Box-shaped bridge structure and construction method thereof

Abstract

The application relates to the technical field of box-shaped bridges, in particular to a box-shaped bridge structure which comprises a box body used for being installed below an existing line, the box body is a prefabricated part, at least two sections of the box body are spliced and fixedly connected with each other, a supporting pile for supporting the box body is arranged below the box body, a pushing device for placing and moving the box body is arranged on the supporting pile, a pouring hole is arranged in the lower bottom surface of the box body, the pouring hole corresponds to the end of the supporting pile and is used for taking out the pushing device, and a post-poured bottom plate is formed by pouring concrete from the pouring hole and extending into the pouring hole. The application also relates to a box-shaped bridge construction method. The application has the effect of reducing the construction difficulty of a box body with a large size.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of a box-shaped bridge, in particular to a box-shaped bridge structure and a construction method thereof. BACKGROUND

[0002] The box-shaped bridge is a bridge structure, and is usually constructed by jacking. The bridge body of the box-shaped bridge is in a frame form. The box-shaped bridge is usually arranged below an existing line, such as an existing railway, so as to reduce the influence on the normal operation of the existing line. The railway can be normally used, and then the frame form bridge body is jacked horizontally below the railway to complete the construction of the box-shaped bridge.

[0003] In the related art, a box-shaped bridge structure is disclosed, which comprises a box body. The box body is constructed by on-site pouring. A working pit is excavated on the ground, a sliding plate is constructed on the bottom surface of the working pit, an isolation layer is arranged on the sliding plate, a formwork for pouring the box body is erected, and the bottom plate part of the box body is poured first when the box body is poured. The working pit is located on one side of the existing line, and a back support is arranged on the side of the box body away from the existing line. The back support is inserted into a position below the ground. A plurality of hydraulic cylinders are arranged between the back support and the box body. One end of the hydraulic cylinder abuts against the back support, and the other end of the hydraulic cylinder abuts against one end of the box body. The box body is moved downward of the existing line by synchronous movement of the plurality of hydraulic cylinders. During the movement of the box body, the side of the box body away from the back support is excavated synchronously, so that the box body enters the lower side of the existing line. During the extension and retraction of the hydraulic cylinders, support blocks are arranged between the hydraulic cylinders and the back support. The length of the box body is usually greater than the width of the existing line, so that the box body can penetrate the lower side of the existing line.

[0004] However, the box body in the above structure is integrally poured to form a structure, which is difficult to construct when the existing line is wide and the box body structure is large. SUMMARY

[0005] In order to reduce the construction difficulty when the size of the box body is large, the application provides a box-shaped bridge structure and a construction method thereof.

[0006] The application provides a box-shaped bridge structure, which adopts the following technical scheme:

[0007] The box-shaped bridge structure comprises a box body, the box body is used for being installed below an existing line, the box body is a prefabricated part, and at least two sections of the box body are connected to each other and fixedly connected, a support pile for supporting the box body is arranged below the box body, a pushing device for placing support and moving the box body is arranged on the support pile, a pouring hole is formed in the lower bottom surface of the box body, the pouring hole corresponds to the end of the support pile, and the pouring hole is used for taking out the pushing device; and a post-poured bottom plate is formed by pouring concrete from the pouring hole, and the post-poured bottom plate extends into the pouring hole.

[0008] By adopting the technical scheme, when in use, the box body is formed by using a prefabricated part and at least two sections of the box body are connected to each other, the box body can enter one by one when being translated below the existing line, the box body is supported by the support pile, the pushing device arranged on the support pile translates the box body, the support pile is used for supporting the box body, the settlement of the box body in the later use process is reduced, the box body is assembled, the large work pit required when the box body is poured on site is reduced, the difficulty of construction of the box body with a large size is reduced, the post-poured bottom plate formed below the box body can connect the box body and the support pile, and the connection firmness of the box body and the support pile is further improved.

[0009] Preferably, the support pile comprises a base part and a support part, the diameter of the base part is greater than that of the support part, the base part is located below the support part, and a secondary grouting pipe for grouting cement slurry to the bottom of the support pile is arranged in the support pile, and the cement slurry flows into the bottom of the support pile through the secondary grouting pipe to form a modified soil layer.

