Composite foundation structure for transition section of deep soft foundation railway bridge abutment
By setting up pile-length bidirectional cement mixing piles in the transition section of the deep soft foundation railway abutment, and setting up the diameter expansion sections up and down the pile body, the problem of differential settlement between rigid and flexible foundations is solved, ensuring the stability and smooth operation of the railway.
Patent Information
- Application Number
- CN202421949218.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-12
- Publication Date
- 2025-05-27
- Estimated Expiration
- 2034-08-12
AI Technical Summary
In solving the composite foundation structure of the deep soft-based railway abutment transition section, it is difficult to effectively slow down the differential settlement between the rigid-flexible foundation, resulting in differential settlement between the railway abutment and the roadbed, affecting the smooth operation and safety of high-speed trains.
By setting up pile-length bidirectional cement mixing piles in the transition section of the abutment and the roadbed, the pile length gradually decreases along the bridge-road direction, and the top and bottom diameter expansion sections are set up above and below the pile body to enhance the bearing capacity and stability of the pile body.
A smooth transition has been achieved, effectively slowing down the differential settlement problem between rigid-flexible foundations, and ensuring the stability of the railway structure and long-term smooth operation.
Smart Images
Figure CN222908432U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of soft soil foundation treatment in geotechnical engineering, and particularly relates to a composite foundation structure for the transition section of a railway bridge abutment in deep soft foundation. Background Art
[0002] At the connection between the embankment and the bridge of high-speed railway, due to differences in foundation conditions, backfill materials of the subgrade behind the bridge abutment, structures of the bridge abutment and the subgrade, as well as different actual construction qualities, and the stiffness difference between the embankment and the bridge, differential settlement generally exists between the bridge abutment and the subgrade, affecting the smooth operation of high-speed trains, driving safety and riding comfort.
[0003] In the prior art, CN110512598B provides a composite foundation structure of variable-diameter high-pressure jet grouting piles and variable-diameter dry jet mixing piles applicable to deep soft soil and its construction method. The patent improves the bearing capacity of foundation soil by setting variable-diameter high-pressure jet grouting pile bodies. The method adopted in this patent has a certain effect of slowing down the settlement along the extension direction of the railway track, but it will cause a new stiffness difference between the foundation of the transition section and the foundation of the general section, resulting in a new differential settlement problem, and it cannot meet the requirements of variable stiffness settlement control and leveling between different nature sections during the construction and operation of high-speed railways, and it is difficult to ensure the long-term smooth operation of trains.
[0004] Therefore, how to provide a composite foundation structure for the transition section of a railway bridge abutment in deep soft foundation is an urgent technical problem to be solved at present. Summary of the Invention
[0005] Aiming at the deficiencies existing in the prior art, the utility model provides a composite foundation structure for the transition section of a railway bridge abutment in deep soft foundation. By gradually reducing the pile length of the variable-pile-length bidirectional cement mixing pile along the bridge-road direction, smooth transition can be achieved, and the differential settlement problem between rigid and flexible foundations can be effectively alleviated.
[0006] The utility model provides a composite foundation structure for the transition section of a railway bridge abutment in deep soft foundation, including variable-pile-length bidirectional cement mixing piles. The variable-pile-length bidirectional cement mixing piles are arranged in parallel to the railway extension direction in the soft soil foundation under the railway subgrade, and are equally spaced from the midline of the soft soil foundation to the inside of the road shoulder; the pile length of the variable-pile-length bidirectional cement mixing piles gradually decreases along the bridge-road direction. The top of the variable-pile-length bidirectional cement mixing pile is provided with a top enlarged diameter section, and the bottom is provided with a bottom enlarged diameter section; the top of the top enlarged diameter section is on the same horizontal plane as the top surface of the bearing platform.
[0007] In this technical solution, the pile length of the variable-pile-length bidirectional cement mixing pile gradually decreases along the bridge-road direction, enabling smooth transition and effectively reducing the differential settlement problem between rigid and flexible foundations. By setting the top-expanded diameter section and the bottom-expanded diameter section, the bearing capacity and stability of the pile body are enhanced, further reducing the post-construction settlement and ensuring the stability of the railway structure.
[0008] In some of these embodiments, the variable-pile-length bidirectional cement mixing pile is constructed using dry jet cement mixing pile; the length of the top-expanded diameter section is 3.0 m, and the pile diameter is 1.0 m; the length of the bottom-expanded diameter section is 1.0 m - 3.0 m, and the pile diameter is 1.0 m; the length of the middle section of the variable-pile-length bidirectional cement mixing pile is calculated according to the thickness of the soft soil foundation in combination with the construction specifications, and the pile diameter is 0.6 m.
