Pile foundation removal and parameter control method within the tunneling range of shield tunneling

Abstract

The present invention provides a method for removing pile foundations and controlling parameters within the scope of a shield tunnel that passes through an intrusion limit. The specific steps of the construction method are as follows: first, an inclinometer is buried in the central lead hole of the intrusion limit pile, and plain concrete positioning piles are constructed around the intrusion limit pile. The positioning piles are constructed to a height of 1 / 3-1 / 2 of the intrusion limit pile, and then the soil is backfilled and a rotary jet pile is constructed in the area above the positioning pile. Then, a protective sleeve is installed on the ground on the top of the intrusion limit pile, and the intrusion limit pile can be removed by the pile flushing method. After the pile body is removed, concrete is backfilled in the impact hole to form a replacement pile. When the shield tunnel passes through the plain pile, specific excavation parameters are targetedly adjusted. At the same time, according to the surface settlement monitoring situation, WSS tracking grouting is used to timely fill the underground subsidence soil to ensure ground stability. The present invention has the advantages of good construction effect and convenient implementation, and effectively assists in flushing the pile foundation that invades the tunnel range, avoiding the risk of the cutter head being entangled and tied by steel bars during shield construction.

Description

Technical Field

[0001] The present invention is aimed at the field of urban rail construction, and in particular is a method for removing pile foundations and controlling parameters within a shield over-intrusion tunnel range. Background Art

[0002] With the continuous development of my country's national economy and urban transportation construction, the country has set off a climax of underground rail transit construction. In the planning and construction scope of the subway, it is impossible to completely avoid the underground reinforced concrete pile foundation. The subway tunnel is shallow, which often causes the reinforced concrete pile foundation to invade the tunnel scope. The subway tunnel is mostly constructed by shield method. If the shield directly cuts the intrusion pile foundation, it is easy to cause the pile foundation steel bar to wrap around the shield machine cutter head and continue to detour around the surrounding soil or even lock the shield machine cutter head. In order to ensure the smooth construction of the shield, the intrusion pile foundation needs to be removed.

[0003] Generally, there are several construction methods for removing obstacle piles, such as pile extraction, pile driving, and blasting. Compared with pile extraction and blasting, pile driving is a method with lower cost and higher construction efficiency. Specifically, a punching pile driver is used to directly remove the pile foundation that intrudes into the tunnel. However, in the process of removing reinforced concrete pile foundations by the pile driving method, the hammer of the punching pile driver can easily drive the broken steel bars into the soil around the intruding piles and leave them within the tunnel. When the shield passes through, there are still risks such as shield machine blockage and ground collapse. Therefore, in order to ensure the smooth removal of the intruding piles, it is very necessary to study a method for removing the pile foundation within the shield tunnel. Summary of the invention

[0004] In order to solve the above technical problems, the present invention describes a method for removing pile foundations and controlling parameters within the tunnel range where a shield machine has intruded beyond a certain limit. This method can quickly and efficiently remove pile foundations within the tunnel range and reduce the risk of the cutterhead being entangled and tied up by steel bars during shield construction.

[0005] In order to ensure the removal of pile foundations within the scope of a shield tunnel, the present invention provides a method for removing pile foundations within the scope of a shield over-intrusion tunnel, which is characterized by comprising the following steps:

[0006] (1) Determine the position of the limiting pile within the shield tunnel, then drill a hole through the drill rig and bury the inclinometer tube in the center of each limiting pile. The drilling depth is below the bottom of the limiting pile, and the top of the inclinometer tube is higher than the top of the limiting pile. The integrity of the limiting pile body is determined by coring, and after the inclinometer tube is buried, the length and inclination of the limiting pile are determined by the inclinometer, and the plane range of the construction pile flushing is determined based on the determined pile length and inclination;

[0007] (2) According to the positioning position of the limit pile, plain concrete positioning piles are constructed in four directions of the limit pile, and the outer edge of the positioning pile in each direction is 10 to 20 cm away from the edge of the limit pile; first determine the position of the positioning pile, use a rotary drilling rig to construct the pile hole to a position below the bottom of the limit pile, then pour underwater concrete to 1 / 3 to 1 / 2 the height of the limit pile to form the positioning pile, and then backfill the pile hole with soil to the top of the limit pile;

