Construction method for pulling out volcanic ash stratum bridge pile foundation

Abstract

The invention discloses a construction method for pulling out a bridge pile foundation in a volcanic ash stratum. The construction method for pulling out the bridge pile foundation in the volcanic ash stratum comprises the steps that S1, construction preparation is conducted, a construction site is determined, the pile length of an original pile foundation is checked, and the position of the exposed pile foundation after a bearing platform is broken and removed is measured; s2, the pile position center is measured, the center of each auxiliary hole is measured according to the pile position center, and auxiliary hole construction and backfilling are conducted; s3, a slewing drilling machine is installed, a steel sleeve with an inner cutter in the slewing drilling machine is used for cutting and drilling, and after an original pile foundation is twisted to be broken, the pile is pulled out and slag is removed; and S4, the pile hole is backfilled, and the steel sleeve is pulled out. The technical scheme aims to adapt to the situation that the hardness distribution of the volcanic ash stratum is uneven, and the pile pulling reliability is improved.

Description

Technical Field

[0001] This invention relates to the field of civil engineering technology, and in particular to a method for removing bridge pile foundations in volcanic ash strata. Background Technology

[0002] In recent years, with the vigorous development of tunnel construction technology, more and more problems have been encountered, especially the problem of removing bridge pile foundations in the tunnel area during construction. Compared with ordinary strata, the strength of volcanic ash increases after cementation and the distribution of softness and hardness is uneven, which leads to problems such as slow drilling of steel casing during pile extraction. Summary of the Invention

[0003] The main objective of this invention is to propose a method for removing bridge pile foundations in volcanic ash strata, which aims to adapt to the uneven distribution of soft and hard volcanic ash strata and improve the reliability of pile extraction.

[0004] To achieve the above objectives, this invention proposes a method for removing bridge pile foundations in volcanic ash strata. This method includes: Step S1, construction preparation, 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 and backfilling the auxiliary holes, installing a bearing platform, and ensuring each auxiliary hole supports the bearing platform; Step S3, installing a rotary drilling rig on the bearing platform, using a steel sleeve with an internal cutter in the rotary drilling rig to cut and drill, twisting and breaking the original pile, then removing it and cleaning the debris; Step S4, backfilling the pile hole and removing the steel sleeve.

[0005] In some embodiments, determining the center of each auxiliary hole based on the pile location center includes: determining the number of auxiliary holes according to the following formula: Among them, N a Number of auxiliary holes; D p δ is the pile diameter; δ is the ground disturbance coefficient, with a value of 1.8 to 2.2 for volcanic ash strata; K v This is a correction factor for the cementing strength of volcanic ash, with a value ranging from 0.15 to 0.25.

[0006] In some embodiments, the diameter of the auxiliary hole is 1.8m to 2.2m.

[0007] In some embodiments, when drilling using a steel sleeve with an internal cutter in a rotary drilling rig, it is necessary to control the maximum torque T of the rotary drilling rig. max Satisfy the following formula: Where τ is the shear strength of the volcanic ash formation; D c L is the diameter of the steel casing. s f is the length of the sleeve. sFor safety factors, the value is between 0.6 and 0.8.

[0008] In some embodiments, when backfilling the pile hole and removing the steel sleeve, the process is carried out in stages and multiple times, satisfying the following formula: Among them, H f ∆H represents the height of a single backfill operation. b To synchronize the tube removal height.

[0009] In some embodiments, when drilling using a steel sleeve with an inner cutter in a rotary drilling rig, the method further includes: controlling a water jet to clean the slag between the steel sleeve and the pile foundation.

[0010] In some embodiments, the pressure of the water gun is adjusted to 3 MPa to 5 MPa; the spray angle is 30° to 45°.

[0011] In some embodiments, when constructing and backfilling auxiliary holes, it is necessary to control the construction depth of the auxiliary holes to be 2m to 3m greater than the original pile length.

[0012] In some embodiments, the inclination angle of the inner cutter of the rotary drilling rig is 45° to 60°, and the height is 1.5 times the wall thickness of the steel sleeve.

