Road and bridge transition section stepped pile plate structure, design method and construction method

Abstract

The invention relates to the technical field of road and bridge construction, in particular to a road and bridge transition section stepped pile plate structure, a design method and a construction method.The road and bridge transition section stepped pile plate structure is used for connecting a bridge abutment and a roadbed and comprises a transition pile foundation, a bearing plate and a transition block; the multiple transition pile foundations are arranged on the extension line, facing the roadbed, of the bridge abutment, and the multi-span bearing plate is fixed to the multiple transition pile foundations. N span bearing plates are sequentially arranged on the extension line, facing the roadbed, of the bridge abutment, and the upper surface of the first span bearing plate on the extension line, facing the roadbed, of the bridge abutment is flush with the lower bottom surface of the railway track plate; by means of the structure, the first-span bearing plate and the Nth-span bearing plate can evenly distribute borne force to the roadbed filling body and the transition pile foundation of the roadbed, sedimentation of the road and bridge transition section can be reduced, every two adjacent bearing plates are connected through the transition block, and the uniform transition performance of the road and bridge transition section can be enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of road and bridge construction. Specifically, it relates to a stepped pile - plate structure for road - bridge transition sections, as well as a design method and a construction method thereof. Background Art

[0002] High - speed railways require that the track structure has high smoothness. The transition section between the subgrade and the bridge is an important part of high - speed railways and has a significant impact on the smoothness of the line. Differential settlement is the main control factor for the smooth and comfortable operation of trains on the road - bridge transition section. Excessive differential settlement in the road - bridge transition section will pose a threat to the operation safety of high - speed railways.

[0003] In the prior art, a trapezoidal - inverted transition section is usually used to connect with the abutment, or a bearing - plate structure and a trapezoidal - inverted transition section are used together to connect with the abutment. Both transition - section forms have the problem of stiffness mutation due to the large difference between the structural form and the material, which will affect the safe operation and comfort of trains and are difficult to meet the requirements of higher train - operation speeds. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the transition form of the existing stepped pile - plate structure for road - bridge transition sections has the problems of stiffness mutation and differential settlement due to the large difference between the structural form and the material, which will affect the safe operation and comfort of trains.

[0005] To solve the above problems, the present invention proposes the following technical solutions: A stepped pile - plate structure for road - bridge transition sections, used to connect the abutment and the subgrade. The stepped pile - plate structure for road - bridge transition sections includes transition pile foundations, bearing plates, and transition blocks. A plurality of the transition pile foundations are arranged on the extension line of the abutment towards the subgrade, and multiple spans of the bearing plates are fixed on the plurality of transition pile foundations; The extension line of the abutment towards the subgrade includes N spans of the bearing plates arranged in sequence. The upper surface of the first - span bearing plate on the extension line of the abutment towards the subgrade is flush with the lower bottom surface of the railway track slab; the upper surface of the second - span bearing plate on the extension line of the abutment towards the subgrade is flush with the lower bottom surface of the foundation surface layer; the upper surface of the N - th span bearing plate on the extension line of the abutment towards the subgrade is flush with the lower bottom surface of the (N - 1) - th span bearing plate, and N≥2. The lower bottom surface of the N - th pile - plate is flush with the lower bottom surface of the subgrade filling body; Step corners are formed at the connection between the N - th span bearing plate and the subgrade filling body and at the connection between the N - th span bearing plate and the (N - 1) - th span bearing plate. The transition blocks are respectively arranged at a plurality of the step corners, and two side walls of the transition block are respectively connected to the vertical surface and the horizontal surface of the corresponding step corner.

[0006] The stepped pile - slab structure for the road - bridge transition section provided by the present invention has the following beneficial effects compared with the prior art, but is not limited to: The railway track slab is installed on the first - span bearing plate on the extension line of the abutment towards the subgrade direction. The upper surface of the N - th - span bearing plate on the extension line of the abutment towards the subgrade direction is flush with the lower bottom surface of the (N - 1) - th - span bearing plate, and N≥2. The transition block is arranged on the upper surface of the N - th - span bearing plate, and one side wall of the transition block is connected to the side wall of the (N - 1) - th - span bearing plate. This structure enables the first - span bearing plate and the N - th - span bearing plate to evenly distribute the forces they bear to the transition pile foundation, which is beneficial to reducing the settlement of the road - bridge transition section. Moreover, the adjacent two bearing plates are connected by the transition block, which is beneficial to strengthening the uniform transition of the stiffness of the overlying filling soil in the road - bridge transition section. The structure is relatively simple and the materials are relatively unified, which can effectively avoid the problem of stiffness mutation due to large differences between the structural form and materials, thereby improving the safe operation and comfort of trains and meeting the requirements of higher train operation speeds.

