Construction method for cast-in-situ bored pile close to subway tunnel

Abstract

The invention relates to the technical field of intelligent construction, in particular to a construction method for a cast-in-situ bored pile close to a subway tunnel, which comprises the following steps: setting a pile position, burying a steel casing, fixing the bottom of the casing by adopting concrete, and following to a rock stratum; drilling is conducted, whether the perpendicularity of the drill bit is qualified or not is determined based on the vibration frequency of the drill bit in the drilling process, and if the perpendicularity is not qualified, the reason for the unqualified perpendicularity is determined based on the frequency change condition in the drilling process; adjusting a drilling parameter or a grouting parameter based on the determined cause; hole sweeping is conducted, and the adjusted parameters are corrected according to the hole parameters in the hole sweeping process; the steps of drilling and hole sweeping are repeated until the pile hole is drilled, and after the pile hole is drilled, a reinforcement cage is put down and concrete is poured; according to the method, the construction efficiency is improved by improving the accuracy of analyzing the reason for the unqualified perpendicularity of the drill bit.

Description

Technical Field

[0001] This invention relates to the field of intelligent construction technology, and in particular to a method for constructing bored piles near subway tunnels. Background Technology

[0002] Drilled piles are a widely used foundation type in bridges, high-rise buildings, and other engineering projects. However, when carrying out pile foundation construction in densely populated urban areas, it is often necessary to work adjacent to operating subway tunnels. Subway tunnel structures are extremely sensitive to the deformation of the surrounding soil, and the allowable value for differential settlement is usually measured in millimeters. Therefore, pile foundation construction near subway tunnels must strictly control its disturbance to the surrounding soil to ensure the absolute safety of subway operation.

[0003] In existing technologies, the construction of bored piles typically includes steps such as installing casing, drilling, cleaning the hole, lowering the reinforcing cage, and pouring concrete. Among these, the verticality of the borehole is a critical factor affecting the quality of the pile and the safety of the surrounding environment. If the pile hole tilts, it will not only reduce the bearing capacity of the pile foundation but also cause excessive compression or disturbance to the surrounding soil during drilling. This adverse effect can be transmitted to nearby subway tunnels, causing tunnel displacement and deformation, seriously threatening the structural and operational safety of the subway.

[0004] Chinese Patent Publication No. CN102747725A discloses a method for micro-disturbance construction of bored piles. The technical problem this invention aims to solve is to eliminate the impact of existing bored pile construction methods on nearby existing subway tunnels. The specific steps are as follows: First, the ground at the construction site is hardened; then, preparations are made for the spun steel casing and the borehole center is positioned; subsequently, the steel casing is spun into the soil and fixed to the ground; then, soil is removed and the borehole is formed using a mud-wall positive circulation method; finally, the borehole is cleaned, a reinforcing cage is lowered into the hole, and concrete is poured. The advantages of this invention are that the construction of bored piles only causes micro-disturbance to nearby existing subway tunnels, ensuring that the displacement and convergence deformation of the subway tunnel are controlled within 10mm, meeting the requirements of subway protection regulations, and offering high construction efficiency and low construction costs.

[0005] However, existing technologies still have the following problems: Relying on physical isolation and fixed processes, it lacks the ability to monitor and dynamically control the drilling process in real time, cannot intelligently adjust construction parameters according to geological changes, and is difficult to maintain the verticality of the borehole in complex strata, thus limiting its protection of subway tunnels. Summary of the Invention

[0006] Therefore, the present invention provides a method for constructing bored piles near subway tunnels, which overcomes the problems of existing technologies that rely on physical isolation and fixed processes, lack the ability to monitor and dynamically control the drilling process in real time, cannot intelligently adjust construction parameters according to geological changes, and have difficulty in maintaining the verticality of the borehole in complex strata, thus limiting the protection of subway tunnels.

[0007] To achieve the above objectives, the present invention provides a method for constructing bored piles near subway tunnels. It includes: Step S1: Set the pile location, install steel casing, with the bottom of the casing fixed with concrete, and continue to the rock strata; Step S2: Drill a hole, and determine whether the drill bit's perpendicularity is qualified based on the drill bit's vibration frequency during the drilling process; Step S3: If the verticality is not up to standard, determine the reason for the failure to meet the standard based on the frequency changes during the drilling process. Step S4: Adjust the drilling parameters or grouting parameters based on the determined cause; Step S5: Scan the hole and correct the adjusted parameters based on the hole parameters obtained during the scanning process; Step S6: Repeat the drilling and cleaning steps until the pile hole drilling is completed. After the pile hole drilling is completed, lower the reinforcing cage and pour concrete.

