Large-span wide-width bent cap structure system of small-clear-distance over-crossing existing tunnel and construction method of large-span wide-width bent cap structure system

Abstract

The invention discloses a large-span wide-width bent cap structure system of a small-clear-distance over-crossing existing tunnel and a construction method thereof, the large-span wide-width bent cap structure system comprises a pile foundation, a bearing platform, a buffer layer and a cast-in-place prestress bent cap, the bearing platform is arranged on the pile foundation, and the cast-in-place prestress bent cap is arranged on the bearing platform; a rubber temporary support is mounted on the bearing platform; a vertical unbonded prestressed steel bar is arranged in the bearing platform, and a transverse prestressed steel strand is arranged in the cast-in-place prestressed cover beam; a post-cast strip for system conversion is reserved between the cast-in-place prestress cover beam and the bearing platform, the bridge cover beam is directly arranged on the bearing platform, a bridge structure system is simplified, meanwhile, joint treatment in the construction process is reduced, structural deformation and stress concentration caused by untight connection are reduced, and therefore the influence on an existing tunnel is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of bridge engineering, and in particular to a large-span wide cap beam structure system for crossing an existing tunnel with a small clearance and a construction method thereof. Background Art

[0002] The bridge cap is a part of the bridge structure. Generally, the cap is set on the piers, transferring the load from the main beam to the piers and finally to the foundation. The connection methods mainly include integral cast-in-place, prestressed connection, grouting sleeve connection, etc.

[0003] With the continuous development of urban construction, in order to make full use of space and avoid urban congestion, new lines will inevitably intersect or meet with existing lines at close range. When a new bridge is constructed over an existing tunnel with a small clearance, in order to avoid the existing tunnel, the bridge cap beam often has a large span and wide structural characteristics. The design and construction of the bridge cap beam structure system needs to consider the following aspects:

[0004] Accurately calculate the dynamic and static loads of the bridge cap beam, including vehicle loads, pedestrian loads, wind loads, earthquake effects, etc., and ensure that these loads can be reasonably distributed to the foundation or supporting structure to avoid adverse effects on the tunnel;

[0005] Select materials suitable for long-span and wide structures, such as high-strength concrete or prestressed concrete, as well as appropriate reinforcement and prestressing tendons;

[0006] In large-span and wide-width cap beam structures, joints and connections are weak links. If not handled properly, cracks or deformations may occur, affecting the overall performance of the structure.

[0007] Select appropriate construction methods and use vibration-free or low-vibration technology whenever possible to reduce the impact on the tunnel.

[0008] When designing and constructing a large-span, wide bridge cap with a small clearance over an existing tunnel, it is necessary to consider a variety of factors to ensure the safety of the existing tunnel and the stability of the new bridge. Summary of the invention

[0009] The purpose of the present invention is to address the deficiencies of the prior art and provide a large-span wide cap beam structure system that spans an existing tunnel with a small clear distance, including a pile foundation, a cap, a buffer layer and a cast-in-place prestressed cap beam, wherein the cap is arranged on the pile foundation, and the minimum horizontal clear distance requirement is met between the pile foundation and the existing tunnel structure; the cast-in-place prestressed cap beam is arranged on the cap, and the cap is arranged on both sides of the existing tunnel, and the two ends of the cast-in-place prestressed cap beam directly fall on the two caps, and the middle is suspended across the existing tunnel; a rubber temporary bearing is installed on the cap as a temporary vertical force transmission structure; a vertical unbonded prestressed steel rod is arranged in the cap, and the vertical unbonded prestressed steel rod passes through the cap and extends into the cast-in-place prestressed cap beam, and the arrangement of the vertical unbonded prestressed steel rod is carried out according to the principle of equal replacement of the number of vertical structural reinforcements; a transverse prestressed steel strand is arranged in the cast-in-place prestressed cap beam; a post-cast strip for system conversion is reserved between the cast-in-place prestressed cap beam and the cap.

[0010] Preferably, the overlapping area between the cap and the cast-in-place prestressed cap beam is simulated as a rectangular column, the force system connecting the cap and the cast-in-place prestressed cap beam is simulated as a rectangular column connected to the pile foundation, and the vertical unbonded prestressed steel rod is arranged within the range of the rectangular column.

[0011] Preferably, the cap is simulated as a rigid arm, and the maximum bending moment of the pile top in the transverse and longitudinal directions when the cap beam and the cap are fixedly connected is extracted. The maximum bending moment of the pile top is divided into the bending moment of the pile top under the basic load combination and the bending moment of the pile top under the frequent load combination. The basic load combination is a combination of the permanent action design value effect and the variable action design value effect, and the combined effect expression is: Where: Sud is the effect combination design value of the basic combination of actions under the ultimate limit state of bearing capacity; γ0 is the structural importance coefficient, γGi and QGik are the partial coefficients and standard values ​​of the i-th permanent action effect; γQ1 and Q1k are the partial coefficients and standard values ​​of the vehicle load effect; γQj and Qjk are the partial coefficients and standard values ​​of other variable action effects except the vehicle load; ψc is the combination coefficient of other variable action effects except the vehicle load effect.

[0012] Preferably, the frequent load combination is a combination of the permanent action standard value effect, the automobile load frequent value, and other variable action quasi-permanent values, and the combined effect expression is: Where: Sfd is the design value of the frequent combined effect of actions; ψf1 is the frequent value coefficient of the vehicle load (ignoring the impact effect).

