunnel main structure closely below the top ring beam on the inner side of the foundation pit.

[0015] Preferably, the original bridge pier, the expanded pier and the tunnel top plate in the integrated structure are cast-in-situ reinforced concrete structures, and work together after being formed into a whole by pouring concrete.

[0016] Preferably, the expanded bridge cap entirely wraps the original bridge cap;

[0017] The net distance between the upper and lower surfaces of the expanded pier and the upper and lower surfaces of the original bridge pier is not less than 0.5 meters;

[0018] The sides of the expanded pier shall be no less than 2 meters away from the sides of the original bridge pier, and the upper surface shall not be higher than the ground after completion;

[0019] If there is a group of several original bridge abutments that are not connected to each other, the range of the expanded abutment can be adjusted so that all the original bridge abutments in a group are wrapped in the same expanded abutment.

[0020] Preferably, the bottom surface of the top plate of the tunnel is at the same elevation as the bottom surface of the expanded platform near the expanded platform, and is locally adjusted at the top ring beam position to be flush with the bottom surface of the top ring beam;

[0021] The upper surface of the tunnel top plate does not exceed the elevation of the top surface of the expanded pedestal.

[0022] Preferably, the reinforcement piles are bored cast-in-place piles, the bottoms of the piles enter the rock strata, and each of the original bridge caps is provided with a row of reinforcement piles on both sides along the bridge axis.

[0023] The reinforcement piles are arranged at intervals, and each of the original bridge piers corresponds to no less than 4 reinforcement piles in total.

[0024] Preferably, the retaining piles are bored cast-in-place piles, with the bottoms of the piles entering the rock layer and arranged along the edges of both sides of the foundation pit. They are mainly used as retaining piles during the foundation pit excavation stage, and are simultaneously connected to the integrated structure through casting through the top ring beam, and are subjected to overall stress.

[0025] Preferably, an MJS pile water-stop curtain is further provided outside the foundation pit outside the retaining piles;

[0026] The bottom depth of the MJS pile water-stop curtain is the same as that of the retaining piles, which has the function of isolating the hydraulic connection between the inside and outside of the foundation pit and reinforcing the soil outside the foundation pit.

[0027] Preferably, a row of several temporary piers are provided on both sides of the original bridge cap along the longitudinal direction of the bridge, and a temporary pier is provided on the top of each reinforcement pile;

[0028] The main body of the temporary pier is made of steel pipe columns, and steel cross braces and steel diagonal braces should be set between adjacent steel pipe columns to form a frame structure to enhance the overall stability of the temporary pier.

[0029] An integrated underpinning construction method for a bridge in a deep foundation pit of an urban tunnel comprises the following steps:

[0030] S1. Measure the top surface elevation of the bridge structure as the benchmark elevation for jack control in subsequent construction, inspect the bridge structure, and assess its safety status;

[0031] S2. Use specialized miniaturized machinery to construct reinforcement piles, retaining piles, and MJS pile water-stop curtains under the bridge;

[0032] S3, the first force conversion:

[0033] S3.1. Construction of temporary buttresses: Install temporary buttresses between the top surface of the supporting pile and the bottom surface of the bridge structure. Install jacks on the top surface of the temporary buttresses, and control the extended end of the jack to slightly lift it so that the top surface of the extended end is tightly pressed against the bottom surface of the bridge structure.

[0034] S3.2. Construction of the expanded cap: Excavate the soil around the original bridge cap to the bottom of the expanded cap. Roughen the soil around the original bridge cap and the piers within the scope of the expanded cap, plant reinforcement, and cast the expanded cap. The expanded cap will now encompass the original bridge cap, the tops of the original bridge piles, the bottoms of the piers, and the junctions between the reinforced piles and the temporary piers.

[0035] S3.3. Construction of the Tunnel Top Slab: Further excavate and expand the soil around the cap to the inside of the retaining piles. Concrete the top ring beam and the tunnel top slab together. The tunnel top slab, the expanded cap, and the original bridge cap form an integrated underpinning structure. The integrated underpinning structure is connected to the reinforcement piles, top ring beam, and retaining piles as a whole.

