Fixing structure for tunnel bottom steel pipe pile of underneath passing subgrade tunnel and reinforcing method of fixing structure

Abstract

The invention discloses an underneath crossing roadbed tunnel bottom steel pipe pile fixing structure which comprises a plurality of steel arches arranged at the tunnel bottom and a plurality of steel pipe piles arranged below the steel arches at intervals, the steel arches are detachably connected, the steel pipe piles are arranged according to a quincunx structure, and every two adjacent steel pipe piles are connected through a connecting mechanism. The top of the steel pipe pile is connected with the bottom of the steel arch through an adjusting and fixing mechanism; the invention further discloses a reinforcing method which comprises the following steps that S1, a tunnel construction site is surveyed, and the physical and mechanical parameters of the tunnel bottom of the tunnel are obtained; s2, determining a train load in the tunnel; s3, the bearing capacity needed by the tunnel bottom is calculated according to the train load, and the specification and number of the steel pipe piles are determined according to the bearing capacity; and S4, based on the determined specification and number of the steel pipe piles, the tunnel bottom steel pipe pile fixing structure of the underpass roadbed tunnel is installed and arranged in a tunnel bottom reinforcing area, and reinforcing pile groups are formed. The technical problem that the bearing capacity of a tunnel base is insufficient can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering, and in particular relates to a steel pipe pile fixing structure at the bottom of an underpass roadbed tunnel and a reinforcement method thereof. Background Art

[0002] With the rapid development of high-speed rail networks, there are more and more cases where railway tunnels pass under highway roadbeds. Highway roadbeds are often made of artificial fill soil, which has large differences in mechanical properties. This often brings certain risks to tunnel construction and has an adverse impact on the subsequent tunnel operation settlement.

[0003] In order to ensure the stability of the tunnel during operation, steel pipe piles are often used to reinforce the tunnel bottom during tunnel construction. However, the current parameter design of steel pipe piles is mostly determined based on experience, and factors such as geological conditions and train operation conditions are not reasonably considered, which often leads to unnecessary waste due to large safety reserves. Moreover, during the current construction of steel pipe piles, steel arch frames are only erected on the steel pipe piles without a definite connection method, which makes the support unstable and may overturn when the train is running. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a steel pipe pile fixing structure at the bottom of an underpass roadbed tunnel and a reinforcement method thereof.

[0005] The first object of the present invention is to provide a steel pipe pile fixing structure at the bottom of an underpass roadbed tunnel, comprising a plurality of steel arch frames arranged at the bottom of the tunnel and a plurality of steel pipe piles arranged at intervals below the steel arch frames, the plurality of steel arch frames being detachably connected, the plurality of steel pipe piles being arranged in a plum blossom structure, two adjacent steel pipe piles being connected by a connecting mechanism, and the top of the steel pipe pile being connected to the bottom of the steel arch frames by an adjusting fixing mechanism.

[0006] Preferably, the connecting mechanism includes a connecting piece and two fixing rings, two slots are symmetrically provided on the outer surface of each steel pipe pile, two buckles are symmetrically arranged on the inner wall of each fixing ring, the two fixing rings are respectively sleeved on two adjacent steel pipe piles, and the two buckles on each fixing ring are respectively engaged with the corresponding two slots, and the two fixing rings are connected by a connecting piece.

[0007] Preferably, threaded holes are symmetrically arranged on both sides of the top of each steel arch frame, and two adjacent steel arch frames are connected by fixing screws and corresponding threaded holes.

[0008] Preferably, the adjusting and fixing mechanism includes a plurality of first threaded rods and a plurality of second threaded rods, the plurality of first threaded rods are arranged on the steel arch frame, the steel arch frame is connected to the top of the corresponding steel pipe piles directly below the steel arch frame through the first threaded rods, the plurality of second threaded rods are rotatably connected to the fixing screws, and the second threaded rods are connected to the corresponding steel pipe piles that are not directly below the steel arch frame.