[0013] Preferably, the cap beam is verified as a Class A prestressed concrete member. The Class A prestressed concrete member has tensile stress on the tensile edge of the positive section under the frequently encountered combination of actions. pt ≤0.7ftk To control, σ pt is the tensile stress, f tk is the standard value of concrete axial tensile strength, and the vertical unbonded prestressed steel bars are arranged according to σ con ×A p ≥f sd ×A S Perform verification, where σ con The controlled stress value of the vertical unbonded prestressed steel bar under the steel anchor is A p Total cross-sectional area of ​​the prestressed steel bar, f sd is the design value of tensile strength of ordinary steel bars, A s It is the total cross-sectional area of ​​ordinary steel bars.

[0014] Preferably, a vertical unbonded prestressed steel bar fixed end is installed at the bottom of the pedestal, and the fixed end components are, from bottom to top, an anchor nut, an anchor baffle, an anchor nut, an anchor plate and a spiral reinforcement. The vertical unbonded prestressed steel bar anchor plate is connected to the ordinary steel bars of the pedestal through positioning steel bars. A vertical unbonded prestressed steel bar tensioning end is installed on the top surface of the cap beam, and the tensioning end components are, from bottom to top, a spiral reinforcement, an anchor plate, an anchor nut, an anchor baffle and an anchor nut. The vertical unbonded prestressed steel bar anchor plate is connected to the cap beam steel bars through positioning steel bars.

[0015] A construction method comprises the following steps:

[0016] S1. After the pile foundation construction is completed, the cap is set up: Before the pile foundation construction, three rows of grouting holes are set between the pile foundation and the existing tunnel structure, and cement water glass slurry is evenly injected into the soil from the grouting holes. The first row of grouting holes is 1m away from the tunnel edge, with a hole spacing of 0.5m. The depth of each grouting hole is 15m, the single hole diameter is 0.12m, and the row spacing is 2m. The pile foundation construction adopts the full-swing drilling rig full-casing follow-up construction process;

[0017] S2. While tying the cap reinforcement, install the cap embedded parts: the cap embedded parts include vertical unbonded prestressed steel bars and support pad stone reinforcement. The vertical unbonded prestressed steel bars are embedded and positioned before the upper reinforcement of the cap is closed, and the support pad stone reinforcement is embedded after the cap reinforcement skeleton is tied; install the cap formwork, and pour the cap concrete and support pad stone concrete;

[0018] S3. Install temporary rubber bearings: one end uses a sliding bearing and the other end uses a fixed bearing;

[0019] S4. Before constructing the cap beam, set the cap beam bottom formwork above the tunnel top plate according to the vertical distance between the cap beam and the tunnel top plate: set a buffer layer above the tunnel top plate, lay steel mesh on the graded crushed stone, and pour C20 concrete as the cap beam bottom formwork;

[0020] S5, cap beam construction, cap beam reinforcement binding and transverse prestressed beam installation: a vertical unbonded prestressed steel bar tensioning end is set at the top of the cap beam, and the side formwork is assembled as a whole using bamboo plywood. After the formwork is assembled, the cap beam concrete is poured and cured;

[0021] S6. When the concrete strength of the cap beam reaches 85%, the transverse middle prestressed steel strands of the cap beam are tensioned first. Before tensioning the prestressed steel strands, weighting measures are taken to balance or offset the upward uplift force caused by the tensioning force on the existing tunnel. Then the transverse middle prestressed steel strands are tensioned symmetrically. After tensioning, pipeline grouting is carried out. At this time, the deformation of the existing tunnel is monitored simultaneously.

[0022] S7. After the grouting strength of the transverse middle prestressed steel bundle pipe of the cap beam reaches 100% and it is ensured that there is no continuous deformation of the tunnel, the upper and lower transverse prestressed steel bundles of the cap beam are tensioned, and the weight is gradually removed after the tensioning is completed;

[0023] S8. Consolidation of cap beam and pedestal: Cast the post-cast strip between the pedestal and the cap beam immediately 28 days after the cap beam is cast. Roughen the base surface of the post-cast strip at the pedestal before the cap beam is constructed. The post-cast strip adopts self-leveling shrinkage compensation concrete. Concrete pouring is carried out through the grouting holes pre-buried at the bottom of the cap beam. The pre-buried pipe adopts PVC pipe with a diameter of 5 cm. A total of 8 locations are set at each post-cast strip node. Grouting is completed when viscous slurry emerges from each pre-buried pipe opening.

[0024] S9. When the concrete strength of the cap beam and post-cast strip reaches more than 90% of the design strength grade, the vertical unbonded prestressed tendons are tensioned. After the tensioning is completed, all prestressed tensioning grooves are closed.

[0025] Preferably, in step S2, before tying the reinforcement at the bottom of the pedestal, the position of each steel rod is marked with red paint. After the reinforcement at the bottom of the pedestal is laid and firmly positioned, the fixed-end positioning ribs are installed according to the red paint markings. The positioning ribs and the bottom plate force-bearing reinforcements are first connected by tying. After the position of the positioning ribs is confirmed to be correct, spot welding is performed for reinforcement. The end of the fixed-end steel rod is at least 6 cm away from the outside of the anchor pad. The anchor nut is first tightened into place at the fixed end, and then the anchor baffle is installed, and finally the anchor nut is locked.