[0010] By adopting the technical scheme, the diameter of the base part is greater than that of the support part, the support pile has a larger support surface, the secondary grouting pipe arranged at the bottom of the support pile can inject cement slurry to the bottom of the support pile, and the support capacity of the support pile is further improved by forming the modified soil layer.

[0011] Preferably, the lower end of the secondary grouting pipe is provided with a plurality of grouting pipes, the grouting pipes are arranged along the radial direction of the grouting pipe and are distributed in a scattering manner, a plurality of grouting holes are formed in the side wall of the grouting pipe and are uniformly distributed along the length direction of the grouting pipe, and the grouting holes are downwardly arranged.

[0012] By adopting the technical scheme, the grouting pipes are arranged along the radial direction and distributed in a scattering manner, the grouting pipes can be distributed below the support pile, and the hard modified soil layer below the support pile can be formed through the plurality of grouting holes.

[0013] Preferably, the existing line is provided with a support beam for temporarily supporting the existing line, the support beam is supported between the box through the arrangement of a pushing device, the pushing device comprises an intermediate body, a lifting hydraulic cylinder and a translation hydraulic cylinder, the lifting hydraulic cylinder is vertically arranged on the intermediate body, the translation hydraulic cylinder is horizontally arranged on the intermediate body, and the lifting hydraulic cylinder below the box and the lifting hydraulic cylinder above the box have opposite telescopic actions, and the translation hydraulic cylinder below the box and the translation hydraulic cylinder above the box have the same telescopic action.

[0014] By adopting the above technical scheme, the lifting hydraulic cylinder is vertically arranged, the translation hydraulic cylinder is horizontally arranged, the lifting hydraulic cylinder below the box and the lifting hydraulic cylinder above the box have opposite telescopic actions, thereby keeping the height of the support beam unchanged during the up-down movement of the box, and thereby keeping the safety when the vehicle passes through the existing line.

[0015] Preferably, the edge position of the upper end surface of the support pile is provided with a support ring, the middle of the support ring is formed with a placement groove for placing the pushing device; a plurality of notches are uniformly arranged on the circumference of the support ring, and the position of the notches is arranged for pouring concrete for the post-poured bottom plate.

[0016] By adopting the above technical scheme, the placement groove is arranged in the middle of the support ring for placing the pushing device, so that the upper end of the support ring can support the box, and the position of the notches is used for pouring the post-poured bottom plate, thereby further improving the connection strength between the support pile and the box through the position of the notches of the formed post-poured bottom plate.

[0017] Preferably, one end of the box is provided with a flange, the other end is provided with a groove, the flange is arranged along the inner edge of the box, the groove is used for cooperating with the flange of another box, a pre-tensioning bar is arranged between the adjacent two boxes, the pre-tensioning bar pulls the two boxes along the length direction of the box, a U-shaped bolt is arranged between the adjacent two boxes, and the U-shaped bolt penetrates the two boxes from the outer side of the box to the inner side of the box at the position of the flange.

[0018] By adopting the above technical scheme, the flange of one box is connected into the groove of another box, and the length direction of the two boxes is limited through the pre-tensioning bar, so that the connection strength of the two boxes spliced with each other is higher, and the U-shaped bolt is further installed to further reduce the disconnection of the two boxes.

[0019] Preferably, the existing line is provided with a slope protection pile on both sides, the slope protection pile is located at the connection between the box and the roadbed of the existing line, and the slope protection pile is arranged to be inclined downward and to the middle position of the existing line.

[0020] The slope protection pile strengthens the soil layer around the box body, reduces collapse in the construction process, improves construction safety, and transitions at the connection between the box body and the existing line roadbed, reducing uneven hard and soft roadbeds.