[0036] S3.4. Cut off the original bridge piles: Excavate the foundation pit below the integrated underpinning structure until the second support of the foundation pit is reached, cut off the original bridge piles, and complete the first load transfer. At this time, the reinforcement piles and retaining piles jointly bear the upper bridge load transferred by the integrated underpinning structure.

[0037] S4, the second force conversion:

[0038] S4.1. Excavate the soil layer by layer downward and erect supports until the foundation pit reaches the designed pit bottom elevation. Build the main tunnel structure upward until it connects with the bottom surface of the tunnel top plate. At this point, the integrated underpinning structure and the main tunnel structure are connected as a whole.

[0039] S4.2. Remove the supporting piles inside the tunnel main structure that affect tunnel operation, completing the second load transfer. At this time, the integrated underpinning structure and the tunnel main structure act as a permanent structure to bear the upper load of the bridge.

[0040] S4.3. Restore the elevation of the pier top surface support to match the benchmark elevation, remove the temporary piers and jacks, backfill the soil above the integrated underpinning structure, and restore the original ground condition.

[0041] Preferably, the jack is provided with an automatic servo system for assisting in controlling the settlement of the bridge structure within a safe range;

[0042] During the construction of S3.2~S4.2, the jacks are automatically controlled to rise or retract according to the deformation monitoring data of the bridge structure, so that the top surface of the bridge structure is kept in a safe range near the reference elevation during construction. If necessary, the jacks are manually controlled to rise and the top surface supports of the piers are replaced with those of appropriate heights, and then the jacks are controlled to retract to restore the support force.

[0043] (3) Beneficial effects

[0044] The integrated underpinning structure and construction method for a bridge in a deep foundation pit of an urban tunnel provided by this application have the following beneficial effects:

[0045] (1) The integrated underpinning structure for a bridge in a deep foundation pit of an urban tunnel provided by the present invention has the advantage that the integrated underpinning structure formed by the original bridge cap, the expanded cap, and the tunnel top plate is a permanent structure and does not require the removal of the original bridge cap, thereby greatly reducing the amount of demolition work.

[0046] (2) The integrated underpinning structure for bridges in deep foundation pits of urban tunnels provided by the present invention has the advantage that the expanded pier and the top plate of the tunnel have good lateral stiffness after being combined, which can effectively improve the ability of the reinforced original bridge pier to resist lateral deformation and uneven settlement, thereby ensuring the safety of the bridge structure;

[0047] (3) The integrated underpinning structure for bridges in deep foundation pits of urban tunnels provided by the present invention has the advantage that the tunnel top plate and top ring beam in the integrated underpinning structure are connected. The integrated underpinning structure serves as the first support for the retaining structure of the tunnel deep foundation pit and has good support stiffness, which is conducive to controlling the deformation of the retaining structure and reducing the disturbance to the adjacent bridge piers.

[0048] (4) The integrated underpinning structure for bridges in deep urban tunnel foundation pits provided by the present invention has the advantage that the structural scope is limited to the construction range of the tunnel foundation pit, and ultimately forms a new bridge foundation with the main tunnel structure, without occupying additional valuable urban space.

[0049] (5) The integrated underpinning construction method for a bridge in a deep foundation pit of an urban tunnel provided by the present invention has the advantages of adopting an integrated underpinning structure and utilizing the tunnel enclosure structure and the tunnel main structure as the bearing structure at different stages. While effectively controlling the deformation of the bridge and ensuring the normal operation of traffic, it can save investment and construction time, and has important reference value for similar projects.