[0009] In some of these embodiments, the composite foundation structure of the deep soft foundation railway abutment transition section further includes variable-pile-length triaxial cement mixing piles, which are arranged parallel to the railway extension direction in the soft soil foundation under the railway shoulder and extend from the inner side of the shoulder to the outer side of the shoulder; the pile length of the variable-pile-length triaxial cement mixing piles gradually decreases along the bridge-road direction. In this technical solution, by gradually decreasing the pile length of the variable-pile-length triaxial cement mixing piles along the bridge-road direction, smooth transition can be achieved, effectively reducing the differential settlement problem between rigid and flexible foundations. At the same time, the variable-pile-length triaxial cement mixing piles can improve the lateral restraint effect of the entire foundation, contribute to controlling the post-construction settlement of the subgrade, and simultaneously control the settlement of the shoulder and slope.
[0010] In some of these embodiments, the variable-pile-length triaxial cement mixing pile is constructed using dry jet cement mixing pile, and the pile diameter is 0.65 m.
[0011] In some of these embodiments, a capping beam is provided above the variable-pile-length bidirectional cement mixing pile, and the capping beam is cast parallel to the railway extension direction. In this technical solution, through the setting of the capping beam, the structural integrity is enhanced.
[0012] In some of these embodiments, the capping beam is cast with concrete and uses basalt composite bars as the main reinforcement; the width of the beam cross-section of the capping beam is 1.0 m, and the height of the beam cross-section is 0.3 m.
[0013] In some of these embodiments, a reinforced soil foundation is provided above the capping beam, and a first geogrid is laid in the reinforced soil foundation. One end of the first geogrid parallel to the railway extension direction extends to the abutment, and both ends of the first geogrid perpendicular to the railway extension direction extend to both sides of the shoulder. In this technical solution, through the setting of the first geogrid, a soil arch effect is formed with the capping beam and the variable-pile-length triaxial cement mixing piles, which helps to evenly distribute the stress on the foundation and reduce the phenomenon of local stress concentration.
[0014] In some of these embodiments, a first geogrid is laid every 1 - 3 m in the reinforced soil foundation, and the first geogrid is a steel - plastic three - dimensional geogrid. By setting multiple layers of the first geogrid in this technical solution, the overall stability of the foundation is enhanced.
[0015] In some of these embodiments, a second geogrid is laid between the variable - length two - way cement mixing piles and the capping beam. One end of the second geogrid parallel to the railway extension direction extends to the abutment and is partially laid on the bearing platform, and both ends of the second geogrid perpendicular to the railway extension direction extend to both sides of the road shoulder. Through the setting of the second geogrid in this technical solution, the integrity of the structure is increased, the stress is evenly distributed, the influence of differential settlement on the railway is further reduced, and the smooth operation of the railway is ensured.
[0016] In some of these embodiments, the second geogrid is a steel - plastic three - dimensional geogrid.
[0017] Based on the above - mentioned scheme, in the composite foundation structure of the deep soft - soil railway abutment transition section in the embodiments of the present utility model, the pile length of the variable - length two - way cement mixing piles gradually decreases along the bridge - road direction, which can achieve a smooth transition and effectively reduce the differential settlement problem between the rigid - flexible foundations; through the settings of the top - enlarged section and the bottom - enlarged section, the bearing capacity and stability of the pile body are enhanced, the post - construction settlement is further reduced, and the stability of the railway structure is ensured. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The drawings described herein are used to provide a further understanding of the present utility model and constitute a part of this application. The schematic embodiments of the present utility model and their descriptions are used to explain the present utility model and do not constitute an improper limitation of the present utility model. In the drawings:
[0019] Figure 1 is a cross - sectional view of the composite foundation structure of the deep soft - soil railway abutment transition section when only one railway track is laid in the embodiments of the present utility model;
[0020] Figure 2 is a cross - sectional view of the composite foundation structure of the deep soft - soil railway abutment transition section when two railway tracks are laid in the embodiments of the present utility model;
[0021] Figure 3 is a plan layout view of the composite foundation structure of the deep soft - soil railway abutment transition section in the embodiments of the present utility model;
[0022] Figure 4 is a side view of the composite foundation structure of the deep soft - soil railway abutment transition section in the embodiments of the present utility model.