[0007] Preferably, the stepped pile - slab structure for the road - bridge transition section further includes geotextile. Geotextile is laid on the upper surface of each bearing plate except the first - span bearing plate.

[0008] Preferably, the stepped pile - slab structure for the road - bridge transition section further includes a surface layer of the roadbed bed and a filling layer. The railway track slab is laid on the geotextile of the first - span bearing plate, the surface layer of the roadbed bed is laid on the geotextile of the second - span bearing plate, and filling is laid on the geotextile of the third - span bearing plate and subsequent bearing plates.

[0009] Preferably, the surface layer of the roadbed bed is cast with graded crushed stone admixed with 5% cement.

[0010] The present invention also provides a construction method for the stepped pile - slab structure of the road - bridge transition section, which is used for constructing the stepped pile - slab structure of the road - bridge transition section as described above. This method includes the following steps: S1. First, determine the position of the N - th - span pile - slab bearing plate, and then sequentially determine the positions of the (N - 1) - th - span bearing plate, the (N - 2) - th - span bearing plate until the position of the first - span bearing plate; S2. Determine the mileage of the abutment, construct the abutment pile foundation and the abutment, and use graded crushed stone or C25 concrete to backfill and compact the abutment foundation pit; S3. Excavate steps, use the cut - and - fill of the cutting as filling to construct the back - fill area of the bridge, and the subgrade outside the bearing - plate structure section is filled with filling and is compacted layer by layer to the bottom surface of the N - th - span bearing plate; S4. Mark the position of the transition pile foundation, and then carry out the construction of the transition pile foundation and the construction from the first - span bearing plate to the N - th - span bearing plate; S5. Set the transition block at the step corner formed by the Nth-span bearing plate and the subgrade filling body, and at the step corner formed by the Nth-span bearing plate and the (N - 1)th-span bearing plate. The two side walls of the transition block are respectively connected to the vertical and horizontal planes of the corresponding step corner. S6. Level the area from the 1st-span bearing plate to the Nth-span bearing plate with M35 concrete mortar, and then lay the geotextile. S7. Taking the bearing plate structure constructed in step S4 as the boundary, fill the cutting excavation near the bridgehead side as the filler with a compaction degree not less than 95%. Within the transition section range near the subgrade side, fill qualified materials to the top of the bearing plate structure constructed in step S4 according to the structural type and requirements of the interval subgrade. S8. Repeat the construction of multiple transition pile foundations and the (N - 1)th-span bearing plate in the order of steps S4 to S7 until the construction of the 1st-span bearing plate. S9. After constructing the 1st-span bearing plate structure, fill the graded crushed stone of the subgrade surface layer synchronously with the interval subgrade. Among them, 5% cement is added to the subgrade surface layer within the transition section length range, and the compaction degree is not less than 97%. The transition section length L should not be less than 20m.

[0011] Preferably, in step S3, near the abutment, small machinery is used for compaction without damaging the main structure of the abutment, and the compaction degree is not less than 95%.

[0012] Preferably, in step S4, the diameter of the transition pile foundation is 1.0m, and it is cast with reinforced concrete not lower than grade C35.

[0013] Preferably, the depth of the transition pile foundation entering the weakly weathered layer of the bedrock is determined according to the bearing capacity calculation and shall not be less than 2m.

[0014] Preferably, in steps S4 and S8, the plate width of the Nth-span bearing plate extends 0.5m beyond the stress influence line of the railway track slab; the 1st-span bearing plate is 5.6m long and is aligned with the joint of the track slab; the plate thickness of the 1st-span bearing plate is 1m to 1.5 The present invention also provides a design method for the stepped pile-plate structure of the road-bridge transition section, which is used to design the stepped pile-plate structure of the road-bridge transition section as described above. The method includes the following steps: Step 1. Multi-span combined design 1) Calculate the weighted equivalent stiffness of the bearing plate and the overlying soil on the plate top: In the formula: is the modulus of elasticity of the pile body concrete, with the unit of MPa; is the cross-sectional area of the pile, with the unit of ; is the designed pile length, in m; is the designed plate width of the load-bearing plate, in m; is the designed plate length of the load-bearing plate, in m; is the deformation modulus of the i-th layer of overburden above the load-bearing plate, in MPa; is the thickness of the i-th layer of overburden above the load-bearing plate, in m.