[0008] (3) After the construction of the blocking pile in step (2) is completed, 3 to 5 circles of interlocking jet grouting piles are constructed on the outside of the limiting pile with the center of the trespassing pile as the center of the circle to form a rotary pile reinforcement body, wherein the pile bottom of the jet grouting pile extends to the pile top of the blocking pile in step (2), and the jet grouting piles in contact with the blocking pile are connected as a whole;

[0009] (4) After the construction of the rotary pile reinforcement body in step (3) is completed, a protective sleeve is installed at the position on the ground corresponding to the limit pile. The protective sleeve is fixed on the ground at a height of 0.8 to 1.2 m, and its inner diameter is 20 to 50 cm larger than the impact drill bit, and the internal through hole is directly opposite to the limit pile;

[0010] (5) After the installation of the protective sleeve in step (4) is completed, the inclinometer tube is removed, and then the bentonite mud and clay required for pile driving are poured into the protective sleeve. The impact drill bit of the impact pile driver is suspended and aimed at the center of the protective sleeve for reciprocating impact, so that the pile body of the limiting pile is broken into debris and brought out of the ground through mud circulation; at the same time, during the impact process, the steel bars in the pile body of the limiting pile are broken and sucked out with a strong magnet or directly out of the area below the tunnel bottom elevation using an impact drill bit; the diameter of the impact drill bit is 10 cm to 20 cm larger than the diameter of the limiting pile; the cleaned steel bars are weighed in time to ensure that there is no large amount of steel bars remaining within the tunnel;

[0011] (6) After the intrusion piles in step (5) are flushed out, underwater concrete is poured to form plain concrete replacement piles at the locations of the intrusion piles. The top elevation of the replacement piles is 2 to 5 m above the tunnel top surface, and clay is backfilled at the remaining hole locations to the original elevation of the intrusion piles to ensure that the punched holes are backfilled densely to avoid landslides or even roof collapse during excavation.

[0012] A more preferred technical solution of the present invention is as follows: after the construction of the positioning piles in step (2) is completed and the construction of the rotary jet grouting piles in step (3) is completed, the probe of the inclinometer is placed in the limiting pile through the inclinometer tube to monitor the inclination of the pile body, and to determine whether the construction of the plain concrete positioning piles and the rotary jet grouting piles damages the limiting piles. If damage and inclination occur, the construction needs to be stopped and the construction plan needs to be re-determined.

[0013] The present invention has a relatively good technical solution: in the step (1), a geological drill is used to drill a hole, the diameter of the hole is 75-110 mm, the depth of the hole is 2-5 m to the bottom of the limit pile, the inclinometer tube is a plastic inclinometer tube with a diameter of 35-60 mm, and the top of the inclinometer tube is 0.2-0.3 m higher than the top of the limit pile; the inclinometer tube can verify the length and integrity of the limit pile on the one hand, and on the other hand, detect whether the construction of the blocking concrete pile and the rotary jet pile damages the limit pile before the limit pile is driven, so as to timely grasp the condition of the pile foundation of the limit pile.

[0014] The preferred technical solution of the present invention is as follows: in the step (2), four plain concrete positioning piles are provided, and the four positioning piles are distributed around the limit pile at an angle of 90 degrees, and the pile bottom elevation is 2.5 to 3.5 meters lower than the limit pile. The four positioning piles are all cast with C20 underwater concrete, and each positioning pile is cast to 1 / 3 of the height of the limit pile, which can reduce costs. The diameter of the positioning pile is 550 to 650 mm.

[0015] The preferred technical solution of the present invention is as follows: in the step (3), the diameter of the jet grouting pile is 550-650 mm, the engagement is 100-200 mm, the bottom of the jet grouting pile is connected with the positioning pile, specifically, when the jet grouting pile drill rod is drilled to the top of the positioning pile, the jet grouting is rotated in situ for 1-3 minutes to ensure that the jet grouting pile is connected with the positioning pile; and the short section of the steel bar of the limit pile is prevented from being stuck in the surrounding soil and still within the tunnel range.