[0013] In some embodiments, when drilling using a steel sleeve with an inner cutter in a rotary drilling rig, the verticality deviation of the rotary drilling rig is ≤0.5% by means of two-person orthogonal observation.

[0014] The technical solution of this invention, by determining the center of each auxiliary hole according to the center of the pile location, constructing and backfilling the auxiliary holes, can build a stable rotary drilling rig platform in volcanic ash strata with uneven hardness. Through scientific and reasonable construction steps and process control, it effectively solves the problem of pile extraction in volcanic ash strata, improves construction efficiency, ensures the stability and safety of the construction process, and reduces construction risks and costs. Attached Figure Description

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0016] Figure 1 This is a flowchart of a large-diameter slurry shield tunneling method for frequently occurring earthquake zones, provided in an embodiment of the present invention.

[0017] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0020] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0021] In related technologies, when encountering the challenge of removing bridge pile foundations during tunnel construction, traditional methods typically involve direct pile extraction or impact crushing. Volcanic ash strata, due to cementation, exhibit uneven strength distribution, making it prone to problems such as sudden drops in drilling speed and casing deviation during conventional steel casing drilling. This results in uneven pile foundation fracture surfaces and incomplete subsequent slag removal.

[0022] To address the aforementioned issues, the research team identified the uneven distribution of cementation strength in the volcanic ash strata, leading to abrupt changes in casing cutting resistance, as the core challenge. By analyzing the propagation patterns of strata disturbance, they proposed installing auxiliary holes around the pile to release stress concentration. To resolve the casing deflection problem, a steel sleeve structure with inward-tilting cutters was designed, creating a uniform stress surface through torsional cutting. For the slag removal challenge, a phased slag removal solution was developed, combining high-pressure water jetting with synchronous casing lifting technology.

[0023] Therefore, this application proposes a construction method including construction preparation, auxiliary hole construction, rotary drilling rig operation, and pile hole backfilling. First, the pile foundation parameters are determined through site survey. Auxiliary holes are arranged around the center of the pile location and backfilled to form a stress buffer zone. A rotary drilling rig equipped with a special steel sleeve is used to cut and break the pile, while simultaneously clearing away the excavated soil. Finally, layered backfilling and grouting reinforcement are implemented to ensure ground stability.

[0024] Please see Figure 1 This invention proposes a method for removing bridge pile foundations in volcanic ash strata. The method includes: step S1, construction preparation, determining the construction site, verifying the original pile length, and measuring the location of the exposed pile foundation after the foundation is broken.

[0025] In this step, site surveys are conducted to determine pile foundation parameters and obtain geological conditions of the construction site, laying the groundwork for subsequent steps. Specifically, accurate pile foundation parameters can be obtained by reviewing the original bridge pile foundation construction data and parameters, combined with geological exploration results. Exposed pile heads are then removed and cleared to prepare for subsequent steps.

[0026] Step S2: Determine the center of the pile location, determine the center of each auxiliary hole based on the pile location center, construct and backfill the auxiliary holes, install the bearing platform and make each auxiliary hole support the bearing platform.

[0027] In this step, the centers of each auxiliary hole are determined based on the pile location center. The auxiliary holes are then constructed and backfilled. These auxiliary holes are arranged around the pile location center and backfilled to form a stress buffer zone, adapting to the uneven strength distribution caused by the cementation of the volcanic ash strata. For example, in some embodiments, the auxiliary hole construction can create a stress relief zone through a ring-array arrangement. Specifically, this can be achieved by drilling holes with a rotary drilling rig and then backfilling with a crushed stone mixture.

[0028] Installing the support platform and having the auxiliary holes support it means installing the support platform on the auxiliary holes formed in the aforementioned steps, using multiple auxiliary holes to support the support platform in order to improve its stability.

[0029] Compared to related technologies that use vibratory pile extraction to directly act on the pile body, vibratory pile extraction is prone to inducing ground resonance. In environments with uneven strength distribution in volcanic ash strata, this poses a risk of structural instability, tilting, or even overturning of the pile extraction device. In this embodiment, an auxiliary hole forms a buffer zone, which can effectively absorb the impact energy generated during subsequent pile extraction, improving the reliability of pile extraction operations in volcanic ash strata.