[0015] 2) Calculate the post-construction settlement value of the cross-section of the load-bearing plate: In the formula: is the m-th vertical uniform load on the subgrade surface, including train load and inter-track load, ; is the horizontal distribution width of the m-th load on the subgrade surface, in m.

[0016] 3) Calculate the post-construction settlement value of the subgrade cross-section 5 m away from the edge of the current load-bearing plate , according to the requirements of the current "Code for Design of High-Speed Railways" TB10621, the allowable settlement value of the subgrade =15 mm.

[0017] 4) Calculate the angle of deflection between the load-bearing plate and the subgrade transition section after setting the load-bearing plate

[0018] In the formula: is the calculation length of the uneven settlement in the transition section, with a value of 5 m.

[0019] 5) Determine whether the angle of deflection in the transition section meets the specification limit.

[0020]

[0021] In the formula: is the limit value of the track surface angle of deflection in the transition section. According to the requirements of the current "Code for Design of High-Speed Railways" TB 10621, the limit value of the track surface angle of deflection .

[0022] Step 2. Check of the load-bearing plate 1) Calculation of the force and deformation of the load-bearing plate According to the current "Code for Design of High-Speed Railways" TB10621 and "Technical Regulations for Ground Treatment of Railway Engineering" TB 10106, the multi-span load-bearing plate is considered for the combination of main force, additional force and special force according to non-embedded type, shallow-embedded type (plate top overburden thickness 0 m < h < 1.5 m), and deep-embedded type (plate top overburden thickness 1.5 m ≤ h) respectively. It is advisable to use finite element software to calculate the force and deformation of the load-bearing plate.

[0023] 2) Check of the force on the load-bearing plate components:

[0024] The bearing plate can be designed by the allowable stress method. In the formula: are the allowable compressive stress and allowable shear stress of concrete under different stress types respectively, and their values should be determined according to the load combination model and stress type to be checked, in accordance with the current "Code for Design of Concrete Structures of Railway Bridges and Culverts" TB10092.

[0025] 3) Check of bearing plate deformation: In the formula: is the vertical deflection of the bearing plate under the action of vertical static live load, with the unit of m; is the longitudinal span of the bearing plate, with the unit of m; X is the calculation coefficient of the vertical deflection limit. The calculation coefficient of the vertical deflection limit shall meet the provisions of the current "Technical Regulations for Ground Treatment of Railway Engineering" TB 10106.

[0026]

[0027] In the formula: is the longitudinal angle of the bearing plate along the line, with the unit of rad; is the longitudinal angle limit of the bearing plate along the line, with the unit of rad. The value of the angle limit and the overhanging length of the bearing plate shall meet the provisions of the current "Code for Design of High-Speed Railways" TB10621.

[0028] 4) Check of allowable bearing capacity of single pile:

[0029] In the formula: is the calculated axial force of the pile, with the unit of kN; is the allowable bearing capacity of the pile, with the unit of kN. The allowable bearing capacity of the pile is calculated according to factors such as pile type, construction method, and stress characteristics, in accordance with the current "Code for Design of Foundations of Railway Bridges and Culverts" TB 10093. Description of the drawings

[0030] Figure 1 It is the overall structural schematic diagram of the stepped pile-plate structure of the road-bridge transition section in the embodiment of the present invention; Figure 2 It is the flow chart of the design method of the stepped pile-plate structure of the road-bridge transition section in the embodiment of the present invention.

[0031] Description of the reference numerals: 1 Transition pile foundation, 21 First-span bearing plate, 22 Second-span bearing plate, 23 Third-span bearing plate, 3 Transition block, 4 Subgrade filling body, 5 Subgrade surface layer, 6 Abutment, 60 Abutment foundation pit, 7 Geotextile. Detailed implementation manners

[0032] The following further describes in detail the implementation manners of the present application in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0033] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0034] It should be noted that in the coordinate system XYZ provided herein, the positive direction of the X axis represents the right side, the reverse direction of the X axis represents the left side, the positive direction of the Y axis represents the front, the reverse direction of the Y axis represents the rear, the positive direction of the Z axis represents the upper side, and the reverse direction of the Z axis represents the lower side; the meanings represented by the Z axis, X axis, and Y axis are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0035] Refer to Figure 1 , a stepped pile - plate structure for a road - bridge transition section provided by the present invention is used to connect the abutment 6 and the subgrade. The stepped pile - plate structure for the road - bridge transition section includes transition pile foundations 1, load - bearing plates, and transition blocks 3. A plurality of the transition pile foundations 1 are arranged on the extension line of the abutment 6 towards the subgrade direction, and multiple spans of the load - bearing plates are fixed on the plurality of transition pile foundations 1.