[0009] A second object of the present invention is to provide a method for reinforcing the above-mentioned steel pipe pile fixed structure at the bottom of the underpass roadbed tunnel, comprising the following steps:

[0010] S1. Obtain the train load in the tunnel;

[0011] S2. Calculate the required bearing capacity of the tunnel bottom according to the train load, and determine the specifications and quantity of the steel pipe piles according to the bearing capacity;

[0012] S3. Based on the determined specifications and quantity of the steel pipe piles, the above-mentioned steel pipe pile fixing structure at the bottom of the tunnel under the roadbed is installed and set in the tunnel bottom reinforcement area to form a reinforcement pile group.

[0013] Preferably, step S1 comprises the following steps:

[0014] S11. Calculate the longitudinal average train load and the transverse average train load in the tunnel respectively;

[0015] S12, selecting the maximum value of the longitudinal average train load and the transverse average train load obtained in step S11 as the train load;

[0016] The calculation formula for the average transverse train load is:

[0017]

[0018] Wherein, N1 is the average transverse train load, F1 is the transverse concentrated load, a is the amount of transverse concentrated load, and W is the width of the track plate;

[0019] The calculation formula for the longitudinal average train load is:

[0020]

[0021] Where N2 is the average longitudinal train load, F2 is the longitudinal concentrated load, m is the number of longitudinal concentrated loads, q is the uniformly distributed load, L is the length of the track slab, and l is the distribution length of the longitudinal concentrated load;

[0022] Preferably, step S2 comprises the following steps:

[0023] S21. Calculate the characteristic value of the vertical bearing capacity of a single steel pipe pile according to the train load;

[0024] S22, according to the vertical bearing capacity characteristic value of the single steel pipe pile obtained in step S21, determine the vertical bearing capacity of the single steel pipe pile, and then obtain the steel pipe pile specifications;

[0025] S23, according to the train load obtained in step 22, calculate the required bearing capacity of the tunnel bottom;

[0026] S24. Determine the number of steel pipe piles based on the required bearing capacity of the tunnel bottom obtained in step S23 and the characteristic value of the vertical bearing capacity of a single steel pipe pile obtained in step S21.

[0027] Preferably, in step S22, the relationship between the characteristic value of the vertical bearing capacity of a single steel pipe pile and the vertical bearing capacity of a single steel pipe pile is:

[0028]

[0029] In the formula, R is the characteristic value of the vertical bearing capacity of a single steel pipe pile, K is the safety factor, and K=2; Q is the vertical bearing capacity of a single pile;

[0030] The vertical bearing capacity of a single steel pipe pile is calculated by the following formula:

[0031] Q=Q s +Q p =u∑q si l i +q p A p

[0032] In the formula, Q s , Q p are pile side friction and pile end resistance, q si is the ultimate lateral friction of the i-th layer of soil on the pile side; q p is the ultimate resistance of the pile tip, u and A p are the circumference of the pile and the area of ​​the pile tip, respectively, i is the thickness of the i-th soil layer.

[0033] Preferably, in step S24, the relationship between the required bearing capacity of the tunnel bottom and the characteristic value of the vertical bearing capacity of a single steel pipe pile is:

[0034] F≤nR

[0035] Where F is the total cross-sectional load, n is the number of steel pipe piles, and R is the characteristic value of the vertical bearing capacity of a single pile.