[0008] Further, in step S2, determining whether the drill bit's perpendicularity is acceptable based on the drill bit's vibration frequency includes: Step S21: Obtain amplitude data from vibration sensors at different locations in the borehole; Step S22: Calculate the gradient characterization value based on the amplitude data; Step S23: Determine whether the verticality of this borehole meets the standard based on the gradient characterization value; Among them, a gradient characterization value less than the threshold is considered qualified, and a gradient characterization value greater than or equal to the threshold is considered unqualified.

[0009] Furthermore, in step S3, the reasons for the verticality failure are determined based on the frequency changes during this drilling process, including: Step S31: Obtain the time-frequency curve of frequency change over time during the drilling process; Step S32: Calculate the slope of the time-frequency curve; Step S33, determining the cause based on the slope, includes: When the slope is greater than a preset slope threshold, the cause is determined to be geological change. When the slope is less than or equal to the preset slope threshold, the cause is determined to be non-geological change.

[0010] Furthermore, in step S4, when the cause is determined to be geological change, the drilling parameters are adjusted, including: Step S41: Calculate the ratio of the current formation hardness to the previous formation hardness. Step S42, adjusting the drill bit rotation speed based on the hardness change ratio, includes: When the hardness change ratio is greater than 1, increase the drill bit speed; When the hardness change ratio is less than 1, reduce the drill bit speed; Among them, the absolute value of the difference between the adjustment amount of drill bit speed and the hardness change ratio and 1 is positively correlated.

[0011] Furthermore, in step S42, the process of reducing the rotational speed includes: The mud specific gravity is corrected based on the adjustment range of the rotation speed; The correction amount for the mud specific gravity is positively correlated with the adjustment range of the rotation speed.

[0012] Furthermore, in step S5, the process of reducing the rotational speed also includes: The standard depth of the cleaning hole is adjusted based on the difference between the hardness change ratio and 1. The adjustment amount of the standard depth of the scanning hole is positively correlated with the absolute value of the ratio difference.

[0013] Furthermore, in step S6, if the cause is determined to be non-geological change, or if the drill bit verticality is still unqualified after the drilling parameters have been adjusted, the grouting parameters are adjusted, including: Step S43: Calculate the gradient representation difference between the actual gradient representation value and the preset gradient representation value; Step S44: Based on the gradient characterization difference, increase the grouting volume; The increase in grouting volume is positively correlated with the gradient characterization difference.

[0014] Furthermore, in step S6, after adjusting all parameters, the verticality is re-detected; If the verticality is still not up to standard, repeat the steps of determining the cause and adjusting the parameters; If the verticality is still not up to standard after repeated adjustments reach the critical value, a notification of unqualified positioning pile setting will be issued, and recalibration will be carried out.

[0015] Compared with existing technologies, the advantages of this invention are as follows: By installing vibration sensors on key parts of the drill bit or drill rod, this invention can continuously collect vibration data during drilling, achieving real-time and uninterrupted monitoring of verticality. By converting vibration signals into specific gradient representation values ​​and setting clear thresholds, verticality judgment becomes a quantifiable and objective process, effectively avoiding the problems of inaccurate judgment, missed judgment, or misjudgment caused by differences in the experience of construction personnel in traditional methods, thus improving the consistency and reliability of construction quality. Using the trend of amplitude change with depth rather than a single absolute value of amplitude as the judgment basis can more essentially reflect the stability of the drill bit posture, eliminating the interference of accidental factors such as instantaneous impacts, making the judgment results more accurate and stable. By detecting tilting trends early, measures can be taken immediately to prevent the cumulative expansion of deviation, thereby greatly reducing the risk of unqualified hole formation.

[0016] Furthermore, this invention distinguishes the root causes of tilting by analyzing the slope of the time-frequency curve, transforming vague empirical judgments into precise data analysis. It can intelligently and automatically determine whether the tilting is caused by a sudden change in external geological conditions (geological change) or by improper internal equipment status or process parameters (non-geological change). This provides a precise decision-making basis for subsequent corrective measures. If the cause is determined to be geological change, the drilling parameter (e.g., rotation speed) adjustment process is automatically initiated to adapt to the strata; if the cause is not geological change, the grouting parameter adjustment process is automatically initiated to improve lubrication and support, increasing the efficiency and success rate of correction while saving time and costs. By taking the correct countermeasures at the root, the borehole can be guided back to a vertical state as quickly as possible, minimizing the duration of the abnormal state and thus minimizing disturbance to the surrounding subway tunnel soil, providing dual protection for safe construction.