[0036] On the extension line of the abutment 6 towards the subgrade direction, N spans of the load - bearing plates are arranged in sequence. The upper surface of the first - span load - bearing plate 21 on the extension line of the abutment 6 towards the subgrade direction is flush with the lower bottom surface of the railway track slab; the upper surface of the second - span load - bearing plate 22 on the extension line of the abutment 6 towards the subgrade direction is flush with the lower bottom surface of the foundation surface layer; the upper surface of the N - th span load - bearing plate on the extension line of the abutment 6 towards the subgrade direction is flush with the lower bottom surface of the (N - 1) - th span load - bearing plate, and N≥2. The lower bottom surface of the N - th pile - plate is flush with the lower bottom surface of the subgrade filling body 4.

[0037] Step corners are formed at the connection between the N - th span load - bearing plate and the subgrade filling body 4 and at the connection between the N - th span load - bearing plate and the (N - 1) - th span load - bearing plate. A plurality of the transition blocks 3 are respectively arranged at the plurality of step corners, and the two side walls of the transition block 3 are respectively connected to the vertical surface and the horizontal surface of the corresponding step corner.

[0038] Specifically, the cross-section of the transition block 3 is a right-angled triangle or a right-angled trapezoid structure. One side wall of the bottom of the transition block 3 is fixed on the upper surface of the Nth-span bearing plate, and one side wall of the right-angled side of the transition block 3 is connected to the side wall of the (N - 1)th-span bearing plate facing the Nth-span bearing plate.

[0039] Among them, the transition block 3 is precast with concrete, and the concrete grade is the same as that of the bearing plate.

[0040] In this embodiment, the railway track slab is installed on the 1st-span bearing plate 21 on the extension line of the abutment 6 facing the subgrade direction. The upper surface of the Nth-span bearing plate on the extension line of the abutment 6 facing the subgrade direction is flush with the lower bottom surface of the (N - 1)th-span bearing plate, and N≥2. The transition block 3 is arranged on the upper surface of the Nth-span bearing plate, and one side wall of the transition block 3 is connected to the side wall of the (N - 1)th-span bearing plate. This structure enables the 1st-span bearing plate 21 and the Nth-span bearing plate to evenly distribute the force borne to the transition pile foundation 1, which is beneficial to reducing the settlement of the road-bridge transition section. Moreover, two adjacent bearing plates are connected by the transition block 3, which is beneficial to strengthening the uniform transition of the stiffness of the overlying filling soil in the road-bridge transition section. The structure is relatively simple and the materials are relatively unified, which can effectively avoid the problem of stiffness mutation caused by large differences between the structural form and materials, thereby improving the safe operation and comfort of the train and meeting the requirements of higher train operation speeds.

[0041] Preferably, the stepped pile-plate structure of the road-bridge transition section further includes a geotextile 7, and the geotextile 7 is laid on the upper surfaces of the bearing plates except the 1st-span bearing plate 21.

[0042] In this embodiment, the setting of the geotextile 7 is beneficial to strengthening the overall connection strength of the road-bridge transition section.

[0043] Preferably, the stepped pile-plate structure of the road-bridge transition section further includes a subgrade surface layer 5 and a filling layer. The railway track slab is laid on the geotextile 7 of the 1st-span bearing plate 21, the subgrade surface layer 5 is laid on the geotextile 7 of the 2nd-span bearing plate 22, and the filling layer is laid on the geotextile 7 of the 3rd-span bearing plate and the subsequent bearing plates.

[0044] Preferably, the subgrade surface layer 5 is poured with graded crushed stone mixed with 5% cement.

[0045] In this embodiment, the setting of the filling layer and the subgrade surface layer 5 is used to level the surface of the subgrade for laying the railway, and it is also beneficial to reducing settlement.

[0046] In this embodiment, this structure is beneficial to strengthening the uniform transition performance of the stepped pile-plate structure of the road-bridge transition section and reducing the differential settlement of the road-bridge transition section.