[0026] Preferably, in step S5, a fixing device is installed at the fixed end of the vertical unbonded prestressed steel rod, the fixing device includes a channel steel, a long strip hole is opened on the channel steel, the length direction of the long strip hole is along the longitudinal direction of the bridge, the channel steel spans the templates on both sides of the cap beam, and is connected to the templates on both sides by L-shaped bolts respectively, and the vertical unbonded prestressed steel rod passes through the long strip hole and is connected to the nut.

[0027] Preferably, in step S9, when tensioning the vertical unbonded prestressed steel rod, a prestressed steel rod tensioning bracket arranged outside the slot is provided, including a bracket plate, an adjusting screw, an adjusting nut, a movable handle, and a suspension hook, so that the tensioning bracket is optimized from inside the slot to outside the slot, thereby reducing the diameter of the tensioning end of the jack in the slot.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. In view of the technical problem that the existing cap beam structure system design and its construction method are not suitable for crossing existing tunnels with small clearance, the invention of setting the bridge cap beam directly on the pedestal simplifies the bridge structure system and reduces the joint processing during the construction process, thereby reducing the structural deformation and stress concentration caused by loose connection, thereby reducing the impact on the existing tunnel;

[0030] 2. A new structural system conversion for large-span wide cap beams with small clearance over existing tunnels was invented. In the initial stage, the temporary rubber bearings set on the upper part of the pedestal are used as temporary vertical force transmission structures to absorb and disperse the vibrations generated by the dynamic loads in the initial stage of bridge construction, and adapt to the small deformations that may occur in the large-span wide cap beams in the initial stage due to factors such as temperature changes, concrete shrinkage, and load effects; in the middle stage, the transverse prestressed steel strands of the large-width wide cap beams are tensioned in stages and equipped with weight-bearing measures to reduce the deformation of the tunnel; in the final stage, the non-bonded prestressing technology and the post-casting belt technology are combined as the permanent structural support system for the large-span wide cap beam in the later stage, which increases the stability of the cap beam itself and the connection between it and the pedestal, improves the ductility and seismic resistance of the concrete of the large-span wide bridge cap beam, and ensures that the structure can better withstand the load during long-term use, and improves durability and safety. The new structural system provided by the present invention is reasonably designed, ensures the stability of the large-span wide bridge cap beam, and minimizes the impact of the large-span wide cap beam on the existing tunnel.

[0031] 3. In order to solve the technical difficulties in constructing a large-span and wide cap beam structure with a small clearance over an existing tunnel, three rows of grouting holes are set between the pile foundation and the existing tunnel, which improves the overall stability of the stratum section around the tunnel and reduces the interference of the pile foundation construction on the tunnel; geotextile + graded crushed stone are set on the tunnel roof as a buffer layer to provide structural protection for the tunnel roof and reduce the impact of the cap beam construction process on the existing tunnel; a fixing device is set at the tensioning end of the vertical unbonded prestressed steel rod to solve the problem that the vertical unbonded prestressed steel rod is prone to bending, breakage and other problems that affect the prestress during concrete pouring; a new type of tensioning bracket outside the slot is set on the top of the cap beam, which effectively solves the problem of difficulty in tensioning of the traditional coaxial sleeve bracket when the tensioning slot space is insufficient, realizes normal tensioning when the tensioning slot space is insufficient, and ensures that the force system and prestressing tensioning period of the cast-in-place structure are not affected.

[0032] The large-span and wide-width bridge cap beam structural system and its construction method for crossing an existing tunnel with a small clearance described in the present invention, and other advantages, objectives and features of the present invention will be reflected in part through the following description, and will also be understood by technicians in this field through research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0034] Figure 1 This is the construction process flow chart of a large-span wide cap beam with a small clearance span over an existing tunnel;

[0035] Figure 2 It is a structural system diagram of a large-span wide bridge cap beam that crosses an existing tunnel;

[0036] Figure 3 It is an elevation view of a large-span wide bridge cap structure that spans over an existing tunnel;

[0037] Figure 4 It is a plan view of a large-span wide bridge cap structure that spans over an existing tunnel;

[0038] Figure 5 It is the arrangement diagram of vertical unbonded prestressed steel bars;

[0039] Figure 6 It is a schematic diagram of vertical unbonded prestressed steel rod anchorage;

[0040] Figure 7 It is a schematic diagram of the installation and fixing device of the vertical unbonded prestressed steel rod;

[0041] Figure 8 It is a schematic diagram of vertical unbonded prestressed steel rod tensioning;

[0042] Fig. 9 It is a plan view of the tensioned flat plate support arranged outside the slot;

[0043] Fig.10 It is the plan layout of deep hole grouting between pile foundation and existing tunnel.