[0036] Preferably, step S3 comprises the following steps:

[0037] S31, based on the specifications and quantity of the steel pipe piles determined in step S2, according to the plum blossom structure arrangement form, the steel pipe pile drilling construction is carried out on the top, and after the construction is completed, the position of each steel pipe pile is positioned by laying out the line using a total station, and after the position of each steel pipe pile is determined, the adjacent steel pipe piles are connected by a connecting mechanism to form an integral structure;

[0038] S32, placing each section of the steel pipe pile in the overall structure obtained in step S31 at the position where the buckle is clamped in the clamping slot on the base, and pouring concrete;

[0039] S33, then placing each steel arch frame above the steel pipe pile, connecting it to the corresponding cast steel pipe pile directly below the steel arch frame through the first threaded rod, and connecting the second threaded rod to the steel pipe pile not directly below the steel arch frame to form a reinforced pile group;

[0040] S34, then connect the two adjacent steel arch frames through fixing screws.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The steel pipe pile fixing structure at the bottom of the tunnel under the roadbed provided by the present invention can connect multiple steel pipe piles together to form a whole through the design of the connection mechanism, thereby improving the connection stability with the steel arch frame, thereby improving the stability of the support, and avoiding problems such as cracking of the tunnel support structure due to uneven distribution of train loads;

[0043] (2) The reinforcement method provided by the present invention reasonably calculates the specifications and quantity of steel pipe piles according to the train load and the required bearing capacity of the tunnel bottom, thereby avoiding unnecessary waste of steel pipe piles due to a large safety reserve;

[0044] (3) The reinforcement method provided by the present invention can reinforce the entire tunnel bottom by forming a group of steel pipe piles at the bottom of the tunnel, so that the tunnel bottom can withstand long-term train cyclic loads, and can achieve reinforcement of the tunnel bottom at a low cost, avoiding problems such as cracking of the tunnel support structure due to uneven distribution of train loads. At the same time, the present invention also allows the slurry to flow out from the outside of the pipe wall when grouting the steel pipe piles, filling the gap between the drilled hole and the steel pipe pile, ensuring that the steel pipe pile will not move left and right, thereby overcoming the problems of soil leakage between piles and continuous deformation in areas far from the pile body in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the reinforcement method flow of the present invention;

[0046] Figure 2 A schematic diagram of the transverse train load used in the calculation of the present invention;

[0047] Figure 3A schematic diagram of the longitudinal train load used in the calculation of the present invention;

[0048] Figure 4 A schematic diagram of the plum blossom arrangement of steel pipe piles used for tunnel bottom reinforcement in the present invention;

[0049] Figure 5 This is a schematic diagram of the tunnel bottom reinforcement of the present invention;

[0050] Figure 6 It is a schematic diagram of the connection structure between the steel pipe pile and the connection mechanism in the present invention;

[0051] Figure 7 It is a structural schematic diagram of the steel pipe pile in the present invention;

[0052] Figure 8 A top view of the steel pipe pile fixing structure at the bottom of the underpass roadbed tunnel in the present invention;

[0053] In the figure: 1. steel pipe pile; 2. steel arch frame; 3. connecting piece; 4. fixing ring; 5. slot; 6. buckle; 7. fixing bolt; 8. first threaded rod; 9. second threaded rod; 10. threaded hole. DETAILED DESCRIPTION

[0054] The following is a description of the embodiments of the present invention. Figures 1 to 8 , the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Example 1

[0056] like Figure 8 As shown, an embodiment of the present invention provides a steel pipe pile fixing structure at the bottom of an underpass roadbed tunnel, comprising a plurality of steel arch frames 2 arranged at the bottom of the tunnel and a plurality of steel pipe piles 1 arranged at intervals below the steel arch frames 2, the plurality of steel arch frames 2 being detachably connected, and the plurality of steel pipe piles 1 being arranged in a plum blossom structure, such a structural design enables the slurry to be dispersed to the surroundings from the center of a circle during grouting, so that the slurry can be evenly spread under the steel pipe piles, ensuring that the steel pipe piles will not move left and right; two adjacent steel pipe piles 1 are connected by a connecting mechanism, and the top of the steel pipe pile 1 is connected to the bottom of the steel arch frame 2 by an adjusting fixing mechanism.