[0047] The present invention also provides a construction method for the stepped pile - plate structure of the road - bridge transition section, which is used for constructing the stepped pile - plate structure of the road - bridge transition section as described above. The method includes the following steps: S1. First, determine the position of the pile - plate bearing plate of the N - th span, and then successively determine the positions of the bearing plates of the (N - 1) - th span, the (N - 2) - th span, and so on until the position of the bearing plate 21 of the 1 - st span; S2. Determine the mileage of the abutment 6, construct the abutment pile foundation and the abutment 6, and backfill and compact the abutment foundation pit 60 with graded crushed stone or C25 concrete; S3. Excavate the steps, use the road - cutting excavation as the filling material for the back - filling area of the bridge, the subgrade outside the bearing - plate structure section is filled with the filling material, and is layered and compacted to the bottom surface of the pile - plate bearing plate of the N - th span; S4. Mark the position of the transition pile foundation 1, then construct the transition pile foundation 1, and construct from the bearing plate 21 of the 1 - st span to the bearing plate of the N - th span; S5. Set the transition block 3 at the step corners formed by the pile - plate bearing plate of the N - th span and the subgrade filling body 4, and at the step corners formed by the pile - plate bearing plate of the N - th span and the pile - plate bearing plate of the (N - 1) - th span. The two side walls of the transition block 3 are respectively connected to the vertical and horizontal planes of the corresponding step corners; S6. Level the pile - plate bearing plates from the bearing plate 21 of the 1 - st span to the bearing plate of the N - th span with M35 concrete mortar, and then lay the geotextile 7; S7. Taking the bearing - plate structure constructed in step S4 as the boundary, fill the road - cutting excavation as the filling material on the side close to the bridgehead, with the compaction degree not less than 95%. In the transition section range on the side close to the subgrade, fill qualified materials to the top of the bearing - plate structure constructed in step S4 according to the structural type and requirements of the interval subgrade; S8. Repeat the construction of multiple transition pile foundations 1 and the pile - plate bearing plates from the (N - 1) - th span to the 1 - st span in the order of steps S4 to S7; M35 concrete mortar to level the pile - plate bearing plates from the bearing plate 21 of the 1 - st span to the bearing plate of the N - th span, and then lay the geotextile 7; S9. After constructing the bearing - plate structure of the 1 - st span, fill the graded crushed stone of the subgrade surface layer 5 synchronously with the interval subgrade. Among them, 5% cement is added to the subgrade surface layer 5 within the transition section length range, and the compaction degree is not less than 97%. The transition section length L should not be less than 20m.

[0048] Preferably, in step S3, near the abutment 6, small - scale machinery is used for compaction, without damaging the main structure of the abutment 6, and the compaction degree is not less than 95%.

[0049] Preferably, in step S4, the diameter of the transition pile foundation 1 is 1.0m, and it is cast with reinforced concrete with a grade not lower than C35.

[0050] Preferably, the depth of the transition pile foundation 1 entering the slightly weathered bedrock layer is determined according to the bearing capacity calculation and shall not be less than 2 m.

[0051] Preferably, in steps S4 and S8, the plate width of the Nth-span bearing plate extends 0.5 m beyond the stress influence line of the railway track slab; the length of the first-span bearing plate 21 is 5.6 m and is aligned with the joint of the track slab; the plate thickness of the first-span bearing plate 21 is 1 m to 1.5 m.

[0052] In this embodiment, through the cooperation of the transition pile foundation 1, the bearing plate, the transition block 3, the geotextile 7, the filling layer and the subgrade surface layer 5, the uniform transition performance of the stepped pile-plate structure in the bridge-road transition section is improved, the differential settlement is reduced, and its influence on the smoothness of the bridge-road transition section is reduced; this method can effectively solve the problem of differential settlement in the bridge-road transition section of high-speed railways or expressways, ensure the operation safety of high-speed railway trains and expressway vehicles, and is convenient and feasible for construction with broad application prospects.

[0053] Refer to Figure 2 , the present invention also provides a design method for the stepped pile-plate structure in the bridge-road transition section, which is used to design the stepped pile-plate structure in the bridge-road transition section as described above. This method includes the following steps: Step 1. Multi-span combined design 1 Calculate the weighted equivalent stiffness of the bearing plate and the overlying soil on the plate top: In the formula: is the modulus of concrete of the pile body, with the unit of MPa; is the cross-sectional area of the pile, with the unit of ; is the designed pile length, with the unit of m; is the designed plate width of the bearing plate, with the unit of m; is the designed plate length of the bearing plate, with the unit of m; is the deformation modulus of the i-th layer of overlying soil above the bearing plate, with the unit of MPa; is the thickness of the i-th layer of overlying soil above the bearing plate, with the unit of m.