[0021] The application provides a box bridge construction method, which adopts the following technical scheme:

[0022] The box bridge construction method comprises the following steps: excavating working pits on both sides of an existing line, arranging a plurality of support piles along the length direction of a box body at the bottom of the working pit, placing a pushing device on the support piles, and hoisting a prefabricated box body on the pushing device, translating the box body downward of the existing line through the pushing device, arranging a plurality of support piles again as needed in the process of translation, hoisting another box body into the working pit to splice with the previous box body after one box body enters the existing line, and the translated box body penetrates through both sides of the existing line; then, a pouring hole is formed at the bottom of the box body, and a post-poured bottom plate is formed through the pouring hole.

[0023] Through the above technical scheme, the support piles are arranged along the length direction of the box body at the bottom of the working pit, the pushing device is placed on the support piles to install the box body again, the box body can be conveniently moved under the action of the pushing device, the construction difficulty of the box body in the moving process is reduced, a plurality of box bodies are spliced, the working pit caused by on-site fabrication of the box body is reduced, and thus unnecessary workload can be reduced.

[0024] Preferably, the support pile is arranged with a secondary grouting pipe inside during construction, cement slurry is injected from the secondary grouting pipe after the support pile is completed and solidified for at least 1 day, and the cement slurry is pressed into the soil gap below the support pile to form a modified soil layer.

[0025] Through the above technical scheme, the cement slurry is injected from the secondary grouting pipe after the support pile is completed and solidified for 1 day, so that the cement slurry can more easily enter the soil gap and the modified soil layer formed has a greater depth, and the support capacity of the support pile is improved.

[0026] Preferably, the pouring hole is positioned according to the position of the support pile when the pouring hole is formed, the pouring hole is formed directly above the upper end of the support pile, the pushing device is removed from the pouring hole, and a gap for the post-poured bottom plate to flow through is reserved at the upper end of the support pile.

[0027] Through the above technical scheme, the pouring hole is formed at the position corresponding to the support pile after measurement, the pushing device on the support pile is conveniently removed, and the post-poured bottom plate formed in the pouring hole can make the connection between the box body and the support pile more firm.

[0028] In summary, the application has at least one of the following beneficial technical effects:

[0029] 1. The box is formed by prefabricated parts and at least two sections are spliced together, and the box can enter one by one when translating under the existing line due to the splicing structure, and the box assembly can reduce the large work pit required when the box is cast on site, thereby reducing the difficulty of large box construction.

[0030] 2. The secondary grouting pipe arranged at the bottom of the support pile can inject cement slurry into the bottom of the support pile, thereby further improving the support capacity of the support pile by forming a modified soil layer.

[0031] 3. The length direction of the two boxes is limited by the pre-tensioning rib, so that the connection strength of the two spliced boxes is higher, and the U-shaped bolt is installed, thereby reducing the disconnection of the two boxes. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a schematic diagram of the overall structure of the embodiment of the present application;

[0033] Figure 2 is a schematic diagram of the installation position of the box of the embodiment of the present application;

[0034] Figure 3 is a schematic diagram of the upper end structure of the support pile of the embodiment of the present application;

[0035] Figure 4 is a schematic diagram of the arrangement position of the pushing device in the embodiment of the present application;

[0036] Figure 5 is a schematic diagram of the arrangement of the grouting pipe in the embodiment of the present application;

[0037] Figure 6 is a schematic diagram of the installation position of the U-shaped bolt in the embodiment of the present application.

[0038] BRIEF DESCRIPTION OF DRAWINGS 1, box; 11, pouring hole; 12, flange; 13, groove; 14, pre-tensioning rib; 15, through hole; 16, U-shaped bolt; 17, nut; 2, support pile; 21, support ring; 22, placement groove; 23, notch; 24, base part; 25, support part; 3, post-cast slab; 4, existing line; 5, pushing device; 51, middle body; 52, lifting hydraulic cylinder; 53, translation hydraulic cylinder; 6, support beam; 7, secondary grouting pipe; 71, grouting pipe; 72, grouting hole; 8, gravel layer; 81, sleeper; 9, slope protection pile. DETAILED DESCRIPTION

[0039] The following will be described in detail in combination with the accompanying Figures 1-6 The present application will be further described in detail.

