A field adjustment device, method and application for arch deformation on high-speed railway subgrade

Abstract

This invention provides an on-site adjustment device, method, and application for arching deformation of high-speed railway subgrades. The device includes miniature steel pipe piles, displacement sensors, axial force sensors, a data acquisition instrument, a crimping adapter, pre-tightening nuts, elastic components, and a support plate. This invention treats the high-speed railway subgrade as an anchor plate resisting arching deformation of the foundation rock and soil, and the miniature steel pipe piles as anchor rods. The anchor rods are anchored above the anchor plate using a pre-tightening device. The arching deformation and axial pre-tightening force are collected by sensors and a data acquisition instrument. Based on the monitoring data, the pre-tightening nuts are adjusted on-site, thereby controlling the arching deformation of the high-speed railway subgrade caused by expansive rock within an allowable range. Compared with existing technologies, this invention features simple operation, high accuracy, strong safety, and low cost. It provides a new approach and means to solve the problem of arching deformation of high-speed railway subgrades in expansive rock strata areas, and has significant engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of high-speed railway subgrade disaster prevention and control technology, specifically relating to an on-site adjustment device, method and application for arch deformation of high-speed railway subgrade. Background Technology

[0002] By the end of 2023, my country's high-speed railway operating mileage had exceeded 43,700 kilometers, inevitably traversing areas with expansive rock distribution, such as red bed soft rock. Expansive rock is highly susceptible to arching deformation due to factors such as water expansion, stress relaxation, excavation unloading, tectonic stress, and rheological properties. If appropriate measures are not taken to address this arching deformation, it will severely affect the comfort of high-speed train operation and even threaten operational safety. Currently, during the construction phase of high-speed railways, a crossing method is often used, employing roadbed pile rafts and pile-slab structures to cross expansive rock, leaving sufficient space between the piles / slabs and the expansive rock for arching deformation. However, this structure is costly. During the operation phase of high-speed railways, methods such as subgrade replacement and thinning of the supporting layer are used to address arching. Subgrade replacement involves excavating the roadbed fill material and injecting high-performance polymers to adjust the track slab elevation to the design elevation; cutting the supporting layer involves removing the supporting layer concrete to lower the track elevation. However, these methods for addressing arching deformation during operation are only applicable when the arching deformation has converged.

[0003] Existing technologies have reported the use of prestressed reinforcement systems to address foundation arching deformation. For example, Chinese utility model patent CN211079770U discloses an anti-uplift support structure for ballastless track high-speed railways. However, existing prestressed reinforcement systems employ direct tensioning technology during construction. Once tensioning is complete, the shape and state of the reinforcement system are fixed and cannot be re-tensioned. This characteristic means that the prestressed reinforcement system cannot be dynamically adjusted or reused after construction. In other words, over-tensioning measures can only be implemented during the prestressing process to offset potential subsequent prestress losses. It is impossible to supplement or adjust the prestress during the service life of the prestressed components, thus constituting passive reinforcement. Furthermore, this reinforcement method involves only one reinforcement treatment in engineering, and for safety reasons, it often tends to apply excessive prestress. However, this prestress may not be fully utilized, leading to wasted resources and unnecessary economic losses. Summary of the Invention

[0004] The purpose of this invention is to provide a field adjustment device, method and application for high-speed railway subgrade arch deformation based on micro steel pipe pile treatment, so that the stress state of micro steel pipe pile is changed from a passive stress state driven by the arch deformation of the surrounding rock and soil to an active control state, thereby realizing the adjustment of the arch deformation of high-speed railway subgrade.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides an on-site adjustment device for arch deformation on a high-speed railway subgrade, comprising a miniature steel pipe pile, a pre-tightening device, a displacement sensor, an axial force sensor, and a data acquisition instrument; the pre-tightening device comprises a pre-tightening nut, an elastic component, and a support plate;

[0007] The lower end of the micro steel pipe pile is a buried section, and the upper end is an anchor head section. The diameter of the anchor head section is smaller than the diameter of the buried section, and a shoulder is formed at the junction of the anchor head section and the buried section. The anchor plate is fitted on the anchor head section and contacts the shoulder.

[0008] An external thread is provided on the anchor head section. The axial force sensor, support plate, and elastic component are sequentially fitted on the anchor head section. The preload nut is screwed onto the external thread to compress the elastic component, so that the axial force sensor and support plate are axially positioned relative to the anchor plate. The preload nut is preferably a flared nut with an enlarged lower end, which facilitates the connection and stabilization of the elastic component.

[0009] The support plate is equipped with a displacement sensor. The measuring probe of the displacement sensor is in contact with the upper surface of the anchor plate. The displacement sensor, the axial force sensor and the data acquisition instrument are electrically connected. The data acquisition instrument can acquire the monitoring data of the displacement sensor and the axial force sensor in real time, that is, acquire the monitoring data of the arch deformation and the axial preload of the preload device in real time.

[0010] Furthermore, the micro steel pipe pile is made of seamless steel pipe, with the diameter of the buried section being less than or equal to 300 mm and the slenderness ratio generally greater than or equal to 30; the wall thickness of the micro steel pipe pile is greater than or equal to 5.5 mm.

[0011] Furthermore, the maximum compressive deformation of the elastic component is greater than or equal to the maximum upward arching deformation of the roadbed design, and the maximum allowable working load is greater than or equal to the design value of the axial preload of the on-site adjustment device; the elastic component is preferably a high-strength compression spring or a high-elasticity, high-strength rubber pad.

[0012] Furthermore, the length of the external thread at the upper end of the anchor head section of the miniature steel pipe pile is greater than or equal to the sum of the heights of the elastic component and the preload nut.

[0013] Secondly, the present invention provides a field adjustment method for a field adjustment device for arch deformation on a high-speed railway subgrade, comprising the following steps:

[0014] S1, the micro steel pipe pile is buried under the concrete track slab and extends into the foundation rock and soil, and an on-site adjustment device is installed.

[0015] S2. After the on-site adjustment device is installed, the pre-tightening nut is initially tightened to provide the high-speed railway subgrade with the initial pre-tightening force (set to within 1 / 4 of the axial pre-tightening force design value (approximately 0~50kN for an 8m pile length). Under this pre-tightening force, part of the upward arching force can be effectively offset, and the components can be prevented from bearing excessive stress for a long time, thereby ensuring the stability and safety of the structure). Then, the monitoring data of the displacement sensor and axial force sensor are initialized (reset to zero).

[0016] S3, the data acquisition instrument continuously collects monitoring data from the displacement sensor and axial force sensor. When an upward arching displacement occurs, the preload nut is tightened on site, and the axial force monitoring value is controlled to be less than or equal to the axial preload design value.