[0054] 2 Calculate the post-construction settlement value of the bearing plate section: In the formula: is the m-th item of vertical uniform load on the subgrade surface, including train load and line load between tracks, ; is the horizontal distribution width of the m-th item of load on the subgrade surface, with the unit of m.

[0055] 3 Calculate the post-construction settlement value of the subgrade section 5 m away from the edge of the current bearing plate , according to the requirements of the current "Code for Design of High-Speed Railways" TB10621, the allowable settlement value of the subgrade = 15mm.

[0056] 4 After calculating and setting the bearing plate, the deflection angle between the bearing plate and the subgrade transition section

[0057] In the formula: is the calculation length of the uneven settlement in the transition section, with a value of 5m.

[0058] 5 Determine the deflection angle of the transition section Whether it meets the specification limit value.

[0059]

[0060] In the formula: is the limit value of the rail surface deflection angle in the transition section. According to the requirements of the current "Code for Design of High-Speed Railways" TB 10621, the limit value of the rail surface deflection angle .

[0061] Step 2. Checking the bearing plate 1 Calculating the force and deformation of the bearing plate According to the current "Code for Design of High-Speed Railways" TB10621 and "Technical Regulations for Ground Treatment of Railway Engineering" TB 10106, considering the combination of main forces, additional forces and special forces for the multi-span bearing plates respectively according to non-buried type, shallow-buried type with the soil cover thickness on the top of the plate 0m < h < 1.5m, and deep-buried type with the soil cover thickness on the top of the plate 1.5m ≤ h, it is advisable to use finite element software to calculate the force and deformation of the bearing plate.

[0062] 2 Checking the force on the bearing plate components:

[0063] The bearing plate can be designed using the allowable stress method. In the formula: are the allowable compressive stress and allowable shear stress of concrete under different stress types respectively, and their values should be determined according to the load combination model and stress type to be checked in accordance with the current "Code for Design of Concrete Structures of Railway Bridges and Culverts" TB10092.

[0064] 3 Checking the deformation of the bearing plate: In the formula: is the vertical deflection under the vertical static live load of the bearing plate, with the unit of m; is the longitudinal span of the bearing plate, with the unit of m; X is the calculation coefficient of the vertical deflection limit value. The calculation coefficient of the vertical deflection limit value meets the provisions of the current "Technical Regulations for Ground Treatment of Railway Engineering" TB 10106.

[0065]

[0066] In the formula: is the longitudinal line rotation angle of the load-bearing plate, with the unit of rad; is the limit value of the longitudinal line rotation angle of the load-bearing plate, with the unit of rad. The value of the rotation angle limit and the overhanging length of the load-bearing plate shall meet the requirements of the current "Code for Design of High-Speed Railways" TB10621.

[0067] 4 Check the allowable bearing capacity of a single pile of the pile body:

[0068] In the formula: is the calculated axial force of the pile body, with the unit of kN; is the allowable bearing capacity of the pile, with the unit of kN. The allowable bearing capacity of the pile is calculated according to the current "Code for Design of Subgrade and Foundation of Railway Bridges and Culverts" TB 10093 based on factors such as the type of pile body, construction method, and force-bearing characteristics.

[0069] In this embodiment, the transition section deflection angle is determined by strictly controlling the load-bearing plate, the weighted equivalent stiffness of the soil covering on the plate top, and the post-construction settlement value of the load-bearing plate cross-section to check whether it meets the specification limit value, and through the stress analysis of the load-bearing plate component, the stepped pile-plate structure of the road-bridge transition section has sufficient rigidity. This design method has simple steps, convenient calculation, and good effects.