[0016] The present invention has a relatively good technical solution: the protective sleeve in step (4) is welded by an upper cylinder and a lower annular fixing seat, a plurality of triangular ribs are welded between the cylinder and the annular fixing seat, a plurality of anchor holes are provided on the annular fixing seat, the upper cylinder is made of an annular steel plate with a thickness of 2 to 3 cm, and the annular fixing base is fixed to the ground by 6 to 8 rivets. The protective sleeve is fixed to the ground with a long rivet bolt, providing space for storing bentonite mud and a small amount of clay required for pile driving, which can prevent concrete debris from splashing and injuring people. At the same time, the protective sleeve also plays a role in fixing the hammer, ensuring that the hammer of the pile driver will not tilt or deviate when it hits the limit pile.

[0017] A more preferred technical solution of the present invention is as follows: the step (5) breaks the pile body of the limiting pile into debris and brings it out of the ground through mud circulation. Specifically, the mud is pumped with a mud pump while impacting, so that the mud is ejected from the bottom of the drill bit, mixed with the pile body debris, and continuously overflows from the bottom of the hole to the hole mouth in a positive circulation manner, thereby bringing the debris out of the ground.

[0018] The present invention provides a parameter control method for a shield machine intruding into a limited tunnel range, which is characterized by the following specific steps: after the pile foundation within the shield machine intruding into a limited tunnel range is cleared according to the above method, when the shield machine passes through the intrusion into the limited tunnel range, its shield excavation speed is controlled at 10-15mm / min, torque 2700-3000knm, cutter head speed 1.5r / min, thrust 4500-5000t, and soil bin pressure is 0.1-0.3bar greater than the soil pressure on the top of the cutter head; and according to the surface settlement monitoring situation, WSS tracking grouting is used to fill the underground subsidence soil in time.

[0019] The present invention has a relatively better technical solution: in the area where the surface settlement exceeds 10mm, WSS tracking grouting is carried out, the drilling depth is 5m above the shield machine, the grouting adopts double liquid slurry composed of water glass and cement slurry, the grouting depth is above 2-3m of the cutter head, the water-cement ratio of the cement slurry is 1:1, the initial setting time of the double liquid slurry is controlled at 30-40s, and the grouting final hole pressure is controlled at 1Mpa; the tracking grouting is used to reinforce the stratum around the replacement pile, and a grouting curtain is formed at the edge of the pile foundation to ensure that the soil bin pressure is normal during the shield machine excavation process to prevent pressure relief.

[0020] Beneficial effects of the present invention:

[0021] (1) Before the pile foundation is cleared, the present invention drills a hole in the center of the limiting pile and embeds a positioning detection tube, so that the length and integrity of the limiting pile can be detected before construction, and before the limiting pile is flushed, it can be detected whether the construction of the positioning concrete pile and the rotary jet pile has damaged the limiting pile. The situation of the limiting pile can be accurately understood in advance, providing a basis for the subsequent flushing of the limiting pile.

[0022] (2) The present invention constructs four plain concrete retaining piles at the bottom of the limiting pile, which effectively solves the problem of displacement of the pile foundation when a small section of the pile foundation is left in the process of flushing the limiting pile, and ensures that the limiting pile can be completely flushed out of the tunnel range. The retaining piles are cast to 1 / 3 of the height of the limiting pile, which reduces the cost, and then the remaining part is backfilled with original soil;

[0023] (3) In the present invention, the limiting pile is taken as the center, and interlocking jet grouting piles are constructed on the periphery of the limiting pile to reinforce the soil around the limiting pile, thereby reducing the adverse effects of disturbance on the surrounding strata during construction and solving the problem of ground collapse when the pile driver flushes the limiting pile. Moreover, since a jet grouting stratum is formed around the limiting pile, the soil strength is increased, thereby avoiding the possibility of steel bars being retained in the surrounding soil during the pile punching process.

