A slurry wall protection method for highway bridge pile foundation construction in karst areas

Abstract

The invention relates to a slurry wall protection method for pile foundation construction of highway bridges in karst areas, comprising a slurry injection pipe and a plurality of steel pipe piles, wherein the lower end of the slurry injection pipe is connected to a liquid level sensor; the method further comprises the following steps: firstly, a pile foundation hole is drilled in a construction section by a drilling rig, and when the liquid level sensor of the slurry injection pipe is lowered and triggered, the slurry injection pipe is moved away from the pile foundation hole, and the steel pipe pile is sunk by a vibration hammer; the wall protection slurry is injected into the pile foundation hole through the slurry injection pipe, and when the liquid level of the wall protection slurry in the pile foundation hole rises and triggers the liquid level sensor, the slurry injection pipe is moved up again, and this process is repeated; when the liquid level sensor is not triggered within a predetermined time t, the slurry injection pipe is moved away from the pile foundation hole, and at least one steel pipe pile is sunk by a vibration hammer until the bottom end of the steel pipe pile abuts against the bottom end of the pile foundation hole or the top end of the steel pipe pile, and the pile foundation hole is filled with the slurry; the method solves the technical problems in the prior art of slurry wall protection method for pile foundation construction of bridges in karst areas that a large amount of yellow mud is consumed and the construction period is long.

Description

Technical Field

[0001] The invention relates to the technical field of bridge construction, in particular to a slurry wall protection method for pile foundation construction of highway bridges in karst areas. Background Art

[0002] my country's karst regions are widespread, and many are home to numerous caves. Caves are primarily formed when limestone is gradually eroded by water, acidic substances, and microorganisms, creating cavities. Therefore, wherever there is limestone, there are caves. Pile foundation construction in karst areas has always been a challenge for the engineering community. When bridge pile foundation construction is located in a karst geological zone, the pile driving process often encounters caves when the pile hole reaches a certain depth. This causes the retaining slurry injected into the pile hole to suddenly drop and flow into the caves, sometimes quickly depleting the slurry. The current method involves gradually pouring yellow mud into the caves and then slowly compacting them with an impact hammer until the caves in the pile foundation area are blocked and seepage is stopped, allowing pile driver construction to continue. However, this method not only requires a large amount of yellow mud, but also takes a very long time to plug the caves, resulting in a prolonged construction period. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a mud wall protection method for bridge pile foundation construction in karst areas, which does not require the use of yellow mud to block caves and can shorten the construction period.

[0004] To solve the above technical problems, the present invention provides a slurry wall protection method for pile foundation construction of highway bridges in karst areas, comprising a slurry injection pipe and a plurality of steel pipe piles, wherein the slurry injection pipe is axially continuous, a liquid level sensor is connected to the outer peripheral wall of the lower end of the slurry injection pipe, and the liquid level sensor is externally connected to a control display, and each steel pipe pile is provided with a connection mechanism at the upper and lower ends for connecting to the upper and lower adjacent steel pipe piles, and the height of a single steel pipe pile is H; and the method further comprises the following steps:

[0005] S1. Drill a pile foundation hole in the construction section using a drilling rig. The pile foundation hole has a depth of L and the outer diameter of the mud injection pipe is smaller than the inner diameter of the pile foundation hole.

[0006] S2. Lower the mud injection pipe vertically into the pile foundation hole; when the liquid level sensor is not triggered during the lowering process, the lower end of the mud injection pipe is placed at the bottom of the pile foundation hole, and the mud injection pipe rises and the rising distance is h; when the liquid level sensor is triggered when the mud injection pipe is lowered to a distance of l, the mud injection pipe is removed from the pile foundation hole and sunk using a vibrating hammer. 1. Install a steel pipe pile until the bottom of the steel pipe pile touches the bottom of the pile foundation hole, and then lower the mud injection pipe for a distance of lh;