[0030] Understandably, after the support platform is installed, its levelness needs to be inspected to further improve the verticality between the rotary drilling rig and the ground during subsequent pile extraction operations, thus enhancing reliability. Simultaneously, in this step, the actual depth of the pile foundation should be determined based on the pile foundation parameters obtained in step S1. When designing the depth of the auxiliary hole, it should be set to be no less than the actual depth of the pile foundation. For example, the depth of the auxiliary hole can be set to be 2 to 5 meters deeper than the actual depth of the pile foundation to further improve the stability of the support platform and the rotary drilling rig after installation, thereby adapting to the environment of uneven intensity distribution in volcanic ash strata.

[0031] In some embodiments, an excavation of 0.5m to 1m can be carried out first, centered on the location of the pile foundation, and the soil can be replaced with gravel and concrete to initially strengthen the soil strength at the pile foundation location. Then, auxiliary holes can be excavated to improve the reliability of the auxiliary hole excavation. For example, in some embodiments, an excavation of 0.6m can be carried out first, and after replacing the soil with 0.35m of gravel, a 0.25m thick layer of concrete can be poured over the gravel to level it. After the support platform is installed, a steel plate with a thickness of 2cm to 5cm can be laid on the support platform to further reduce the possibility of the rotary drilling rig sinking or deflecting during operation after installation.

[0032] Step S3: Install a rotary drilling rig on the bearing platform, and use the steel sleeve with internal cutter in the rotary drilling rig to cut and drill, twist and break the original pile foundation, then pull it out and clean up the slag.

[0033] This step involves removing the pile foundation. The continuous blades on the inner wall of the steel sleeve are spirally distributed and rotate under hydraulic drive to cut into the ground. Once the steel sleeve completely encloses the pile, continuous torque is applied to cause the pile to torsionally fracture at a predetermined location. During the slag removal stage, a high-pressure water gun can be used to flush the sleeve gaps, and a vacuum slag removal device can be simultaneously activated to clean the broken pile foundation and create a hole.

[0034] In these embodiments of this application, the cutting drilling step of the rotary drilling rig can be carried out in segments, that is, the steel sleeve can be a segmented structure, and an inner cutter is provided in at least the first segment of the steel sleeve. In other words, in the initial pile extraction work of the rotary drilling rig, the steel sleeve with the inner cutter is connected to the rotary drilling rig and rotated under the drive of the rotary drilling rig to cut off part of the pile foundation. Afterwards, the hole cut out by the rotary drilling rig is cleaned of slag. After the mechanism in the rotary drilling rig used to control the advance of the steel sleeve into the ground is reset, the second segment of the steel sleeve is connected between the first segment of the steel sleeve and the rotary drilling rig. The rotary drilling rig again controls the advance of the steel sleeve to extract the remaining part of the pile foundation, and so on until the pile foundation is completely extracted.

[0035] This design allows for the removal of deeper piles while reducing ground disturbance caused by the steel sleeve during operation, further enhancing the stability and reliability of the rotary drilling rig during pile removal.

[0036] Step S4: Backfill the pile hole and remove the steel sleeve.

[0037] The purpose of this step is to strengthen the cavities in the soil after the piles have been removed, maintain the relative stability of the soil, and collect the steel sleeves for the removal of the next pile. Accordingly, a segmented backfilling method can be used in this step. After the final removal of the cavities, the steel sleeves can be removed one section at a time according to their dimensions, and the cavities can be backfilled one section at a time. This process is repeated until the cavities formed by the pile removal are completely backfilled.

[0038] In some embodiments, after the last steel sleeve is removed, the backfilled soil layer at the pile foundation location can be compacted and reinforced to further improve the stability of the stratum after pile foundation removal. Exemplarily, in some embodiments, grouting can also be used to inject grout into the cavity after pile foundation removal to further enhance the stability of the stratum after pile foundation removal.