[0044] In the figure, 1, pile foundation, 11, deep drilling, 2, existing tunnel, 3, cap, 31, vertical unbonded prestressed steel rod, 32, vertical unbonded prestressed steel rod fixed end, 321, fixed end anchor nut, 322, fixed end anchor baffle, 323, fixed end anchor nut, 324, fixed end anchor pad, 325, fixed end spiral reinforcement, 326, fixed end positioning steel bar, 33, support pad stone, 4, rubber temporary support, 5, buffer layer, 51, geotextile, 52, graded crushed stone, 53, steel mesh, 54, C20 concrete, 6, cap beam, 61, grouting hole, 62, vertical unbonded prestressed steel rod tensioning end, 621, tensioning end anchor nut, 622 , tensioning end anchor baffle, 623, tensioning end anchor nut, 624, tensioning end anchor pad, 625, tensioning end spiral reinforcement, 626, tensioning end positioning steel bar, 63, transverse prestressed steel bundle, 631, transverse middle prestressed steel bundle, 632, transverse upper and lower prestressed steel bundle, 64, water tank, 65, tensioning plate bracket, 651, tensioning hole, 652, adjusting screw, 653, adjusting nut, 654, moving handle, 655, suspension hook, 66, jack, 67, locking handle, 68, tensioning rod, 69, vertical unbonded prestressed steel bar installation and fixing device, 7, post-casting strip, 71, steel mesh at the post-casting strip, 72 self-leveling shrinkage compensation concrete. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the embodiments.

[0046] Reference Figures 1 to 10 The present invention provides a large-span and wide-width cap beam structural system for crossing an existing tunnel with a small clear distance, comprising a pile foundation 1, a cap 3, a buffer layer 5 and a cast-in-place prestressed cap beam 6, wherein the cap is arranged on the pile foundation; the cast-in-place prestressed cap beam 6 is innovatively directly arranged on the cap; a rubber temporary bearing 4 is installed on the cap as a temporary vertical force transmission structure; a vertical unbonded prestressed steel rod 31 is arranged in the cap, and the vertical unbonded prestressed steel rod passes through the cap and extends into the cast-in-place prestressed cap beam; transverse prestressed steel strands are arranged in the cast-in-place prestressed cap beam; a post-cast strip 7 for system conversion is reserved between the cast-in-place prestressed cap beam and the cap.

[0047] In the present invention, the minimum horizontal clearance requirement is ensured to be met between the bridge pile foundation and the existing tunnel 2 structure; the pedestals are arranged on both sides of the existing tunnel, and both ends of the cast-in-place prestressed cap beam fall directly on the two pedestals, with the middle portion suspended in the air and spanning the existing tunnel.

[0048] In addition, the overlapping area between the pedestal and the cast-in-place prestressed cap beam is simulated as a rectangular column, the force-bearing system connecting the pedestal and the cast-in-place prestressed cap beam is simulated as a rectangular column connected to the pile foundation, and the vertical unbonded prestressed steel rods are arranged within the range of the rectangular column.

[0049] Secondly, the pedestal is simulated as a rigid arm, and the maximum bending moment of the pile top when the cap beam and the pedestal are fixedly connected in the transverse and longitudinal directions is extracted. The maximum bending moment of the pile top is divided into the bending moment of the pile top under the basic load combination and the bending moment of the pile top under the frequently encountered load combination.

[0050] In the present invention, the basic load combination is a combination of the permanent action design value effect and the variable action design value effect, and the combined effect expression is:

[0051]

[0052] In formula 1: Sud is the effect combination design value of the basic combination of actions under the ultimate limit state of bearing capacity; γ0 is the structural importance factor, and the design safety levels of level 1, level 2 and level 3 are 1.1, 1.0 and 0.9 respectively. γGi and QGik are the partial coefficients and standard values ​​of the i-th permanent effect; γQ1 and Q1k are the partial coefficients and standard values ​​of the vehicle load effect (including impact force and centrifugal force), γQ1=1.4; γQj and Qjk are the partial coefficients and standard values ​​of other variable effects except vehicle load (including impact force and centrifugal force), wind load: γQj=1.1, others: γQj=1.4; ψc is the combination coefficient of other variable effects except vehicle load effect, and the combination coefficient of other variable effects except vehicle load (including impact force and centrifugal force) is 0.75.

[0053] In addition, the frequent combination is a combination of the effect of the permanent action standard value, the frequent value of the vehicle load, and the quasi-permanent value of other variable actions. The expression of the combined effect is:

[0054]

[0055] In formula 2, Sfd is the design value of the frequent combined effect of the action; ψf1 is the frequent value coefficient of the vehicle load (ignoring the impact effect), which is taken as 0.7.

[0056] The present invention further calculates the vertical structural reinforcement within the rectangular column range and verifies whether the crack width meets the requirements. The vertical unbonded prestressed steel bars are arranged according to the principle of equal substitution based on the number of vertical structural reinforcements. The cap beam is verified as a Class A prestressed concrete member. According to the second article of 6.1.2 of the "Design Specifications for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts", Class A prestressed concrete members may have tensile stress on the tensile edge of the controlled positive section under frequent action combinations. According to σ pt ≤0.7ftk To control, σ pt is the tensile stress, f tk is the standard value of concrete axial tensile strength. The vertical unbonded prestressed steel bars are arranged according to σ con ×A p ≥f sd ×A s Perform verification, where σ con The controlled stress value of the vertical unbonded prestressed steel bar under the steel anchor is A p Total cross-sectional area of ​​the prestressed steel bar, f sd is the design value of tensile strength of ordinary steel bars, A s It is the total cross-sectional area of ​​ordinary steel bars.