[0017] Furthermore, this invention employs two independent and highly specific parameter adjustment strategies to address two distinct causes: geological changes and non-geological changes. For geological changes, the core strategy is to adjust drilling parameters (rotation speed) to adapt to the formation. For non-geological changes, the core strategy is to adjust grouting parameters to improve the system state. This avoids the inefficient practice of blindly trying all parameters in traditional methods, greatly improving the success rate of the first correction and significantly saving time and costs. By introducing the hardness change ratio as a key indicator, the adjustment of drill bit rotation speed is no longer fixed but dynamically correlated with the severity of changes in formation hardness. By increasing the hydrostatic column pressure to compensate for the weakened borehole support force that may be caused by a decrease in rotation speed, and through more frequent borehole wall repair operations, it proactively intervenes in and prevents the rheological deformation of soft soil, eliminating potential hazards in their infancy.

[0018] Furthermore, this invention constructs a complete automated closed-loop control system through a cycle of detection, diagnosis, adjustment, and verification. This ensures that the corrective measures are not executed only once, but are verified through re-detection, forming continuous tracking and feedback of the control effect. This greatly improves the reliability and robustness of the pile-forming process and is applicable to working conditions with extremely complex geological conditions or multiple adverse factors. Through multiple rounds of corrective attempts with possible strategy adjustments, it can solve most reversible deviation problems, thereby saving a large number of pile holes that might have been scrapped under traditional methods. When the number of attempts reaches a critical value and still fails, the system will decisively determine failure and initiate a termination procedure, avoiding continuous disturbance and damage to the surrounding soil caused by repeated operations in severely deviated holes for a long time. This effectively controls construction risks and prevents the occurrence of secondary disasters. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the construction process of the bored pile method for use near subway tunnels according to the present invention. Figure 2 This is a flowchart illustrating the process of determining the verticality of a drill bit based on its vibration frequency in the construction method of bored piles near a subway tunnel, according to the present invention. Figure 3 This is a flowchart illustrating the process of determining the cause of verticality non-compliance based on frequency changes during the drilling process in the bored pile construction method for nearby subway tunnels according to the present invention. Detailed Implementation

[0020] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0021] It should be noted that the data in this embodiment are all derived from a comprehensive analysis and evaluation of historical data from the six months prior to this determination and the corresponding historical determination results by the system described in this invention. Those skilled in the art will understand that the system described in this invention can determine the above-mentioned parameters for a single item by selecting the value with the highest proportion based on the data distribution as the preset standard parameter, using weighted summation to obtain the value as the preset standard parameter, substituting each historical data point into a specific formula and using the value obtained by that formula as the preset standard parameter, or other selection methods, as long as the system described in this invention can clearly define different specific situations in the single-item determination process through the obtained values.

[0022] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0023] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0024] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] Please see Figures 1-3 As shown, Figure 1 This is a flowchart illustrating the construction process of the bored pile method for use near subway tunnels according to the present invention. Figure 2 This is a flowchart illustrating the process of determining the verticality of a drill bit based on its vibration frequency in the construction method of bored piles near a subway tunnel, according to the present invention. Figure 3 This is a flowchart illustrating the process of determining the cause of verticality non-compliance based on frequency changes during the drilling process in the bored pile construction method for nearby subway tunnels according to the present invention.

[0026] The drilling and grouting pile construction method for adjacent subway tunnels provided in this embodiment includes: Step S1: Set the pile location, install steel casing, with the bottom of the casing fixed with concrete, and continue to the rock strata; Step S2: Drill a hole, and determine whether the drill bit's perpendicularity is qualified based on the drill bit's vibration frequency during the drilling process; Step S3: If the verticality is not up to standard, determine the reason for the failure to meet the standard based on the frequency changes during the drilling process. Step S4: Adjust the drilling parameters or grouting parameters based on the determined cause; Step S5: Scan the hole and correct the adjusted parameters based on the hole parameters obtained during the scanning process; Step S6: Repeat the drilling and cleaning steps until the pile hole drilling is completed. After the pile hole drilling is completed, lower the reinforcing cage and pour concrete.