[0017] Furthermore, when the monitored value of the upper arch displacement exceeds 90% of the allowable upper arch deformation (4mm), i.e., 3.6mm, the preload nut is tightened on-site using a pipe wrench or wrench to control the upper arch deformation within the range of less than or equal to 90% of the allowable upper arch deformation; when the monitored value of the axial force is greater than the design value of the axial preload, an alarm is triggered.

[0018] Furthermore, the design value of the axial preload of the on-site adjustment device is determined according to the following method:

[0019] The design value of axial preload is determined by both the ultimate pull-out force and the ultimate tensile strength of the micro steel pipe pile. The smaller value between the two axial preloads is taken as the design value of the axial preload of the on-site adjustment device; that is, it is determined according to formula (1):

[0020] (1)

[0021] In the formula: This is the design value of the axial preload of the on-site adjustment device; The axial preload is determined by the ultimate pull-out resistance of the micro steel pipe pile; The axial preload is determined by the ultimate tensile strength of the micro steel pipe pile;

[0022] Among them, the axial preload is determined by the ultimate pull-out resistance of the micro steel pipe pile. Determine according to formula (2):

[0023] (2)

[0024] In the formula: The ultimate pull-out force of the micro steel pipe pile is obtained from the field pull-out test; The safety factor for pull-out bearing capacity is taken as 0.9;

[0025] Among them, the axial preload is determined by the ultimate tensile strength of the micro steel pipe pile. Determine according to formula (3):

[0026] (3)

[0027] In the formula: The yield strength tensile stress of the micro steel pipe pile. The critical cross-sectional area of ​​the threaded section of the miniature steel pipe pile; For the tensile strength safety factor, when the material of the micro steel pipe pile is carbon steel, When the material of the micro steel pipe pile is alloy steel, .

[0028] Furthermore, the design value of the axial preload of the on-site adjustment device is greater than or equal to the axial preload required to resist the maximum upward arching deformation of the roadbed, and preferably the design value of the axial preload is 1.2-1.5 times the axial preload required to resist the maximum upward arching deformation of the roadbed.

[0029] Furthermore, the axial preload required to resist the maximum upward arching deformation of the roadbed design is determined by the following method:

[0030] Based on engineering experience, geological survey data, and literature, the maximum design arch deformation of the subgrade was determined. An indoor model device matching the on-site adjustment device was designed. Through indoor model tests, the relationship curve between the preload displacement and the axial preload force (measured by an axial force sensor) of the preload device when the subgrade reached the maximum design arch deformation was obtained. Based on the allowable arch deformation (the existing "High-Speed ​​Railway Design Specification TB10621-2014" stipulates that the allowable arch deformation of fasteners during ballastless track operation is 4mm), the corresponding design preload displacement was determined. The axial preload force required to resist the maximum design arch deformation of the subgrade was obtained based on the design preload displacement. Regression analysis was used to fit the experimental data when determining the relationship curve between the preload displacement and the axial preload force.

[0031] The indoor model device is designed according to the following method:

[0032] Miniature steel pipe pile simulation: The buried section of the miniature steel pipe pile is divided into an anchorage section and a free section. The anchorage section is the part of the buried section of the miniature steel pipe pile that is constrained by the surrounding soil or rock, and the free section is the part of the buried section of the miniature steel pipe pile that is not constrained by the surrounding soil or rock. In the indoor simulation of the miniature steel pipe pile, the influence of time-related factors such as stress relaxation and creep on the pile performance is ignored. The bottom of the miniature steel pipe pile is firmly welded to the base steel plate to simulate the anchorage section of the miniature steel pipe pile. The free section of the steel pipe pile is set to 0.8-1.2m, preferably 1m, to simulate the part of the miniature steel pipe pile that is not constrained by the surrounding soil or rock. This part of the pile can perform relatively free small expansion and contraction movements when subjected to external forces.

[0033] High-speed railway subgrade simulation: Although the high-speed railway subgrade is mainly composed of track slabs, self-compacting concrete layers and concrete bases, since the arching phenomenon of the subgrade ultimately manifests as the deformation of the track slabs, only track steel plates are used to simulate concrete track slabs, without considering the self-compacting concrete layers and concrete bases.

[0034] Simulation of arch deformation: Two jacks are symmetrically set on both sides of the micro steel pipe pile. The two jacks are located between the base steel plate and the track steel plate. The track steel plate is lifted by the two jacks to simulate the arch deformation caused by the expansion of the rock.

[0035] The indoor model device was tested using the following method:

[0036] Assemble the indoor model device; control two jacks to push the track steel plate up until the deformation of the track steel plate reaches the maximum arch deformation designed for the roadbed; initially tighten the nuts to make them contact the support plate, initialize the axial force sensor, and record the deformation monitoring data; select the maximum preload test value, tighten the preload nuts, and make the preload reach the maximum preload test value in multiple stages. After each stage of preload stabilizes, record the deformation monitoring data; obtain the relationship curve between preload displacement and axial preload based on the deformation monitoring data under each stage of preload.

[0037] Thirdly, the on-site adjustment device for arch deformation on high-speed railway subgrade of the present invention is designed according to the following method when applied:

[0038] Based on engineering experience, geological survey data and literature, determine the target value for controlling the arch deformation, that is, determine the maximum arch deformation of the roadbed design, determine the design value of the axial preload based on the axial preload required to resist the maximum arch deformation of the roadbed design, and preliminarily design the cross-sectional dimensions and pile length of the buried section of the micro steel pipe pile based on the design value of the axial preload.

[0039] Small-sample horizontal resistance tests and vertical pull-out tests were conducted on-site within the construction site to obtain the physical and mechanical properties of the soil and rock, the ultimate pull-out force of the micro-steel pipe piles, and the ground stress or lateral pressure. The cross-sectional dimensions and pile length of the buried section of the micro-steel pipe piles were adjusted and determined based on the ultimate pull-out force of the micro-steel pipe piles.

[0040] Based on the measured physical and mechanical properties of the soil and rock at the site, the ground stress or lateral pressure, and the adjusted cross-sectional dimensions and pile length of the buried section of the micro steel pipe pile, the preliminary layout scheme of the pile group (including the row spacing and column spacing of the pile group) is determined, and the amount of roadbed arching deformation after pile group treatment is calculated by formula method or numerical simulation method.

