Construction methods for removing bridge pile foundations in volcanic ash formations

Abstract

This invention discloses a method for removing bridge pile foundations in volcanic ash strata. The method includes steps S1: construction preparation, including determining the construction site, verifying the original pile length, and measuring the exposed pile position after the foundation cap is removed; Step S2: determining the pile center, determining the center of each auxiliary hole based on the pile center, constructing the auxiliary holes, and backfilling; Step S3: installing a rotary drilling rig, using a steel sleeve with an internal cutter to cut and drill, twisting and breaking the original pile, then removing it and cleaning the debris; Step S4: backfilling the pile holes and removing the steel sleeve. This invention aims to adapt to the uneven distribution of soft and hard volcanic ash strata and improve the reliability of pile extraction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of civil engineering, in particular to a construction method for removing bridge pile foundation in tuff stratum. BACKGROUND

[0002] In recent years, with the vigorous development of tunnel construction technology, more and more problems are encountered, especially the problem of removing bridge pile foundation in tunnel area during construction. Compared with ordinary stratum, the strength of tuff after cementation increases and the distribution of soft and hard is uneven, which leads to slow drilling of steel casing during pile removal. SUMMARY

[0003] The main purpose of the present application is to provide a construction method for removing bridge pile foundation in tuff stratum, which aims to adapt to the uneven distribution of soft and hard in tuff stratum and improve the reliability of pile removal.

[0004] To achieve the above purpose, the present application provides a construction method for removing bridge pile foundation in tuff stratum, which comprises the following steps: step S1, construction preparation, determining the construction site, verifying the original pile foundation length, measuring the exposed pile foundation position after the removal of the pile cap; step S2, determining the pile position center, determining the center of each auxiliary hole according to the pile position center, conducting auxiliary hole construction and backfilling, installing a bearing platform and supporting the bearing platform with each auxiliary hole; step S3, installing a rotary drilling machine on the bearing platform, cutting and drilling with the steel sleeve with an inner cutter in the rotary drilling machine, and removing and cleaning the slag after torsional pile breaking of the original pile foundation; step S4, backfilling the pile hole and removing the steel sleeve.

[0005] In some embodiments, determining the center of each auxiliary hole according to the pile position center comprises: determining the number of auxiliary holes according to the following formula:

[0006] Wherein, N a is the number of auxiliary holes; D p is the diameter of the pile foundation; δ is the stratum disturbance coefficient, the value of tuff stratum is 1.8 to 2.2; K v is the tuff cementation strength correction coefficient, the value is 0.15 to 0.25.

[0007] In some embodiments, the diameter of the auxiliary hole is 1.8m to 2.2m.

[0008] In some embodiments, when cutting and drilling with the steel sleeve with an inner cutter in the rotary drilling machine, the maximum torque T max of the rotary drilling machine needs to be controlled to meet the following formula:

[0009] Wherein, τ is the shear strength of tuff stratum; D c is the diameter of the steel casing; L sis the length of the casing; f s is a safety factor, and is 0.6 to 0.8.

[0010] In some embodiments, the pile backfilling and the steel sleeve pulling out are performed in a segmented and multiple times manner, and the following formula is met:

[0011] wherein, H f is the single backfilling height, and AH b is the synchronous pipe pulling height.

[0012] In some embodiments, when the steel sleeve with an inner cutter in the rotary drilling machine is used for cutting drilling, the high-pressure water gun is controlled to clean the muck between the steel casing and the pile foundation.

[0013] In some embodiments, the pressure of the high-pressure water gun is adjusted to 3MPa to 5MPa, and the spraying angle is 30° to 45°.

[0014] In some embodiments, when the auxiliary hole construction and backfilling are performed, the auxiliary hole construction depth needs to be controlled to be greater than the original pile foundation pile length by 2m to 3m.

[0015] In some embodiments, the inclination angle of the inner cutter of the rotary drilling machine is 45° to 60°, and the height is 1.5 times the wall thickness of the steel sleeve.

[0016] In some embodiments, when the steel sleeve with an inner cutter in the rotary drilling machine is used for cutting drilling, the verticality deviation of the rotary drilling machine is made to be less than or equal to 0.5% through the double-person orthogonal observation.