[0027] In step S1 of this embodiment, precise measurement and layout can be carried out according to the construction design drawings to determine the center of the pile position, and cross positioning piles can be set as guide piles so as to check and restore the center of the pile position at any time during the construction process. Subsequently, the steel casing is buried. In this embodiment, a steel casing made of Q235 steel plate with a wall thickness of not less than 12mm is selected. Its inner diameter is 200mm larger than the designed pile diameter to ensure that there is enough gap for correction and isolation. When burying, the center of the pile position is used as a reference, and a vibratory hammer is used to press the steel casing vertically into the soil. The burial depth of the casing needs to penetrate the surface fill soil and other soft and unstable soil layers, and penetrate into the stable stratum by not less than 1.5 meters. After the casing sinks to the predetermined depth, early-strength concrete is immediately poured into the annular space between the bottom of the casing and the borehole wall to form a concrete consolidation ring with a height of not less than 1.0 meter. After the initial fixation is completed, the casing follow-up operation continues. After the borehole exposes the rock layer, the steel casing is driven downward to embed its bottom into the strongly weathered rock layer by not less than 0.5 meters.

[0028] Specifically, in step S2, determining whether the drill bit's perpendicularity is acceptable based on the drill bit's vibration frequency includes: Step S21: Obtain amplitude data from vibration sensors at different locations in the borehole; Step S22: Calculate the gradient characterization value based on the amplitude data; Step S23: Determine whether the verticality of this borehole meets the standard based on the gradient characterization value; Among them, a gradient characterization value less than the threshold is considered qualified, and a gradient characterization value greater than or equal to the threshold is considered unqualified.

[0029] In this embodiment of the invention, at least three vibration sensors (e.g., piezoelectric accelerometers) evenly distributed along the circumference are installed at the drill bit or a key part of the drill rod near the drill bit. These sensors are responsible for real-time acquisition of vibration acceleration data of the drill bit in the length, width, and height axes, and wirelessly transmitting the data to the ground control unit via a measurement-while-drilling (MWD) system. The control unit receives the raw vibration signals from the sensors at different locations in the borehole. First, the signals are preprocessed, including filtering (removing high-frequency noise) and amplification. Then, the processed time-domain signal is subjected to a Fast Fourier Transform (FFT) to convert it to the frequency domain. The normal operating vibration of the drill bit has a dominant frequency range; the system extracts the vibration amplitude at this dominant frequency as the effective frequency range. Amplitude data is collected as the drilling depth (synchronously acquired via a drill pipe advance sensor) increases. The system records a set of amplitude data at preset depth intervals (e.g., every 0.5 meters of drilling), forming an amplitude dataset along the drilling depth. Based on this amplitude data, a gradient characterization value is calculated. The core of this gradient characterization value is to quantify the trend of amplitude change with drilling depth. In this embodiment, a linear regression slope is used as the gradient characterization value. Multiple data points (depth-amplitude pairs) acquired within the current detection cycle are organized, with depth as the independent variable (X1) and the amplitude of the corresponding point as the dependent variable (Y1). A univariate linear regression analysis is performed to fit a straight line Y1=kX1+b that best represents the trend of change. The slope k of this fitted line is... This is the gradient characterization value used in this embodiment. It can be understood that k≈0 indicates that the amplitude does not change with depth and the drilling is smooth; k>0 indicates that the amplitude increases with depth, which is a typical characteristic of uneven force on the drill bit and tilting; the case of k<0 may occur in theory, but it is rare in practice and is usually regarded as abnormal.

[0030] The threshold mentioned in this embodiment of the invention can be determined by the following method: Based on the mechanical model of the drill rod-drill bit system, the upper limit of the allowable amplitude increase with depth under ideal vertical conditions is obtained through simulation calculation; on the test bench, the drilling process under different strata and different inclination angles is simulated, and the corresponding gradient characterization values ​​are recorded; in the initial stage of this construction (e.g., the first 2-3 piles), a conservative threshold is used for control; after these pile holes are completed, a high-precision ultrasonic borehole wall measuring instrument or gyro inclinometer is immediately used to accurately measure the verticality of the hole to obtain the real verticality deviation data; the measured verticality deviation is back-correlated and statistically analyzed with the gradient characterization values ​​calculated during the drilling process; finally, the maximum gradient characterization value corresponding to meeting the design specifications (e.g., verticality deviation ≤ 1 / 100) is established as the final threshold applicable to the site of this project, but the above value is not limited to this, and those skilled in the art can adjust it according to the actual situation.