[0039] Through the above technical solutions, this application achieves safe and efficient extraction of pile foundations in volcanic ash strata. The auxiliary borehole system significantly reduces stress concentration in the strata, preventing settlement of surrounding structures caused by construction. The specially designed steel sleeve structure ensures uniform stress distribution during the cutting process, preventing equipment jamming due to sudden changes in stratum hardness. The segmented backfilling and grouting process forms a dense filling body, effectively restoring the stratum's bearing capacity. This integrated construction method ensures project progress while controlling stratum disturbance within permissible limits.

[0040] In some embodiments, determining the center of each auxiliary hole based on the pile location center includes: determining the number of auxiliary holes according to the following formula: Among them, N a Number of auxiliary holes; D p δ is the pile diameter; δ is the ground disturbance coefficient, with a value of 1.8 to 2.2 for volcanic ash strata; K v This is a correction factor for the cementing strength of volcanic ash, with a value ranging from 0.15 to 0.25.

[0041] In these embodiments of the present application, the formation disturbance coefficient refers to a quantitative parameter that reflects the structural changes of volcanic ash formations caused by external forces during construction. Specifically, it can be calibrated using geological exploration data combined with field tests. For example, the coefficient can be determined by comparing the formation deformation under different construction parameters, and its value range can balance construction efficiency and formation stability.

[0042] The correction factor for volcanic ash cementation strength refers to the adjustment parameter that characterizes the influence of cementation between volcanic ash particles on the overall formation strength. Specifically, it can be determined by measuring the shear strength of the cemented material through indoor geotechnical mechanics tests and combining it with in-situ test data. Its role is to quantify the reverse adjustment requirement of cementation strength on the density of auxiliary holes.

[0043] In the removal of bridge pile foundations from volcanic ash strata, determining the number of auxiliary holes requires comprehensive consideration of the pile diameter, stratum disturbance characteristics, and cementation strength. By substituting the pile diameter into a formula, combined with pre-calibrated stratum disturbance coefficients and cementation strength correction coefficients, the appropriate number of auxiliary holes for the current geological conditions can be calculated. For example, when the pile diameter is 2 meters, if the stratum disturbance coefficient is taken as 2.0 and the cementation strength correction coefficient as 0.2, the number of auxiliary holes is approximately 17. This formula mathematically correlates geological parameters with construction parameters, ensuring that the arrangement of auxiliary holes effectively disperses the concentrated stress on the stratum during construction while avoiding resource waste caused by excessive drilling.

[0044] Traditional methods typically rely on experience to estimate the number of auxiliary holes, failing to establish a quantitative relationship with formation cementation strength and disturbance sensitivity. This can easily lead to insufficient holes causing casing jamming or excessive holes increasing construction costs. This solution introduces a formation disturbance coefficient and a cementation strength correction coefficient, incorporating the unique non-uniform distribution of cementation strength and susceptibility to disturbance characteristics of volcanic ash formations into the calculation model, thus matching the number of auxiliary holes with the actual mechanical response of the formation.

[0045] Through the above technical solution, this application can accurately adapt to the complex mechanical properties of volcanic ash strata, while ensuring the stability of the strata during the pile foundation extraction process, optimizing the construction scale of auxiliary holes, avoiding the problem of sudden changes in casing sinking resistance or reduced drilling efficiency caused by unreasonable hole number design, thereby improving the controllability and economy of the construction process.

[0046] In some embodiments, the diameter of the auxiliary hole is 1.8m to 2.2m.

[0047] Auxiliary holes refer to auxiliary boreholes arranged around the center of the pile location. They can be drilled using rotary drilling rigs or impact drilling rigs, and their diameter range is determined by balancing ground disturbance control and construction efficiency.

[0048] The 1.8m to 2.2m diameter range refers to the actual diameter of the auxiliary hole, which can be achieved by adjusting the drill bit size or using a staged reaming process. This range is adapted based on the cementation strength and shear resistance of the volcanic ash formation.