[0017] The technical scheme of the present application can determine the center of each auxiliary hole according to the center of the pile position, perform auxiliary hole construction and backfilling, build a stable rotary drilling machine construction platform in the uneven soft and hard volcanic ash stratum, effectively solve the problem of pile foundation pulling out in the volcanic ash stratum through scientific and reasonable construction steps and process control, improve the construction efficiency, ensure the stability and safety of the construction process, and reduce the construction risk and cost. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical scheme in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 The flowchart of the multi-frequency seismic belt large-diameter slurry shield method provided by an embodiment of the present application.

[0020] The objectives, functional features and advantages of the present application will be further described with reference to the embodiments in combination with the accompanying drawings. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0022] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative positional relationship, movement condition, etc. between components in a certain posture, and if the certain posture changes, the directional indications also change accordingly.

[0023] In addition, if the embodiments of the present application involve descriptions such as “first”, “second”, etc., the descriptions of “first”, “second”, etc. are only for description purposes, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by “first” and “second” can explicitly or implicitly include at least one of the features. In addition, “and / or” or “and / or” appearing throughout the text means that the three parallel solutions are included, taking “A and / or B” as an example, including A solution, or B solution, or A and B solutions are satisfied at the same time. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person of ordinary skill in the art can realize it, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0024] In the related art, when a bridge pile foundation removal problem is encountered in the tunnel construction process, the traditional method usually adopts direct pile pulling or impact breaking mode. Due to the uneven strength distribution formed by the cementation of the volcanic ash stratum, the conventional steel sleeve drilling process is prone to problems such as sudden reduction of footage speed, sleeve deflection, etc., resulting in uneven pile foundation fracture surface and incomplete subsequent slag removal.

[0025] In order to solve the above problems, the research and development team found that the uneven cementation strength distribution of the volcanic ash stratum leads to sudden change of sleeve cutting resistance, which is the core difficulty. By analyzing the stratum disturbance propagation law, it is proposed to set auxiliary holes around the pile to release stress concentration. In order to solve the problem of sleeve deflection, a steel sleeve structure with an inner inclined cutter is designed to form a uniform stress surface through torsional cutting. In view of the slag removal problem, combined with high-pressure water jet and sleeve synchronous lifting technology, a phased slag removal scheme is formed.

[0026] Therefore, the application provides a construction method including construction preparation, auxiliary hole construction, rotary drilling machine operation and pile hole backfilling. First, pile foundation parameters are determined through site survey, auxiliary holes are arranged around the pile position center and backfilling is performed to form a stress buffer zone. A rotary drilling machine equipped with a special steel sleeve is used to implement cutting pile breaking, and slag cleaning is simultaneously performed. Finally, layered backfilling and grouting reinforcement are implemented to ensure the stability of the stratum.

[0027] Referring to Figure 1 The application provides a bridge pile foundation pulling construction method for a tuff stratum, which comprises the following steps: S1, construction preparation, determining a construction site, verifying the length of an original pile foundation, and measuring the position of a pile foundation exposed after a pile cap is broken.

[0028] In this step, pile foundation parameters are determined through site survey to obtain the geological conditions of the construction site, which lays a foundation for subsequent steps. The parameters of the original bridge pile foundation can be obtained by referring to the construction data and parameters of the original bridge pile foundation and combining the geological exploration results. The pile head exposed by the pile foundation is broken and cleaned to prepare for subsequent steps.

[0029] S2, determining the pile position center, determining the center of each auxiliary hole according to the pile position center, performing auxiliary hole construction and backfilling, installing a bearing platform and enabling each auxiliary hole to support the bearing platform.

[0030] In this step, the center of each auxiliary hole is determined according to the pile position center, auxiliary hole construction and backfilling are performed, auxiliary holes are arranged around the pile position center and backfilling is performed to form a stress buffer zone to adapt to the uneven strength distribution of the tuff stratum due to the cementation effect. In some embodiments, the auxiliary hole construction can form a stress release zone in a ring array hole arrangement mode, and the hole can be formed by a rotary drilling machine and then backfilled with a mixture of crushed stones.

[0031] Installing the bearing platform and enabling each auxiliary hole to support the bearing platform means that the bearing platform is installed on the auxiliary hole formed in the foregoing step, and the bearing platform is supported by the plurality of auxiliary holes to improve the stability of the bearing platform.