[0041] Determine whether the obtained roadbed arch deformation is less than or equal to the allowable arch deformation of 4mm. If it is satisfied, the micro steel pipe pile layout scheme is obtained. If it is not satisfied, the design parameters of the buried section of the micro steel pipe pile (section size, pile length, pile row spacing and column spacing, etc.) are optimized and recalculated until it is satisfied.

[0042] Based on the design value of axial preload, determine the materials and dimensions of the preload nut, elastic component, and anchor head section of the micro steel pipe pile in the on-site adjustment device, and select the displacement sensor and axial force sensor.

[0043] The beneficial effects of this invention are as follows:

[0044] 1) Since the high-speed railway subgrade is made of reinforced concrete, its stiffness is much greater than that of the foundation rock and soil. Therefore, this invention regards the high-speed railway subgrade as an anchor plate to resist the arching deformation of the foundation rock and soil, and regards the micro steel pipe pile as an anchor rod. The anchor rod is anchored above the anchor plate by pre-tightening nuts, thereby controlling the arching deformation of the high-speed railway subgrade caused by the expansion rock within the allowable range.

[0045] 2) Existing prestressed reinforcement systems employ direct tensioning technology during construction. Once tensioning is complete, the shape and state of the reinforcement system are fixed and cannot be re-tensioned. This characteristic makes it impossible to dynamically adjust or reuse the prestressed reinforcement system after construction. This invention, however, can acquire axial force and deformation monitoring data in real time using sensors, and then adjust the prestressing device on-site based on the monitoring data. This achieves precise control of the prestressing force, enabling rapid response, simple operation, high accuracy, and improved resource utilization, which is beneficial for ensuring the safe operation of high-speed railways.

[0046] 3) During service, based on the adjustment effect of the on-site adjustment device and in accordance with the requirements of the design working conditions, the micro steel pipe piles can be pre-tightened and prestressed to maintain the stability and safety of the structure without stopping operation, thereby indirectly reducing operational losses.

[0047] 4) This invention has the advantage of low cost. Compared with the straddle-type design for preventing arch deformation, it can save more than 50% of the construction cost. Excavation and replacement, and cutting of the support layer involve route deceleration or shutdown, resulting in incalculable losses. This invention provides a new approach and method for solving the problem of arch deformation in high-speed railway subgrades in expansive rock strata areas, and has significant engineering application value. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the on-site adjustment device being installed on the high-speed railway subgrade.

[0049] Figure 2 This is a schematic diagram of the on-site adjustment device of the present invention.

[0050] Figure 3This is a schematic diagram of the preload nut.

[0051] Figure 4 This is a schematic diagram of sensor installation on the support plate.

[0052] Figure 5 Figure 1 shows the pull-out test curves for different pile lengths; Figure 2 shows the pile length of 8m, Figure 3 shows the pile length of 10m, and Figure 4 shows the pile length of 12m.

[0053] Figure 6 This is a schematic diagram of the indoor model device of the present invention.

[0054] Figure 7 This is a schematic diagram of the pre-tightening device in the indoor model device of the present invention.

[0055] Figure 8 This is the curve showing the relationship between the preload and the arch deformation of the indoor model device of this invention.

[0056] Figure 9 This is a schematic diagram of the excavated roadbed in Example 2.

[0057] Figure 10 Figure (a) is a schematic diagram of the layout of miniature steel pipe piles in Example 2; where Figure (b) is a plan view and Figure (a) is a vertical cross-section view.

[0058] Figure 11 This refers to the amount of upward arch deformation control for single micro steel pipe columns of different pile lengths under different pre-tightening forces in Example 2.

[0059] Figure 12 This is a diagram showing the distribution of arching deformation on the roadbed surface after treatment with single micro steel pipe columns of different pile lengths in Example 2.

[0060] Figure 13 Figure (a) shows the cloud diagram of pile group treatment when the longitudinal pile spacing is 5D in Example 2; Figure (b) shows the treatment before treatment and Figure (a) shows the treatment after treatment.

[0061] Figure 14 Design flowchart for micro steel pipe piles used in high-speed railway subgrades to resist arching deformation in expansive rock strata.

[0062] In the diagram: 1. Preload nut, 2. High-strength compression spring, 3. Sensor mounting base, 4. Displacement sensor, 5. Support plate, 6. Circular axial force sensor, 7. Miniature steel pipe pile anchor head section, 8. Anchor plate, 9. Miniature steel pipe pile buried section, 10. Data acquisition instrument, 11. High-speed rail track, 12. Concrete track slab, 13. Self-compacting concrete layer, 14. Concrete base, 15. Foundation (including expansive rock layer), 16. Signal transmission connector, 17. Track steel plate, 18. Free section of steel pipe pile, 19. Jack, 20. Base steel plate, 21. Fixed crossbeam, 22. Displacement sensor, 23. Preload nut, 24. Circular axial force sensor, 25. Displacement sensor digital display, 26. Axial force sensor digital display. Detailed Implementation

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0064] Example 1;

[0065] See Figure 1-7 ;

[0066] This embodiment provides an on-site adjustment device for arch deformation on a high-speed railway subgrade, including a miniature steel pipe pile buried section 9, a pre-tightening device, a displacement sensor 4, an axial force sensor, and a data acquisition instrument 10; the pre-tightening device includes a miniature steel pipe pile anchor section 7, a pre-tightening nut 1, an elastic component, and a support plate 5;

[0067] The lower end of the micro steel pipe pile is a buried section, and the upper end of the micro steel pipe pile is an anchor head section. The top of the buried section is provided with a positioning shoulder. The diameter of the anchor head section 7 of the micro steel pipe pile is smaller than the diameter of the buried section 9 of the micro steel pipe pile. The anchor plate 8 is sleeved on the anchor head section 7 of the micro steel pipe pile and contacts the positioning shoulder.

[0068] The outer periphery of the micro steel pipe pile anchor head section 7 is coaxially fitted with an axial force sensor, a support plate 5, and an elastic component from bottom to top. The upper end of the micro steel pipe pile anchor head section 7 is provided with an external thread. The pre-tightening nut 1 is screwed onto the external thread to compress the elastic component, so that the axial force sensor and the support plate 5 are axially positioned relative to the anchor plate 8. The axial force sensor is a ring-shaped axial force sensor 6. The pre-tightening nut 1 is preferably a flared nut with an enlarged lower end, which facilitates the connection and stabilization of the elastic component.

[0069] The displacement sensor 4 is mounted on the support plate 5. The measuring probe of the displacement sensor 4 is in perpendicular contact with the upper surface of the anchor plate 8. The displacement sensor 4, the axial force sensor and the data acquisition instrument 10 are connected. The data acquisition instrument 10 can acquire the monitoring data of the displacement sensor 4 and the axial force sensor in real time, that is, acquire the monitoring data of the upper arch deformation and the axial preload of the preload device in real time. The displacement sensor 4 is equipped with a signal transmission connector 16 and is connected to the data acquisition instrument 10.