[0057] The connection mechanism includes a connecting piece 3 and two fixing rings 4. Two slots 5 are symmetrically provided on the outer surface of each steel pipe pile. Two buckles 6 are symmetrically provided on the inner wall of each fixing ring 4. The two fixing rings 4 are respectively sleeved on two adjacent steel pipe piles 2, and the two buckles 6 on each fixing ring 4 are respectively engaged with the corresponding two slots 5. The two fixing rings 4 are connected by the connecting piece 3. The connecting piece 3 in this embodiment can specifically be a steel bar, and the fixing rings 4 are connected by the steel bar. Since there is still a certain distance between the steel pipe pile 1 and the soil during concrete pouring, the steel pipe pile 1 may move during grouting, resulting in uneven force on the pile group. By connecting multiple steel pipe piles 1 into a whole, the steel pipe pile 1 will not move during grouting.

[0058] Threaded holes 10 are symmetrically arranged on both sides of the top of each steel arch frame 2, and two adjacent steel arch frames 2 are connected by fixing screws 7 and corresponding threaded holes 10. In the specific design, a plurality of threaded holes 10 are arranged at intervals on both sides of the steel arch frame 2 along its longitudinal direction, and the connection of two adjacent steel arch frames 2 is achieved by connecting the fixing screws 7 to the corresponding two threaded holes 10 on the two adjacent steel arch frames 2.

[0059] The adjusting and fixing mechanism includes a plurality of first threaded rods 8 and a plurality of second threaded rods 9. The plurality of first threaded rods 8 are arranged on the steel arch frame 2. The steel arch frame 2 is connected to the top of the corresponding steel pipe pile 1 directly below the steel arch frame 2 through the first threaded rods 8. The plurality of second threaded rods 9 are rotationally connected to the fixing screw 7. Specifically, the fixing screw 7 is connected to the second threaded rod 9 through a nut. Such a design can facilitate the connection of the fixing screw 7 with the second threaded rod 9, and the second threaded rod 9 is connected to the corresponding steel pipe pile 1 below. Since the steel pipe pile 1 is arranged in a plum blossom shape and there is a spacing between each steel arch frame 2, individual steel pipe piles 1 are not below the steel arch frame 2. Therefore, it is necessary to connect the steel arch frame 2 with the steel pipe pile 1 directly below or not directly below it through the adjusting and fixing mechanism. Specifically, the steel arch frame 2 is connected to the steel pipe pile 1 directly below it through the first threaded rod 8, and the steel arch frame 2 is connected to the steel pipe pile 1 not directly below it through the second threaded rod 9. By connecting the steel arch frame 2 and the steel pipe piles 1 together, the force of the steel arch frame 2 can be directly transmitted to the steel pipe piles 1 instead of being transmitted between the multiple steel pipe piles 1.

[0060] During construction, it is difficult to connect the two steel arches 2 first and then connect them to the steel pipe piles 1 below. Therefore, the first threaded rod 8 should be fixed to the steel pipe piles 1 first, and then the two steel arches 2 should be fixed by moving the fixing screw rod 7.

[0061] Example 2

[0062] like Figure 1As shown, the embodiment of the present invention provides a method for reinforcing the steel pipe pile fixed structure at the bottom of the tunnel under the roadbed based on embodiment 1, which specifically includes the following steps:

[0063] S1. Obtaining the train load in the tunnel includes the following steps:

[0064] S11. Calculate the longitudinal average train load and the transverse average train load in the tunnel respectively;

[0065] S12, selecting the maximum value of the longitudinal average train load and the transverse average train load obtained in step S11 as the train load N;

[0066] The calculation formula for the average transverse train load is:

[0067]

[0068] Wherein, N1 is the average transverse train load, F1 is the transverse concentrated load, a is the amount of transverse concentrated load, and W is the width of the track plate;

[0069] Taking high-speed railway as an example, the calculation diagram of the average transverse train load is as follows: Figure 2 As shown, the load is symmetrically distributed, with a total of four transverse concentrated loads F1, and each concentrated load is 250kN, with a spacing of 1.6m. The calculation formula for the average transverse train load is:

[0070]

[0071] Therefore, the average transverse train load N1 is 208.3 kN;

[0072] The calculation formula for the longitudinal average train load is:

[0073]

[0074] Where N2 is the average longitudinal train load, F2 is the longitudinal concentrated load, m is the number of longitudinal concentrated loads, q is the uniformly distributed load, L is the length of the track slab, and l is the distribution length of the longitudinal concentrated load.