[0049] Specifically, in volcanic ash formations, if the diameter of the auxiliary borehole is less than 1.8m, insufficient clearance between the borehole wall and the pile foundation may lead to excessive formation resistance during steel casing cutting; if it exceeds 2.2m, the increased borehole volume may result in a significant increase in backfill material consumption. By controlling the borehole diameter within the range of 1.8m to 2.2m, the drilling resistance of the steel casing can be reduced while avoiding increased construction costs caused by excessively large borehole diameters. For example, when using an auxiliary borehole with a diameter of 2.0m, the clearance requirement can be met directly through a single borehole formation, reducing the need for borehole enlargement. In some embodiments, when drilling using a steel sleeve with an internal cutter in a rotary drilling rig, it is necessary to control the maximum torque T of the rotary drilling rig. max Satisfy the following formula: Where τ is the shear strength of the volcanic ash formation; D c L is the diameter of the steel casing. s f is the length of the sleeve. s For safety factors, the value is between 0.6 and 0.8.

[0050] The shear strength τ of volcanic ash formations refers to the formation's ability to resist shear failure. It can be specifically measured through in-situ tests, such as vane shear tests.

[0051] Steel casing diameter D c This refers to the outer diameter of the sleeve, which can be matched using standardized pipe diameter specifications, such as selecting the corresponding sleeve based on the pile diameter. Sleeve length L s This refers to the effective working section length of the steel sleeve drilled into the strata, which can be determined based on the pile foundation depth.

[0052] Safety factor f s It refers to the engineering safety reserve coefficient, which can be determined based on the fluctuation range of geological conditions. For example, a lower limit value can be selected in areas with poor stability.

[0053] When drilling with steel casings in volcanic ash formations, a maximum torque limit is calculated using a formula to control the actual output torque of the rotary drilling rig within the calculated threshold range. This formula comprehensively considers the shear resistance of the formation, casing size parameters, and safety redundancy. The coefficient 0.7 is an empirical reduction factor used to offset additional resistance generated during dynamic construction. During construction, operators monitor the torque value in real time, and an automatic speed reduction protection mechanism is triggered when the torque approaches the calculated value.

[0054] Traditional pile extraction techniques often set torque thresholds based on equipment rated power, without considering the dynamic matching relationship between formation characteristics and casing parameters. This solution establishes a mechanical calculation model to couple the cementation strength, casing dimensions, and safety factor specific to volcanic ash formations, forming a quantitative control standard.

[0055] In some embodiments, when backfilling the pile hole and removing the steel sleeve, the process is carried out in stages and multiple times, satisfying the following formula: Among them, H f ∆H represents the height of a single backfill operation. b To synchronize the tube removal height.

[0056] The segmented, multi-stage approach involves dividing the pile hole backfilling and steel sleeve removal process into several alternating operations. Specifically, this can be achieved by backfilling material in stages while simultaneously lifting the sleeve. By controlling the amount of material removed in each operation, the risk of ground disturbance is reduced. The single backfilling height H... f This refers to the vertical height to which material is filled into the pile hole each time. It can be calculated by measuring the volume of the backfill material and the cross-sectional area of ​​the pile hole.

[0057] Synchronous tube extraction height ∆H b This refers to the amount of upward displacement of the steel sleeve during each backfilling process, which can be monitored and controlled in real time using a hydraulic system in conjunction with a displacement sensor.

[0058] In volcanic ash formations, due to uneven distribution of cementation strength, if the pile hole backfilling and casing removal are completed in one go, the hole wall may collapse or the backfill material may be insufficiently compacted due to sudden changes in formation stress. By performing multiple operations in sections, and immediately removing the steel casing at the corresponding height after each backfilling, the backfill material is gradually compacted within a limited space. At the same time, the interaction between the material's own weight and the formation forms a temporary support structure.

[0059] According to the above formula, setting the single backfill height to 1.2 to 1.8 times the casing extraction height ensures that the backfill material fully fills the gaps during casing extraction, preventing voids caused by material settling. Traditional methods typically employ a rough approach of continuous backfilling and overall casing extraction, which can easily lead to poor bonding between the backfill material and the borehole wall, potentially causing localized collapse, especially in volcanic ash formations. This solution, through segmented control and a height-related formula, achieves dynamic matching between material filling and casing displacement, significantly improving borehole wall stability.