[0070] A high-speed rail track 11 is provided above the concrete track slab 12, and a self-compacting concrete layer 13 and a concrete base 14 are provided below it. The concrete base 14 is located on the foundation 15. The buried section 9 of the micro steel pipe pile passes through the concrete track slab 12, the self-compacting concrete layer 13, the concrete base 14, the foundation 15, and the upper expansive rock layer, and its lower end is buried in the foundation soil layer. The positioning shoulder at the top of the buried section 9 of the micro steel pipe pile is flush with the concrete track slab 12. The anchor head section 7 of the micro steel pipe pile is exposed on the concrete base 14, and the bottom surface of the anchor plate 8 is in contact with the upper surface of the concrete track slab 12.

[0071] The micro steel pipe piles are made of seamless steel pipes. The diameter of the buried section 9 of the micro steel pipe pile is less than or equal to 300 mm, and the slenderness ratio is generally greater than or equal to 30. The diameter of the anchor section 7 of the micro steel pipe pile is greater than or equal to 80% of the diameter of the buried section 9. The wall thickness of the micro steel pipe pile is greater than or equal to 5.5 mm. Since the micro steel pipe piles in this on-site adjustment device are mainly subjected to tension, when designing the micro steel pipe piles, the local rock strata parameters are first investigated according to the project requirements to determine the maximum upward arch deformation of the roadbed and the axial preload required to resist the maximum upward arch deformation and the design value of the axial preload. Then, combined with the results of the on-site in-situ pull-out test, 0.9 times the ultimate pull-out force of the micro steel pipe pile is selected as the maximum value of the axial preload that can be applied. Finally, based on the ultimate pull-out force and the design value of the axial preload, the pile length of the micro steel pipe pile is determined.

[0072] The inner diameter of the elastic component is greater than or equal to the outer diameter of the micro steel pipe pile anchor head section 7; the maximum compression deformation is greater than or equal to the maximum upward arching deformation of the roadbed design; and the maximum allowable working load is greater than or equal to the design value of the axial preload of the on-site adjustment device. The elastic component is preferably a high-strength compression spring 2 or a high-elasticity, high-strength rubber pad. When using a high-strength compression spring 2, based on the above requirements, the maximum allowable working load F of the high-strength compression spring 2 can be determined. n With the maximum compressive deformation f n Then, based on the main dimensions and parameters of the spring given in Table 2 of "Dimensions and Parameters of Ordinary Cylindrical Helical Compression Springs" (GB / T 2089-2009), select key parameters such as the number of spring coils, material, spring mean diameter, spring outer diameter, and free height.

[0073] The length of the external thread at the upper end of the anchor head section 7 of the miniature steel pipe pile is greater than or equal to the sum of the heights of the elastic component and the preload nut 1.

[0074] This embodiment provides a field adjustment method for a field adjustment device for arch deformation on a high-speed railway subgrade, including the following steps:

[0075] S1, Install the on-site adjustment device: Bury the micro steel pipe pile buried section 9 under the concrete track slab 12 and extend it into the foundation soil. Install the anchor plate 8, axial force sensor, support plate 5, displacement sensor 4, elastic component, and pre-tightening nut 1 on the micro steel pipe pile anchor head section. Connect the axial force sensor and displacement sensor 4 to the data acquisition instrument 10.

[0076] S2. After the on-site adjustment device is installed, the preload nuts are initially tightened to provide initial preload force for the high-speed railway subgrade (determined by indoor model tests: the initial preload force can be set to 0~1 / 4 of the axial prestress design value. Under this preload force, part of the upward arching force can be effectively offset, and the components can be prevented from bearing excessive stress for a long time, thereby ensuring the stability and safety of the structure). Then, the monitoring data of the displacement sensor and axial force sensor are initialized (reset to zero).

[0077] S3, the data acquisition instrument continuously collects monitoring data from the displacement sensor and axial force sensor. When the monitored value of the camber deformation exceeds 90% of the allowable camber deformation of 4mm for fasteners during the operation period of ballastless track as specified in the high-speed railway design specification TB10621-2014, i.e., 3.6mm, and the monitored value of the axial force is less than or equal to the design value of the axial preload, the preload nut is tightened on-site with a pipe wrench or wrench to control the camber deformation within the range of less than or equal to 90% of the allowable camber deformation. When the monitored value of the axial force is greater than the design value of the axial preload, an alarm is triggered.

[0078] The design value of the axial preload of the on-site adjustment device is determined according to the following method:

[0079] The design value of axial preload is determined by both the ultimate pull-out force and the ultimate tensile strength of the micro steel pipe pile. The smaller value between the two axial preloads is taken as the design value of the axial preload of the on-site adjustment device; that is, it is determined according to formula (1):

[0080] (1)

[0081] In the formula: This is the design value of the axial preload of the on-site adjustment device; The axial preload is determined by the ultimate pull-out resistance of the micro steel pipe pile; The axial preload is determined by the ultimate tensile strength of the micro steel pipe pile;

[0082] Among them, the axial preload is determined by the ultimate pull-out resistance of the micro steel pipe pile. Determine according to formula (2):

[0083] (2)

[0084] In the formula: The ultimate pull-out force of the micro steel pipe pile is obtained from the field pull-out test; The safety factor for pull-out bearing capacity is taken as 0.9;

[0085] Among them, the axial preload is determined by the ultimate tensile strength of the micro steel pipe pile. Determine according to formula (3):

[0086] (3)

[0087] In the formula: The yield strength tensile stress of the micro steel pipe pile. The critical cross-sectional area of ​​the threaded section of the miniature steel pipe pile; For the tensile strength safety factor, when the material of the micro steel pipe pile is carbon steel, When the material of the micro steel pipe pile is alloy steel, .

[0088] The design value of the axial preload of the on-site adjustment device is greater than or equal to the axial preload required to resist the maximum upward arching deformation of the roadbed. The preferred design value of the axial preload is 1.2-1.5 times the axial preload required to resist the maximum upward arching deformation of the roadbed.

[0089] Furthermore, the axial preload required to resist the maximum upward arching deformation of the roadbed design is determined using the following method:

[0090] Based on engineering experience, geological survey data, and literature, the maximum design arch deformation of the roadbed is determined. An indoor model test is then conducted to match the design of the on-site adjustment device. This indoor model test yields the relationship curve between the preload displacement and axial preload when the roadbed reaches its maximum design arch deformation. The corresponding preload displacement is determined based on the allowable arch deformation, and subsequently, the corresponding axial preload. The allowable arch deformation control limit is determined by specifications, generally 4 mm. Regression analysis can be used to fit the test data when determining the relationship curve between the preload displacement and axial preload.