[0050] (6) The integrated underpinning construction method for bridges in deep foundation pits of urban tunnels provided by the present invention has the advantage that the retaining piles, supporting piles and MJS pile water-stop curtains can all be constructed using miniaturized machinery under low clearance conditions under the bridge. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a schematic diagram of the integrated underpinning structure of a bridge in a deep foundation pit of an urban tunnel;

[0052] Figure 2 for Figure 1 AA schematic diagram;

[0053] Figure 3 This is a schematic diagram of the cross section of S3.3;

[0054] Figure 4 This is a schematic diagram of the cross section of S3.4;

[0055] Figure 5 This is a schematic diagram of the cross section of S4.1;

[0056] Reference numerals:

[0057] 1: Original bridge pier; 2: Expanded pier; 3: Tunnel top slab; 4: Bridge pier; 5: Bridge structure; 6: Original bridge piles; 7: Reinforced piles; 8: Retaining piles; 9: Top ring beam; 10: MJS pile water-stop curtain; 11: Temporary pier; 12: Jack; 13: Planted reinforcement; 14: Second support for foundation pit; 15: Tunnel main structure. DETAILED DESCRIPTION

[0058] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0059] like Figure 1-Figure 5 As shown: This embodiment provides an integrated underpinning structure for a bridge in a deep foundation pit of an urban tunnel, comprising: an original bridge pedestal 1, an expanded pedestal 2 and a tunnel top plate 3.

[0060] The original bridge pier 1, the expanded pier 2 and the tunnel top plate 3 are fixedly connected in sequence from the inside to the outside to form an integrated structure.

[0061] It should be noted that this integrated structure is the integrated underpinning structure protected in this embodiment. It serves as both the bridge underpinning and load-transmitting structure, the roof of the newly constructed tunnel, and the primary support for the tunnel's deep foundation pit retaining structure. The original bridge cap 1 has, from bottom to top, piers 4 and a bridge structure 5 on its upper portion, and original bridge piles 6 at its lower portion. The expanded cap 2 is equipped with reinforcement piles 7 at its bottom and, during construction, with temporary buttresses 11 on its top. Jacks 12 are located on top of these temporary buttresses 11 to help control the settlement of the bridge structure 5 within a safe range during tunnel construction.

[0062] The top plate 3 of the tunnel is extended to the top ring beam 9 of the tunnel on both sides along the cross-section direction of the foundation pit and is connected to the top ring beam 9, and is connected to the tunnel main structure 15 at the lower part of the top ring beam 9 on the inner side of the foundation pit.

[0063] The original bridge pier 1, the expanded pier 2, and the tunnel top plate 3 in the integrated structure are cast-in-situ reinforced concrete structures, and work together after being formed into a whole by pouring concrete.

[0064] The enlarged pier 2 in this embodiment completely wraps the original bridge pier 1; the upper and lower surfaces of the enlarged pier 2 have a net distance of not less than 0.5 meters from the upper and lower surfaces of the original bridge pier 1; the sides of the enlarged pier 2 have a net distance of not less than 2 meters from the sides of the original bridge pier 1, and the upper surface is not higher than the ground after completion.

[0065] If there is a group of several original bridge abutments 1 that are not connected to each other, the range of the expanded abutment 2 can be adjusted so that all the original bridge abutments 1 in a group are wrapped in the same expanded abutment 2.

[0066] In this embodiment, the bottom surface of the tunnel top plate 3 is at the same elevation as the bottom surface of the expanded platform 2 near the expanded platform 2, and is locally adjusted at the position of the top ring beam 9 to be flush with the bottom surface of the top ring beam 9; the upper surface of the tunnel top plate 3 does not exceed the elevation of the top surface of the expanded platform 2.

[0067] The reinforcement piles 7 in this embodiment are bored cast-in-place piles, with the bottoms of the piles entering the rock strata. Each of the original bridge piers 1 is provided with a row of reinforcement piles 7 on both sides along the bridge axis. The reinforcement piles 7 are arranged at intervals, and each of the original bridge piers 1 corresponds to no less than 4 reinforcement piles 7 in total.

[0068] The retaining piles 8 in this embodiment are bored cast-in-place piles, the bottom of which enters the rock layer and is arranged along the edges of both sides of the foundation pit. During the excavation stage of the foundation pit, they are mainly used as retaining piles 8. At the same time, they are connected to the integrated structure by casting through the top ring beam 9, and are subjected to overall force.