[0060] In some embodiments, when drilling using a steel sleeve with an internal cutter in a rotary drilling rig, the method further includes: controlling a water jet to clear the debris between the steel sleeve and the pile foundation. The pressure of the water jet is adjusted to 3 MPa to 5 MPa; the spray angle is 30° to 45°.

[0061] Water jet cleaning refers to flushing away drill cuttings deposits in the gap between the steel casing and the pile body using a high-pressure water jet. This can be achieved using a plunger pump with an adjustable pressure valve and a fan-shaped nozzle, for example, by controlling the pump pressure within the range of 3MPa to 5MPa. Adjusting the spray angle involves directing the water flow at a 30° to 45° angle into the area of ​​drill cuttings accumulation; this can be achieved by rotating the nozzle support. In summary, these embodiments of the present application demonstrate that by utilizing water impact to disrupt the adhesion structure of the drill cuttings, the formation of a hardened layer of drill cuttings in confined spaces can be prevented.

[0062] During the rotary drilling process of the steel casing cutting into the volcanic ash formation, as the debris generated by the inner cutter cutting the pile body continuously sinks along the outer wall of the casing, the operator activates the water jet system to clean the annular gap between the casing and the pile body in real time. When the rotary drilling rig completes 0.5 meters of drilling, the water jet performs a spiral spray operation along the circumference of the casing, for example, using three sets of nozzles arranged at 120° intervals working alternately. The high-pressure water flow penetrates the cemented structure of the volcanic ash debris, expelling particles smaller than 5 cm with the mud from the borehole, while larger fragments are broken down into pumpable particles by the impact of the water flow.

[0063] In these embodiments of the present application, a water jet is set to spray water at a pressure of 3MPa to 5MPa along an inclined direction of 30° to 45°. While impacting the slag, the water jet forms a spiral cleaning trajectory along the circumference of the casing, which can effectively decompose cementing substances and allow slag particles to be discharged along a predetermined path by controlling the angle.

[0064] When the pressure is below 3 MPa, the cemented layer cannot be penetrated; when it exceeds 5 MPa, it may erode the formation and cause borehole wall collapse. An injection angle of less than 30° will reduce the lateral shear force, while an angle greater than 45° will cause the water flow to impact the casing wall vertically, resulting in energy waste.

[0065] For example, in some embodiments of this application, the pressure of the water gun can be set to 3.5MPa, 4MPa or 4.5MPa; the spray angle can be, but is not limited to, 35° or 40°.

[0066] In these embodiments of the present application, the technical problem of easy cementation and accumulation of drilling cuttings during pile extraction in volcanic ash formations is solved, ensuring the cleanliness of the working surface between the casing and the pile body, enabling the steel casing to continuously and stably cut downwards; at the same time, it can effectively prevent casing jamming caused by soil compaction, ensure the continuity of pile body torsional fracture operation, and reduce the risk of abnormal equipment wear.

[0067] In some embodiments, when constructing and backfilling auxiliary holes, it is necessary to control the construction depth of the auxiliary holes to be 2m to 3m greater than the original pile length.

[0068] The auxiliary hole depth refers to the extension length of the bottom of the borehole relative to the original pile foundation. This can be achieved using ground-penetrating radar detection combined with borehole record verification. The goal is to ensure the bottom of the auxiliary hole penetrates the original pile foundation to a certain distance, creating an effective stress release zone. The original pile length refers to the total length of the bridge pile foundation from the bottom of the abutment to the pile tip. This can be determined by reviewing construction drawings and using ultrasonic pile integrity testing to establish a baseline value for deepening the auxiliary hole.

[0069] Specifically, in volcanic ash strata, due to uneven distribution of cementation strength, there may be residual sections or cemented material in the original pile foundation that have not been completely broken down. By controlling the depth of the auxiliary hole to exceed the original pile length by a certain range, such as 2m to 3m, a circumferential stress relief 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, followed by backfilling with a cement-volcanic ash mixture. This makes the auxiliary hole a temporary support structure, preventing pile hole collapse and weakening the soil's enveloping effect on the pile foundation.