[0032] Compared with the way of directly acting on the pile body by using the vibration pile pulling method in the related art, the vibration pile pulling is prone to cause stratum resonance, and in the environment of uneven strength distribution of the tuff stratum, there is a risk of causing the structure of the pile pulling device to be unstable and tilted or even overturned. In the embodiments of the application, the buffer zone formed by the auxiliary holes can effectively absorb the impact energy generated during subsequent pile pulling, thereby improving the reliability of the pile pulling operation in the tuff stratum.

[0033] It can be understood that after the installation of the bearing platform is completed, the levelness of the bearing platform needs to be accepted to further improve the perpendicularity between the rotary drilling machine and the ground in the subsequent pile pulling operation, and the reliability is higher. Meanwhile, in this step, the actual depth of the pile foundation should be determined according to the pile foundation parameters obtained in step S1, and when the depth of the auxiliary hole is designed, the depth of the auxiliary hole should be set to be not less than the actual depth of the pile foundation. Exemplarily, the depth of the auxiliary hole can be set to be 2-5 meters deeper than the actual depth of the pile foundation, so as to further improve the stability of the bearing platform and the rotary drilling machine after installation, and then adapt to the environment of uneven strength distribution of volcanic ash stratum.

[0034] In some embodiments, the ground can also be excavated 0.5-1 meters in the position where the pile foundation is located first, and the stone slag and the concrete are replaced, so as to preliminarily strengthen the stratum strength in the position where the pile foundation is located, and then the auxiliary hole is excavated and set, so as to improve the reliability when the auxiliary hole is excavated. Exemplarily, in some embodiments, the ground can be excavated 0.6 meters first, and then 0.35 meters of stone slag is replaced, and then 0.25 meters of concrete is poured on the stone slag to fill it up. After the bearing platform is installed, a steel plate with a thickness of 2-5 cm can be laid on the bearing platform, so as to further reduce the possibility of sinking and deflection of the rotary drilling machine when it is working after installation.

[0035] Step S3, installing the rotary drilling machine on the bearing platform, and cutting and drilling by using the steel sleeve with inner cutter in the rotary drilling machine to twist and break the original pile foundation and then pull it out and clean the slag.

[0036] This step is the step of pulling out the pile foundation, and the continuous cutter blades on the inner wall of the steel sleeve are distributed in a spiral shape and are rotated to cut into the stratum under the hydraulic drive. When the steel sleeve completely wraps the pile body, a continuous torque is applied to make the pile foundation twist and break at the preset position. In the slag cleaning stage, the gap between the sleeve can be washed by using a high-pressure water gun, and a vacuum slag suction device is started synchronously to clean the broken pile foundation out of the hole.

[0037] In these embodiments of the present application, the cutting and drilling step of the rotary drilling machine can be performed in sections, that is, the steel sleeve can be a sectional structure, and at least the first section of the steel sleeve is provided with an inner cutter. That is, in the initial pile pulling work of the rotary drilling machine, the steel sleeve provided with the inner cutter is connected with the rotary drilling machine, and is rotated into the ground under the drive of the rotary drilling machine to cut part of the pile foundation. After that, the hole drilled by the rotary drilling machine is cleaned, and after the mechanism for controlling the steel sleeve to advance into the ground in the rotary drilling machine is reset, the second section of the steel sleeve is connected between the first section of the steel sleeve and the rotary drilling machine, and the rotary drilling machine controls the steel sleeve to advance again to pull out the remaining part of the pile foundation, and so on until the pile foundation is completely pulled out.

[0038] Such a design can remove the deep pile foundation, and can also reduce the disturbance of the steel sleeve to the stratum during work, further improving the stability and reliability of the rotary drill during the pile foundation removal process.

[0039] Step S4, backfilling the pile hole and removing the steel sleeve.

[0040] The purpose of this step is to strengthen the cavity stratum after the pile foundation is removed, maintain the relative stability of the stratum, and remove and collect the steel sleeve for the removal of the next pile foundation. Accordingly, a segmented backfilling method can be used in this step, that is, after the cavity formed after the last pile foundation removal is cleaned, the steel sleeve can be removed by size, one section at a time, and the cavity is backfilled once. In this way, the cavity formed by the pile foundation removal is completely backfilled.