[0075] Taking high-speed railway as an example, the calculation diagram of the average longitudinal train load is as follows: Figure 3 As shown in the figure, the load is symmetrically distributed. There are four longitudinal concentrated loads F2 in the middle, each of which is 200kN, and each is 1.6m apart. The concentrated load at the edge is 0.8m away from the uniformly distributed load. The two sides are uniformly distributed loads q, with a size of 64kN / m, which covers the entire track slab. The calculation formula for the average longitudinal train load is:

[0076]

[0077] l=1.6+1.6+1.6+0.8+0.8=6.4m

[0078] Then select the maximum value of N1 and N2 as the train load;

[0079] S2. Calculate the required bearing capacity of the tunnel bottom according to the train load N, and determine the specifications and quantity of the steel pipe piles 1 according to the bearing capacity, which specifically includes the following steps:

[0080] S21. According to the train load N, the vertical bearing capacity characteristic value R of a single steel pipe pile 1 is calculated, and the vertical bearing capacity characteristic value R of a single steel pipe pile 1 should meet the following requirements:

[0081] N≤R

[0082] Where N is the train load, R is the characteristic value of the vertical bearing capacity of a single steel pipe pile 1;

[0083] S22, according to the vertical bearing capacity characteristic value R of the single steel pipe pile 1 obtained in step S21, determine the vertical bearing capacity Q of the single steel pipe pile 1, and then obtain the specifications of the steel pipe pile 1, the specifications of the steel pipe pile 1 include the pile body perimeter u and the pile end area A p The relationship between the vertical bearing capacity characteristic value R of a single steel pipe pile 1 and the vertical bearing capacity Q of a single steel pipe pile 1 is:

[0084]

[0085] In the formula, R is the characteristic value of the vertical bearing capacity of a single steel pipe pile, K is the safety factor, and K=2; Q is the vertical bearing capacity of a single pile;

[0086] The vertical bearing capacity of a single steel pipe pile in this embodiment can be calculated by the following formula:

[0087] Q=Q s +Q p =u∑q si l i +q p A p

[0088] In the formula, Q s , Q p are pile side friction and pile end resistance, q si is the ultimate lateral friction of the i-th layer of soil on the pile side; q p is the ultimate resistance of the pile tip, u and A p are the circumference of the pile and the area of ​​the pile tip, respectively, i is the thickness of the i-th soil layer.

[0089] In the above calculation process, the pile circumference u and the pile end area A pFor design parameters, multiple trial calculations should be performed until the calculation requirements for the characteristic value R of the vertical bearing capacity of a single pile are met;

[0090] S23. According to the train load N, the required bearing capacity F of the tunnel bottom is calculated;

[0091] S24, according to the required bearing capacity F of the tunnel bottom obtained in step S23 and the characteristic value R of the vertical bearing capacity of the single steel pipe pile 1 obtained in step S21, the number of steel pipe piles 1 is determined, and the relationship between the required bearing capacity F of the tunnel bottom and the characteristic value R of the vertical bearing capacity of the single steel pipe pile 1 is:

[0092] F≤nR

[0093] Where F is the total cross-sectional load (i.e., the required bearing capacity F of the tunnel bottom), n is the number of steel pipe piles, and R is the characteristic value of the vertical bearing capacity of a single pile.

[0094] In specific calculations, calculations must be performed along the longitudinal and transverse directions of the tunnel and the requirements must be met to determine the number of piles required for the tunnel bottom in the transverse and longitudinal directions. Each track plate should be designed separately.