[0069] In this embodiment, an MJS pile water-stop curtain 10 is further provided on the outside of the foundation pit outside the retaining pile 8; the pile bottom depth of the MJS pile water-stop curtain 10 is the same as that of the retaining pile 8, which not only has the function of isolating the hydraulic connection between the inside and outside of the foundation pit, but also has the function of reinforcing the soil outside the foundation pit.

[0070] In this embodiment, a row of several temporary piers 11 are set on both sides of the original bridge pier 1 along the longitudinal direction of the bridge, and a temporary pier 11 is set on the top of each reinforcement pile 7; the main body of the temporary pier 11 is made of steel pipe columns, and steel cross braces and steel diagonal braces are preferably set between adjacent steel pipe columns to form a frame structure to enhance the overall stability of the temporary pier 11.

[0071] This embodiment also provides an integrated underpinning construction method for a bridge in a deep foundation pit of an urban tunnel, which specifically includes the following steps:

[0072] S1. Measure the top surface elevation of the bridge structure 5 as a reference elevation for control by the jack 12 in subsequent construction, inspect the bridge structure 5, and assess the safety status of the bridge structure 5;

[0073] S2. Use specialized miniaturized machinery to construct reinforcement piles 7, retaining piles 8, and MJS pile water-stop curtains 10 under the bridge;

[0074] S3, the first force conversion:

[0075] S3.1. Construction of temporary buttress 11: Install temporary buttress 11 between the top surface of the supporting pile and the bottom surface of the bridge structure 5. Install jack 12 on the top surface of temporary buttress 11. Slightly lift the extended end of jack 12 so that the top surface of the extended end is pressed tightly against the bottom surface of the bridge structure 5.

[0076] S3.2. Construction of Expanded Cap 2: Excavate the soil around the original bridge cap 1 to the bottom surface of the expanded cap 2. Roughen the area around the original bridge cap 1 and around the pier 4 within the scope of the expanded cap 2, plant rebar 13, and cast the expanded cap 2. The expanded cap 2 will now encompass the original bridge cap 1, the top of the original bridge pile, the bottom of the pier, and the junction between the reinforcement pile 7 and the temporary pier 11.

[0077] S3.3. Construction of Tunnel Top Slab 3: Further excavate the soil around the expanded cap 2 until it reaches the inside of the retaining piles 8. Concrete the top ring beam 9 and the tunnel top slab 3 together. The tunnel top slab 3, the expanded cap 2, and the original bridge cap 1 now form an integrated underpinning structure. The integrated underpinning structure is connected to the reinforcement piles 7, top ring beam 9, and retaining piles 8 as a whole.

[0078] S3.4. Cut off original bridge pile 6: Excavate the foundation pit below the integrated underpinning structure until the second support of the foundation pit is reached, cut off original bridge pile 6, and complete the first load transfer. At this time, the reinforcement pile 7 and the retaining pile 8 jointly bear the upper bridge load transferred by the integrated underpinning structure.

[0079] S4, the second force conversion:

[0080] S4.1. Excavate the soil layer by layer downward and erect supports until the foundation pit reaches the designed pit bottom elevation. Build the tunnel main structure 15 upward until it connects with the bottom surface of the tunnel top plate 3. At this point, the integrated underpinning structure and the tunnel main structure 15 are connected as a whole.

[0081] S4.2. Remove the supporting piles inside the tunnel main structure 15 that affect tunnel operation, completing the second load transfer. At this time, the integrated underpinning structure and the tunnel main structure act as a permanent structure to bear the upper load of the bridge.

[0082] S4.3. Restore the pier top surface support elevation to match the benchmark elevation, remove the temporary pier 11 and jack 12, backfill the soil above the integrated underpinning structure, and restore the original ground surface.

[0083] In detail, the jack 12 is equipped with an automatic servo system for assisting in controlling the settlement of the bridge structure 5 within a safe range; during the construction of S3.2 to S4.2, the jack 12 is automatically controlled to rise or retract according to the deformation monitoring data of the bridge structure 5, so that the top surface of the bridge structure 5 is maintained within a safe range near the reference elevation during construction. If necessary, the jack 12 is manually controlled to rise and then the pier top surface support of a suitable height is replaced, and then the jack 12 is controlled to retract to restore the support force.