[0031] This invention utilizes vibration sensors installed at key locations on the drill bit or drill rod to continuously collect vibration data during drilling, enabling real-time, uninterrupted monitoring of verticality. By converting vibration signals into specific gradient values ​​and setting clear thresholds, verticality assessment becomes a quantifiable and objective process. This effectively avoids the problems of inaccurate, missed, or misjudged assessments caused by differences in the experience of construction personnel in traditional methods, thus improving the consistency and reliability of construction quality. Using the trend of amplitude variation with depth, rather than a single absolute amplitude value, as the basis for judgment more fundamentally reflects the stability of the drill bit's posture, eliminating interference from accidental factors such as instantaneous impacts, resulting in more accurate and stable assessment results. Early detection of tilting trends allows for immediate measures to prevent the cumulative expansion of deviation, thereby significantly reducing the risk of substandard borehole formation.

[0032] Specifically, in step S3, the reasons for the verticality failure are determined based on the frequency changes during the drilling process, including: Step S31: Obtain the time-frequency curve of frequency change over time during the drilling process; Step S32: Calculate the slope of the time-frequency curve; Step S33, determining the cause based on the slope, includes: When the slope is greater than a preset slope threshold, the cause is determined to be geological change. When the slope is less than or equal to the preset slope threshold, the cause is determined to be non-geological change.

[0033] In this embodiment of the invention, vibration data within the same time period (i.e., from the start of the current verticality judgment cycle until the judgment is unqualified) is extracted from the vibration signal preprocessing stage in step S21. A fast Fourier transform is performed on the continuous time series signal (e.g., one data frame every 0.1 seconds) to accurately identify and record the frequency with the most concentrated vibration energy in each time frame, i.e., the dominant frequency. All data points are connected with time as the horizontal axis and the dominant frequency as the vertical axis to form the time-frequency curve of the drilling process. Similarly, a univariate linear regression method is used to fit the time-frequency curve, with time as the independent variable (X2) and the dominant frequency as the dependent variable (Y2), to fit the straight line Y2 = k_f * X2 + b_f. The slope k_f of this fitted straight line is the slope of the time-frequency curve to be calculated in this step. It can be understood that a large k_f value (positive or negative) indicates that the frequency has changed drastically in a short period, while a k_f value close to 0 indicates that the frequency remains relatively stable.

[0034] The preset slope threshold mentioned in this embodiment of the invention can be determined by the following method: collecting a large amount of historical construction data under local or similar geological conditions, and selecting data segments of two typical situations: Known geological change segment: clearly recording time-frequency curve data when crossing a sudden change in hardness (e.g., from clay to strongly weathered rock) or encountering obstacles (e.g., boulders) in the borehole log; Known operation or process cause segment: recording time-frequency curve data when deviation is confirmed to be caused by non-geological reasons such as improper drilling pressure, initial bending of the drill rod, or failure of mud lubrication. Calculate the slope k_f of the time-frequency curve for each of the above two types of data segments and perform statistical analysis (e.g., calculating the mean, variance, and probability distribution). Train a large number of samples using a machine learning classification algorithm (e.g., Support Vector Machine, SVM) to find the optimal classification boundary, and use it as the preset slope threshold. However, the above values ​​are not limited to these, and those skilled in the art can adjust them according to the actual situation.

[0035] This invention distinguishes the root causes of tilting by analyzing the slope of the time-frequency curve, transforming vague empirical judgments into precise data analysis. It can intelligently and automatically determine whether the tilting is caused by a sudden change in external geological conditions (geological change) or by improper internal equipment status or process parameters (non-geological change). This provides a precise decision-making basis for subsequent corrective measures. If the cause is determined to be geological change, the system automatically initiates a drilling parameter (e.g., rotation speed) adjustment process to adapt to the strata; if the cause is not geological change, the system automatically initiates a grouting parameter adjustment process to improve lubrication and support, thus increasing the efficiency and success rate of correction and saving time and costs. By taking the correct countermeasures at the root, the borehole can be guided back to a vertical state as quickly as possible, minimizing the duration of the abnormal state and thus minimizing disturbance to the surrounding subway tunnel soil, providing double protection for safe construction.