[0023] In the figures:
[0024] 1. Variable - length two - way cement mixing pile; 101. Top - enlarged section; 102. Bottom - enlarged section;
[0025] 2. Variable pile length triaxial cement mixing pile; 3. Capping beam; 4. Reinforced soil foundation; 5. First geogrid; 6. Second geogrid; 7. Soft soil foundation; 8. Abutment; 9. Cap; 10. Rail. Detailed implementation manners
[0026] The technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.
[0027] In the description of the present utility model, it should be understood that the orientation or positional relationship indicated by the terms "center", "transverse", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present utility model 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 should not be construed as a limitation of the present utility model.
[0028] The terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.
[0029] In the description of the present utility model, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific situations.
[0030] The terms "system", "unit" and "module" used herein are a method for distinguishing different components, elements, parts, portions or components at different levels, and these terms can be replaced by other expressions that can achieve the same purpose.
[0031] Such as Figures 1 - 4As shown in the figure, in an embodiment of the composite foundation structure for the transition section of a deep soft foundation railway abutment of the present utility model, the composite foundation structure for the transition section of a deep soft foundation railway abutment includes variable-length bidirectional cement mixing piles 1. The variable-length bidirectional cement mixing piles 1 are arranged parallel to the railway extension direction in the soft soil foundation 7 under the railway subgrade, and are equally spaced from the midline of the soft soil foundation 7 to the inside of the road shoulder; the pile length of the variable-length bidirectional cement mixing piles 1 gradually decreases along the bridge-road direction. The top of the variable-length bidirectional cement mixing piles 1 is provided with a top enlarged diameter section 101, and the bottom is provided with a bottom enlarged diameter section 102; the top of the top enlarged diameter section 101 is on the same horizontal plane as the top surface of the bearing platform 9.
[0032] In the above-mentioned schematic embodiment, the composite foundation structure for the transition section of a deep soft foundation railway abutment can achieve a smooth transition by gradually reducing the pile length of the variable-length bidirectional cement mixing piles 1 along the bridge-road direction, effectively reducing the differential settlement problem between the rigid and flexible foundations; through the settings of the top enlarged diameter section 101 and the bottom enlarged diameter section 102, the bearing capacity and stability of the pile body are enhanced, further reducing the post-construction settlement and ensuring the stability of the railway structure.
[0033] In some embodiments, the pile spacing of the variable-length bidirectional cement mixing piles 1 is determined according to the high embankment subgrade and the upper use load, and the longest pile length of the variable-length bidirectional cement mixing piles 1 is determined according to the thickness of the soft soil foundation 7; through the differential settlement calculation results and the railway slope requirements, the layout range of the variable-length bidirectional cement mixing piles 1 along the direction away from the abutment 8 is determined, and the shortening amount of each pile length is determined.
[0034] In some embodiments, the variable-length bidirectional cement mixing piles 1 are constructed by dry jet cement mixing piles; the length of the top enlarged diameter section 101 is 3.0 m, and the pile diameter is 1.0 m; the length of the bottom enlarged diameter section 102 is 1.0 m - 3.0 m, and the pile diameter is 1.0 m; the length of the middle section of the variable-length bidirectional cement mixing piles 1 is calculated according to the thickness of the soft soil foundation 7 in combination with the construction specifications, and the pile diameter is 0.6 m.
[0035] Furthermore, as Figure 3 shown, the composite foundation structure for the transition section of a deep soft foundation railway abutment further includes variable-length triaxial cement mixing piles 2. The variable-length triaxial cement mixing piles 2 are arranged parallel to the railway extension direction in the soft soil foundation 7 under the railway road shoulder, and extend from the inside of the road shoulder to the outside of the road shoulder; the pile length of the variable-length triaxial cement mixing piles 2 gradually decreases along the bridge-road direction. By gradually reducing the pile length of the variable-length triaxial cement mixing piles 2 along the bridge-road direction, a smooth transition can be achieved, effectively reducing the differential settlement problem between the rigid and flexible foundations. At the same time, the variable-length triaxial cement mixing piles 2 can improve the lateral restraint effect of the entire foundation, contribute to controlling the post-construction settlement of the subgrade, and at the same time control the settlement of the road shoulder and the slope.
[0036] In some embodiments, the variable pile length three-axis cement mixing pile 2 is constructed using a dry jet cement mixing pile with a pile diameter of 0.65 m.
[0037] In some embodiments, as Figure 2 shown, a capping beam 3 is provided above the variable pile length two-way cement mixing pile 1, and the capping beam 3 is cast parallel to the railway extension direction. By setting the capping beam 3, the structural integrity is enhanced.