[0007] S3. Injecting the retaining wall slurry into the pile foundation hole through the slurry injection pipe; when the retaining wall slurry level in the pile foundation hole rises and triggers the liquid level sensor, the slurry injection pipe rises again by a distance h, and this process is repeated; when the liquid level sensor is not triggered within the approved time t, the slurry injection pipe is lifted and removed from the pile foundation hole, and at least one steel pipe pile is sunk using a vibrating hammer until the bottom end of the steel pipe pile abuts against the bottom end of the pile foundation hole or the top end of the steel pipe pile located in the pile foundation hole;

[0008] S4. Lower the mud injection pipe until the liquid level sensor is triggered, then the mud injection pipe rises a distance h, and the wall protection mud is injected into the pile foundation hole and the steel pipe pile located in the pile foundation hole through the mud injection pipe; when the wall protection mud level in the pile foundation hole rises and triggers the mud pressure sensor, the mud injection pipe rises again a distance h, and this process is repeated; if the liquid level sensor is not triggered within the approved time t, lift the mud injection pipe and make it leave the pile foundation hole, and use a vibration hammer to sink at least one steel pipe pile until the bottom end of the steel pipe pile touches the top end of the steel pipe pile located in the pile foundation hole;

[0009] S5. Repeat step S4 until the retaining wall slurry fills the pile foundation hole and the steel pipe piles located in the pile foundation hole.

[0010] After adopting the above structure, the mud wall protection method for pile foundation construction of highway bridge in karst area of the present invention has the following advantages: when constructing in karst area, a part of the pile foundation hole is located in the karst cave area after being formed. If there is no water accumulation in the pile foundation hole during the lowering of the mud injection pipe, the mud injection pipe can be directly lowered to the bottom of the pile foundation hole and subsequent steps are carried out. If the pile foundation hole is water-accumulated due to the karst cave area, the liquid level sensor will immediately lower the steel pipe pile after detecting the water accumulation so as to form a mud wall. After that, a certain amount of guard arm mud is injected using the mud injection pipe, and the mud is output according to the signal of the liquid level sensor. The depth of the cave is determined. When the liquid level sensor does not detect the wall protection mud within the approved time, it means that the wall protection mud has been lost due to the cave. At this time, steel pipe piles are continuously driven in and the step is repeated until all the cave areas are supported by steel pipe piles. In this way, after the wall protection mud is injected, arm protection mud can be formed in the steel pipe piles and pile foundation holes. There is no need to use yellow mud to seal the cave during the entire construction process, which shortens the construction period. In addition, there is no need to survey and determine the depth of the cave before construction. Moreover, steel pipe piles do not need to be buried in the entire pile foundation hole, which saves costs.

[0011] As an improvement, the numerical range of the approved time t is: D is the inner diameter of the pile foundation hole, Q is the injection flow rate of the wall protection mud; using this structure, according to the theoretical value, when the wall protection mud is not lost, the theoretical time for the liquid level sensor to sense the wall protection mud should be The verification time is set between 1 and 1.5 times of the theoretical time to prevent erroneous operation caused by the liquid level sensor failing to detect the arm slurry within the theoretical time due to dimensional error, and to reduce the waste of arm slurry on this basis.

[0012] As an improvement, h<H<2h; adopting this structure ensures that when a single steel pipe pile is lowered, the top of the uppermost steel pipe pile can be higher than the lower end of the previous mud injection pipe, thereby improving construction efficiency.

[0013] As an improvement, in step S3 and step S4, the number of times the mud injection pipe rises due to the liquid level sensor being triggered is n, and the number of steel pipe piles sunk by the vibration hammer is This structure ensures that the overall height of the steel pipe piles after one lowering can exceed the bottom of the cave, further improving construction efficiency.

[0014] As an improvement, several liquid level sensors are connected to the outer wall of the lower end of the mud injection pipe at equal intervals along the circumferential direction; with this structure, the mud injection pipe will only rise a distance h when all the liquid level sensors are triggered, preventing the position of the liquid level sensor from being offset due to the tilt of the mud injection pipe, which would cause errors affecting construction efficiency.