[0095] S3. Based on the determined specifications and quantity of the steel pipe piles 1, the steel pipe pile fixing structure at the bottom of the tunnel under the roadbed proposed in Example 1 is installed and arranged in the tunnel bottom reinforcement area to form a reinforcement pile group.

[0096] In step S3, when reinforcing the tunnel bottom, the tunnel bottom is reinforced by grouting steel pipe piles. The steel pipe piles 1 are arranged in a plum blossom shape, as shown in 4. For the convenience of construction, the steel pipes are arranged in sections of 2m each, and the last section of the steel pipe is specially processed. The steel pipe piles 1 are embedded in the bearing layer by no less than 0.5m. After the initial support of the steel arch frame 2, the steel pipe piles 1 are reinforced by grouting. The ends of the steel pipe piles 1 are exposed 3 to 5cm above the ground (generally, the tunnel will be over-excavated, so there is still a small distance between the ground and the steel arch frame 2) to facilitate subsequent grouting construction. The steel pipe piles 1 in the middle part of the steel arch frame 2 are vertically driven and delivered by a drilling rig. Considering the lack of space for construction machinery on both sides, they can be deflected 15 to 20° to the centerline of the tunnel. Specifically, Figure 5 As shown. During the drilling process of steel pipe pile 1, slag samples are taken at regular intervals and retained to ensure that the pile bottom is embedded in the bearing layer by 0.5m, and the steel pipe grouting is completed in time. The grouting pressure is 0.5~1.0MPa, and grouting is required in alternate holes.

[0097] In order to ensure that the tunnel and vehicle loads are well transferred to the steel pipe pile 1, it is first necessary to ensure that the steel pipe pile 1 is in a vertical state during construction (no lateral displacement occurs), and then form the steel pipe pile 1 and the steel arch frame 2 into a whole to ensure that the whole is stressed.

[0098] When driving piles, first drill holes and then install the steel pipe piles 1. The internal space of the tunnel is limited. For the convenience of installation, the piles can be installed in sections, and each section is driven down 2 meters. In order to ensure that the piles do not move laterally, slots 5 are set on both sides of the top steel pipe pile 1, and then fixed rings 4 are set to fix the steel pipe pile 1. Figure 7 shown.

[0099] Step S3 specifically includes the following steps:

[0100] S31. Based on the specifications and quantity of the steel pipe piles 1 determined in step S2, holes are drilled at corresponding positions in accordance with the plum blossom-shaped structure arrangement. Since there is a certain gap between the drilled hole and the steel pipe pile 1, the steel pipe pile 1 needs to be fixed. Therefore, after the drilling construction is completed, the steel pipe is not inserted into the drilled hole first. The position of each steel pipe pile 1 is positioned by laying out the line using a total station. After the position of each steel pipe pile 1 is determined, the adjacent steel pipe piles 1 are connected by a connecting mechanism to form an integral structure. Specifically, the adjacent fixing rings 4 are connected by connecting members 3 to fix the adjacent steel pipe piles 1. In the specific design, the inner diameter of the fixing ring 4 is slightly larger than the outer diameter of the steel pipe pile 1, so that it can be just inserted into the fixing ring 4. Figure 6 As shown;

[0101] S32, placing the clamping groove 2 on each section of the steel pipe pile 1 in the overall structure obtained in step S31 at the position where the clamping buckle 6 is clamped, and pouring concrete;

[0102] S33, then place each steel arch frame 2 above the steel pipe pile 1. Since the steel pipe piles are arranged in a plum blossom shape and there is a gap between each steel arch frame, individual steel pipe piles are not below the steel arch frame. Therefore, they are connected to the corresponding cast steel pipe piles 1 directly below the steel arch frame 2 through the first threaded rod 8, and two adjacent steel arch frames 2 are connected through the fixing screws 7; specifically, the fixing screws 7 are equidistantly arranged on the steel arch frame 2;

[0103] S34. When the steel pipe pile 1 is not below the steel arch frame 2, multiple second threaded rods 9 are set on the fixed screw 7, and connected with the corresponding steel pipe piles 1 below through the second threaded rods 9 to form a reinforced pile group. In the specific design, the second threaded rod 9 can be rotated and moved up and down along the fixed screw 7, and then moved down to connect with the steel pipe pile 1 below.