[0040] The embodiment of the application discloses a box-shaped bridge structure, referring to Figure 1 and Figure 2 , comprising a box 1, the box 1 is located below an existing line 4, the existing line 4 is a railway, a plurality of boxes 1 are arranged along the extension direction of the box 1, two in the embodiment, the plurality of boxes 1 are all prefabricated in a factory and are spliced with each other at a construction site. The length of each box 1 can be arranged to be between 2m-2.5m. A plurality of support piles 2 are arranged below the box 1, the support piles 2 are vertically arranged, a post-cast floor 3 is arranged at the upper end of the support pile 2, the post-cast floor 3 is connected with the upper end of the support pile 2, the box 1 is located on the upper surface of the post-cast floor 3, and the upper surface of the box 1 is used for laying the existing line 4. Since the support pile 2 is buried below the box 1, the support pile 2 can provide support force for the box 1, and for a wet and soft foundation, the support pile 2 can reduce the sinking of the box 1, thereby ensuring the safety of the box-shaped bridge.

[0041] Referring to Figure 2 and Figure 3 , a support ring 21 is arranged at the edge position of the upper end surface of the support pile 2, the support ring 21 is an integral structure with the support pile 2, the middle position of the support ring 21 is a placing groove 22, the pushing device 5 for lifting and translating the box 1 is placed in the placing groove 22, a plurality of notches 23 are arranged on the support ring 21 and are spaced apart, and the plurality of notches 23 are distributed around the support pile 2 in the circumferential direction. The position of the notch 23 is used to pour concrete into the support ring 21 after the box 1 is jacked into the lower side of the existing line 4, so that the concrete reaches the lower side of the box 1 along the notch 23, and then the post-cast floor 3 is formed. A pouring hole 11 is arranged at the bottom of the box 1 and corresponds to the support pile 2. The pouring hole 11 needs to be moved to the lower side of the existing line 4, then the position of the pouring hole 11 is measured according to the arrangement position of the support pile 2, then the pouring hole 11 is drilled on the bottom plate of the box 1, and the pushing device 5 is exposed, the pushing device 5 is taken out from the pouring hole 11, after the pouring of the post-cast floor 3 is completed, the concrete in the pouring hole 11 is filled, so that the connection strength between the post-cast floor 3 and the box 1 is greater, and meanwhile the upper end of the support pile 2 can be connected with the box 1, and the translation of the box 1 at the upper end of the support pile 2 is reduced.

[0042] Referring to Figure 3 and Figure 4, in order to make the box 1 in the process of translation makes the existing line 4 more stable, the support beam 6 is arranged below the existing line 4, both ends of the support beam 6 can be located directly above the support pile 2. In construction, the support beam 6 crosses the existing line 4 from below, and the support pile 2 supports the support beam 6 when the box 1 does not enter below the support beam 6; when the box 1 enters below the support beam 6, another pushing device 5 is placed between the box 1 and the support beam 6, so that the lower surface of the pushing device 5 abuts against the upper surface of the box 1, and the upper surface of the pushing device 5 abuts against the lower surface of the support beam 6, so that the box 1 supports the support beam 6, so that the existing line 4 keeps normal vehicle traffic, reduces the line interruption caused by construction. The pushing device 5 comprises an intermediate body 51, a lifting hydraulic cylinder 52 and a translation hydraulic cylinder 53, the lifting hydraulic cylinder 52 is vertically arranged on the intermediate body 51, and the working direction of the lifting hydraulic cylinder 52 is vertical state, the translation hydraulic cylinder 53 is horizontally arranged on the intermediate body 51, so that the working direction of the translation hydraulic cylinder 53 is horizontal state. The translation hydraulic cylinder 53 in the pushing device 5 located in the placing groove 22 is used to abut against the lower surface of the box 1, and the translation hydraulic cylinder 53 in the pushing device 5 located below the support beam 6 is used to abut against the upper surface of the box 1. In operation, the lifting hydraulic cylinder 52 below the box 1 is first elongated, and the lifting hydraulic cylinder 52 above the box 1 is shortened, thereby lifting the box 1 upward, then the translation hydraulic cylinder 53 moves the box 1 horizontally along the length direction of the box 1, then the lifting hydraulic cylinder 52 places the box 1 downward on the support pile 2, the translation hydraulic cylinder 53 is reset without vehicle passing on the existing line 4, and the above process is repeated for multiple times, so that the box 1 is gradually translated to the position below the existing line 4.