[0015] As an improvement, a protrusion is axially connected to the outer wall of the mud injection tube, and a through hole is provided on the protrusion along the axial direction of the mud injection tube. The signal line of the liquid level sensor is located in the through hole. With this structure, the protrusion protects the signal line of the liquid level sensor.

[0016] As an improvement, the connecting mechanism includes a protrusion and a recessed portion, both of which are annular. The protrusion is connected to the lower end face of the steel pipe pile, and the recessed portion is connected to the upper end face of the steel pipe pile. The steel pipe pile, the protrusion and the recessed portion are all coaxially arranged, and the protrusion on each steel pipe pile can be interference fit with the recessed portion on another steel pipe pile. This structure has the advantage of simple structure, which makes it easier for the vibration hammer to connect the two steel pipe piles in the pile foundation hole.

[0017] As an improvement, the connecting mechanism also includes an annular guide portion, which is connected to the lower end of the protrusion and is coaxially arranged with the protrusion. The outer diameter of the guide portion gradually increases from bottom to top and the outer diameter of the lower end of the guide portion is smaller than the diameter of the recessed portion, and the outer diameter of the upper end of the guide portion is the same as the diameter of the protrusion. With this structure, the guide portion facilitates the connection of two steel pipe piles.

[0018] As an improvement, a searchlight and a searchlight camera are connected to the outer peripheral wall of the lower end of the mud injection pipe, and the searchlight camera is externally connected to a display device. The searchlight and the searchlight camera are both located at the liquid level sensor. With this structure, the situation inside the pile foundation hole is monitored by the searchlight and the searchlight camera, and the depth of the molten rock layer can be roughly estimated by the searchlight and the searchlight camera combined with the descending distance of the mud injection pipe. According to the depth, the corresponding number of steel pipe piles required to block the molten rock layer is estimated and the steel pipe piles are pre-installed on the ground, thereby improving the work efficiency of driving the steel pipe piles in steps S3 and S4. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the mud injection pipe lowered into the pile foundation hole in the present invention.

[0020] Figure 2 It is a structural schematic diagram of the mud injection pipe in the present invention.

[0021] Figure 3 It is a structural schematic diagram of the steel pipe pile in the present invention.

[0022] Figure numerals: 1, mud injection pipe; 2, steel pipe pile; 3, liquid level sensor; 4, pile foundation hole; 5, protrusion; 6, through hole; 7, protrusion; 8, recessed portion; 9, guide portion; 100, rock and soil layer; 200, lava layer. DETAILED DESCRIPTION

[0023] The following describes in detail a slurry wall protection method for pile foundation construction of highway bridges in karst areas according to the present invention in conjunction with the accompanying drawings.

[0024] like Figures 1 to 3 As shown, a slurry wall protection method for pile foundation construction of highway bridges in karst areas includes a mud injection pipe 1 and a plurality of steel pipe piles 2. The mud injection pipe 1 is axially continuous, and a liquid level sensor 3 is connected to the outer peripheral wall of the lower end of the mud injection pipe 1. The liquid level sensor 3 is externally connected to a control display, such as Figure 2As shown, a number of liquid level sensors 3 are equidistantly connected to the outer circumferential wall of the lower end of the mud injection tube 1 along the circumferential direction, a protrusion 5 is connected to the outer circumferential wall of the mud injection tube 1 along the axial direction, and a through hole 6 is provided on the protrusion 5 along the axial direction of the mud injection tube 1, and the signal line of the liquid level sensor 3 is located in the through hole 6; in this embodiment, there are a total of six liquid level sensors 3 and six protrusions 5, and the liquid level sensors 3 and the protrusions 5 are equidistantly distributed along the circumferential direction of the outer circumferential wall of the mud injection tube 1, the signal line of each liquid level sensor 3 passes through the through hole 6 and extends to the outside of the mud injection tube 1 and is connected to the control display, and each liquid level sensor 3 is connected to the outer circumferential wall of the mud injection tube 1 by bolts, and the protrusion 5 is integrally formed with the mud injection tube 1. Each steel pipe pile 2 is provided with a connecting mechanism at both ends thereof for connecting with the upper and lower adjacent steel pipe piles 2. The height of a single steel pipe pile 2 is H. The connecting mechanism includes a protrusion 7 and a recessed portion 8. Both the protrusion 7 and the recessed portion 8 are annular. The protrusion 7 is connected to the lower end face of the steel pipe pile 2, and the recessed portion 8 is connected to the upper end face of the steel pipe pile 2. The recessed portion 8 is an annular groove on the upper end face of the steel pipe pile 2. The steel pipe pile 2, the protrusion 7 and the recessed portion 8 are all coaxially arranged. The protrusion 7 on each steel pipe pile 2 is It can be interference fit with the recessed portion 8 on another steel pipe pile 2; the connecting mechanism also includes an annular guide portion 9, which is connected to the lower end of the protrusion 7 and is coaxially arranged with the protrusion 7. The outer diameter of the guide portion 9 gradually increases from bottom to top and the outer diameter of the lower end of the guide portion 9 is smaller than the diameter of the recessed portion 8, and the outer diameter of the upper end of the guide portion 9 is the same as the diameter of the protrusion 7. It should be noted that the height H of the steel pipe pile 2 referred to in this embodiment does not include the connecting mechanism, that is, it does not include the protrusion 7, the recessed portion 8 and the guide portion 9.