[0070] Compared to related technologies, traditional pile extraction processes often involve auxiliary holes only reaching the same depth as the original pile length, resulting in the inability to completely remove the remaining pile section at the bottom. This can easily lead to ground collapse or pile fracture during extraction. This solution, by deepening the auxiliary holes, ensures that the bottom of the pile is completely enclosed within the reinforced area created by the auxiliary holes. This not only prevents the remaining pile from obstructing the drilling of the steel casing but also enhances the stability of the surrounding soil through backfill grout.

[0071] In some embodiments, the inclination angle of the inner cutter of the rotary drilling rig is 45° to 60°, and the height is 1.5 times the wall thickness of the steel sleeve.

[0072] The inclination angle of the inner cutter refers to the angle formed between the cutting edge and the axis of the steel sleeve. This can be achieved through welding or an adjustable cutter holder structure. This angle range balances cutting resistance and slag removal efficiency. The inner cutter height refers to the vertical dimension of the cutting edge protruding from the inner wall of the steel sleeve. This can be achieved by calculating the sleeve wall thickness and machining the cutter base proportionally. This dimensional relationship ensures sufficient structural strength for the cutting edge while avoiding excessive weakening of the sleeve's rigidity.

[0073] Specifically, when cutting the sleeve in volcanic ash formations, the inner cutter cuts into the pile foundation concrete at an angle of 45° to 60°. This angle range allows the cutting surface to form a continuous fracture zone. For example, using a 55° angle can reduce cutting torque fluctuations and guide debris towards the center of the sleeve through the inclined cutter face. When the inner cutter height is set to 1.5 times the sleeve wall thickness, for example, when the sleeve wall thickness is 40 mm, a 60 mm cutting edge is configured. This ensures that the cutting edge has sufficient flexural section modulus to resist the impact of hard interlayers in the formation, while also avoiding stress concentration at the sleeve welding points due to excessive height.

[0074] In some specific implementations, high-strength alloy steel plates can be machined into trapezoidal cross-section cutting edges using laser cutting, and then connected to the inner wall of the sleeve using bevel welding. After welding, ultrasonic flaw detection is performed. The sleeve wall thickness can be verified on-site using an electromagnetic thickness gauge, and the machining dimensions of the cutting edge base can be adjusted based on the measured values.

[0075] Compared to related technologies, traditional pile extraction equipment often employs vertical or small-angle cutting designs for its internal blades, which can easily lead to drill jamming due to discontinuous cutting surfaces in volcanic ash formations. This solution, however, optimizes the inclination angle range to create a progressively fractured surface during cutting. Furthermore, by controlling the ratio of blade height to sleeve wall thickness, it maintains the overall structural stability of the sleeve while ensuring cutting efficiency.

[0076] In some embodiments, when drilling using a steel sleeve with an inner cutter in a rotary drilling rig, the verticality deviation of the rotary drilling rig is ≤0.5% by means of two-person orthogonal observation.

[0077] Two-person orthogonal observation refers to the real-time monitoring of the drilling rig's verticality by two operators in two mutually perpendicular planes. This can be achieved using a total station or laser rangefinder in conjunction with an angle sensor. This observation method eliminates measurement errors from a single perspective, ensuring the consistency between the drilling rig's axis and the design axis.

[0078] The verticality deviation of ≤0.5% refers to the maximum permissible offset in the vertical direction, converted from the tilt angle between the drilling rig axis and the design axis. This can be achieved by dynamically adjusting the hydraulic system of the drilling rig support platform. This control standard can prevent increased friction between the steel casing and the pile foundation due to drilling rig deviation, thereby reducing the risk of pile breakage.

[0079] During the steel sleeve cutting drilling process, two operators set up measuring equipment along the transverse and longitudinal directions of the pile foundation to collect the verticality data of the drilling rig in real time. When the deviation in a certain direction approaches the threshold, drilling is immediately paused and a correction program is initiated to restore the verticality by adjusting the height difference between the support points of the drilling rig base. For example, if the longitudinal deviation reaches 0.4%, the drilling rig is tilted backward by reducing the pressure of the front support cylinder until the deviation value falls back to the allowable range.