[0024] (4) The present invention takes actual conditions into consideration and replaces the steel casing in the original pile driving with a special sleeve seat on the ground. On the one hand, it provides a space for storing mud for pile driving, while at the same time ensuring the verticality of the impact drill during the pile driving process, thereby reducing the construction cost, saving the time for burying the steel casing, and greatly improving the construction efficiency.

[0025] (5) In the present invention, WSS tracking grouting is carried out in a timely manner during the shield excavation process to fill the gaps around the pile foundation and the surrounding soft strata, thereby preventing the shield machine from passing through the plain concrete piles and entering the soft strata for excavation and causing irregular ground settlement, thereby ensuring the safety of ground buildings during the excavation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the construction structure of an embodiment of the present invention;

[0027] Figure 2 yes Figure 1 Middle AA section;

[0028] Figure 3 yes Figure 1 Middle BB section;

[0029] Figure 4 It is a structural schematic diagram of the protective sleeve in the present invention.

[0030] In the figure: 1—limit pile, 2—inclinometer tube, 3—protective sleeve, 3-1—cylinder, 3-2—annular fixing seat, 3-3—triangular rib, 4—positioning pile, 5—jet grouting pile, 6—tunnel range. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with embodiments.

[0032] The embodiment is for a shield tunnel section of Guangzhou Metro, which is constructed by shield method. The left line of the section is 1098.87m long, the right line of the section is 1099.188m long, the covering soil depth of the section tunnel vault is about 7.5m~13.8m, and the line depth is about 13.5~19.8m. On the downline advancement line of this section, there are 35 original reinforced concrete pile foundations of houses. The pile foundations invade the top plate of the shield tunnel by about 3 meters, and the pile foundations invade the shield downline, with a distance of 0~3m from the center of the tunnel downline. The limit pile is 12m long and the pile body diameter is 12m. The steel cage is 11.8m long, the main reinforcement is Φ20 threaded steel, and the stirrups are Round steel, C30 concrete poured underwater. The groundwater level in this section is mostly porous groundwater, with a static water level of 1m to 2.9m. The geological conditions in the pile foundation area are as follows from top to bottom: <1-1>, <1-2> artificial fill layers, <4-2A>, <4-2B>, <4N-2> alluvial soil layers (partially mixed with <3-2> medium-coarse sand layers), followed by <3-2>, <3-3> sand layers and <9C-2> slightly weathered rock layers. The pile foundations of the houses are mainly located in the fill layer, silty clay layer and sand layer. The tunnel mainly passes through the sand layer and slightly weathered rock layer. The shield method is used in this section, and the cutterhead and cutter prepared for shield excavation cannot cut the reinforced concrete limit piles.

[0033] For this construction project, the construction method for removing pile foundations within the shield tunnel range of the present invention is used for construction, which specifically includes the following steps:

[0034] (1) Burying the inclinometer tube 2: First, find out the position of the limit pile 1, and use a geological drill to drill a hole in the center of each limit pile 1. The diameter of the hole is 90 mm, and then bury a plastic inclinometer tube 2 with a diameter of 70 mm. The inclinometer tube 2 should extend 2m below the bottom of the pile, and the buried inclinometer tube 2 should be 0.2m out of the pile head. During the burial process, the sealing of the inclinometer tube connection must be ensured to be complete, and the verticality of the inclinometer tube must also be ensured. The inclinometer probe is placed into the inclinometer tube through the inclinometer tube to detect the limit pile body. It is found that the pile length is 11m-13m. Except for the cracks in the middle of piles 3 and 12, the other limit piles are intact.

[0035] (2) Construction of lower plain concrete blocking piles 4: Since most of the pile body of the limiting pile 1 is located in the silty clay layer and sand layer, in order to prevent the limiting pile from shifting during the pile flushing process, four plain concrete cast-in-place piles with a diameter of 600 mm are constructed in four different directions of each limiting pile 1, cast with C20 underwater concrete. The outer edge of the blocking pile is 10-20 cm away from the edge of the limiting pile, and the pile bottom elevation is 3 m lower than that of the limiting pile. It is cast to 1 / 3 of the height of the limiting pile, and the upper part of the bored hole of the blocking pile is backfilled to the ground level, such as Figure 3 As shown, the four retaining piles are distributed in four directions around the limit pile and form a 90-degree angle at the center of the limit pile.