[0091] The indoor model test was designed according to the following method, and the structural schematic diagram of the indoor model device is shown below. Figure 6 A schematic diagram of the pre-tightening device in the indoor model device is shown below. Figure 7 :

[0092] ① Simulation of micro-steel pipe piles: The buried section of the micro-steel pipe pile is divided into an anchoring section and a free section. The anchoring section is the part of the buried section of the micro-steel pipe pile that is constrained by the surrounding soil or rock, and the free section is the part of the buried section of the micro-steel pipe pile that is not constrained by the surrounding soil or rock. In the process of simulating micro-steel pipe piles indoors, the influence of time-related factors such as stress relaxation and creep on the performance of the pile is ignored. The bottom of the micro-steel pipe pile is firmly welded to the base steel plate 20 to simulate the anchoring section of the micro-steel pipe pile. The length of the free section 18 of the micro-steel pipe pile is set to 0.8-1.2m, preferably 1m, to simulate the part of the micro-steel pipe pile that is not constrained by the surrounding soil or rock. When the pile body is subjected to external forces, it can perform small expansion and contraction movements relatively freely.

[0093] ② High-speed railway subgrade simulation: Although the high-speed railway subgrade consists of a concrete track slab 12, a self-compacting concrete layer 13, and a concrete base 14, the arching phenomenon of the subgrade is ultimately manifested as the deformation of the concrete track slab 12. Therefore, only the track steel plate 17 is used to simulate the concrete track slab 12, and the self-compacting concrete layer 13 and the concrete base 14 are not considered.

[0094] ③ Simulation of arch deformation: Two jacks 19 are symmetrically set on both sides of the micro steel pipe pile. The two jacks are located on the base steel plate 20 and between the track steel plate 17. The track steel plate 17 is lifted by the two jacks 19 to simulate the arch deformation caused by the expanding rock.

[0095] ④ Pre-tightening device simulation: A through hole is set on the track steel plate 17, allowing the free section 18 of the steel pipe pile to pass through the through hole. An anchor plate 8, support plate 5, and pre-tightening nut 1 are installed on the anchor head section of the micro steel pipe pile. No elastic component is provided in this embodiment.

[0096] ⑤ Simulation monitoring: A ring-shaped axial force sensor 24 is installed on the outer periphery of the steel pipe pile, located between the anchor plate 8 and the support plate 5. The ring-shaped axial force sensor 24 is connected to the data acquisition instrument 10. In addition, in order to monitor the upward arching deformation of the base steel plate, a displacement sensor 22 is also installed on the track steel plate 17. The base of the displacement sensor 22 (a dial indicator can be used to measure the displacement in the indoor simulation device) is fixed on the fixed crossbeam 21 outside the indoor simulation device. In this experiment, the data acquisition instrument 10 includes a displacement sensor digital display 25 and an axial force sensor digital display 26.

[0097] By installing pile groups and the aforementioned on-site adjustment devices (excluding displacement sensors, axial force sensors, and data acquisition instruments) within the arch area of ​​the high-speed railway subgrade, and combining this with on-site arch deformation monitoring (leveling method, total station method, and radar interferometry method), on-site control of arch deformation can be achieved. However, on-site monitoring is relatively inconvenient, and due to the impact of high-speed railway operation, it is not possible to conveniently and quickly obtain arch deformation data. Based on the aforementioned on-site adjustment devices, automatic data acquisition methods (including displacement sensors, axial force sensors, and data acquisition instruments) can further improve the monitoring rate and shorten the control response time, thereby ensuring operational safety.

[0098] Furthermore, the field adjustment device is installed in the following manner:

[0099] Miniature steel pipe piles: The holes are formed by water drilling with a geological drilling rig, and mud slurry is used to protect the hole wall to prevent collapse. The holes are drilled into the foundation rock and soil on the surface of the high-speed railway subgrade. After the holes are formed, the miniature steel pipe pile buried section 9 is inserted into the holes so that the top of the miniature steel pipe pile buried section 9 is flush with the concrete track slab 12. The steel pipe is used as the skeleton and cement mortar or fine stone concrete is poured. Grouting is carried out inside the steel pipe. After the grouting is completed, the grouting pressure should be maintained for a period of time until the grout no longer absorbs grout or the grout returns to the hole.

[0100] Anchor plate 8 is fitted onto the anchor head section 7 of the micro steel pipe pile, making the anchor plate 8 contact the surface of the concrete track slab 12 and the top of the buried section 9 of the micro steel pipe pile. Then, an annular axial force sensor 6, a support plate 5, and a high-strength compression spring 2 are fitted around the outer periphery of the anchor head section 7 of the micro steel pipe pile. A pre-tightening nut 1 is installed at the upper end of the anchor head section 7 of the micro steel pipe pile. Tightening the pre-tightening nut 1 makes the anchor plate 8, annular axial force sensor 6, support plate 5, high-strength compression spring 2, and pre-tightening nut 1 contact. At least two displacement sensors 4 are installed on the side of the support plate 5, so that the measuring probe of the displacement sensor 4 abuts against the upper surface of the anchor plate 8. The displacement sensor 4 and the annular axial force sensor 6 are connected to the data acquisition instrument 10.

[0101] The detailed installation method and process of the on-site adjustment device after the micro steel pipe piles are driven are as follows:

[0102] ① Anchor plate 8 is installed on the outer periphery of the anchor head section 7 of the miniature steel pipe pile: the anchor plate 8 is positioned in contact with the positioning shoulder and the upper surface of the concrete track slab 12. The function of the anchor plate 8 is to provide a stable connection surface to ensure the accurate installation of the component and the accurate monitoring of the displacement sensor.

[0103] ② Install the annular axial force sensor 6: Install the annular axial force sensor 6 on the outer periphery of the micro steel pipe pile anchor head section 7, located above the anchor plate 8, to ensure that the connection between the annular axial force sensor 6 and the micro steel pipe pile anchor head section 7 is tight and stable.

[0104] ③ Install support plate 5: Place support plate 5 around the outer periphery of the micro steel pipe pile anchor head section 7 and above the annular axial force sensor 6 to ensure the correct position and stability of the annular axial force sensor 6.