[0025] The present invention further comprises the following steps:

[0026] S1, using a drilling rig to drill a pile foundation hole 4 in the construction section, the depth of the pile foundation hole 4 is L, and the outer diameter of the mud injection pipe 1 is smaller than the inner diameter of the pile foundation hole 4;

[0027] S2. Lower the mud injection pipe 1 vertically into the pile foundation hole 4; when the liquid level sensor 3 is not triggered during the lowering process of the mud injection pipe 1, the lower end of the mud injection pipe 1 is placed at the bottom of the pile foundation hole 4, and the mud injection pipe 1 rises and the rising distance is h; when the liquid level sensor 3 is triggered when the mud injection pipe 1 is lowered to a distance of l, the mud injection pipe 1 is removed from the pile foundation hole 4 and sunk using a vibration hammer. 2 until the bottom of the steel pipe pile 2 touches the bottom of the pile foundation hole 4, and then lower the mud injection pipe 1 for a distance of lh;

[0028] S3. Inject the wall protection mud into the pile foundation hole 4 through the mud injection pipe 1; when the wall protection mud level in the pile foundation hole 4 rises and triggers the liquid level sensor 3, the mud injection pipe 1 rises again and the rising distance is h, and this process is repeated; when the liquid level sensor 3 is not triggered within the approved time t, the mud injection pipe 1 is lifted and the mud injection pipe 1 is moved away from the pile foundation hole 4, and at least one steel pipe pile 2 is sunk using a vibration hammer until the bottom end of the steel pipe pile 2 is against the bottom end of the pile foundation hole 4 or the top end of the steel pipe pile 2 located in the pile foundation hole 4;

[0029] S4. Lower the mud injection pipe 1 until the liquid level sensor 3 is triggered, then the mud injection pipe 1 rises by a distance h, and the wall protection slurry is injected into the pile foundation hole 4 and the steel pipe pile 2 located in the pile foundation hole 4 through the mud injection pipe 1; when the wall protection slurry level in the pile foundation hole 4 rises and triggers the liquid level sensor 3, the mud injection pipe 1 rises again by a distance h, and this process is repeated; when the liquid level sensor 3 is not triggered within the approved time t, lift the mud injection pipe 1 and make the mud injection pipe 1 leave the pile foundation hole 4, and use a vibration hammer to sink at least one steel pipe pile 2 until the bottom end of the steel pipe pile 2 is against the top end of the steel pipe pile 2 located in the pile foundation hole 4;

[0030] S5 , repeat step S4 until the wall protection slurry fills the pile foundation hole 4 and the steel pipe piles 2 located in the pile foundation hole 4 .