[0041] In some embodiments, after the last section of the steel sleeve is removed, the soil layer at the pile foundation position can be tamped and reinforced to further improve the stability of the stratum after the pile foundation is removed. Illustratively, in some embodiments, the grouting method can also be used to further improve the stability of the stratum after the pile foundation is removed.

[0042] Through the above technical solutions, the present application realizes safe and efficient removal of the pile foundation in the volcanic ash stratum. The auxiliary hole system significantly reduces the stratum stress concentration phenomenon and avoids the settlement of the surrounding structure caused by construction. The specially designed steel sleeve structure ensures uniform stress during cutting to prevent equipment from being stuck due to sudden changes in stratum hardness. The segmented backfilling and grouting process forms a dense filling body, effectively restoring the stratum bearing capacity. This integrated construction method ensures project progress while controlling stratum disturbance within the allowable range.

[0043] In some embodiments, determining the center of each auxiliary hole according to the center of the pile position includes determining the number of auxiliary holes according to the following formula:

[0044] wherein N a is the number of auxiliary holes; D p is the diameter of the pile foundation; δ is the stratum disturbance coefficient, which is 1.8 to 2.2 for the volcanic ash stratum; K v is the volcanic ash cementation strength correction coefficient, which is 0.15 to 0.25.

[0045] In these embodiments of the present application, the stratum disturbance coefficient is a quantitative parameter reflecting the structural change of the volcanic ash stratum under external action during construction. It can be calibrated by geological exploration data combined with field tests, for example, by comparing the stratum deformation under different construction parameters to determine the coefficient, and its value range can balance the construction efficiency and stratum stability.

[0046] The volcanic ash cementation strength correction coefficient is an adjustment parameter representing the influence of the cementation between volcanic ash particles on the overall stratum strength, and can be determined by a laboratory geotechnical test on the shear strength of the cementation and combined with in-situ test data.

[0047] In the bridge pile foundation pulling construction in the volcanic ash stratum, the determination of the number of auxiliary holes needs to comprehensively consider the pile foundation diameter, stratum disturbance characteristics and cementation strength. By substituting the pile foundation diameter into the formula, combined with the pre-calibrated stratum disturbance coefficient and cementation strength correction coefficient, the number of auxiliary holes suitable for the current geological conditions can be calculated. For example, when the pile foundation diameter is 2 meters, if the stratum disturbance coefficient is 2.0 and the cementation strength correction coefficient is 0.2, the number of auxiliary holes is about 17. The formula associates the geological parameters with the construction parameters through mathematical relationship, ensuring that the auxiliary hole arrangement can effectively disperse the concentrated stress of construction on the stratum, and can also avoid the waste of resources caused by excessive drilling.

[0048] The traditional method usually relies on experience to estimate the number of auxiliary holes, and does not establish a quantitative relationship with the stratum cementation strength and disturbance sensitivity, which is easy to lead to insufficient holes causing casing jamming or excessive holes increasing construction cost. The present scheme introduces the stratum disturbance coefficient and the cementation strength correction coefficient, and incorporates the non-uniform distribution characteristics of the cementation strength and the easy disturbance characteristics of the volcanic ash stratum into the calculation model, so that the number of auxiliary holes matches the actual mechanical response of the stratum.

[0049] Through the above technical scheme, the present application can accurately adapt to the complex mechanical properties of the volcanic ash stratum, while ensuring the stability of the stratum during the pile foundation pulling process, optimizing the construction scale of the auxiliary hole, avoiding the sudden change of the casing sinking resistance or the reduction of the drilling efficiency caused by unreasonable hole number design, thereby improving the controllability and economy of the construction process.

[0050] In some embodiments, the auxiliary hole has a diameter of 1.8m to 2.2m.

[0051] The auxiliary hole refers to an auxiliary drilling hole arranged around the center of the pile, which can be realized by rotary drilling rig or impact drilling rig, and the diameter range is determined by balancing stratum disturbance control and construction efficiency.

[0052] The diameter range of 1.8m to 2.2m refers to the actual drilling diameter of the auxiliary hole, which can be realized by adjusting the size of the drill bit or the staged reaming process, and the range is adapted based on the cementation strength and shear strength of the volcanic ash stratum.