[0105] ④ Install the pre-tightening nut 1: Place the high-strength compression spring 2 around the outer periphery of the micro steel pipe pile anchor head section 7 and above the support plate 5. Install the pre-tightening nut 1 on the threaded part of the micro steel pipe pile anchor head section 7. Initially tighten the pre-tightening nut 1 to contact the high-strength compression spring 2 and perform initial pre-tightening on the on-site control device.

[0106] ⑤ Install displacement sensor mounting base 3 and displacement sensor 4: Two sensor mounting bases 3 are symmetrically arranged on the side of the support plate 5. The displacement sensor 4 is directly installed on the sensor mounting base 3 of the support plate 5 and the two are fixed together by bolts or other fasteners.

[0107] ⑥ Inspection and Adjustment: After installation, check that all components are installed correctly and ensure that the connections between them are tight and stable.

[0108] Real-time acquisition of axial preload can be used to determine the pull-out resistance of micro steel pipe piles. When it reaches 0.9 times the ultimate pull-out resistance, it indicates that the on-site adjustment device has reached the most dangerous state and can no longer control the arching deformation of the roadbed, thus avoiding blind adjustment that could lead to the steel pipe pile being pulled out. When the axial preload reaches the design value of the axial preload (usually 0.9 times the ultimate pull-out resistance), an alarm should be triggered, and further measures should be taken to deal with the arching deformation, such as adding micro steel pipe columns.

[0109] The ultimate pull-out force of micro-steel pipe piles needs to be determined through on-site vertical pull-out tests. These tests are conducted near the roadbed. If the errors in multiple test sets are small, the average value can be used as the final pull-out force. If the test data are highly discrete, error analysis should be performed and supplementary tests should be conducted until a reliable pull-out force is obtained. The on-site pull-out test includes five parts: micro-pile drilling, installation, grouting and curing, determination of pull-out force, and test loading. The specific process is as follows:

[0110] (1) Micro-pile drilling: The geological drilling rig is used for water drilling, and mud is used to protect the hole wall to prevent it from collapsing.

[0111] (2) Installation of micro piles: After drilling is completed, the steel pipe piles are vertically lowered to the center of the borehole using a geological drilling rig, and the steel pipe piles are centered by adding a welded centering bracket on top of the piles so that the steel pipe piles are installed firmly.

[0112] (3) Grouting and curing: Grouting was performed intermittently from bottom to top using a grouting pipe, followed by static curing for 28 days. The compressive strength after 28 days of curing was tested by sampling.

[0113] (4) Determine the pull-out resistance: Calculate the standard value of the ultimate pull-out bearing capacity of a single pile with different pile lengths according to the formula for the ultimate pull-out bearing capacity in the current "Technical Specification for Building Pile Foundations (JGJ94-2008)". Subsequently, according to the "Technical Specification for Testing Building Pile Foundations" (JGJ106-2014), use an anchor pile beam device and hydraulic jacks to achieve graded loading through the slow-speed sustained load method.

[0114] (5) Test loading: During loading, ensure that the centroid of the bottom surface of the jack coincides with the center of the cross-section of the test pile. The loading amount for each stage is 0.1 times the ultimate bearing capacity. Load until failure or no further loading is possible. Measure the vertical deformation of the test pile using two dial gauges with a range of 50 mm symmetrically arranged at the pile head, with a measurement accuracy of 0.01 mm.

[0115] Based on the results of the in-situ pull-out test, 0.9 times the ultimate pull-out force was selected as the maximum applicable preload (Np).

[0116] The design value of the preload provided by the on-site adjustment device should be greater than or equal to the axial preload required to resist the maximum upward arching deformation of the roadbed. The design value of the preload is usually preferably 1.2 to 1.5 times the axial preload. When designing the preload, the maximum upward arching deformation of the roadbed should be set according to engineering experience. However, during the operation of high-speed railway, it is possible that the actual arching deformation exceeds the set maximum upward arching deformation of the roadbed. Therefore, making the design value of the preload greater than the set value of the axial preload can increase the adjustment margin of the on-site adjustment device and improve safety. However, if the design value of the preload is too large, it will lead to material waste and lack of economy.

[0117] Example 2;

[0118] like Figure 1-13 This embodiment is based on a project in Hengyang City on the Nanning-Hengyang High-Speed ​​Railway. The project is located in a deep excavation section of red bed soft rock, with a maximum excavation depth of 34.0m. The railway is a ballastless track with a roadbed width of 13.6m, a double-track spacing of 5m, and a single-track distance of 4.3m from the roadbed edge. Figure 9 This is a schematic diagram of the excavated roadbed. Figure 10 Figure (a) is a schematic diagram of the layout of micro steel pipe piles; and Figure (b) is a plan view and a vertical section view.

[0119] Based on the site's geological conditions, the initial design for the buried section 9 of the micro-steel pipe pile was a cross-sectional diameter of 170mm and a pile length of 8-12m, with a wall thickness of 5.5mm. In the pretreated red-bed soft rock site, piles were drilled using the initially designed pile cross-sectional dimensions and length, and small-scale vertical pull-out tests were conducted on-site. The results are shown in […]. Figure 5 The relevant design parameters (ultimate pull-out force, range of applicable prestress, etc.) of the buried section 9 of the micro steel pipe pile are obtained and are shown in Table 1.

[0120] Table 1 Prestressing Application Parameters

[0121]

[0122] Based on the results of the in-situ pull-out test, 0.9 times the ultimate pull-out force is selected as the maximum applicable preload (Np); the axial preload is calculated by using the applied torque value through equation (7).

[0123] Based on borehole data and literature, the maximum upward arching deformation of the roadbed was set at 9.5 mm. The axial preload corresponding to the maximum upward arching deformation was obtained through indoor model tests. The indoor model tests were conducted according to the following steps:

[0124] Assemble the indoor model device; control the two jacks to push the track steel plate up until the deformation of the track steel plate 17 reaches the estimated maximum arch deformation of the roadbed of 9.5mm, then stop pressurizing; initially tighten the preload nut 23 to make the structure contact but not generate preload force; initialize the reading of the ring axial force sensor 24; and record the deformation monitoring data; select the maximum preload test value, tighten the preload nut 23, and make the preload force reach the maximum preload test value in multiple stages. After each stage of preload force stabilizes, record the deformation monitoring data; according to the pull-out test results, this embodiment selects 200kN as the maximum preload value. During the tightening of the preload nut 23, under the five stages of preload force of 0kN, 50kN, 100kN, 150kN and 200kN respectively, after the preload force stabilizes, record the size of the arch deformation at this time;

[0125] Based on the deformation monitoring data under each level of preload, the relationship curves between different preloads and the upper arch deformation of the indoor model device were obtained, such as... Figure 8 The relationship curve between preload displacement and axial preload force can also be obtained from this curve (not shown in this embodiment). From Figure 8 As can be seen, as the preload increases, the upper arch deformation gradually decreases. When the preload reaches 200kN, the upper arch deformation decreases to about 2mm.