[0031] The specific operation process of the above steps is: first use a drilling rig to drill a pile foundation hole 4 in the construction area, the inner diameter of the pile foundation hole 4 is D, and the depth is L, and the outer diameter of the mud injection pipe 1 used is smaller than the inner diameter of the pile foundation hole 4; then lower the mud injection pipe 1 vertically into the pile foundation hole 4, wherein the mud injection pipe 1 can be lowered by a crane, and a displacement sensor is set at the opening of the pile foundation hole 4 or on the crane to detect the depth of the mud injection pipe 1 lowered; if a part of the pile foundation hole 4 below the molten rock layer 200 is caused by water accumulation due to the molten rock layer 200, the liquid level sensor 3 will be triggered during the lowering of the mud injection pipe 1, and the lowering depth of the mud injection pipe 1 when the liquid level sensor 3 is triggered is recorded as l It should be noted that the lowering depth of the mud injection pipe 1 involved in this embodiment refers to the distance between the bottom end of the mud injection pipe 1 and the top of the pile foundation hole 4, and then the mud injection pipe 1 is raised to make it leave the pile foundation hole 4, and then it is sunk by a vibration hammer. The steel pipe piles 2 are connected until the bottom of the steel pipe pile 2 at the bottom is against the bottom of the pile foundation hole 4. The steel pipe piles 2 in this part are the steel pipe piles 2 pre-connected outside the pile foundation hole 4. Then the mud injection pipe 1 is lowered again and the lowering distance is lh, and h<H<2h, h is a preset value, which is set according to the actual construction situation and is as large as possible on the basis of being less than the height of the steel pipe pile 2; if the steel pipe pile 2 at this time has blocked all the molten rock layers 200 in the pile foundation hole 4, it is only necessary to fill the pile foundation hole 4 with the wall slurry through the mud injection pipe 1; if the pile foundation hole 4 is not watered due to the molten rock layer 200, the liquid level sensor 3 is not triggered, and the lower end of the mud injection pipe 1 is placed at the bottom of the pile foundation hole 4 Afterwards, the mud injection pipe 1 rises and the rising distance is h; then the wall protection mud is injected from the mud injection pipe 1 into the pile foundation hole 4, and the wall protection mud forms a mud wall in the pile foundation hole 4 or in the steel pipe pile 2; when the liquid level sensor 3 is still located in the rock layer 100, the liquid level sensor 3 will be triggered due to the rising liquid level of the wall protection mud, and the mud injection pipe 1 will rise h at this time, and continue to inject mud, and repeat this process; if the liquid level sensor 3 is not triggered within the approved time, it means that the liquid level sensor 3 is already located in the karst layer 200, and the mud injection pipe 1 is lifted and away from the pile foundation hole 4, and at least one steel pipe pile 2 is sunk by a vibration hammer, wherein the specific number of steel pipe piles 2 sunk at this time is n is the number of times the mud injection pipe 1 rises due to the triggering of the liquid level sensor 3; if there is no steel pipe pile 2 in the pile foundation hole 4 at this time, the bottom end of the steel pipe pile 2 will be against the bottom end of the pile foundation hole 4; if there is a steel pipe pile 2 in the pile foundation hole 4, the bottom end of the steel pipe pile 2 will be connected to the top end of the steel pipe pile 2 in the pile foundation hole 4 by a connecting mechanism and will be against each other; at this time, the mud injection pipe 1 is lowered again until the liquid level sensor 3 is triggered, and the mud injection pipe 1 rises a distance h, and the wall protection mud is injected into the pile foundation hole 4 through the mud injection pipe 1 and steel pipe pile 2, when the wall slurry level in the pile foundation hole 4 rises and triggers the liquid level sensor 3, the mud injection pipe 1 rises again and the rising distance is h, and this process is repeated; when the liquid level sensor 3 is not triggered within the approved time t, the mud injection pipe 1 is lifted and the mud injection pipe 1 is moved away from the pile foundation hole 4, and at least one steel pipe pile 2 is sunk by the vibration hammer until the bottom end of the steel pipe pile 2 is against the top end of the steel pipe pile 2 in the pile foundation hole 4, and the number of steel pipe piles 2 sunk by the vibration hammer is also The above process is then repeated until the retaining wall slurry fills the pile foundation hole 4 and the steel pipe pile 2 located in the pile foundation hole 4; the numerical range of the above-mentioned approved time t is: Q is the injection flow rate of the wall protection mud. If necessary, the accumulated water in the steel pipe pile 2 can be pumped out first.