[0070] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A stepped pile-plate structure for a road-bridge transition section, which is used to connect an abutment (6) and a roadbed, and is characterized in that The stepped pile - plate structure of the road - bridge transition section includes transition pile foundations (1), load - bearing plates, and transition blocks (3). A plurality of the transition pile foundations (1) are arranged on the extension line of the abutment (6) towards the roadbed direction. Multiple spans of the load - bearing plates are fixed on the plurality of the transition pile foundations (1). On the extension line of the abutment (6) towards the roadbed direction, there are N spans of the load - bearing plates arranged in sequence. The upper surface of the first - span load - bearing plate (21) on the extension line of the abutment (6) towards the roadbed direction is flush with the lower bottom surface of the railway track slab. The upper surface of the second - span load - bearing plate (22) on the extension line of the abutment (6) towards the roadbed direction is flush with the lower bottom surface of the foundation surface layer. The upper surface of the N - th span load - bearing plate on the extension line of the abutment (6) towards the roadbed direction is flush with the lower bottom surface of the (N - 1) - th span load - bearing plate, and N≥2. The lower bottom surface of the N - th pile - plate is flush with the lower bottom surface of the roadbed filling body (4). Step - angle corners are formed at the joints between the N - th span load - bearing plate and the roadbed filling body (4) and between the N - th span load - bearing plate and the (N - 1) - th span load - bearing plate. A plurality of the transition blocks (3) are respectively arranged at the plurality of step - angle corners, and the two side walls of the transition block (3) are respectively connected to the vertical surface and the horizontal surface of the corresponding step - angle corner.

2. The stepped pile-slab structure of the road-bridge transition section according to claim 1, wherein It further includes geotextiles (7), and geotextiles (7) are laid on the upper surfaces of the load - bearing plates except the first - span load - bearing plate (21).

3. The stepped pile-slab structure for the road-bridge transition section according to claim 2, wherein, It further includes a subgrade surface layer (5) and a filling layer. The railway track slab is laid on the geotextiles (7) of the first - span load - bearing plate (21). The subgrade surface layer (5) is laid on the geotextiles (7) of the second - span load - bearing plate (22). The filling layer is laid on the geotextiles (7) of the third - span load - bearing plate and the subsequent load - bearing plates.

4. The stepped pile-slab structure of the road-bridge transition section according to claim 3, wherein, The subgrade surface layer (5) is poured with graded crushed stone admixed with 5% cement.

5. A construction method of a stepped pile-slab structure for a road-bridge transition section, characterized in that, For constructing the stepped pile - plate structure of the road - bridge transition section as described in any one of claims 1 - 4, the method includes the following steps: S1. First, determine the position of the N - th span pile - plate load - bearing plate, and then sequentially determine the positions of the (N - 1) - th span load - bearing plate, the (N - 2) - th span load - bearing plate, and so on until the position of the first - span load - bearing plate (21). S2. Determine the mileage of the abutment (6), construct the abutment pile foundation and the abutment (6), and backfill and compact the abutment foundation pit (60) with graded crushed stone or C25 concrete. S3. Excavate steps, use the cut - and - fill of the road cutting as filler for the back - filling area of the bridge, and the roadbed outside the load - bearing plate structure section is filled with filler and compacted layer by layer to the bottom surface of the N - th span load - bearing plate. S4. Mark the positions of the transition pile foundations (1), and then carry out the construction of the transition pile foundations (1), and the construction from the first - span load - bearing plate (21) to the N - th span load - bearing plate. S5. Place the transition block (3) at the step corner formed by the Nth-span bearing plate and the subgrade filling body (4), and at the step corner formed by the Nth-span bearing plate and the (N - 1)th-span bearing plate. The two side walls of the transition block (3) are respectively connected to the vertical surface and the horizontal surface of the corresponding step corner. S6. Use M35 concrete mortar to level the bearing plates from the 1st-span bearing plate (21) to the Nth-span bearing plate, and then lay the geotextile (7). S7. Taking the bearing plate structure constructed in step S4 as the boundary, fill the cutting excavation near the bridgehead side as filler, with the compaction degree not less than 95%. Within the transition section range near the subgrade side, fill qualified materials to the top of the bearing plate structure constructed in step S4 according to the structural type and requirements of the interval subgrade. S8. Repeat the construction of multiple transition pile foundations (1) and the (N - 1)th-span bearing plate in the order of steps S4 to S7 until the 1st-span bearing plate. S9. After constructing the 1st-span bearing plate (21) structure, fill the graded crushed stone of the subgrade surface layer (5) synchronously with the interval subgrade. Among them, 5% cement is added to the subgrade surface layer (5) within the transition section length range, and the compaction degree is not less than 97%. The transition section length L should not be less than 20 m.

6. The construction method of the stepped pile-slab structure for the road-bridge transition section according to claim 5, characterized in that, In step S3, use small machinery to roll near the abutment (6) without damaging the main structure of the abutment (6), and the compaction degree is not less than 95%.

7. The construction method of the stepped pile-slab structure for the road-bridge transition section according to claim 5, characterized in that In step S4, the diameter of the transition pile foundation (1) is not less than 1.0 m, and it is cast with reinforced concrete with a grade not lower than C35.