[0036] (3) Construct the middle and upper soil reinforcement jet grouting piles. Since the soil where the limit pile 1 is located is relatively soft, in order to prevent the limit pile from being washed away, steel bars are reserved within the tunnel. The project department decided to focus on the limit pile. Figure 2 As shown in the figure, three circles of mutually interlocking jet grouting piles 5 are constructed around each limit pile. The diameter of adjacent jet grouting piles 5 is 600mm, the interlocking is 150mm, the pile center spacing is 450mm, the jet grouting pile 5 is connected to the clamping position 4, and the pile top elevation is the ground elevation. The jet grouting pile reinforcement adopts PO 42.5R silicate early strength cement, and the slurry water-cement ratio is 1-1.5; during the construction process, the pressure is controlled at 22-25MPa, the slurry flow rate is 40L / min-70L / min, the jet grouting lifting speed should be controlled within the range of 5-25cm / min, and the rotation speed should be controlled within the range of 10-20r / min. When the drill rod drills to the top of the clamping position pile, the rotary grouting is rotated in situ for 1-3min to ensure that the jet grouting pile is connected to the clamping position pile. After the jet grouting pile construction is completed, the pile body of the limit pile is tested again through the positioning monitoring pipe, and it is found that the clamping position pile construction and the jet grouting pile construction have no effect on the pile body of the limit pile.

[0037] (4) Install the ground protection sleeve 3. A special ground protection tower is made in advance with a 2 cm thick annular steel plate. The structure of the protection sleeve is as follows: Figure 4 As shown, the protective sleeve 3 is composed of an upper cylinder 3-1 and a lower annular fixing seat 3-2, and a plurality of triangular ribs 3-3 are welded between the cylinder 3-1 and the annular fixing seat 3-2; the diameter of the cylinder 3-1 is 1.4m, and the height is 1.2m. Annular wing plates are set up at the upper and lower ends, and the width of the upper annular wing plate is 5cm, and the width of the lower annular wing plate is 50cm to form an annular fixing seat 3-2 to increase the contact area between the sleeve seat and the ground. 6-8 round holes are left on the annular fixing seat 3-2, and rivets are inserted to fix it on the ground before pile punching; 1cm wide annular and vertical ribs are set on the sleeve seat body, and the rib spacing is 20cm.

[0038] (5) Construction of flushing out the limit piles: This project uses an impact pile driver to flush out the limit piles, and the impact drill bit has a diameter of 1m. After the installation of the protective sleeve in step (4) is completed, the inclinometer tube is removed. After the pile driver is in place, the prepared bentonite mud and a small amount of clay are added to the inside of the protective tower 3 installed in step (4). The colloid ratio of the bentonite mud and clay is 95%, and the sand content is less than 4%; then the impact pile foundation suspension impact drill bit is turned on and aimed at the center of the protective sleeve for reciprocating impact, the pile body of the limit pile is broken into debris, the steel bars in the pile body of the limit pile are broken, and it is sucked out with a strong magnet or directly out of the area below the tunnel bottom elevation using an impact drill bit; at the same time, the mud is pumped with a mud pump to make the mud ejected from the bottom of the drill bit, mixed with the pile body debris, and continuously overflowed from the bottom of the hole to the hole mouth in a positive circulation manner, bringing the debris out of the ground. During the impact process, the penetration should be properly controlled. At the bottom of the sleeve seat, the drilling should be slow to ensure a good wall protection effect at the bottom; after drilling to 1m below the bottom of the casing, it can be drilled at a normal speed according to the actual situation. When sucking out with a magnet, first absorb the steel bars around the hole wall, then absorb the steel bars in the hole, and stop when all the steel bars are absorbed three times without steel bars. The absorbed steel bars are stacked separately, and the weight is weighed and recorded after the steel bars are dried to ensure that all the steel bars are sucked out.