[0043] Reference Figure 2 and Figure 5, the support pile 2 includes a foundation part 24 and a support part 25, the foundation part 24 is located below the support part 25, and the diameter of the foundation part 24 is larger than that of the support part 25, so that the foundation part 24 has a larger supporting bottom surface, which can improve the supporting capacity of the support pile 2 and reduce the downward movement of the support pile 2. Meanwhile, a secondary grouting pipe 7 is arranged in the support pile 2, the upper end of the secondary grouting pipe 7 is exposed from the upper end of the support pile 2, the lower end of the secondary grouting pipe 7 is provided with a plurality of grouting pipes 71, and the plurality of grouting pipes 71 are horizontally arranged on the bottom surface of the support pile 2. The grouting pipes 71 are arranged along the radial direction, and the plurality of grouting pipes 71 are distributed in a scattered manner. A plurality of grouting holes 72 are formed in the side wall of the grouting pipe 71, the grouting holes 72 are arranged downward, and the plurality of grouting holes 72 are uniformly distributed along the length direction of the grouting pipe 71. When the support pile 2 is poured, the grouting holes 72 are embedded in the soil, and after the support pile 2 is completed and solidified for at least 1 day, the secondary grouting pipe 7 is used to inject cement slurry under pressure, so that the cement slurry seeps into the soil through the grouting holes 72 of the grouting pipe 71, and at the same time, the cement slurry is extruded into the gap of the soil in a pressurized manner, so that the lower bottom surface of the support pile 2 forms a modified soil layer, which can further improve the supporting capacity of the support pile 2, thereby reducing the sinking of the box body 1.

[0044] Reference Figure 6 A flange 12 is arranged at one end of the box body 1, and a groove 13 is arranged at the other end. The flange 12 is arranged along the inner edge of the box body 1, and the flange 12 is used to fit into the groove 13 of another box body 1, so that the two box bodies 1 can withstand shear forces. A plurality of pre-tensioned bars 14 are arranged along the length direction of the box body 1, and the plurality of pre-tensioned bars 14 are located at the four corners of the box body 1. Through holes 15 are formed in the box body 1 for installing the pre-tensioned bars 14. In use, first, two box bodies 1 are relatively close to each other, then the pre-tensioned bars 14 are installed into the through holes 15, and then the two box bodies 1 are inserted into each other through the pre-tensioned bars 14, so that the plurality of box bodies 1 can be spliced with each other. For a wider existing line 4, during the construction of the box body 1, a work pit with a size only slightly larger than that of one box body 1 is formed, and then another box body 1 is hoisted into the work pit during the process of translating the box body 1 downward along the existing line 4, and a plurality of box bodies 1 are connected in sequence, thereby avoiding the need to form a large work pit for on-site production of a monolithic box body, which causes a large amount of construction. In order to improve the connection strength of two adjacent box bodies 1, a plurality of U-shaped bolts 16 are connected between the two box bodies 1. The U-shaped bolts 16 pass through the outside of the box body 1 into the inside of the box body 1 and are threadedly connected with nuts 17. The U-shaped bolts 16 pass through the flange 12, so that the U-shaped bolts 16 can penetrate the two box bodies 1 at the same time, thereby further improving the connection strength of the two box bodies 1 through the U-shaped bolts 16. During installation, the two box bodies 1 can be first brought close to each other through the pre-tensioned bars 14, and then the U-shaped bolts 16 are installed, so that the installation of the U-shaped bolts 16 is more convenient.

[0045] ReferenceFigure 1 After the box 1 is moved below the existing line 4, the upper surface of the box 1 is paved with the gravel layer 8 and the sleeper 81, so that the existing line 4 restores the normal bearing condition. The slope protection piles 9 are arranged at the connection between the box 1 and the roadbed of the existing line 4 and along the length direction of the existing line 4, and the slope protection piles 9 are arranged in multiple, and the slope protection piles 9 are arranged from the ground to the position in the middle of the existing line 4, so that the slope protection piles 9 strengthen the soil strength around the box 1, reduce the collapse in the construction process, improve the construction safety, and form a transition section at the connection between the box 1 and the roadbed of the existing line 4, and prevent the uneven hard and soft roadbed.