[0032] In addition, a searchlight and a searchlight camera are connected to the outer peripheral wall of the lower end of the mud injection pipe 1, and the searchlight camera is externally connected to a display device. The searchlight and the searchlight camera are both located above the liquid level sensor 3. Similar to the liquid level sensor 3, a protrusion 5 is also provided on the outer peripheral wall of the mud injection pipe 1, and a through hole 6 is provided on the protrusion 5. The signal lines of the searchlight and the searchlight camera are located in the through hole 6, and the situation in the pile foundation hole 4 is viewed through the display device; in steps S3 and S4, when the molten rock layer 200 is observed for the first time, the injection time is recorded. The depth to which the mud pipe 1 is lowered, when the lower end of the molten rock layer 200 or the top of the steel pipe pile 2 is observed through the display device, the depth to which the mud injection pipe 1 is lowered at this time is recorded, and the difference between the two depths is calculated to obtain the approximate depth of the molten rock layer 200 that needs to be blocked. According to the depth, several steel pipe piles 2 are spliced on the ground so that the total height of the connected steel pipe piles 2 is greater than the above-mentioned estimated depth. The connected steel pipe piles 2 are then driven into the pile foundation hole 4 to improve the efficiency of driving the steel pipe piles 2 in steps S3 and S4.

[0033] The above describes the embodiments of the present invention in detail with reference to the accompanying drawings, but the present invention is not limited to the above-mentioned embodiment. All other embodiments obtained by those skilled in the art without making any creative work shall fall within the scope of protection of the present invention.

Claims

1. A slurry wall protection method for pile foundation construction of highway bridges in karst areas, characterized in that: The invention comprises a mud injection pipe (1) and a plurality of steel pipe piles (2), wherein the mud injection pipe (1) is axially continuous, a liquid level sensor (3) is connected to the outer peripheral wall of the lower end of the mud injection pipe (1), and the liquid level sensor (3) is externally connected to a control display. The upper and lower ends of each steel pipe pile (2) are provided with a connection mechanism for connecting with the upper and lower adjacent steel pipe piles (2), and the height of a single steel pipe pile (2) is H. The invention also comprises the following steps: S1, using a drilling rig to drill a pile foundation hole (4) in the construction section, wherein the depth of the pile foundation hole (4) is L, and the outer diameter of the mud injection pipe (1) is smaller than the inner diameter of the pile foundation hole (4); S2, lowering the mud injection pipe (1) vertically into the pile foundation hole (4); when the liquid level sensor (3) is not triggered during the lowering of the mud injection pipe (1), the lower end of the mud injection pipe (1) is placed at the bottom end of the pile foundation hole (4), and the mud injection pipe (1) rises and the rising distance is h; when the liquid level sensor (3) is triggered when the mud injection pipe (1) is lowered to a distance of l, the mud injection pipe (1) is moved away from the pile foundation hole (4) and is sunk using a vibration hammer. The steel pipe pile (2) is inserted until the bottom end of the steel pipe pile (2) abuts against the bottom end of the pile foundation hole (4), and then the mud injection pipe (1) is lowered by a distance of lh; S3, injecting the wall protection mud into the pile foundation hole (4) through the mud injection pipe (1); when the wall protection mud level in the pile foundation hole (4) rises and triggers the liquid level sensor (3), the mud injection pipe (1) rises again and the rising distance is h, and repeats this process; when the liquid level sensor (3) is not triggered within the approved time t, the mud injection pipe (1) is lifted and the mud injection pipe (1) is moved away from the pile foundation hole (4), and at least one of the steel pipe piles (2) is sunk by a vibration hammer until the bottom end of the steel pipe pile (2) abuts against the bottom end of the pile foundation hole (4) or the top end of the steel pipe pile (2) located in the pile foundation hole (4); S4, lowering the mud injection pipe (1) until the liquid level sensor (3) is triggered, the mud injection pipe (1) rises and the rising distance is h, and the wall protection mud is injected into the pile foundation hole (4) and the steel pipe pile (2) located in the pile foundation hole (4) through the mud injection pipe (1); when the wall protection mud level in the pile foundation hole (4) rises and triggers the liquid level sensor (3), the mud injection pipe (1) rises again and the rising distance is h, and this process is repeated; when the liquid level sensor (3) is not triggered within the approved time t, the mud injection pipe (1) is lifted and the mud injection pipe (1) is moved away from the pile foundation hole (4), and at least one of the steel pipe piles (2) is sunk by a vibration hammer until the bottom end of the steel pipe pile (2) abuts against the top end of the steel pipe pile (2) located in the pile foundation hole (4); S5. Repeat step S4 until the wall protection slurry fills the pile foundation hole (4) and the steel pipe pile (2) located in the pile foundation hole (4).