8. The construction method of the stepped pile-slab structure for the road-bridge transition section according to claim 5, characterized in that, In step S4, the depth of the transition pile foundation (1) entering the weakly weathered layer of the bedrock is determined according to the bearing capacity calculation and shall not be less than 2 m.

9. The construction method of the stepped pile-slab structure for the road-bridge transition section according to claim 5, characterized in that, In steps S4 and S8, the width of the Nth-span bearing plate exceeds the stress influence line of the railway track slab by 0.5 m; the 1st-span bearing plate (21) is 5.6 m long and is aligned with the slab joint of the track slab; the thickness of the 1st-span bearing plate (21) is 1 m to 1.5 m.

10. A design method for a stepped pile - slab structure in a road - bridge transition section, characterized in that, For designing the stepped pile-slab structure of the road-bridge transition section as described in any one of claims 1 - 4, the method includes the following steps: Step 1. Multi-span combined design 1) Calculate the weighted equivalent stiffness of the bearing plate and the soil covering on the top of the plate: Wherein: is the modulus of concrete of the pile body, with the unit of MPa; is the cross-sectional area of the pile, with the unit of ; is the designed pile length, with the unit of m; is the designed plate width of the bearing plate, with the unit of m; is the designed plate length of the bearing plate, with the unit of m; is the deformation modulus of the i-th layer of overburden above the bearing plate, with the unit of MPa; is the thickness of the i-th layer of overburden above the bearing plate, with the unit of m. 2) Calculate the post-construction settlement value of the cross-section of the bearing plate: Where: is the m-th vertical uniform load on the subgrade surface, including train load and load between lines, with the unit of ; is the horizontal distribution width of the m-th load on the subgrade surface, with the unit of m. 3) Calculate the post-construction settlement value of the subgrade section at a distance of 5 m from the edge of the current bearing plate , according to the requirements of the current "Code for Design of High-Speed Railway" TB10621, the allowable settlement value of the subgrade = 15 mm. 4) Calculate the fold angle between the bearing plate and the subgrade transition section after setting the bearing plate. In the formula: is the calculation length of the uneven settlement in the transition section, with a value of 5 m. 5) Determine the transition section deflection angle to check if it meets the specification limits. In the formula: is the limit value of the rail surface deflection angle in the transition section. According to the requirements of the current "Code for Design of High-Speed Railways" TB 10621, the limit value of the rail surface deflection angle . Step 2. Checking the bearing plate 1) Calculating the force and deformation of the bearing plate According to the current "Code for Design of High-Speed Railways" TB10621 and "Technical Regulations for Ground Treatment of Railway Engineering" TB 10106, consider the combination of main forces, additional forces, and special forces for multiple-span bearing plates respectively as non-embedded type, shallow-embedded type (the soil cover thickness on the top of the plate is 0 m < h < 1.5 m), and deep-embedded type (the soil cover thickness on the top of the plate is 1.5 m ≤ h). It is advisable to use finite element software to calculate the force and deformation of the bearing plate. 2) Checking the force of the bearing plate components: The bearing plate can be designed using the allowable stress method. In the formula: are the allowable compressive stress and allowable shear stress of concrete under different stress types respectively, and their values should be taken according to the load combination model and stress type to be checked in accordance with the current "Code for Design of Railway Bridge and Culvert Concrete Structures" TB10092. 3) Deformation check of the bearing plate: In the formula: is the vertical deflection under the vertical static live load of the bearing plate, with the unit of m; is the longitudinal span of the bearing plate, with the unit of m; X is the calculation coefficient of the vertical deflection limit. The calculation coefficient of the vertical deflection limit shall meet the requirements of the current "Technical Specification for Ground Treatment of Railway Engineering" TB 10106. In the formula: is the longitudinal line rotation angle of the said load-bearing plate, with the unit of rad; is the limit value of the longitudinal line rotation angle of the said load-bearing plate, with the unit of rad. The value of the rotation angle limit and the cantilever length of the load-bearing plate shall comply with the provisions of the current Code for Design of High-Speed Railways TB10621. 4) Checking the allowable bearing capacity of a single pile of the pile body: In the formula: is the calculated axial force of the pile shaft, with the unit of kN; is the allowable bearing capacity of the pile, with the unit of kN. The allowable bearing capacity of the pile is calculated according to the current "Code for Design of Subgrade and Foundation of Railway Bridges and Culverts" TB 10093 based on factors such as pile shaft type, construction method, and stress characteristics.

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