[0126] In this indoor test, the axial force data acquisition instrument used was the B920 model manufactured by Zhongxin Raytek, with a range of 1000kN, an accuracy of 1kN, and a sampling rate of 10 times / second. The miniature steel pipe piles demonstrated a significant effect in controlling the arching deformation of the roadbed. The test showed that the greater the prestressing force, the stronger the control effect. This fully verifies the feasibility of dynamically adjusting the prestressing magnitude according to actual conditions and further proves the practicality of this method.

[0127] Because field tests to study the reinforcement effects of different pile lengths, pile spacings, and pile diameters are time-consuming, labor-intensive, and costly, and it is impossible to directly observe the dynamic evolution of the reinforcement effect of micro steel pipe piles, Midas GTS NX software is used for numerical simulation to calculate the protective effect of micro steel pipe piles in order to analyze the influence of pile diameter, pile length, and pile spacing on the protective effect.

[0128] Based on the actual working conditions of the target site, a plane strain model was established. The model has a horizontal length of 164m, a slope height of 34m above the roadbed surface, a calculation depth of 40m below the roadbed surface, and a slope model width of 10m. The left, right, and bottom of the model are fixed boundaries, the top is a free boundary, and the front and rear boundaries are hinged (restricting displacement along the longitudinal direction of the track, but allowing displacement in the vertical and horizontal directions). The software's built-in mapping and meshing function was used to mesh the entire model's soil and rock mass, with fine-tuned mesh size control, resulting in a total of 67,200 nodes and 381,000 elements. The effect of initial horizontal ground stress was simulated by applying lateral pressure to the rock mass below the roadbed surface. Rock mass parameters were selected using data provided by the survey and analyzed using the Mohr-Coulomb constitutive model. The calculation parameters are shown in Table 2. A 3m long free section was uniformly set at the top of the micropiles, while the bottom was an anchored section. The pile diameter was 0.17m and the wall thickness was 5.5mm. The strongly weathered silty mudstone is a type of red bed soft rock.

[0129] Table 2 Material Parameters

[0130]

[0131] For single-pile analysis, three cases are considered: pile lengths of 8m, 10m, and 12m. For group pile analysis, only the 12m pile length is considered, and the remediation effects are compared under different group pile spacings (3D~6D, where D is the diameter of the micro-steel pipe pile). Micro-steel pipe piles are arranged on both sides of the track centerline and the left and right sides of the train track slab, with a spacing of 5 times the pile diameter (5D) perpendicular to the route direction. Along the route direction, the group pile spacing is arranged at 3D~6D, and the group pile layout method is described in [reference needed]. Figure 10 .

[0132] Numerical calculations show that the 12m long micro-steel pipe pile exhibits the best effect in controlling the upward arch deformation. After treatment with the 12m long micro-steel pipe pile, the controlled upward arch deformation under a preload of 0~1.0NP (0~200kN) is 2.7~5.0mm, with an upward arch reduction of approximately 28.4%~52.6%. Furthermore, it shows a significant effect within a 2.5 times pile diameter area around the steel pipe pile. The treatment effect is shown in [see figure]. Figure 11 and Figure 12 Therefore, the optimal spacing of the micro-steel pipe pile group can be determined to be 5D. After treatment with the micro-steel pipe pile group, the treatment effect is obvious, and the treatment effect of the pile group is evident. Figure 13 The reduction can reach about 70%. During the operation phase after the track is laid, the arching deformation of the test section subgrade can be controlled within 4mm.

[0133] Example 3;

[0134] In practical engineering applications, arching deformation usually occurs in a certain area below the roadbed. Using a single micro steel pipe pile cannot achieve the best adjustment effect, and a pile group design is required to resist the arching deformation of the roadbed. Therefore, this embodiment proposes a design method for applying an on-site adjustment device in practical engineering.

[0135] The specific design process for micro steel pipe piles in expansive rock strata is as follows, see flowchart. Figure 14 :

[0136] Based on engineering experience, geological survey data, and literature, the target value for controlling the deformation of the upper arch [S] was determined. u [S], that is, to determine the maximum upward arching deformation of the roadbed design. u [The design value of axial preload was determined, and then the cross-sectional dimensions and pile length of the buried section 9 of the micro steel pipe pile were preliminarily designed;]

[0137] Drilling and pile formation within the construction site area, and conducting on-site small-sample horizontal resistance tests and vertical pull-out tests to obtain the site's soil and rock physical and mechanical properties, the ultimate pull-out force of the micro-steel pipe piles, and the ground stress or lateral pressure; adjusting and determining the cross-sectional dimensions and pile length of the buried section 9 of the micro-steel pipe piles based on the ultimate pull-out force of the micro-steel pipe piles.

[0138] Based on the measured physical and mechanical properties of the soil and rock at the site, the ground stress or lateral pressure, and the adjusted cross-sectional dimensions and pile length of the buried section 9 of the micro steel pipe piles, a preliminary pile group layout scheme was determined (including the determination of pile location, row spacing, and column spacing). The camber deformation of the roadbed after pile group treatment was calculated using numerical simulation. g ];

[0139] Determine the amount of roadbed arch deformation [S] obtained in step (3). g If the allowable arch deformation is less than or equal to 4mm, and the axial force of the pile body is less than or equal to 0.9 times the ultimate pull-out force of the pile, then the micro steel pipe pile layout scheme is obtained. If it is not satisfied, the design parameters (section size, pile length, pile row spacing and column spacing, etc.) of the buried section 9 of the micro steel pipe pile are adjusted and recalculated until they are satisfied.

[0140] Based on the design value of axial preload, determine the materials and dimensions of the preload nut and elastic component in the on-site adjustment device, as well as the micro steel pipe pile anchor section 7, and select the displacement sensor and axial force sensor.

[0141] The on-site adjustment device used in this invention costs approximately 500 yuan per set for the pre-tightening device and approximately 1000 yuan per unit for the data acquisition instrument, which can simultaneously collect displacement and pressure data from 10 pile heads. The cost of the micro-steel pipe piles is approximately 180 yuan per meter. Based on a row of 6 piles, a pile length of 12 meters, and a spacing of 5 times the pile diameter per row, the cost of 100 linear meters of double-track track is approximately 1.356 million yuan. Compared to the method of using a straddle-type design to prevent arching deformation of the high-speed railway subgrade, this method can save more than 50% of the cost. Excavation, replacement, and cutting of the support layer involve deceleration or shutdown of the line, resulting in incalculable losses. Therefore, the device described in this invention has advantages such as simple operation, safety, reliability, and low cost.