2. The slurry wall protection method for pile foundation construction of highway bridges in karst areas according to claim 1 is characterized in that: The numerical range of the approved time t is: D is the inner diameter of the pile foundation hole (4), and Q is the injection flow rate of the wall protection slurry.

3. The slurry wall protection method for pile foundation construction of highway bridges in karst areas according to claim 1 is characterized in that: h<H<2h.

4. The slurry wall protection method for pile foundation construction of highway bridges in karst areas according to claim 1 is characterized in that: In step S3 and step S4, the number of times the mud injection pipe (1) rises due to the triggering of the liquid level sensor (3) is n, and the number of the steel pipe piles (2) sunk by the vibration hammer is 5. The slurry wall protection method for pile foundation construction of highway bridges in karst areas according to claim 1 is characterized in that: A plurality of liquid level sensors (3) are connected to the outer peripheral wall of the lower end of the mud injection pipe (1) at equal intervals along the circumferential direction.

6. The slurry wall protection method for pile foundation construction of highway bridges in karst areas according to claim 1 is characterized in that: A protrusion (5) is axially connected to the outer peripheral wall of the mud injection pipe (1), a through hole (6) is provided on the protrusion (5) along the axial direction of the mud injection pipe (1), and a signal line of the liquid level sensor (3) is located in the through hole (6).

7. The slurry wall protection method for pile foundation construction of highway bridges in karst areas according to claim 1 is characterized in that: The connecting mechanism comprises a protrusion (7) and a recess (8), both of which are annular. The protrusion (7) is connected to the lower end surface of the steel pipe pile (2), and the recess (8) is connected to the upper end surface of the steel pipe pile (2). The steel pipe pile (2), the protrusion (7) and the recess (8) are all coaxially arranged, and the protrusion (7) on each steel pipe pile (2) can be interference-fitted with the recess (8) on another steel pipe pile (2).

8. The slurry wall protection method for pile foundation construction of highway bridges in karst areas according to claim 7, characterized in that: The connecting mechanism further comprises an annular guide portion (9), the guide portion (9) being connected to the lower end of the protruding portion (7) and being coaxially arranged with the protruding portion (7), the outer diameter of the guide portion (9) gradually increasing from bottom to top, the outer diameter of the lower end of the guide portion (9) being smaller than the diameter of the recessed portion (8), and the outer diameter of the upper end of the guide portion (9) being the same as the diameter of the protruding portion (7).

9. The slurry wall protection method for pile foundation construction of highway bridges in karst areas according to claim 1, characterized in that: A searchlight and a searchlight camera are connected to the outer peripheral wall of the lower end of the mud injection pipe (1); the searchlight camera is externally connected to a display device; and both the searchlight and the searchlight camera are located above the liquid level sensor (3).

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