[0084] The integrated support structure of the bridge in the deep foundation pit of the urban tunnel in this embodiment has the advantage that the integrated support structure formed by the original bridge pedestal 1, the expanded pedestal 2 and the tunnel top plate 3 is a permanent structure and does not require the demolition of the original bridge pedestal 1, which greatly reduces the demolition workload; the integrated support structure of the bridge in the deep foundation pit of the urban tunnel has the advantage that the expanded pedestal 2 and the tunnel top plate 3 have good lateral stiffness after being combined, which can effectively improve the ability of the reinforced original bridge pedestal 1 to resist lateral deformation and uneven settlement, and ensure the safety of the bridge structure; the integrated support structure of the bridge in the deep foundation pit of the urban tunnel has the advantage that the tunnel top plate 3 in the integrated support structure is connected to the top ring beam 9, and the integrated support structure serves as the first support of the tunnel deep foundation pit retaining structure, has good support stiffness, is conducive to controlling the deformation of the retaining structure, and reduces the disturbance to the adjacent bridge piers 4.

[0085] The technical principles of the present invention have been described above in conjunction with specific embodiments. These descriptions are intended solely to illustrate the principles of the present invention and are not to be construed in any way as limiting the scope of protection of the present invention. Based on the explanations herein, those skilled in the art will be able to devise other specific embodiments of the present invention without inventive effort, and such embodiments will fall within the scope of protection of the present invention.

Claims

1. An integrated underpinning structure for a bridge in a deep foundation pit of an urban tunnel, characterized in that: include: Original bridge abutments, expanded abutments and tunnel top slabs; The original bridge cap, the expanded cap and the tunnel top plate are fixedly connected in sequence from the inside to the outside to form an integrated structure; The integrated structure serves as both the bridge support and force transmission structure, the roof of the newly constructed tunnel, and the primary support for the tunnel's deep foundation pit retaining structure. The upper part of the original bridge cap is composed of bridge piers and bridge structure from bottom to top, and the lower part is the original bridge pile; The bottom of the expanded cap is provided with reinforcement piles, and the top is provided with temporary piers during construction; The top surface of the temporary pier is provided with a jack, which is used to assist in controlling the settlement of the bridge structure within a safe range during tunnel construction; The top plate of the tunnel is extended to the top ring beam of the tunnel on both sides along the cross section of the foundation pit and is connected to the top ring beam, and is connected to the tunnel main structure closely below the top ring beam on the inner side of the foundation pit.

2. The integrated support structure according to claim 1, characterized in that: The original bridge pedestal, the expanded pedestal and the tunnel top plate in the integrated structure are cast-in-situ reinforced concrete structures, and work together after being formed into a whole by pouring concrete.

3. The integrated support structure according to claim 1, characterized in that: The expanded pier entirely wraps the original bridge pier; The net distance between the upper and lower surfaces of the expanded pier and the upper and lower surfaces of the original bridge pier is not less than 0.5 meters; The sides of the expanded pier shall be no less than 2 meters away from the sides of the original bridge pier, and the upper surface shall not be higher than the ground after completion; If there is a group of several original bridge abutments that are not connected to each other, the range of the expanded abutment is adjusted so that all the original bridge abutments in the group are wrapped in the same expanded abutment.

4. The integrated support structure according to claim 1, characterized in that: The bottom surface of the top plate of the tunnel is at the same elevation as the bottom surface of the expanded platform near the expanded platform, and is locally adjusted at the top ring beam position to be flush with the bottom surface of the top ring beam; The upper surface of the tunnel top plate does not exceed the elevation of the top surface of the expanded pedestal.

5. The integrated support structure according to claim 1, characterized in that: The reinforcement piles are bored cast-in-place piles, the bottoms of which penetrate into the rock strata, and each of the original bridge caps is provided with a row of reinforcement piles on both sides along the bridge axis; The reinforcement piles are arranged at intervals, and each of the original bridge piers corresponds to no less than 4 reinforcement piles in total.