[0038] In some embodiments, the capping beam 3 is cast using concrete and basalt composite bars are used as the main bars; the width of the beam section of the capping beam 3 is 1.0 m, and the height of the beam section is 0.3 m. The stress bars are made of basalt composite bars, effectively exerting the advantages of high tensile strength and light weight of basalt composite bars.
[0039] In some embodiments, as Figure 4 shown, a reinforced soil foundation 4 is provided above the capping beam 3. A first geogrid 5 is laid in the reinforced soil foundation 4. One end of the first geogrid 5 parallel to the railway extension direction extends to the abutment 8, and both ends of the first geogrid 5 perpendicular to the railway extension direction extend to both sides of the road shoulder. By setting the first geogrid 5, an arching effect is formed with the capping beam 3 and the variable pile length three-axis cement mixing pile 2, which helps to evenly distribute the stress on the foundation and reduce the local stress concentration phenomenon. As Figure 1 shown, even if the railway tracks 10 do not cover the entire subgrade, it can still effectively prevent excessive deformation of the soft soil foundation 7, improve the overall deformation coordination of the foundation, and maintain the flatness of the railway. In this embodiment, the composite foundation structure of the deep soft foundation railway abutment transition section can ensure that the post-construction settlement of the transition section of the deep silt foundation abutment 8 is less than 30 mm, the differential settlement between the abutment 8 and the subgrade transition section shall not exceed 5 mm / 20 m, and the angle formed by the settlement of any two sections of the subgrade shall not exceed 1 / 1000.
[0040] In some embodiments, as Figure 4 shown, a layer of the first geogrid 5 is laid every 1 - 3 m in the reinforced soil foundation 4, and the first geogrid 5 is a steel-plastic three-way geogrid. The width of the first geogrid 5 does not exceed the road shoulder, and the first geogrid 5 in the lower layer is 3 - 5 m shorter than the first geogrid 5 in the upper layer. By setting multiple layers of the first geogrid 5, the overall stability of the foundation is enhanced, the stress is evenly distributed, and the deformation of the foundation is reduced.
[0041] In some embodiments, as Figure 4As shown in the figure, a second geogrid 6 is laid between the variable pile length bidirectional cement mixing pile 1 and the capping beam 3. One end of the second geogrid 6 parallel to the railway extension direction extends to the abutment 8 and is partially laid on the bearing platform 9, and both ends of the second geogrid 6 perpendicular to the railway extension direction extend to both sides of the road shoulder. Through the setting of the second geogrid 6, the integrity of the structure is increased, the stress is evenly distributed, the influence of differential settlement on the railway is further reduced, and the smooth operation of the railway is ensured.
[0042] In some embodiments, the second geogrid 6 adopts a steel-plastic three-way geogrid. The steel-plastic three-way geogrid has the advantages of high strength and good durability, and can ensure the long-term safety and reliability of the railway subgrade structure.
[0043] The construction method of the composite foundation structure of the deep soft foundation railway abutment transition section of the present utility model will be described below:
[0044] S1. Determine the pile positions in the soft soil foundation 7 area of the transition section, and arrange the variable pile length bidirectional cement mixing pile 1 and the variable pile length triaxial cement mixing pile 2 according to the design.
[0045] S2. Construct the variable pile length bidirectional cement mixing pile 1, and adopt the construction process of "two mixing and one spraying". The specific construction process is as follows:
[0046] S201. The pile driver is in place: the mixer reaches the designated pile position and is centered.
[0047] S202. Sink and mix: At the same time, turn on the ash feeding pump to spray cement powder into the soil body, and the two groups of blades rotate forward and backward at the same time to sink until the design depth of the bottom surface of the top enlarged diameter section 101.
[0048] S203. Contract the blades: Change the rotation direction of the inner and outer drill pipes, contract the mixing blades to a diameter of 500 mm, the two groups of blades rotate forward and backward at the same time, and the mixer continues to sink until the design depth of the top surface of the bottom enlarged diameter section 102.
[0049] S204. Extend the blades: Change the rotation direction of the inner and outer drill pipes, extend the mixing blades to a diameter of 900 mm - 1000 mm, the mixer continues to sink, and the two groups of blades rotate forward and backward at the same time until the mixing of the bottom enlarged diameter section 102 is completed.
[0050] S205. Lift and mix: Turn off the ash feeding pump, and the two groups of blades rotate forward and backward at the same time to mix until the top surface of the bottom enlarged diameter section 102.