[0080] Compared to related technologies, single-point observation methods are limited by blind spots and struggle to accurately determine drilling rig attitude in complex formations. Dual-person orthogonal observation, through multi-dimensional data cross-validation, significantly improves the reliability of verticality control. The 1% verticality deviation standard commonly used in related technologies can easily cause casing jamming in volcanic ash formations. This solution, through stricter deviation limits, effectively reduces abnormal torque fluctuations caused by skewness.

[0081] This application solves the problem of increased friction between steel casing and pile foundation and reduced pile breakage efficiency caused by drilling rig deviation in volcanic ash formations. By using real-time dual-dimensional deviation correction, it ensures that the casing is drilled accurately along the designed path, thereby improving the success rate of pile foundation extraction and reducing the amount of slag removal work.

[0082] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for removing bridge pile foundations in volcanic ash strata, characterized in that, include: Construction preparation includes determining the construction site, verifying the original pile length, and measuring the location of exposed piles after the foundation cap is demolished. Determine the center of the pile location, determine the center of each auxiliary hole based on the pile location center, construct and backfill the auxiliary holes, install the bearing platform and make each of the auxiliary holes support the bearing platform; A rotary drilling rig is installed on the bearing platform. The steel sleeve with an inner cutter in the rotary drilling rig is used to cut and drill, and the original pile foundation is twisted and broken, then pulled out and the slag is removed. The pile hole was backfilled and the steel sleeve was removed.

2. The method for removing bridge pile foundations in volcanic ash strata according to claim 1, characterized in that, The determination of the center of each auxiliary hole based on the pile location center includes: The number of auxiliary holes is determined using the following formula: Among them, N a Number of auxiliary holes; D p δ is the pile diameter; δ is the ground disturbance coefficient, with a value of 1.8 to 2.2 for volcanic ash strata; K v This is a correction factor for the cementing strength of volcanic ash, with a value ranging from 0.15 to 0.

25.

3. The method for removing bridge pile foundations in volcanic ash strata according to claim 2, characterized in that, The diameter of the auxiliary hole is 1.8m to 2.2m.

4. The method for removing bridge pile foundations in volcanic ash strata according to claim 1, characterized in that, When drilling using a steel sleeve with an internal cutter in a rotary drilling rig, it is necessary to control the maximum torque T of the rotary drilling rig. max Satisfy the following formula: Where τ is the shear strength of the volcanic ash formation; D c L is the diameter of the steel casing. s f is the length of the sleeve. s For safety factors, the value is between 0.6 and 0.

8.

5. The method for removing bridge pile foundations in volcanic ash strata according to claim 1, characterized in that, When backfilling the pile hole and removing the steel sleeve, the process is carried out in stages and multiple times, and the following formula must be satisfied: Among them, H f ∆H represents the height of a single backfill operation. b To synchronize the tube removal height.

6. The method for removing bridge pile foundations in volcanic ash strata according to claim 1, characterized in that, The method of drilling using a steel sleeve with an internal cutter in a rotary drilling rig also includes: Use a water jet to clean the slag and soil between the steel casing and the pile foundation.

7. The method for removing bridge pile foundations in volcanic ash strata according to claim 6, characterized in that, The pressure of the water gun is adjusted to 3MPa to 5MPa; the spray angle is 30° to 45°.

8. The method for removing bridge pile foundations in volcanic ash strata according to claim 1, characterized in that, When constructing and backfilling the auxiliary holes, it is necessary to control the construction depth of the auxiliary holes to be 2m to 3m greater than the original pile length.

9. The method for removing bridge pile foundations in volcanic ash strata according to claim 1, characterized in that, The inclination angle of the inner cutter of the rotary drilling rig is 45° to 60°, and its height is 1.5 times the wall thickness of the steel sleeve.

10. The method for removing bridge pile foundations in volcanic ash strata according to any one of claims 1 to 9, characterized in that, When drilling using a steel sleeve with an internal cutter in a rotary drilling rig, the verticality deviation of the rotary drilling rig is kept ≤0.5% by using orthogonal observation by two people.

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