[0053] Specifically, in the tuff formation, if the diameter of the auxiliary hole is less than 1.8m, the formation resistance may be too large when the steel casing is cut due to insufficient gap between the hole wall and the pile foundation; if it exceeds 2.2m, the backfill material consumption may increase significantly due to the increase in the volume of the hole. By controlling the hole diameter within the range of 1.8m to 2.2m, the steel casing drilling resistance can be reduced while avoiding the increase in construction cost caused by excessive hole diameter. For example, when using a 2.0m diameter auxiliary hole, the gap requirement can be directly met by single-hole forming, reducing the reaming process.

[0054] In some embodiments, when cutting drilling with a steel sleeve with an inner cutter in a rotary drill, the maximum torque T max satisfies the following formula:

[0055] where τ is the shear strength of the tuff formation; D c is the diameter of the steel casing; L s is the length of the casing; f s is the safety factor, with a value of 0.6 to 0.8.

[0056] The shear strength τ of the tuff formation refers to the ability of the formation to resist shear failure, which can be measured by in-situ tests, such as the vane shear test.

[0057] The diameter D c of the steel casing refers to the outer diameter of the sleeve, which can be matched with standardized pipe specifications, such as selecting a corresponding casing according to the diameter of the pile foundation. The length L s of the casing refers to the effective working section length of the steel sleeve drilled into the formation, which can be determined according to the depth of the pile foundation.

[0058] The safety factor f s is the engineering safety reserve factor, which can be valued according to the fluctuation range of the geological conditions, such as selecting the lower limit value in areas with poor stability.

[0059] When drilling with a steel sleeve in the tuff formation, the maximum torque limit value is calculated by the formula, and the actual output torque of the rotary drill is controlled within the calculated threshold range. The formula takes into account the shear properties of the formation, the size parameters of the casing, and the safety redundancy, with a 0.7 coefficient as an empirical reduction factor to offset the additional resistance generated during dynamic construction. During construction, the operator monitors the torque value in real time, and automatically triggers the speed reduction protection mechanism when it approaches the calculated value.

[0060] The pulling of the pile in the related art is often set according to the rated power of the equipment, without considering the dynamic matching relationship between the formation characteristics and the casing parameters. This scheme couples the cementation strength specific to the tuff formation, the casing size, and the safety factor for quantitative control standards through the establishment of a mechanical calculation model.

[0061] In some embodiments, the pile backfilling and the steel sleeve pulling out are performed in a segmented and multiple times manner, and the following formula is met:

[0062] wherein H f is a single backfilling height, and AH b is a synchronous pipe pulling height.

[0063] The segmented and multiple times manner refers to splitting the pile backfilling and the steel sleeve pulling out process into several times of alternating operations. Specifically, the material can be backfilled in stages and the sleeve can be lifted synchronously to achieve this. By controlling the amount of operation in each time, the risk of stratum disturbance is reduced. The single backfilling height H f refers to the vertical height of the material filled into the pile hole each time, which can be calculated by measuring the volume of the backfilling material and the cross-sectional area of the pile hole.

[0064] The synchronous pipe pulling height AH b refers to the displacement of the steel sleeve upward each time during the backfilling process, which can be monitored and controlled in real time by using a hydraulic system in combination with a displacement sensor.

[0065] In the tuff stratum, due to uneven distribution of cementation strength, if the pile backfilling and the sleeve pulling out are completed at one time, the hole wall may collapse or the backfilling material may not be compacted enough due to the sudden change of stratum stress. By segmented and multiple times operations, the steel sleeve of the corresponding height is pulled out immediately after each backfilling, so that the backfilling material is gradually compacted in a limited space, and a temporary support structure is formed by the interaction of the material weight and the stratum.

[0066] According to the above formula, by setting the single backfilling height as 1.2 to 1.8 times of the pipe pulling height, it can be ensured that the backfilling material fills the gap sufficiently when the sleeve is pulled out, and the void caused by the sinking of the material is avoided. The traditional method usually adopts a rough operation of continuous backfilling and overall pipe pulling, which easily leads to poor combination of the backfilling material and the hole wall, and especially in the tuff stratum, it may cause local collapse. The present scheme realizes the dynamic matching of material filling and sleeve displacement by segmented control and height correlation formula, which significantly improves the stability of the hole wall.

[0067] In some embodiments, when the steel sleeve with an inner cutter in the rotary drilling rig is used for cutting drilling, the method further comprises: controlling a high-pressure water gun to clean the sludge between the steel sleeve and the pile foundation. The pressure of the high-pressure water gun is adjusted to 3 MPa to 5 MPa, and the spraying angle is 30° to 45°.