[0036] Specifically, in step S4, when the cause is determined to be geological change, the drilling parameters are adjusted, including: Step S41: Calculate the ratio of the current formation hardness to the previous formation hardness. Step S42, adjusting the drill bit rotation speed based on the hardness change ratio, includes: When the hardness change ratio is greater than 1, increase the drill bit speed; When the hardness change ratio is less than 1, reduce the drill bit speed; Among them, the absolute value of the difference between the adjustment amount of drill bit speed and the hardness change ratio and 1 is positively correlated.

[0037] In this embodiment of the invention, the increase in drill bit speed is the product of the absolute value of the difference between the hardness change ratio and 1, the current drill bit speed, and a first proportional coefficient. The first proportional coefficient is a hardness-speed coefficient (e.g., 0.1-0.3) determined experimentally. The decrease in drill bit speed is the product of the absolute value of the difference between the hardness change ratio and 1, the current drill bit speed, and a second proportional coefficient. The second proportional coefficient can be obtained in a laboratory setting using a rotary shear apparatus and a soil tank to simulate the drilling process of the drill bit in different soft soil layers (such as loose sand layers and fluid silt). By changing the magnitude of the speed reduction, the critical point of borehole wall stability (i.e., the moment when necking or borehole collapse begins) is observed and measured to determine the maximum allowable speed reduction rate that can safely maintain borehole wall stability. The second proportional coefficient can then be derived from this. However, the above values ​​are not limited to these values, and those skilled in the art can adjust them according to actual conditions.

[0038] Specifically, in step S42, the process of reducing the rotational speed includes: The mud specific gravity is corrected based on the adjustment range of the rotation speed; The correction amount for the mud specific gravity is positively correlated with the adjustment range of the rotation speed.

[0039] In this embodiment of the invention, the correction amount for the mud specific gravity is the product of the mud correction coefficient and the absolute value of the rotation speed adjustment amount and the current rotation speed. The mud correction coefficient can be determined by experiment, but the above value is not limited to this. Those skilled in the art can adjust it according to the actual situation.

[0040] Specifically, in step S5, the process of reducing the rotational speed also includes: The standard depth of the cleaning hole is adjusted based on the difference between the hardness change ratio and 1. The adjustment amount of the standard depth of the scanning hole is positively correlated with the absolute value of the ratio difference.

[0041] In this embodiment of the invention, the adjustment amount of the standard depth of the borehole is the product of the borehole depth correction coefficient, the current standard depth of the borehole, and the absolute value of the ratio difference. The borehole depth correction coefficient is relatively large (e.g., 1.5-2.5) for strata with significant rheological properties, such as highly sensitive soft clay and loose fine sand. During test piles, different borehole depth correction coefficients are used for testing at different absolute values ​​of the ratio difference, and the borehole wall is periodically scanned using an ultrasonic borehole wall measuring instrument to observe the flatness of the borehole wall and whether there is any diameter reduction. Finally, a borehole depth correction coefficient that can always maintain the integrity of the borehole wall is determined. However, the above value is not limited to this, and those skilled in the art can adjust it according to the actual situation.

[0042] Specifically, in step S6, if the cause is determined to be non-geological change, or if the drill bit verticality is still unqualified after the borehole parameters have been adjusted, the grouting parameters are adjusted, including: Step S43: Calculate the gradient representation difference between the actual gradient representation value and the preset gradient representation value; Step S44: Based on the gradient characterization difference, increase the grouting volume; The increase in grouting volume is positively correlated with the gradient characterization difference.

[0043] In this embodiment of the invention, the actual gradient characterization value (k_actual) is the amplitude-depth gradient value calculated from the currently unqualified borehole section (i.e., in the latest verticality test) (i.e., k in claim 2); the preset gradient characterization value (k_preset) represents the desired gradient target under ideal vertical drilling conditions, and is usually set to a positive value very close to 0 (e.g., on the order of 0.001~0.005), indicating that the amplitude hardly increases with depth; the gradient characterization difference Δk = |k_actual - k_preset|, this difference Δk The severity of the current borehole verticality deviation was quantified. It can be understood that a larger Δk indicates a more pronounced tilting trend, a more serious problem, and a greater need for stronger corrective measures. The increase in grouting volume is the product of the gradient characterization difference, the third proportional coefficient, and the current grouting volume. The third proportional coefficient can be determined by the following method: a theoretical initial value is determined based on the engineering geological survey report and construction design parameters. For soft strata with small internal friction angles and low cohesion, the initial value of this coefficient is larger; for strata with relatively good soil conditions, the initial value of this coefficient is smaller. Then, dynamic calibration is performed on-site during the test pile construction stage. During the test pile process, different values ​​of the third proportional coefficient are manually set, and the improvement effect of increasing the borehole verticality, changes in borehole wall stability, and mud usage and economic indicators are observed and recorded under different values. Finally, the optimal value is determined through comprehensive analysis to obtain the best corrective effect while ensuring borehole wall stability and economy, which will be the final value adopted for subsequent formal construction.