[0046] The embodiment also discloses a box-shaped bridge construction method for constructing the box-shaped bridge structure, which comprises the following steps: constructing slope protection piles 9 and support piles 2 on both sides of the existing line 4, the support piles 2 can be constructed by using the artificial hole digging pile method during construction, the support piles 2 are completed, and then the existing line 4 is supported, a support beam 6 is arranged below the existing line 4, both ends of the support beam 6 are supported by the support piles 2, meanwhile, a temporary beam is arranged on both sides of the existing line 4, so that the existing line 4 can be stably opened to traffic; then one side of the existing line 4 is excavated to form a working pit, the size of the working pit is at least greater than the size of one box body 1, at least two support piles 2 are constructed at the bottom of the working pit, the support piles 2 are located below the box body 1 to be placed, a pushing device 5 is placed on the upper surface of the support pile 2, then the box body 1 is lifted up by the pushing device 5 and translated along the length direction of the box body 1, after translation, the box body 1 is placed on the top end of the support pile 2, until the box body 1 moves below the support beam 6, another pushing device 5 is arranged between the support beam 6 and the box body 1, so that the multiple pushing devices 5 cooperate to gradually translate the box body 1 below the existing line 4, during the translation process, multiple support piles 2 can be arranged along the moving direction of the box body 1 to support the placement of the pushing device 5, since the pushing device 5 is arranged, the translation of the box body 1 is relatively convenient, and the multiple support piles 2 and the pushing device 5 make it easier to move the relatively long box body 1. When one box body 1 enters below the existing line 4, another box body 1 is hoisted and placed in the working pit, and the two box bodies 1 are spliced, during splicing, the two box bodies 1 are first abutted in place by the pre-tensioning rib 14, and then the U-shaped bolt 16 is installed, so that the two box bodies 1 are firmly connected, multiple box bodies 1 are spliced in turn until the existing line 4 is penetrated. Since the pushing device 5 pushes the box body 1 to translate from below the box body 1, the rear support that needs to be removed in the later stage is not constructed at one end of the box body 1, the construction difficulty is further reduced, and waste is reduced. When the box body 1 penetrates the existing line 4, the positions of the support piles 2 are measured at the inner bottom of the box body 1, a pouring hole 11 is drilled at the bottom of the box body 1, the pushing device 5 located at the upper end of the support pile 2 is taken out, and concrete is poured from the pouring hole 11, so that the post-poured bottom plate 3 is formed below the box body 1, the concrete of the post-poured bottom plate 3 is extended into the pouring hole 11, so that the box body 1 is firmly connected with the support pile 2, and then the gravel layer 8 and the sleeper 81 are laid on the box body 1 below the existing line 4, and the traffic conditions of the existing line 4 are restored.

[0047] The above are all preferred embodiments of the present application, and do not limit the protection scope of the present application, therefore: all equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A box bridge structure comprising a box (1) for installation under an existing line (4), characterized in that: The box (1) is a prefabricated part and at least two sections of the box (1) are connected to each other and fixedly connected, a support pile (2) for supporting the box (1) is arranged below the box (1), a pushing device (5) for placing support and moving the box (1) is arranged on the support pile (2), a pouring hole (11) is arranged on the lower bottom surface of the box (1), the pouring hole (11) corresponds to the end of the support pile (2), and the pouring hole (11) is used to take out the pushing device (5); a post-poured bottom plate (3) is formed by pouring concrete from the pouring hole (11) below the box (1), and the post-poured bottom plate (3) extends into the pouring hole (11); A support beam (6) for temporarily supporting the existing line (4) is arranged below the existing line (4), the support beam (6) and the box (1) are supported by arranging the pushing device (5) therebetween, the pushing device (5) comprises an intermediate body (51), a lifting hydraulic cylinder (52) and a translation hydraulic cylinder (53), the lifting hydraulic cylinder (52) is vertically arranged on the intermediate body (51), the translation hydraulic cylinder (53) is horizontally arranged on the intermediate body (51), and the lifting hydraulic cylinder (52) located below the box (1) and the lifting hydraulic cylinder (52) located above the box (1) have opposite extension actions, and the translation hydraulic cylinder (53) located below the box (1) and the translation hydraulic cylinder (53) located above the box (1) have the same extension action. An edge position of an upper end surface of the support pile (2) is provided with a support ring (21), a placing groove (22) for placing the pushing device (5) is formed in the middle of the support ring (21); a plurality of notches (23) are uniformly arranged on the circumference of the support ring (21), and the notches (23) are arranged at positions for pouring concrete for pouring the post-poured bottom plate (3).