[0039] (6) Casting of replacement plain concrete piles. After the pile driver completes the pile driving, the hole is immediately cleaned by the slurry replacement method. After the hole is cleaned, concrete pouring begins. The replacement piles are poured from the bottom of the hole formed by the pile driver to 5m above the tunnel. The replacement piles are poured by the conduit method. The conduit diameter is 250mm. The poured concrete is C20 underwater concrete. The concrete should have good workability, with a crushed stone grading of 5-25mm, medium-coarse sand, and a water-reducing agent. The slump is controlled at 18-22cm, and the water-cement ratio is not greater than 0.6. The first concrete pouring is not less than 2m3 (standard slot section) to ensure that the first poured concrete can bury the conduit. The pouring process should be continuous, and the interruption time should not exceed 30 minutes to ensure the integrity of the replacement pile body.

[0040] (7) After all the intruding piles in the shield area have been cleared, the shield excavation process can be carried out. Due to the low strength of the plain piles themselves, large pieces are easily generated during the excavation process. Therefore, attention should be paid to controlling the excavation parameters during the excavation process. The speed should be controlled at 10-15mm / min, the torque at 2700-3000knm, the cutter head speed at 1.5r / min, and the thrust at 4500-5000t. At the same time, the excavation volume and soil bin pressure should be strictly monitored. Attention should be paid to monitoring the shield soil bin pressure, the excavation situation at the excavation port, and the ground settlement. The soil bin pressure is generally 0.2bar greater than the soil pressure at the top of the cutter head. When the shield excavated to pile No. 18, the monitoring found that the ground settlement at the cutter head and the tail of the shield machine was 12mm. In order to ensure the safety of the ground buildings, the project department took emergency shutdown measures to maintain pressure, and promptly carried out WSS tracking grouting at the corresponding positions of the shield tail and the cutter head of the shield machine. The drilling depth was 5m above the shield machine. Grouting uses a double liquid slurry consisting of water glass and cement slurry, with a water-cement ratio of 1:1. The initial setting time of the double liquid slurry is controlled at 30-40s, and the final hole pressure of grouting is controlled at 1Mpa. Grouting reinforces the soft strata between the piles and fills the larger cracks caused by the plain concrete piles. After the grouting is completed, the ground settlement is controlled and the pressure in the shield machine soil bin is normal.

[0041] After the construction method of clearing the pile foundation within the shield tunnel range of the present invention was adopted in the above construction project, the shield was helped to pass through the limiting piles smoothly, the quality of the formed tunnel was ensured, and a strong guarantee was provided for the tunnel penetration.

[0042] The above is only one embodiment of the present invention, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the attached claims.

Claims

1. A method for removing pile foundation within the tunneling range of a shield tunnel, characterized in that The specific steps include: (1) Determine the position of the limiting piles within the shield tunnel, then drill a hole through the drill rig and bury the inclinometer tube in the center of each limiting pile. The drilling depth is below the bottom of the limiting pile, and the top of the inclinometer tube is higher than the top of the limiting pile. The integrity of the limiting pile body is determined by coring the hole. After the inclinometer tube is buried, the length and inclination of the limiting pile are determined by the inclinometer, and the flushing plane range of the pile is determined based on the determined pile length and inclination. (2) According to the location of the limit pile, plain concrete positioning piles are constructed in four directions of the limit pile. The outer edge of the positioning pile in each direction is 10 to 20 cm away from the edge of the limit pile. First, determine the location of the positioning pile, use a rotary drilling rig to construct the pile hole to a position below the bottom of the limit pile, then pour underwater concrete to 1 / 3 to 1 / 2 the height of the limit pile to form the positioning pile, and then backfill the pile hole to the top of the limit pile. (3) After the construction of the blocking pile in step (2) is completed, 3 to 5 circles of interlocking jet grouting piles are constructed on the outside of the limiting pile with the center of the limiting pile as the center of the circle to form a rotary pile reinforcement body, wherein the bottom of the jet grouting pile extends to the top of the blocking pile in step (2), and the jet grouting piles in contact with the blocking pile are connected as a whole; (4) After the construction of the rotary pile reinforcement body in step (3) is completed, a protective sleeve is installed at the position on the ground corresponding to the limit pile. The protective sleeve is fixed on the ground at a height of 0.8 to 1.2 m. Its inner diameter is 20 to 50 cm larger than the impact drill bit, and the internal through hole is directly opposite to the limit pile. (5) After the installation of the protective sleeve in step (4) is completed, the inclinometer tube is removed, and then the bentonite mud and clay required for pile driving are poured into the protective sleeve. The impact drill bit of the impact pile driver is suspended and aimed at the center of the protective sleeve for reciprocating impact, so that the pile body of the limiting pile is broken into debris and brought out of the ground through mud circulation; at the same time, during the impact process, the steel bars in the pile body of the limiting pile are broken and sucked out by a strong magnet or directly out of the area below the tunnel bottom elevation by an impact drill bit; the diameter of the impact drill bit is 10 cm to 20 cm larger than the diameter of the limiting pile; (6) After the removal of the limiting piles in step (5), pour underwater concrete to form plain concrete replacement piles at the locations of the limiting piles. The top elevation of the replacement piles is 2 to 5 m above the tunnel top surface, and clay is backfilled at the remaining hole locations to the original elevation of the limiting piles.