6. The integrated support structure according to claim 1, characterized in that: The bored cast-in-place piles, with the bottom of the piles entering the rock layer, are arranged along the edges of both sides of the foundation pit and are used as retaining piles during the foundation pit excavation stage. At the same time, they are cast and connected with the integrated structure through the top ring beam to bear the force as a whole.

7. The integrated support structure according to claim 6, characterized in that: An MJS pile water-stop curtain is also provided outside the foundation pit outside the retaining piles; The bottom depth of the MJS pile water-stop curtain is the same as that of the retaining piles, which has the function of isolating the hydraulic connection between the inside and outside of the foundation pit and reinforcing the soil outside the foundation pit.

8. The integrated support structure according to claim 1, characterized in that: A row of several temporary piers are arranged on both sides of the original bridge cap along the longitudinal direction of the bridge, and a temporary pier is arranged on the top of each reinforcement pile; The main body of the temporary pier is made of steel pipe columns, and steel cross braces and steel diagonal braces should be set between adjacent steel pipe columns to form a frame structure to enhance the overall stability of the temporary pier.

9. An integrated underpinning construction method for a bridge in a deep foundation pit of an urban tunnel, characterized in that: The steps include: S1. Measure the top surface elevation of the bridge structure as the benchmark elevation for jack control in subsequent construction, inspect the bridge structure, and assess its safety status; S2. Use specialized miniaturized machinery to construct reinforcement piles, retaining piles, and MJS pile water-stop curtains under the bridge; S3, the first force conversion: S3.

1. Construction of temporary buttresses: Install temporary buttresses between the top surface of the supporting pile and the bottom surface of the bridge structure. Install jacks on the top surface of the temporary buttresses, and control the extended end of the jack to slightly lift it so that the top surface of the extended end is tightly pressed against the bottom surface of the bridge structure. S3.

2. Construction of the expanded cap: Excavate the soil around the original bridge cap to the bottom of the expanded cap. Roughen the soil around the original bridge cap and the piers within the scope of the expanded cap, plant reinforcement, and cast the expanded cap. The expanded cap will now encompass the original bridge cap, the tops of the original bridge piles, the bottoms of the piers, and the junctions between the reinforced piles and the temporary piers. S3.

3. Construction of the Tunnel Top Slab: Further excavate and expand the soil around the cap to the inside of the retaining piles. Concrete the top ring beam and the tunnel top slab together. The tunnel top slab, the expanded cap, and the original bridge cap form an integrated underpinning structure. The integrated underpinning structure is connected to the reinforcement piles, top ring beam, and retaining piles as a whole. S3.

4. Cut off the original bridge piles: Excavate the foundation pit below the integrated underpinning structure until the second support of the foundation pit is reached, cut off the original bridge piles, and complete the first load transfer. At this time, the reinforcement piles and retaining piles jointly bear the upper bridge load transferred by the integrated underpinning structure. S4, the second force conversion: S4.

1. Excavate the soil layer by layer downward and erect supports until the foundation pit reaches the designed pit bottom elevation. Build the main tunnel structure upward until it connects with the bottom surface of the tunnel top plate. At this point, the integrated underpinning structure and the main tunnel structure are connected as a whole. S4.

2. Remove the supporting piles inside the tunnel main structure that affect tunnel operation, completing the second load transfer. At this time, the integrated underpinning structure and the tunnel main structure act as a permanent structure to bear the upper load of the bridge. S4.

3. Restore the elevation of the pier top surface support to match the benchmark elevation, remove the temporary piers and jacks, backfill the soil above the integrated underpinning structure, and restore the original ground condition.

10. The construction method according to claim 9, characterized in that: The jack is equipped with an automatic servo system to assist in controlling the settlement of the bridge structure within a safe range; During the construction of S3.2~S4.2, the jacks are automatically controlled to rise or retract according to the deformation monitoring data of the bridge structure, so that the top surface of the bridge structure is kept in a safe range near the reference elevation during construction. If necessary, the jacks are manually controlled to rise and the top surface supports of the piers are replaced with those of appropriate heights, and then the jacks are controlled to retract to restore the support force.

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