[0057] Preferably, the bottom of the cap is equipped with a vertical unbonded prestressed steel bar fixed end 32, and the fixed end components are, from bottom to top, anchor nut, anchor baffle, anchor nut, anchor pad and spiral reinforcement, and the vertical unbonded prestressed steel bar anchor pad is connected to the cap common reinforcement through the positioning reinforcement. The top surface of the cap beam is equipped with a vertical unbonded prestressed steel bar tensioning end 62, and the tensioning end components are, from bottom to top, spiral reinforcement, anchor pad, anchor nut, anchor baffle and anchor nut, and the vertical unbonded prestressed steel bar anchor pad is connected to the cap beam common reinforcement through the positioning reinforcement.

[0058] The construction stages in the present invention are as follows: Construction stage one, construct the pile foundation and the pedestal, reserve the rebar insertion hole when casting the pedestal, set a fixed rubber bearing at one end of the pedestal and a sliding rubber bearing at the other end, then cast the cap beam, when the cap beam concrete reaches 85% of the design strength, the cap beam is placed on the rubber bearing, at this time the cap beam structure is simply supported, and the constant load only considers the deadweight of the cap beam; Construction stage two, before tensioning the transverse prestressed steel bundle of the cap beam, take appropriate weighting measures to balance or offset the upward uplift force generated by the tensioning force on the existing tunnel, then symmetrically tension the transverse middle prestressed steel bundle, after the tensioning is completed Pipe grouting is carried out, and the deformation of the existing tunnel is monitored simultaneously; in the third construction phase, after the grouting strength of the transverse middle prestressed steel bundle pipe of the cap beam reaches 100% and it is ensured that the tunnel has no continuous deformation, the upper and lower transverse prestressed steel bundles of the cap beam are tensioned, and the weight is gradually removed after the tensioning is completed; in the fourth construction phase, the post-cast strip concrete for system conversion at the connection between the pedestal and the cap beam is poured, and the concrete strength of the cap beam and the post-cast strip reaches more than 90% of the design strength grade, and the vertical unbonded prestressed steel bars are tensioned. At this time, the structural form of the cap beam is changed from simply supported to rigid frame, and the constant load considers the self-weight of the cap beam, the upper structure load and the second phase load, etc.

[0059] The construction method of the present invention is described in detail as follows:

[0060] S1: After the pile foundation construction is completed, the pedestal is set up. Before the pile foundation construction, three rows of deep boreholes 11 are set up between the pile foundation 1 and the existing tunnel 2 for grouting. Cement-water glass slurry is evenly injected into the soil from the grouting hole to form a soil with high strength and good stability, which prevents the tunnel structure from being disturbed and effectively protects the safety and stability of the existing tunnel. The first row of grouting holes is 1m away from the tunnel edge, with a hole spacing of 0.5m. The depth of each grouting hole is 15m, the single hole diameter is 0.12m, and the row spacing is 2m. The construction of pile foundation 1 adopts the full-swing drilling rig full-casing follow-up construction process;

[0061] S2: While tying the steel bars of the cap, install the embedded parts of the cap. The embedded parts of the cap include vertical unbonded prestressed steel bars and support pad stone steel bars. The vertical unbonded prestressed steel bars are embedded and positioned before the upper steel bars of the cap are closed. Specifically, the bottom of the vertical unbonded prestressed steel bar 33 is connected to the fixed end 32 of the vertical unbonded prestressed steel bar at the bottom of the cap 3. From bottom to top, they are the fixed end anchor nut 321, anchor baffle 322, fixed end anchor nut 323, fixed end anchor pad 324 and fixed end spiral reinforcement 325. The fixed end anchor pad 324 is connected to the ordinary steel bars of the cap 3 through the fixed end positioning reinforcement 326. The vertical unbonded prestressed steel bar 33 is embedded and positioned before the upper steel bars of the cap 3 are closed, and the steel bars of the support pad 34 are embedded after the steel bar skeleton of the cap 3 is tied. Before the steel bars at the bottom of the cap 3 are tied, the position of each vertical unbonded prestressed steel bar 33 is marked with red paint. After the steel bars at the bottom of the cap 31 are laid and firmly positioned, the fixed end positioning steel bars 326 of the vertical unbonded prestressed steel bar are positioned and installed according to the red paint markings. The fixed end positioning steel bars 326 and the bearing steel bars of the bottom plate of the cap 3 are first connected by binding. After the position of the fixed end positioning steel bars 326 is confirmed to be correct, spot welding reinforcement is performed. The top of the fixed end positioning steel bars 326 needs to be uniformly leveled to ensure that the fixed end anchor pad 324 is level. The end of the vertical unbonded prestressed steel bar 33 of the cap fixed end 32 is at least 6 cm away from the outside of the fixed end anchor pad 324, that is, the end exceeds the fixed end anchor nut 321 by at least 1 cm. First tighten the fixed end anchor nut 323 in place, then install the anchor baffle 322, and finally lock the fixed end anchor nut 321. Before pouring concrete on the cap 3, check whether the embedded vertical unbonded prestressed steel rods 33, the support pad stone 34 steel bars and the steel mesh dowel bars of the post-casting belt 7 are installed in place one by one. After meeting the requirements, pour concrete;