2. A method for removing pile foundations within a shield tunneling over-limit tunnel according to claim 1, characterized in that: After the construction of the retaining piles in step (2) is completed and the construction of the jet grouting piles in step (3) is completed, the probe of the inclinometer is placed in the limit pile through the inclinometer tube to monitor the inclination of the pile body to determine whether the construction of the plain concrete retaining piles and the jet grouting piles damages the limit piles. If damage occurs, the construction is stopped and the construction plan is adjusted.

3. The method for removing pile foundation within the tunneling range of a shield tunnel according to claim 1, characterized in that: In the step (1), a geological drill is used to drill a hole with a diameter of 75 to 110 mm and a depth of 2 to 5 m to the bottom of the limit pile. The inclinometer tube is a plastic inclinometer tube with a diameter of 35 to 60 mm, and the top of the inclinometer tube is 0.2 to 0.3 m higher than the top of the limit pile.

4. The method for removing pile foundation within the tunneling range of a shield tunnel according to claim 1, characterized in that: In the step (2), there are four plain concrete positioning piles, which are distributed around the limit pile at an angle of 90 degrees. The pile bottom elevation is 2.5 to 3.5 meters lower than the limit pile. The four positioning piles are all cast using C20 underwater concrete. Each positioning pile is cast to 1 / 3 of the height of the limit pile and has a diameter of 550 to 650 mm.

5. The method for removing pile foundation within the tunneling range of a shield tunnel according to claim 1, characterized in that: In step (3), the diameter of the jet grouting pile is 550-650 mm, the engagement is 100-200 mm, and the bottom of the jet grouting pile is connected with the positioning pile. Specifically, when the jet grouting pile drill rod is drilled to the top of the positioning pile, the jet grouting is rotated in situ for 1-3 minutes to ensure that the jet grouting pile is connected with the positioning pile.

6. The method for removing pile foundation within the tunneling range of a shield tunnel according to claim 1, characterized in that: The protective sleeve in step (4) is welded by an upper cylinder and a lower annular fixing seat, a plurality of triangular ribs are welded between the cylinder and the annular fixing seat, a plurality of anchor holes are opened on the annular fixing seat, the upper cylinder is made of an annular steel plate with a thickness of 2 to 3 cm, and the annular fixing base is fixed to the ground by 6 to 8 rivets.

7. The method for removing pile foundation within the tunneling range of a shield tunnel according to claim 1, characterized in that: The step (5) breaks the pile body of the limiting pile into debris and brings it out of the ground through mud circulation. Specifically, the mud is pumped with a mud pump while impacting, so that the mud is ejected from the bottom of the drill bit and mixed with the pile body debris, and continuously overflows from the bottom of the hole to the hole mouth in a positive circulation manner, thereby bringing the debris out of the ground.

Images