[0044] This invention addresses two distinct causes—geological and non-geological changes—by employing two independent and highly specific parameter adjustment strategies. For geological changes, the core strategy is to adjust drilling parameters (rotation speed) to adapt to the formation. For non-geological changes, the core strategy is to adjust grouting parameters to improve the system state. This avoids the inefficient practice of blindly trying all parameters in traditional methods, significantly improving the success rate of initial correction and saving considerable time and cost. By introducing the key indicator of hardness change ratio, the adjustment of drill bit rotation speed is no longer fixed but dynamically correlated with the severity of changes in formation hardness. By increasing the hydrostatic column pressure to compensate for the weakened borehole support force that may be caused by a decrease in rotation speed, and through more frequent borehole wall repair operations, it proactively intervenes in and prevents the rheological deformation of soft soil, eliminating potential hazards at the outset.

[0045] Specifically, in step S6, after adjusting all parameters, the verticality is re-detected; If the verticality is still not up to standard, repeat the steps of determining the cause and adjusting the parameters; If the verticality is still not up to standard after repeated adjustments reach the critical value, a notification of unqualified positioning pile setting will be issued, and recalibration will be carried out.

[0046] In this embodiment of the invention, after completing one round of parameter adjustment and borehole sweeping, the system automatically returns to step S2. During subsequent drilling (e.g., after drilling another 1.0 meter), the verticality detection process is restarted. The control unit acquires amplitude data again, calculates a new gradient characterization value, and compares it with a preset qualified threshold. If the verticality is qualified: the system determines that the current correction measures are effective, clears the previous fault record, and continues the normal drilling process. If the verticality is still unqualified: the system determines that the correction has not achieved the expected effect and automatically repeats steps S3 to S5, namely: re-diagnosing the cause: based on the new frequency change data, re-analyzing whether the tilt is caused by geological changes or non-geological changes; re-adjusting parameters: based on the new diagnostic results, performing a new round of parameter adjustment. This may be a further optimization based on the previous adjustment, or it may be a switch in adjustment strategy (e.g., from adjusting drilling parameters to adjusting grouting parameters); re-sweeping and correcting the borehole: based on the new borehole parameters, verifying and fine-tuning the adjusted parameters; a critical value for the number of repeated adjustments is set (e.g., 3 times). This threshold value is set based on engineering experience. Each time the repeated execution process is triggered within the same depth range, the system counter is incremented once. Once the number of repeated adjustments reaches or exceeds this threshold value, and the verticality is still unqualified, it will be determined that this pile position cannot meet the verticality requirements under the current technical means. The following actions will be performed immediately: Issue a notification: Send an alarm notification of unqualified positioning pile setting to the operator interface and construction management center, clearly indicating the pile position number, current depth, and the final detected gradient characterization value; Automatically stop the operation of drilling rigs, mud pumps, and other major equipment, and guide the operator to carry out subsequent processing according to the preset safety procedures. This usually includes: Backfilling the pile hole: Use high-quality clay or cement slurry to completely backfill and compact the currently unqualified pile hole to eliminate its potential hazards to the surrounding soil and subway tunnel; Pile displacement: According to the design allowable range, at a position a certain distance away from the original pile position (e.g., more than 1.5 times the pile diameter), repeat steps S1 to S6 to carry out new bored pile construction.