[0068] The high-pressure water gun cleaning refers to the cleaning of the drill slurry deposits in the gap between the steel casing and the pile body by high-pressure water flow. Specifically, it can be achieved by using a plunger pump with an adjustable pressure valve in combination with a fan-shaped nozzle, for example, the pump pressure is controlled in the range of 3 MPa to 5 MPa. The jet angle adjustment refers to the water flow cutting into the slurry accumulation area at an inclination angle of 30° to 45°. In these embodiments of the present application, by using hydraulic impact to destroy the adhesion structure of the slurry, the formation of the hardened layer of the drill slurry in the narrow space can be avoided.

[0069] During the rotation of the steel casing into the tuff formation, as the debris generated by the inner cutter cutting the pile body continuously sinks along the outer wall of the casing, the operator starts the high-pressure water gun system to clean the annular gap between the casing and the pile body in real time. When the rotary drilling machine completes 0.5 meters of footage, the high-pressure water gun performs spiral jetting operation along the circumference of the casing, for example, three groups of nozzles arranged at intervals of 120° work alternately. The high-pressure water flow penetrates the cemented structure of the tuff debris, and the particles with a particle size of less than 5 cm are discharged outside the hole with the mud, while the larger debris is broken down by the water flow into pumpable particles.

[0070] In these embodiments of the present application, the high-pressure water gun is arranged to jet water flow at a pressure of 3 MPa to 5 MPa in a 30° to 45° inclined direction, and the water flow forms a spiral cleaning track along the circumference of the casing while impacting the slurry, which can effectively break down the cemented material and make the slurry particles discharge along the predetermined path through angle control.

[0071] When the pressure is less than 3 MPa, it cannot break through the cemented layer; when it exceeds 5 MPa, it may wash the formation and cause the hole wall to collapse. A jet angle less than 30° will reduce the transverse shear effect, and a jet angle greater than 45° will cause the water flow to impact the casing wall vertically, resulting in energy waste.

[0072] For example, in some embodiments of the present application, the pressure of the high-pressure water gun can be but is not limited to 3.5 MPa, 4 MPa, or 4.5 MPa; the jet angle can be but is not limited to 35° or 40°.

[0073] In these embodiments of the present application, the technical problem of easy cementation and accumulation of drill slurry during pile pulling in tuff formation is solved, the cleanliness of the working surface between the casing and the pile body is ensured, and the steel casing can be continuously and stably cut; at the same time, the phenomenon of casing jamming caused by slurry hardening is effectively prevented, the continuity of the pile body torsional fracture operation is ensured, and the risk of abnormal wear of the equipment is reduced.

[0074] In some embodiments, when auxiliary hole construction and backfilling are performed, the auxiliary hole construction depth needs to be controlled to be greater than the original pile foundation pile length by 2 m to 3 m.

[0075] The auxiliary hole construction depth refers to the extension length of the bottom of the hole relative to the bottom of the original pile foundation, which can be achieved by geological radar detection combined with drilling record review. By ensuring that the bottom of the auxiliary hole penetrates the bottom of the original pile foundation by a certain distance, an effective stress release zone is formed. The original pile foundation pile length refers to the total length of the bridge pile foundation from the bottom of the pile cap to the pile tip, which can be achieved by construction drawing review combined with ultrasonic pile integrity testing, and is used to determine the reference value for deepening the auxiliary hole.

[0076] Specifically, in the tuff stratum, due to uneven distribution of cementing strength, there may be a residual section or stratum cementing body that is not completely broken at the bottom of the original pile foundation. By controlling the auxiliary hole construction depth to be a certain range, such as 2m to 3m, beyond the length of the original pile foundation, a circumferential stress release zone can be formed at the bottom of the pile foundation, reducing the frictional resistance at the pile-soil interface. During construction, a rotary drilling rig is first used to penetrate the bottom of the original pile foundation, and then a cement-tuff mixed slurry is injected for backfilling, so that the auxiliary hole becomes a temporary support structure, preventing the pile hole from collapsing and weakening the wrapping effect of the stratum on the pile foundation.