[0062] S3: Install the temporary rubber bearing. After the concrete pouring of the cap 3 is completed, install the temporary rubber bearing 4, with a sliding bearing at one end and a fixed bearing at the other end;

[0063] S4: Before constructing the cap beam 6, a buffer layer 5 is set according to the vertical distance between the cap beam 6 and the top plate of the existing tunnel 2. The buffer layer 5 is made of geotextile 51 + graded crushed stone 52. The graded crushed stone 52 needs to be compacted layer by layer and compacted by a small compacting machine. A steel mesh 53 is distributed on the graded crushed stone 52, and C20 concrete 54 is poured as the bottom formwork of the cap beam 6;

[0064] S5: cap beam construction, cap beam reinforcement binding and transverse prestressed beam installation, vertical unbonded prestressed steel bar tensioning end is set at the top of the cap beam, the side formwork is assembled as a whole with bamboo plywood, and the cap beam concrete is poured and maintained after the formwork is assembled. Before the construction of the cap beam 6, the base surface of the post-cast strip 7 is roughened, and then the cap beam 6 is constructed, including binding the cap beam 6 reinforcement, installing the transverse prestressed steel beam 63, pre-buried grouting holes 61 at the bottom of the cap beam 6, and vertical unbonded prestressed steel bar tensioning end 62. The tensioning end 62 components are tensioning end spiral reinforcement 625, tensioning end anchor pad 624, tensioning end anchor nut 623, tensioning end anchor baffle 622 and tensioning end anchor nut 621 from bottom to top. The tension end anchor pad 624 is connected to the common steel bars of the cap beam 6 through the tension end positioning steel bars 626. The vertical unbonded prestressed steel bar 31 is checked for verticality by the vertical unbonded prestressed steel bar installation fixture 69. After the verification, the cap beam 6 concrete is poured and maintained. The vertical unbonded prestressed steel bar fixed end is installed with a fixture, which includes a channel steel, and a long strip hole is opened on the channel steel. The length direction of the long strip hole is along the longitudinal direction of the bridge. The channel steel spans the templates on both sides of the cap beam and is connected to the templates on both sides by L-shaped bolts. The vertical unbonded prestressed steel bar passes through the long strip hole and is connected to the nut to ensure the verticality of the vertical unbonded prestressed steel bar and ensure the quality and safety of the prestressed construction.

[0065] S6: When the concrete strength of the cap beam 6 reaches 85%, the transverse middle prestressed steel strand 631 of the cap beam 6 is tensioned first. Before tensioning the prestressed steel strand 631, appropriate weighting measures can be taken to balance or offset the upward uplift force caused by the tensioning force on the existing tunnel. Taking the weighted water tank 64 as an example, before the cap beam 6 is tensioned, the water tank 64 is gradually filled so that the weight of the water in the water tank 64 can balance or offset the upward uplift force caused by the tensioning force on the tunnel 2. The filling process should be carried out slowly in order to monitor the deformation of the existing tunnel 2. According to the monitoring data, the water level in the water tank 64 is adjusted when necessary to optimize the weighting effect; then the transverse middle prestressed steel strand 632 is tensioned symmetrically, and after the tensioning is completed, the pipeline is grouting is carried out, and the deformation of the existing tunnel 2 is monitored synchronously at this time;

[0066] S7: After the grouting strength of the transverse middle prestressed steel bundle 632 reaches 100% and it is ensured that the tunnel 2 has no continuous deformation, the upper and lower transverse prestressed steel bundles 633 of the cap beam are tensioned. After the tensioning is completed, the water tank 64 weight is gradually removed; after the tensioning and grouting of the cap beam 6 is completed, first clean the bottom mold of the cap beam 6 in the post-casting strip 7, and then use a high-pressure water gun to rinse the inside of the post-casting strip 7 to ensure that the inside is clean and free of debris. The steel mesh 71 of the post-casting strip 7 passes through the support cushion stone 34. Part of the steel mesh 71 is constructed first when the support cushion stone 33 is constructed, and the rest is tied and positioned before the concrete construction of the post-casting strip 7;

[0067] S8: Consolidate the cap beam 6 and the pedestal 3. After the cap beam 6 is cast, immediately cast the post-casting strip 7 for system conversion between the pedestal 3 and the cap beam 6 28 days after the cap beam 6 is cast. The post-casting strip 7 for system conversion uses self-leveling shrinkage compensation concrete 72, which is cast through the grouting hole 61 pre-buried at the bottom of the cap beam 6. The pre-buried pipe uses a PVC pipe with a diameter of 5 cm. There are 8 nodes of the post-casting strip 7 for system conversion. The grouting is completed when the viscous slurry emerges from each pre-buried pipe opening;