[0142] Matters not covered in this invention are existing technologies.

[0143] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Any modifications or substitutions made by other people skilled in the art to the technical solution, as long as they do not depart from the connotation of the technical solution of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for on-site adjustment of arch deformation on high-speed railway subgrade, characterized in that: The on-site adjustment device includes miniature steel pipe piles, anchor plates, pre-tightening devices, displacement sensors, axial force sensors, and data acquisition instruments; the pre-tightening device includes a crimping adapter, a pre-tightening nut, an elastic component, and a support plate; The lower end of the micro steel pipe pile is a buried section, and the upper end is an anchor head section. The diameter of the anchor head section is smaller than the diameter of the buried section, and a shoulder is formed at the junction of the anchor head section and the buried section. The anchor plate is fitted on the anchor head section and contacts the shoulder. An external thread is provided on the anchor head section. The axial force sensor, support plate, and elastic component are sequentially installed on the anchor head section. The preload nut is screwed onto the external thread to compress the elastic component, so that the axial force sensor and support plate are axially positioned relative to the anchor plate. The support plate is equipped with a displacement sensor. The measuring probe of the displacement sensor is in contact with the upper surface of the anchor plate. The displacement sensor, the axial force sensor and the data acquisition instrument are electrically connected. The field adjustment device is adjusted in the field as follows: S1, the micro steel pipe pile is buried under the concrete track slab and extends into the foundation rock and soil, and an on-site adjustment device is installed. S2, initially tighten the preload nuts to provide initial preload for the high-speed railway subgrade and initialize the monitoring data of the displacement sensor and axial force sensor; the initial preload is set to 0~1 / 4 of the axial prestress design value. Under this preload, part of the upward arching force is effectively offset and the components are prevented from bearing excessive stress for a long time, thereby ensuring the stability and safety of the structure. S3, the data acquisition instrument continuously collects monitoring data from the displacement sensor and axial force sensor. When an upward arch displacement occurs, the preload nut is tightened on-site, and the axial force monitoring value is controlled to be less than or equal to the axial preload design value. Under the premise that the axial force monitoring value is less than or equal to the axial preload design value, when the upward arch displacement monitoring value exceeds 90% of the allowable upward arch deformation, the preload nut is tightened on-site to control the upward arch deformation within the range of less than or equal to 90% of the allowable upward arch deformation. When the axial force monitoring value is greater than the axial preload design value, an alarm is triggered.

2. The on-site adjustment method as described in claim 1, characterized in that: The diameter of the buried section of the micro steel pipe pile is less than or equal to 300 mm, the slenderness ratio is greater than or equal to 30, and the wall thickness is greater than or equal to 5.5 mm.

3. The on-site adjustment method as described in claim 1, characterized in that: The elastic component is a high-strength compression spring.

4. The on-site adjustment method as described in claim 1, characterized in that: When the monitored value of the upper arch displacement exceeds 90% of the allowable upper arch deformation, tighten the preload nuts on site to control the upper arch deformation within the range of less than or equal to 90% of the allowable upper arch deformation.

5. The on-site adjustment method as described in claim 1, characterized in that: The design value of the axial preload of the on-site adjustment device is determined according to formula (1): （1） Where: is the design value of the axial preload of the on-site adjustment device; is the axial preload determined by the ultimate pull-out resistance of the micro steel pipe pile; is the axial preload determined by the ultimate tensile strength of the micro steel pipe pile; Among them, it is determined according to formula (2): （2） Where: is the ultimate pull-out force of the micro steel pipe pile obtained from the field pull-out test; is the safety factor for pull-out bearing capacity; Among them, it is determined according to formula (3): （3） In the formula: is the yield limit tensile stress of the micro steel pipe pile, is the critical cross-sectional area of ​​the micro steel pipe pile thread; is the tensile strength safety factor.

6. The on-site adjustment method as described in claim 1 or 5, characterized in that: The design value of the axial preload of the on-site adjustment device is greater than or equal to the axial preload required to resist the maximum upward arching deformation of the roadbed.

7. The on-site adjustment method as described in claim 6, characterized in that: The axial preload required to resist the maximum upward arching deformation of the roadbed design is determined by the following method: Based on engineering experience, geological survey data, and literature, the maximum design arch deformation of the roadbed is determined. An indoor model device matching the on-site adjustment device is designed. Through indoor model tests, the relationship curve between the preload displacement and the axial preload force of the preload device when the roadbed reaches the maximum design arch deformation is obtained. The corresponding design preload displacement is determined based on the allowable arch deformation. The axial preload force required to resist the maximum design arch deformation of the roadbed is obtained based on the design preload displacement.

8. The application of the on-site adjustment method as described in any one of claims 1-4, characterized in that: Design according to the following method: Based on engineering experience, geological survey data and literature, the maximum upward arching deformation of the roadbed is determined. Based on the axial preload required to resist the maximum upward arching deformation of the roadbed, the design value of the axial preload is determined. Based on the design value of the axial preload, the cross-sectional dimensions and pile length of the buried section of the micro steel pipe pile are preliminarily designed. On-site horizontal resistance tests and vertical pull-out tests are conducted within the construction site area to obtain the physical and mechanical properties of the site's soil and rock, the ultimate pull-out force of the micro-steel pipe piles, and the ground stress or lateral pressure of the strata; the cross-sectional dimensions and pile length of the buried section of the micro-steel pipe piles are adjusted and determined based on the ultimate pull-out force of the micro-steel pipe piles. Based on the measured physical and mechanical properties of the soil and rock at the site, the ground stress or lateral pressure, and the adjusted cross-sectional dimensions and length of the buried section of the micro steel pipe pile, the pile group layout scheme is preliminarily determined, and the amount of roadbed arching deformation after pile group treatment is calculated by formula method or numerical simulation method. Determine whether the obtained roadbed arch deformation is less than or equal to the allowable arch deformation. If it is satisfied, the micro steel pipe pile layout scheme is obtained. If it is not satisfied, the design parameters of the buried section of the micro steel pipe pile are adjusted and recalculated until it is satisfied. The design parameters include cross-sectional dimensions, pile length, row spacing, and column spacing. Based on the design value of axial preload, determine the materials and dimensions of the preload nut and elastic component in the on-site adjustment device, as well as the dimensions of the micro steel pipe pile anchor head section, and select the displacement sensor and axial force sensor.

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