[0077] Compared with related technologies, the auxiliary hole depth in the traditional pile pulling process is only the same as the length of the original pile foundation, which makes it difficult to completely break the residual section at the bottom of the pile, and may cause stratum collapse or pile body fracture during the pile pulling process. The present scheme deepens the auxiliary hole depth, so that the bottom of the pile foundation is completely wrapped in the reinforced range formed by the auxiliary hole, which not only avoids the interference of the residual pile body with the steel casing drilling, but also enhances the stability of the stratum around the pile by backfilling the slurry.

[0078] In some embodiments, the inner cutter of the rotary drilling machine has an inclination angle of 45° to 60° and a height of 1.5 times the wall thickness of the steel sleeve.

[0079] The inclination angle of the inner cutter refers to the angle between the cutting edge and the axis of the steel sleeve, which can be achieved by a welded fixed or adjustable cutter seat structure. This angle range can balance the cutting resistance and the efficiency of slag removal. The height of the inner cutter refers to the vertical dimension of the cutting edge protruding from the inner wall of the steel sleeve, which can be achieved by calculating the sleeve wall thickness and then machining the cutting edge base in proportion. This size relationship can ensure that the cutting edge has sufficient structural strength while avoiding excessive weakening of the sleeve stiffness.

[0080] Specifically, when cutting the sleeve in the tuff stratum, the inner cutter cuts into the pile foundation concrete at an inclination angle of 45° to 60°. This angle range can form a continuous broken zone on the cutting surface, for example, using a 55° inclination angle can not only reduce the fluctuation of cutting torque, but also guide the slag to the center of the sleeve by the inclined cutting surface. When the height of the inner cutter is set to 1.5 times the wall thickness of the sleeve, for example, a 60mm cutting edge is configured when the sleeve wall thickness is 40mm, which can ensure that the cutting edge has sufficient bending section modulus to resist the impact of hard layers in the stratum, and can avoid stress concentration at the welded part of the sleeve due to excessive height.

[0081] In some embodiments, the high-strength alloy steel plate can be processed into a trapezoidal cross-section blade through a laser cutting process, and then connected with the inner wall of the sleeve using a bevel welding process. After welding, ultrasonic flaw detection is performed. The sleeve wall thickness can be reviewed on site by an electromagnetic thickness gauge, and the blade base processing size is adjusted according to the measured value.

[0082] Compared with related technologies, the inner cutter of the conventional pile pulling equipment is designed for vertical cutting or small-angle cutting, which is prone to cause the drill jamming phenomenon due to discontinuous cutting surface in the tuff formation. The present scheme optimizes the inclination range to form a progressive fracture surface during cutting, and controls the ratio of the cutter height to the sleeve wall thickness to maintain the overall structural stability of the sleeve while ensuring the cutting efficiency.

[0083] In some embodiments, when the steel sleeve with an inner cutter in the rotary drilling rig is used for cutting drilling, the verticality deviation of the rotary drilling rig is less than or equal to 0.5% through the double-person orthogonal observation method.

[0084] The double-person orthogonal observation refers to real-time monitoring of the verticality of the drilling rig by two operators in two mutually perpendicular planes. This can be achieved by using a total station or a laser range finder in combination with an angle sensor. This observation method eliminates the measurement error of a single perspective to ensure the consistency of the drilling rig axis and the design axis.

[0085] The verticality deviation of less than or equal to 0.5% refers to the maximum allowable deviation of the inclination angle between the drilling rig axis and the design axis in the vertical direction, which can be achieved by dynamically adjusting the hydraulic system of the drilling rig support platform. This control standard can avoid increasing the friction between the steel sleeve and the pile foundation due to the inclination of the drilling rig, thereby reducing the risk of broken pile.

[0086] During the steel sleeve cutting drilling process, two operators arrange the measuring equipment along the transverse and longitudinal directions of the pile foundation, respectively, to collect the verticality data of the drilling rig in real time. When the deviation in a certain direction approaches the threshold value, the drilling is immediately paused and the correction program is started to restore the vertical state by adjusting the height difference of the drilling rig base support points. For example, if the longitudinal deviation reaches 0.4%, the drilling rig is tilted backward by reducing the pressure of the front support oil cylinder until the deviation value falls within the allowed range.