[0104] During construction, if the two steel arches 2 are connected first and then connected to the steel pipe piles 1 below, it will be difficult to connect. Therefore, the first threaded rod 8 should be fixed to the steel pipe piles 1 on site first, and then the two steel arches should be fixed by moving the fixing screw rod 7.

[0105] Through the connection holes of the steel pipe piles 1 below the steel arch frame 2, it can be ensured that the spacing of the steel arch frame 2 is consistent with the design during construction.

[0106] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A steel pipe pile fixing structure at the bottom of a tunnel under a roadbed, characterized in that: The invention comprises a plurality of steel arch frames (2) arranged at the bottom of a tunnel and a plurality of steel pipe piles (1) arranged at intervals below the steel arch frames (2); the plurality of steel arch frames (2) are detachably connected; the plurality of steel pipe piles (1) are arranged in a plum blossom structure; two adjacent steel pipe piles (1) are connected via a connecting mechanism; and the top of the steel pipe pile (1) is connected to the bottom of the steel arch frame (2) via an adjustable fixing mechanism.

2. The steel pipe pile fixing structure at the bottom of a tunnel under a roadbed as claimed in claim 1, characterized in that: The connection mechanism comprises a connection piece (3) and two fixing rings (4), two slots (5) are symmetrically provided on the outer side of each steel pipe pile, two buckles (6) are symmetrically provided on the inner wall of each fixing ring, the two fixing rings (4) are respectively sleeved on two adjacent steel pipe piles (2), and the two buckles on each fixing ring are respectively engaged with the corresponding two slots, and the two fixing rings (4) are connected via the connection piece (3).

3. The steel pipe pile fixing structure at the bottom of a tunnel under a roadbed as claimed in claim 1, characterized in that: Threaded holes (10) are symmetrically arranged on both sides of the top of each steel arch frame (2), and two adjacent steel arch frames (2) are connected via a fixing screw (7) and the corresponding threaded holes (10).

4. The steel pipe pile fixing structure at the bottom of a tunnel under a roadbed as claimed in claim 3, characterized in that: The adjusting and fixing mechanism comprises a plurality of first threaded rods (8) and a plurality of second threaded rods (9), wherein the plurality of first threaded rods (8) are arranged on the steel arch frame (2), and the steel arch frame (2) is connected to the top of the corresponding steel pipe pile (1) directly below the steel arch frame (2) through the first threaded rods (8), and the plurality of second threaded rods (9) are rotationally connected to the fixing screw rods (7), and the second threaded rods (9) are connected to the steel pipe piles (1) not directly below the steel arch frame (2).

5. A method for reinforcing a steel pipe pile fixing structure at the bottom of a tunnel under a roadbed as claimed in claim 1, characterized in that: The following steps are involved: S1. Obtain the train load in the tunnel; S2. Calculate the required bearing capacity of the tunnel bottom according to the train load, and determine the specifications and quantity of the steel pipe piles (1) according to the bearing capacity; S3. Based on the determined specifications and quantity of the steel pipe piles (1), the steel pipe pile fixing structure at the bottom of the tunnel under the roadbed is installed and arranged in the tunnel bottom reinforcement area to form a reinforcement pile group.