[0051] S206. Second contraction of the blades: Change the rotation direction of the inner and outer drill pipes, contract the mixing blades to a diameter of 500 mm, the two groups of blades rotate forward and backward at the same time, and the mixer continues to lift until the design depth of the bottom surface of the top enlarged diameter section 101.
[0052] S207, Secondary Stretching Blades: Change the rotation direction of the inner and outer drill pipes, stretch the mixing blades to a diameter of 900 mm - 1000 mm, continue to lift the mixer, and rotate the two groups of blades in both forward and reverse directions simultaneously until the mixing of the top enlarged diameter section 101 is completed, thus completing the construction of the variable pile length two-way cement mixing pile 1;
[0053] S3, Construct the variable pile length triaxial cement mixing pile 2, adopting the "two mixing and one spraying" construction process. The specific construction process is as follows:
[0054] S301, Pile Driver Positioning: Move the mixer to the designated pile position and align it;
[0055] S302, Sinking and Mixing: Simultaneously turn on the high-pressure air pump and the slurry feeding pump, mix and sink until the designed pile length. The pile length of the variable pile length triaxial cement mixing pile 2 is the same as that of the variable pile length two-way cement mixing pile 1 at the same cross-section;
[0056] S303, Lifting and Mixing: Turn off the slurry feeding pump, continue to turn on the high-pressure air pump, and lift and mix;
[0057] S304, Repeat steps S302 and S303 to complete the construction of the single-row variable pile length triaxial cement mixing pile 2;
[0058] S4, Level the pile heads of the variable pile length two-way cement mixing pile 1 and the variable pile length triaxial cement mixing pile 2 respectively, and the soft soil foundation 7 site, and lay the second geogrid 6;
[0059] S5, Bind the steel bars of the capping beam 3, set up the formwork, and pour the concrete of the capping beam 3;
[0060] S6, Backfill the backfill material of the wall back layer by layer, and lay the first geogrid 5 until the backfill reaches the designed elevation.
[0061] In the above illustrative embodiments, through precise pile layout, efficient construction, optimized pile body structure, uniform stress distribution, and layer-by-layer backfilling, the differential settlement problem of the transition section of the deep soft foundation railway abutment 8 is effectively solved, the bearing capacity and stability of the foundation are significantly improved, and the smooth and safe operation of the railway is ensured.
[0062] In some embodiments, in step S2, the construction process parameters of the variable pile length two-way cement mixing pile 1 are as follows: The cement used is 42.5 slag Portland cement, the cement admixture amount is 25% - 40% of the mass of the reinforced wet soil, the drilling speed is 0.8 - 1.2 m / min, the lifting speed is 0.4 - 0.6 m / min, the rotation speed is 30 - 50 revolutions / min, and the ash spraying pressure during drilling is 0.5 - 0.7 Mpa.
[0063] In some embodiments, in step S3, the construction process parameters of the variable-pile-length triple-axis cement mixing pile 2 are as follows: 42.5 slag Portland cement is used as the cement, the cement admixture is 20%-40% of the mass of the wet soil to be reinforced, the water-cement ratio is selected as 1.50, the drilling speed is 0.4-0.6 m / min, and the lifting speed is 0.4-0.6 m / min.
[0064] Through the description of multiple embodiments of the composite foundation structure for the transition section of the deep soft foundation railway abutment of the present invention, it can be seen that the embodiments of the composite foundation structure for the transition section of the deep soft foundation railway abutment of the present invention have at least one or more of the following advantages:
[0065] 1. For the composite foundation structure for the transition section of the deep soft foundation railway abutment provided by the present invention, by gradually reducing the pile length of the variable-pile-length bidirectional cement mixing pile 1 along the bridge-road direction, smooth transition can be achieved, effectively reducing the differential settlement problem between the rigid and flexible foundations; through the settings of the top enlarged diameter section 101 and the bottom enlarged diameter section 102, the bearing capacity and stability of the pile body are enhanced, further reducing the post-construction settlement and ensuring the stability of the railway structure;
[0066] 2. For the composite foundation structure for the transition section of the deep soft foundation railway abutment provided by the present invention, by gradually reducing the pile length of the variable-pile-length triple-axis cement mixing pile 2 along the bridge-road direction, smooth transition can be achieved, effectively reducing the differential settlement problem between the rigid and flexible foundations. At the same time, the variable-pile-length triple-axis cement mixing pile 2 can improve the lateral restraint effect of the entire foundation, contribute to controlling the post-construction settlement of the subgrade, and at the same time control the settlement of the road shoulder and slope;
[0067] 3. For the composite foundation structure for the transition section of the deep soft foundation railway abutment provided by the present invention, through the setting of the first geogrid 5, an arching effect is formed with the capping beam 3 and the variable-pile-length triple-axis cement mixing pile 2, which helps to evenly distribute the stress on the foundation, reduce the phenomenon of local stress concentration. Even if the railway tracks 10 do not cover the entire subgrade, it can still effectively prevent excessive deformation of the soft soil foundation 7, improve the overall deformation coordination of the foundation, and maintain the flatness of the railway.