[0087] Compared with related technologies, the single-point observation method is limited by the visual angle blind area and is difficult to accurately determine the drilling rig posture in complex strata, while the double-person orthogonal observation significantly improves the reliability of verticality control through multi-dimensional data cross-validation. The common 1% verticality deviation standard in related technologies is prone to cause sleeve jamming in the tuff formation, while the present scheme effectively reduces the abnormal torque fluctuation caused by inclination through more stringent deviation limitation.

[0088] The application solves the problem of the intensified friction between the steel casing and the pile foundation and the reduced pile breaking efficiency caused by the drill inclination in the volcanic ash stratum, and ensures the accurate drilling of the casing along the designed path through real-time two-dimensional correction, so as to improve the one-time success rate of pile foundation pulling and reduce the amount of slag cleaning operation.

[0089] The above is only the preferred embodiment of the application, and does not limit the patent scope of the application. Any equivalent structural transformation, direct / indirect application in other related technical fields, or the like made under the inventive concept of the application and based on the content of the specification and drawings is included in the patent protection scope of the application.

Claims

1. A method for removing a bridge pile foundation in a volcanic ash stratum, characterized by, The method comprises the following steps: construction preparation, determining the construction site, checking the original pile foundation pile length, measuring the exposed pile foundation position after the destruction of the pile cap; determining the center of the pile position, determining the center of each auxiliary hole according to the center of the pile position, constructing and backfilling the auxiliary hole, installing a bearing platform and supporting the bearing platform by each auxiliary hole, wherein the auxiliary hole refers to an auxiliary drilling hole arranged around the center of the pile position; installing a rotary drilling machine on the bearing platform, cutting and drilling with a steel sleeve with an inner cutter in the rotary drilling machine, and then pulling out and cleaning the slag after twisting and breaking the original pile foundation; backfilling the pile hole and pulling out the steel sleeve; determining the center of each auxiliary hole according to the center of the pile position comprises: determining the number of auxiliary holes according to the following formula: Wherein, N a is the number of auxiliary holes; D p is the diameter of the pile foundation; δ is the stratum disturbance coefficient, and the value of the tuff stratum is 1.8 to 2.2; K v is the tuff cementation strength correction coefficient, and the value is 0.15 to 0.

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2. The construction method of removing a pile foundation of a volcanic ash stratum bridge according to claim 1, characterized by, The diameter of the auxiliary hole is 1.8m to 2.2m.

3. The construction method of removing a pile foundation of a volcanic ash stratum bridge according to claim 1, characterized by, When the steel sleeve is cut by the in-hole cutter of the rotary drilling machine, the maximum torque T of the rotary drilling machine needs to be controlled max satisfies the following formula: Wherein, τ is the shear strength of the tuff formation; D c is the diameter of the steel casing; L s is the length of the casing; f s is the safety factor, which is 0.6 to 0.

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4. The construction method of a pile foundation for removing a volcanic ash stratum bridge pile according to claim 1, characterized by, When backfilling the pile hole and pulling out the steel sleeve, it is carried out in a segmented and multiple manner, and meets the following formula: where H f is the single backfill height, AH b is the synchronous extubation height.

5. The construction method of removing a pile foundation of a volcanic ash stratum bridge according to claim 1, characterized by, When cutting and drilling with a steel sleeve with an inner cutter in the rotary drilling machine, it further comprises: controlling the high-pressure water gun to clean the slag between the steel sleeve and the pile foundation.

6. The construction method of removing a pile foundation of a volcanic ash stratum bridge according to claim 5, characterized by, The pressure of the high-pressure water gun is adjusted to 3MPa to 5MPa, and the spraying angle is 30° to 45°.

7. The construction method of a pile foundation for removing a volcanic ash stratum bridge pile according to Claim 1, characterized by, When constructing and backfilling the auxiliary hole, the construction depth of the auxiliary hole needs to be controlled to be greater than the original pile foundation pile length by 2m to 3m.

8. The construction method of a pile foundation for removing a volcanic ash stratum bridge according to claim 1, characterized by, The inclination angle of the inner cutter of the rotary drilling machine is 45° to 60°, and the height is 1.5 times the wall thickness of the steel sleeve.

9. A method according to any one of claims 1 to 8, wherein, When cutting and drilling with a steel sleeve with an inner cutter in the rotary drilling machine, the perpendicularity deviation of the rotary drilling machine is ≤0.5% through the double-person orthogonal observation.

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