6. The method for reinforcing the steel pipe pile fixed structure at the bottom of a tunnel under a roadbed as claimed in claim 5, characterized in that: Step S1 comprises the following steps: S11. Calculate the longitudinal average train load and the transverse average train load in the tunnel respectively; S12, selecting the maximum value of the longitudinal average train load and the transverse average train load obtained in step S11 as the train load; The calculation formula for the average transverse train load is: Wherein, N1 is the average transverse train load, F1 is the transverse concentrated load, a is the amount of transverse concentrated load, and W is the width of the track plate; The calculation formula for the longitudinal average train load is: Where N2 is the average longitudinal train load, F2 is the longitudinal concentrated load, m is the number of longitudinal concentrated loads, q is the uniformly distributed load, L is the length of the track slab, and l is the distribution length of the longitudinal concentrated load.

7. The method for reinforcing the steel pipe pile fixed structure at the bottom of a tunnel under a roadbed as claimed in claim 5, characterized in that: Step S2 comprises the following steps: S21. Calculate the vertical bearing capacity characteristic value of a single steel pipe pile (1) according to the train load; S22, determining the vertical bearing capacity of the single steel pipe pile (1) according to the characteristic value of the vertical bearing capacity of the single steel pipe pile (1) obtained in step S21, and then obtaining the specifications of the steel pipe pile (1); S23. Calculate the required bearing capacity of the tunnel bottom according to the train load; S24, determining the number of steel pipe piles (1) based on the required bearing capacity of the tunnel bottom obtained in step S23 and the characteristic value of the vertical bearing capacity of a single steel pipe pile (1) obtained in step S21.

8. The method for reinforcing the steel pipe pile fixed structure at the bottom of a tunnel under a roadbed as claimed in claim 5, characterized in that: In step S22, the relationship between the characteristic value of the vertical bearing capacity of a single steel pipe pile and the vertical bearing capacity of a single steel pipe pile is: In the formula, R is the characteristic value of the vertical bearing capacity of a single steel pipe pile, K is the safety factor, and K=2; Q is the vertical bearing capacity of a single pile; The vertical bearing capacity of a single steel pipe pile is calculated by the following formula: Q=Q s +Q p =u∑q si l i +q p A p In the formula, Q s , Q p are pile side friction and pile end resistance, q si is the ultimate lateral friction of the i-th layer of soil on the pile side; q p is the ultimate resistance of the pile tip, u and A p are the circumference of the pile and the area of ​​the pile tip, respectively, i is the thickness of the i-th soil layer.

9. The method for reinforcing the steel pipe pile fixed structure at the bottom of a tunnel under a roadbed as claimed in claim 5, characterized in that: In step S24, the relationship between the required bearing capacity of the tunnel bottom and the characteristic value of the vertical bearing capacity of a single steel pipe pile is: F≤nR Where F is the total cross-sectional load, n is the number of steel pipe piles, and R is the characteristic value of the vertical bearing capacity of a single pile.

10. The method for reinforcing the steel pipe pile fixed structure at the bottom of a tunnel under a roadbed as claimed in claim 5, characterized in that: Step S3 includes the following steps: S31, based on the specifications and quantity of the steel pipe piles (1) determined in step S2, drilling construction of the steel pipe piles (1) is carried out in accordance with the plum blossom structure arrangement form. After the construction is completed, the positions of the steel pipe piles (1) are positioned using a total station. After the positions of the steel pipe piles (1) are determined, the adjacent steel pipe piles (1) are connected together by a connecting mechanism to form an integral structure; S32, placing the clamping groove (5) on each section of the steel pipe pile (1) in the overall structure obtained in step S31 at the position where the clamping buckle (6) is clamped on the base, and pouring concrete; S33, then placing each steel arch frame (2) above the steel pipe pile (1), connecting it with the corresponding cast steel pipe pile (1) directly below the steel arch frame (2) through the first threaded rod (8), and connecting the second threaded rod (9) with the steel pipe pile (1) not directly below the steel arch frame (2), so as to form a reinforced pile group; S34, then connect the two adjacent steel arch frames (1) via fixing screws (7).

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