[0068] S9: After the concrete strength of the cap beam 6 and the post-cast strip 7 reaches more than 90% of the design strength grade, the vertical unbonded prestressed steel rod 31 is tensioned. The vertical unbonded prestressed steel rod 31 is tensioned according to three-level loading and single-end one-time tensioning. The two ends of the same cap beam 6 are tensioned symmetrically. According to the principle of symmetry and tensioning from the inside to the outside, the vertical unbonded prestressed steel rods 31 at the four corners are tensioned first, which plays a role in limiting and fixing the consolidation nodes. The vertical unbonded prestressed steel rod 31 tensioning adopts the YGD-300-80 through-type jack 66. First, install the tensioning flat plate bracket 65, place the opening of the flat plate bracket 65 directly opposite the steel rod 31 to be tensioned, adjust the four corners of the flat plate adjustment nuts to ensure the level, and if the steel rod 31 is located on the side of the structure, use wire rope and hand winch to suspend and fix the flat plate bracket 65 through the suspension hook. The jack 66 is inserted as a whole. The jack 66 is provided with a self-locking device. The end thread of the prestressed steel rod 31 is connected through the tensioning rod 68. The locking handle 67 is rotated while applying stress to lock the anchor nut 623. Then the anchor baffle 622 is inserted from the ends of the two unbonded prestressed steel rods 33 at the same time. After the anchor baffle 622 is pushed to fit the outer side of the anchor nut 623, the anchor nut 621 is locked in turn. After the tensioning is completed, all the prestressed tensioning slots are closed. When tensioning the vertical unbonded prestressed steel rod, a prestressed steel rod tensioning bracket arranged outside the slot is provided, including a bracket plate, an adjusting screw, an adjusting nut, a movable handle, and a suspension hook. The tensioning bracket is optimized from inside the slot to outside the slot, reducing the diameter of the tensioning end of the jack in the slot, and realizing normal tensioning when the tensioning slot space is insufficient.

[0069] As above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A large-span wide cap beam structure system with a small clearance spanning over an existing tunnel, characterized by: It includes a pile foundation, a cap, a buffer layer and a cast-in-place prestressed cap beam. The cap is arranged on the pile foundation, and the minimum horizontal clearance requirement is met between the pile foundation and the existing tunnel structure; the cast-in-place prestressed cap beam is arranged on the cap, and the cap is arranged on both sides of the existing tunnel. The two ends of the cast-in-place prestressed cap beam directly fall on the two caps, and the middle is suspended in the air across the existing tunnel; a temporary rubber bearing is installed on the cap as a temporary vertical force transmission structure; vertical unbonded prestressed steel bars are arranged in the cap, and the vertical unbonded prestressed steel bars pass through the cap and extend into the cast-in-place prestressed cap beam. The arrangement of the vertical unbonded prestressed steel bars is carried out according to the principle of equal replacement of the number of vertical structural reinforcements; transverse prestressed steel strands are arranged in the cast-in-place prestressed cap beam; a post-cast strip for system conversion is reserved between the cast-in-place prestressed cap beam and the cap.

2. The large-span wide cap beam structure system with a small clearance spanning over an existing tunnel according to claim 1 is characterized in that: The overlapping area between the pedestal and the cast-in-place prestressed cap beam is simulated as a rectangular column, the force bearing system connecting the pedestal and the cast-in-place prestressed cap beam is simulated as a rectangular column connected to the pile foundation, and the vertical unbonded prestressed steel rods are arranged within the range of the rectangular column.

3. A large-span wide cap beam structure system with a small clearance spanning over an existing tunnel, characterized by: The cap is simulated as a rigid arm, and the maximum bending moment of the pile top in the transverse and longitudinal directions when the cap beam and the cap are fixedly connected is extracted. The maximum bending moment of the pile top is divided into the bending moment of the pile top under the basic load combination and the bending moment of the pile top under the frequent load combination. The basic load combination is a combination of the permanent action design value effect and the variable action design value effect. The combined effect expression is: Where: Sud is the effect combination design value of the basic combination of actions under the ultimate limit state of bearing capacity; γ0 is the structural importance coefficient, γGi and QGik are the partial coefficients and standard values ​​of the i-th permanent action effect; γQ1 and Q1k are the partial coefficients and standard values ​​of the vehicle load effect; γQj and Qjk are the partial coefficients and standard values ​​of other variable action effects except the vehicle load; ψc is the combination coefficient of other variable action effects except the vehicle load effect.

4. A large-span wide cap beam structure system with a small clearance spanning over an existing tunnel, characterized by: The frequently encountered load combination is a combination of the permanent action standard value effect, the automobile load frequent value, and other variable action quasi-permanent values. The combined effect expression is: Where: Sfd is the design value of the frequent combined effect of actions; ψf1 is the frequent value coefficient of the vehicle load (ignoring the impact effect).

5. A large-span wide cap beam structure system with a small clearance spanning over an existing tunnel, characterized by: The cap beam is verified as a Class A prestressed concrete member. The Class A prestressed concrete member has tensile stress on the tensile edge of the positive section under the frequently encountered combination of actions. pt ≤0.7f tk To control, σ pt is the tensile stress, f tk is the standard value of concrete axial tensile strength, and the vertical unbonded prestressed steel bars are arranged according to σ con ×A p ≥f sd ×A S Perform verification, where σ con The controlled stress value of the vertical unbonded prestressed steel bar under the steel anchor is A p Total cross-sectional area of ​​the prestressed steel bar, f sd is the design value of tensile strength of ordinary steel bars, A S It is the total cross-sectional area of ​​ordinary steel bars.