2. A box girder structure according to claim 1, wherein: The support pile (2) comprises a base part (24) and a support part (25), the diameter of the base part (24) is greater than the diameter of the support part (25), the base part (24) is located below the support part (25), and a secondary grouting pipe (7) for grouting to the bottom of the support pile (2) is arranged in the support pile (2), cement slurry flows into the bottom of the support pile (2) through the secondary grouting pipe (7) and forms a modified soil layer.

3. A box girder structure according to claim 2, wherein: A plurality of grouting pipes (71) are arranged at the lower end of the secondary grouting pipe (7), the grouting pipes (71) are arranged along the radial direction of the grouting pipes (71) and are distributed in a scattering manner, a plurality of grouting holes (72) are arranged on the side wall of the grouting pipes (71), the grouting holes (72) are uniformly distributed along the length direction of the grouting pipes (71), and the grouting holes (72) are arranged downward.

4. A box girder structure according to claim 1, wherein: One end of the box (1) is provided with a flange (12), the other end is provided with a groove (13), the flange (12) is arranged along the inside edge of the box (1), the groove (13) is used for cooperating with the flange (12) of another box (1), and the pre-tensioning rib (14) is arranged between the two adjacent boxes (1), the pre-tensioning rib (14) pulls the two boxes (1) along the length direction of the box (1), the U-shaped bolt (16) is arranged between the two adjacent boxes (1), and the U-shaped bolt (16) penetrates the two boxes (1) from the outside of the box (1) to the inside of the box (1) at the position of the flange (12).

5. A box girder structure according to claim 1, wherein: The existing line (4) is provided with slope protection piles (9) on both sides, the slope protection piles (9) are located at the connection between the box (1) and the roadbed of the existing line (4), and the slope protection piles (9) are arranged inclined downward and to the middle position of the existing line (4).

6. A method for constructing a box girder bridge according to any one of claims 1 to 5, wherein: The working pit is excavated on both sides of the existing line (4), a plurality of support piles (2) are arranged along the length direction of the box (1) at the bottom of the working pit, the pushing device (5) is placed on the support piles (2), and the prefabricated box (1) is hung on the pushing device (5); the box (1) is translated downward of the existing line (4) through the pushing device (5), a plurality of support piles (2) are arranged again as needed in the process of translation, when one box (1) enters the lower side of the existing line (4), another box (1) is hoisted into the working pit and spliced with the previous box (1), until the translated box (1) penetrates the both sides of the existing line (4); then the pouring hole (11) is formed at the bottom of the box (1), and the concrete is poured through the pouring hole (11) to form the post-poured bottom plate (3).

7. The method of constructing a box girder bridge as claimed in claim 6 wherein: During the construction of the support pile (2), the secondary grouting pipe (7) is arranged in the support pile (2), the cement slurry is injected from the secondary grouting pipe (7) after the support pile (2) is completed pouring and solidified for at least 1 day, and the cement slurry is pressed into the soil gap below the support pile (2) to form a modified soil layer.

8. The method of constructing a box girder bridge as claimed in claim 7 wherein: When the pouring hole (11) is formed, the pouring hole (11) is positioned according to the position of the support pile (2), the pouring hole (11) is formed opposite to the upper end of the support pile (2), the pushing device (5) is taken out from the pouring hole (11), and a gap (23) for flowing through the post-poured bottom plate (3) is reserved at the upper end of the support pile (2).

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