[0047] This invention constructs a complete automated closed-loop control system through a cycle of detection, diagnosis, adjustment, and verification. This ensures that corrective measures are not executed only once, but are verified through re-detection, forming continuous tracking and feedback of the control effect. This greatly improves the reliability and robustness of the pile-forming process and is suitable for working conditions with extremely complex geological conditions or multiple adverse factors. Through multiple rounds of corrective attempts with possible strategy adjustments, it can solve most reversible deviation problems, thus saving a large number of pile holes that might have been scrapped under traditional methods. When the number of attempts reaches a critical value and still fails, the system will decisively determine failure and initiate a termination procedure, avoiding continuous disturbance and damage to the surrounding soil caused by prolonged repeated operation in severely deviated holes. This effectively controls construction risks and prevents secondary disasters.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing bored piles near subway tunnels, characterized in that, include: Step S1: Set the pile location, install steel casing, with the bottom of the casing fixed with concrete, and continue to the rock strata; Step S2: Drill a hole, and determine whether the drill bit's perpendicularity is qualified based on the drill bit's vibration frequency during the drilling process; Step S3: If the verticality is not up to standard, determine the reason for the failure to meet the standard based on the frequency changes during the drilling process. Step S4: Adjust the drilling parameters or grouting parameters based on the determined cause; Step S5: Scan the hole and correct the adjusted parameters based on the hole parameters obtained during the scanning process; Step S6: Repeat the drilling and cleaning steps until the pile hole drilling is completed. After the pile hole drilling is completed, lower the reinforcing cage and pour concrete.

2. The method for constructing bored piles near subway tunnels according to claim 1, characterized in that, In step S2, determining whether the drill bit's perpendicularity is acceptable based on the drill bit's vibration frequency includes: Step S21: Obtain amplitude data from vibration sensors at different locations in the borehole; Step S22: Calculate the gradient characterization value based on the amplitude data; Step S23: Determine whether the verticality of this borehole meets the standard based on the gradient characterization value; Among them, a gradient characterization value less than the threshold is considered qualified, and a gradient characterization value greater than or equal to the threshold is considered unqualified.

3. The method for constructing bored piles near subway tunnels according to claim 2, characterized in that, In step S3, the reasons for the verticality failure are determined based on the frequency changes during the drilling process, including: Step S31: Obtain the time-frequency curve of frequency change over time during the drilling process; Step S32: Calculate the slope of the time-frequency curve; Step S33, determining the cause based on the slope, includes: When the slope is greater than a preset slope threshold, the cause is determined to be geological change. When the slope is less than or equal to the preset slope threshold, the cause is determined to be non-geological change.

4. The method for constructing bored piles near subway tunnels according to claim 3, characterized in that, In step S4, when the cause is determined to be geological change, the drilling parameters are adjusted, including: Step S41: Calculate the ratio of the current formation hardness to the previous formation hardness. Step S42, adjusting the drill bit rotation speed based on the hardness change ratio, includes: When the hardness change ratio is greater than 1, increase the drill bit speed; When the hardness change ratio is less than 1, reduce the drill bit speed; Among them, the absolute value of the difference between the adjustment amount of drill bit speed and the hardness change ratio and 1 is positively correlated.

5. The method for constructing bored piles near subway tunnels according to claim 4, characterized in that, In step S42, the process of reducing the rotational speed includes: The mud specific gravity is corrected based on the adjustment range of the rotation speed; The correction amount for the mud specific gravity is positively correlated with the adjustment range of the rotation speed.

6. The method for constructing bored piles near a subway tunnel according to claim 4, characterized in that, In step S5, the process of reducing the rotational speed also includes: The standard depth of the cleaning hole is adjusted based on the difference between the hardness change ratio and 1. The adjustment amount of the standard depth of the scanning hole is positively correlated with the absolute value of the ratio difference.

7. The method for constructing bored piles near subway tunnels according to claim 4, characterized in that, In step S6, if the cause is determined to be non-geological change, or if the drill bit verticality is still unqualified after the borehole parameters have been adjusted, the grouting parameters are adjusted, including: Step S43: Calculate the gradient representation difference between the actual gradient representation value and the preset gradient representation value; Step S44: Based on the gradient characterization difference, increase the grouting volume; The increase in grouting volume is positively correlated with the gradient characterization difference.

8. The method for constructing bored piles near a subway tunnel according to claim 7, characterized in that, In step S6, after adjusting all parameters, the verticality is re-checked; If the verticality is still not up to standard, repeat the steps of determining the cause and adjusting the parameters; If the verticality is still not up to standard after repeated adjustments reach the critical value, a notification of unqualified positioning pile setting will be issued, and recalibration will be carried out.

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