6. A large-span wide cap beam structure system with a small clearance spanning over an existing tunnel, characterized by: A vertical unbonded prestressed steel bar fixed end is installed at the bottom of the pedestal, and the fixed end components are, from bottom to top, an anchor nut, an anchor baffle, an anchor nut, an anchor plate and a spiral reinforcement. The vertical unbonded prestressed steel bar anchor plate is connected to the ordinary steel bars of the pedestal through positioning steel bars. A vertical unbonded prestressed steel bar tensioning end is installed on the top surface of the cap beam, and the tensioning end components are, from bottom to top, a spiral reinforcement, an anchor plate, an anchor nut, an anchor baffle and an anchor nut. The vertical unbonded prestressed steel bar anchor plate is connected to the cap beam steel bars through positioning steel bars.

7. A construction method, comprising the large-span wide cap beam structure system with a small clearance spanning over an existing tunnel as claimed in claim 1, characterized in that: The steps include: S1. After the pile foundation construction is completed, the cap is set up: Before the pile foundation construction, three rows of grouting holes are set between the pile foundation and the existing tunnel structure, and cement water glass slurry is evenly injected into the soil from the grouting holes. The first row of grouting holes is 1m away from the tunnel edge, with a hole spacing of 0.5m. The depth of each grouting hole is 15m, the single hole diameter is 0.12m, and the row spacing is 2m. The pile foundation construction adopts the full-swing drilling rig full-casing follow-up construction process; S2. While tying the cap reinforcement, install the cap embedded parts: the cap embedded parts include vertical unbonded prestressed steel bars and support pad stone reinforcement. The vertical unbonded prestressed steel bars are embedded and positioned before the upper reinforcement of the cap is closed, and the support pad stone reinforcement is embedded after the cap reinforcement skeleton is tied; install the cap formwork, and pour the cap concrete and support pad stone concrete; S3. Install temporary rubber bearings: one end uses a sliding bearing and the other end uses a fixed bearing; S4. Before constructing the cap beam, set the cap beam bottom formwork above the tunnel top plate according to the vertical distance between the cap beam and the tunnel top plate: set a buffer layer above the tunnel top plate, lay steel mesh on the graded crushed stone, and pour C20 concrete as the cap beam bottom formwork; S5, cap beam construction, cap beam reinforcement binding and transverse prestressed beam installation: a vertical unbonded prestressed steel bar tensioning end is set at the top of the cap beam, and the side formwork is assembled as a whole using bamboo plywood. After the formwork is assembled, the cap beam concrete is poured and cured; S6. When the concrete strength of the cap beam reaches 85%, the transverse middle prestressed steel strands of the cap beam are tensioned first. Before tensioning the prestressed steel strands, weighting measures are taken to balance or offset the upward uplift force caused by the tensioning force on the existing tunnel. Then the transverse middle prestressed steel strands are tensioned symmetrically. After tensioning, pipeline grouting is carried out. At this time, the deformation of the existing tunnel is monitored simultaneously. S7. After the grouting strength of the transverse middle prestressed steel bundle pipe of the cap beam reaches 100% and it is ensured that there is no continuous deformation of the tunnel, the upper and lower transverse prestressed steel bundles of the cap beam are tensioned, and the weight is gradually removed after the tensioning is completed; S8. Consolidation of cap beam and pedestal: Cast the post-cast strip between the pedestal and the cap beam immediately 28 days after the cap beam is cast. Roughen the base surface of the post-cast strip at the pedestal before the cap beam is constructed. The post-cast strip adopts self-leveling shrinkage compensation concrete. Concrete pouring is carried out through the grouting holes pre-buried at the bottom of the cap beam. The pre-buried pipe adopts PVC pipe with a diameter of 5 cm. A total of 8 locations are set at each post-cast strip node. Grouting is completed when viscous slurry emerges from each pre-buried pipe opening. S9. When the concrete strength of the cap beam and post-cast strip reaches more than 90% of the design strength grade, the vertical unbonded prestressed tendons are tensioned. After the tensioning is completed, all prestressed tensioning grooves are closed.

8. A construction method according to claim 2, characterized in that: In step S2, before tying the reinforcement at the bottom of the pedestal, use red paint to mark the position of each steel rod. After the reinforcement at the bottom of the pedestal is laid and firmly positioned, the fixed-end positioning reinforcement is installed according to the red paint marking. The positioning reinforcement and the bottom plate force-bearing reinforcement are first connected by binding. After the position of the positioning reinforcement is confirmed to be correct, spot welding is performed for reinforcement. The end of the fixed-end steel rod is at least 6 cm away from the outside of the anchor pad. First, tighten the anchor nut at the fixed end into place, then install the anchor baffle, and finally lock the anchor nut.

9. A construction method according to claim 2, characterized in that: In step S5, a fixing device is installed at the fixed end of the vertical unbonded prestressed steel rod, and the fixing device includes a channel steel, on which a long strip hole is opened. The length direction of the long strip hole is along the longitudinal direction of the bridge. The channel steel spans the templates on both sides of the cap beam and is connected to the templates on both sides by L-shaped bolts. The vertical unbonded prestressed steel rod passes through the long strip hole and is connected to the nut.

10. A construction method according to claim 2, characterized in that: In step S9, when tensioning the vertical unbonded prestressed steel rod, a prestressed steel rod tensioning bracket arranged outside the slot is provided, including a bracket plate, an adjusting screw, an adjusting nut, a movable handle, and a suspension hook, so that the tensioning bracket is optimized from inside the slot to outside the slot, thereby reducing the diameter of the tensioning end of the jack in the slot.

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