[0068] Finally, it should be noted that: the various embodiments in this specification are described in a progressive manner, and the key point of each embodiment is the difference from other embodiments. The same or similar parts between the various embodiments can be referred to each other.
[0069] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: still modifications can be made to the specific implementation manners of the present invention or equivalent replacements can be made to some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered within the scope of the technical solutions claimed by the present invention.
Claims
1. A composite foundation structure for a transition section of a railway abutment with a thick soft foundation, characterized in that: It comprises a variable-length bidirectional cement mixing pile, which is arranged in the soft soil foundation below the railway bed in parallel with the extension direction of the railway, and is arranged at equal intervals from the center line of the soft soil foundation to the inner side of the shoulder; the pile length of the variable-length bidirectional cement mixing pile gradually decreases along the bridge-road direction, and the variable-length bidirectional cement mixing pile is provided with a top diameter expansion section at the top and a bottom diameter expansion section at the bottom; the top end of the top diameter expansion section is on the same horizontal plane as the top surface of the pedestal.
2. The deep soft foundation railway abutment transition section composite foundation structure according to claim 1 is characterized in that: The variable-length bidirectional cement mixing pile is constructed using powder-sprayed cement mixing piles; the length of the top expansion section is 3.0m, and the pile diameter is 1.0m; the length of the bottom expansion section is 1.0m-3.0m, and the pile diameter is 1.0m; the length of the middle section of the variable-length bidirectional cement mixing pile is calculated based on the thickness of the soft soil foundation and the construction specifications, and the pile diameter is 0.6m.
3. The deep soft foundation railway abutment transition section composite foundation structure according to claim 1 is characterized in that: It also includes variable pile long three-axis cement mixing piles, which are arranged in the soft soil foundation below the railway shoulder parallel to the extension direction of the railway and extend from the inner side of the shoulder to the outer side of the shoulder; the pile length of the variable pile long three-axis cement mixing pile gradually decreases along the bridge-road direction.
4. The deep soft foundation railway abutment transition section composite foundation structure according to claim 3 is characterized in that: The variable pile length three-axis cement mixing pile is constructed using powder spray cement mixing piles, and the pile diameter is 0.65m.
5. The deep soft foundation railway abutment transition section composite foundation structure according to claim 1 is characterized in that: A cap beam is arranged above the variable-length bidirectional cement mixing pile, and the cap beam is cast parallel to the extension direction of the railway.
6. The deep soft foundation railway abutment transition section composite foundation structure according to claim 5 is characterized in that: The cap beam is cast with concrete, and basalt composite reinforcement is used as the main reinforcement; the beam section width of the cap beam is 1.0m, and the beam section height is 0.3m.
7. The deep soft foundation railway abutment transition section composite foundation structure according to claim 5 is characterized in that: A reinforced soil foundation is provided above the cap beam, and a first geogrid is laid in the reinforced soil foundation. One end of the first geogrid parallel to the extension direction of the railway extends to the abutment, and the two ends of the first geogrid perpendicular to the extension direction of the railway extend to both sides of the shoulder.
8. The deep soft foundation railway abutment transition section composite foundation structure according to claim 7 is characterized in that: A layer of the first geogrid is laid every 1-3 m in the reinforced soil foundation, and the first geogrid is a steel-plastic three-dimensional geogrid.
9. The deep soft foundation railway abutment transition section composite foundation structure according to claim 5 is characterized in that: A second geogrid is laid between the variable-length bidirectional cement-mixed pile and the cap beam, one end of the second geogrid parallel to the extension direction of the railway extends to the abutment and is partially laid on the pedestal, and the two ends of the second geogrid perpendicular to the extension direction of the railway extend to both sides of the shoulder.
10. The deep soft foundation railway abutment transition section composite foundation structure according to claim 9, characterized in that: The second geogrid is a steel-plastic three-dimensional geogrid.